Batch vacuum dryers are substantially the same as tray dryers, except that they operate under a vacuum, and heat transfer is largely by conduction or by radiation. The trays are enclosed in a large cabinet. The water vapour produced is generally condensed, so that the vacuum pumps have only to deal with non-condensable gases.
In the vacuum freeze dryer, moisture sublimes directly from the solid state to vapor, thus producing a product with controllable moisture, no need for cooking or refrigeration. The process is first to freeze the water content in the ingredients into solid form, and then store in a vacuum sealed space, let the ice changes to vapor in the closed environment and capture it by freeze equipment. The process is completed until the ice content drop below 3 to 5% to reach a higher value. The designed full-liquid type low temperature control with the vacuum pump is able to generate adequate energy. The