Effects of velocity and temperature of air on the drying rate constants of apple cubes

Drying rate constants of apple cubes were calculated after performing experiments with a computer-controlled laboratory scale tunnel drier in 1.7-3.0 mis air velocity and 78-94 degrees C air temperature ranges. There was only one falling rate period in the experiments with linearly decreasing air temperatures, but two consecutive falling rate periods were observed when air temperature was constant. Variation of the drying rate constants with temperature were described by an Arrhenius-type expression. The Arrhenius expression and drying rate constants of the falling rate period increased with air velocity. The second falling rate period was a diffusion-controlled process. It was confirmed by the experimental results that the velocity of air flow does not affect the drying rate constants in the second falling rate period Within the range of the experiments, drying rate constants decreased with the initial particle size of the cubes, implying that the thickness effects suppressed the surface area effects. Copyright (C) 1996 Elsevier Science Limited