HFC134a水平二维与三维肋管外冷凝换热特性

环保工质与高效冷凝管的应用对制冷行业实现节能减排意义重大，工质在强化管外膜状凝结换热特性是二者推广应用的关键。建立了水平管外膜状凝结换热试验系统，研究了HFC134a在4种二维肋管与2种三维肋管外的膜状凝结传热特性。试验管公称外径为19.05 mm、有效换热长度为1000 mm；试验中，通过改进的Wilson图解法获取试验管水侧对流传热系数。结果表明： HFC134a水平二维与三维肋管外冷凝传热系数分别达到同热通量下光管的11倍与19倍以上；HFC134a工质对应最佳二维肋管的肋密度在1069～1575fpm（肋每米）之间、肋高在0.7～1.5 mm之间，对应最优三维肋管（与本文试验肋型相似）肋密度低于2000fpm；既有二维肋管膜状凝结换热模型需要进一步完善，肋管结构优化过程中应遵循优先提升肋密度的原则。

Film condensation characteristics of HFC134a on enhanced horizontal tubes with two dimensional and three dimensional integral fins

Design of shell-tube condenser with finned tubes with two dimensional (2D) or three dimensional (3D) fins for HFC134a needs reliable models for the film condensation, which is usually based on reliable experimental data. A new test facility was established to investigate experimentally film condensation characteristics of HFC134a on six enhanced tubes (four kinds of 2D finned tubes and two kinds of 3D finned tubes) and the reliability of existing models and the effect of fin density and fin height on film condensation of HFC134a were discussed. Equivalent outside diameter and active length of test tubes are 19.05 and 1000 mm, respectively. In the experiment, water-side convection heat transfer coefficient for all test tubes is determined by the modified Wilson plot method. The results are as follows. Condensation heat transfer coefficient (CHTC) of HFC134a on single smooth tube is a little higher (5%—8%) than that predicted by the Nusselt model; CHTC of the best 2D (or 3D) finned tubes is 11.5 (or 19) times higher than that of single smooth tube under the same heat flux; the best fin density and fin height of 2D finned tubes are in the regions of 1069—1575 fins per meter (fpm) and 0.7—1.5 mm, respectively; the best fin density of the 3D finned tubes is less than 2000 fpm; the deviations between existing models and experimental results are not acceptable, due to their bad stability or poor accuracy. More work should be done to improve the models for film condensation of HFC134a on 2D finned tubes and develop models for that on 3D finned tubes in the future. The result can be used to guide the design of shell-tube condenser with HFC134a.