In this study drying process of a single body in a dryer has been modeled. The proposed model was validated with the experimental data obtained from drying the spherical potatoes. Samples of spherical potatoes at temperatures of 40, 50 and 60°C were dried in a pilot scale dryer and moisture content, surface temperature data was extracted. The proposed model by applying mass and heat balance equations based on thermodynamic equations predicted changes of sample temperature, samples moisture and also entropy generation and exergy. The results show that the moisture content of the samples has a downward and change of air velocity has little effect on drying, but increases the diameter longer drying time. Entropy generation increased rapidly at first and then will deteriorate. Exergy as energy increased during the drying time. Comparison of model results with experimental data approved the proposed model