Radially graded metal foams arrangement in heat storage device of photothermal utilization systems

Metal foam was adopted for improving inherent low thermal conductivity of traditional thermal energy storage (TES), which conducted higher solar energy conversion efficiency. With consideration of more energy response and the mixing enhancement effect on heat conduction and natural convection, this work investigated a vertical TES tube in solar energy photothermal utilization systems, embedded in metallic foam with radial gradient porosity and pore density. Experiments and simulations have both been carried out. It is thoroughly examined how the liquid fraction, solid-liquid interface, temperature field, and velocity field evolve, and the properties of energy storage, such as heat transfer density and energy storage quantity, are further assessed. Results demonstrated that the melting duration was shortened by 11.2% for the positive radially graded porosity arrangement and prolonged by 16.8% for the negative, in comparison to the homogeneous structure. Meanwhile, influenced by the varied porosity, the temperature uniformity was enhanced by 4.9% for the positive and was deteriorated by 15.1% for the negative. In addition, positive and negative gradient pore density respectively increased the temperature uniformity of by 15.1% and 16.7%. Based above, metal foam tube with negative gradient porosity and pore density was suggested to build the more efficient photothermal solar energy con-version systems due to faster melting process and more homogeneous temperature uniformity.