United States National Risk Management Environmental Protection Research Laboratory Agency Cincinnati, OH 45268 Research and Development EPA/600/SR-96/Q63 June 1996 EPA Project Summary Miscibility, Solubility, and Viscosity Measurements for R-236ea with Potential Lubricants S. C. Zoz and M. B. Pate Miscibility, solubility, and viscosity data are needed to determine the suit- ability of refrigerant/lubricant combina- tions for use in refrigeration systems. Miscibility data have been obtained for R-236ea and three potential lubricants. The lubricants are a mineral oil, alkylbenzene, and polyol ester, each with a nominal viscosity of 68 cSt. The miscibility tests were performed in a test facility consisting of a series of miniature test cells in a constant tem- perature bath. The bath temperature was precisely controlled over a tem- perature range of -50 to 90°C (-58 to 194°F). The test cells are constructed to allow for complete visibility of the refrigerant/lubricant mixtures under all test conditions. Critical solution tem- peratures obtained from the miscibility data are presented for each refrigerant/ lubricant combination. In addition to miscibility data, both solubility and viscosity data were ob- tained for R-236ea and the most prom- ising lubricant. These data were ob- tained for a refrigerant concentration range of 0 to 40 wt % refrigerant over a temperature range of 40 to 120°C. This range of conditions represents the area of interest necessary for the proper de- sign of compressors. For comparison purposes, data were also taken for the existing U.S. Navy shipboard chiller re- frigerant and lubricant concentration, namely R-114 and a naphthenic oil. The report was prepared with fund- ing from the Strategic Environmental Research and Development Program (SERDP). This report was developed by the National Risk Management Research Laboratory's Air Pollution Prevention and Control Division, Research Triangle Park, NC, to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering infor- mation at back). Introduction The development of acceptable alterna- tive refrigerants requires the identification of compatible lubricants so that refrigera- tion systems will operate properly. The first requirement of a compatible lubricant is that it be miscible with the refrigerant over the operating temperatures of the system. Refrigeration systems require a miscible refrigerant/lubricant mixture for compressor lubrication, for maximum heat transfer performance in the evaporator, and for proper lubricant return to the com- pressor. To satisfy these needs, miscibility data were taken in this study. Obtaining misci- bility data requires that one visually ob- serve and record the physical conditions of a refrigerant/lubricant mixture at a spe- cific temperature. The procedure is re- peated for desired ranges of temperatures and refrigerant concentrations. Visual in- spection of the mixture allows for determi- nation of whether the mixture showed signs of cloudiness, floe or precipitate forma- tion, and the formation of a second liquid phase. In addition to miscibility data, designers also require accurate and extensive data on the solubility, density, and viscosity of ------- alternative refrigerant and lubricant mix- tures. To support the design of equipment using R-236ea, data on the viscosity, den- sity, and solubility of lubricant/refrigerant mixtures at various pressures and tem- peratures were also taken in this study. Scope The scope consisted of a study of mis- cibility of various refrigerant/lubricant con- centrations and then a study of solubility and viscosity for the lubricants which dem- onstrated miscibility with R-236ea. Initial miscibility tests were performed on R- 236ea/lubricant mixtures for refrigerant concentrations of 25 and 50% by weight. Additional tests were performed for refrig- erant concentrations of 75 and 95% if the initial tests showed complete miscibility (that is, miscible over the entire test tem- perature range). In addition, solubility and viscosity tests were conducted on R-236ea/IS068 pentaerythritol ester mixed-acid mixtures and R-114/IS068 naphthenic mineral oil mixtures, with the latter used for compari- son purposes. Miscibility of R-236ea and Lubricant Mixtures Miscibility Test Facility The test facility includes test cells ca- pable of withstanding the high pressures and the extreme temperatures encoun- tered in the study of refrigerant/lubricant mixtures. The facility was designed for the purpose of determining the miscibility char- acteristics of refrigerant/lubricant mixtures over the temperature range of -50 to 90°C (-58 to 194°F) and for pressures up to 3.5 MPa (500 psia). The test cells are im- mersed in one of two constant tempera- ture baths and have glass viewports so that the miscibility characteristics of the mixture can be observed and recorded. These tests were performed by keeping the refrigerant/lubricant mixture visible at all times, by controlling temperatures to ±1°C (+1.8°F), and by agitating the test cells to ensure uniform mixture. Each re- frigerant/ lubricant combination was tested for miscibility in 10°C (18°F) increments over the test temperature range of -40 to +90°C (-40 to +194°F). When a refrigerant/lubricant mixture is miscible, it appears as one homogeneous transparent solution. However, when a re- frigerant/lubricant mixture is immiscible, there is either cloudiness (evidence of par- ticles dispersed throughout the mixture) or two liquid phases present in the cell. The presence of two liquid phases was the only form of immiscibility encountered in this study. Miscibility Results Results of the measurements of R- 236ea in each lubricant are presented in Tables 1-3. For every refrigerant/ lubri- cant combination investigated, the data set consists of the concentration, tempera- ture, and visual characteristics of the con- tents of the cell. The tables summarize the data for each lubricant and R-236ea pair. Additional data were taken at 75 and 95% refrigerant for the pentaerythritol es- ter mixed-acid (IS068) lubricant since the 25 and 50% mixtures showed complete miscibility. Based on observation of these tables, the naphthenic mineral oil and the alkylbenzene lubricant would be unsuit- able as lubricants in refrigerants and air- conditioning equipment operating with R- 236ea because of the lack of miscibility. In contrast, the pentaerythritol ester mixed- acid (IS068) is completely miscible at all temperatures and is recommended for use with R-236ea. Solubility, Density, and Viscosity of Refrigerant Lubricant Mixtures Solubility and Viscosity Test Facility The test facility utilized in this study can be used for measuring the solubility, vis- cosity, density, and miscibility of lubricant/ refrigerant mixtures. The test facility con- sists of a pressure vessel for preparing the refrigerant/lubricant concentrations, a Table 1. Summary of Miscibility Data for R-236EA and the Naphthenic Mineral Oil(ISO68) Mass Fraction Observations Refrigerant 0.25 immiscible from -40 to 90 °C 0.48 immiscible from -40 to 90°C Table 2. Summary of Miscibility Data for R-236EA and the Alkylbenzene Lubricant(IS068) Mass Fraction Observations Refrigerant 0.22 miscible from 50 to 90° C immiscible from -40 to 50°C 0.48 immiscible from -40 to 90 °C Table 3. Summary of Miscibility Data for R-236EA and the Pentaerythntol Ester Mixed- Acid Lubricant (IS068) Mass Fraction Observations Refrigerant 0.21 miscible throughout tempera- ture range -40 to 90°C 0.44 miscible throughout tempera- ture range -40 to 90°C 0.77 miscible throughout tempera- ture range -40 to 90°C 0.95 miscible throughout tempera- ture range -40 to 90"C commercially available viscometer, and windows for observation of the contents. The viscosity measurement range is from 1 to 200 cP, but this range may be easily extended. Precise and convenient charg- ing of mixtures with refrigerant composi- tions ranging from 0 to 100% was pro- vided. Operating temperature and pres- sure ranges for the test facility are 20°C (70°F) to 150°C (300°F), and 0 to 3.5 MPa (0 to 500 psia), respectively. Solubility and Viscosity Results Data were collected for R-236ea/IS068 pentaerythritol ester mixed-acid and R- 114/IS068 naphthenic mineral oil mixtures. These tests provide solubility, density, and viscosity information for temperatures as high as 100°C (212°F) and for pressures up to 1.4 MPa (200 psia). The results are presented as solubility, viscosity, and den- sity charts, as well as in graphical form. The solubility graphs show pressure as a function of temperature, while the viscos- ity and density graphs show liquid viscos- ity and liquid density as functions of refrig- erant concentration, respectively. Also pro- vided are empirical correlating equations (applicable only over the range of data collected) that allow convenient interpola- tion of the data. Conclusions Miscibility data for the R-236ea in each of the three test lubricants have been col- lected for refrigerant concentrations of 25 and 50%. The raw data were presented and the results were summarized. Addi- tionally, data for the pentaerythritol ester mixed-acid (IS068) lubricant were taken at 75 and 95% (by weight) refrigerant. The pentaerythritol ester mixed-acid (IS068) lubricant was found to be com- pletely miscible over the temperature and concentration ranges tested. 2 ------- These tests provide solubility, density, and viscosity information for temperatures as high as 100°C (212°F) and for refriger- ant mass fractions from 0 to 50%, subject to a maximum pressure limitation of 1.4 MPa (200 psia). The results are presented as solubility, viscosity, and density charts and graphs that give pressure, liquid vis- cosity, and liquid density as functions of temperature and refrigerant concentration. Empirical correlating equations (applicable only over the range of data collected) that allow convenient interpolation of the data are also presented. 3 ------- S. Zoz and M. Pate are with Iowa State University, Ames, IA 50011. Theodore G. Brna is the EPA Project Officer (see below). The complete report, entitled "Miscibility, Solubility, and Viscosity Measurements for R-236ea with Potential Lubricants," (Order No. PB96-183884; Cost: $21.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air Pollution Prevention and Control Division National Risk Management Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency National Risk Management Research Laboratory (G-72) Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-96/063 ------- |