It is difficult to keep fresh during the growing season of vegetables. In order to facilitate storage, people will choose to make all kinds of fresh vegetables into dried vegetables, which is convenient for preservation and in case of emergencies.


During the drying process of the air energy heat pump, when the vegetables are in contact with the air energy, they will absorb a large amount of heat from the air energy, part of which is used to increase the temperature of the vegetables, and the other part is used for the migration and evaporation of water in the vegetables. The air can continuously transfer heat to the vegetables, and the process of evaporating and taking away the water in the vegetables is the continuous process of drying. This process is divided into three stages: the heating stage, the constant speed drying stage, and the deceleration drying stage.

1. The heating stage of vegetable drying:

The initial stage of vegetable drying is heating, and the temperature should be 40-50°C. The first is that the moisture on the surface of the vegetable absorbs energy and turns into water vapor, and then evaporates in large quantities. This is also called the external diffusion of vegetable moisture. The diffusion speed has a certain relationship with the surface area of the vegetable, air velocity, temperature and relative humidity of the air. When the air flow rate is faster, the temperature is higher, and the relative humidity of the air is lower, the diffusion speed is faster, that is, the evaporation speed of vegetables is faster, and the moisture content decreases at the same time, and the drying speed is accelerated.

2. Constant speed drying stage of vegetables:

When the temperature of the vegetables rises to the wet bulb temperature of the air energy, and all the heat absorbed from the air energy is used to evaporate water, the drying speed remains constant at this time, and it enters the second stage of drying. Vegetable evaporated water is free water.

The water in vegetables such as vegetables and green vegetables usually exists in three different states: free water, colloidal bound water, and combined water. Most of the free water and colloidal bound water are removed during the drying process. It does not depend entirely on the temperature of the dry air, but on the humidity of the air. The lower the relative humidity, the faster the water will migrate and evaporate.

3. Vegetable deceleration drying stage

When the water evaporation rate of vegetables reaches about 50-60%, the free water is greatly reduced, and a part of the colloidal bound water begins to evaporate. At this time, the water diffusion speed inside the vegetables slows down, which is slower than the water vaporization speed on the surface. This stage is called the deceleration drying stage of vegetables. At this stage, part of the heat provided by the air energy in the operation of the heat pump vegetable dryer is used for the further evaporation of the dried vegetables, and the other part is still heat-treated for the semi-dried vegetables, so that the temperature gradually rises and the moisture content reaches An equilibrium moisture content, when the moisture content of dried vegetables is about 15%, the evaporation of water stops, and the drying is completed.



Take a set of 8P vegetable drying machine as an example to dry about 650 kg of vegetables. Depending on the initial moisture content, the entire drying process is completed in 8-15 hours. The moisture content of dried vegetables is accurate and stable, and all parts can be dried evenly. Drying costs are low. The vegetable dryer can achieve energy saving, environmental protection, high efficiency and automatic operation for the drying and production of various vegetables such as cabbage, green vegetables, kohlrabi, lettuce, garlic slices, ginger slices, etc.