Effective tube-in-tank PCM thermal storage for CSP applications, Part 2: Parametric assessment and impact of latent fraction. (1st December 2016) - Belusko, M.
Highlights: PCM systems of high latent fraction should apply counterflow to the HTF. PCM systems of low latent fraction should apply parallel flow to the HTF. Heat transfer with counterflow tubes can have a reduced performance in some cases. Abstract: The tube-in-tank is a compact configuration well suited for PCM thermal storage systems. However limited research has investigated the impact of the boundary condition applied to the PCM achieved through differing tube arrangements. In Part 1, using CFD and considering the discharging condition for CSP applications, it was determined that when the heat transfer fluid flow was in parallel, poor extraction of latent energy occurs, whereas in a counterflow arrangement maximum latent energy is extracted. In Part 2, the impact of mass flow rate and PCM thermal conductivity on the extraction of latent energy for these tube arrangements was investigated. It was discovered that the counterflow arrangement can experience poorer heat transfer which can be avoided through design. Furthermore, little investigation has considered the impact of the effectiveness of heat transfer with PCM systems with increased amounts of sensible energy, typical for CSP applications. It was determined that for latent dominant storage systems, the counterflow tube arrangement should be applied, while for sensible dominant PCM storage systems, parallel flow should be considered.