NUSSELT NUMBER AND FRICTION FACTOR CORRELATIONS FOR SOLAR AIR HEATER DUCT HAVING TRIANGULAR PROTRUSIONS AS ROUGHNESS ELEMENTS ON ABSORBER PLATE

In order to enhance the heat transfer rate of solar air heater apparatus, triangular protrusions are provided on the surface of the aluminum absorber plate to act as artificial roughness. Three kinds of absorber plates other than a smooth absorber plate with protrusions of varying apex angles are chosen for this work. The respective apex angles of protrusions on the three absorber plates are 30 0 , 45 0 , and 60 0 . The mass flow rate is maintained between 0.017-0. 0182Kg/sec. The rate of air flow corresponds to Reynolds number (Re) ranging from 10 500-12000, Nusselt number range is 50-110, friction factor is 4.5-6.7x10 -3 , and Stanton number is 6-14x10 -5 . The heat transfer rate and thermo- hydraulic performance obtained is observed to be highest for 45 0 . Finally comparison of heat transfer and friction factor from both smooth and roughened plate under the similar condition of air flow is made. A mathematical correlations is developed in t he form Nusselt Number Nu=Re a .Pr b Tan α c and friction factor f = Re d .Tan α e .