Science topics: ThermodynamicsPressure
Science topic

Pressure - Science topic

A type of stress exerted uniformly in all directions. Its measure is the force exerted per unit area. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Questions related to Pressure
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Want to compare FEM results to gain confidence.
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Thank you for the link given above.
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Assuming cylinder pressure data is available what is the best way to model NOx?
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An extended Zeldovich mechanism is commonly used for modeling NO formation in combustion engines. It has been well described in Combustion Engines Fundamentals by Heywood. Its chemical kinetics based.
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Pressure variation of superconducting state parameters.
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Yes. The transition between the superconducting and usual state is accompanied by the thermodynamic transition between two phases (the transition of the second kind). See any book on statistical physics, this transition are usually it well described there.
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Hello,
I would like to know whether there is a general dependence of the boiling temperature of a liquid on the surrounding pressure? I am trying to determine by how much I should decrease the pressure in order for the liquid to boil at a temperature below its boiling point.
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You are looking for vapor pressure of a substance. At a certain temperature the liquid will boil when vapor pressure a characteristic property of a liquid equals ambient  pressure. 
Normally it is calculated by Antoine equation for pure liquids. There are on literature several books with Antoine's equation constants, the formula and the temperature range of validation, for several substances, like The Yaws Handbook of Thermodynamic Properties for Hydrocarbons and Chemicals.
For liquid mixtures, however, the calculation is a little more trickle. It is calculated by boiling point calculations and can involve deviations of ideality. 
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whether the Refractive index of piezoelectric materials (Example: Polyvinylidene fluoride-PVDF ) changes by the application of pressure, strain or force ?
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There is change of refractive index in any crystalline materials when direct pressure or force is applied (except comprehensive hydrostatic compression) due to Curie principle. Polymer piezoelectrics have some non-centrosymmetric structure, so their refractive index must be changed too if some strain takes place, why not?
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While giving inlet Boundary conditions(In Ansys work bench under fluent) as velocity inlet and outlet as pressure outlet, please note that the default value of gauge pressure is zero. 
1) What does it signifies?
2) Assume that if water inlet and outlet source is a common open vessel what should be the value of it?
3) Please also note that if you set a value at inlet or outlet of a pipe the pressure value is fixed, then how to determine pressure drop for a given velocity inlet?
any info will be of great help?
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Dear Pathak,
(1) The setting of outlet pressure depends on the operating pressure that you set in FLUENT and in real field. Firstly, you have to think about how much total pressure (operating pressure + gauge pressure) at the outlet of your computational domain in practice.
Let say, you have total pressure of 101325 Pa at the outlet of the domain in practice. Therefore, if you set operating pressure 101325 Pa in FLUENT, then you can set the outlet pressure zero. It means that you are working in atmosphere. If you set operating pressure zero, you can set outlet pressure 101325 Pa. It means that you are working in zero pressure environment. Thus, you have to think about operating pressure and the outlet pressure at the same time to obtain the same condition as practice.
Here please note that for incompressible fluids (e.g water), FLUENT does not use total pressure. It uses gauge pressure in calculation and the results are also shown in gauge pressure values. The results (gauge pressure values) depend on how much you set at the outlet. However, it will show the same total pressure at outlet whatever you choose from two conditions that I mentioned above.
(2) My suggestion in No.1 is usable for your question 2.
(3) When inlet-outlet pressures are the same and you set inlet velocity, the pressure drop will be frictional pressure drop and elevational pressure drop ( g Z) if the pipe is not horizontal. Here, the pipe must have the same cross-sectional area at the inlet and outlet.
Hope my suggestions are match with your questions and partially helpful for you.
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With the increase in shock layer temperature, how is the pressure and density of shock layer going to change?
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I see this problem from the perspective of 'viscous interaction' of Hypersonic flows. I am not sure whether my answer is applicable to your case.
So in Hypersonic flows over flat plates, a viscous layer (boundary layer)  starts developing over the flat plate downstream. Now the velocity decrease due to viscous forces causes temperature to rise (your case of increasing T, remember enthalpy is constant since no heat is added). Since, pressure downstream is same for a particular oblique shock angle, therefore from ideal gas law we see that for increase T, density decreases. This causes the flow at a particular mass flow rate to pass via a bigger volume. Implying the boundary layer increases. The increase in layer causes flow deflection angle to slightly increase (theta) causing stronger shocks at same upstream Mach number. Hence the Pressure static increases but total Pressure decreases. The density decreases as earlier mentioned.
Let me know if I messed up somewhere.... 
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35 answers
Both magnitude of a pressure and mass flow rate of any fluid is affected by the geometry of flowing in and out.
Any book or paper which has lots of examples to show pressure drop and discharge for various geometry will be of great help.
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Hi
Ira H. Abbott - Theory of wing sections- Including a Summary of Airfoil Data
or another... search keyords (wind turbine blade design end so on).
Best regards
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4 answers
like i can built a small pump with some plastic tube where pressure can be changed accordingly.
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Hi Rizwan,
it depends on the type of pressure sensor and the medium and the pressure range you defined as "slight". If it was air consider using the gas law. We have used a simple setup based on a water column and an enclosed air space kept at a certain constant temperature to set up precise pressure steps. One millimeter of a Brodie fluid would make a pressure of about 1/10000 the ambient air pressure. You can also inject a tiny amount of air in a relative big volume of air kept at a constant tmperature.
If you want to drive your system atomatically consider a stepper motor connected to a syringe.
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8 answers
The plasma temperature is usually found to decrease with increasing the gas pressure. Did any one see the opposite behavior in any experiment specially the cold plasma like glow discharge for example? What might be the reasons?
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Dr. Abd Al-Halim  , as in case of the electrothermal plasma , especially in case of capillary sources, it can happen , as the confined structure limits the volumetric expansion. But the extent of  rise in peak ( or avg. ) temperature will depend on the amount of change in the peak ( or avg. ) bulk density . Which intuitively comes from the equation of state. 
What is the effect of pressure on foamability?
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30 answers
I am wondering what is the effect of pressure on foam generated by sparging (bubbling)?
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I have a few references for you that may be applicable.  Sydney Ross has published much about an ideal foam law.  He published S. Ross, Ind. Eng. Chem.61, (10), 48 (1969) which is the original representation for his Equation of State for Foam. Two other papers (Ross published many follow-up papers) are: Ian D Morrison and Sydney Ross Journal of Colloid and Interface Science Volume 95, Issue 1, September 1983, Pages 97–101 The equation of state of a foam Abstract An equation of state of foam relates the six state variables of volume and pressure, moles of gas and temperature, surface area of liquid and surface tension. The equation for several special cases can be established as Previous attempts to prove this equation as a universal law, applicable to any foam, are reviewed and shown to be limited in their application. Nevertheless, the probability is high that the equation is indeed generally applicable, although a rigorous proof is still lacking. PV + (2/3)σA = nRT A third paper purports to prove his equation: Hassan Aref and Dmitri L. Vainchtein The equation of state of a foam Phys. Fluids 12, 23 (2000) A search will bring up an abstract of this one too.  If your work is supported you might have a means to download the original papers. Good luck.  I'd like to get a copy of the first paper but I am retired.  I may have the original hard copy of the journal somewhere among my hoarded documents. Chuck Cronan PhD Cronan Creative Solutions, LLC
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Suppose for some quantity x we have a derivative with respect to temperature (dx/dT)P, i.e. at constant pressure. Can we somehow link it to a derivative with respect to volume, at, let’s say, constant temperature, i.e. (dx/dV)T? This is just an example and I’m wondering, maybe there are some universal rules, which enable to perform such substitutions? 
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Maxwell Relations:
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To simulate a pressure driven flow in a complex geometry like porous media, usually the constant body-force has been used.
Why the development of the force field is simply neglected? Does not make sense?
In my point of view, the pressure field will develop based on the geometry while a body force like gravity would act on every liquid molecule the same every where.
How NS handles this situation?
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This is an interesting question. In fact you can use a constant body force to mimic a pressure gradient. The system will then find a state where you have a local pressure gradient on top. The "real" pressure is then a the integral over the body force plus the resolved pressure gradient. In order to make this work you have to ensure that the force field is divergence-free (which is the case for a constant force field).
The starting point is to realise that nabla p is replaced by the body force. While you do not know p in advance, you have to impose the force field f. The system will then find the required difference nabla p - f = nabla p_d. You can find p from the sum of p_d and the integral of f (to invert the gradient). This is straightforward for a constant body force along a major axis.
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deflection due to wind pressure
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you can get huge articles if you try use Google scholar
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3 answers
As we know water in soil, especially fine grained soil which has been shown to be able to sustain very high tension. So, I would like to know the  plausible explanation for the high water tension (much greater than 100 kPa pressure, commonly consider cavitation pressure) that has been directly measured in soils
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Gardner type irrometer/tensiometers can prove what the cavitation pressure value on average could be for your soil/field. If there is a difference of 3-7 kPa between your two consecutive matric potentials in a short time (say from morning to noon), which happens suddenly,  the tensiometers show this disconnection of hydraulic column between the soil and the tensiometer porous cup.  However, I would suggest to use a neutron probe or a TDR with accurate precision range for sure.
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I would like to know if there is a way to calculate the temperature rise and hence the wear rate of two bodies in sliding contact theoretically?
The data I have are contact pressure, sliding surface are, sliding velocity, and details about the material in contact. 
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Hello, 
I know this simple formula to calculate the flash temperature within a sliding contact between two parts (it comes from Friction, wear and lubrication of materials, Rabinowicz) : 
delta_T=(7800*mu*Wab*v)/(J*(k1+k2))
delta_T = rise in temperature
mu = coefficient of friction
Wab = surface energy of adhesion 
v = sliding speed
J = mechanical equivalent of heat
k1, k2 = heat conductivity of the two materials
Hope it helps
rémi
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7 answers
I wanted to prepare a pellet from a powder using a uniaxial press and a matrix attached to a pump, but with the pressure and the holding time that I have chosen, the pellet obtained breaks up.
Are there a way to determine the correct pressure and holding time before launching tests?
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The best results are obtained by successive trials and errors, and they depend on your material(s). In a general way, too high presures are to be avoided, as they produce shear stress in the sample, leading to delamination.
I agree with Francisco that it is always better to condition the samples before. Otherwise the repeatability willnot be achieved.
Alain
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I have an acrylic cylindrical tube which is closed at one end and other end applying fluid pressure. 
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This depends on the nature of the pressure. If it is intermittent, that is relatively simple. Any pressure is transmitted to the cylinder surface which much hold it. The measured pressure is also the force per unit area on the cylinder surface.  If we know the area of a cylindrical section, we can calculate the total force. This is then divided by the cross-sectional area (wall thickness times the section width). If the result is as large as the breaking strength of the polymer, the tube will fail rapidly. 
For continuous pressure, the polymer will fail eventually at much lower force. There are many old papers (pre 1970)  relating the stress on acrylics to failure time.
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2 answers
Hi, I got a grid with logarithmic refinement and I need to sectorize a sub-cell from the principal cell, when I tried it, CMG sectorized all the cell not the sub-cell that I need. Is a 9*9 refinement, and I need to obtain pressure data from the sub cell 5 5 1. 
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The dynamic grid refinement in CMG is done by selecting the specific area by mouse, then you can apply the refining scale to get the sub-scale setting you want.
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I want to study the effect of "Pressure on the kinetics of diffusion" in diffusion bonding between Al and Ni.
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Applied stress affects the diffusion in two different ways.  They  may generated a driving force on  the diffusion through their gradients if any, which results the following additional term in the Fick's second law:  
Drift flux:   JX= C  D/RTgrad( Sigma), which results additional convective term. Fick's second law gives the following:
dC/dt= D d2 C( dX+  dC/dX  (D/RT) grad Sigma.  
Where  D/RT  is the mobility according to the Einstein-Nerst  Theory.
Second effect may be on the activation enthalpy of diffusion:   d DEl H/d P = DeL V >0 (activation volume). This relationship shows that hydrostatic pressure increases the activation enthalpy in Arrhenius relationship   D=Do exp (-Del H/RT). On the other hand triaxial tension decreases it. Where Do  involves entropy part of activation free energy  DeLS/R, which is called steric factor. 
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I want to solve a CFD problem. 
the inlet of my domain is connected to the Specified pump so my flow pressure and flow rate are known,
for modeling the inlet boundary condition I have two options (I use fluent software)
velocity or pressure inlet Bc
With velocity inlet bc, I have correct flow rate but my pressure is incorrect, and when I use pressure inlet bc I have correct pressure, but this time my flow rate is incorrect, so what can I do? and what is the best boundary conditions for my inlet?
Thank you
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For Subsonic inflow, it is the correct physics to specify the total pressure at the inlet and the required static pressure (e.g. atmospheric) or radial equilibrium at the outlet, depending on the losses in your domain, a particular mass flow would be achieved. For some CFD codes, if you specify the mass flow, let’s say at the exit, for a given the total pressure at the inlet, the back pressure is adjusted to achieve the required mass flow (but watch out for choked M=1 flow there), alternatively, if you specify a required inlet mass flow, the code may iterate on the total inlet pressure to achieve the required mass flow.  For a very low speed flow, i.e. incompressible flow, where density is constant, you may specify the velocity or dynamic head and in Fluent this is equivalent to the (inlet) flow rate you want, hence as you say may not get the total pressure too, because it is a function of the loss in your system and the exit boundary condition.
Hence, in summary, the inlet boundary condition is not just needed but also one exit boundary condition is also needed, together they will give you the mass flow rate and total pressure, if this is not what you want, you may adjust the exit static pressure until you achieve the desired mass flow rate.  In order to compare to other cases or experimental values, I will try to match the total pressure at the Inlet exactly, and then adjust the exit (back) static pressure to achieve the mass flow you were after, hopefully the density or temperature will also match at the inlet, do your CFD simulation and compare total pressure at the exit to the total presser at the inlet (or temperature) that would be the level of loss in your system.
Hope this is helpful.
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5 answers
I want to make CO and Si thin films. I am using 29w,30 sccm,Ar,1.8E-1 pressure.
but the plasma is not seen .
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You need to find the optimal parameters to start the plasma, once started you can slighty modify then to you desired values (for this you need a shutter so you not start the deposition too soon).
1. Check that you do not have a shortcircuit between anode and cathode
2. Check that distance between anode and cathode is adequate (this depends on the pressure, for 0.018 (mbar?) with 1 mm is quite enough. But check your magnetron manual first.
3. Check that you have Argon inside (start from a low base perssure and let the gas go into the chamber). Watch out here the pumps and vacuum gauge range!
4. You probably will need a pressure shock, a Power shock or both: go first to higher pressure and higher power (0.3 mbar, 50 W, I would say) 
5. Optimize your Matching box for the pressure range (you may need vary the capacitande or the inductance: check the manual of you RF source). Otherwise you reflected power would be so high that no forward power is transmitted to the plasma.
6. Check vacuum leaks, electronic contacts and, above all, check your machine manuals.
7. Once you have a beautiful pink Argon glow, send us a picture.
Good luck!
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4 answers
The flow rate and input power of positive displacement pumps are varying with speed. Is there any variation in input power when the pressure difference or load is increasing at constant speed?
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in PD pumps (and machines in general) flow rate is proportional to revolution speed. however, at higher pressure ratios the volumetric efficiency of the machine tends to slightly decrease.
therefore, I totally agree with Mr Doan but I would also take into account the effect of pressure ratio on the flow rate.
please refer to the attached publication where an operating map of a volumetric machine is presented.
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17 answers
Hi to everyone,
I am trying to simulate cavitation inside nozzle with kOmega SST turbulence model using interPhaseChangeFoam (at least for this case).When i run the case, after 40 or 50 time-steps always giving following floating point error:
smoothSolver: Solving for alpha.water, Initial residual = 4.1184e-06, Final residual = 3.80347e-09, No Iterations 1
Phase-1 volume fraction = 0.98612 Min(alpha1) = 0.000310125 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Liquid phase volume fraction = 0.98612 Min(alpha1) = 0.000310125 Max(alpha1) = 1
smoothSolver: Solving for Ux, Initial residual = 1.98514e-05, Final residual = 1.02782e-09, No Iterations 2
smoothSolver: Solving for Uy, Initial residual = 5.44074e-06, Final residual = 1.94705e-10, No Iterations 2
smoothSolver: Solving for Uz, Initial residual = 8.8507e-05, Final residual = 3.80435e-09, No Iterations 2
GAMG: Solving for p_rgh, Initial residual = 2.79212e-08, Final residual = 2.04895e-10, No Iterations 1
GAMG: Solving for p_rgh, Initial residual = 6.59936e-09, Final residual = 6.59936e-09, No Iterations 0
GAMG: Solving for p_rgh, Initial residual = 6.61102e-09, Final residual = 6.61102e-09, No Iterations 0
GAMGPCG: Solving for p_rgh, Initial residual = 6.61138e-09, Final residual = 6.61138e-09, No Iterations 0
smoothSolver: Solving for omega, Initial residual = 5.4048e-06, Final residual = 6.75835e-10, No Iterations 2
smoothSolver: Solving for k, Initial residual = 9.03591e-06, Final residual = 2.43949e-09, No Iterations 2
ExecutionTime = 97153.3 s ClockTime = 98393 s
Max pressure: 323086
Min pressure: -35072.5
Max velocity: 28.9586
Min velocity: 0
Courant Number mean: 0.00779459 max: 0.0996774
deltaT = 3.50877e-08
Time = 0.01051926
smoothSolver: Solving for alpha.water, Initial residual = 4.11863e-06, Final residual = 3.80331e-09, No Iterations 1
Phase-1 volume fraction = 0.986119 Min(alpha1) = 0.000310159 Max(alpha1) = 1
MULES: Correcting alpha.water
MULES: Correcting alpha.water
Liquid phase volume fraction = 0.986119 Min(alpha1) = 0.000310159 Max(alpha1) = 1
smoothSolver: Solving for Ux, Initial residual = 1.98021e-05, Final residual = 1.02634e-09, No Iterations 2
smoothSolver: Solving for Uy, Initial residual = 5.44207e-06, Final residual = 1.94729e-10, No Iterations 2
smoothSolver: Solving for Uz, Initial residual = 8.84228e-05, Final residual = 3.80449e-09, No Iterations 2
GAMG: Solving for p_rgh, Initial residual = 2.58283e-08, Final residual = 1.86337e-10, No Iterations 1
[5] #0 Foam::error::printStack(Foam::Ostream&) at ??:?
[5] #1 Foam::sigFpe::sigHandler(int) at ??:?
[5] #2 in "/lib/x86_64-linux-gnu/libc.so.6"
[5] #3 Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
[5] #4 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::operator/<Foam::fvPatchField, Foam::volMesh>(Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > const&, Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > const&) at ??:?
[5] #5 Foam::phaseChangeTwoPhaseMixtures::SchnerrSauer::pCoeff(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) const at ??:?
[5] #6 Foam::phaseChangeTwoPhaseMixtures::SchnerrSauer::mDotP() const at ??:?
[5] #7 Foam::phaseChangeTwoPhaseMixture::vDotP() const at ??:?
[5] #8
[5] at ??:?
[5] #9 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
[5] #10
[5] at ??:?
[baris-desktop:10415] *** Process received signal ***
[baris-desktop:10415] Signal: Floating point exception (8)
[baris-desktop:10415] Signal code: (-6)
[baris-desktop:10415] Failing at address: 0x3e8000028af
[baris-desktop:10415] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x36d40) [0x7ff21608cd40]
[baris-desktop:10415] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x39) [0x7ff21608ccc9]
[baris-desktop:10415] [ 2] /lib/x86_64-linux-gnu/libc.so.6(+0x36d40) [0x7ff21608cd40]
[baris-desktop:10415] [ 3] /home/baris/OpenFOAM/OpenFOAM-2.3.1/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4Foam6divideERNS_5FieldIdEERKNS_5UListIdEES6_+0xd5) [0x7ff21734cc05]
[baris-desktop:10415] [ 4] /home/baris/OpenFOAM/baris-2.3.1/platforms/linux64GccDPOpt/lib/libphaseChangeTwoPhaseMixtures.so(_ZN4FoamdvINS_12fvPatchFieldENS_7volMeshEEENS_3tmpINS_14GeometricFieldIdT_T0_EEEERKS8_SA_+0x19b) [0x7ff21ae2aaab]
[baris-desktop:10415] [ 5] /home/baris/OpenFOAM/baris-2.3.1/platforms/linux64GccDPOpt/lib/libphaseChangeTwoPhaseMixtures.so(_ZNK4Foam27phaseChangeTwoPhaseMixtures12SchnerrSauer6pCoeffERKNS_14GeometricFieldIdNS_12fvPatchFieldENS_7volMeshEEE+0x33c) [0x7ff21ae2f3cc]
[baris-desktop:10415] [ 6] /home/baris/OpenFOAM/baris-2.3.1/platforms/linux64GccDPOpt/lib/libphaseChangeTwoPhaseMixtures.so(_ZNK4Foam27phaseChangeTwoPhaseMixtures12SchnerrSauer5mDotPEv+0xff) [0x7ff21ae2ff8f]
[baris-desktop:10415] [ 7] /home/baris/OpenFOAM/baris-2.3.1/platforms/linux64GccDPOpt/lib/libphaseChangeTwoPhaseMixtures.so(_ZNK4Foam26phaseChangeTwoPhaseMixture5vDotPEv+0xa2) [0x7ff21ae18242]
[baris-desktop:10415] [ 8] MRinterPhaseChangeFoam() [0x431350]
[baris-desktop:10415] [ 9] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5) [0x7ff216077ec5]
[baris-desktop:10415] [10] MRinterPhaseChangeFoam() [0x433792]
[baris-desktop:10415] *** End of error message ***
When I check the results of Pressure, velocity and α distributions seem OK? What I did is:
==> Run the case single and parallel (nothing changed same problem)
==> Increased the mesh number gradually (Still same problem)
==> Change initial conditions, schemes of k and omega (nothing changed)
==>Tried with RNGkeps model. (Fortunately it worked)
==>As a result, i recognized that I am getting this floating error since Omega value is excessively high. 
So, does anyone have any idea why it happens? By the way, is there anyone who already obtained good result with kOmegaSST using multiphase solvers of OpenFOAM?
Thanks in advance.
Baris
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My CFL number is quite small around 0.1 and mesh quality is already tested. Also, I already tried with Kunz model and RNG epsilon model and got good result. However, I would like know the reason why kwSST model does not work properly for the same conditions? Let me know which turbulence model did you use with interPhaseChangeDyFoam? have you ever tried with kwSST model? and obtained good result with multiphase solvers? Also let me know please for which cases Sauer model can give unstable results and WHY?
Thank you.
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4 answers
In his "Treaties on thermodynamics" Max Planck derives an expression for the specific heat at constant pressure. I attached a screenshot of his derivation from the book. I do not understand how the third formula, in which he substitutes (du/dtheta)_p, is derived. I really would appreciate if someone could help me to understand this relation.
The definitions of the symbols are:
c_p ... specific heat at constant pressure
u ... inner energy
theta ... temperature
p ... pressure
v ... volume
I also attached a link to the book where you can find the complete derivation on page 56.
btw: I actually read a hard copy of the book. For this question I searched for an online pdf of the book and found this one. The version I found contained the handwritten notes on the right side. So there was someone before who had this question.
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I can try to deduce the equation without special characters. The only change in nomenclature is that Theta=”T”.
A total differential du may be,
du=(du/dT)vdT+(du/dv)Tdv   (1)
or
du=(du/dT)pdT+(du/dv)Tdp   (2)
Substituting left part of (2) in (1) and considering than dp=0.
(du/dT)pdT=(du/dT)vdT+(du/dv)Tdv   (3)
Divide (3) by dT and considering that the process is a constant p,
(du/dT)p=(du/dT)v+(du/dv)T(dv/dT)p   (4)
Which is the desired equation.
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5 answers
I need to know the density of water steam in the Temperature interval 1273 K-1873 K and Pressure interval 0.1-300 MPa. I didn't find anything for pressures higher than 10 MPa and temperatures higher than 1273 K. Any suggestions?
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That's perfect, thank you very much!
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3 answers
Hi every body. As you know at CNG stations, Turbine meter location is before of compressor. my purpose is to know how this pulsations, affect the accuracy of this turbine, while the gas flow is In the opposite direction.
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Mostafa,
Your english as a second language is good and I am also trying to understand you to help you.
And so, don't feel badly, but I must restate your question so as to accurately respond. You claim that your upstream ‘turbine’ meter, for measuring CNG flow rate, exhibits fluctuating readings that causes inaccuracies caused from your downstream reciprocating compressor pump which is used to create the flow of your CNG?
To correct this you can do one of two things:
1) You must dampen the upstream flow meter’s tiny pressure sensor tube so that the downstream reciprocating compressor pumping actions are not felt. This means you must insert some porous material (like cotton) into the tiny connector tube which transports the CNG gas pressure to the sensor which then reads it. The amount of porous material you stuff in this tiny pipe is trail and error until you stop sensing the fluctuations. Make sure your damping material doesn’t get pushed into your sensor, to plug it up, so have a physical stop barrier.
2) Dampen the main CNG flow duct. Much more effort, not easily done.
A quick way however is to increase the ducting distance between the pump and the flow meter reader. Longer distances will naturally dampen pressure pulses from moving and being felt upstream. However, the longer the ductwork, the more burdened the pump gets to move the required CNG flows. You must find the correct duct length balance that stops pressure pulses yet still lets your pump flow enough CNG.
The hard way is to introduce a Muffler between the meter and pump. The Muffler would be very similar to a car’s muffler which both deadens noise and pressure pulses and provides a consistent back-pressure to keep the engine running smoothly. In your case the Muffler is located upstream of the pump. Remember that your reciprocating pump acts like a car’s engine in creating pressure pulses that needs muffling.
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5 answers
Hello!
I am trying to study fatigue properties of polymer tubes due to cyclic internal pressure. Any help regarding a system that could enable me to produce this type of pressure would be really appreciated.
Thanks,
Sia
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One of the ways would be to connected the tube with a peristaltic pump in a circulatory system with pipe. You can apply a pressure sensor to record the pressure vacation and a pressure valve ( can be modified as per requirement) to vary the pressure. I do something similar but the pressure variation is between 100-200 mm Hg with step of around 30-60 mm hg
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Neutral markers provide insight into levels of variation but do not take into account selective environmental pressures of a species and therefore  do not provide information in an evolutionary context as would the use of non-neutral markers. 
Is there any key significance or insight in using a neutral and non-neutral marker in conjunction for a population genetic study? 
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To begin with, it must be said that you may have some a priori idea about whether a given marker is neutral or has been under selection, however, you cannot know for sure. A coding locus with alleles responsible for different phenotypes could be neutral (phenotypes have or had the same fitness). A microsatellite or other "junk" DNA could be linked to a locus under selection and hitch-hike or have an unknown function and be responsible for changes in fitness. So beware of your assumptions about using a priori neutral and non-neutral markers.
Current widely accepted approach is to consider that the vast majority of the genome behaves neutral and only a handful of loci have been under recent selection. Therefore, we can perform demographic inference from lots of (randomly selected along the genome) markers. If some markers under selection are included, it is assumed that their signal is "crushed" compared to the main neutral signal carried by the overwhelming majority of neutral markers. See however Ewing & Jensen (2016, doi:10.1111/mec.13390).
Once the demographic history of the populations under study has been inferred one can try to detect loci that present diversity pattern incompatible to that history. These can be assumed to have been under selection.
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hi
i work at modeling of thermoacoustic phenomenon in rijke tube with ansys fluent
i want to show pressure oscillation in this phenomenon
i modeled a tube with 1m length and include just one segment of heat convertor
then i run steady-state solution with p(inlet)=0.5 and p(outlet)=0
and wall temprature (tempratue of heat convertor)=3000k
and when this solution convergenced next step is imposed pressure pulse at outlet such as p=30sin(2*pi*f*t) with udf for 2000 time step with time step 1e-5
and then change pout=0 and run transient solution for 100000 time step with time step=1e-5
i cant see any oscillation in pressure
anyone can help me?
thanks
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Dear Hamid,
In general, it is not that easy to capture instabilities in the form of pressure oscillations using CFD.
You need to use compressible solvers with time steps small enough to capture propagation of sound waves.
This means that you should use density based solver in Fluent and calculate the speed of sound in your hot region and depending on  your grid size, choose a suitable time step. It will usually be in the order of a few e-7. 1e-5 is definitely too large to capture acoustics.
Take a look at the attached article.
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What is the material of the sensor used in continuous indiect type tyre pressure monotoring system?
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You can use a diaphragm inside a capacitive-type pressure transducer. Best wishes
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hi
i need the 3d profile dynamic air blast pressure in a non venting confinement.
who can help or addressed me about it?
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Ithink , the P(x,y,z,t) can explained in P(x,y,z)*p(t).
p(t)=p0*f(t)
f(t) like a exponential or harmonic or combined of this function form.
so what is the p0?
what is the P(x,y,z)?
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Hi,
I found that the contact pressure is reported to be zero for a bonded contact and non zero (nearly equal to normal stress) for a frictional mate. Why is it so? Why doesn't it report 'the contact pressure' in case of bonded contact?
I read in link below that contact pressure = contact stiffness*contact penetration. Does this mean it represents how bad the contacts penetrate? Or it really does reflect contact pressure?
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Bonded bodies are treated as a single entity together. That's why you got zero contact pressure. You can check that by adding Frictional pressure to the solution and you will find similar trends for the contact pressure and Frictional pressure in all cases.Please let me know if I could help. Feel free to ask any further questions.
Best of luck!
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Any color-changing or other variation by pressure or other stimulus
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Pressurex pressure indicating sensor film from Sensor Products Inc. can reveal pressure distribution and magnitude between any two contacting surfaces. This thin plastic sensor film is placed at the actual contact surfaces and instantaneously and permanently captures the pressure profile by changing color. The color Pressurex turns is directly proportional to the amount of force applied and can be quantified.
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if flow at the inlet of the pipe is 1m/s and at the exit the pressure is zero bar. i wanted to study the flow behaviour at the exit of the pipe.
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I assume you are talking about incompressible Newtonian fluids or compressible Newtonian fluids at low Mach number. In this case, the answer depends on the Reynold number Re. For Re >> 1, the flow at the exit is the same as the flow upstream. For low Reynolds number Re << 1, the flow at the exit depends on what is happening down stream, i.e. outside the pipe. Just specifying the pressure is not sufficient. 
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Hi
I want to heat my substrate up to 400C in vacuum around 5E-4 Torr and in argon gas in 5E-2Torr. What are the characteristics of heater that I should consider in these pressures? What are good materials for such goals and of course they must be cheap.
thanks
masoud
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Hi,
You can use a furnace having a cold resistance of about 5 ohms. The electric power supplied to the heater is about 150 W . The heating element, based on the indirect principle of  heating by  resistance, may consist of a  coil made with a nichrome wire wound around your sample. To minimize heat losses, it is necessary to equip the furnace for example with concentric   reflectors (screens) which may consist of a polished molybdenum strip, 0.1 mm thick, in order to reflect a portion of the heat flux. The temperature measurements of the sheath of the heating element can be performed by a chromel-alumel thermocouple. The heating element must be connected to the heating circuit via supply wire of adequate current. This furnace was manufactured by a lab technician. I could get a pressure of 10-7 mbar after 24 hours of pumping.
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I am currently designing the hydraulic system of a refuse compactor vehicle. I'm having a problem in choosing the correct method to choose the best working pressure and temperature in order to produce high efficiency.
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Keep It Simple and Stupid...KISS...forget about temperature rise as garbage compactors in garbage trucks do no run continuosly
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I am working on turbulence. I actually want to know about the significance of pressure spectrum in practical application.
Does any body know about pressure spectrum and it's application?
Thanks.
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Turbulent pressure fluctuation and its correlation on a surface determines the flow induced vibration of the wall. In a car or aircraft this results into sound that you hear in the cabine. For a ship or submarine this can result into wall vibration and sound diffraction that allows detection by means of sonars. For this reason it is difficult to find experimental data on wall surface pressure pressure correlation in turbulent flows. Most data are military secret.
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We know that all element have sensitivity due to temperature.
Which element has the most sensitivity?
d (density)/ d (temp)= MAX
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In solid Cerium, you can induce the isostructural gamma-to-alpha Cerium transition by applying pressure. This goes along with a volume contraction of about 15%.
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Hello everybody!
How can it be possible to feel no pain in a full-squat, but feel pain in the knee when deadlifting with a wider stance (Sumo-deadlift)? Is the pressure on the meniscus greater when greater abduction occurs in the hips?
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Dear Kristian, it is because of anatomy and biomechanics. Medial meniscus is more vulnerable to injury because of its anatomical attachments and pathomechanics involved in squatting. Lateral meniscus is attached with joint capsule so that it will be moved outward while we squatting. But medial meniscus trapped between bones during squatting. The weight through medial compartment will be increased with wider stance. In stance anterior horn is more vulnerable and as the flexion increases weight on meniscus will shift to posterior horn. So the optimal position for squatting is legs in shoulder width apart. Both too narrow and too wider stance are not biomechanically correct. Simple Answer to your question is wider stance will increase pain in medial meniscus.
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Anyone have any idea on how to harvest the acoustic energy from a line sound source? The line sound source is in small scale, maybe in a centimeter range, and the sound pressure is very small, around uPa I guess. 
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Many pressure transducers work by converting acoustic energy to electrical energy, and therefore could be said to be 'harvesting' the acoustic energy (though I would expect the process to be fairly inefficient). I would probably start by looking at piezo-type transducers - a quick Google search brought up some likely options.
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Greeting.
I have a Capillary Electrophoresis Agilent G1600 (3D CE system) that has been having problems lately. The system can not achieve stable pressure and crashes afterwards with the errors 5207 and 5210.
In the logbook, it says to check bottle and screws for fitting. I have done this and the errors still occurs. 
Can some help me?
I don´t have the Service Diagnostic Disk. Can someone provide it for me? Or give me the link to it?
Thank you very much
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This is a common set of error messages (5207 and 5210). In 99% of cases it means you have a pressure problem. The cause is often a bad seal (The o'ring) on the Buffer bottle cap or loose tube fitting. Check these connections and carefully clean ALL salt residues off their surfaces. Also, be sure and use the "Change Bottle" feature in the software when you release pressure in the buffer bottle so the system can reset properly. Failure to do so will also cause this error to be set. *The pumps usually last for ten years, but these older CE units are long past that date so I would always consider that the pump may be bad too (remove and check level).
Another cause could be a contaminated air inlet filter. These filters are designed to be replaced on a regular basis and I see a lot of clients ignore them (and then they are clogged with dirt). If this filter is clogged, the pump can not operate correctly.
Sorry, do not have a diagnostic disk file available to measure pressures or manipulate the valves with.
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I used the Widom test particle method to calculate the chemical potential. The chemical potential I get for gaseous phase is consistent with literature. However, the value for denser phase is consistently lower especially at lower temperature. All other variables, internal energy, pressure, density seem OK. I am really confused with this. 
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Widom's expression  (for  the N,V,T,ensemble), is valid at all conditions in the Gibbs
ensemble. If this probability cannot  be neglected it is shown that only the chemical potential of the total system can be calculated. Strictly the Widom Equation is only valid for the canonical ensemble. 
All cases where the system is highly dense, the new inverse Widom scheme affords a significant better results^:
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Dear all,
The constitute model is mooney-rivlin, C1=0.004,C2=0.016,D1=0, or I even tried a simple one: a linear elastic model with poisson's ratio 0.49. Since the material is very soft, I confront the convergence issue that I want to add a big pressure like around 5MPa on it but it diverge when the pressure reach 0.3MPa. For the geometry, just consider simple cantilever beam. The warning always shows Excessive distortion at a total of XXX integration points in solid elements. And I have tried refine the mesh and change mesh element type, it does not work.
Really feel appreciated if someone could help.
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Hi, regarding convergence issues you can increase the time steps (load per increment) or you can apply two load cases starting with a smaller and gradual load followed by faster loading. This might help.
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Is there any method for multi-zone combustion modeling in diesel engines using experimental in-cylinder data like cyclic variation of temperature, heat flux or pressure? Please let me know the procedures and study contents. 
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Dear Mishra
I suggest you take a look at this paper, it can help you.
Best regards
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i want to analysis a plate problem with uniformly distributed load by meshless collocation method. the unit of uniformly distributed load in the equation of plate is (N/m^2) but the unit of the applied force on per node is (N), i want to know what force is applied to each node?
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Use the principle of virtual work. The virtual work of the applied pressure for a virtual displacement MUST be equal to the virtual work of the nodal forces for the same virtual displacement.
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Hi
How can one get the relationship between pressure & adiabatic compressibility of a liquid when the graph of temperature vs adiabatic compressibility is known ?
TIA
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Unfortunately the ideal gas law ( as used by Saumitra) does not hold for a liquid. 
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I've done an experiment and there's a problem because of different atmospheric pressure for different days of experiment. It is quite large that effects my analysis. How can I overcome this problem?
Examples: The first day of exp: 101250 atm Pressure. The second day: 101590 atm Pressure. This will effect the total pressure for wind tunnel experiment. How can I overcome this type of problem? Any idea?
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You do not mention how these variations actually affect the analysis...
Nontheless, I can not see the problem if the ambient atmospheric (ambient) pressure varies from day to day. If you really want a constant stagnation (total) pressure, for some reason, you can probably adjust for that by fine-tuning the RPM of the fan unit and by recording the stagnation pressure using a Pitot tube. If the problem relates to the air speed the air density can be easiliy corrected for using the ideal gas law. If the fan unit is not speed-controlled you may correct for the variations afterwards; the variations you mention are actually quite tiny, less than +/- 0.2% !
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I am starting a project to review the Integrated Production Modeling approach in one area of our field. I think is the best way to evaluate the effect of flowing pressure (or back pressure) on the rate and hence improve accuracy of Type Curves. It is also a good way to evaluate the production network under actual operational constraints. Is there anyone doing something similar?
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course an oil well simulator is used to explain many operations that take place in a real well. This course / workshop consists of theoretical (50%) and practical (50%) sessions with experienced professionals.
The participants will simulate the operation of different artificial lift systems used to produce oil (Electric Submersible Pumps, Gas Lift, Progressive Cavity Pumps) under several operating conditions and its effect on the production system. Water and air are used to simulate two-phase flow (oil and gas).
The standard configuration of the Oil Well Simulator uses an Electric Submersible Pump with a Variable Speed Drive allowing the variation of the pump speed (RPM). This feature is used to optimize production and well performance. A "Work–Over" can be performed by changing the artificial lift system from ESP to Gas Lift.
The configuration of the Oil Well Lab allows the visualization of the reservoir, wellbore, flow lines, choke performance and most common artificial lift systems. Additionally, the effect of damage removal, pump speed, gas injection rates and down hole pressure can be analyzed to generate optimization opportunities.
Oil Well Laboratory
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I need Physical and chemical properties for L-arginine like critical temperature, critical pressure and critical volume. Thanks.
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For L-arginine: molecular formula C6H14N4O2; Molecular weight: 171.19 g/mol; Density: 0.7 ; Fusion point: 238 C; Solubity in water: 150 g/l @ 20 C.
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I need HTC values for different water pressures or water velocities as mentioned in the attached article.
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In general there is no direct effect of temperature or pressure variation on the heat transfer coefficient. Based on similarity numbers definitions we should take into account the important influence of these parameters on the values of cpecific heat, density, viscosity and conductivity of the fluid, esspeciallu in the near-critical range of state parameters.
You can find some recomendations in the following papers:
Regards, Jan Gorski, AGH Cracow, PL
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I am commingling production at the surface, and I am trying to determine the order in which to open the wells so that the high pressure wells will not flow into those of lower pressure. (Picture attached for further explanation)
Should I open the well of highest pressure first and wait for its pressure to decrease before opening the second, or should I choke all wells to make their pressures equal to that of the lowest pressure well? Is there a standard equation that I can apply to each situation (given initial pressures, IDs, and flow rates) that can allow me to compare the overall final flow rate?
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Dear Danielle,
It depends on the pressure difference and rates you are talking about. You are absolutely right about your conclusions. 
So, assume the first case: when you choke high pressure wells to get a pressure that is equal to lowest well pressure, howmuch did you lose from production? 
Also, if you open the highest pressure wells till their pressures decline, howmuch will you lose from not producing the lower wells for certain a period of time?
If you quantify both, your will be able to make an economic decision.
For your question about equations, basically it is flow through pipes. You have flow rates through connected two pipes with pressure for two streams that mixed in one stream and you can define the final pressure using choke to determine flow rate. For softwares, you can use: hysys, pipesim.. Etc 
Good luck. 
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Like which geometry and arrangement of perforations can reduce the pressure drop?
The perforated plate is used as an element in flame arrestor. So i want to know which arrangement of perforations reduces the pressure drop across the element
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The question is that, how is the flow? does it pass through the holes or it passes parallel to the plate?
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When using the Acetonitrile (HPLC grade) (100% Pump B) for long time, there is pressure variation in Pump A & B.
Now I solving this problem by ultra sonication of Pumb B filter.
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Do you use a Shimadzu HPLC? If it's the case, the reason is the gem ball in check valve will become sticky in pure acetonitrile. That's a design flaw present in Shimadzu HPLC of some old model (maybe also in some other brands). The resolution is to take apart the check valve and ultrasonicate it by MeOH/water. Or use a 90% acetonitrile instead of pure one.
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Detonation Pressure
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Hi,
An interesting bool where you can find many information:
Dobratz, B. M., "LLNL Explosives Handbook. Properties of Chemical Explosives
and Explosive Simulants", UCRL-52997, Lawrence Livermore National
Laboratory, March 1981. UNCLASSIFIED
A previous version is avalaible at
Pascal Galon
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How can we prevent joule Thomson effect on valves (natural gas plant)? and how should we deal with this effect in case it happen to a valve (pressure drop)? is there any procedure regard this matter?
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Dear Mohammad
The Joule Thomson effect cause Temperature drop when occur pressure drop in a valve especially in a pressure gas reduction station in a city gate station (CGS) in natural gas transmission pipeline. This effect is unavoidable  which cause a bad effect in device in pipeline system. but with preheating natural gas before pressure reduction we can decrease these effects. I have a paper in this field. I advice you study this useful source.
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Dear all,
to study the effect of pressure on the structural properties, I suppose that there is a relation between lattice parameter A and pression P. I want to know this relation please.
Thanks
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See any theory of elasticity text book for the bulk modulus defined as (the ratio of pressure increment, ΔP, required to induce unit change in volume per unit volume, (ΔV)/V))
K = (ΔP)/((ΔV)/V), K = E/(3(1 - 2ν))  
of a linearly elastic material. (E is modulus of elasticity, ν is Poisson’s ratio)
ΔV/V = 3((Δa)/a) + 3((Δa)/a)^2 + ((Δa)/a)^3
where "a" is the so called "lattice constant" and "Δa" is the increment in "a".
ΔV/V ≈ 3((Δa)/a)
ignoring the terms with square and the cube of ((Δa)/a) for small strains. Hence,
Δa ≈ ((ΔP)/(3K))a
or substituting K in terms of E and ν,
Δa ≈ ((ΔP)/(E/(1 - 2ν)))a
(The higher order terms cannot be ignored for compressible materials.)
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We need the vapour pressure curve for Bis(ethycyclopentadienyl)magnesium metalorganic.
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Hi Miguel,
The vapour pressure curve for Cp2Mg is available here.
Sometimes, there are minute variation in the vapour pressure or the constants (A and B) used in the calculation of vapour pressure, I would suggest you to use the data from your MO manufacturer.
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 α = (po-pt) / (p0-peq)
Where, p0 is the initial pressure, pt is the pressure at time t and peq is the final equilibrium pressure.
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Reacted fraction α(t) shows how fast (and according to what decaying law) the time-dependent perturbation given by pt will reach its equilibrium value peq. The latter is defined as a long-time (mathematically, infinite) limit of pt. Typical example of α(t) describing a fast (Debye-like) relaxation of any ordered system to its equilibrium state is given by the exponential law: α(t)=1-exp(-t/t0) where t0 is the relaxation time. 
On the other hand, kinetics of a disordered (amorphous or glassy) system follows a non-exponential (non-Debye) relaxation law, like e.g. logarithmic  α(t)=log(t/t0),  power-like α(t)=1/(1+t/t0)n, or the stretched exponential dependence: α(t)=1-exp[-(t/t0)m] where 0<m<1.
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What should be the most easiest approach to analyse foot pressure and knee loading during osteoarthritis? Any software for analysis of it?
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Hi,
Good Software to analyze knee loads is anybody.You can apply motion and then compute in vivo loads. Its a commercial Software package.they just won The grand challenge On predicting in vivo knee loads,See attached link
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Is there a way to measure the pressure in the coronary artery?
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Please do not hesitate to ask questions. Scientist should be like you. All the best.
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I see temperature but what pressure and humidity did you have?
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When I worked with Motorola, we used to use autoclave from Priorclave. Since most of the industrial autoclave system, were made for medical-grade units and they are not 100% suitable for our lead-free solder samples. Talk to them or visit ther website (Priorclave), Nick.. Wishing you all the best then..
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My initial and final pressures are 1.45 atm but the pressure fluctuates from approximately -3200 to +1500 atm! What is my fault? My fix command is:
fix NPT all npt temp 93.7 93.7 50 iso 1.45 1.45 100000
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fix NVE + langevin thermostat (or/and barostat) are not physical ensembles. After relaxing the structure, you should use a real ensemble simulation, fix NVT or fix NPT.
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There are several possibilities for the realization of the pressure load.
For example, when I apply a pressure to an area (lets say, thin rectangular plate) the area of the plate grows during the deformation process. One possibility is to keep the pressure per unit area constant (in this case the total force acting on a plate grows during the deformation) and the second is to keep constant the total force acting on the plate (in this case the force per unit area decreases with the deformation). I looked through the help, but I wasn't able to find which option is chosen in ANSYS. I would appreciate any hints.
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Thank you. I understand that the vector of pressure follows the shape of the structure. My question is about the pressure per unit area. Since the area of the plate grows with the deformation there are two possibilities: to fix the total force, that is applied to the plate at the beginning or to fix the pressure per unit area. Do you khow which option is implemented in ANSYS?
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Pressure transient.
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Thanks hassan, i'm grateful
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Could you give me some reference? On the Q. and reference on pop ratio for both of them? Or the answer of the Q is the best?
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The difference came from their sources. Wave induced pore pressure would be generated because of the elevated water surface during sea wave. Meanwhile, seismic induced pore pressure is a result of soil dilatancy during a seismic event. As you know, the latter can lead to the so called liquefaction.
Significant studies have been devoted to liquefaction. But, as far as I know, there are limited studies about wave induced pore pressure built up.
Obviously, seismic induced pore pressure can be much more destructive than wave induced one.
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I am working on enhancement of heat transfer in a square channel through broken ribs. I need to calculate friction factor f so I need pressure drop across the periodic duct. I am using FLUENT 6.3.26 for simulation with periodic and symmetric conditions. The upper and lower walls are heated walls where constant heat flux of 2500 W/m2 is applied and other two walls are adiabatic, and adiabatic ribs were provided on heated walls. I am using the k-ep turbulence model. Is there any other method to calculate friction factor in this case?
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@Shrish Shukla, Dear Shukla, please carefully go through the question. Its a periodic domain..
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How can sensor charge produced by the steady pressure be held for a longer duration?
What kind of signal conditioning circuitry I can implement?
Here is the sensor product link:
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The short answer is no. A static pressure on a piezoelectric will generate a fixed charge on the piezoelectric. PVDF has a high input impedance and in order to read out the charge induced on the piezoelectric an electronic circuit is used. The charge will be slowly leaked out of the piezoelectric due to losses in the system. Any of the piezo sensor sites such as http://www.pcb.com/techsupport/tech_pres.aspx#.Uw35emyYaUk
provide a description of the mechanism for losing electrons
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This instrument shows the pressure frequency at one point.
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You might find your answer in
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I have a basic doubt regarding Bernoulli's Theorem. Assume a constant area pipe with P1 pressure at inlet and Patm pressure at outlet. Assuming inviscid flwo and applying Bernoulli's theorem, how does pressure varies along the length of the pipe. P1 > Patm. Now the doubt is since area is same using continuity equation velocity has to be same at all points along the length of the pipe. P1 + 0.5 rho V1^2= Patm+0.5 rho Vexit^2 (Assuming levels are same) This gives P1=Patm. Please help!!!!
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For a constant diameter duct with constant flow-rate, with no height difference, an inviscid fluid has constant velocity and the same static pressure at inlet and exit according to Bernoulli’s equation which is proved along a streamline. However, in real fluids friction makes the difference. For example, for an incompressible fluid the velocity is constant everywhere, whereas the pressure upstream has to pay the exit pressure and every kind of power losses, which are exclusively accounted for on static pressure. In a University, it takes several courses to clarify things about the flows (inviscid, incompressible, compressible, Low or High Mach, supersonic, steady or nonsteady, viscous, and a lot more). This is why the Navier-Stokes equations describe all kinds of flows but they have no universal solution and they have to be solved for each case according to its limitations and specific conditions.
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I want to model a helical pipe and I have oscillating pressure gradient boundary condition. Now my question is how can I apply this boundary in commercial codes (FLUENT,CFX,...) and if I can't solve this with these codes what should I do?
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You can refer the paper titled "Torsion and Curvature Effects on Fluid Flow in a Helical Annulus"
this has been explained the boundary conditions.
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I am currently studying gait and posture analysis. What are the factors that you need to consider while dealing with pressure sensors? (Example: type of sensors used in force platforms)
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Anvita! When selecting any sensor you have to consider the following: time response, range, non-linearity, drift, accuracy, repeatability, among other factors. Our experience with Force Sensing Resistors (FSR) proved to be very effective for Plantar Pressures though we did have to improvise certain augmentations to the structure of the sensor and the method of sensor calibration. You may look at some of our articles for further clarifications.
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I'm using ammonia as a reagent gas for chemical ionization MS. Set at 2 bar, the pressure on the pressure reducer drops during a series of analyses to -1 bar, resulting in a drop from 1.5 mL/min flow to a steady 0.4 mL/min. Of course, this non-optimal flow yields serious losses in sensitivity and inconsistent measurements.
The pressure reducer is suited for ammonia and two types have been tested, the tubing has a large amount of windings stacked in a vertical position and was replaced by a longer one, and even the entire module with mass flow controller and valves inside the MS was replaced. No results. The technicians from both the MS company and from the gas supplier do not see the cause.
Has anyone experienced similar issues, or does anyone have an idea about potential solutions to this problem?
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I had a similar experience with NH3. You run 1-2 samples and then the cylinder looks almost empty. I found the following advice in http://ww2.chemistry.gatech.edu/~bostwick/stms/ammonia.txt. "If you are using a small ammonia cylinder - stick it in a thermostatically controlled bath and you will hold the vapour pressure constant and make it easy to regulate with a needle valve."
Hope this will be of help to you.
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See above
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Incorporating carbon into copper via electrolytic co-deposition of single wall carbon nanotubes and copper can improve conductivity by 30 percent or more.
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The diameter of the plate is 140mm, while the diameter of the perforation is 3mm. I want to calculate the pressure drop for various flow rates.
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There is a good information in Malavasi et al., "On the pressure losses through perforated plates", Flow Measurement and Instrumentation 28 (2012), DOI: 10.1016/j.flowmeasinst.2012.07.006
May be there is interesting information at this handbook: tp://www.qualityperf.com/media/ipa.pdf
I found the link below, that is an online calculator (I cannot guarantee that it runs ok!)
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I want to use a water lute to balance the pressure in a CVD instrument, the pressure in the chamber is increasing from 1 Pa to more than 1 atm, because this instrument will leak higher than 1 atm, so I have to open the valve before the pressure reach 1 atm, e.g 0.9 atm, and also make sure there is no air bubbles at the water lute valve position or the air will leak into the chamber.
Is there any specialist who can help me design a new water lute valve? Can I use a ball valve at the water lute position to seal the water and the vacuum in the beginning when the pressure is about 1 Pa?
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Scientific Canadian Mechanics' Magazine and Canadian Patent Office Record, Feb.1881. Volumes 7-9.  #12228, 
regarding building and using a  "Water luting" valve.  Google found this in a patent for "Improvements to steam engine technology.  
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What about other materials with high vapour pressure in room temperature (eg. In,Sb,Sn,Pb)?
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According to data for vapour pressures of elements listed at Table 1.44 at the James G. Speight (Ed.) "Lange's Handbook of Chemistry" (16th ed., 2005, McGraw-Hill), the temperatures that correspond to the equilibrium vapour pressure of 1E-08 mmHg (*) increase in the order: Sb < Pb < Bi < In < Sn. Ultra-high vacuum requires pressures below 1E-09 mmHg.     
(*) pressure unit inferred by comparing with other sources but not stated at the table.
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In adiabatic flame temperature formula, the molar heat capacity of products at constant pressure has equation for each compound. Do I need to calculate the average compound? At what temperature should I calculate for each compound?
T(ad)=T(0) + H (enthalpy changes due to combustion)/ C(p)
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go through this pdf file.
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I'm after a sensor to measure the difference in pressure between two areas of flow. Can anyone direct me to a sensor I can buy, or schematics to construct one? I want to measure the difference in pressure between the stream bed surface and subsurface. Thanks in advance
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Validyne provides differential pressure sensor such as DP15 and DP103 for your problem. You can easily check their website for details. In my experience, DP15 is better for maintenance, but DP103 provides a wider pressure range. 
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Is there any standard method available to model the same for hydraulic systems?
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In a nutshell, the answer depends on the nature of unsteady flow event, and I am assuming here you have a one-dimensional system. If you have a fast transient (definition follows below) in a single-phase (homogeneous) flow, you need a solution approach that accounts for water/pipe wall/system elasticity in the formulation, such as numerical models based on the traditional Method of Characterstics. Slow transients (which occur within times much larger than the time scale L/a - pipeline length divided by the acoustic wavespeed of pressure waves in the pipe) can be modeled/described with lumped inertia models. Finally, if you are looking into other types of surges (air/water compression), you may have to investigate deeper into modeling alternatives accounting for air-water interactions.
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Hi
Dear friends.
I'm trying model a simple rectangular channel steady-state flow on Fluent by VOF: open channel condition.
Something cause a problem and affect the results.
the geometry of my channel is 30x30cm by 0.002 slope which the channel length is 10 m ; and the flow depth is 10cm.
According to the
and
boundary conditions considered as pressure- inlet &outlet and the top of my channel considered as pressure inlet according to the Fluent Help!
I've tried many B.C. to all the boundaries. but the velocity of air at the inlet considered about 90m/s!!!!! which it increases along the channel to end and reaches to 690m/s!!!!!!!!!!!
how can it possible???? and i cant fix it
also, density reports shows the water (Secondary phase) is under the air (First phase), which it is true.
but the main problem is the air velocity in Domain. Pics.>>>>>
Please help me to solve this problem.
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Maybe you keep on applying the inlet & exit pressure BCs for WATER to the air region. Physically, for the air region, the pressure should be all ambient pressure
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The co-relation between the foot pressure and the knee back injury risk.  Any valuable suggestions and evidence based studies available?
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Check articles on Knee Adduction Moment.
Its a prime reason of pain in knee which can be reduced or increased based on footwear parameters like, material, lateral wedge, medial arch, heal raise. etc
If you need any help feel free to message me.
Wish you luck for your project.
Regards Parth.
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I am aware of the individual definitions of both static and absolute pressure.
Will the magnitude of static and absolute pressure be the same, even though  definition wise they represent different concepts?
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Absolute pressure refers to the absolute value of theforce per-unit-area exerted on a surface by a fluid. Thereforethe absolute pressure is the difference between the pressure at a given point in a fluid and the absolute zero of pressure or a perfect vacuum.Gage pressure is the measurement of the difference between the absolute pressure and the localatmospheric pressure. Local atmospheric pressure can vary
depending on ambient temperature, altitude and local weather conditions.
Pabs= Atmoshperic pressure + gauze pressure
There are two types of fluid systems; static systems and dynamic systems. As the names imply, a static system is one in which the fluid is at rest and a dynamic system is on in which the fluid is moving.The pressure measured in a static system is static pressure.The pressure increases with depth in the fluid and acts equally in all directions. The increase in pressure at a deeper depth is essentially the effect of the weight of the fluid above that depth. The pressure in a static liquid can be easily calculated if the density of the liquid is known. The absolute pressure at a depth H in a liquid is defined as:
Pabs = P + (ρ x g x H); P is the external pressure at the top of the liquid. For most
open systems this will be atmospheric pressure.For fluids like air column, the product of (ρ x g x H) is negible, as does not have any effect. Then in that case, absolute pressure is equal to P itself.
The concept of static pressure comes into picture, for liquid fuels, where density has appropriate value.
In case of gaseous fluids like air in air craft applications, the concept of stagnationpresure is an important patamter, which is equal to
Stagnation pressure= Static pressure + dynamic pressure, in which dynamic pressure is a fucntion of density and velocityof fluid, while static pressure is calculated from application of altitude and pressure relations. 
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(e.g., high-Ba-Sr granitoids, low-silica adakites)
I know that plagioclase in the source, and its pressure dependence play an important role on it, but there is no plagioclase in mantle rocks, is there?  
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Indeed, the mantle does not contain plagioclase, so that cannot be the reason for rocks that are mantle-derived. But if you are asking about granitoids - they are not mantle-derived; at least not directly. They could be derived by fractional crystallisation of mantle-derived magmas, but only if plagioclase did not fractionate, since this would reduce Sr concentrations.
The best way to generate Sr-rich magmas is to start out with a mantle that is enriched in Sr, for instance by subduction processes. If you look at primitive arc magmas, they will show a positive Sr-anomaly in MORB- or PM-normalised trace element diagrams (the idea is that Sr and other fluid-mobile elements were added by an aqueous fluid coming from the subducted slab). To increase Sr concentrations (irrespective if you start with a subduction-related magma or something else), you will need fractionation of minerals in which Sr is incompatible. This could be garnet (at high pressure), or amphibole (at intermediate pressure). For the latter you of course also need volatiles, so that's most easily done, again, in a subduction environment.
Of course you can also start by partially melting something in the stability field of garnet (whereby Sr goes into the melt), and that is how some people believe adakites are generated (melting of the subducted slab, generating high Sr/Y magmas). However, you don't NEED slab melting to get something with an adakitic signature, fractionation of garnet +/-amphibole can do the same trick.
Hope this helps somewhat to clarify the matter! I attach something I wrote about arc magmatism, which talks about the positive Sr anomaly in arc magmas.
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I mean other things without the pressure and pipe diameter.
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If there are encrustations due to CaCO3 deposition or rusting in case of iron pipes,that could reduce flow velocity. Sometimes ficus roots that could penetrate in side the pipe, especially through the joints,could also reduce flow velocity.
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A method to measure the surface tension of a liquid, relies on creating an air bubble beneath the surface of the liquid, (see diagram). A syringe needle (circular in section) with a sharp tip of a known radius is used to form the air bubble.
How and why can the maximum pressure exerted in forming the bubble be related directly back to the surface tension ? 
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Why are the descriptions on the internet not sufficient to answer your question?
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I am doing triaxials tests on fine sand (Leighton Buzzard, fraction E, particle size distribution 90-150 um). Sample dimentions are 50 x 100 mm. At the top and bottom of my sample I put a saturated stone porous discs. Applied isotopic, confining pressure is 70 kPa and back pressure is 50 kPa.
How can I estimate time needed to saturate my sample using calculation of the Darcy's law? Is there any method to measure the permeability of this porous discs?
I have attached the photo how this disk looks like. I cannot find any information at the manufacture's website. Any advice or previous experience would be really helpful!
Thanks,
Aleksandra
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Dear All,
Thank you for all kind replies for my question. All of them are very helpful.
My intention was to predict the length of time needed for saturation of my sample and compare it with experimental time. The reason why I want to use low pressure it that later in my project I will work with unsaturated state in order to landslide event, that is why I am  interested in shallow soil layers, whose confining pressure is usually low. In the case of sand, the suction and confing pressure should be reasonably low. But if 
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I am considering there is small asymmetry of right left leptons in the early universe due to some reason. 
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To classify the leptons into left or right one needs to have the leptons moving exactly with speed of light. Am I correct? They are luminal leptons you wrote about? But even the neutrinos do have mass - it is strong faith of conventional Physics. So the leptons are not moving with speed of light, aren't they? So they can not be classified as left or right ones, can they?
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Are there any reliable and valid measurement tools?
I have heard of pressure gauges, but no other measurement tool.
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I struggle to comprehend the assessment of 'core strength'. There seems to be alot of ambiguites connected to this? It seems that the aforthementioned assessments are valid but in essence are all evaluating different capacities? Surely a pressure gauge does not establish 'strength' of the 'core'? The McGills assessments with many merits in terms of planes of movement are isometric in nature and endurance based. Do these evaluate 'core strength', which conceptually depicts a rather more global dynamic assessment of this musculature. With the excellent article written by Eyal Ledermann on the Myths of Core Stability...link here: http://www.craigliebenson.com/wp-content/uploads/2010/08/sdarticle.pdf .....maybe it is time to re-evaluate what the 'core' is and specifically its 'functional roles'. This then will hopefully lead to more meaningful assessments being selected for the specific objective in question. Thanks for the original question, but at the minute I think we are 'stabbing in the dark' and is an area of much needed research!
How does band gap structure change under pressure?
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I have question regarding band gap structure of semiconductors.
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In general, pressure leads to a smaller atomic distance, resulting in a larger bandgap (apart from some IV-VI semiconductors, such as PbSe). For small changes in the lattice constant, bandgap increases linearly with pressure: only at very high pressures (>20kbar) the relationship tends to be sublinear. Also, the deformation caused by high pressure may cause valley shifting, resulting in a bandgap switch from direct to undirect (or vice versa).
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I would like to know what sort of pressure sensors are appropriate for measuring the nasal pressure?
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Dear Shilpa.,
yould you please define the pressure you want to measure?
If you are interested to know the pressure at the choanae, you may use anterior Rhinomanometry. With posterior Rhinometry, you can measure pressure within the nose - but careful: the Placement of any sensor within the nose may affect the nasal cycle, may lead to nasal congestion and will certainly affect your results. You may also think about rhinoresistometry. This would give you also a more dynamic Information e.g. regarding the effect of a nasal wing collapse.
Kind regards,
Achim
How can I model the evaporation loss or calculate the evaporation rate from subcooled boiling water in a closed vessel?
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I would like to model an evaporation process realizing in a closed vessel which is initially filled with a preheated water having a temperature of 80°C. About 3/4 of the vessel is filled with water, and the remaining portion is naturally filled by air with a relative humidity of 20%. The water is heated gradually up to the boiling temperature of 100°C at 1 atm. At this time interval, mass transfer occurs at the liquid-gas interface due to diffusion and some of the water is evaporated until the water boils. It is known that the evaporation rate will change with time during this process. When the boiling temperature reaches 100°C, the pressure valve opens by periodically allowing some steam to escape to keep the pressure inside the vessel at 1 atm , thus preventing any excess pressure buildup. In the light of the given knowledge, how to model the process for calculating the evaporation loss. Regards.
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Ibrahim, The process you  are interested in solving is quite complicated but some progress can be made by considering the first stage  before boiling occurs. I have attached some notes that show how one might go about analyzing this problem. Check for typos and minor errors, but the basic method is sound, in my view. Have fun!
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It is a rarely used method in our institution and if aspirated what are the adverse effects expected and what are the early signs to identify the complications?
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aspiration is definitely not recommended, since the risk of damaging small meningeal vessels during suction is very high. once damaged, they would contaminate the csf with blood. so, highly not recommended...
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I need to determine theoretically pressure drop for a multi-channel cold-plate across input and output for a single phase liquid. I have referred  poiseuille number equation for the pressure drop, but those are for cylindrical  shape channels. The channel for which i want to find out pressure drop is in serpentine shape, where length, width, depth are variables.
And please note that ends of channel are not sharp they have an arc profile.
Any information in context with the matter will be really helpful. 
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In the regime that you need i think your best bet would indeed be CFD.
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I want to know how these kinds of modes created and what is the source of this kind of modes.
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Essentially, in the case of the Sun (and other stars with a similar interior structure: basically a radiative core and a convective envelope) the oscillation normal modes are stocastically excited by the convection at the envelope of the star. The restoration force is the pressure in the p-modes. There are also other types of modes: the g-modes (whose restoration force is the gravity) are theoretically expected to propagate deep in star but there isn't yet an uncontroversial detection of them in the Sun due to the "noise" produced by convective features.
Take a look at the links at the Prof. Jørgen Christensen-Dalsgaard's web page.
You can start with this:
and then go through "The Bible":
How can I measure the hydrodynamic pressure drop in a microchannel due to a single droplet?
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Is there a formula to calculate the Hydrodynamic pressure drop in a microchannel due to a single droplet in a two phase flow with continuous or on demand droplet generation?
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If your questions is about the flow of a non-wetting-incompressible drop or drops that are carried by the wetting fluid moving a long a capillary of non-circular cross section moving at constant rate look at:  Zhou D, Blunt MJ, Orr FM, 1997, Hydrocarbon Drainage Along Corners of Noncircular Capillaries, Journal of Colloid and Interface Science, Vol: 187, Pages: 11-21
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Is there anyone who is working with ONYX-3 Magnetron Sputtering Cathode? i meet some problems with plasma generation: i measure a current without having a plasma even if i use the appropriate Argon gas at the appropriate pressure 10-2 mbar! Thanks for Help
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hi, be sure you have no short-cut somewhere..
before closing your vacuum chamber, check the the conductivity between cathode (sputtering material) and chamber wall or anode. Infinite resistance should be shown (use a conventional ohmmeter/voltmeter, may be disconnect the power supply plug).
it is easy to make mistakes when fixing the anode ring and the distance cathode-anode is not well set, too big or too small.. 2 mm should be fine.
lukas
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The effects if soft tissue mobs on tibialis anterior or any other muscle when measured with pressure algometer.
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Dear Losiute,
Pain pressure threshold increased in soft tissues mobilization and long-term use of muscle training.
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Suppose a gas like hydrogen is stored in a tank of given volume at given temperature and pressure. If the tank has developed a leak of 1 mm diameter, how much time system will take to reach 50% of the original pressure? How to proceed to solve this problem
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The information provided by the above respondents is sufficient to solve this problem.  In general, a first order differential equation needs to be solved that uses the PVT behavior of the fluid in the tank and a mass balance on the tank. Depending on th eaccuracy you need, the ideal gas law should suffice for the PVT behavior, but if not, use Peng Robinson for H2 or some similar more accurate PVT formula. The flow across the presumed hole in the tank can be estimated from choked flow at least initially (until the pressure gets much below half, but you are only interested in the results to reach half the init. pressure so you can safely use choked flow to that point).  So per each second of time, say, a certain flow would result with a certain amount of mass leaving the tank.  Then the mass remaining in the tank is known and the PVT equation is used to recalculate the pressure and temperature (there would be a cooling or heating as the mass in the tank is expanded - for H2 it could be a heating since it is one of the rare molecules that has a reverse joule thomson expansion coefficient.  This type of problem is treated in basic chemical engineering thermodynamics textbooks, but has real world importance in sizing relief valves and in determining emergency shutdown procedures.
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Suppose we have to inject CO2 within a deep geological formation, we have overburden and pore pressures given. How do we decide the maximum pressure which the formation can allow to rise without leading to formation failure? 
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Thank you Sir for the information.