Effect of heat exchanger configuration and operating conditions of thermal energy storage unit for liquid air energy storage

This paper presents the study on a thermal energy storage unit (TESU) with its effectiveness greater than 0.9. A heat diffusion model is developed to predict the precise thermal behavior of the TESU and determine its detailed specifications. Based on this model, the TESU is designed and manufactured for laboratory-scale experiments. The TESU is tested with various shuttle masses (6 g–18 g) of cryogenic nitrogen at an operating pressure of 30 bar. Under the experimental conditions, a higher mass flow rate in the range increases the efficiency of the TESU. Using the spiral-plate type heat exchanger instead of the coil type improves thermal performance by reducing the thermally dead volume and enhancing the active heat exchange. The effectiveness of each spiral-plate type or coil type heat exchangers is achieved up to 0.92 or 0.82, respectively. The comparative analysis between the thermal model and the experiments reveals the strong influence of the operating conditions on thermally dead volume, emphasizing the need for precise TESU design tailored to the specific LAES system requirements. The validated heat diffusion model shows that minimizing temperature non-uniformity in the heat exchanger reduces entropy generation and exergy loss due to heat diffusion. This study experimentally demonstrates the feasibility of achieving high effectiveness value of a TESU and suggests that the proposed approach should be extended to actual-scale LAES systems.