Theoretical And Experimental Study On The Phase Equilibrium Of The Absorption Working Fluids For Fluorohydrocarbons+ Organic Absorbents

Absorption refrigeration cycle is an important way to utilize low-grade heat. The vapor-liquid equilibrium (VLE) of the absorption working fluid is one of the fundamental researches to solve the problems of absorption refrigeration.The most used working fluids are H2O/LiBr and NH3/H2O. The system with H2O/LiBr can not be used to produce the cooling capacity below 0℃, and has the risk of corrosion and crystallization. The difference between the normal boiling points of NH3 and H2O is not high enough, thus a rectification device is needed after the generator when NH3/H2O is used as the working fluid. The mixture (fluorohydrocarbons (HFCs) +organic solvents) have become promising absorption working fluids as their good performance and the diversity of HFCs.HFC-32 and HFC-161 have good environmental properties and cycle performances, which are considered as the promising absorption working fluids combined with organic solvents. However, there are no experimental VLE data of HFC-161 in the common organic solvents DMETrEG and HFC-32 in DMETrEG and NMP. Meanwhile, most of EoS/GE which are used to correlate the VLE data of HFCs+organic solvents can not reproduce the activity coefficient model, which may finally cause some deviations in predicting other properties. Though the EXACT zero reference pressure mixing rule can reproduce the gE from the activity coefficient model, its a=a/bRT is implicit, and can not be used to correlate the VLE at the reduced temperatures (Tr) above 0.9.On the basis of the above-mentioned limiation, the main aims in this work are as follows.(1)The theroretical study of VLE for HFCs+organic solvents(a)The proposal of MR1 mixing rule. To solve the implicit expression of a=a/bRT (for the mixture) in EXACT zero reference pressure mixing rule, combining the cubic equation of state and a/b mixing rule, the expression of um are derived, and an EoS/GE mixing rule (MR1) is proposed;(b)The proposal of MR2 mixing rule. By analyzing the influence of the excess volume term on the excess Gibbs free energy, an EoS/GE mixing rule (MR2) with the system pressure as the reference pressure is derived. The mixing rule with the exact form of the EXACT mixing rule can be used at the high reduced temperatures, and reproduce the gE from the activity coefficient model;(c)The proposal of MR3 mixing rule. By combining the advantage of MR1 and MR2, an EoS/GE mixing rule (MR3) is proposed. The mixing rule not only can overcome the limitation that MR1 can not be used at reduced temperatures Tr above 0.9, but also can partly reproduce the gE from the activity coefficient model.(2)Experimetal study on the VLE experiment for HFCs+ organic solvents(a)The vapor-liquid equilibrium apparatus for HFCs+organic solvents was modified and improved. The uncertainties on the measurement of temperature, pressure and composition are 11 mK,1.4 kPa and 0.010, respectively;(b)Isothermal VLE data for the three promising working fluids of HFC-32+ DMETrEG, HFC-32+NMP and HFC-161+DMETrEG are measured. The experimental data of the binary systems are correlated by the mixing rule MR3 proposed by this paper and MHV1 mixing rule.The correlated results of MR3 are better than those of MHV1.