Evaporation heat transfer and pressure drop of R245fa inside a horizontal smooth tube.

This study experimentally investigates the evaporation heat transfer and pressure drop characteristics of R245fa, which is used as a working refrigerant for a high-temperature heat pump and binary generator inside a horizontal smooth tube. The experimental apparatus consists of the refrigerant pump, Coriolis flowmeter, water preheater, electric preheater, test section, after-condenser, and receiver tank. The test section is a 4.5-m-long counter flow-type double pipe heat exchanger. In this section, the refrigerant flows through the inner test smooth tube, which is an 8.3 mm inner diameter copper tube, and the heat source water flows in the annulus surrounding the inner tube. The annulus is divided into five subsections, each 600 mm long. The evaporation experiment is conducted under a mass velocity range of 50 to 300 kg/(m2s) and saturation temperature range of 30 to 40°C. The measured evaporation heat transfer and frictional pressure drop characteristics of R245fa are clarified for the effects of mass velocity, vapor quality, saturation temperature, and heat flux. Furthermore, experimental results are compared with several previous correlations.