Optimization of shell and tube thermal energy storage unit based on the effects of adding fins, nanoparticles and rotational mechanism

Abstract According to the high storage capacity of latent heat thermal energy storage (LHTES) systems, finding a suitable solution to compensate for the weakness of these systems is logical. The main weakness of these systems is the low thermal conductivity of phase change materials (PCMs) as the storage reservoir of thermal energy. Many methods have been proposed previously to overcome this limitation. Most of these methods can be divided into three types that including changes in the geometric configurations, improving thermophysical properties of PCMs and applying external conditions to improve the LHTES systems' performance. Nonetheless, limited studies have been conducted with combination approaches between these methods. In line with this, the present study investigates the effect of combining three different types of improvement methods in the applicable ranges simultaneously. These methods are selected based on utilizing three different ways to heat transfer rate enhancement. So that these ways include increasing heat transfer area (by adding fins), increasing natural convection effect (by adding rotational mechanism) and improving the thermal conductivity of PCM (by adding Cu nanoparticles). Results show that the combination of these methods has a significant effect on the improving performance of LHTES system during charge and discharge processes. So that increasing productivity of each method leads to decreasing melting and solidification times and following this heat transfer rate enhancement. Based on comparing results, rotational speed increment has the highest effect on increasing heat transfer rate in charge and discharge processes. Moreover, since storage and release capacities are important parameters in the LHTES systems, to shed further light on the impact of utilizing combination methods on reducing these capacities, an optimization process is conducted by the response surface methodology (RSM). Optimization results present an optimal case based on the highest heat transfer rate with the highest storage and release capacities in charge and discharge process. Comparing results between simple and optimal cases show that applying optimal conditions leads to enhancing heat transfer rate significantly based on decreasing melting and solidification time at about 74% and 70%. While based on this comparison, storage and release capacities are reduced by just 2.5% and 4.1%, respectively.