Abstract:

A set of atmospheric freeze-drying experimental equipment was established based on vortex tube refrigeration
to dry Chinese yam. Effects of inlet pressure of vortex tube, thickness and shape of fresh sample, heating mode on the
drying process were investigated in the experiment. Results showed that the properties and internal structure of the material
had considerable influences on the drying rate during the drying process. Drying rate was improved through reducing the
thickness of fresh material and using combination of convection and radiation. When the temperature of drying oven was
slightly higher than the eutectic temperature of the material, the atmospheric freeze-drying process was still manipulated.
The optimal refrigeration efficiency for Chinese yam was obtained when the inlet pressure was 0.3 MPa and the cold air
flow rate μ was between 0.4 and 0.5.

Key words: atmospheric freeze-drying, vortex tube, Chinese yam, drying rate