Dear,

you should simulate natural convection in this case. So, turn on the gravity force and also consider fluid density as a function of temperature. Remember to solve the problem in unsteady type

Regards

Hossain Nemati thank you for your reply actually i will be dealing with furnace with liquid in it which in copper tank and there is coil which heats tank , there is air in-between copper tank and coil .

Dear Adesh,

It depends on how deep you want to know about phenomena and what you need to calculate. However, It is better to attach a sketch.

Hossain Nemati thank you for reply i have attached a sketch of cross section of tank

as a first approximation, you can model only the liquid and uniformly distribute the total heat fluxes from coils on the liquid wall. As I mentioned before, you should consider liquid density as a function of temperature.

For the next step. you can also consider coils. There is no need to solve heat transfer inside the coil. It is just enough to consider heat flux as the coil boundary condition. Again, you should assume the air density as a function of temperature.

and finally, you can consider radiation from the coil that makes your model time-consuming.

thank you for help.