transient analysis; hybrid solar water heater; rock bed air heater; air-to-water transverse; fin shell-and-tube heat exchanger
A transient analysis has been carried out on a hybrid solar water heater which comprises a rock bed air heater with optimum design parameters in conjunction with an air-to-water transverse fin shell-and-tube heat exchanger (mixed air and unmixed water type) in which cold water from the storage tank receives heat from the hot air coming out of the air heater which flows in the shell at right angles to the water flowing in the tubes. The system's performance has been evaluated for typical winter weather conditions in Delhi for different combinations of flow rates of air and water for different volumes of the water storage tank. No hot water is assumed to be withdrawn from the tank to serve the load. A comparative analysis of the system's performance with and without a rock bed in the air heater reveals about 11°C higher temperature of storage tank in the former at 50 kg/h m2 air flow rate. With both the air heater types, although the system performance was observed to increase with the rates of air and water flow, no significant improvement in system performance was achieved at Mw > 2Ma.