Pore-scale investigation on effects of void cavity distribution on melting of composite phase change materials

Composite Phase Change Materials (PCMs) incorporated with metal foams are promising candidates for thermal management for space exploration. However, void cavities are generated as a result of the volume change of PCM during the melting process, introducing a resistance to heat transfer due to the low thermal conductivity of the void. In this work, the effects of void cavity distribution on the conduction-dominated melting of composite PCMs under microgravity conditions are studied by a two-dimensional pore-scale lattice Boltzmann method, in which a microstructural description of the metal foam is experimentally characterized with the help of X-ray micro-Computed Tomography. Two typical distribution patterns of void cavities are analsed and computed performance is compared (1) a near-wall void cavity, and (2) randomly distributed void cavities. The evolutions of temperature distributions and melting interfaces are compared, and the average liquid fraction and energy stored per width are deduced to describe the energy storage performance. Moreover, the influence of the volume fraction of void cavities is investigated by comparing temperature distributions and energy storage performances of composite PCMs with four different volume fractions of void cavities (0%, 3.7%, 7.6%, 15.2%). After introducing void cavities, the energy stored per width is reduced by 5.7%, 12.3% and 20.2% for randomly distributed void cavities when volume fraction of void cavities is 3.7%, 7.6%, and 15.2%, respectively, and reduced by 42.2%, 64.1% and 79.7% for the near-wall void cavity, respectively. This work initiates the study of the effects of void cavity distribution on composite PCMs, which will stimulate work on structural optimization of thermal management systems.