On the basis of reported experimental vapor-liquid equilibrium(VLE)data of NH3-1-ethyl-3-methylimidazolium acetate(NH3-[Emim]Ac),NH3-1-butyl-3-methylimidazolium tetrafluoroborate(NH3-[Bmim][BF4]),NH3-1,3-dimethylimidazolium dimethyl phosphate(NH3-[Mmim]DMP)and NH3-1-ethyl-3-methylimidazolium ethylsulfate(NH3-[Emim]EtOSO3)binary systems,the interaction parameters of 14 new groups have been regressed by means of the UNIFAC model.To validate the reliability of the method,these parameters have been used to calculate the VLE data with the average relative deviation of pressures of less than 9.35%.The infinite dilution activity coefficient(1)and the absorption potential(1)are important evaluation criterions of the affinity between working pair species of the absorption cycle.The UNIFAC model is implemented to predict the values of1and1of 16 sets of NH3-ionic liquid(IL)systems.The work found that the1gradually increases following the impact order:1([Cn mim][BF4])1([Cn mim]EtOSO3)1([Cn mim]DMP)1([Cn mim]Ac)(n 1,2,3,)at a given cation of IL species and constant temperature,and 1([Mmim]X)1([Emim]X)1([Pmim]X)1([Bmim]X)(X Ac,[BF4],DMP or EtOSO3)at a given anion of IL species and constant temperature.Furthermore,the 1gradually increases with increasing temperature.Then,it could be concluded that the working pair NH3-[Bmim]Ac has the best potential research value relatively.
Based on the analysis and investigation of calibration systems for high-accuracy low temperature thermometers,a new facility for automatic calibration of high-accuracy low temperature thermometers was developed.Continuous calibration for multiple points can be made automatically with this device.According to the thermophysical characteristics of the constant-temperature block in this device,segmented Fuzzy-PID (proportional-integral-differential) algorithm was applied.The experimental results showed that the temperature fluctuation was smaller than ±0.005 K in 30 min.Therefore,this new device can fully meet the calibration requirement of high-precision low temperature thermometers.
CHEN GuangMing,GAO Xu,ZHANG ShaoZhi,CHEN Qi,TANG LiMing & LAN YuQi Institute of Refrigeration and Cryogenics,Zhejiang University,Hangzhou 310027,China
In absorption cycles,ionic liquid(IL)1,3-dimethylimidazolium tetrafluoroborate([Dmim]BF4)may be a promising absorbent of working pair using water as refrigerant.The vapor pressures of[Dmim]BF4 aqueous solution were measured with the boiling-point method in the temperature range from 312.25 to 403.60 K and in the mass concentration range of 65%to 90%of[Dmim]BF4.The experimental data were correlated with an Antoine-type equation and the Non-Random Two-Liquid(NRTL)model,and the average absolute deviations between the experimental and calculated values were 1.06%and 1.15%,respectively.For the[Dmim]BF4 aqueous solution,the experimental vapor pressures show negative deviations from the calculated data with Raoult's law.For higher mass concentration of the IL,the deviation is more negative.In addition,the vapor pressures,the hydrophilicity and the solubility of[Dmim]BF4 aqueous solutions were compared with those of[Dmim]Cl aqueous solutions and [Bmim]BF4 aqueous solutions at IL-mole fraction of 0.20.
