The influence of brine flow on the flow boiling refrigerant heat transfer coefficient in a compact brazed plate heat exchanger

The present article investigates the heat transfer coefficient on the refrigerant side in an compact brazed plate heat exchanger used as evaporator with different brine flows. The experimental equipment consisted of a test rig, simulating a domestic heat pump. Two different heat loads were tested, 5 kW and 10 kW, which corresponds to approx. 2.5 kW/m2 and 5.0 kW/m 2. The inlet quality to the evaporator was kept within 0.18 - 0.20. The pressure was kept within 2.93 - 2.97 bar(a) and R134a was used as refrigerant. The experiment showed for both heat loads a significant increase in the refrigerant area averaged heat transfer coefficient with increasing brine flow. It may be concluded that the temperature profile on the brine side has a significant influence on the refrigerant area averaged heat transfer coefficient. It is suggested that the higher wall superheat on the refrigerant side near the inlet of refrigerant is enhancing the heat transfer.