Development of a sensible heat packed bed energy storage system for medium temperature applications

Abstract

Utilization of solar energy can be a strategy to provide clean and cheap energy for various purposes such as cooking. Unfortunately, solar energy is intermittent and unreliable for continuous usage. As a result, it necessitates exploiting thermal energy storage systems which can store heat for most cooking needs. The thermal energy storage media can be latent heat materials, sensible heat materials and thermochemical heat materials. Several studies reviewed showed that the system designs for the latent heat energy storage and thermochemical heat energy storage were costly and complicated to fabricate as opposed to the sensible heat energy storage systems. Therefore, based on these limitations, the purpose of this research was to develop and determine the experimental and simulation thermal performance of three sensible thermal energy storage systems at three different flow rates of 4 ml s−1, 8 ml s−1 and 12 ml s−1, respectively, in the medium temperature range (100 oC to 300 oC). Two granite rock pebbles (diameters: 10.5 mm and 31.9 mm) packed bed storages using sunflower oil as the heat transfer fluid were compared with an oil-only storage tank. The results obtained showed that the thermal energy storage performance of the oil-only based storage was enhanced by the addition of the pebbles. Furthermore, higher energy rates and exergy rates were exhibited with the small pebbles storage during charging cycles. On the other hand, the discharging results indicated that the highest cooking temperature was achieved with the small pebbles storage, although the stratification and discharging thermal exergy recovery efficiency were best promoted by the large pebbles size storage. Considering modeling, a good level of agreement existed between the experimental and simulation results with an overall mean deviation of 7%. In conclusion, the small pebbles storage was better for cooking applications in terms of the parameters evaluated in this study, due to the highest quality energy (total exergy) of 1.0 MJ generated. This energy was comparably higher than the quality energy of 0.8 MJ dissipated from the pressure cookers. However, the researcher noted that there was need for further study on development of cascaded hybrid thermal energy storage systems for high temperature applications.