布液孔间距对水平管降膜蒸发器换热特性的影响研究

Effect of Hole Spacing on Heat Transfer Characteristics of Falling Film Evaporator in Horizontal Tube

在水平管降膜蒸发器液体布液器的设计中,布液孔间距影响着液体的成膜质量,为了简化设计计算,提出了利用有限元数值计算软件研究不同开孔间距与液膜在换热管外壁面形成情况的关系。采用VOF模型,制冷剂采用R134a,布液孔处制冷剂的流速为0.2 m/s,对换热管外壁面液膜流动形态进行Fluent模拟,探讨不同开孔间距(6 mm、8 mm、9 mm、10 mm、15 mm)下的液膜厚度及传热系数。结果表明,当布液孔的开孔间距不同时,管外液膜厚度随周向角度的变化规律是相同的,都随着圆周角度的增加呈现出先迅速减小后趋于平稳最后再增大的趋势。当布液孔沿管长方向之间的间距s=6 mm时,液膜在管外铺展较厚,换热效果不佳;s=8 mm、s=9 mm和s=10 mm时,液膜在管外更加均匀的铺展;而s=15 mm时,换热管管壁外没有形成片状流动的液膜,液膜流动不连续,干涸面积较大。S=8 mm时,换热效率较高,平均换热系数为4538.76 W/(m^2·K),具有较好的换热效果。

In the design of liquid distributor for falling film evaporator of horizontal tube,the spacing of liquid holes affects the quality of liquid film forming.In this paper,the VOF model was adopted,the refrigerant was R134a,and the flow rate of the refrigerant at the distribution hole was 0.2m/s.The liquid film flow pattern on the external wall of the evaporation tube was simulated with Fluent,and the liquid film thickness and heat transfer coefficient at different hole spacing(6 mm,8 mm,9 mm,10 mm,15mm)were discussed.The results show that the thickness of liquid film outside the tube varies with the circumferential Angle when the spacing of liquid holes along the pipe length is different.When the spacing between the liquid distribution holes along the direction of tube length s=6 mm,the liquid film spread out thickly outside the tube,and the heat transfer effect was not good.When s=8 mm,s=9 mm and s=10 mm,the liquid film spreads more evenly outside the tube.However,when s=15 mm,there was no liquid film with sheet flow outside the tube wall of the heat exchange tube,the liquid film flow was discontinuous,and the dry area was large.When s=8 mm,the heat transfer efficiency is higher,the heat transfer coefficient is 4538.76 W/(m^2·K),and the heat transfer effect is better.