The device performance of cross-corrugated double-pass solar air heaters under external recycle conditions was investigated experimentally and theoretically, and solved numerically using the Newton method. Comparisons were made and represented graphically among three different configurations of the single-pass, flat-plate double-pass and cross-corrugated double-pass devices. Air flowing simultaneously over the wavelike corrugated absorbing plate and in-between both wavelike cross-corrugated absorbing and transverse bottom plates was conducted under double-pass operations. A considerable heat-transfer efficiency enhancement is obtained employing such a recycling double pass device with welding cross-corrugated absorbing plates, instead of using the flat-plate device. An effective thermal performance was achieved because the heat transfer area is doubled and the turbulent intensity is enhanced as well. The power consumption increment owing to the reduction in the cross-sectional area was taken into account associated with the heat-transfer efficiency enhancement for comparisons in determining the optimal design on an economic consideration for the recycling cross-corrugated double-pass device.
