Effect of Gas Humidity on Drying of a Wetted Starch Ball in High Temperature Flow

Abstract

A wetted starch ball as a model sample was treated in high temperature gases over a wide range of humidity, using hot air, humid air and superheated steam. The effect of gas humidity on the drying process and product condition was investigated by continuous measurement of the material core temperature and weight changes during treatment. From experimental results, the sample kept its shape during treatment in low humidity gas. Whereas, in the case of high humidity air, the sample burst accompanied both by temperature and mass drops during the treatment. In superheated steam, the sample puffed near the surface. The gas conditions are shown on the steam partial pressure-gas temperature chart, and it shows the important values of dew point temperature as determined by simple estimation technique using wet-bulb temperature and gas temperature. With this chart, we can see that the relationships of initial sample temperature, boiling point, dew point, wet-bulb, dry-bulb and gelatinizing temperatures for food processing of starches are important in order to achieve the desired results.