Fang Wang

A phase change heat storage device based on rotating annular-flow-channel finned tube (PCHS-RAFCFT) has been proposed in this paper. Bidirectional fins have been integrated into the RAFCFT design, aiming to enlarge the heat exchange surface, and the rotation mechanism has been introduced to improve heat exchange effectiveness at the solid-liquid interface of phase change material (PCM). The effects of fin structural parameters on the PCHS-RAFCFT heat storage performance have been studied. It is indicated that heat storage performance improves with increasing fin number. However, the improvement becomes marginal once the number of fins exceeds 8. Compared with other fin heights, the fin height of 3mm yields superior melting rate and heat storage rate. Accordingly, 8 fins with the height of 3mm has been identified as the optimal structural configuration. The superiority of the PCHS-RAFCFT has further validated through comparison with the unidirectional finned tube based PCHS unit. Furthermore, the effects of operating parameters such as rotational speed and heat transfer fluid temperature have also been analyzed, based on the optimized structure. It is found that increasing the heat transfer fluid’s temperature and RAFCFT’s rotational speed accelerate PCM melting, while this enhancement becomes insignificant beyond 40rpm. Therefore, the recommended rotational speed for the PCHS-RAFCFT is 40rpm. The proposed PCHS-RAFCFT offers an effective solution to PCM heat-transfer hysteresis, the obtained structural and operating parameters can support its practical design and operation.

An annular flow-channel finned tube based latent heat thermal storage unit (AFFT-LHTSU) has been proposed in this study. In the AFFT-LHTSU, bidirectional thermal transfer can be achieved through the AFFT formed by nesting an inward finned tube and an outward finned tube, thereby enhancing the thermal exchange efficiency between the heat transfer medium (HTM) and the Phase Change Material (PCM). Then the thermal charging performance of the AFFT-LHTSU has been investigated, with the specific analysis of the effects of the AFFT’s structural parameters on the performance, including mean diameter of the AFFT, as well as the fin’s height and quantity. Results indicate that a larger mean diameter of the AFFT leads to a higher thermal charging rate of the AFFT-LHTSU, while the total thermal storage capacity decreases significantly due to the reduced PCM filling volume. Then a mean diameter of the AFFT of 50 mm yielded the optimal thermal storage performance has been determined as a result. Increasing the fin’s height and quantity both effectively enhanced the thermal storage rate. Systematic parametric analysis indicates that the optimal configuration for the AFFT is a mean diameter of 50 mm, a fin’s height of 9 mm, and 12 fins. Additionally, a comparative analysis between the optimized AFFT-LHTSU and a conventional unidirectional thermal transfer finned tube unit has been conducted. Results demonstrate that, under conditions of identical shell size, fin’s count, fin’s height, and PCM filling volume, the AFFT-LHTSU achieved a 165.3% increase in the average thermal charging rate.