Thermal behavior in a solar air heater channel roughened with delta-shaped vortex generators

Abstract

Despite the various techniques used in strengthening the Solar Air Heater (SAH) through extended surfaces (obstacles) on the absorber plate, its thermal performance remains far from the optimal rate. Accordingly, an experimental study has been conducted to improve the SAH thermal performance. The technique consists in investigating the heat transfer, friction factor and thermal enhancement factor of flow in a rectangular channel artificially roughened with two longitudinally curved delta-shaped baffles configurations. Two cases have been dealt with perforated and non-perforated baffles. This study encompassed for the range of Reynolds number (Re) from 2500 to 12,000, relative longitudinal length of the obstacles on the absorber plate Pl/e from 3 to 5, relative transversal length of the obstacles on the absorber plate Pt/b from 0.6 to 1, relative roughness height (e/H = 0.8) and single attack angle (α = 45°). The obtained results averred a significant augmentation in heat transfer and reduction in pressure drop. Whereas, heat transfer (Nu) and in airflow friction (f) have reached respectively 6.94 and 45.83 times more than smooth channel. In case of perforated longitudinally curved delta-shaped baffles (LCD), the maximum thermal enhancement factor (TEF) rate was found to be around 2.26 when Pl/e and Pt/b are respectively equal to 0.3 and 0.6. However, the non-perforated LCD has reached a maximum of about 2.21. Following a correlation on experimental data of the heat transfer and airflow friction based on the adopted rates, the two parameters have attained deviations of about 12% and 7%, respectively.