Study On Heat Transfer And Membrane Absorption Process Of Lithium Bromide Solution

Lithium bromide absorption chiller can use low-grade heat energy that is difficult to use for its own drive,with water as the refrigerant and lithium bromide concentrated solution as the absorbent.The process is not only environmentally friendly but also harmless to the human body,so it is favored in the air conditioning and refrigeration industry.Compared with other thermal equipment,the heat and mass transfer efficiency inside the bromine cooler is low.The absorber is one of the main components that affect the refrigeration efficiency of the bromine cooler.However,there are still insufficient studies on the energy conversion relationship between the two phases when the solution absorbs the vapor during the falling film absorption process in the absorber,the heat and mass crossover phenomenon in the heat and mass transfer process,and the mechanism of action.In view of this,this paper takes the absorber in the bromine cooler as the research object,carries out theoretical calculation,numerical simulation and thermodynamic analysis on the falling film absorption process of lithium bromide in the absorber,and proposes a method to strengthen the heat and mass transfer in the falling film absorption process of lithium bromide in the absorber.Firstly,the physical model of the falling film absorption process is established,and the theoretical calculation of the solution falling film absorption process is carried out.The variation of the liquid film thickness,flow rate,heat and mass transfer coefficient with Reynolds number and circumferential angle is obtained.Secondly,the fluid simulation software FLUENT was used to simulate and analyze the falling film absorption process of lithium bromide solution.The flow pattern,liquid film thickness,flow velocity,temperature and concentration distribution of the solution were obtained,and the simulation results were compared with the theoretical calculation results.Finally,according to the thermodynamic coupling and generalized field synergy thermodynamic mechanism,the thermodynamic analysis of the heat and mass transfer variation law obtained by theoretical calculation and numerical simulation is carried out,and a method for enhancing the heat and mass transfer efficiency of falling film absorption process is proposed.The results show that:(1)The liquid film thickness,liquid film velocity and heat and mass transfer between solution and water vapor in the solution falling film process change with the change of Reynolds number and circumferential angle.(2)In the falling film absorption process,the heat and mass transfer effect of the flow pattern between tubes is the best when the spray density of the solution is 0.12kg/(m·s),and the continuous stability of the liquid column at t=0.49 s is beneficial to heat and mass transfer.(3)When the circumferential angle of a single horizontal tube tends to 90°,the liquid film thickness and liquid film temperature have a minimum value,and the liquid film velocity has a maximum value.(4)The falling film absorption process in the absorber contains a water vapor phase change heat and mass transfer process that conforms to the generalized field synergy mechanism and a gas absorption heat and mass transfer process that conforms to the thermodynamic coupling mechanism.(5)When the temperature difference between the system and the outside world increases,the heat transfer driving force of the falling film absorption heat transfer process will increase,and the mass transfer ability of the lithium bromide solution in the absorber to absorb water vapor will increase.The greater the temperature difference between the high and low heat sources,the greater the driving force of the system heat transfer process,and the stronger the ability of the lithium bromide solution in the absorber to absorb water vapor.