Study on Vegetable and Fruit Drying by Alternating-direction Hot-air Penetrating

The result of study and test on alterating direction hot-air drying with compeas as a kind of typical vegetable and fruits was described. The drying test was carried out on the hot-air penetrating drying test-bed. There were twelve layers of vegetable and fruits in the drying test tank. The initial moisture content of compeas was 88%～89%.The hot - air reversion time varied by 1/2 hour interval from 1/2 hour to four hours. The average ladder of the moisture content of different layers of vegetable and fruits was used as an index to estimate the evenness of distribution of drying.The results showed that alternating direction hot-air drying had important effect upon the evenness of drying espe-cialy in the middle period of drying.The study on the effect of different hot-air reversion time upon the drying process gave drying curves and drying speed curves showing that alternating direction hot-air could increase drying rate in the initial and middle periods of drying. In the middle and last periods of drying the drying rate was much less than that of drying with no alternating direction hot-air. By means of alteruating direction hot-air drying time could be shortened.From studying the influence of hot-air reversion drying upon energy consumption, regression equation of hot-air reversion time and energy consumption could be obtained (y=3. 347341 + 0. 089777x²). When hot -air reversion time is 0. 5 hour, energy consumption was the towest.