Research Status of Heat Pump Drying at Home and Abroad

- May 07, 2019 -

The research status of heat pump drying in foreign countries

about the basic principle of heat pump is generally considered to originate from Kano's works in the early 19th century and his papers on Kano cycle published in 1824. Willian Thomsan, later named Lord Kelvin, first proposed a practical heat pump system (also known as thermal amplifier) in 1852.

Using heat pump technology to dry materials is a new method with obvious energy-saving effect and practicable in recent years. In 1943, Sulzer Company adopted heat pump technology in basement dehumidification unit built in Germany. Thereafter, the application of heat pump technology in drying field has developed rapidly. The United States patented heat pump drying in 1950. From 1970 to 1977, nearly 1,000 heat pump wood dryers were installed in France. By 1980, about 3,000 wood drying plants had adopted heat pump drying technology. Japan began to study heat pump drying technology in the 1960s. By 1987, there were about 3000 heat pump drying devices, and heat pump drying technology was used in 12% of the existing drying devices. In Ontario, Canada, 45% of wood is dried by heat pump technology, saving 60% energy. In recent years, foreign scholars have made new progress in the application of heat pump drying. Cardond et al. (2002) experimentally studied heat pump-assisted drying instead of freeze-drying for lactic acid bacteria in seed culture. It was found that heat pump-assisted drying had lower investment and operation costs than freeze-drying. Alvesfilho (2002) put forward a new type of fluidized bed heat pump dryer, which uses CO2 as drying medium, heat pump and drying medium closed cycle clean operation, can save considerable energy, and produce high quality drying products. Chua et al. (2000) experimented with heat pump drying of coke, guava and potato. It was found that heat pump drying could improve the driving force of drying and the color of products. The effects of different temperature-time modes of heat pump tunnel drying on the quality of dried agricultural products were studied in detail.

Heat pump drying equipment research mainly focuses on process control and refrigeration components, especially compressor research. The energy efficiency and size of scroll compressor are more suitable for heat pump drying than general compressor. Advanced heat exchangers with ribbed surface and external corrugated fins can better heat transfer and reduce the size of heat exchanger. These factors make the heat pump dryer smaller and more efficient.

Heat pump drying and other heating methods constitute a combined drying device is also a new direction of heat pump drying research in recent years. The essence of heat pump drying is still hot air convection drying, which has a low heat transfer rate. Especially in the slow drying stage, the low drying efficiency of heat pump leads to poor working conditions and long drying time. Marshall and Metaxas (1998) carried out experiments on drying bricks and clay masses by high frequency (RF) combined with traditional heat pumps. The results showed that the performance coefficient (COP) and unit energy consumption dehumidification (SMER) of heat pump drying were improved by high frequency heating with pulsation test. The research and application of heat pump drying in China started in the 1980s, and the Shanghai Institute of Energy began to develop heat pump wood dryer in 1985. Thereafter, several topics related to heat pump drying were completed, and the development of heat pump grain seed drying device was started in 1992.

From 1989 to 1993, Beijing Forestry University and Beijing Refrigerator Factory jointly developed RCG series dual heat source wood dehumidifier products and obtained national patent. This product has been extended to more than ten provinces and cities in China and sold abroad, and achieved good economic and social benefits. Double heat source desiccant dryer adopts the combined drying technology of solar energy and dehumidifier, which makes up for the defect of using solar energy alone. Solar energy and dehumidifier can operate independently and jointly. The operation process of combined drying system is automatically controlled by computer.

Ma Yitai and Zhang Jiahui of Tianjin University Institute of Thermal Energy analyzed and calculated the optimum working conditions of heat pump drying by equivalent temperature method in detail, and put forward the concept of optimum evaporation temperature of heat pump drying device, which has guiding significance for energy-saving operation of heat pump drying device. The drying effects of different refrigerants were compared, and the energy-saving principle of regenerative cycle was studied. It is also pointed out that the advantages of drying seeds and other biomaterials sensitive to temperature with low temperature and humid air with strong drying ability are obvious.

Wang Jianfeng and Ouyang Yingxiu of Institute of Refrigeration and Cryogenic Engineering, Zhejiang University, etc. were used in heat pump drying experiments. It was pointed out that the application of phase change materials in the later stage of heat pump drying had obvious energy-saving effect. When the drying temperature is 45 C and the average mass percentage of the material is 24.3%, the phase change material can save 21.9% energy. For different drying materials, phase change materials can be placed in the system during appropriate drying period, which can not only maintain a certain drying and dehumidification speed, but also save the energy consumed by the heat pump drying system. In addition, Li Yuanzhi of South China Agricultural University and Zheng Chunming of Guangdong Institute of Agricultural Machinery also studied the application of heat pump drying in dehydrated vegetable processing. The results show that the quality of dehydrated vegetables processed by heat pump drying is good and the drying technology is feasible. Tian Xiaoliang and Sun Hui of Qingdao University applied heat pump drying system to the drying of soft rubber pills. TXL soft rubber pills heat pump dryer was developed. The drying period was shortened from 24 hours to 7 hours to 10 hours, and the energy consumption was only 1/9 of the original energy consumption.

上一篇:Development Trend of Heat Pump Drying 下一篇:没有了

Related News

Related Products