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In this study, a two-dimensional CFD (computational fluid dynamics) analysis was performed to investigate the heat-transfer and fluid-friction characteristics in a solar air heater having a transverse triangular block at the bottom of the air duct. The Reynolds number, block height (e), pitch (P), and length (l) were chosen as design parameters. The results are validated by comparing the Nusselt number predicted by simulation with available experimental results. Renormalization-group (RNG) k-ε model with enhanced wall-treatment was selected as the most appropriate turbulence model. From the results, it was found that the presence of a transverse triangular block produces a higher Nusselt number than that of smooth air duct. The enhancement in Nusselt number varied from 1.19 to 3.37, according to the geometric conditions investigated. However, the use of transverse triangular block also results in significantly higher friction losses. The thermohydraulic performance (THPP) was also estimated and has a maximum value of 1.001 for height (e) of 20 mm, length (l) of 120 mm, and pitch (P) of 150 mm, at Reynolds number of 8000. Furthermore, in the present study, correlations of the Nusselt number and friction factor were developed as a function of geometrical conditions of the transverse triangular block and Reynolds number, which can be used to predict the value of Nusselt number and friction factor with the absolute percentage deviations of 3.29% and 7.92%, respectively. solar air heater having non-uniform cross-section transverse rib roughness on the absorber plate. Akpinal and Koçyiǧit [7] analyzed the performance of a solar air heater supplied with various obstacles experimentally. Singh et al. [8] evaluated the effect of multiple arc-shaped ribs on the heat-transfer and friction characteristics, with various geometrical parameters. Singh et al. [9] investigated the heat and fluid-flow characteristics in a rectangular duct roughened with periodic discrete V-down rip. Kumar and Kim conducted a CFD-based analysis to investigate heat transfer and friction characteristics in rectangular channel with discrete multi-V-pattern ribs [10].The other method to improve the performance of a solar air heater is modifying the absorber plate. Karim and Hawlader [11] examined the performance of three types of solar air collectors having a flat-plate, v-corrugated, and finned absorber. Ho et al. [12] conducted an experimental and theoretical analysis of the double-pass cross-corrugated and double-pass V-corrugated solar air collector. Zheng et al. [13] performed experimental investigation of solar air heaters having perforating corrugated plate, slit-perforated plate, and corrugated packing. In addition to this, a number of studies have been conducted, and they mainly focused on the performance improvement by artificially roughened rip mounted on the absorber plater or modified absorber structure [14][15][16][17].Another technique to increase the heat-transfer performance of solar air heater is modifying the air duct or the shape ...

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