Energy and Exergy evaluation of conventional solar air heaters with multigap V-down and staggered ribs

In the world, energy using rates are rapidly raised. Solar energy has the greatest potential and even a small amount of solar energy is enough to supply the total energy demand. In the solar air heater collectors the solar energy gain is low because of unfavorable properties of air such as low density, low heat capacity and low values of heat transfer coefficients. The use of artificial roughness can essentially improve the performance of the solar air heaters. In this study, conventional solar air heater with attaching of multi-gap V-down and staggered ribs on the absorber plate improved. The performance analysis of solar air heater has been conducted by writing mass balance, energy balance and exergy efficiency equations under steady state conditions and solved by semi analytical method. Thermal performance evaluation has been studied using different parameters such as outlet air temperature, useful energy gain, energy and exergy efficiencies. The results shown that with applying multi-gap V-down and staggered ribs can be increased the outlet air temperature and efficiency significantly comparison to the conventional SAH. This amount of enhancement reduces with increasing the Reynolds number. Other results indicate that attaching this ribs lead to decrease the exergy efficiency remarkably. The variation of structural ribs parameters such as relative roughness pitch, relative roughness height and angle of attack have little effect on the thermal performance of SAH in the considering conditions. Also, increasing the solar intensity results in increasing the outlet temperature, energy gain and efficiency.

Keywords:

Solar Energy , Air heater , Multi-gap V-down ribs , staggered ribs