In this article, an absorber plate of solar air heater attached with a combination of opposite apex triangular cross-sectioned rib roughness is experimentally analyzed. A series of experiments are carried out to investigate the turbulent airflow for various rib arrangements. This study aims to find effect of pitch of rib roughness element on the heat and friction properties in solar air heater. The studied parameters are relative roughness height of 0.045 and relative roughness pitch from 5 to 12.5 for Reynolds number range from 3000 to 18,000. Highest enhancement in Nusselt number and friction factor was found to be 3.05 and 4.14 times of smooth duct respectively. Highest thermohydraulic performance (2.02) was recorded at relative roughness pitch of 10. A new heat transfer correlation is also presented in this article for the rib roughened solar air heater. A linear stepwise regression algorithm is used to reduce the resulting data to correlation. The developed correlation accurately predicts all Nusselt number and friction factor data to within ± 6 relative absolute deviation.
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