Experimental and numerical study of a shell-and-tube latent thermal energy storage for solar thermal applications

Shell-and-tube latent thermal energy storage plays a key role in buffering intermittent solar heat supply and ensuring reliable hot-water delivery in solar thermal systems. Previous studies have shown that shell-side flow maldistribution can cause short-circuiting and uneven heating between phase change material tubes, thereby degrading thermal performance. To address this issue, a perforated-plate-assisted latent thermal energy storage prototype was experimentally investigated, and a validated numerical model was used to clarify its internal thermodynamic behavior. The results show that the perforated plate markedly improves shell-side flow distribution and leads to excellent inter-tube uniformity during both charging and discharging. The liquid-fraction non-uniformity index between tubes is only 0.012 during charging and 0.0017 during discharging. However, the dominant non-uniformity appears as vertical stratification within individual tubes, with corresponding indices of 0.09 and 0.11. This vertical non-uniformity reduces effective heat utilization and degrades exergy performance. Higher flow rates enhance both charging and discharging rates. The maximum charging power and heat exchange capacity rate reach 3.1 kW and 343.61 W/K, respectively, while the maximum useful discharging power and heat exchange capacity rate reach 13.31 kW and 608.37 W/K. However, for practical domestic hot water applications, higher flow rates involve a trade-off: they increase hot water yield, but also lead to higher charging energy demand, lower average outlet temperature, and shorter useful supply duration. These findings show that the perforated plate effectively mitigates inter-tube non-uniformity, while future optimization should focus on suppressing intra-tube vertical stratification and adapting the flow-rate strategy to specific domestic hot water demands.