Thermohydraulic Performance of Packed Bed Solar Air Heater

An experimental investigation is carried out as per ASHRAE standards on a high porosity packed bed solar air heater. Packed bed is generally used to enhance the heat transfer area and also for storage of thermal energy. The work covers a particular range of design and operating parameters. Design parameters include the colour of packing material (black and normal metal colour), packing Reynolds number (900–8000), porosity (0.9 and 0.8) and equivalent diameter of packing material (1.55 mm). Operating parameter includes a wide range of mass flow rate ranging from 0.01 to 0.04 kg/s. It is found that black-coated wool gives a better thermal efficiency. Further, both heat transfer coefficient and friction factor are strong functions of geometrical parameters of the porous packed bed. A decrease in porosity level increases the volumetric heat transfer coefficient. A maximum of 91.7% thermal efficiency is achieved at a mass flow rate of 0.04 kg/s and at a porosity of 0.8.