DRYING PROMOTION OF AGRICULTURAL PRODUCTS USING CORONA DISCHARGE

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Drying of agricultural products is promoted by ion wind from corona discharge. They say the forced convection caused by ion wind results this promotion, however, this is not explained perfectly. In order to explain this mechanism, the forced convection with air ion and that without air ion were used for water evaporation test and radish drying test. The former convection was called "with-air-ion" and the latter "non-air-ion". Both were made from ion wind. In addition drying of shiitake mushroom using corona discharge was evaluated.The evaporation rate using non-air-ion increased linearly with voltage, and that using with-air-ion increased in step. From -4 kV to -10 kV the evaporation rate using with-air-ion was higher than non-air-ion, and was equal to or lower than non-air-ion from -10kV to -14 kV.There were little difference between drying rate of radish using with-air-ion and non-air-ion at 9.8kV.It was appeared that the effect of air ion on radish drying was little, however, considering water evaporation test, drying test at another voltage should be performed.After corona discharge the evaporation rate of water was sometimes retarded in comparison with natural evaporation. The evaporation was enhanced under the corona discharge so that water temperature decreased owing to latent heat loss. It seems that the change of heat balance on account of water temperature drop caused the evaporation retardation.The drying promotion of shiitake mushroom using corona discharge was recognized under various experimental conditions The ratio of drying rate of corona discharge method to conventional method was 1.6 max. As a result of measurements of shirinkage, color and water absorption of dried shiitake mushroom, shrinkage decreased and color was little more yellow and absorption didn't change on account of using corona discharge.