تجزیه و تحلیل عملکرد ذخیره سازی-انجماد انرژی حرارتی تماس مستقیم

Performance of a direct-contact latent heat energy storage during discharging process has been investigated. The storage medium used is sodium thiosulphate pentahydrate of which the melting temperature is 48°C and the heat exchanging fluid is heat transfer oil. An empirical expression to evaluate the volumetric heat transfer coefficient has been carried out. A lumped analysis is also found to be quite suitable to analyze the temperature of the storage medium and its solid fraction including the temperature of the oil leaving the storage. The results agree well with those of the experiments.

Energy storage is essential whenever the supply of energy cannot meet the demands. In latent heat storage, thermal energy is stored in materials which undergo change of phase in a suitable temperature range. Solid–liquid transformation is most commonly utilized and the energy stored could be discharged at a constant crystallization temperature. However, most of the solid-phase materials usually have low thermal conductivity, therefore, during the discharging process, as a material solidifies onto the heat transfer surface, high thermal resistance is obtained. Direct-contact heat transfer is another technique to enhance the heat transfer. Fig. 1 shows the physical system under consideration. Full-size image (7 K) Fig. 1. Schematic of the direct-contact thermal energy storage. Figure options During the discharging process, a liquid lower in density and immiscible with the storage material is injected at the bottom of the storage unit. The liquid rises through, agitates the storage medium, extracts heat and leaves from the top of the storage tank and transfers heat in a heat exchanger. High heat transfer coefficients at the storage have been reported by several workers [1], [2] and [3]. In this study, thermal behavior of a sodium thiosulphate pentahydrate storage exchanging heat directly with a heat transfer oil during the discharging process has been investigated. Effects of several parameters such as the flow rate of the heat transfer oil and the volume of the storage medium on the heat transfer coefficient are also considered.

High heat transfer rate is obtained with the direct-contact heat transfer technique. The temperature of the storage medium during the discharging process is nearly uniform and the lumped model could be performed. With the lumped analysis, the simulated temperatures of the oil outlet, the average storage medium and the solid fraction could be evaluated. The results agree well with those of the experiments.