Modeling of Double-Pass Solar Air Heaters with External Refluxes

Publisher Summary This chapter explores the effects in collector efficiency for air flowing between two parallel-plate channels with the absorbing plate inserted for conducting recycle flow, and with total mass flow rate fixed. The results obtained exhibit that the recycle can enhance the collector performance compared with that of the devices with only one flow channel over or under the absorbing plate resulting in considerable improvement in collector performance. The improvement in collector efficiency by employing the double-flow type solar air heater is best illustrated by calculating the percentage increase in collector efficiency based on the downward-type single-flow device with same total flow rate and same collector size of total height. The comparison of collector efficiencies between the devices with recycle and the one of single-pass operation without recycle is also observed in the chapter.