Liquid-sensible heat storage units for short-term low-temperature applications: configurations and thermal analysis

Abstract

Two configurations of liquid-sensible heat storage systems are proposed for low-temperature solar applications. The first is an air-based system, where the storage element is water, while the charging and distributing heat transfer fluids are air. The second is a water-based system, where the storage element is thermal oil, while the heat transfer fluid is water. Regarding the second configuration, sunflower oil, and engine oil are tested for heat storage. The inlet temperatures of hot heat transfer fluids have been measured experimentally
using air and water flat-plate solar collectors. Using the existing mathematical equations, the duration of a complete charge-discharge cycle for each storage element was calculated. The temperature variation of the storage element during the entire storage cycle was also examined. During the storage process, we noted that the temperature of the storage media increases with the rise of inlet temperature of the hot transfer fluid. It has been proven that water-based configuration using thermal oils is more efficient than air-based  configuration. However, the discharge duration is longer for the air-based system than the water-based system. Moreover, we  investigated and discussed the effect of both storage media volume (mass) and cooled transfer fluid’s flow rate on the storage material temperature during the whole charge-discharge cycle.