Introduction To The Use Of Fruit Drying Equipment

  • Sublimation drying of Fruit Drying Equipment (primary drying)
    The frozen product is heated in a closed vacuum container, and its ice crystals will sublimate into water vapor to escape and dehydrate the product. Drying gradually moves inward from the outer surface, and the remaining space after the ice crystals sublimate becomes the escape channel for sublimation water vapor. The interface between the dried layer and the frozen part (actually a thin layer) is called the sublimation interface. In the drying of biological products, the sublimation interface is advanced inward at a speed of about 1 mm / h. When all the ice crystals are removed, the sublimation drying is completed, and about 90% of the water can be removed at this time. The sublimation of ice in the product is performed at the sublimation interface. The heat required for sublimation is provided by the heating equipment (through the shelf). The heat transferred from the shelf is transmitted to the sublimation interface of the product in the following ways: solid conduction, radiation, and gas convection.
    The product is sublimated by the following temperature limits:
    The temperature of the frozen part of the product should be lower than the temperature of the product's co-melting point.
    The temperature of the dried part of the product should be lower than its disintegration temperature or the maximum allowable temperature (not scorched or deformed).

    Maximum shelf temperature.
    Analytical drying (secondary drying)
    The first stage of drying removes water in the form of ice crystals. Therefore, the temperature of the lyophilized layer and the pressure at the sublimation interface must be controlled below the product's co-melting point (or disintegration temperature) to prevent the ice crystals from melting. But for adsorbed water, its adsorption energy is high, and if it does not provide enough energy for Z, water cannot be resolved from the adsorption. Therefore, the temperature of the product at this stage should be sufficiently high as long as it does not exceed the maximum allowed temperature, does not burn the product, and does not cause the product to overheat and denature. At the same time, in order to have sufficient driving force for the desorbed water vapor to escape from the product, a large vapor pressure difference must be formed inside and outside the product, so a high vacuum must be maintained inside the box T at this stage. After the second stage of drying, the residual moisture content of the product can generally be controlled between 0.5% -4%.

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