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利用界面结构效应实现蒸汽滴状冷凝对能源动力系统的高效化和集成化具有至关重要的作用.深入认识液滴动态特性对传热性能的影响有利于探究低压蒸汽冷凝中传热控制机理和研发高效紧凑的传热强化技术.本文系统地研究了蒸汽滴状冷凝中液滴脱落特性,提出了低压蒸汽冷凝液滴脱落滞后效应.随着蒸汽压力降低,冷凝液滴黏度增加,引起自身脉动特性下降,接触线移动受阻,接触角滞后现象明显,导致脱落尺寸明显增加而脱落速度大大降低.与常压蒸汽冷凝中液滴的快速启动连续下落不同,低压蒸汽冷凝中液滴长至脱落尺寸后表现出了“阶跃式”下落的现象,即液滴脱落滞后效应.在液滴整个生命周期中,低过冷度时液滴生长速度控制着传热过程,而高过冷度时液滴脱落滞后延缓了表面更新,降低了有效换热面积,成为了控制传热过程的因素.通过液滴脱落效应解释了传热通量随过冷度非线性增加现象的内在机理,明晰了蒸汽冷凝传热控制机制,为低压蒸汽冷凝传热强化指明了方向.
The use of the interface structure effect to achieve steam droplet condensing is crucial to the energy efficiency and integration of the energy and power system.It is helpful to understand the heat transfer control mechanism of low pressure steam condensing Research and development of highly efficient and compact heat transfer enhancement technology.This paper systematically studied the droplet characteristics of steam droplet condensation and proposed the droplet hysteresis effect of low pressure steam condensate.The droplet viscosity of condensate droplet increases with the decrease of steam pressure, The characteristics of contact lines are obstructed and the contact angle hysteresis is obvious, resulting in the obvious increase of the size of the drop off and the speed of falling off greatly.Different from the rapid start-up and fall-off of liquid droplets in atmospheric vapor condensation, After the drop showed “drop-off ” phenomenon, that is, drop off lag effect.In the whole life cycle of the droplet, the droplet growth rate controls the heat transfer process, and the degree of supercooling When the droplet lag hysteresis slows the surface renewal, reduces the effective heat exchange area, has become the control heat transfer process factor.Through the droplet shedding effect explained The inherent mechanism of heat transfer with nonlinear increase of undercooling clarifies the heat transfer control mechanism of steam condensation and points out the direction for heat transfer enhancement of low pressure steam condensing.