Enhancement of thermal energy storage in a phase change material heat exchanger having elliptical and circular tubes with & without fins

Abstract

The objective of this study is to examine the thermal performance of a heat exchanger having multiple elliptical tubes and a phase change material (PCM) filled in the cylindrical shell of a heat exchanger. To improve the heat transmission from elliptical tubes to PCM, two and four fins are incorporated on the circumference of the elliptical tubes. The use of elliptical tubes with fins in the enhancement of heat transfer is an innovative approach in thermal performance studies of heat storage systems. The geometry of heat exchangers having elliptical tubes without fin, with two fins, and four fins are compared with the geometry of heat exchanger with circular tubes having no fin, two fins, and four fins respectively. The current investigation is carried out with the use of a 2D CFD model using a physical enthalpy-porosity technique to explore the phase transition of the solid PCM. The effect of integrating a number of fins on heat transfer has also been explored, and outcomes of elliptical and circular tube geometries in terms of PCM mean temperature and liquid percentage at two different temperatures of 50 °C and 60 °C have been compared. Results show, that PCM melting time is being reduced to 550 s in PCM heat exchanger geometry having elliptical tubes with four fins compared to 585 s for the same heat exchanger with two fins and 665 s for heat exchanger without fin at 50 °C resulting 12 % & 17 % reduction in melting time by applying two and four fins respectively. Whereas PCM melting time is 515 s in PCM heat exchanger geometry having circular tubes with four fins compared to 560 s for heat exchanger with two fins and 655 s for heat exchanger without fin resulting 14.5 % and 21 % reduction in melting time by applying two and four fins respectively. It has been concluded that adding fins on the circumference of elliptical and circular tubes enhances the heat transmission and reduces melting time as well as more heat can be transferred by circular tube geometry compared to elliptical tube heat exchanger geometries. The findings of the investigations are validated with the available simulation data and show good agreement, suggesting a 3.8 percent deviation.