Abstract
Drying characteristics and the thermal conductivities as well as permeabilities have been measured for the dried layers of sliced and mashed apples undergoing freeze-drying. Both samples were frozen with a copper plate at its surface temperatures ranging from -27 to -44℃. They were freeze-dried at the constant surface temperatures ranging from -10 to 70℃. A mathematical model were applied to the drying data in order to determine the transport properties for the dried layer of the sample undergoing freeze-drying. The surface temperature of sliced samples was found to be impossible to set at more than 10℃, while that of mashed were allowed to heat up to 70℃. Values of thermal conductivity were found to be almost the same between sliced and mashed samples, but the permeability data for the mashed samples were more than 4 times greater than that for sliced ones. Both temperature and pressure dependence on these transport properties were not recognized apparently, and the effects of freezing rate on transport properties were critical for the mashed samples. The results indicated that the drying rate of sliced samples was limited by the transfer rate of water-vapor flowing through the dried layer.
