Investigating heat transfer enhancement for PCM melting in a novel multi-tube heat exchanger with external fins

Abstract

The low thermal conductivity coefficient is the limiting parameter of phase change materials (PCMs) for using in thermal energy storage systems. Various heat transfer enhancement methods such as utilizing extended surfaces techniques which include finned tubes and multi-tubes are studied. In this paper the melting of a PCM is investigated in a novel multi-tube heat exchanger (MTHX). RT35 and water are used in the outer and inner tube as the PCM and the heat transfer fluid (HTF), in turn. The main purpose of this study is to peruse the effect of installing external longitudinal fins on the inner tube (tubes) during the charging process. Two, three, and four tubes are engaged to check the effect of inner tubes number on the melting process with a constant amount of PCM and the HTF mass flow rate. A two-dimensional finite volume method based on the enthalpy–porosity technique has been developed using FLUENT software. A comparison between MTHX without fins and with external fins shows that adding of fins improves the heat transfer rate, more uniform temperature distribution, and reduced melting time. The PCM melting time was reduced by 27.84 %, 33.8 %, 29.84 %, and 29.55 % in cases A, B, C, and D, respectively, by installing external fins on the MTHX.