Dear colleges,
I'm working a heat pipe simulation using the CFX code and I having some difficulty to model it. First of all, the device operates with 40% of volume fraction using water at a pressure of ~0.31bar (Saturation temperature ~25°C).
Initially I've divided the geometry (an annular space) in 2 parts: one representing the liquid and the other representing the gas. In the CFX-pré, I've created 2 domains (fluid-fluid).
In this point I have a question: for the gas, it is necessary to consider a mixture of water steam and air or only the steam? Second In CFX I've not find a way to set that in one domain I have boiling of liquid water while in the other domain I have condensation occurring at the same time. Is it possible? My question is motivated due to in CFX I can define that a fluid in continuous, dispersed and so on. But I can't define that its morphology is different in the other domain (for example: while the liquid water is continuous in one domain, it is a dispersed phase (droplets) in the other. The same is valid for the steam (or the air-steam mixture): it is a dispersed phase in one domain and a continuous fluid in the other (where condensations takes place)).
The heat pipe have no adiabatic section, but only the evaporator (where the liquid initially relays) and condenser (in which initially there is an evacuated space with some air or steam - as mentioned, I have no idea if its necessary to consider both or only the steam because I've tried both approaches a not one have resulted in a converged simulation).
I would be wonderful if some one could could give a clue of which way I should follow.
Thanks in advance.
Why you should use two domains? the paper discussed two fuid phases in one domain prepared in cfx, I hope it will help you https://www.researchgate.net/publication/349412363_Numerical_analysis_of_fluid_flow_dynamics_around_a_yawed_half-submerged_cylinder_inside_an_open_channel
Thanks for both colleges. I'm trying to implement the suggestions.
Regarding the question of Malik Al-Amayreh, I think initially that one domain is for liquid water and the other for the gaseous. But I have no previous experience in this kind of problem and I do not know if this is the correct form to model the problem in CFX. I'm trying several alternatives.
For now, I have simulate using only 1 domain and with the gas phase as only air. The simulation converges but the results are not good. For example, there is no more any liquid and the gas phase (which seems to become be a mix of steam+air) have a variable volume fraction (I think the liquid should be present if the gas volume fraction is less than 1, but this is not the case as the results of CFX demonstrates).
Regarding pressure, it have a value very different from the operation (saturation) pressure. I've read in some forums that for a enclosed domain the pressure is not an important variable. This is only for reference for calculate the fluid properties. In my case, the saturation could be simulated based on temperature. But I expect that the pressure be equal to the value of saturation pressure. However, this is not the case.
I would be wonderful for other hints and thanks for the previous help.
@Deiglys Borges Monteiro. In CFX you have many models, if the flow is one phase exists as particles, droplets, or bubbles named as Dispersed System. For case Multiphase Gas-Liquid Flow Regimes in Pipes, the regime depends on the vapor and liquid flow rates, this tutorial may help you, Good luck,
https://www.youtube.com/watch?v=1uX5EpyyRUM&ab_channel=XSCIENCEY
Dear Malik Al-Amayreh,
Thanks for the suggestion. I'll watch and try to implement some modifications in the simulations. If I solve this puzzle, I'll post news.
Thank you very much.
Sincerely,
Prof. Deiglys Borges Monteiro
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