Heat transfer and friction factor correlations development for double pass solar air heater artificially roughened with perforated multi-V ribs

Thermo-hydraulic performance of a Double Pass Parallel Flow Solar Air Heater (DPPFSAH) roughened with perforated multi-V ribs has been studied experimentally in a prior study and the effect of variation in open area ratio and change in relative roughness width has been analysed and reported. The current work builds upon the aforementioned earlier study by discussing in detail the methodology and various steps involved in the development of a correlation for variable parameters with Nusselt number and friction factor for DPPFSAH. The outcomes show that perforations in the multi-V ribs lead to a considerable rise in the Nusselt number, a 9.66 times increase in the thermo-hydraulic performance parameter and nearly a four times increase in friction factor compared to multi-V ribs with smoothed walls. Empirical correlations for the Nusselt number and friction factor were obtained for the double pass parallel flow solar air heater with perforated multi-V ribs established with ±14% and ±7%.