Design and experimental verification for double-loop countercurrent dry-expansion evaporators

Based on the asymmetric space heat transfer concept, designs a novel double-loop counter-currrent dry-expansion evaporator equipment, and installs it to an air-source heat pump unit and performs the experiment. Theoretical calculation and test results show that the calculated value of the overall surface coefficient of heat transfer is 1 709.4 W/（m²·K）, and the measured value is 1 938.1 W/（m²·K） for dry-expansion evaporator under cooling condition, the latter is 11.8% higher than the former; and that the corresponding values under heating condition are 1 834.9 W/（m²·K）and 2 226.4 W/（m²·K）respectively, the latter is 17.5% higher than the former. Analyses the error cause and concludes that the flow velocity in shell-side of the measured evaporator is increased, and the fouling resistance of heat exchanger tube in the measured evaporator is nearly zero.