A comprehensive evaluation of the vertical triplex-tube heat exchanger with PCM, concentrating on flow direction, nanoparticles and multiple PCM implementation

Abstract

To mitigate the intermittency of renewable resources and tackle with discrepancy in supply and demand, heat storage systems offer a promising solution. Among various storage systems, latent heat storage attracted a lot of attention. In these systems, the phase change material plays the major role in the storage mechanism. In the present study, a three-dimensional numerical study was performed on a triplex-tube vertical unit containing paraffin RT50 and RT82. The aim of this study was to investigate the effect of fluid direction, temperature, and employment of two materials and nanoparticles. According to the results, during the melting process, regardless of the inlet fluid temperature of 368 or 373 K, the use of bottom injection for both tubes can accelerate the phase change rate by up to 13%. The temperature of the inlet fluid, by increasing by 5°compared to 368 K, is capable of providing a growth of almost 24% in different inlet directions. In the axial arrangement of two materials, the best result is obtained if the material is used with higher melting temperature at higher altitudes and top injection mode. However, the best type of placement is the radial positioning in which the material with the higher melting temperature is adjacent to the outer tube. In this case, on average, a 30% improvement is achieved compared to the worst location. The results of applying nanoparticles in the state of single-material and double-materials at 3 different concentrations showed the performance improvement of 10% to 18.5% compared to the corresponding cases without nanoparticles.