Evaluation of drying of apple slices in a rotating-tray air dryer equipped with heat exchanger

In the present study, a pilot thin-layer rotary tray dryer was designed and fabricated and equipped with an air-to-air cross-flow plate heat exchanger. Experiments were conducted to assess the effects of the experimental variables (air temperatures of 50, 65 and 80°C, air velocities of 1 and 2 m/s, tray rotation speeds of 0, 6, and 12 rpm with and without application of the heat exchanger) on the thin layer drying dynamics, effective moisture diffusivity and activation energy of apple slices. According to the statistical results (RMSE, SSE and R2), the Midilli et al. model was the best fitted for describing the drying behavior of apple slices. Results indicated that temperature has the most important effect on drying time (75.5%), followed by air velocity (17.6%) and tray rotation (7.8%). The highest effective diffusion was found to be 8.37×10-9 m2s-1 at air temperature, air velocity and speed rotation of 80 ºC, 2 ms-1 and 12 rpm, respectively. The lowest effective diffusion was 2.7×10-9 m2s-1 at air temperature, air velocity and speed rotation of 50 ºC, 1 ms-1 and 0 rpm, respectively. The activation energy value of apple slice varied between 16.41- 24.16 kJ/mol. The use of heat exchanger reduced energy consumption of the dryer by 33%. The results of this study can be applied for recovering the waste heat from exhaust air and improving the performance of forcedconvection dryers.