Garg, H P; Jha, Ranjana; Choudhury, C; Datta, Gouri
Mathematical model; Air heaters; Heat energy; Air temperature; Rectangular fins
This paper deals with efforts to improve the performance of conventional, duct- type air heaters by providing rectangular fins in the air passage between the absorber and the rear plate. For this configuration, a mathematical model is developed by writing the energy balance equations at various interfaces of the system. Numerical simulation of this theoretical model is carried out in order to evaluate the effect of the number of rectangular fins, the length of the fins (equal to the length of the plates), the depth of the air channel, the air flow rate, etc. on the thermal performance of the air heater. These results are then compared with data for a conventional air heater with the same duct depth and length. The outlet air temperature and hence the total heat energy collected are found to increase with an increase in the number of fins and with a decrease in the duct depth, while all other design and operational parameters are kept constant. The shallower duch depth improves the thermal performance of the air heater but also increases the pressure drop, thereby increasing the energy expended in pumping the air through the collector. To account for this expended energy, the new term effective heat gain is introduced and computed separately for different cases.