Critical analysis of the energy and exergy performance of an air heater duct with perforated 60-degree V-down baffles affixed to the heated surface

Abstract

The indirect-mode solar dryer, with a solar air heater as a vital component, is commonly preferred for enhancing agricultural product quality. Energy and exergy analyses for an air heating system assess thermal gain and irreversibility in energy conversion. According to the literature, the easiest way to enhance the SAH’s energy and exergy performance is by incorporating flow-modifying elements or turbulators in the air passage. And the effective-energy assessment accounts for the increased airflow pumping power demands. This work aims to experimentally compare the energy and exergy performance of a smooth air heater duct with one integrated with perforated V-shaped baffles while critically examining the factors leading to the efficiency variations. The racetrack-shaped perforated V-baffles with 60-degree air attack angles are installed on the heated surface with V-down and staggered hole arrays, covering a turbulent flow Reynolds number (Re) range of 5400–13,100 during experimentation. The investigation involves varying the pitch-to-duct depth ratio (p/H) of baffles (with values of 1, 2 and 3) and considering two different hole-aspect ratio (w/d) values of 5.04 and 2.68, with the same open area ratio. The results reveal that baffles with w/d of 2.68 at p/H of 3, causing enhanced airflow turbulence and momentum diffusivity, provide the highest effective-energy ( ${\eta }_{\mathrm{ef}}$ ) and exergy ( ${\eta }_{\mathrm{ex}}$ ) efficiencies values of 88.7% and 12.44%, respectively, at Re of 11,816 and 8765. Based on the operating and geometrical parameters used in the experiments, the correlations of ${\eta }_{\mathrm{ef}}$ and ${\eta }_{\mathrm{ex}}$ developed demonstrate good accuracy. The values for mean absolute error, root mean squared error and R ² (coefficient of determination) in the correlations, developed using the statistical computing R software, are 0.012427, 0.014837 and 0.9913 for ${\eta }_{\mathrm{ef}}$ and 0.004332, 0.005047 and 0.9557 for ${\eta }_{\mathrm{ex}}$ , respectively.