Biomimetically calabash-inspired phase change material capsule: Experimental and numerical analysis on thermal performance and flow characteristics

The propositions of bionics have led to the evolution of engineering technologies, such as solar energy utilization and thermal energy storage. Inspired by the idea of the natural calabash structure concept, the present study designed and proposed the bionic-calabash-shaped capsule to enhance the thermal performance of phase change material (PCM) capsules used in thermal energy storage (TES). The melting properties and flow characteristics of three capsules with different shapes were investigated numerically and experimentally. A visualized experimental system was established to observe the melting front of the bionic-calabash-shaped capsule during the constrained melting process. Experimental and numerical results indicated that the throat of bionic-calabash encapsulation accelerated the constrained melting process, and the constrained melting time of bionic-calabash-shaped capsules was reduced by 18.2% compared to that of the sphere capsule. The drag coefficient of the novel structure capsule was 34.2% lower than that of the spherical capsule. The bionic-calabash-shaped capsule, with geometric parameters of L/R = 1.53 and L/r = 2.53, was inferred to be the optimal structure for heat storage based on the optimization analysis of the thermal behavior and flow peculiarities.