Article pubs.acs.org/jced
Experimental Data and Description of the Phase Equilibrium in the Binary System of Ethyl Fluoride and Polyol Ester Oil (Planetelf ACD 32) Yingjie Xu, Zanjun Gao, Xiaorong Yuan, Xuehui Wang, Xiaohong Han,* and Guangming Chen Institute of Refrigeration and Cryogenics, Zhejiang University, Hangzhou, 310027, P. R. China ABSTRACT: Experimental measurement for the vapor−liquid equilibrium (VLE) of a binary mixture of ethyl fluoride (HFC-161) and polyol ester (POE) lubricant oil is an important task in the practical refrigeration system. In this work, the reliable p−T−x data of HFC-161 + POE (Planetelf ACD 32) are obtained from T = (283.15 to 343.15) K and over a complete range of compositions. Throughout the experiment, there was no stratification and no sediment generation, and the color of mixture liquid remained unchanged. Additionally, the vapor pressure of lubricant oil is negligibly small compared with the one of HFC-161 at the same temperature. Therefore, the mixture vapor is approximated as being pure HFC-161 in this work. The experimental data are correlated by the nonrandom two-liquid (NRTL) model. From the correlated results, the average relative deviation (ARD) of the pressure is 1.94 %, and the maximum relative deviation of the pressure is 5.71 %. The results showed a good agreement with the experimental data.
1. INTRODUCTION Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were widely used as working fluids in heat pump and refrigeration systems. However, their well-known and undesired ozone depletion property has led to the Montreal Protocol and some other international agreements, which mean CFCs and HCFCs will be progressively phased out. Increasing interest has risen in alternative refrigerants, and quite a lot of attention has been focused on the hydrofluorocarbons (HFCs) and their mixtures. For example, HFC-410A is a widely used HFC to replace HCFC-22 with a higher coefficient of performance (COP) and a zero ozone depletion potential (ODP).1 However, it also may be phased out in the future because of its high global-warming potential (GWP), determined as 2100.2 Ethyl fluoride (HFC-161) is a promising refrigerant among many new candidates because of its environmentally friendly propertiesno ODP and a low GWP of 12as well as excellent thermodynamic properties.3 However, HFC-161 is flammable. To overcome the flammability of HFC-161, the flame retardant is introduced into the HFC-161 and formed the new blended refrigerant based on it.4,5 Some research of the mixtures has already been done.6−9 With the technology development of refrigeration, it can be seen that propane with a strong flammability has already been considered to use in the small-scale resident air-conditioning system according to recent research.10 As the flammability of HFC-161 is a little lower than propane,2 and the latent of HFC-161 is higher than propane,11 it may be a potential refrigerant to be used in small-scale refrigeration systems.1 However, the presence of the lubricant oil in refrigerants may significantly change the thermodynamic properties, and the © XXXX American Chemical Society
refrigerants will also influence the viscosity and other characteristics of lubricant oil. Additionally, the proper solubility of the refrigerants and lubricant oil is often required in the circulation of system. Thus, the study of refrigerant-oil mixture solubility is very important for design of airconditioning and refrigeration systems. Taking polarity into account, polyol ester oil and alkyl benzene oil may be suitable for HFC-161, and it is usually thought that the larger the viscosity is, the better the protection provided to the compressor of refrigeration system by lubricant is. However, a larger viscosity leads to the side effect in coefficient of performance (COP), because it makes compressor consume more energy while working. Generally speaking, branch-chain base oil endows better lubricating performance to the lubricant oil, while the straight-chain one makes it more stable at low temperature as well as high temperature. In this work, the experimental measurements for VLE of binary mixtures containing HFC-161 and a commercial lubricant POE with a trade name of Planetelf ACD 32 were taken, while another commercial POE (Sunice T-68, Japan Sun Oil Company, Ltd.) with a different viscosity and different molecular structure was studied in our previous work.12 In addition, the phase behavior of the mixture (refrigerant + lubricant oil) has been successfully correlated by several approaches in recent literatures, such as PC-SAFT (perturbed-chain statistical associating fluid theory) equations,13 modified CEOS,14 activity coefficient models,15 and so forth. Received: May 6, 2013 Accepted: June 12, 2013
A
dx.doi.org/10.1021/je400302f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Figure 1. Schematic diagram of the experimental apparatus; 1, equilibrium cell; 2, thermostat bath; 3, valve; 4, stirrer; 5, platinum resistance thermometer; 6, calibrated platinum resistance thermometer; 7, heater; 8, refrigeration system; 9, temperature control instrument; 10, circulation pump; 11, differential-pressure sensor; 12,13, pressure sensor; 14, piston pressure gauge; 15, data collecting system; 16, vacuum pump; and 17, sample.
where mR is the total mass of refrigerant in the equilibrium cell, mV,R is the mass of vapor-phase refrigerant, and mO is the mass of POE added in the equilibrium cell. Since the vapor pressure of a typical lubricant is estimated by Spauschus21 to be 1.6·10−13 MPa at 30 °C, while the vapor pressure of HFC-161 is 1.0382 MPa at the same temperature, the mixture vapor may be reasonably approximated as being pure HFC-161 and yR (molar fraction of refrigerant in vapor phase) equals 1. 22 Therefore mV,R is obtained by the following equation:
Usually, the cubic equation of state is proposed for simple small particles, so most of them may be theoretically unsuitable to treat long-chain molecules, such as the oil studied in this work.16,17 The statistical associating fluid theory (SAFT) is adequate to describe the systems for the high molecular weight or the long-chain compounds.18 However, SAFT equations are relatively complicated. Therefore, the nonrandom two-liquid (NRTL) model19 is used to correlate the VLE data in this paper.
mV,R = ρV
2. EXPERIMENT 2.1. Apparatus. VLE data of binary mixtures containing HFC-161 and POE oil (Planetelf ACD 32) at various temperatures and pressures were measured in an equilibrium apparatus with a continuous vapor-phase circulation. The apparatus is the same one used by Wang et al.,20 and the schematic is shown in Figure 1. It consists mainly of an equilibrium cell, a thermostat, a pressure transducer, a platinum temperature sensor, temperature controllers, and a motor stirrer. The equilibrium cell can be maintained within ± 0.01 K in the operating temperature range (253.15 to 363.15) K by means of a high accurate temperature control equipment (Japan Shimaden) thermostat. The temperature of the equilibrium cell is measured with a four-lead 25 Ω platinum resistance thermometer (Yunnan Instrument, WZPB-2). The overall temperature uncertainty of the system is less than ± 15 mK (98 % confidence level). The equilibrium pressure is measured with a pressure transducer (Druck PMP4010) and an atmospheric pressure gauge (Ningbo Instrument, DYM-1). The whole pressure measurement system has an uncertainty of ± 1.6 kPa (95 % confidence level). The masses of the samples are determined with the electronic scales (Beijing Sartorius (Sartorius) Limited company, BS4000S). The mass fraction of HFC-161 in the liquid phase is calculated by: wR =
where ρ is the density of vapor-phase refrigerant, obtained from REFPROP,11 and volume of vapor refrigerant V consists of two parts, stainless steel pipe volume V1 and the upper vapor space volume V2 in the equilibrium cell. In this work, the vapor measurement uncertainty of total volume is ± 1.15 cm3 (95 % confidence level), the total uncertainty of wR is within ± 0.002 (90 % confidence level) and wR is the mass fraction of liquid refrigerant. 2.2. Materials. HFC-161 (CAS Registry No. 353-36-6), provided by Zhejiang Lantian Environmental Protection Co., Ltd. (FLTCO), with a mass fraction purity of > 99.97 %. The lubricant POE (Planetelf ACD 32), whose molecular is straightchain type, was supplied by TOTAL Lubricants China Co., Ltd. with a mass fraction purity of ≥ 97 %. Some typical physical properties of the lubricant were shown in Table 1, while other information of HFC-161 and the POE (Planetelf ACD 32) was listed in Table 2. 2.3. Procedure. Before each experiment, the system was preflushed with alcohol for several times and then dried under vacuum at room temperature for more 30 min. After drying, the system was purged with HFC-161 to make sure there were no impurities in the system. Inert gases in the system were removed by the evacuation pump first. Then lubricant oil was weighed into the cell. The system was evacuated again before the desired amount of refrigerant was charged into the cell. Then the recycle pump began running, and temperature controller was turned on too. The entire assembly was positioned on top of a stir plate and submerged in a thermostat.
mR − mV,R mR + mO − mV,R
(2)
(1) B
dx.doi.org/10.1021/je400302f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
3. THEORY
Table 1. Typical Properties of the POE Lubricant Oil (Planetelf ACD 32) property
unit
test method
POE
density (20 °C) kinematic viscosity (40 °C) kinematic viscosity (100 °C) pour point flash point acid number Water content
kg/m3 mm2/s mm2/s °C °C mg KOH/g ppm
ISO 3675 ISO 3104 ISO 3104 ISO 3016 ASTM D92 ASTM D974 Karl Fisher
984 34.6 6.0 −54 250
