CFD And Test Study On Air Side Heat Transfer Performances And Pressure Drops Of Parallel Flow Condensers

Parallel flow condensers have been widely applied to saloon cars, trucks, minibuses and even coaches, and are the most promising condenser form. The technology trend of parallel flow condensers focuses on features of high efficiency, miniaturization, light weight and low cost. Recently, research interest on increase of the air side heat transfer coefficients and reduction of the air side pressure drops of parallel flow condensers and alike compact heat interchangers has became one of the hot spots in heat transfer enhancement domain. Researchers from all over the world have carried out thorough and systematic studies on the areas: the effect of air side structure parameters on air side performances; and heat transfer enhancement mechanism. However, these studies have their obvious limitations as following:①Because of the significant disparity in air side structure parameters of research objects, different conclusions may be drawn by different researchers even for the same topic. Moreover, the thicknesses of most condensers studied were larger than 16mm. If results based on these studies are directly used in engineering design of highly effective parallel flow condensers, which are normally thinner than 16mm, a significant bias can be introduced.②These studies put excessive attention on the universal research in air side performance enhancement, while neglected the particular research in performance attenuation. However, it is particularity that can often foment innovation and bring essence change for engineering design.To address the two issues described above, both experimental and CFD studies on air side heat transfer and pressure drop characteristics for 47 kinds of parallel flow condensers have been performed by this study. Main study results are:①Three dimensional CFD simulation model has been established. This model can accurately reflect the air flow and heat transfer characteristics on the air side of parallel flow condensers. Compared with experimental results, air side heat transfer coefficients and air side pressure drops obtained through CFD simulation analysis demonstrate average errors within±5.28%.②It was found that under the same air frontal velocity, the air side overall performances of parallel flow condensers could be improved by reducing tube thicknesses, unanimously proved by both experimental and CFD analysis. Therefore, reducing tube thicknesses is an important method to develop high efficiency and energy saving parallel flow condensers.③CFD study indicated that under the same Reynolds number, changing overturning lengths could hardly influence the air side integrated performances of parallel flow condensers. And along with the increase of louver pitches, a peak value of integrated coefficients appeared. Furthermore, as condenser thicknesses being reduced, integrated coefficients would keep increase. Therefore, reducing condenser thicknesses is another important method to develop high efficiency and energy saving parallel flow condensers. With this as a basis, reasonably choosing louver pitches in engineering design is helpful to obtain the best air side overall performances of parallel flow condensers.④Through CFD analysis, the phenomenon of"compulsory order flow"was discovered. Effect of the phenomenon on air side heat transfer coefficients and pressure drops was only related to louver structure parameters, especially to louver angles and fin pitches. When"compulsory order flow"appears, attenuation of air side integrated performances could be caused. Therefore, it is very important in engineering design to avoid causing"compulsory order flow".⑤αcorrelations, which is specifically applicable for developing high efficiency parallel flow condensers with condenser thickness range from 10mm to 16mm, was derived in this paper. The results calculated byαcorrelations within±10% error band is 44% higher or more than those obtained by Webb correlations, Chang correlations and Kim correlations, which are generally acknowledged to have relatively high forecast precision.The contributions of innovation of this paper are as follows:①Phenomenon of"compulsory order flow"was discovered and defined.②Computational method of"impact angle"was proposed."Impact angle"was taken as an independent variable creatively in works of correlation deriving thereafter.③CFD analysis data was used inαcorrelations deriving. This is not found in the developing process of similar correlations. However, the fact thatαcorrelations introduced higher forecast precision than Webb correlations, Chang correlations and Kim correlations indicates that deriving correlations with CFD results is fully feasible. This fact also brings forth an important developing trend for correlations research in the future.The study results of this paper can completely be applied to engineering design. The study is practically important in improving the research and development of parallel flow condensers and alike compact heat interchangers, and thus, will generate huge social and economic values for China automotive industry.