Optimization of Nusselt number and friction factor for a two-sided curvilinear rib-roughened solar air heater

The artificial roughness on the absorber plate of a solar air heater improves its performance characteristics and efficiency. Geometrical and flow parameters of roughness play a vital role. Along with the selection of geometry, the range of roughness parameters at optimum values creates a keen interest in the research field. Present works include the optimization of the performance characteristics for a two-sided curvilinear transverse rib roughened solar air heater. Response surface methodology (RSM) is selected to optimize the roughness parameters. The main roughness and flow parameters for two-sided curvilinear rib roughness were the relative roughness height (e/Dh) ranging from 0.7 to 1.4, relative roughness pitch (p/e) ranging from 10 to 25, and Reynolds number (Re) varying from 3800 to 18,000. The RSM suggested that design of the experiment (DOE) was performed by numerical simulation. Data collected from simulation are used to develop a mathematical model using the analysis of variance (ANOVA) approach. To select the significant model predicted value, the coefficient of regression (R2) and confidence interval (p-value and F-value), with a probability of 95%, was considered. Nusselt number and friction factor achieve their optimal value (Nu maximum and f minimum) of 123.84 and 0.012 at e/Dh = 0.031, p/e = 21.42, and Re = 10900.