CHARGING AND DISCHARGING CHARACTERISTICS OF A MOVING GRANULAR BED THERMAL ENERGY STORAGE SYSTEM FOR HUMIDIFICATION-DEHUMIDIFICATION DESALINATION
Direct absorption moving granular bed (DAMGB) thermal energy storage (TES) for humidification dehumidification (HDH) desalination cycle has been investigated. Sand is used as granular particle due to its wide availability and lower cost. Solar HDH while being attractive suffers from drawbacks set by intermittent nature of solar energy. TES coupled with solar HDH has potential to run continuously as a stand-alone system. DAMGB using sand grains can be utilized for a wide range of temperatures (60°C−700°C). In DAMGB system granular particle fulfills function of TES and absorber both, hence it eliminates the need of heat transfer fluid (HTF) and losses incurred by HTF. A parametric study has been carried out to understand the performance characteristics of thermal charging under constant as well as sinusoidally varying solar flux numerically. Assuming continuum, effective thermal properties were prescribed for the flowing sand, and heat loss from the absorber was also accounted using well established approach. The optimum design parameter for charging period has been reported. An analytical solution available from the literature has been used to characterize discharging process. Charging numerical calculation and discharging analytical solution both combined together to characterize charging-discharging cycle. Typical results of desalinated water production per day from 1m2 collector area has been reported. Results of cycle efficiency for sand based TES system was found to be higher than solid/liquid phase change (PCM) based TES system.