低温流体在竖直通道中降膜蒸发研究进展

Research Progress of Falling Film Evaporation of Cryogenic Fluid in Vertical Channels

降膜蒸发作为一种高效传热传质技术,已经在空分领域得到了应用。本文介绍了空分膜式主冷凝蒸发器的原理和特点,从波状特性和破断特性方面阐述了下降液膜的动态特性,总结了入口流量、壁面结构、工质组分和热流密度因素对传热传质的影响,重点介绍了低温液氮在大空间平板上降膜过程的临界热流密度规律和过热壁面再湿润动态特性,并对现有竖直通道内降膜蒸发过程换热关联式进行了归纳。由于低温工质物性和通道结构的特殊性,已有的常温工质换热关联式应用于空分膜式主冷凝蒸发器的传热设计还存在较大差距。最后指出小传热温差条件下,复杂狭窄通道内低温流体降膜蒸发过程需要进一步研究。

Falling film evaporation, whicil is one efficient technology of heat and mass transfer, has been used in air separation field. The principles and characteristics of the main downflow condenser/reboiler in air separation are analyzed, the dynamic characteristies of tailing film are illustrated from the aspects of the wave characteristics and breakdown characteristics, the influence of inlet flow tale, wall structure, components of working medium and heat flux density on the heat and mass transfer are reviewed in this paper. The occurrence regularity of critical heat flux and the dynamic characteristics of the superheated surface rewetting with liquid film for the progress of falling film of cryogenic liquid nitrogen in the large space plate are emphasized, some available heat transfer correlations for the progress of falling film evaporation in the vertical channels are concluded. Due to the speciality of physical property and channel structure, there is a significant gap applying the existing heat transfer correlations of working medium with normal temperature to the main downflow condenser/reboiler in air separation field. At last, it is pointed out that the further study of falling fihn evaporation of cryogenic fluid in the complex narrow channel under the small heat transfer temperature difference is needed.