The steady-state experiment using liquid crystal thermography has been conducted for the analysis of Nusselt number distribution over the absorber surface of solar air heater (SAH) duct having a gap with the staggered arrangement in inclined rib geometry to recuperate its thermal performance. The heat transfer experiment is performed with uniform heat flux and thermo-chromic liquid crystal (TLC) is utilized to show the temperature distribution profile over the ribbed surfaces of the rectangular duct of aspect ratio of 5. The colored pattern image of TLCs was acquired using a 3CCD (charged couple device) camera and exported to a Tagged Image File Format (TIFF) file format using frame grabbing SOFTWARE SAPERALT which was further processed to get hue, saturation, intensity (HSI) values. The flow parameters considered in this present investigation are Re, d/W, and g/e varied from 4000 − 12,500, 0.15 − 0.45, and 1 − 4, respectively. Experiments has been performed with fixed P/e, r/e, p′/P, α, and e/Dh of 10, 2, 0.6, 60 deg, and 0.0303, respectively. The influence of relative gap position and relative gap width on flow pattern has been analyzed. The maximum augmentation in Nu and f over the smooth duct was obtained as 4.01 and 4.28 times, respectively, at the optimum value of d/W = 0.35 and g/e = 2 under similar flow conditions. The maximum value of THPP obtained at d/W and g/e of 0.35 and 2, respectively, and Reynolds number of 12,445.