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

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.