The thermal efficiency of conventional solar air collectors is found to have low thermal efficiency mainly due to higher top losses and low heat transfer rate from absorber plate to flowing air due to low specific heat of air. Use of packed bed solar collector helps in reducing the top layer temperature by absorption of heat energy in depth, thus minimizing the top losses. Also, heat transfer coefficient between the packing element and flowing air is increased as a result of air flows through the tortuous path. Heat transfer area is also increased in packed bed air heaters. Overall effect is the enhanced thermal efficiency of the collector along with increased pressure drop. Rounded V-grooved absorber plate have also been used for increasing the thermal efficiency of conventional smooth collectors taking advantage of large amount of intercepted radiation on the absorber plate, without any increase in the pressure drop. Use of rounded V-grooved absorber plate is made in packed bed air heaters in the present investigation which is found to further increase thermal efficiency of a packed bed collector, without additional pressure drop penalty in packed bed. Experiments are conducted on a solar collector under simulated conditions using wire screen matrices in its air flow duct for varying operating parameters. It has been observed that the maximum thermal efficiency of 85.2% with outlet temperature of 56.1 oC is obtained at a mass flow rate of 0.035 kg/s.m2 and a fixed insolation of 1100 W/m2. These results in thermal efficiency enhancement by approximately 65% compared to the conventional smooth collector. For a mass flow rate of 0.015 kg/s.m2, the increase in efficiency has been found to be 46% higher compared to conventional collector for same value of insolation with air outlet temperature of 68.9 oC It is seen that the efficiency of the collector increases with increase in mass flow rate and insolation. It has been found that geometry of absorber plate significantly affects the performance of the collector.
