Analysis of refrigerant pipe pressure drop of a CO2 air conditioning unit for vehicles

Abstract

This study investigates the pressure drop in refrigerant pipes of a CO2 automotive air conditioning unit. A test rig to measure the pressure drop of arbitrarily shaped pipes is presented. As boundary conditions at the inlet of the test section, mass flow, pressure and enthalpy of the refrigerant are independently adjustable to values that cover the whole operating range of a CO2 automotive air conditioning system for cars in the premium segment. Numerical analysis using CFD and a one-dimensional modelling tool is carried out. The pressure drop for the suction pipe reaches values of up to 500 mbar. CFD simulation predicts the pressure drop with an error of 25.7% for single-phase flow whereas the deviation using one-dimensional models is 46.5%. During two-phase flow the error increases to 55.8% with one-dimensional models and 42.4% using CFD.