The heat pump drying unit can realize closed circulation drying of low temperature air, and the drying quality of materials is good. By controlling the working conditions of the device, the temperature of the hot dry air in the drying chamber is between 20 and 80 °C, which can meet the quality drying requirements of most heat-sensitive materials; the closed circulation of the drying medium can avoid the possibility of exchange with the outside air. Impurity pollution to materials. So what is the drying principle of materials in the heat pump dryer?

The use of heat pump dryer to dry the material is to reduce the moisture in the material by vaporization. The surface of the drying medium in contact with the water becomes a free surface. In addition, since the moisture vaporizes on the free surface, a layer is naturally formed on the surface of the cover. A thin layer of saturated water vapor. If the partial pressure of water vapor on the free surface is greater than the partial pressure of water vapor in the drying medium, the water in the drying medium vaporizes and gradually diffuses into the medium. At this time, if the difference between the partial pressure of water vapor between the surface of the material and the drying medium is increased, the drying speed can be quickly increased.

Conversely, if the partial pressure of water vapor on the surface of the material is less than that of the drying medium, then the situation is opposite, the material absorbs the moisture in the drying medium, and its moisture content increases, which in turn becomes a hygroscopic process. In both cases, after a period of time. The partial pressure of water vapor in the material is equal to the partial pressure of the drying medium, that is, at this time, the water exchange between the two reaches a dynamic equilibrium state, the water in the material is balanced, and the relative humidity in the surrounding medium is also affected. It is called the equilibrium relative humidity.



When the material is first dried in the heat pump dryer, the temperature of the drying medium gradually increases, and the material absorbs heat from it, but at this stage, the moisture in the material is basically unchanged. Then the temperature of the material reaches a certain value, and the subsequent stage is called the constant speed drying stage. In this process, the temperature of the material remains unchanged, the precipitation rate is a fixed value, the temperature of the surface of the material is equal to the wet bulb temperature, and the temperature of the material center is relatively low due to , the water is constantly moving outward, evaporating on the surface. Therefore, the drying speed of the process is a fixed value, the constant speed drying stage ends, reaches the critical point, and enters the deceleration drying stage. At this stage, the water inside the material evaporates more slowly than the surface, and the temperature inside the material does not rise as fast as the surface.

The drying process of the heat pump dryer continues in this way until the moisture balance between the material and the drying medium is reached, and the temperature of the material and the drying medium are equal.