[Johan M]

Hi Everyone,
I am doing a simplified scenario of simulating a helical cooling jacket that will wrap around a motor. The fluid is water. The inlet of the jacket is 20C and the outlet is expected to be 30C.The motor will release a heat load of 1900W.
This simulation did not model the conduction of the walls surrounding the jacket. Instead, I worked out the heat flux produced by the motor from the heat transfer rate of 1900W and the motor exterior surface area. I applied this heat flux to the inner faces of the cooling jacket in the thermal section of the boundary condition tab as a heat flux condition. I had a pressure inlet with a fixed thermal pressure, and a mass flow outlet.
My simulation results displayed a 6C increase in outlet temperature and and negative heat rate of -1800W. The heat transfer rate through my inner walls were +800W and suspiciously the inlet was +1000W. The net heat transfer rate was more or less 0W
I can’t seem to understand:
1. Why there is a heat transfer rate across the inlet?
2. Why the heat transfer rate through the inner wall is not 1800W?
My reference values for enthalpy were 0.
Additionally, I ran an area weighted average of the wall flux with the Total surface heat flux variable on the inner wall and got the heat flux I specified at the start of the simulation. The inlet is at 20C as specified.
Any advice would be appreciated

[MKuhn]

The energy balance deals with enthalpy differences. So the difference the heat flux of inlet and outlet should be your heat from the motor. The net heat transfer rate should be 0 (so all right here, maybe you can add a screenshot), if not, you have to run the simulation some more iterations, even if the energy residuals are already converged. What is the mass flow?

[Johan M]

Originally Posted by MKuhn

The energy balance deals with enthalpy differences. So the difference the heat flux of inlet and outlet should be your heat from the motor. The net heat transfer rate should be 0 (so all right here, maybe you can add a screenshot), if not, you have to run the simulation some more iterations, even if the energy residuals are already converged. What is the mass flow?

Thanks Mkuhn,

The mass flow rate differences were very low. Other temperature monitors were flat lined. I didn't realize that the temperature at the inlet brings a heat transfer rate of its own into the system

Kind regards,
Johan

[MKuhn]

Originally Posted by Johan M

Thanks Mkuhn,

I didn't realize that the temperature at the inlet brings a heat transfer rate of its own into the system

And the outlet brings the same heat transfer out of the system plus your motor heat.