| With the increasingly serious energy shortage and environmental problems,the efficient use of energy to reduce its cost in industrial production has become an important proposition for building a beautiful China and achieving the goal of “double carbon”.The data shows that the energy consumption of the building accounts for 46.5% of the total energy consumption in China,and the energy consumption caused by the use of air conditioning in building is accounts for 50%-70%.Therefore,absorption refrigeration technology driven by low-grade heat energy has attracted extensive attention.In the absorption refrigeration system,the characteristics of flow and heat and mass transfer in the absorber and generator determine the energy conversion efficiency and economic benefit of the whole system.Horizontal falling film flow in absorber is considered as the most common heat and mass transfer mode,which has the advantages of high heat and mass transfer performance and low pressure drop.In addition,lithium bromide/water and water/ammonia gas are usually used as working pairs in absorption refrigeration systems.However,problems such as limited operating temperature,easy crystallization of lithium bromide and corrosion of equipment are encountered during operation.In view of this,the green solvent of 1-ethyl-3-methylimidazolium acetate（[EMIm]Ac）ionic liquid,which has advantages of strong hypersonic ability,good stability and wide liquid range was used as the absorbent.The falling film flow and heat and mass transfer experimental platform was established,and the influencing factors and laws of falling film flow pattern transition and heat and mass transfer characteristics of [EMIm]Ac aqueous solution were analyzed,which can provide reference for the practical application of [EMIm]Ac aqueous solution.The main research contents and conclusions are as follows:（1）Firstly,the saturated absorption performance and dynamic characteristics of[EMIm]Ac aqueous solution were studied.The vapor pressure of [EMIm]Ac aqueous solution under different temperature and humidity conditions was calculated by the NRTL equation.The relationship between saturated absorption performance and saturated vapor pressure of[EMIm]Ac aqueous solution was discussed.The absorption/desorption rate of [EMIm]Ac aqueous solution was measured and its dynamic characteristics were analyzed.The results showed that the change of total mass after absorption equilibrium increases with the increase of relative humidity and mass fraction of the [EMIm]Ac.Under certain relative humidity,regardless of the initial concentration,the equilibrium concentration tends to be consistent,and the deviation between the vapor pressure at the final equilibrium concentration of [EMIm]Ac aqueous solution and the vapor partial pressure in the air increases with the decrease of relative humidity.The decrease of experimental pressure and the addition of surfactant improved the absorption efficiency.The desorption amount and desorption rate increased with the increase of desorbent temperature,while increase with the decreasing experimental pressure and mass fraction of [EMIm]Ac.（2）Secondly,the falling film flow pattern transition characteristics between the [EMIm]Ac aqueous solution and deionized water were compared.The effects of spray density,cooling water temperature,solution temperature and tube spacing on the critical Reynolds number of the flow pattern transition were analyzed.The prediction formula of the critical Reynolds number is established.The results showed that the critical Reynolds number increases with the increase of the Galileo number.There is an obvious lag phenomenon in the process of flow pattern transition.Due to different physical properties of the solution,the phenomena of in-line column flow and staggered column flow will be formed between tubes.When the viscosity is large,the phenomenon of in-line column flow occurs,on the contrary,staggered column flow occurs.（3）Finally,the effects of cooling water temperature,surfactant,solution concentration,tube spacing and spray density on the heat and mass transfer performance during the water vapor absorption/desorption processes by the [EMIm]Ac aqueous solution are discussed.The results showed that in the falling film absorption process,the interfacial mass transfer coefficient gradually increased with the decrease of cooling water temperature,the increase of tube spacing,the increase of spray density and the addition of surfactant.After the addition of200 ppm 1-octanol,the heat transfer and mass transfer coefficient increased by 179.1 % and393.6 %,respectively.In the process of falling film desorption,the increase of cooling water temperature greatly improves the interfacial heat transfer coefficient,and the heat transfer coefficient at 80℃ is 262.8% higher than that at 40℃. |
