Vapor–liquid equilibria of difluoromethane + N,N-dimethylacetamide, difluoromethane + dimethylether diethylene glycol and 1,1-difluoroethane + dimethylether diethylene glycol systems
Introduction
In recent years, under the condition of the energy crisis, absorption refrigeration cycle can make full use of low-grade thermal energy and save a large amount of electricity, which becomes the focus of many researchers’ attention. Compared with absorption refrigeration cycle, the absorption–compression hybrid refrigeration cycle was brought up to solve the disadvantages of absorption refrigeration cycle, such as being unable to get refrigeration temperature below 0 °C. However, now the main focus on the absorption–compression hybrid refrigeration cycle is investigating the cycle mechanism of saving energy and developing novel working pairs, so exploring and developing advanced working pairs for various practical applications to improve the cycle performance, play an important role in the absorption–compression hybrid refrigeration cycle [1], [2], such as the research work using fluorocarbon refrigerant + organic absorbent as the working pair [3]. Thus, many of the fluorocarbon refrigerant + organic absorbent combinations are of interest to researchers.
Nowadays some fluorinated refrigerants have been used in absorption refrigeration cycle or the absorption–compression hybrid refrigeration cycle, owing to their thermophysical properties [4]. Hydrofluorocarbons (HFCs) have been proposed as potential alternative refrigerants of hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs), because of their zero Ozone Depletion Potential (ODP) and low Global Warming Potentials (GWP). HFCs mainly include 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), pentafluoroethane (R125), trifluoromethane (R23), difluoromethane (R32) [5], [6], 1,1-difluoroethane (R152a) [7], [8], [9], etc, which are demanded to be developed in a harmless way and accompanied with high capacity and high efficiency in many applications [10], [11], [12], [13], [14], [15]. Wahlstrom and Vamlinc [16] studied the solubility of R125, R134a, R143a and R152a in n-eicosane, n-hexadecane, n-tridecane and 2, 6, 10, 14-tetramethylpentadecane. Moreover the results showed that solubility for HFCs decreased in the following order: R152a > R134a > R143a > R125. Yelisetty and Visco [17] investigated the solubility of R32, R125, R152a and R143a in three polyols, the results exhibited that both R32 and R152a both had good solubility in the organic solvents.
The organic solvents mainly deal with N,N-dimethylacetamide (DMAC) [18], N,N-dimethylformamide (DMF), dimethylether diethylene glycol (DMEDEG) [19], [20], dimethylether trietraethylene glycol (DMETrEG), dimethylether tetrathylene glycol (DMETEG), etc. Karthikeyan et al. [21] studied six sets of working pairs composed by monochlorodifluoromethane (R22) and different absorbents: DMAC, DMF, DMETEG, DMETrEG, DMEDEG, and NMP (N-methyl-2-pyrrolidone). Ileri [22] investigated the performance of a solar-aided R22-DMEDEG absorption heat pump system. Muthu et al. [23] carried out experimental studies on R134a + DMAC hot water based on vapor absorption refrigeration systems. Jelinek et al. [24] studied fluorocarbon refrigerants and organic absorbents in single-and double-stage absorption cycles. Songara et al. [25] performed the thermodynamic studies on R134a + DMAC double effect and cascaded absorption refrigeration systems. Zehioua et al. [26] studied the solubility of R134a in DMEDEG and DMETrEG, respectively. Coronas et al. [27] measured the solubility of R134a in DMETrEG. Tseregounis and Riley [28] studied the solubility of R134a in DMETEG and found that R134a was highly dissolved in DMETEG. Han et al. [29], [30], [31] measured the solubility of refrigerant R134a, R32 and R23 in DMF, respectively. The combinations DMEDEG, DMETrEG, DMETEG and HFCs as well as DMF, DMAC and HFCs were researched more in absorption refrigeration systems. DMEDEG, DMETrEG and DMETEG are belong to glycol-type compounds; DMF, DMAC are belong to homologues. The absorbents DMEDEG and DMAC have lower viscosity, lower saturated vapor pressure in HFCs [26], [32]. There is no VLE data of HFCs in DMEDEG, DMAC except R134a.
In this work, the refrigerants R32, R152a and the absorbents DMAC, DMEDEG, were selected to be research combinations for investigating the possibility as new working pair options of the absorption–compression hybrid refrigeration cycle. The VLE data of the three binary systems R32 + DMAC, R32 + DMEDEG and R152a + DMEDEG were measured by the static-analytical method with liquid phase sampling of the online model over a temperature range from 293.15 to 353.15 K, and were correlated by the five-parameter nonrandom two-liquid (NRTL) model. The affinity between the selected combinations and the absorption characteristics were assessed.
Section snippets
Materials
Materials used in this work were described in detail in Table 1. The purities of both refrigerants (R32 and R152a) are 99.98% in mass fraction; the purities of both absorbents (DMAC and DMEDEG) are better than 99.9% in mass fraction. All materials were used without any further purification.
Apparatus
The phase equilibrium apparatus used in this study have been described thoroughly [33], [34], [35], using the static-analytical method with liquid phase sampling of the online mode. This apparatus mainly
Correlation
The VLE data of R32-DMAC, R32-DMEDEG and R152a-DMEDEG systems were determined at seven temperatures (T = 293.15–353.15 K). Many activity coefficient models were able to describe the experimental VLE data very well, such as the NRTL model, etc. Among these activity coefficient models, the NRTL model shows particularly advisable for polar/polar systems [37]. So in this work, all the experimental data were correlated with the NRTL model [27], [29], [30].
The NRTL model is given below:
Results and discussion
The values of the parameters (α, a12, b12, a21 and b21) in the NRTL model are given in Table 3. The experimental and calculated isothermal VLE data as well as the relative deviations of the pressure for R32 + DMAC, R32 + DMEDEG and R152a + DMEDEG at temperatures (293.15–353.15 K) at 10 K intervals are presented in Table 4, Table 5, Table 6, respectively, and they are illustrated in Fig. 2, Fig. 3, Fig. 4, Fig. 5 correspondingly. For the three binary systems R32 + DMAC, R32 + DMEDEG, and R152a + DMEDEG, the
Conclusion
In this work, the VLE data of the three binary systems R32 + DMAC, R32 + DMEDEG and R152a + DMEDEG were measured over the temperature range 293.15–353.15 K using the static-analytical method with liquid phase sampling of the online mode, and correlated by the NRTL model with five parameters. The modeling reduced results were essential in agreement with the experimental data. The average relative deviations of the pressure were 1.25%, 1.66% and 1.67%, respectively, and the maximum relative deviations
Acknowledgments
The supports provided by the National Natural Science Foundation of China (No. 50890184) and the National Basic Research Program of China (No. 2010CB227304) for the completion of the present work are gratefully acknowledged.
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