Solar Air Heater Thermal Performance Enhancement using V-Up Continuous Ribs

Abstract

The viability of renewable energy sources (emphasizing solar energy) helps reduce the barrier of fossil energy depletion. Despite the issue of low thermal performance, different techniques are projected to gain high energy to boost the heat transfer for the solar energy system. This experimental work evaluates the thermal performance enhancement of two designed solar air heaters with and without V-rib (smooth plate). Using V-up continuous ribs, the impact of various attack angles (α) at 30°, 45°, and 60° on the thermal-hydraulic performance of artificially roughened solar air heater duct is investigated. Thermal performance consideration involves the intensification of heat transfer (Nusselt Number, Nu) and diminution of friction factor (f). The tests were performed as an indoor experiment where the intensity of solar energy was simulated by heating the absorber plate using the electric heater to gain 1000 W/m2 of constant heat flux. Furthermore, adjusting the air-flow rates provides the Reynolds number (Re) values between 3480 – 9980. The results showed that the solar air heater with V-up continuous ribs experienced the maximum thermal performance when α reached 60° then gradually decreased with increasing of α. Compared with the smooth plate, the presence of Vribs in solar air heaters gained a higher value of Nu, f, and thermal-hydraulic performance. Adjusting the α at 30°, 45°, and 60° of V-up continuous ribs improves the Nu in the maximum value of 123% for α of 60°as compared to those of the smooth tube. Besides, it also occurs that the maximum increment of f and thermal performance factor was 2.85 times and 1.26 for α of 60°. Moreover, empirical correlations developed from current results can predict the Nu and f with a reasonable agreement between the experimental predicted values.