Why is the temperature change across my "Mass Flow Rate Source" block very large?

I have a simple model with a "Mass Flow Rate Source" connected to a "Pipe" with a thermal input. For some reason the temperature across my "Mass Flow Rate Source" is dropping by almost 30K. While I understand the changes in pressure and kinetic energy could cause some change in temperature it should not be anywhere close to 30K.

Why is the temperature changing so much?

Answer 1

[MathWorks Support Team]

This most commonly occurs when the output of the "Mass Flow Rate Source" has a different cross sectional area than the pipe. When the cross sectional areas are different, the velocities must be different in order to maintain the constant flow rate. The change in velocity causes a change in kinetic energy, which means that the temperature must change in order to maintain a constant enthalpy. If you set the cross sectional area at the output of the "Mass Flow Rate Source" block and the cross sectional area of the pipe to be the same, then you should not see this change in temperature.

In the Gas domain if the "Mach number threshold for flow reversal" in the "Gas Properties" block is high, and if setting the cross sectional areas in the "Mass Flow Rate Source" and "Pipe" does not reduce the change in temperature across the "Mass Flow Rate Source", then try reducing the "Mach number threshold for flow reversal" in the "Gas Properties" block.