Investigation of the pressure drop in refrigerant pipes of an R744 automotive air conditioning system

This paper presents a test rig to measure the pressure drop of the refrigerant R744 (CO2) in refrigerant pipes of an automotive air conditioning system. The experimental layout is basically a cooling cycle. In a measurement section, arbitrary shaped pipes of an automotive air conditioning system can be installed. As boundary conditions mass flow, pressure and enthalpy of the refrigerant at the inlet are independently adjustable to values that cover the whole operating range of an R744 automotive air conditioning system. In addition to the experimental investigations, a numerical analysis with CFD software is conducted. The results are compared with the test rig results to validate the numerical model. Finally, the impact of the refrigerant pipes pressure drop on system behavior is analyzed with a comparison of two models of an R744 air conditioning system in Modelica. One model includes the resistance coefficients based on experimental data and the other model uses simplified state of the art pipe models