Thermal Performance Evaluation of Circular-Stadium Double Pipe Thermal Energy Storage Systems

Abstract

Thermal Energy Storage (TES) systems are employed in numerous practical applications, owing to their capability to solve the problems related to the reliability of thermal energy systems by using phase change materials (PCM). In this study, the charging and discharging processes of N-eicosane in a circular-stadium double pipe TES system for various aspect ratios (1, 0.35, 0.25, and 0.15) and angular orientations (0°, 30°, 60°, and 90°) of the inner stadium tube are numerically investigated using enthalpy-porosity formulation. The zero-heat flux is applied to the outer tube of TES systems while the inner tube wall is retained at constant temperatures. The numerical results are compared with the experimental results of the concentric double-pipe TES system which shows an accuracy with 2.34% error. The findings revealed that the best thermal performance is provided by the X/Y=0.15 case with 90° angular orientation which contributes the highest increase in the charging rate while the discharging rate is not substantially affected by aspect ratio and angular orientation. The melting time decreases by 59% and solidification time raises by 27%. The overall efficiency of the TES system is 75% which is 26% higher than a base case (X/Y=1). The results further conceived that gravitational acceleration plays an important role in the natural convection heat transfer during the charging process of PCM.