Research Progress on Frost Formation Mechanism of Air-source Heat Pump and Its Defrosting/Anti-frosting Technology
Through the promotion policy of energy saving and emission reduction in China, space heating has been gradually transformed from the traditional small coal-fired boiler to a clean heating mode. As a key technology of clean heating, the application and development of air-source heat pump is growing r...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | zho |
| Published: |
Journal of Refrigeration Magazines Agency Co., Ltd.
2018-01-01
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| Series: | Zhileng xuebao |
| Subjects: | |
| Online Access: | http://www.zhilengxuebao.com/thesisDetails#10.3969/j.issn.0253-4339.2018.05.010 |
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| Summary: | Through the promotion policy of energy saving and emission reduction in China, space heating has been gradually transformed from the traditional small coal-fired boiler to a clean heating mode. As a key technology of clean heating, the application and development of air-source heat pump is growing rapidly due to its energy conservation, high efficiency and environment protection. However, frost occurs on the surface of the finned-tube heat exchanger when the surface temperature is below both the dew point temperature of ambient air and the freezing point temperature. Frosting on the surface of the evaporator increases the heat transfer resistance of the heat exchanger and then decreases its heat transfer coefficient and the COP of the system so that the application and popularization of the air source heat pump system is seriously limited under the clean heating policy of substituting coal with electricity in China. Thus, it is of great significance that the frosting mechanism on a cold surface is investigated to explore the defrosting technology of high efficiency and long-term-effective anti-frosting technology for the development of air-source heat pump technology and the promotion of clean heating policy. In the present paper, firstly, the research status of frosting mechanism on the cold surface is briefly described, as based on the growth law of a frost layer and its physical properties. Various factors, including air temperature, air relative humidity, air flow rate, surface characteristic, surface temperature, structure of finned-tube heat exchanger, etc., affecting the frosting process and the corresponding defrosting/anti-frosting method, such as reverse cycle, hot gas bypass, electric heater, low-frequency oscillation, hot water spray, ultrasonic vibration, electric field, magnetic field, changing the characteristics of inlet ambient air, changing surface temperature, surface treatment methods and so on are summarized. The research progresses of three kinds of common defrosting methods, including reverse cycle defrosting, hot gas bypass defrosting and electric heating defrosting are reviewed. The electric heating defrosting method can improve the indoor comfort during defrosting in comparison with the other two methods. The anti-frosting effects are analyzed based on changing air parameters, cold surface temperature, and heat exchanger structure. The research progress of anti-frosting technology is summarized for changing surface characteristics methods. Finally, the limitation of the thermal conductivity model of frost layers and the problems existing in defrosting/anti-frosting technology are pointed out. Based on the previous review and analysis, it is suggested that effects on defrosting technology of indoor comfort and energy consumption should be further studied; several measures should be taken to explore the anti-frosting technology, which can strongly inhibit different stages of frosting process, such as condensation of water vapor, condensate water freezing, frost layer melting and collapse. In addition, because of the limitation of the length of the article, research progress and existing gaps of other defrosting and anti-frosting techniques are not provided. This paper can be used for guiding the future design and system optimization for air source heat pump. |
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| ISSN: | 0253-4339 |