Solidification analysis in an ice-on-coil ice storage system: Experimental and numerical approaches

Rapid economic growth has led to energy resources shortages, creating unique challenges for developing countries whose activities depend on energy. Thermal energy storage is an important field of technology that can be deployed as a reliable method to decrease net energy usage. For example, ice storage systems are one of the most efficient methods for saving cold energy. In this work, a combined experimental and numerical study has been carried out on the freezing process or solidification as charge mode in a novel ice-on-coil cold storage system with coil tube. Initial experimental results show that the initially designed evaporator, horizontal shell and coil tube heat exchanger (used to transfer cold energy between a mixture of water/ethylene glycol and refrigerant) failed to form uniform ice on the outer surface of the coil tube inside the ice tank. Also, the thickness of ice decreases from the top to the bottom of the coil, while trying to create a uniform thickness of ice around the coil is one of the main challenges in improving the performance of the proposed cold storage system. In the second part of this work, baffles are inserted inside the evaporator to create transverse fluid flows and to prevent shortcut flow, which leads to better heat transfer rates and, consequently, more uniform ice production around the coil tube. The results depict that although baffle placement demonstrates a slightly positive impact on improving the ice thickness along the coil, overall, it fails to eliminate the non-uniformity of ice production along the entire length of the coil tube. In the third section, a modified evaporator with four connected horizontal-placed coils is employed. According to the obtained results, it can be concluded that after 180 min, by employing the modified evaporator, ice thickness has increased by 14.71, 13.51, and 3.39 % in the bottom, middle, and top of the coil, respectively. It can be seen that utilizing the modified version of evaporator with four horizontal-placed coils leads to enhancement in the ice thickness specially at the bottom of the coil where the ice thickness is less than for the rest of the examined points, which was considered as one of the weaknesses of the primary system. Finally, in the last section, to realize better the solidification process around the coil tube inside the ice storage tank, the ice production process is modeled by performing three-dimensional simulations based on the finite volume method. The proposed model is then validated by using the experimental results.