Heat Transfer and Friction Factor Correlations for Rectangular Solar Air Heater Duct Having 60° Inclined Continuous Discrete Rib Arrangement

The heat transfer coefficient between the absorber plate and air can be considerably increased by using artificial roughness on the underside of the absorber plate of the solar air heater. An experimental study has been carried out for enhancement of heat transfer coefficient of a solar air heater having roughened air duct provided with artificial roughness in the form 60° inclined discrete rib. Increment in friction factor by provided with such artificial roughness element has also been studied. The effect of system parameters such as relative roughness height (e/D), relative roughness pitch (P/e) and relative gap position (d/W) have been studied on Nusselt number (Nu) and friction factor (f) with relative gap width (g/e) 1 and Reynolds number (Re) varied from 4105 to 20526. Considerably enhancement in heat transfer coefficient has been achieved with such roughness element. Using experimental data correlations for Nusselt number and friction factor have also been developed for such solar air heaters, which gives a good agreement between predicted values and experimental values of Nusselt number and friction factor.