Development and Application of Heat Pump Dryer

- May 08, 2019 -

Henan microwave equipment Net News: For a long time, heat pump dryer has been used in the drying process of wood and grain processing. In the process of food production, processing and storage, air temperature and relative humidity have a great impact on its quality and appearance, so the dryer is of great significance for food processing and storage.

So what is heat pump dryer ?

heat pump dryer is mainly composed of heat pump system (evaporator, compressor, condenser, throttle valve, etc.) and air system (drying chamber, fan, electric heater, etc.) as shown in Figure 1. Therefore, the heat pump drying cycle includes two cycles: (1) vapor compression cycle of refrigerant. (2) Circulation of dry air. Refrigeration cycle

Refrigeration cycle: High temperature and high pressure refrigerant gas from the compressor enters the condenser, transfers heat to air, condenses into normal temperature and high pressure liquid, then enters the evaporator through expansion valve throttling, absorbs heat from the wet air from the drying chamber, and becomes low temperature and low pressure gas, which is inhaled and compressed by the compressor, so on reciprocating cycle.

air system: wet air is cooled below dew point temperature in evaporator, condensate water is precipitated, moisture content decreases, then enters condenser, absorbs heat of refrigerant and increases temperature, relative humidity decreases, and then sends to drying chamber.

Fig.1 Heat pump drying cycle system diagram

classification of heat pump dehumidifier:

(1) According to air circulation system, it can be divided into closed-circuit circulating system and open-circuit circulating system

closed-circuit circulating system refers to all circulating use of drying medium in dryer, and open-circuit circulating system refers to evaporator and heat pump workers whose drying medium leaves drying chamber and enters heat pump. After mass heat transfer, it is directly evacuated.

(2) According to refrigeration system, it can be divided into general type, cooling type and temperature regulating type. General type

< p> refers to air cooling and dehumidification by evaporator, heating by condenser, reducing relative humidity, the system outlet temperature can not be adjusted, can only be used for heating and drying. The

cooling type refers to the addition of external water-cooled or air-cooled condensers to a general type of system. The condensation heat of refrigerants is entirely taken away by the additional condensers, and the air temperature remains unchanged after passing through the main condenser. The system can be used for drying thermosensitive biological materials or for cryogenic storage. The

temperature-regulating type refers to that the condensation heat of refrigerant is taken away by water-cooled or air-cooled condenser, and the residual condensation heat is used to heat the air passing through the evaporator. The outlet temperature of the system can be adjusted.

Since the 1970s, the United States, Japan, France, Germany and other countries have carried out research on heat pump dehumidification and drying. The International Energy Center (IEA) has concentrated a large number of research results on heat pump drying technology. China also introduced this technology in the 1980s. The earliest and most widely used technology is wood drying. Because of the low temperature of heat pump drying which is close to natural drying, it has been gradually applied to the drying of food and agricultural by-products in recent years. Good economic benefits have been achieved and the added value of products has been greatly improved. Especially the implementation of our government's energy saving and environmental protection policy has greatly promoted the development of heat pump dehumidification and drying technology. At present, the universities and research institutes that study heat pump drying technology are mainly concentrated in Southwest Agricultural University, Zhejiang University, Tianjin University, Beijing University of Technology, Beijing Forestry University, Guangdong Agricultural Machinery Research Institute, Shanghai Sangling Energy Research Institute and other units. The drying materials are also concentrated in wood, grain, food, agricultural by-products, textiles and paper. The popularization rate of heat pump dehumidifiers in the south is better than that in the north. At present, there are 8-mdash manufacturers producing dehumidifiers; 10 domestic dehumidifiers account for about 70%. The imported dehumidifiers in China are mainly concentrated in Japan, the United States, Canada and other countries.

Henan Microwave Equipment Network Recommended Reading: Heat Pump Dryer What is it?

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