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A detailed study on Solar Air Heaters (SAHs) with single-pass roughening with plastic net perforated multi-V and continuous multi-V ribs was investigated and compared for its effectiveness. Improvements in the Nusselt number ratio (Nu/Nus) and the friction factor ratio (f/fs) studied with the Reynolds number (Re) ranged from 2000–18000 for a relative roughness height (e/Dh) of 0.043, a relative roughness pitch (P/e) of 10, an aspect ratio (W/H) of 12, and an angle of attack (α) of 60°, maintaining a similar flow scenario. For a syntactically roughened channel with a perforated multi-V rib, the significant enhancement was recorded in thermo-hydraulic performance with a slight decrease in pumping power. The study was extended to analyze the effect of perforation in a double pass parallel flow SAH. [ABSTRACT FROM AUTHOR]

After analyzing the effect of perforation in a single pass solar air heater in part A, an experimental comparative study was performed on a Double Pass Parallel Flow Solar Air Heater (DPPFSAH) roughened with continuous and perforated multi-V rib roughness. In DPPFSAH, for perforated rib roughness, the gain in Nu/Nus, f/fs, and Thermo-hydraulic performance parameter (THPP) for W/w = 6 are 8.33, 9.09, and 2.97, respectively. While for continuous rib for W/w = 6 the values of Nu/Nus, f/fs, and THPP are 5.93, 10.83, and 1.82, respectively, as compared to the smooth plate. The results strongly support the application of perforation in artificial roughness. [ABSTRACT FROM AUTHOR]