[JCamilo]

Hi everybody, I'm trying to simulate a conjugated heat transfer problem in Fluent, in a kind of shell and tubes heat exchanger, which consists in a cylinder through which flows a saturated mixture of liquid/vapor ammonia at low temperature (entering at the bottom and exiting at the top), in this same direction (inside the cylinder) there is a series of tubes containing liquid water (not flowing), which will be frozen by giving heat to the saturated mixture of ammonia through the wall of the tubes, at the time that the liquid ammonia will evaporate (there is going to be mass transfer from the liquid to the vapor), in other words, I have three cell zones, one fluid zone where there is a mixture of two phase; a different cell zone (fluid) not in contact with the first and containing liquid water that will solidify; and a third cell zone (solid) representing the tubes containing the water.
I'll be using the VOF model (with 2 Eulerian phases) since the Eulerian model doesn't allow me to use simultaneously the solidification/melting model (necessary for the water). According to the user's manual I set the primary and secondary phases for ammonia along with his interaction (evaporation-condensation) but I just don't know how I must specify the material for the water, I thought I should define a third phase and assign it to the water, but in that case, when I specify this cell zone as another phase (water-liquid) fluent automatically changes the ammonia cell zone to water-liquid instead of mixture, I mean, Fluent set the same phase to all the fluid zones
Does anyone of you know how I should deal with this problem? Any suggest is welcome.
Thanks in advance!

[sam_cfdd]

Hi,

I am running Fluent to simulate nozzle which spraying water and air. I assume two different inlet boundaries for water and air. I am using k-epsilon turbulence model and Eulerian multiphase. I want to find out particles size distribution after spraying. Solution is diverge every time which I run. I snapshot or error and geometry of my case. I know I should choose small amount for under-relaxation factor but how small?. and is there another thing else than under-relaxation to affect on convergence?. Thanks.

[sam_cfdd]

Hi,

I am simulating nozzle spraying water and air in Fluent. I am using Eulerian model. which model is suitable for interaction between phases for drag and lift coefficient?.

[haze_1986]

I try to see if I got your question correctly, in a normal lets say shell and tube heat exchanger, you can specify a material for the tube and another for the shell. However, once multiphase is turned on you can no longer do that, since FLUENT specifies them as mixtures. Is that what you're asking?

Originally Posted by JCamilo

Hi everybody, I'm trying to simulate a conjugated heat transfer problem in Fluent, in a kind of shell and tubes heat exchanger, which consists in a cylinder through which flows a saturated mixture of liquid/vapor ammonia at low temperature (entering at the bottom and exiting at the top), in this same direction (inside the cylinder) there is a series of tubes containing liquid water (not flowing), which will be frozen by giving heat to the saturated mixture of ammonia through the wall of the tubes, at the time that the liquid ammonia will evaporate (there is going to be mass transfer from the liquid to the vapor), in other words, I have three cell zones, one fluid zone where there is a mixture of two phase; a different cell zone (fluid) not in contact with the first and containing liquid water that will solidify; and a third cell zone (solid) representing the tubes containing the water.
I'll be using the VOF model (with 2 Eulerian phases) since the Eulerian model doesn't allow me to use simultaneously the solidification/melting model (necessary for the water). According to the user's manual I set the primary and secondary phases for ammonia along with his interaction (evaporation-condensation) but I just don't know how I must specify the material for the water, I thought I should define a third phase and assign it to the water, but in that case, when I specify this cell zone as another phase (water-liquid) fluent automatically changes the ammonia cell zone to water-liquid instead of mixture, I mean, Fluent set the same phase to all the fluid zones
Does anyone of you know how I should deal with this problem? Any suggest is welcome.
Thanks in advance!

[soumitra2102]

Originally Posted by haze_1986

I try to see if I got your question correctly, in a normal lets say shell and tube heat exchanger, you can specify a material for the tube and another for the shell. However, once multiphase is turned on you can no longer do that, since FLUENT specifies them as mixtures. Is that what you're asking?

I think the question asked here is right. I also have the same question. In fluent once I define multiple phases (primary, secondary), I can not apply any (other) fluid material to any zone. It is like it assumes all fluid zones in the model are only and only for the multiple phases defined.

For example, if I have two zones one for multi_phase-water and another for single_phase-oil separated by a solid domain, then I can not assign oil to any fluid domain.

[Arhaam_Mubarak]

Did you found the solution? I have similar problem.
I am trying to run multiphase VOF simulation. I am working on simulation of Heat transfer in Shell and Tube Heat Exchanger 3D problem. The length of Shell and Tube Heat Exchanger is 22ft. The inner diameter of shell is 2.25in and tubes inner diameter is 0.56in. At first, I am considering the Shell fluid propylene is at constant temperature -50F so there is no fluid inlet and outlet in shell. I will model baffles and multiple passes later. Ethylene enter in tubes at 160F. The saturation temperature of ethylene is -43F. When I turn the multiphase model ON with VOF then only mixture can be selected in Cell zone conditions and and Boundary conditions.
Q1. How can I separately define the propylene in shell domain and ethylene in tube domain with multiphase VOF on?
Q2. How can I consider the propylene as static fluid in shell?

Originally Posted by soumitra2102

I think the question asked here is right. I also have the same question. In fluent once I define multiple phases (primary, secondary), I can not apply any (other) fluid material to any zone. It is like it assumes all fluid zones in the model are only and only for the multiple phases defined.

For example, if I have two zones one for multi_phase-water and another for single_phase-oil separated by a solid domain, then I can not assign oil to any fluid domain.

[soumitra2102]

Originally Posted by Arhaam_Mubarak

Q1. How can I separately define the propylene in shell domain and ethylene in tube domain with multiphase VOF on?
Q2. How can I consider the propylene as static fluid in shell?

I think when you set boundary conditions like inlet/outlet, you can set them for each (primary/secondary) phase (Note that that this option depends upon the phase model you choose). Then you can set '0' volume fraction for the phase that you don't want there.

In my problem, I had a significantly large cooling/heating fluid volume. Due to its large volume the temperature changes in the domain were going to be negligible. Therefore, I simplified the problem by not being interested in knowing its thermal-hydraulics as part of the simulation results. So, I "Patched" that particular fluid domain with '0' velocity' and a constant temperature that I wanted. In other words, that domain could now act as a "constant temperature heat sink/source" for other adjacent domains through "Conjugate Heat Transfer". And so forth, thus it was may be rather irrelevant what material/fluid properties that heat source/sink domain has. Because that "Constant" temperature can be provided by anything, let it be oil or even wood.
This simplification was necessary in my problem as it becomes much more complex if you are considering bother condensation and boiling phenomenon in a single simulation setup. You can focus on one phenomenon taking place in domain.

P.S. Patching can be done at Solution Initialization.

[soumitra2102]

Originally Posted by soumitra2102

In fluent once I define multiple phases (primary, secondary), I can not apply any (other) fluid material to any zone. It is like it assumes all fluid zones in the model are only and only for the multiple phases defined.

For example, if I have two zones one for multi_phase-water and another for single_phase-oil separated by a solid domain, then I can not assign oil to any fluid domain.

Ansys CFX has a specific solution to this problem.
multiple fluid domain

[Arhaam_Mubarak]

Originally Posted by soumitra2102

This simplification was necessary in my problem as it becomes much more complex if you are considering bother condensation and boiling phenomenon in a single simulation setup. You can focus on one phenomenon taking place in domain.

P.S. Patching can be done at Solution Initialization.

Thank you. My this case is similar to yours. I am considering shell domain as static fluid at constant temperature and pressure. I ran the case with patched constant temperature of -55F and constant pressure of 16.7psi. But with multiphase on, the options of individual fluid selection replaces with mixture.