Thermal analysis of phase change materials storage in solar concenter

Abstract

Thermal analysis of high-temperature phase change materials (PCM) is conducted with the consideration of a 20% void and buoyancy-driven convection in a stainless-steel capsule. The effects of the thermal expansion and the volume expansion due to phase change on the energy storage and retrieval process are explored. The used water to fill the void between two different wax paraffin and stearic acid spheres is considered as a potential PCM for concentrated solar power. The charging/discharging process into and from the capsule wall is simulated under different boundary conditions for laminar and turbulent flows. Computational models are conducted by applying an enthalpy-porosity method and volume of fluid method to calculate the transport phenomena within the PCM capsule, including an internal air void. A simplified two-dimensional model of the PCM contained within the spheres is constructed and thermal analyses are performed for the transition from solid to liquid states. Simulated charging process modes are compared with the theory. According to experiments, the temperature distributions from 40-60 mm without and with 60 mm with copper fin have different behavior. The paraffin takes less time than stearic acid for total transformation at a rate of 0.5. The size of the sphere increases over the amount of time and the phase of the sphere to complete changes as stearic acid expands more than paraffin during the transition. Inserting a rectangular fin, that is made from copper into the ball reduces the cycle time and increases output.