Experimental Study On The Characteristics Of Falling Film Absorption Process In Micro-scale Liquid Film Tube Of NH₃-LiNO₃ Solution

The absorption refrigeration system takes heat energy as the driving force,can use low-grade energy,has the characteristics of clean and environmental protection,and has great potential for development and application.However,the low working efficiency of the absorber leads to the low coefficient of performance,which seriously limits the application scene of absorption refrigeration technology.compared with steam compression refrigeration system in small-scale applications,it is not economically competitive.Therefore,the research of enhanced absorption technology has important academic significance and engineering application value for the further development and promotion of absorption refrigeration system,especially in the field of miniaturization.The purpose of this paper is to investigate the experimental characteristics of falling film absorption process in microscale liquid film tube of NH₃-LiNO₃ solution.An absorber for obtaining free surface microscale liquid film by sticking spray in solution tube is proposed and fabricated,and a complete experimental platform of absorption refrigeration system is built based on this.A comprehensive evaluation absorption characteristics has been accomplished of microscale falling film absorber under various working conditions,effects on absorption parameters caused by absorption pressure,pressure potential,solution inlet subcooling,flowing features,as well as absorber heat load have been discussed,also,a numerical study had been done for the thickness of falling film.The absorption performance of the absorber is compared with that of an adiabatic absorber with structured packing.After that,the impact on system cycle performance caused by generation temperature,evaporation temperature,condensation temperature,solution state at the inlet and outlet of the absorber have been discussed.The experimental results show that under relatively low absorption pressure,the absorption rate of the proposed microscale liquid film absorber is generally more than 1×10^-3 kg/（m²·s）,is significantly higher than that of the adiabatic absorber with structured packing 0.3～0.4×10^-3 kg/（m²·s）,which indicates that the microscale liquid film absorber can produce strong mass transfer capacity per unit area under the premise of limited mass transfer area.By numerical solution,it is found that the thickness of the liquid film in the stable descending section of the proposed microscale liquid film absorber is about 300-400μm,which shows the expected micro-scale liquid film in the experiment has been formed.Under normal operating conditions,the absorption refrigeration cycle COP of the proposed microscale liquid film absorber is always stable in a high range（>0.4）,and the highest evaporation temperature of the experimental device is as low as-27.7℃.At the same time,it is found that the change of solution viscosity has a significant effect on the solution flow rate of the proposed microscale liquid film absorber,which is often ignored in the design and research of common absorbers.The free surface microscale liquid film absorber proposed in this paper not only strengthens the absorption process,but also has the potential to realize air cooling,which has a certain guiding significance for solving the problem of miniaturization and air cooling of absorption refrigeration system.