Numerical study on the performance of shell-and-tube thermal energy storage using multiple PCMs and gradient copper foam

Most phase change materials employed in latent heat thermal energy storage suffer from poor thermal conductivity both in liquid and solid phases, leading to low heat transfer effectiveness. To overcome this limitation, multiple PCMs and gradient copper foam have been used to accelerate the melting of phase change materials and improve the heat transfer effectiveness. The heat transfer performance of shell-and-tube thermal energy storage unit consisting of radial multiple PCMs and single PCM was numerically investigated. The utilization of single PCM showed better heat transfer effectiveness compared to that using radial multiple PCMs. The time saving for complete melting was up to 87.5%. The results implied that the radial multiple PCMs have no advantage in thermal storage compared to single PCM. Based on single PCM system, three types of gradients of copper foam, named positive gradient, non-gradient and negative gradient were designed in this study. The results indicated that the negative gradient type offers better heat transfer effectiveness than the non-gradient and positive gradient types. However, the temperature distribution of non-gradient type was more uniform compared to positive and negative types. Besides, an optimal configuration 0.99–0.97-0.89 of negative gradient was recommended to further reduce the complete melting time by 23.7%.