Heat Transfer and Pressure Drop during Evaporation of R134a in Microchannel Tubes

The paper presents result for heat transfer and pressure drop in evaporation of R134a in microchannel tubes conducted in a facility with a 6 m long tube, modified to provide realistic situations for refrigerant blends with even the highest glide. The concept of the experimental facility is to measure heat transfer coefficient and pressure drop on the refrigerant side in condensation and evaporation with or without oil with heat exchanger in mind. The auto-controlled test line has 6 test sections for testing and 5 conditioning sections to preset the inlet quality of each test section. This facility provides data in the complete process of evaporation (quality from 0 to 1) or condensation (quality from 1 to 0) in a single pass. The secondary fluid in coolant loop for heating or cooling is water. By controlling the inlet water temperature of each test section, both constant wall temperature and constant heat flux conditions or anything in-between can be achieved. The tertiary loop is a chiller loop running with glycol/water mixtures to cool the water and refrigerant. First results with R134a in this facility show heat transfer coefficient and pressure drop changes with vapor quality and represent excellent starting point (baseline) for explorations of mixtures of low pressure and low GWP refrigerants that are replacements for R410A.