Study on Heat Transfer Performance of Eccentric Triplex-Tube Helical-Coil Heat Exchanger

Abstract

The eccentric arrangement of the inner tube can effectively improve the heat storage and heat release performances of the shell and tube heat exchanger. Downward inner tube eccentricity improves heat storage. Upward eccentricity improves heat release. It's difficult to increase both performances in a single heat exchanger. This study proposes an eccentric triplex-tube helical-coil heat exchanger to solve this issue. By combining eccentric and helical structures, both performances can be improved simultaneously. In this study, the influence of different eccentricities on the heat transfer performance of the heat exchanger is analyzed based on the heat transfer indexes. These indexes encompass the average heat storage/release rate, melting/solidification time, and liquid fraction of PCM. Secondly, the entropy weight-TOPSIS method is used to evaluate straight triplex-tube and eccentric triplex-tube helical-coil heat exchangers with different eccentricities. Finally, the effect of the inlet temperature of heat transfer fluid(HTF) on solidification performance and optimal eccentricity is studied. The results show that with the increase in eccentricity, the melting time gradually shortens, and the average heat storage rate gradually increases. The solidification time first decreases and then increases, and the average heat release first increases and then decreases. The eccentric triplex-tube helical-coil heat exchanger with an eccentricity of 10 mm has the best heat transfer performance. Compared with the straight triplex-tube heat exchangers, the total storage and release time is shortened by 22.96%. The average heat storage rate is increased by 39.74%, and the average heat release rate is increased by 19.64%. By reducing the inlet temperature of HTF, the heat release time of the eccentric triplex-tube helical-coil can be obviously reduced. Additionally, the inlet temperature of HTF does not affect the optimal eccentricity.

Keywords: helical-coil, eccentricity, triplex-tube, natural convection, Optimization, entropy weight -TOPSIS