The geometry of duct is the important factor influencing heat transfer for any end use in laminar and turbulent flow. The basic requirement of industries is of high heat transfer rate and less pumping power. Since the flow of fluid in industries is turbulent in nature. Many studies are performed to understand the performance of duct in non circular( rectangular, semicircular, square, ellipse etc.) in shape. This paper present the review on the various studies performed on triangular duct. In this article natural and forced convection using newtonian fluid based experimental and numerical studies are considered. In order to improve the heat transfer through duct various geometry of roughness are embedded in the absorber plate and results obtained are used to compare the performances with smooth solar air heater and correlations are generated for different geometry. It is observed that among all other boundary conditions uniform heat flux gives optimum heat transfer.