V型导液槽对HFC245fa水平管束外冷凝换热影响

Effects of V-type ducts on condensation heat transfer of HFC245fa on horizontal tube bundles

试验研究了HFC245fa在水平光管与强化管管束外的冷凝换热特性,提出在管束中加装V型导液槽来消除管束效应的方法,并通过试验研究了V型导液槽对管束冷凝换热特性的影响。试验管束由4列排深为5排的列管构成,带导液槽管束的前4排管下方加装了两段长度为450mm的导液槽;试验换热管公称外径为19.05mm、换热长度为1000mm。试验中,以Wilson描点法获得强化换热管水侧对流传热系数,以对比试验方法研究了V型导液槽对水平管束外冷凝换热性能的影响。结果表明:传统的管束效应模型仅在较小的热通量范围适用;凝液在管间的迁移形态与流态随管上作用凝液量的系列变化是导致管束效应变化的主要因素;加装导液槽可有效控制凝液在管间的迁移,控制管束效应;加装导液槽使光管单管冷凝传热能力下降10%左右,使光管管束总体换热能力提升4.5%～9.5%;加装导液槽对强化管单管冷凝换热性能的影响比对光管影响强近4倍。本文研究成果对引入导液槽开发新型高效卧式冷凝管束具有指导意义。

In a horizontal condensation tube-bundle, the inundation effect, resulted from local condensation film and falling condensate from upper tube rows, may reduce the condensation heat transfer coefficient （CHTC） considerably.This paper presents an experimental study on condensation heat transfer characteristic of HFC245fa on horizontal tube bundles.A scheme was proposed to reduce the tube row effect resulted from falling condensate with V-type ducts, and the effect of the duct on CHTC of the tube bundles was investigated experimentally.The tube bundle consisted of 4 columns, each with 5 tubes, with smooth tubes and enhanced tubes, separately.Two columns out of the four were equipped with the duct.The equivalent outside diameter and effective length for heat transfer of tubes were 19.05 mm and 1000 mm respectively.In the experiment, water-side heat transfer coefficient was obtained by modified Wilson plot method, the temperature difference between saturated vapor and cooling water was obtained by two-junction thermopiles （precision, ±0.05℃）, and the temperature difference of cooling water was obtained by thermocouples with small period standardization method （precision, ±0.02℃）.The experimental results show that the condensate flow regime and flow pattern between adjacent tubes, determined by the quantity of flowing condensate, are key factors that affect the inundation effect.The flow regime and flow pattern of the condensate can be well controlled by the V-type duct fixed in the tube bundle.The total CHTC of the smooth tube bundle with ducts is 4.5%—9.5% higher than that of the reference smooth tubes.Due to the structure of the duct and the method of installation, CHTC of smooth tubes and enhanced tubes with ducts are reduced by 10% and 40% respectively.The results can be used to guide the design of high efficient tube bundles for condenser.