升膜蒸发管内流型可视化及传热性能

Experimental study of heat transfer performance and flow visualization in the climbing film evaporation pipe

为了探究热流密度、真空度和流量对升膜蒸发器传热性能的影响,以及对升膜加热管内流体流型进行观测和分析,本文建立了升膜蒸发系统传热实验平台,对升膜蒸发器的传热特性和流体流型进行实验研究。实验所用升膜管管长2200mm,升膜管采用镀透明导电膜石英管,工作介质为水;升膜管蒸发侧采用电加热方式;研究了热流密度(6.71k W/m2≤q≤26.79k W/m2)、流量(20L/h≤M≤100L/h)和真空度(0≤P≤15k Pa)对升膜加热管流体流型和传热特性的影响。结果表明:通过电加热的方式可以实现石英管内溶液的升膜蒸发,并能观测到泡状流、块状流、弹状流、柱塞流、环状流和雾状流;热流密度低于6.71k W/m2时无法形成升膜蒸发,随着蒸发侧热流密度的增大,升膜管内环状流长度增大,管内传热系数增大;随着流量的增大,升膜管内液体湍流强度增大,管内传热系数增大;真空度对流体流型影响较大。

In order to explore the effects of the heat flux density,vacuum degree and flow on heat transfer performance of climbing film evaporator,this paper observed and analyzed the fluid flow pattern in the climbing film heating pipe,established the heat transfer experimental platform of climbing film evaporation system,and studied the heat transfer characteristics and fluid flow pattern of climbing film evaporator. The length of the climbing film evaporation pipe used in the experiment was 2200 mm,the climbing film pipe was a quartz tube coated with transparent conductive film,the working medium was water,and electrical heating was employed in the evaporation section. The effects of the heat flux densities（6.71 k W/m2≤q≤26.79 k W/m2）,flow rates（20L/h≤M≤100L/h）and vacuum degrees（0≤P≤15k Pa） on fluid flow pattern and heat transfer characteristics of the climbing film heating pipe were studied. The results showed that climbing film evaporation for the solution in the quartz pipe could be achieved in the way of electric heating. And bubbly flow,bulk flow,slug flow,plug flow,annular flow and mist flow were observed. When heat flux was less than6.71 k W/m2,climbing film evaporation was not formed. With the increase of the evaporation side heat flux density,annular flow length increased in the climbing film pipe,and the inner pipe heat transfer coefficient increased. With the increases of the flow,liquid turbulence intensity increased inside the climbing film pipe,the inner pipe heat transfer coefficient increased as well. And vacuum degree had a significant influence on the fluid flow pattern.