Koua et al. investigated the behavior of the thin layer drying of plantain banana, mango, and cassava experimentally in direct solar dryer and performed mathematical modeling by using thin layer drying models encountered in literature. Seven statistical models, which were empirical or semi-empirical, were tested to validate the experimental data. The Henderson and Pabis drying model was found to be the most suitable for describing the solar drying curves of plantain banana, mango and cassava and the drying data of these products were analyzed to obtain the values of the effective diffusivity during the falling drying rate phase. Both a heat pump and solar dryer were designed, manufactured and experimentally analyzed by drying apples, and a comparison was made between the two by Aktas et al. For both system , the moisture ratio was analyzed with the Statgraphice program by using semi-theoretical models and compared with the empirical values ; correlation coefficients of the equations were calculated and standard error of estimation (SEE) and r2 values were obtained .