Experimental investigation of multiple tube heat transfer enhancement in a vertical cylindrical latent heat thermal energy storage system

Thermal energy storage in phase change materials (PCMs) received considerable attention due to the capability of tackling the time mismatch between energy supply and demand, especially for renewable energy sources. Nevertheless, PCMs suffer from some drawbacks preventing their widespread commercialization. In this study, a geometrical heat transfer enhancement technique was investigated to increase the rate of heat transfer from the heat transfer fluid (HTF) to the PCM in a shell-and-tube heat exchanger. The performance of two designs of single and multiple (five) tube heat exchangers (i.e. STHX and MTHX, respectively) were experimentally investigated and compared in terms of average PCM temperature, liquid fraction and stored heat during a complete charging and discharging cycle. It was found that the MTHX out-performed the STHX in terms of phase change duration and stored heat. Furthermore, the validity of a common simplifying assumption in numerical investigation of MTHXs which is considering an artificial cylindrical boundary around each tube was experimentally investigated. This assumption was found to result in inaccuracy meaning that it should no longer be considered in future numerical studies.