Kang, H. M. L.

Pate, M. B.

Zoz, S. C.

English

Iowa State University Computer Science Technical Reports

Solubility of HFC-32, HFC-125, and HFC-134a with Three Potential Lubricants

Purdue E-Pubs

Purdue UniversityPurdue e-PubsInternational Refrigeration and Air ConditioningConference School of Mechanical Engineering1994Solubility of HFC-32, HFC-125, and HFC-134awith Three Potential LubricantsH. M. L. KangIowa State UniversityS. C. ZozIowa State UniversityM. B. PateIowa State UniversityFollow this and additional works at: http://docs.lib.purdue.edu/iraccThis document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu foradditional information.Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/Herrick/Events/orderlit.htmlKang, H. M. L.; Zoz, S. C.; and Pate, M. B., "Solubility of HFC-32, HFC-125, and HFC-134a with Three Potential Lubricants" (1994).International Refrigeration and Air Conditioning Conference. Paper 286.http://docs.lib.purdue.edu/iracc/286SOLUBILITY OF HFC-32, HFC-125, AND HFC-134A WITH THREE POTENTIAL LUBRICANTS H.M. Lee Kang, S.C. Zoz, and M.B. Pate Iowa State University Department of Mechanical Engineering Ames, Iowa 50011 ABSTRACT This paper presents solubility data for three difTerent HFC refrigerants, HFC-32, HFC-125, and HFC-134a mixed with three different lubricants, namely polypropylene glycol dial, pentaerythritol ester mixed acid, and pentaerythritol ester branched acid. These three refrigerants are important because when combined, either in groups of two or three, they form refrigerant mixtures which have been identified as potential replacement fluids for R-22. The solubility tests were performed in a test facility consisting of a series of miniature test cells submerged in a constant temperature bath. The bath temperature was precisely controlled over a temperature range of -30 C to 60 C (-22 F to 140 F). The contents of each cell were monitored by pressure and temperature sensors. In addition, each cell was charged with a known refrigerant/lubricant concentration, so that, along with temperature and pressure data, the solubility (P, T, C) could be determined. The test cells were constructed to allow for complete visibility of refrigerant/lubricant mixtures under all test conditions. INTRODUCTION The solubility data obtained in this study were for three different pure refrigerants, HFC-32, HFC-125, and HFC-134a with three difTerent lubricants. These refrigerants arc hereafter designated as R-32, R-125, and R-134a, respectively. Each of the three HFCs was tested for solubility (namely, pressure, temperature, and concentration), when mixed with three difierent lubricants. which were polypropylene glycol dial (hereafter called polypropylene glycol), pentaerythritol ester mixed acid (hereafter called mixed acid ester), and pentaerythritol ester branched acid (hereafter called branched acid ester). The viscosity for these three lubricants was ISO 32. The solubility data was obtained for refrigerant/lubricant mixtures subjected to the following conditions: 1. Composition: 0 to 100 weight percent refrigerant 2. Temperature: -30°C to 60°C (-22°F to 140°F) 3. Pressure: 0 to.3.5 MPa (0 to 500 Psia) The following sections describe the methodology for a new approach to measuring the solubility of refrigerant/lubricant mixtures. This new approach was developed to allow for the faster measurement of solubility, which is important considering the urgency of developing alternative refrigerant systems to replace existing CFC and HCFC systems. The solubility results for the refrigerant/lubricant pairs studied are presented in the form of graphs and equations. During the solubility tests. the contents of each cell were observed for miscibility. Solubility data for other refrigerants and lubricants have been collected by Glova (1984), Thomas and Pham (1992), and Van Gaalcn et al ( 1990) by using testing methods different than that used in this study. However, there are no reports in the open literature of solubility data for the refrigerant/lubricant pairs reported herein. EXPERIMENTAL METHODS AND TEST FACILITY DESCRIPTION Each test cell consists of a double-port, seal-cap type liquid indicator, which is essentially a 31.75 mm (1.25 inch) pipe cross with sight windows screwed into opposing ports. A valve for charging the refrigerant into the cell was screwed into one of the two remaining ports. An 1/8 inch by 8.89 mm (3 112 inch) length copper tube was attached into the other port, and then this tube was attached to a pressure transducer for the purpose of measuring pressure inside of the cell during the test. The usc of a copper tube was to avoid contact between the pressure transducer and fluids when the cells are submersed in the bath, while simultaneously preventing condensation during the heating operation and 437 minimizing overall volume of the each cell. The pressure transducers were calibrated with the use of a dead weight pressure tester, and the pressure data uncertainty is ±2. 97 kPa (0.43 psia). -The temperatures of the cells were controlled by placing them in one of two constant temperature baths. A hot bath WaS USed to maintain temperatures from l0°C (50°f) tO 60°C ( 140°f), While a COJd bath WaS USed tO maintain temperatures in the range of l0°C (50°F) to -30°C ( -22°F). The precise temperatures of the baths were measured by two internal resistance temperature detectors (RTD). These RTDs were calibrated, and the temperature measurements had an uncertainty of ±0.1 oc (0.2°F). Thermal equilibrium conditions were usually obtained about thirty minutes after a temperature change. Computerized data acquisition methods were used to obtain the temperature and pressure data. A microcomputer, along with data acquisition hardware and software. monitored and recorded all signals generated by the installed sensors Experimental Procedure The charging of lubricant into each test cell was done with the use of syringe through the front window space. Then, the window was replaced and tightened. A vacuum pump was hooked up to the valve, and a vacuum was pulled to remove any dissolved moisture or air from the lubricant inside the cell. The vacuum process took approximately 2 to 3 hours to be completed. A refrigerant was then injected into the cells from a refrigerant canister with the use of a manifold that allowed for the evacuation of the connecting lines. The cells were weighed on a scale, which has an uncertainty of ±0.01 gram, before and after the injection of the lubricant and refrigerant. During cell charging. each cell was filled with the mh .. ture of refrigerant/lubricant so that the vapor space was less than 15ry, of the total volume. In addition, since temperature and pressure data are available, changes in the liquid concentration due to the refrigerant present in the vapor space could be calculated. The pressure and temperature were measured for each test point. These data allowed for the calculation of the refrigerant concentration at each test condition to be calculated. In addition to calculations of the actual liquid concentration, correlating equations that fit the solubility data, including pressure, temperature, and concentrntion, were derived. Six test cells were placed in the frame assembly, and then they were submersed, excluding the top portion of the cells where the pressure transducers are attached, in one of the two 20 x 12 x 12 inch glass baths. The glass allowed for visibility of the test cells so that one could observe various phenomena inside of the cell. such as miscibility due to temperature changes occurring throughout the tests. Data Reduction After the data had been taken and reduced for each refrigerant/lubricant combination. a multi-linear regression analysis was performed. Thus, an equation for pressure· as function of temperature and concentration was obtained. This equation was used to graphically plot results, and interpolate results at intermediate states for which the data were not directly obtained. The linear regression was performed using SAS (Statistical Analysis and System, 1993), which allows for the determination of the set of coefficients for the following empirical equation. P "' Psat (A0 + A1C + A2T + A3CT + A4C2 + A5C2T + A6CT2 + A7T2 + A8C2T2 + ~C3) where P = the absolute pressure. MPa C = the mass fraction of refrigerant in the liquid T == the temperature in °K divided by a reference temperature of 293°K Psat = reference saturation pressure at temperature T Pure refrigerant properties were obtained with usc ofREFPROP (NJST. 1993) The above equation is non-linear, but it is linearized by using the following variable substitutions: X 1 = C; X2 = T; X3 = CT; X4 = C2; ·x5 = C2T; X6 = CT2; X7 = T2; X8 = C2T2; X9 = C3 438 After these substitutions the equation can be linearized in the nine variables, X1 through ~- Table 1 lists the coefficients for the empirical correlations of solubility for refrigerant/lubricant mixtures. The resulting equations are empirical fits of the data, and thus not based on any theoretical consideration. Also, some of the coefficients do not significantly contribute to the correlation. The correlations for the pressure of refrigerants/lubricant mixtures are well fit to the test data, being within ±5'X.. Table l. Coefficients for Empirical Correlation of Solubility Data for Refrigerant/Lubricant Mixtures R·32 R·125 R·134a Term propylene mix~d branch~d propyl~nc mixed branched propylene mixed branched glycol add ester acid ester glycol a<.:id ester acid ester glvcol acid ester acid ester An. 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 c 4.3604 4.3440 4.6133 0.0000 1.7585 2.8598 1.9304 1.0157 0.0000 T 0.1542 0.2567 0.1197 0.0000 0.0000 0.0000 0.1123 0.0000 0.0000 CT 0.0000 0.2671 0.0000 2.5158 0. 0000 0.0000 10.563 9.3640 7.7127 C2 6.4446 7.0375 6.9716 0.5355 0.5883 2.9163 0.0000 0.0000 1.4575 C2T 0.1440 0.0000 0.0000 2.0182 1.5540 0.0000 9.2971 9.3226 6.9599 CT2 0.0000 0.0000 0.0000 0.29-1-2 0.8116 0.0000 4.8830 4.7213 4.0372 T2 0.1466 0.2391 0.1077 0.0000 0.0000 0.0045 0.1144 0.0000 0.0000 c2T2 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 4.3102 4.7176 3.6877 C3 2.9460 3.4292 3.3584 0.2581 0.5600 1.0554 2.2542 1.9804 2.0625 RESULTS AND DISCUSSION The solubility data for three different pure refrigerants. namely, R-32, R-125, and R-134a with three different lubricants, referred to as a polypropylene glycol. mixed acid ester. and branched acid ester are shown in Figures 1 through 9. Shown in each figure arc ten isotherms which were produced by a partial third-order empirical multi-regression curve fit over the data for nine compositions. These plots show that for a given nominal concentration the vapor pressure increases with increasing temperature and increasing refrigerant concentration. As a mle, lubricants which have a higher solubility for refrigerant will produce lower values of pressure over the refrigerant/lubricant mixture. Observation of Figures 1 through 9 reveal that the polypropylene glycol dial has a somewhat higher solubility than the two esters. R-32 --The solubility ofR-32 in the polypropylene glycol. mixed acid ester, and branched acid ester is shown in Figures 1, 2, and 3, respectively. For all three lubricants. it can be seen that the vapor pressure of the solution increases gradually over 40 percent refrigerant. It should be mentioned that the pressure falls oiT rapidly when the refrigerant concentration is below 40 percent. This fall in pressure is greater at higher refrigerant concentrations and temperatures while the fall in pressure is gentler for the more soluble lubricants (e.g .. polypropylene glycol). The polypropylene glycol dial has a slightly higher solubility than the two esters based on comparing Figures l through 3. The order of increasing solubility of R-32 with these three lubricant mixtures is pentaerythritol ester branched acid, pentacfythritol ester mixed ·acid. polypropylene glycol dial R-125 The solubility of R-125 in the polypropylene glycol. mixed acid ester, and branched acid ester is shown in Figures 4, 5, and 6, respectively. For all three lubricants, it can be seen that the solubility pressure is fairly constant at concentrations over 80 percent refrigerant. The vapor pressure then falls oiT rapidly when the refrigerant concentration is below 80 percent. As mentioned earlier. this fall in pressure is greater at higher refrigerant concentrations and temperatures while the fall in pressure is gentler for more soluble lubricants. 439 Based on comparing Figures ~ through 6 the polypropylene glycol diol has a somewhat higher solubility than the two esters, while the pentacrythritol ester branched acid has a somewhat higher solubility than the pentaerythritol ester mixed acid. The order of increasing solubility of R·l25 with these three lubricant mixtures is pentaerythritol ester mixed acid, pentaerythritol ester branched acid. and polypropylene glycol dial, which is the same order of solubility found for the R-32. R-134a ~e solubility ofR·l34a in the polypropylene glycol, mixed acid ester, and branched acid ester is shown in Figures 4, 5, and 6, respectively. For all three lubricants, it can be observed that the solubility pressure is fairly constant between 50 and 80 percent refrigerant. and then the pressure increases again at concentrations over 80 percent refrigerant. The pressure falls off rapidly when the refrigerant concentration is below 50 percent refrigerant. As with the other two refrigerants, this fall in pressure is greater at higher refrigerant concentrations and temperatures while the fall in pressure is gentler for more soluble lubricants The esters have a somewhat higher solubility than the polypropylene glycol dial while the pentaerythritol ester branched acid has a somewhat higher solubility than the pentaerythritol ester mixed acid at concentrations over 40 percent refrigerant, based on comparing Figures 7 through 9. The order of increasing solubility of R-134a with these three lubricant mixtures is polypropylene glycol dial. pentaerythritol ester mixed acid, pentaerythritol ester branched acid. CONCLUSIONS A new method was dcYcloped for clctcnmmng the solubility (pressure, temperature, and concentration) of refrigerant/lubricant mixtures. Data ha,·c been collected for mixtures of three pure HFC refrigerants, namely, R·32, R-125, and R-134a with three different lubricants. which were polypropylene glycol diol, pentaerythritol ester mixed acid, and pentaerythritol ester branched <lCicl. These solubility data arc for temperatures from -30°C ( -24°F) to 60°C (140°F) and for pressures up to 3.5 MPa (500 psi a). The results arc presented as solubility plots showing pressure as a function of temperature and refrigerant concentration. The solubility data have been analyzed using a empirical multi-linear regression analysis and the result of empirical correlating equation developed from this data allows convenient interpolation of the data at specific property conditions. The solubility plots show that for a given nominal concentration, the pressure of the mixture increases with increasing temperature and increasing refrigerant concentration. The order of increasing solubility or R-32 with these three lubricant mixtures is pentaerythritol ester branched acid, pentaerythritol ester mixed acid. and polypropylene glycol clio!. The order of increasing solubility of R-125 with these three lubricant mixtures is pentacrythritol ester mixed acid, pcntacrythritol ester branched acid, and polypropylene glycol diol. The order of increasing solubility of R·l3~a with these three lubricant mixtures is polypropylene glycol diol, pentaerythritol ester mixed acid. and pcntacrythritol ester branched acid. REFERENCES NIST Standard Reference Database 23. 1993. NIST Thermodynamic Properties of Refrigerants and Refrigerant Mixtures Database (REFPROP). Thermodynamics DiYision. National Institute of Standards and Technology. SAS 1993. Statistical Analvsis and Svstcm. Cal}. NC: SAS Institute, Inc. D.J. Glova, 1984. "High·Temperaturc Solubility of Refrigerants in Lubricant Oil." ASHRAE Transactions, Vol. 90, Pt. 2B, pp. 806-825. R.H.P. Thomas and H.T. Pham. 1992. "Solubility and Miscibility of Environmentally Safer Refrigerant/Lubricant Mixtures." ASHRAE Transactions. Vol. 92·5-1. pp. 783-788. N.A. Van Gaalen, M.B. Pate. and S.C. Zoz. 1990. "The Measurement of Solubility and Viscosity of Oil/Refrigerant Mixtures at High Pressures and Temperatures: Test Facility and Initial Results for R-22/Naphthenic Oil Mixtures." ASHRAE Transactions. Vol. 96. Pt 2. pp. 183-190. 440 500 40C ~ 300 ~ "' ~ ., 200 rt 100 Mass fracruon Figure 1 Solubility ofR-32 in polypropylene glycol diol ~ 300 s ., ~ "' 200 d: 0.0 0.2 0.4 0,6 0.8 1.0 Mass fractior Figure 3 Solubility ofR-32 in pentaerythritol ester branched acid .. 300 -;;; e:. ~ "' 200 rt 0_0 0.2 0.4 0.6 0.8 1.0 Mass traction FigureS Solubility ofR-125 in pentaerythritol ester mixed acid 500 50C ~00 ~0 c " 300 30C -;;; .a "' ~ "' 200 rt 10C 0 100 -10 c -20C 0_6 0.8 1.0 Mass trac:11cn Figure 2 Solubility ofR-32 in pentaerythritol ester mixed acid .,.. 300 ·;;; e:. ., i "' 200 rt 0.2 0.~ 0.6 0.8 Mass traa.,n Figure 4 Solubility ofR-125 in polypropylene glycol diol I 300 e:. • i 200 a: 0.2 0.~ 0-6 O.B Mass traelion 1.0 ,_0 •. Figure 6 Solubility ofR-125 in pentaerythritol ester branched acid 441 250 200 ~ 1~ f ~ 100 a: Mass lraction Figure 7 Solubility ofR-l34a in polypropylene glycol dial 200 .. 150 -o; ~ ., :; il 100 a: Mass lraction Figut·c 9 Solubility ofR-l34a in pcntaerythritol ester branched acid 442 200 .. 150 . ., ~ .. :; ., ' 100 a: Fi~'llrc 8 Solubility ofR-l34a in pentaerythritol ester mixed acid 

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1285&amp;context=iracc

Solubility of HFC-32, HFC-125, and HFC-134a with Three Potential Lubricants

Abstract

Similar works

Full text

Available Versions

Iowa State University Computer Science Technical Reports

Purdue E-Pubs