Experimental Study On Falling-film Generation/absorption Process Outside A Vertical Tube With Two Working Pairs

Solar energy absorption system has received extensive research and application at home and aboard because it takes advantage of solar energy which is a clean,renewable and readily available energy,combining the mature absorption refrigeration technology which is friendly to the environment.To improve the utilization of low energy sources such as solar energy and the heat and mass transfer performance of working pairs in absorption refrigeration systems.A falling film absorber/generator which has a cold/heat source inside the tube is proposed to improve the heat and mass transfer performance in the process of absorption and generation,making the of the temperature change of cold/heat source temperature matching the temperature change of solution outside the tube.At the same time,a falling film experimental setup with inner cold/heat source has been designed and built,and the heat and mass transfer process of falling film outside the vertical tube with two different working pairs has been experimentally and theoretically studied in the system.An experimental setup for falling-film generation/absorption has been designed and built referring to related design manual and literature.The functions and key design points of experimental setup have been expounded especially the body of falling film device.The operating procedure of the experimental setup has been briefly covered,and error analysis of the experimental results has been carried out in the end.The heat and mass transfer performance of LiCl-H2O solution and LiBr-H2O solution in the falling-film generation process has been experimentally studied on the experimental setup.The solutions' film are all in wavy laminar flow under the experimental conditions which intermediate pressure is 2.5-3kPa.The heat and mass transfer performance of solution film and temperature difference of heat source have been examined under variable heat source temperature and flow,solution concentration,generation pressure and solution flow.What's more,the contrast falling-film generation experiments between LiCl-H2O solution and LiBr-H2O solution have been conducted under the pressure 8?10kPa,and the results show two solutions have the similar heat and mass transfer performance.For the convenient design of falling film generator with LiCl-H2O solution in the future,correlations of Nu number and Sh number are acquired by the experimental data.The heat and mass transfer performance of LiCl-H2O solution in the falling-film absorption process has been experimentally studied on the experimental setup.The heat and mass transfer experiment under different conditions have been studied as well,which provide key parameters for the absorption model of LiCl-H2O solution.In addition,the contrast falling-film absorption experiments between LiCl-H2O solution and LiBr-H2O solution have been conducted under the pressure 2.5-3kPa,and the results show LiCl-H2O solution has an higher absorption rate than LiBr-H2O solution,proving LiCl-H2O solution has a better mass transfer performance than LiBr-H2O solution and it contributes to the miniaturize of absorber.And heat and mass transfer correlations are also fitted by the absorption experiment results.A theoretical model of heat transfer for LiCl-H2O solution falling film absorption based on finite volume method is firstly developed.Temperature distribution and concentration distribution of solution have been obtained using calculated program.Based on the experimental data measured under the variable operation conditions,convective heat transfer coefficient for LiCl-H2O solution lies between 510 W·m·2.K-1and 710 W·m-2·K-1,and rises as the solution film Re increases.Moreover,the rib tube or surface treatment tube has been suggested for heat transfer enhancement aiming to increase the temperature difference between cool water and solution because the convective heat transfer coefficient at the solution side is the main factor influences the whole heat transfer coefficient.The ranges of the solution flow rate could be enlarged to show the absorption rate trends to a limit value as the increase of solution flow rate since the rise of the solution film in thickness.