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Fluent phase change problem

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Old   July 31, 2013, 03:59
Default Fluent phase change problem
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Hi, MY problem is as follows
Under the Cell Zone condition. my fluid is initially in solid state which after taking heat from wall melts. My question is when i check the porosity zone what should i select under Solid material name(default alum) and what should be the porosity value(fluid porosity). I am confussed as under the heading Heat Transfer Settings Solid material Name is coming as some metal
but in my problem that is a solid state of WAX.(which i defined as liquid).Since i want to capture the amount of liquid melted over a period of time.So initially my fluid porosity will be 0(solid) which keeps on changing upto 1(completely melted).

Suggest me what should be the correct way for this.
see the screen shot (sorry for the bad pics due to limitation of size) but i tried to explain it
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Old   July 31, 2013, 07:56
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Hello again
As I am a bit familiar whith the case you are trying to simulate, I will try to help. From the information you gave so far, I dont see why you need a porous material.

You have 3 different kinds of material: the surrounding fluid at a high temperature, the solid wall which encloses the phase change material
and the phase-change material itself which is initialized with a temperature below the solidus temperature. No porous material needed...

Because CFD is so much fun, I set up a quick&dirty simulation of what I understand you want to model. Did I get that correctly?
liquid_fraction.jpg
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Old   July 31, 2013, 13:22
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Yes sir you very well understood my problem. I have one doubt for making the nodes share between htf(inner),tube(carrying Heat transfer fluid) and the material(PCM), they are made one part in design modeller.So the solid tube(having fins) also gets the mesh. But in your geometry there is no mesh. Do i should suprress the tube in my case. Wont it effect the results? Also literature suggests that enthalpy-porosity formulation for PCM analysis since there is lot of energy associated with phase change(latent heat) So i want to know how that is taken care in fluent. I am using only solidification melting model. without pull velocites
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Old   July 31, 2013, 13:50
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I am not too familiar with the theory of the enthalpy-porosity technique used in fluent.
But since there doesnt seem to be too much movement in your PCM, the porosity in the mushy zone should not affect the results.
In Fluent, you specify solidus and liquidus temperature and the "pure solvent melting heat" (->latent heat) . Thats it.
The fluent theory guide surely knows more about this topic than I do.

I actually dont understand the first part of your question.
Of course my geometry is represented by a mesh in the finite volume solver.
You dont see the contour of the liquid fraction in the solid material because it is not defined here.
You dont have to model the solid surrounding the PCM if it is thin enough. You might aswell incorporate its effect at the interface between the PCM and the fluid.
But no matter how you do it, you need at least two separate zones for fluid and PCM and thus also separate parts in the geometry.
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Old   August 6, 2013, 01:43
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Sir
if my heat transfer fluid is turbulent which model is suitable for the said analysis.
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Old   November 1, 2017, 14:10
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Quote:
Originally Posted by flotus1 View Post
I am not too familiar with the theory of the enthalpy-porosity technique used in fluent.
But since there doesnt seem to be too much movement in your PCM, the porosity in the mushy zone should not affect the results.
In Fluent, you specify solidus and liquidus temperature and the "pure solvent melting heat" (->latent heat) . Thats it.
The fluent theory guide surely knows more about this topic than I do.

I actually dont understand the first part of your question.
Of course my geometry is represented by a mesh in the finite volume solver.
You dont see the contour of the liquid fraction in the solid material because it is not defined here.
You dont have to model the solid surrounding the PCM if it is thin enough. You might aswell incorporate its effect at the interface between the PCM and the fluid.
But no matter how you do it, you need at least two separate zones for fluid and PCM and thus also separate parts in the geometry.
I am doing a simulation on solidification and melting of water inside spherical capsules as the heat transfer fluid passes over them. Although I have done the setup, I do not get reasonable result in terms of the liquid fraction over time. I would highly appreciate it if anyone could guide me in the simulation.
Thank you in advance.
setup details are as follows...


General:
1.Mesh seems to be ok with positive values for “minimum volume” and “minimum face area”.
2.Solver Pressure Based, Time unsteady, Gravity checked (-9.81 in Y direction), 2D-space Planner.
Models:
1.Multiphase model (VOF) with 2 eulerian phase. I have activated the check mark of “Implicit” for volume fraction parameters and “implicit body force” for body force formulation.
2.Standard K-epsilon model is used with EWT (Enhanced Wall Treatment).
3.Solidification/melting is ON (so as the energy equation)
Phases:
HTF (ethylene glycol solution) -primary, and PCM (water)- secondary.
Material:
Introduction of two fluids (HTF and PCM which is water in this case)
Cell zone condition:
Zone (PCM) Phase(mixture)
Boundary condition:
1.“velocity inlet” is set as the inlet B.C. and “outflow” is selected for the outlet that is placed far enough.
2.Both fluid zones are automaticly set as “interior”.
Solution method:
Scheme: SIMPLE, Discretization for pressure PRESTO, for Moment “first order upwind”, for Energy “first order upwind”,, for volume fraction Geo-Reconstruct
Solution control: Solution control is left untouched.
Solutin initialization : Standard. first, both fluid zones are given the temperature of (e,g 275 k) . Then I “marked” the fluid zone inside capsule and “patched” the temperature of (e,g 273.11) for it to simulate solidification. I entered the values of the temperature so that I quickly notice that whether I am doing the simulation correctly or not.
Then, I run the simulation by time step size of 0.1s
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Old   April 5, 2018, 18:47
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Quote:
Originally Posted by dinesh View Post
Yes sir you very well understood my problem. I have one doubt for making the nodes share between htf(inner),tube(carrying Heat transfer fluid) and the material(PCM), they are made one part in design modeller.So the solid tube(having fins) also gets the mesh. But in your geometry there is no mesh. Do i should suprress the tube in my case. Wont it effect the results? Also literature suggests that enthalpy-porosity formulation for PCM analysis since there is lot of energy associated with phase change(latent heat) So i want to know how that is taken care in fluent. I am using only solidification melting model. without pull velocites
have you used enthalpy updating technique for your problem ?
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