Experimental Study of Heat Transfer and Frictional Characteristics of Impinging Jet Solar Air Heater With Stepped Ribs Having Varying Length of Jet Plate

An experimental study on the effect of shortening of jet plate perforation length on the thermal and frictional performance of an impinging jet solar air heater with ribs (RIJSAH) was conducted. The jet span length was shortened to 80% and 60% of the total length, while the jet diameter (D_jet) considered were 3, 6, and 9 mm. There was an increase in the Nusselt number (Nu) with a decrease in jet span length (JSL) for D_jet = 6 mm. It was found that, at Reynolds number (Re) equal to 11,465, the Nu developed by ribbed IJSAH with D_jet = 6 mm and JSL = 60% was only 5.06% less than that developed by RIJSAH with D_jet = 3 mm while suffering a friction factor 24.13% less than that generated by the latter. The thermohydraulic performance parameter (THPP) attained generally decreased with a decrease in JSL, but at higher Re, the THPP attained by RIJSAH with D_jet = 6 mm and 60% JSL was higher than that achieved by RIJSAH with D_jet = 6 mm and 80% JSL. There was a clear decrease in temperature difference between the fluid and the absorber plate with a decrease in JSL, which enhanced the thermal performance of the system. In conclusion, it is recommended that RIJSAH be fabricated with D_jet = 6 mm and 60% JSL to achieve well-optimized thermal performance.