Cooling of a tank
 

Hi guys,

I am not new to ANSYS as we have done Fluent as well as mechanical exercises in the past. We have never done Heat Transfer and that is what Im struggling with so I thought I will post it here.

I have a square tank FULL of liquid kerosene that cools down slowly. I set the temperature of the walls at -55deg and fluid at 23 to start with. Took few hours and it all cooled down. Got the right results, allowed the gravity and energy methods so the cold fluid dropped down to the bottom of the tank. All great - happy with my initial results.

Then I added outflow from the tank:
To do it I created an inlet where air was coming in at the same volume flow rate as the fluid coming out. I allowed multiphase and when trying to select the air coming in as air, this is when it selected the fluid in the tank also as air. When I changed the fluid into kerosene, it selected the air as kerosene. I could select mixture but then everything becomes a mixture.

I am very new to heat transfer in fluent hence I am not sure what it is that Im doing wrong and whether Im tackling the problem in the right way.

I know someone will probablu reply 'one thing at a time' but I would also like to add the wall temperature and pressure to vary.
I know that I need to create a UDF file but I do not know how to do it.
I want the temperature and pressure to fall for the first 20 minutes stay at constant values during cruise and then increase during the landing.
If it is easy, please let me know. If its more complicated - I found few bits online so can look through them. Its just that I do not know what I need and whether its more complicated than I think.

Thank you for help