## Fluids

#### How to maintain saturation Temperature and Pressure during nucleate POOL boiling in ANSYS?

• Anadi_Mondal
Subscriber

Hello,

I did saturated nucleate boiling experiment for two saturation temperatures using the two refrigerant(R134a and R123). Now I want to simulate this saturated nucleate boiling using ANSYS. I have attached the 3D drawing of the experimental setup and the 2D drawing that I am planning to simulate in ANSYS.

During the experiment when I applied heat flux at the bottom of test surface , the temperature and pressure of refrigerant inside the pool increased .So, I used two chillers(WATER BATH) to reduce the temperate and pressure of liquid and vapor, and maintained same saturation temperature and pressure during whole experiment.

Would anyone tell me how can I maintain the saturation temperature and pressure inside the pool after applying heat flux at test surface in ANSYS? Another word, how can I do the work of chillers in ANSYS?

I attached four thermocouples with test surface and used Fourier Law to get the top surface temperature , finally got wall superheat by substracting saturation temperature from top surface temperature.

Regards,

Anadi

Original Setup:

• DrAmine
Ansys Employee
Extraction of energy can be a way to do that if you know the amount the chillers will extract. **** variant will be to model them in the system.
• Anadi_Mondal
Subscriber
I don't know the amount of energy that chiller extracts. Actually I don't need to know this for experiment. My primary focus is to maintain the saturation temperature and pressure in the pool anyhow. I inserted two coils (one in vapor and another in liquid) in the pool that was connected with chillers. I just reduced/increased chiller temperature manually to maintain saturation temperature and pressure in the pool without considering any mathematical formula. If saturation temperature and pressure are maintained in the pool , I don't need to consider how much I increase or decrease chiller temperature. Sometimes, I need to reduce one chiller temperature by 5 degree(not exact, just for example) and another chiller by 3 degree OR first chiller by 4 degree and 2nd chiller by 4 degree to get same experimental condition in pool. So, chillers temperatures are also not fixed. Will you tell any other alternate way to handle this in ANSYS?
• Rob
Ansys Employee
You may be able to use a UDF or Expression to alter a heat flux based on a temperature but you'd need a relationship between the two and some damping to avoid an oscillating solution. Otherwise, you'll need to do it as you do in the experiment.
• DrAmine
Ansys Employee
Yes to add: you can create a sort of controlled heat flux using some integrated values and target values. This can be achieved via Fluent Expressions too: example in the User's Guide. If you cannot do that: you need to do it like Rob said.
• Anadi_Mondal
Subscriber
& Sorry , I did not understand your idea properly. Would you explain your idea little more? Which type of UDF and expression I need to use? It would be better if you use any example for explanation.
will you mention exact example you are mentioning in User's Guide?
q''=h(T_wall- T_sat), I know q'', T_sat only, and determined T_wall(top surface temperature of test surface after applying heat flux) while kept the liquid and vapor temperature and pressure at saturation state in pool.
Here is my published article on it-
https://www.researchgate.net/publication/332007396_NUCLEATE_POOL_BOILING_OF_R-134A_ON_ENHANCED_HORIZONTAL_SURFACES_HAVING_PORES_ON_SUB-TUNNELS
Regards Anadi
• DrAmine
Ansys Employee
and q'' where it is applied?
The idea was either you find a way to mimic the effect of the cooler / chiller or you need to incorporate it in you case as part of the mesh and as an additional zone.
• Anadi_Mondal
Subscriber

Please see the image attached at the top(2nd). I marked the location by 'Location of applied heat flux'. Moreover, I got a conference paper where they set the top wall as the pressure outlet boundary condition to maintain saturation condition inside the pool. The backflow temperature was set to the saturation temperature of the water. If the pressure is not increased in the pool , obviously the temperature will not increase. The water temperature inside the pool will be at saturation state.
Do you think this will solve my problem?
I have attached the paper here. If you don't mind, please have a look.
Regards Anadi
• DrAmine
Ansys Employee
Okay I thought it is related to the cooler: applying the heat flux is straightforward then.

Pressure input can be indeed used to maintain the system pressure but you need to put bit far way from the "area" of interest to avoid any "numerical" or non desired "reversal Flow". That will set the operating pressure in your system but you will still have small variations in the gauge pressure which will lead to slight changes in the saturation properties. Just use a Table data for saturation to be on the safe side and monitor the values of the saturation temperature then.
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