Two-phase exchanger with evaporator that loses pressure at the outlet.

Hi,

I created a small two-phase exchanger circuit with evaporator expansion valve, compressor and condenser, using NH3 as the refrigerant fluid by generating the tables and properties of the refrigerant fluid with CoolProp.

The problem that the simulation starts but after a few seconds, the pressure at the outlet of the exchanger collapses.

I have attached the file, the circuit is very simple but I can't figure out if it is a problem with the expansion valve or the evaporator.

Thank you for your attention.

Answer 1

[Yifeng Tang]

Check out this documentation page and carefully follow the workflow.

https://www.mathworks.com/help/hydro/ug/modeling-a-refrigeration-cycle.html

Looking at the parameters you have in some of the blocks, I don't think the parameters throughout the system have been consistently set. For example, the air flow of 0.8kg that is being pushed through a cross section of ~8500mm^2 will lead to ~100m/s local speed, which doesn't look very reasonable. For refrigeration system modeling, parameters and sizes matter a LOT. So, test each component in harness models, as shown in the documentation page above, is VERY important.

After all the sizing work, pay extra attention to the initial conditions as well. The ICs will determine the total amount of refrigerant in the loop, i.e. the charge mass. Like in an actual refrigeration system, charge mass matters in a simulation model.