عملکرد مبدل حرارتی جدید با ذخیره گرمای نهفته
Abstract
1- Introduction
2- Mathematical modeling
3- Data reduction
4- Results and discussion
5- Conclusions
References
Abstract
In this paper, an optimization method is proposed to improve the performance of a novel heat exchanger with latent heat thermal energy storage. Paraffin/expanded graphite composites were used as phase change material filled in annular tube, maintained contact with the shell and tube flow channels simultaneously. The heat transfer and flow characteristics of this novel heat exchanger were investigated in a previous study, which indicated that further research was required to enhance thermal transfer rates. Therefore, in this work, the thermal property of the material and geometric parameters of the heat exchanger, including compression density, tube diameter, and fins and baffle configuration, were studied numerically to improve the thermal behavior of the system. It was found that a composite with density of 600 kg/m3, a tube diameter of 19 mm, and an extended surface and baffle space of 100 mm, can be used for the final optimization result. The results show that, after optimization, the thermal conductivity of the phase change material can reach 5.16 W/m K and the latent thermal energy stored in system could be twice that previously obtained. The solidification rate can increase to a maximum of 50% while the shell side Nu/Pr1/3 can reach 29.98. The improved heat exchanger shows better energy storage capacity and working power.
Introduction
Currently, thermal energy storage (TES) plays an important role in overcoming the lack of balance between energy supply and demand. TES can be divided into three technologies: sensible, latent, and thermochemical. Latent heat thermal energy storage (LHTES) based on a phase change material (PCM) is considered to be a promising technique, because it has high energy storage density and low-fluctuation operating temperature [1]. Owing to the superior performance of the LHTES unit, it is employed in many fields, such as industrial waste heat recovery [2], solar energy utilization [3], thermal management of electron device [4], and building energy conservation [5]. A heat exchanger based on latent heat storage is the key of the LHTES unit. A cylindrical shell-and-tube heat exchanger is commonly used for heat storage system owing to its robust structure, easy maintenance, and high heat transfer rate [6]. Cano et al. [7] studied four types of PCMs filled in the shell side of the heat exchanger and the influence of the heat transfer flow rate, and different operation modes (watertight and countercurrent PCM flow) were evaluated. It was found that the shell-side PCM countercurrent flow system showed the best energy transfer performance. Hosseini et al. [8] investigated the melting and solidification performance of paraffin RT50 in the shell side of a shell-and-tube heat exchanger and found that by increasing the inlet water temperature from 70 C to 80 C, the charging and discharging efficiency of the heat exchanger rose from 81.1% to 88.4% and 79.7% to 81.4%, respectively. Kibria et al. [9] experimentally and numerically studied the latent heat storage system with shell and tube arrangement, where the PCM was filled in the shell and water passed through the tube. It was found that the influence of inlet temperature of the fluid on the solidification and melting of the PCM is considerable, whereas that of the mass flow rate is negligible. In spite of the great potential of the LHTES system, the low thermal conductivity of the PCM still limits its practical feasibility.