Influence of different categories of condensates on film condensation of R-134a on in-line arranged 3D finned tubes

Abstract

The condensates generated in the process of film condensation, such as condensing, falling, and acting condensates, are identified and defined to obtain precise inundation effect model of 3D finned tube bundle. Furthermore, the influence of three categories of condensates on the film condensation under different heat fluxes and condensing temperatures is experimentally investigated via the homologous method. A test bench with a test section contains two arrays of 8 horizontal tubes is initially constructed. Experimental results show that the inundation effect coefficient decreases from 1.00 to 0.78 as acting condensate Re increases from 75 to 1860. The influence of heat flux on three categories of condensates is more significant than that of condensing temperature. As tube row depth increases from 1 to 6, the proportion of condensing condensate Re to acting condensate Re decreases from 100% to 15.0%, whereas the proportion of falling condensate Re to acting condensate Re increases from 0 to 85.0%. Furthermore, the condensation heat transfer model of single 3D finned tube and inundation effect model are established, and the deviations of results between experiments and models are almost within ±3.0%. The deviations of inundation effect coefficients between experiment and model proposed in this study are 92.5% and 50.0% less than those between experiment and models using routine method and considering single condensate with homologous method, respectively. Moreover, the inundation effect model proposed in this study reveals that different proportions of condensing or falling condensates to acting condensate lead to different inundation effect coefficient at the same acting condensate Re. The research results will lay the foundation for further revealing the mechanism of film condensation on 3D finned tube bundle and guide the thermal design of 3D finned tubes applied in shell-and-tube condensers.