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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]

The effect of variation in open area ratio (β) in multi-V rib roughened single pass solar air heater (SPSAH) is computed in this study. Different perforated plastic ribs are used to develop variations in perforation. Four values of the open area ratio (β) ranged from 0 to 0.31, six values of relative roughness width (W/w) ranged from 2 to 10, and nine values of the Reynolds number (Re) ranged from 2000 to 18,000. These values were under consideration, along with fixed values of other parameters. Optimum values of performance parameters achieved at an open area ratio β = 0.27 with W/w = 6. The optimum range of improvement in Nusselt number ratio (Nu/Nus) and thermo-hydraulic performance parameter (THPP) was 6.33–8.19 and 3.78–5.41, while duct friction ratio (f/fs) was recorded within the range of 3.68–4.78 when compared to the flat channel, respectively. A correlation for Nusselt number and friction factor with varying parameters was also established with ±12% and ±7.5% accuracy, respectively. [ABSTRACT FROM AUTHOR]