Impacts of Experimental Factors on Radio Frequency Drying Characteristics of Scallion Stem
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    Abstract:

    Through analyzing the temperature rise, radio frequency(RF)output power, and water loss during the RF drying of scallion stem under the different experimental conditions, the impacts of form of scallion stem to be heated and its parts, container material and its placement position, scallion layer height, electrode gap, and target temperature on the RF drying characteristics of scallion stem were clarified. The results could provide reasonable and efficient experimental parameters and factors’ scopes for the subsequent research of scallion stem RF drying. It was found that the temperature rise rate of chopped scallion stem was about three times that of scallion stem slice, and the drying period required for scallion core was twice that for scallion white under the same RF parameters. Therefore, scallion white and scallion core should be RF dried separately to avoid excessive drying of scallion white. Compared with containers made of polytetrafluoroethylene(PTFE) and polyethylene(PE)material, the temperature rise rate of chopped scallion stem in polypropylene (PP)container was higher. Therefore, PP container was more suitable to be used for scallion stem RF drying. Using the selected PP container, the chopped scallion white with the minimum layer height of 14 mm and mass of 650 g could achieve a fast temperature rise rate. The range of electrode gap between 77 mm and 87 mm could ensure that the scallion white of the maximum layer height of 28 mm avoided overcurrent and burnt under the minimum electrode gap, and that the scallion white of the minimum layer height of 14 mm reached the target temperature of 75 ℃ quickly under the maximum electrode gap. In addition, the scallion white with layer heights of 14 mm and 28 mm were subjected to the same RF drying at conditions of raising container 11 mm and no raise, respectively. It was found that RF power variations and water loss changing tendency under these two conditions for the scallion white with different layer heights were different. Moreover, the scallion white of 14 mm layer height with no container raise improved drying efficiency about 8% compared with that with container raise, while the scallion white of 28 mm layer height obtained the same RF drying periods under those two conditions. Therefore, the scallion white or its container without raise of 11 mm was more conducive to its RF drying research due to the different effects of container raise on the drying characteristics of scallion white with different layer heights under the same RF drying parameters.

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History
  • Received:July 20,2024
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  • Online: December 10,2024
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