Comparative experimental study on the thermal and hydraulic performances of capillary box heat exchanger and helical coil heat exchanger for surface water-source heat pump

Abstract

The thermal and hydraulic performances of front-end heat exchangers significantly influence the energy efficiency of surface water-source heat pumps. To evaluate the performance of a capillary box heat exchanger (CBHE), a comparative study between the CBHE and a conventional helical coil heat exchanger (HCHE) was conducted under different tube velocities, heat transfer media, and temperatures. The comparison considered not only traditional metrics, such as the heat transfer coefficient, heat transfer efficiency, and pressure drop, but also the volume heat transfer coefficient and two thermal-hydraulic comprehensive performance parameters: the modified Colburn–Fanning factor ratio (JF_K) with larger-the-better characteristics and the electricity consumption to extracted or rejected heat quantity ratio (EHR) with smaller-the-better characteristics. The results indicated that the heat transfer coefficient, heat transfer efficiency, and volume heat transfer coefficient of the CBHE were 10.1 W/(m^2.°C)–25.58 W/(m^2.°C), 34 %–45 %, and 1140 W/(m^3.°C)–1416 W/(m^3.°C) larger than those of the HCHE, whereas its total pressure drop was only 15 %–21 % of that of the HCHE. Additionally, the JF_K and EHR of the CBHE were approximately three times and 11 %–16 %, respectively, those of the HCHE. This study serves as a reference for selecting and designing front-end heat exchangers.