Solidification of nanoparticle-based PCM in a fin-aided triplex-tube energy storage system for cooling applications

Abstract

Accomplishing a better solidification rate to enhance the Thermal Energy Storage (TES) systems' performance is crucial. One such storage system is the Triplex-tube heat exchanger (TTHX), which is preferable due to its larger heat exchanger area that makes the phase change rate faster. The present study demonstrates a combination of different heat transfer enhancement techniques to improve the performance of the TTHX system. The heat transfer performance of the entire solidification process in the heat exchanger is numerically studied. The system is designed for low-temperature cooling applications with water as PCM placed in between the annulus region of the TTHX. Fins have been employed to enhance the low heat transfer rate due to the poor thermal conductivity of the water as PCM. The effect of incorporating maximum fin length between the annulus region on the discharging performance is evaluated. In this regard, two fin arrangements – attached and detached are investigated. The influence of different cooling methods, namely both-side, inside and outside, are evaluated for mentioned fin arrangements in terms of the required solidification time, liquid–solid interfaces, and heat transfer rate. The impact of including CuO nanoparticles on the thermal and flow structure under different volume fractions is investigated. The results demonstrate that detached fins perform superior under a given heat transfer fluid temperature among other fin cases. In comparison, both-side cooling expedites the process better than other cooling methods. Inclusion of 7% nanoparticles along with fins results in an even faster freezing process, which helps to reduce full solidification time in all cases by nearly 29% and 25% in attached and detached fins, respectively.