The simplicity of solar flat plate air collector and freely availability of solar energy sources attracts attention to collector optimization. This study aims to evaluate the effect of double pass airflow on the performance of flat plate air collectors. Indirect type solar dryer performance characteristics analysis was done through CFD simulation with three different shapes (smooth, rough, and V-grooved) keeping the collector insulated and drying chamber act as a vertical chimney. The average thermal efficiency of the V-grooved surface, smooth surface, and rough surface is 90%, 78%, and 62% respectively. The total area of the collector is 1.20 * 2.0 = 2.60 m2 with the drying cabinet 1.20 * 0.65 * 1.00 m (width * depth * height) and 0.005m thick glass cover. Observed pressure drop at the inlet of the drying chamber is high in the case of smooth surface, medium in a rough surface, and low in a v-grooved plate that will allow enough gas pressure to pass through all the compartment of the process at full-scale. The air mass flow rate is the most important and effective factor during drying. The humidity of the air, as well as air velocity, is also an important factor for improving the drying rate.