Study On Thermophysical Properties Of Ionic Liquid Absorbing Working Pairs

Absorption heat pump can be converted to low grade energy to get the required high grade energy.Heat pump is of great significance to the reuse of energy,the recovery of industrial waste heat and the protection of environment.The biggest factor affecting the working efficiency of the heat pump is the absorption refrigerating working medium pair.The traditional absorption refrigerating working medium pair is mainly NH₃/H₂O and Li Br/H₂O,but both of them have certain defects and cannot meet the production needs.Therefore,looking for a new type of refrigerating medium has gradually become a research hotspot in recent years.Ionic liquid,as a new green solvent,this paper measured the lithium bromide（Li Br）aqueous solution,1-ethyl-3-methyl imidazole acetate（[EMIM][OAC]）,1-butyl-3-methyl imidazole thiocyanate（[BMIM][SCN]）,1-ethyl-3-methyl imidazole salt bromine（[C₂MIM]Br）,1-propyl-3-methyl imidazole salt bromine[C₃MIM]Br and 1-butyl-3-methyl imidazole salt bromine[C₄MIM]Br five kinds of ionic liquid density,viscosity and surface tension of water,and the measurement results are analyzed and calculated.At atmospheric pressure,the density and viscosity of the above six binary mixed aqueous solutions in the temperature range of 303.15-343.15 K were measured by electronic densimeter and viscometer respectively.The surface tension values of the above solutions were measured by automatic surface tensiometer at 283.15-323.15 K.First of all,the moisture of the ionic liquid was measured with the Karl Fischer instrument.According to the experimental requirements,the ionic liquid was dried with the rotary evaporator to remove the moisture before each measurement of the physical properties of the ionic liquid.After drying,the ionic liquid could be used for the measurement of thermal physical property data.The results of density measurement show that the density of lithium bromide and ionic liquid decreases linearly with the increasing of temperature,and the density decreases with the increase of the number of carbon atoms in the imidazole ring.The viscosity measurement results show that the viscosity of the system decreases with the increase of temperature.The viscosity of the ionic liquid studied in this paper is much higher than that of water and lithium bromide.In addition,with the increase of the number of substituted carbon atoms in the imidazole ring,the viscosity gradually increases.The viscosity experimental data are correlated with the viscosity model,and the correlation results are good.Finally,according to the viscosity data,the energy barriers（E_η）of different systems are calculated,and the migration ability of particles in the mixed fluid is discussed.The results show that the surface tension of the mixed system is inversely proportional to the temperature,that is,the higher the temperature is,the smaller the surface tension is.The surface tension of ionic liquid is lower than that of lithium bromide.The surface tension of the ionic liquid mixture decreases with the increase of the number of carbon atoms in the imidazole ring.Finally,the surface entropy and surface enthalpy of the ionic liquid system were calculated based on the surface tension data,and the surface order of several ionic liquids was analyzed and compared by the entropy and enthalpy values.In this paper,the thermophysical properties of lithium bromide and five kinds of ionic liquids are studied,which enriches the data of physical properties of lithium bromide and ionic liquids,which will lay a certain foundation for the application and development of lithium bromide and ionic liquids.