Comparison of performance enhancement in a shell and tube based latent heat thermal energy storage device containing different structured fins

Abstract

In this paper, the enhancement of melting behaviour in a shell and tube thermal energy storage (TES) device containing various structured fins is numerically investigated. Five innovative enhancement structures involving topology optimized fin, tree-shaped fin, snowflake fin, spiderweb fin, and a combined conventional fin and composite phase change material (CPCM) are quantitatively compared and evaluated. Two groups of experiments are carried out to validate the simulation codes for the devices containing topology optimized fin and CPCM, while the numerical models for the devices with longitudinal fin and pure PCM are verified by two sets of literature data. A comprehensive comparison is performed for these five enhanced configurations from multiple perspectives with the emphasis of investigation being placed on assessment of the economic efficiency of these structures through introducing a parameter of TES rate per unit cost. The results show that the use of enhanced structures achieves remarkable enhancement on the melting rate in a shell and tube device. Compared to the device containing no enhancement structure, the complete melting process can be accelerated respectively by 97.2%, 93.6%, 93%, 88% and 83.6% for the devices containing tree-shaped fin, spiderweb fin, snowflake fin, topology optimization fin, and joint longitudinal fin and CPCM. The implementation of tree-shaped fin provides the optimal economical solution to acquire the best utilization efficiency among the five structures, but the enhancement degree on the economic efficiency is intimately tied to the cost ratio of fin to PCM. In order to highlight the advantage of using tree-shaped fin on the improvement of heat transfer rate and economic efficiency, the cost ratio of fin to PCM in such enhanced structure is suggested to be controlled to less than 6.5. Moreover, fin material also presents a significant influence on the selection of performance enhanced structure since it affects not only the melting rate but also the material utilization efficiency within the device. Substituting aluminium alloy with cheaper steel as the fin manufacturing material makes the economic efficiency a whole declined. This indicates for achieving a combined improvement of melting performance and economic efficiency, the enhanced structure should be selected to have a high thermal conductivity and controllable cost that easy to manufacture.