Experimental Study And Molecular Dynamics Simulation Of Basic Properties Of Heat And Mass Transfer For Ionic Liquid Absorption Refrigeration Working Fluids

Efficient energy utilization represents the current remedy to balance energy supply and demand,and a good way to transform the development structure,while absorption refrigeration technology has attracted widespread attention because it can convert low-grade energy into utilization.The defects of traditional absorption refrigerant,such as easy crystallization and corrosion,are main factors that restrict unit safety and increase production costs.Ionic liquid,superior in physical properties,can be integrated with a variety of refrigerants to solve the above problems,so it is regarded as an ideal absorber substitute.In recent years,the exploration of ionic liquids as well as the performance of new refrigerants has become the focus of refrigeration research.In this thesis,the heat and mass trnsfer performance of two ionic liquid refrigerant working pairs was studied through experimental measurement and molecular dynamics simulation,which not only provided new physical property data for working pair screening,but also explored the feasibility of molecular dynamics simulation in predicting the heat and mass transfer performance of working pairs.The main work is as follows:In the experiment,mutual diffusion coefficients of binary solutions mixed by[EMIM]BF₄/CH₃OH and[HMIM]Cl/CH₃OH with different ionic liquid mass fractions were measured by virtue of holographic interferometry.Based on the experimental results,a mathematical model was established to predict mutual diffusivity,and the mutual diffusion properties of two working fluid pairs were also discussed and analyzed.The thermal conductivity of[EMIM]BF₄/CH₃OH and[HMIM]Cl/CH₃OH binary solutions with different ionic liquid mole fractions was measured through 3ωmensuration.Based on the experimental results,the random mixing model used to predict the thermal conductivity of the solutions was associated,and the thermal conductivity of the two working fluid pairs was discussed and analyzed.In terms of molecular dynamics simulation,the all-atom force field was adopted to simulate the binary solutions of[EMIM]BF₄/CH₃OH and[HMIM]Cl/CH₃OH.After verifying the rationality of the force field through density calculation,a new method was presented to predict the mutual diffusion coefficient of the binary system.The mutual diffusion coefficients of two working fluid pairs were calculated and compared with the experimental results.Then the thermal conductivity of the two working fluid pairs was calculated by non-equilibrium molecular dynamics simulation,and the effect of temperature on the thermal conductivity of the working fluid pairs was explored.The research results indicated that the mutual diffusion coefficients of the[EMIM]BF₄/CH₃OH and[HMIM]Cl/CH₃OH binary solutions decreased with the increase of the ionic liquid mass fraction.The addition of CH₃OH could effectively improve the mutual diffusion performance of the working pairs.Under the same condition,the relationship between the mutual diffusion coefficients was as follows:[EMIM]BF₄/CH₃OH>[HMIM]Cl/CH₃OH,and the thermal conductivity of the[EMIM]BF₄/CH₃OH and[HMIM]Cl/CH₃OH binary solutions decreased with the increase of ionic liquid mole fraction while the decreasing trend slowed down gradually.The relationship between thermal conductivities under the same condition was as below:[EMIM]BF₄/CH₃OH>[HMIM]Cl/CH₃OH.In terms of molecular dynamics simulation,the maximum relative deviation of solution densities between the simulation and experiment was 5.7%,which verified the rationality of the force field.The simulation results of mutual diffusion coefficients were the same as those of the experiment in the order of magnitude and variation trend.All component deviations were about 20%except for a relatively large deviation in the condition thatω=0.8,which verified the feasibility of this method in the qualitative prediction for the mutual diffusion coefficient of the binary system.The simulated thermal conductivity had the same trend as that of the experiment with the maximum relative deviation of 24.9%,and the thermal conductivity of the system decreased with the increase of the temperature.