I am trying to simulate the heat flow in a system and the temperatures that I get for the fluid in my system do not match what I expect them to be.

When I expect to see a temperature rise of 3 degree Celsius, I only see 0.6 degree Celsius. When I expect 120C, I see a 21C.

My system is pretty simple: There is a copper box (with adiabatic outer walls) in which there are two FR4 boards (facing each other) (the boards are 2 mm away from the inner walls of the copper box). Each board has 13 chips (chip material = Typical CeramicBGA) on it and they are defined as volume sources (12 of them = 0.5 W and 1 of them = 1W). There is an inlet lid through which water flows in with a volume rate of 0.001Kg/s and temperature 17C and an outlet lid which is set to the standard temperature (25C) and standard pressure. So, everything looks good.

When I run the simulation, I see the water temperature go from 17C (average inlet temp) to 17.48C (average outlet temperature). I should see a ~3.39C rise (17 to 20.39 approx.), but I dont see it!

Here is how I expect to see a 3.39 C rise: (theoretical calculation)

Q = m c T ==> Q = p V c T.

Taking the time derivative of both sides: dQ/dt = p dV/dt c dT.

So, dT = (dQ/dt) / (dV/dt) c. (the p cancels as we are using the volume rate, the units are consistent here with Celsius).

Plugging in all the values, dQ/dt = 14W (from summing up all the powers of the chips), dV/dt = 0.001Kg/s, c = 4120 J/kg K, I get a 3.39 Celsius.

**(p = density, V = volume, m = mass, c = specific heat, T = temperature, Q = heat)**

*I am confident that the calculation above is correct*.

I have tried everything that I could think of and find online: like changing the mesh size, turning on gravity, turbulent/laminar flows, etc. However nothing has helped in getting the simulation to match the theoretical results. Am I doing something wrong?

Thank you very much,

Karishma sent me his model, he thought that the heat inputs were per component vs total. So all components were selected and 0.5 applied, so it was like 15/0.5W instead of 15x0.5W.