Evaluation of the different inner and outer channel geometry combinations for optimum melting and solidification performance in double pipe energy storage with phase change material: A numerical study

Abstract

Phase change materials (PCMs) have become preferable among latent heat storage methods due to their high energy storage densities and low energy losses. These properties of PCMs make it possible to use them in applications such as thermal storage of solar energy, cooling of electronic equipment, energy storage for buildings, and cooling of engines. Double-pipe energy storage (DPTES) with PCM can be used in cases where the production and consumption times of the thermal energy obtained from sources such as solar energy, geothermal water, and waste gas do not match. The fact that the thermal conductivity coefficients are quite low is one of the obstacles to the commercialization of PCMs and their use in more applications. Double-pipe energy storage (DPTES) with PCM can be used especially in cases where the production and consumption moments of the thermal energy obtained from solar energy do not match. In studies on DPTES with PCM, methods including different pipe geometries, extended surfaces, different PCM materials, microencapsulation of PCMs, eccentric inner pipe placement, nanoparticle usage, and metal foam addition have been investigated to increase thermal conductivity. The novelty of this study was to examine the effects of different inner and outer channel combinations on melting and solidification performance. In this direction, nine different inner and outer channel combinations of basic geometric shapes were modeled. Among these combinations, the combination with the highest melting rate and the shortest charging time was determined. Afterward, melting and solidification analyzes were made at the different positions of the inner and outer channels for the combination selected, and the most suitable energy storage design was created to make the most efficient use of the existing heat source. The results of the analysis revealed that the optimum design for melting, and solidification performance was the triangle-in-square configuration. With this configuration, it was increased the melting rate by 1.1 times and accelerated the charging time by 20 % for a 40-minute charging period compared to conventional DPTES (circle-in-circle). In addition, for the melting and solidification periods, the inverted and vertical placement of the triangle in the square revealed the best results. It was observed that the effect of the relative positions of the square and the triangle on the solidification rate was negligible. It is predicted that the results given in this study will be useful in designing the most compatible inner and outer channel geometries to increase energy storage efficiency in DPTES systems.