Vapor–liquid equilibria for R22 + N,N-dimethylformamide system at temperatures from 283.15 to 363.15 K
Introduction
Absorption refrigeration has become attractive for low thermal potential energy sources. Besides the ammonia–water and LiBr–water refrigerant–absorbent pairs presently commercially utilized [1], numerous other refrigerant–absorbent pairs are currently being considered [2], [3], [4], [5]. Among many of these pairs, R22 was used as the refrigerant because of its non-toxic, non-explosive and no-flammable characteristics and N,N-dimethylformamide (DMF) was used as the absorbent because of its several advantages, such as lower cost, lower viscosity and higher absorption capacity for R22 [6], etc. So the use of refrigerant R22 and DMF to be the working fluid of a absorption refrigeration cycle has been suggested and reported by several investigators [7], [8]. The mixture used as refrigerant–absorbent pair is chemically stable over the entire temperature range in an absorption refrigeration system. Thus, mixture of R22 + DMF has been studied as a good candidate for an absorption refrigeration system.
Thermodynamic properties of the mixture, such as vapor–liquid equilibrium (p–T–x), are important to decide the performance of the refrigeration cycles. Agarwal measured the p–T–x data of this system in the different mole ratios [2]. The measurement device is the copper-constantan thermocouple and U-tube manometer. The accuracy is ±0.02 K and ±0.133 kPa in the range of 0–1.6 MPa, respectively.
The isothermal p–T–x data were measured at temperatures from 283.15 to 363.15 K at 10 K intervals. A complete range of compositions was measured in a circulation type apparatus that allows equilibrium measurements from 253 to 383 K for temperatures, and from 0 to 3.5 MPa for pressures. The experimental data are correlated by the Peng–Robinson–Stryjek–Vera equation of state [9], [10] using the Wong–Sandler mixing rule [11] with NRTL model [12].
Section snippets
Materials
The DMF of mass fraction purity 99.99% was supplied by Sam Sung Chem Ltd. and R22 with mass fraction purity 99.99% was supplied by Honeywell Chemical Co. All components were used without further purification in this study.
Experimental apparatus
p–T–x data were measured in an apparatus with a continuous vapor-phase circulation shown in Fig. 1 [13]. It includes a high-accuracy thermostatic bath, an equilibrium cell, a pressure measurement system, a temperature measurement system and vacuum system. The equilibrium cell
Correlations
Experimental data are correlated with Peng–Robinson–Stryjek–Vera equation of state using the Wong–Sandler mixing rule with NRTL model.
Results and discussions
VLE data for the binary system were obtained in the temperature range from 283.15 to 363.15 K. Experimental and calculated data are given in Table 2.
The p–T–x experimental and calculated data with Peng–Robinson–Stryjek–Vera equation of state, Wong–Sandler mixing rule and NRTL model have been plotted on a log p − 1/T diagram (Fig. 2) and pressure–composition diagram (Fig. 3). These diagrams are useful in analyzing the performance of the absorption refrigeration systems. Fig. 3 indicates a negative
Summary
In this study, equilibrium for R22 + DMF system is determined by using a circulation type apparatus in a temperature range from 283.15 to 363.15 K at 10 K intervals. The Peng–Robinson–Stryjek–Vera equation of state using the Wong–Sandler mixing rules with NRTL model is used to fit the experimental data. Satisfactory correlation of results is obtained that the overall deviation of pressure between experimental and calculated results is less than 0.57%. The correlation results show a good agreement
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