Abstract:

Falling film evaporator is characterized by short contact time between the process fluid and the heated surface, high heat transfer coefficients, minimal pressure drop, minimal static head and small process fluid holdup, which make it applicable to small temperature difference heat transfer.However, a circulating pump is a must-be equipment to pump the fluid to the top of the evaporator.In this paper, a new falling film evaporator combined with vapor-lift effect was proposed to realize no pump circulation, which in turn made the system more simple, compact and reliable.A mathematical model based on the slug-flow transportation theory was proposed to analyze the hydrodynamic characteristics of the transportation unit.The results indicated that the proposed falling film evaporator combined with vapor-lift effect could realize stable transportation by vapor slug when the vapor fraction was between 0.3% and 5%.For each liquid flow rate, there was a maximum pumping height and minimum suction height.

Key words:

气提效应, 降膜蒸发, 水力学特性, 弹状流

摘要：

降膜蒸发器具有传热速率高、持液量小、无静液柱引起的沸点上升等特点，适用于小温差传热，但系统需要一个循环泵。本文提出采用蒸汽输送液体的新型降膜蒸发模式来实现无泵循环，使系统结构更为简单、紧凑，可靠性更高。利用现已广泛使用的弹状流输送理论建立输送单元数学模型，研究其水力学特性。结果表明本新型气提输送降膜蒸发器在蒸汽引入率为0.3%～5%时即可实现弹状流的稳定输送。对每一个输送流量，存在一个最大扬程和最小吸程。且在相同液相表观速度下，最大扬程对应最小吸程。

关键词:

气提效应, 降膜蒸发, 水力学特性, 弹状流