Analytical modeling of Nusselt number and friction factor for honeycomb-shaped artificial roughness in solar air heater

Abstract

This research paper investigates the impact of honeycomb-shaped roughness on the thermo-hydraulic performance parameter (THPP), Nusselt number (Nu), and friction factor (FF) in the solar air heater (SAH). The investigation employs computational fluid dynamics (CFD) analysis and experimental validations, focusing on Reynolds numbers (Re, 3000–21000) as the operational parameter. The study explores key design parameters, including relative roughness height (e/D, 0.03–0.05), relative roughness pitch (P/e, 8–12), and the angle of attack (Ø, 90˚ −120˚). Validation of CFD results against experimental findings reveals a maximum Mean Absolute Percentage Error (MAPE) of 8.3 % for the FF and 9.8 % for the Nu, indicating strong agreement between CFD simulations and experimental observations. Key findings include a maximum THPP of 1.7 achieved at an (P/e) of 10, (e/D) of 0.04, and (Ø) of 120˚ with Re of 6000. Additionally, a maximum Nu of 140.65 is attained at an(P/e) of 10, (e/D) of 0.04, (Ø) of 120˚, and Re of 21000. The highest FF of 0.039 is recorded at an (P/e) of 9, (e/D) of 0.05, and (Ø) of 120˚ at Re of 6000. Regression analysis is employed to establish correlations for FF and Nu as functions of (Re) and honeycomb-shaped roughness parameters. Comparisons between the developed equations and CFD results indicate MAPE of 6.1 % for the FF and 4.7 % for the Nu, affirming the accuracy and reliability of the correlations in predicting frictional and heat transfer properties of the system.