Mathematical modeling of pear fruit thin layer drying and study on the effects of drying air temperature and velocity on variation of exhaust air relative humidity

In the present study variation of air relative humidity at the inlet and outlet of a cabinet dryer as well as drying kinetic of pear fruit in thin layer were studied. The experiments were conducted at three temperature levels of 40, 50 and 60^oC and three air velocity levels of 0.5, 1 and 1.5 m/s. It was observed that the difference between input and output air relative humidity increased when drying temperature was increased. This difference followed declining trend at the same level of drying temperature when air velocity was increased. If drying at lower air temperature and higher velocity is desired, for optimum use of energy, a closed loop drying method is appropriate. Otherwise, increasing in air temperature and decreasing in air velocity is recommended. Eight mathematical models were fitted on drying data and the best one was selected according to coefficient of determination (R²) and Chi-square (χ²) statistics for 70 percent of data. The model then validated by statistics of root mean square of error (RMSE), mean bias of error (MBE) and mean relative error (ARE) for 30 percent of remaining data. The approximation of diffusion model with highest R² (0.998), and lowest χ² (0.0001), RMSE (0.01), MBE (0.0008) and ARE (5.2%) was found an appropriate model for estimating the kinetics of thin layer drying of pear cubes drying in a cabinet dryer.