Alternative Working Pairs Research Articles

Performance potential and optimal configuration study for low-GWP R161-DMETEG single-stage absorption refrigeration system via pinch technology

New low-GWP R161-DMETEG mixture showed its high feasibility as an alternative working pair to overcome shortcomings of traditional ones. Its internal heat recovery capacity significantly influences operating performances. To systematically explore its ideal performance potentials and heat integration principles of the traditional single-stage absorption refrigeration system (SSARS), this paper conducted the internal heat recovery optimization and derived optimal systems by establishing an approach via pinch technology as a comprehensive planning. The ideal optimal system for maximum heat recovery under different conditions was derived initially using problem tables and Q-T graphical methods. Among all DMETEG-based fluids, R161-DMETEG exhibits the highest average performance potential of approximately 0.677 and an ideal performance improvement of 108%. Subsequently, a new configuration, called MFD-SSARS, was derived using the gird method. Its actual performances and economic feasibility under different parametrical conditions and control strategies were further explored. MFD-SSARS achieves COPs between SSARS and the ideal potential, and it can flexibly adjust internal heat recovery according to varying conditions to stimulate the performance potential. MFD-SSARS maximumly improvs COPs by approximately 65.953% relative to SSARS, reaching 96.167% of its potential under basic conditions. Despite its higher total capital costs than SSARS, it showed the lowest payback period of 2.23 years, thus proving the economic feasibility. Overall, the adopted environment-friendly working pair with designed high-performance configuration of this work serves as a technical solution to overcome current limitations of traditional absorption refrigeration technologies.

Thermodynamic characterization of {1-ethyl-1-methyl-pyrrolidinium dimethylphosphate, [C1C2PYR][DMP], or 1-hydroxyethyl-1-methylpyrrolidinium dimethylphosphate, [C1C2OHPYR][DMP] (1) + ethanol (2)} binary systems

In this work, {1-ethyl-1-methylpyrrolidinium dimethylphosphate, [C1C2PYR][DMP], or 1-hydroxyethyl-1-methylpyrrolidinium dimethylphosphate, [C1C2OHPYR][DMP] (1) + ethanol (2)} binary systems were studied as an alternative working pair for the absorption heat pump cycle. It is well known that the knowledge of the thermodynamic properties of the working fluid used plays a key role in the coefficients of performance values, and thus in the efficiency of the apparatus. Therefore, in this work thermodynamic and physicochemical characteristics of ethanol solutions of two dimethylphosphate-based ionic liquids are presented. The isothermal VLE was measured by an ebulliometric method within a temperature range from T = (328.15 to 348.15) K with an increment of 10 K and pressures up to 90 kPa. Experimental VLE data have been successfully correlated using the NRTL equation using temperature-dependence parameters. Additionally, experimental VLE data were tested for thermodynamic consistency using the Van Ness test. The liquid density and dynamic viscosity were determined as a function of IL's mole fraction over a wide composition range at temperature from T = (293.15 to 338.15) K with an increment of 5 K at ambient pressure. For the correlation of physicochemical properties, empirical equations were applied. From experimental density data, the excess molar volumes were determined and correlated using the Redlich – Kister type equation. Additionally, thermophysical properties of pure ILs including glass transition temperature, heat capacity at glass transition, temperature and enthalpy of (solid + solid) phase transition as well as temperature and enthalpy of melting were determined using differential scanning calorimetry (DSC) technique. Data presented in this work, compared to the available literature data for ethanolic solutions of other dimethylphosphate-based ILs, allows discussing the impact of the IL's cation structure on the presented physicochemical and thermodynamic properties. In addition, the data presented in this work were compared to data for a water solution of lithium bromide, commercially used in absorption refrigeration technology.

Thermodynamic properties assessment of working mixtures {water + alkylphosphonate based ionic liquids} as innovative alternatives working pairs for absorption heat transformers

Based on a continuously developing portfolio of ionic liquids, the aim of this work is to evaluate the performance of new working pairs composed of {water + alkylphosphonate based IL} as alternative working pairs for absorption heat transformers. Therefore, thorough thermodynamic measurements were conducted for three alkyl phosphonate based ionic liquids and their aqueous binary systems. Experimental measurements of vapour-liquid equilibrium, heat capacity, density and excess enthalpy were measured and successfully represented using NRTL model and adequate equations. Thermal performances of single stage absorption heat transformer were numerically simulated. The influence of the temperature sources and sinks was studied. The best coefficient of performance was obtained with mixtures of water and 1-ethyl-3-methylimidazolium methylphosphonate. The typical coefficient of performance values for this mixture is found to be between 0.40 and 0.45 depending on the temperature conditions. This value is 10% lower than that observed with the classically used {water + lithium bromide} mixture. Nevertheless, {water + ionic liquid} mixture has a wider operating temperature range than conventional working pairs. The higher circulation ratio observed with the proposed mixtures may increase pumping cost.

Thermodynamic properties and performance evaluation of [EMIM] [DMP]‐H 2 O working pair for absorption cooling cycle

The combination of ionic liquid-refrigerant based [EMIM][DMP]-H2O as an alternative working pair for single effect vapor absorption cycles (VACs) is assessed and optimized by using energy and exergy based performances. Thermodynamics properties of binary mixture of [EMIM] [DMP]-H2O like Dühring's (P-T-x1) and h-T-X1 plots are computed from the activity coefficient based non-random two-liquid model (NRTL) model. Further modeling and simulation of VACs are accomplished in open source Scilab as mathematical programing software and used to ascertain the optimal generator temperature established on energetic and exergetic COP. Optimal results include an extensive range of temperatures like Te from 2.5 to 15°C and Ta and Tc from 30 to 45°C. Simulation of the single effect VAC with SHE by using [EMIM][DMP]-H2O mixture at Te = 10°C, Tg = 100°C, Ta = 30°C, and Tc = 40°C were evaluated and compared with the 5 working fluids. Simulation outcomes depicted greater COP of 0.82 for [EMIM][DMP]-H2O in comparison with NH3-H2O, EMISE-H2O, [EMIM][BF4]-H2O and nearly equal to LiBr-H2O (COP = 0.83). In addition, the effect of Tg on the COP, ECOP f, and composition are compared and optimized for the evaporation temperature range from 2.5 to 15°C, Ta/Tc from 30 to 45°C and cooling water (CW) flow in series and parallel. Additionally, the optimal Tg exhibited distinction based on energy and exergy analysis. Thus, it resulted in optimized performances of [EMIM] [DMP]-H2O that can be suitable to replace corrosive aqueous LiBr in VACs.

Thermodynamic Properties of a Ternary AHP Working Pair: Lithium Bromide + 1-Ethyl-3-methylimidazolium Chloride + H2O

A LiBr-[EMIM]Cl/H2O ternary system has been suggested as an alternative absorption working pair in this work. The crystallization temperature, vapor pressure, specific heat capacity, specific enthalpy, specific entropy, density, and viscosity of this ternary system at a mass ratio of 2.5:1 (LiBr/[EMIM]Cl) were measured systematically. The results showed that the vapor pressure of the LiBr-[EMIM]Cl/H2O was nearly identical to that of LiBr/H2O at an 8.5% lower mass fraction. Under the same absorption ability, LiBr-[EMIM]Cl/H2O had a crystallization temperature much lower than LiBr/H2O, as well as much lower viscosity than ionic liquids. LiBr-[EMIM]Cl/H2O shows a certain potential as an alternative working pair in the absorption heat pump system.

Physicochemical and thermodynamic properties of the {1-alkyl-1-methylpiperidinium bromide [C1Cn=2,4PIP][Br], or 1-butylpyridinium bromide, [C4Py][Br], or tri(ethyl)butylammonium bromide [N2,2,2,4] [Br] + water} binary systems

This work is a continuation of our comprehensive study of ionic liquids, ILs (including organic salts with melting temperature above 100 °C) and their aqueous solutions as a novel alternative working pair for the absorption heat pump. A series of organic salts: 1-ethyl-1-methyl-piperidinium bromide, [C1C2PIP][Br], 1-butyl-1-methyl-piperidinium bromide, [C1C4PIP][Br], 1-butylpyridinium bromide, [C4Py][Br] and tri(ethyl)butylammonium bromide, [N2,2,2,4][Br] have been synthesized. The structures of compounds have been confirmed using NMR spectra. The basic thermal characterization of pure organic salts, including temperature and enthalpy of phase transition (Ttr, ΔtrH), temperature and enthalpy of melting (Tfus, ΔfusH) have been measured using a differential scanning microcalorimetry technique (DSC). The physico-chemical properties that are: density (ρ) and dynamic viscosity (η) of the tested binary systems have been determined at wide temperature and composition range. From experimental densities data, the apparent molar volumes (Vϕ,1) were calculated. In order to obtain limiting apparent molar volumes (Vϕ,10), the concentration dependence of apparent molar volumes was correlated with Redlich–Mayer type equation. Additionally, the limiting molar expansibilities (Eϕ0) and isobaric thermal expansion coefficients (αP) have been calculated. Temperature dependence of the dynamic viscosity has been correlated using VFT equation. The solid−liquid phase equilibria (SLE) have been determined using a dynamic method and correlated using NRTL equation. The influence of the alkyl chain length in the piperidinium cation substituent, as well as the cation structure, on investigated properties are presented and discussed.

A novel chemical heat pump cycle for cooling and heating

The absorption heat pump cycle based on LiBr/H2O has shortcomings of easy crystallization, severe corrosion, and the limitation in the temperature rise. In this study, a novel chemical heat pump cycle is proposed to overcome these issues. The thermal performance of the chemical heat pump using NaNO3/H2O is simply calculated for communication. The results show that the chemical heat pump can work at a lower generating temperature of 73.9 °C and avoid the crystallization issue when simultaneously supplying heating and cooling at 60 °C and 7 °C, respectively. Moreover, the annual corrosion rate of carbon steel in the NaNO3/H2O strong solution is only 7.09 μm y−1 at 180 °C. The chemical heat pump has the advantages of lower generating temperature and corrosiveness, as well as larger temperature operating range and temperature rise in comparison to the absorption cycle using LiBr/H2O and other alternative working pairs. However, the chemical heat pump has a lower thermal performance, and the COPc, COPh, and COPo are 0.11, 1.11, and 1.22, respectively. In the future studies, it is expected that the chemical heat pump will achieve a much higher COP, after taking into account of a multiple-effect cycle, as well as a chemical refrigerant with a larger dissolution enthalpy and solubility slope.

Thermophysical properties of lithium nitrate + 1-ethyl-3-methylimidazolium diethylphosphate + water system

Abstract LiNO3-[EMIM][DEP] (1-Ethyl-3-methylimidazolium diethylphosphate)/H2O has been suggested as an alternative working pair for absorption heat pump. The thermophysical properties including crystallization temperatures, densities, viscosities, specific heat capacities, dissolution enthalpies, and thermal diffusivities for this ternary system with a mass ratio (LiNO3:[EMIM][DEP]) of 3:1 were measured. The crystallization temperatures were measured from w = 0.60 to w = 0.74. The densities, viscosities and specific heat capacities were measured at absorbent mass fractions from w = 0.55 to w = 0.70 and temperatures from 303.15 K to 373.15 K. The dissolution enthalpies were measured from w = 0.55 to w = 0.70 at 313. 15 K. The thermal diffusivities were measured from w = 0.55 to w = 0.70 and 303.15 K to 363.15 K. The specific enthalpy differences and thermal conductivities were calculated based on the measured data. Regression equations for the crystallization temperatures, densities, viscosities, specific heat capacities, specific enthalpy differences and thermal conductivities were obtained by a least-squares method. The average absolute relative deviations between the measured data and the calculated data were 0.36%, 0.03%, 0.82%, 0.11%, 0.03% and 0.69%, respectively. These properties were helpful for the calculation and evaluation of the absorption heat pump based on LiNO3-[EMIM][DEP]/H2O.

Physicochemical properties of tri(butyl)ethylphosphonium diethylphosphate aqueous mixtures

This work presents the new experimental data on physical and thermodynamic properties of binary system composed of tri(butyl)ethylphosphonium diethylphosphate and water: solid-liquid equilibrium (SLE) and vapor-liquid equilibrium (VLE) phase diagrams as well as the excess enthalpy of mixing. SLE phase diagram has been determined at wide temperature and composition range using two techniques: dynamic method and differential scanning calorimetry (DSC). Interesting behavior with a solid compound formation was observed for the studied mixture. The isothermal VLE have been measured by an ebulliometric method within temperature range from T=(328.15 to 368.15)K and pressure up to 100kPa. The excess enthalpy for the tested binary system was determined at T=298.15K using isothermal titration calorimeter. Liquid density for pure IL and the binary mixtures with water has been determined at temperature range from T=(298.15 to 348.15)K and from experimental data, the excess molar volumes were calculated. The influence of temperature and composition on measured properties is discussed in terms of IL-water molecular interactions. Furthermore, the binary mixture under study was discussed as an alternative working pair for the absorption heat pump cycle.

Crystallization Temperature, Vapor Pressure, Density, Viscosity, and Specific Heat Capacity of the LiNO3/[BMIM]Cl/H2O Ternary System

The crystallization temperature, vapor pressure, density, viscosity, and specific heat capacity for the ternary system of LiNO3/[BMIM]Cl/H2O with a mass ratio (LiNO3:[BMIM]Cl) of 2:1 were measured. The crystallization temperature was measured from w = 0.65 to 0.75. The vapor pressure was measured from w = 0.55 to 0.75 and 298.15 to 416.45 K. The density, viscosity, and specific heat capacity were measured from w = 0.55 to 0.75 and 293.15 to 373.15 K. Regression equations for the measured values were obtained by a least-squares method. Results showed that LiNO3/[BMIM]Cl/H2O had vapor pressure nearly identical to that for LiNO3/H2O at a 10% lower mass fraction. The crystallization temperature for LiNO3/[BMIM]Cl/H2O was much lower than that for LiNO3/H2O with the same absorption ability. LiNO3/[BMIM]Cl/H2O has a great potential as an alternative working pair.

Thermodynamic properties and corrosivity of a new absorption heat pump working pair: Lithium nitrate + 1-butyl-3- methylimidazolium bromide + water

LiNO3-[BMIM]Br/H2O ternary system has been proposed as a new absorption working pair to improve the shortcomings of high crystallization temperature for LiNO3/H2O and high viscosity for [BMIM]Br/H2O working pairs. The crystallization temperature, vapor pressure, density, viscosity, specific heat capacity, and dissolution enthalpy of this ternary system at a mass ratio of 2:1 (LiNO3 to [BMIM]Br) were measured. The specific enthalpy was calculated based on the measured specific heat capacity and dissolution enthalpy. Regression equations for these thermodynamic properties were obtained by a least-squares method. Results showed that LiNO3-[BMIM]Br/H2O had nearly identical vapor pressure with that for LiNO3/H2O at a 10% lower mass concentration. Meanwhile, under the same absorption ability, LiNO3-[BMIM]Br/H2O had much lower crystallization temperature than LiNO3/H2O, and much lower viscosity than [BMIM]Br/H2O. At the temperature below 587.75 K, LiNO3-[BMIM]Br/H2O has a reliable thermal stability. The corrosivity of LiNO3-[BMIM]Br/H2O to carbon steel and copper was larger than that of LiNO3/H2O, while obviously less than that of LiBr/H2O. As an alternative working pair, LiNO3-[BMIM]Br/H2O shows a great potential in absorption heat pump, especially at high temperature.

Thermodynamic investigation of LiCl-H2O working pair in a double effect absorption chiller driven by parabolic trough collectors

In this study, an alternative working pair, the LiCl-H2O is investigated in a double-effect absorption chiller which is powered by parabolic trough collectors. Moreover, the conventional working fluid LiBr-H2O is examined under the same operating conditions in order to perform a suitable comparison. Three different condensation temperature levels are examined (30°C–35°C–40°C) and four evaporating temperature levels (5.0°C–7.5°C–10.0°C–12.5°C), while the generator temperature varies in the allowed range in every case. The analysis is performed in steady state conditions with EES (Engineering Equator Solver). The final results indicate that the solar cooling performance is 8% higher with the LiCl-H2O compared to the operation with LiBr-H2O. This significant performance enhancement is able to make the solar cooling a more sustainable solution using LiCl-H2O. Furthermore, the demanded specific collecting area is calculated close to 1m2·kW−1 which is a relatively low value. This result is based on the high thermal efficiency of the parabolic trough collectors and on the increased performance of the operation with LiCl-H2O.

An alternative approach towards absorption heat pump working pair screening

The successful market penetration of modern absorption heat pumps (AHP) today is critically dependent on their thermodynamic performance as well as other key factors like cost, reliability and inherent safety. Conventional AHPs have a proven record in the first two aspects but crucial shortcomings in the last two. For this reason it has been imperative to search for alternative working pairs that could potentially provide comparable performance while also satisfying the rest of the conditions to the best extent possible. As part of a systematic approach towards this direction, a detailed cycle analysis was performed, utilizing an idealized AHP system containing a real working pair, which enabled the identification of five dimensionless parameters and key thermophysical properties that influence the system's thermodynamic efficiency and the circulation ratio. In order to validate those findings, these parameters were calculated and compared between conventional and alternative AHP refrigerants. It turned out that low molecular weight ratios between absorbent and refrigerant have a beneficial effect on both coefficient of performance and the circulation ratio. Furthermore, both the refrigerant acentric factor and the absorbent vaporization enthalpy shall be minimized to obtain better performance.

Exergetic and energetic comparison of LiCl-H2O and LiBr-H2O working pairs in a solar absorption cooling system

The objective of this study is to investigate the use of an alternative working pair in a solar absorption cooling system. LiCl-H2O is the new examined pair and it is compared energetically and exegetically with the conventional pair LiBr-H2O, which is the most usual in air-conditioning applications. The simplest solar cooling system is analyzed in order to focus in the comparison between these working fluids. Specifically, flat plate collectors, coupled with a storage tank, feed the single effect absorption chiller which produces 250kW cooling at 10°C. The two pairs are examined parametrically for various heat source temperature levels and for three ambient temperature levels (25°C, 30°C and 35°C). The minimization of the collecting area, which means maximum exergetic efficiency, is the optimization goal in every case. The final results show that LiCl-H2O pair performs better in all cases by giving greater exergetic efficiency. More specifically, about 8% lower collecting area is required to cover the demanded cooling load with this working pair. Another interesting result is that the optimum heat source temperature for the LiCl-H2O is roughly lower than the respective for the LiBr-H2O. The system is analyzed in steady state with the commercial software Engineering Equator Solver (EES).

Investigation and testing of new polymeric-based working pairs for absorption chillers

Absorption chillers are a potential technology for using solar energy or waste heat for cooling and air-conditioning purposes. State-of-the-art working pairs require elaborate system designs and an appropriate material selection to deal with such problems as formation of non-condensable gases, corrosion, and crystallization. The investigation of alternative working pairs is one important possibility to reduce or avoid such problems. A new approach is to use linear- or hyper-branched polymers in combination with water as a working pair. A selected polymer used in this work has the capability to absorb water at suitable vapor pressure levels. Furthermore, the new working pair is expected to potentially diminish the problems of corrosion, formation of non-condensable gases, and damage of the machine due to crystallization and to relax at least the pricing situation. On the other hand, the high viscosity and the low heat conductivity compared to conventional working pairs are crucial for its application. To prove the feasibility of the polymeric-based working pair, experiments have been carried out in a lab-scale single-stage absorption chiller. The lab-scale chiller used falling-film heat exchangers and had a cooling capacity between 60 and 100 W. It is shown that under equal operating conditions, the new working pair is able to reach about one-third of the cooling power compared to lithium bromide/water at vaporizer temperatures suitable for cooling ceilings applications. If used as a drop-in replacement, the cooling power of the new working pair does not reach the performance of lithium bromide/water. Nevertheless, the usage in adapted machines for specific applications should be discussed in the future.

Screening of Ionic Liquid/H2O Working Pairs for Application in Low Temperature Driven Sorption Heat Pump Systems

Due to the known corrosion and crystallization issues of LiBr/H2O, the state-of-the-art working pair in sorption heat pump (SHP) systems, research into alternative working pairs is of high practical relevance. We have studied a wide range of ionic liquids (ILs) for this application in order to find potential new systems with enhanced performance. The screening was conducted with a focus on vapor pressure measurements of, in total, 74 examined working pairs. As common vapor–liquid-equilibrium measurements are very precise but rather time-consuming, we developed a new setup allowing a fast relative determination of humidities with very small sample volumes for screening purposes. By this method we identified seventeen IL/H2O working pairs fulfilling the technical relevant criterion of a water vapor pressure pH2O ≤ 10 mbar at T = 308 K with an IL content of less than 80 wt % (wIL < 0.8). Further evaluation of these candidates with respect to their thermal stability and viscosity allowed us to identify [MMIM]...

Physicochemical and thermodynamic characterization of N -alkyl- N -methylpyrrolidinium bromides and its aqueous solutions

Abstract This work is a continuation of our research of ionic liquids to investigate the physicochemical and thermodynamic properties of (ionic liquid + water) binary mixtures as a novel alternative working pair for the absorption heat pump cycle. In this work, a series of organic salts: N-propyl-N-methyl-pyrrolidinium bromide, [C1C3PYR]Br; N-butyl-N-methylpyrrolidinium, [C1C4PYR]Br and N-pentyl-N-methylpyrrolidinium bromide, [C1C5PYR]Br have been synthesized. The structures of new compounds have been confirmed using NMR spectra and elementary analysis. The basic thermal characterization of pure ILs, including temperature and enthalpy of phase transition (Ttr, ΔtrH), temperature and enthalpy of melting (Tm, ΔmH) have been measured using a differential scanning microcalorimetry technique (DSC). Decomposition temperature of the tested ILs were detected by the simultaneous TG/DTA experiments. The effect of temperature on the density (ρ) and dynamic viscosity (η) is reported over a wide temperature range from 298.15 to 343.15 K at ambient pressure. From experimental density data, the excess molar volumes (VE) were calculated and correlated using Redlich–Kister equation. The isothermal vapour–liquid phase equilibria (VLE) have been measured by an ebulliometric method at wide temperature range from 328.15 to 368.15 K and pressure up to 85 kPa. Experimental data have been correlated by means of NRTL equation. The solid–liquid phase equilibria (SLE) for the tested binary mixtures have been determined over whole composition range using dynamic method. The NRTL equation using parameters obtained from the VLE gives good description of SLE data. The influence of the alkyl chain length in the pyrrolidinium cation on the presented physicochemical and thermodynamic properties were discussed.

Physicochemical and thermodynamic study on aqueous solutions of dicyanamide – based ionic liquids

In this work, the {1-butyl-1-methylpiperidinium dicyanamide, [BMPIP][DCA], or 1-butyl-1-methylpyrrolidinium dicyanamide, [BMPYR][DCA] (1)+water (2)} binary systems were studied as an alternative working pair for the absorption heat pump cycle. The thermodynamic properties of the tested systems including: density, viscosity and (vapor+liquid) phase equilibria were measured as a function of temperature and composition at ambient pressure. The density and dynamic viscosity have been measured at temperature range from (298.15 to 343.15)K. From experimental data, excess molar volumes, VmE and dynamic viscosity deviations, Δη were calculated and correlated using Redlich–Kister equation. The isothermal (vapor+liquid) phase equilibria have been measured by an ebulliometric method within temperature range from (328.15 to 368.15)K and pressure range from (0 to 100)kPa. The excess enthalpies for the tested systems were determined at T=298.15K using isothermal titration calorimeter. NRTL equation was used to correlate (vapor+liquid) phase equilibria and excess enthalpy. The influence of the cation structure on the presented physicochemical and thermodynamic properties were discussed.

Thermodynamic performance of Kalina cycle system 11 (KCS11): feasibility of using alternative zeotropic mixtures

With the ever increasing demand for energy, exploiting low-temperature heat sources has seen significant interest recently. The conventional organic Rankine cycle (ORC) is a typical approach used to exploit low-temperature heat sources but suffers from low efficiency. The Kalina cycle is a reversed absorption cooling system that normally utilizes an ammonia-water binary mixture as the working fluid. This paper investigates, using thermodynamic modelling, the performance of Kalina cycle system 11 (KCS11) used for low-temperature heat sources below 2008C compared with the ORC based on pure ammonia and R134a. The cycle performance was investigated at various operating conditions including the evaporator pressure of 10-50 bars, heat source temperature of 333-473 K, heat sink temperature of 283 K and in the case of KCS11 various ammonia mass fractions at the evaporator outlet. Results show that the KCS11 can produce up to 40% increase in the efficiency compared with the ORC when using ammonia and up to 20% increase when using R134a. Although the ammonia-water working pair has zero ozone depletion potential (ODP) and very low global warming potential (GWP), it is toxic and needs special safety procedures against leak as ammonia is part of this binary mixture. Therefore, further investigation was carried out to explore the feasibility of using alternative working pairs that are non-toxic and outperform the ammonia-water pair for the Kalina cycle. Nineteen working pairs were investigated and results showed that propane and propylene-based mixtures have the potential to replace the ammonia-water pair in the KCS11.

Vapor–liquid equilibria of difluoromethane + N,N-dimethylacetamide, difluoromethane + dimethylether diethylene glycol and 1,1-difluoroethane + dimethylether diethylene glycol systems

The vapor–liquid equilibrium (VLE) data of difluoromethane (R32)+N,N-dimethylacetamide (DMAC), difluoromethane (R32)+dimethylether diethylene glycol (DMEDEG) and 1,1-difluoroethane (R152a)+dimethylether diethylene glycol (DMEDEG) systems have been measured over a temperature range from 293.15 to 353.15K, using the static-analytical method with liquid phase sampling of the online mode. The experimental data were correlated with the five-parameter nonrandom two-liquid (NRTL) model. For the systems R32+DMAC, R32+DMEDEG and R152a+DMEDEG, the average relative deviations of the pressure were 1.25%, 1.66% and 1.67%, respectively and the maximum relative deviations of the pressure were 3.09%, 3.65% and 3.63%, respectively. The calculated results and the experimental data obtained a good consistency. The p–x diagrams related to refrigerant R32 exhibit obviously wider experimental data scale than that related to absorbent DMEDEG. It means that the system pressure mainly depends on the refrigerant but not the absorbent. As the alternative working pair, the suitability order from high to low is arranged as R32+DMEDEG>R134a+DMF>R32+DMAC>R152a+DMEDEG, showing the system R32+DMEDEG is the best. The affinity between the refrigerant and absorbent was assessed on the characteristics of the species molecular structure for the three binary systems