Thermal and hydraulic performance of natural convection in a rectangular storage cavity

The fluid flow and heat transfer performances in a rectangular latent heat thermal energy storage (LHTES) cavity with natural convection are investigated numerically. Paraffin is used as a phase change material (PCM) with phase change temperature of 306.15-308.15 K. The effects of rectangular aspect ratios, varied from 0.1 to 10, on the fluid flow and heat transfer performances are analyzed. The constant temperature 343.15 K is maintained at the bottom wall. It is found that aspect ratios play an important role in the performances of the rectangular LHTES. In other words, the aspect ratios affect dramatically not only the finish time of LHTES but also the natural convection inside the rectangular cavity. The melting rate increases as the aspect ratios increase, especially for aspect ratios >= 1. Further, it is noted that a recirculation region in the liquid PCM region is formed remarkably for aspect ratios due to the stronger natural convection of liquid PCM than aspect ratios <1. Moreover, flow structures and temperature field are employed to express heat transfer mechanisms during different stages of the melting process. It is indicated that heat conduction is the dominant heat transfer mode during the initial stage of melting, then by transition from conduction to convection regime, and convection dominated heat transfer at the final stage. The numerical model is solved using the finite volume method (FVM) and the numerical results are validated with published experimental data. (C) 2015 Elsevier Ltd. All rights reserved.