Solubility and Miscibility for the Mixture of (Ethyl Fluoride +

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Solubility and Miscibility for the Mixture of (Ethyl Fluoride + Alkylbenzene Oil) Lingyun Fang,† Zanjun Gao,† Xiaoyu Wang,‡ Jun Lei,‡ Xiaohong Han,*,† and Guangming Chen† †

Institute of Refrigeration and Cryogenics, Zhejiang University, Hangzhou 310027, P. R. China Zhejiang Quhua Fluorine Chemistry Co., Ltd., Quzhou 324004, P. R. China

‡

ABSTRACT: The vapor−liquid equilibrium (VLE) data of different mass fractions of the mixture (ethyl fluoride (HFC-161) + alkylbenzene (AB) lubricant oil) at a temperature range from (278.15 to 348.15) K were measured by single-phase cycle method, and the solubility and miscibility for the mixture (HFC-161 + AB lubricant oil) were analyzed in this paper. The experimental results showed that there was no stratification, no sediment generation, and no color change during the whole experiment for the mixture (HFC-161 + AB lubricant oil). The vapor pressure decreased with the increase of oil concentration. The experimental results were correlated by the nonrandom two-liquid (NRTL) equation. The parameters of the NRTL equation were regressed. From the correlated results, the average relative pressure deviation was 1.4 %, and the maximum relative pressure deviation was 4.2 %. Meanwhile, the results were compared with those of the HFC-161 + polyol ester (POE) lubricant oil mixture in the temperature range of (278.15 to 328.15) K. For a given HFC-161 mass fraction and temperature, HFC-161 is more soluble in POE lubricant oil than in AB lubricant oil. In this work, AB lubricant oil may be a better choice for HFC-161 than POE lubricant oil to some extent. (as one component), flow boiling heat transfer,13,14 and cycle performance.15 As well, some cycle performance research have been done about different HFC-161 mixtures, such as the HFC-161/125/143a mixture and HFC-161/HFC-134a.16,17 It is well-known that a certain amount of oil is washed from the compressor by the refrigerant fluid. When the operated fluid (the mixture of the refrigerant vapor and droplets or foam of lubricant oil) flows into the condenser, the operated fluid is condensed to liquid. If the refrigerant and the lubricant oil have limited miscibility, there is coexistence for two liquid phases: one is an oil-rich phase, and the other one is a refrigerant-rich phase.18 The high viscosity of the oil-rich phase makes some lubricant oil left in the condenser. When the liquid operated fluid flows into the evaporator, the lubricant oil almost remains liquid in various forms (film, droplets or foam), and most of the refrigerant is evaporated. But there is a little refrigerant which still dissolves in the lubricant oil film. As only a little refrigerant is dissolved in the lubricant oil, it is hard for the lubricant oil to come back to the compressor for the high viscosity of the liquid oil, which results in the oil starvation of compressor. The residual liquid oil film accumulates on the surface of heat exchanger tube walls. In most times, the existence of the liquid film increases the thermal resistance which is negative to enhance the heat transfer. From the above analysis, the good miscibility for the refrigerant and the lubricant oil is preferred.19

1. INTRODUCTION In the past several decades, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been widely used as refrigerants.1 However, a paper in 1974 by Molina and Rowland2 identified that CFC and HCFC refrigerants caused the ozone layer depletion when they escaped to the atmosphere, which led to the appearance of Montreal Protocol focusing on abandoning the ozone-depleting substances (ODSs). Because of the Montreal Protocol and its subsequent amendments and adjustments, the CFCs were completely phased-out as refrigerants in most countries.3 Also, HCFCs are being phased-out worldwide under the Montreal Protocol. According to the agreement of the 19th Meeting of the Parties to the Montreal Protocol in September 2007, they will be completely phased-out by 2030. Hydrofluorocarbons (HFCs) are one of the alternative refrigerants for CFCs and HCFCs because they are zero ozone depletion potential (ODP) substances. However, HFCs are not totally harmless. Some HFCs usually have a high global warming potential (GWP) which can cause serious greenhouse effects. Thus, HFCs with low GWPs are still promising alternative refrigerants due to its outstanding thermodynamic and thermophysical properties. Ethyl fluoride (HFC-161), with excellent environment and thermodynamic properties, is one of the most promising alternatives. It is an environmentally friendly refrigerant that is not destructive to the ozone layer (ODP = 0) and has a low global warming potential (GWP = 12).4 Also, it has a very high cooling capacity, a relatively high volume cooling capacity, and an excellent energy efficiency ratio.5,6 Lots of work has already been done about HFC-161, such like PVT,7 density,8 VLE9−12 © 2014 American Chemical Society

Received: January 27, 2014 Accepted: April 5, 2014 Published: April 23, 2014 1636

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Table 1. Description of the Materials Used chemical name

formula

source

mass fraction purity

CAS Registry No.

ethyl fluoride n-hexadecylbenzene

CH3CH2F C6H5(CH2)15CH3

FLTCO Cognis

>0.9974 >0.9200

353-36-6 1459-09-2

Typically, HFCs are relatively polar; they show limited miscibility and have a low solubility in mineral oils which are used in CFC and HCFC systems,20 which suggests that the mineral oils are not suitable for HFC refrigerants. So it is very important to find out suitable lubricant oils for the HFC systems.21−23 It is reported that potential advantages of synthetic oils are the wide range of operating temperatures, fire resistance, and resistance to oxidation and nuclear radiation. They have been widely used in HFC systems. As the abovementioned merits, HFC-161 is a promising refrigerant in the future. Therefore, the miscibility and solubility of the mixture (HFC-161 + lubricant oil) are important topics to be studied, that is to say, it is necessary for HFC-161 to be matched with proper lubricant oil (synthetic oil) in actual application. There are four kinds of commonly used synthetic lubricant oil types: polyol ester (POE) lubricant oil, polyalkylene glycol (PAG) lubricant oil, alkylbenzenes (AB) lubricant oil, and poly-α-olefin (PAO) lubricant oil.24 PAO lubricant oils are generally used in ammonia systems.24 POE, PAG, and AB lubricant oil are usually used in HFC systems.20,24,25 One of the most widely used synthetic lubricant oils in HFCs system is POE oil. The miscibility and solubility of the mixture of HFC-161 and POE lubricant oil have been presented in the previous work, the results showed that the HFC-161 and POE lubricant oil had good miscibility and solubility.26 However, some research showed that POE lubricant oil and PAG lubricant oil were not fully satisfactory for their chemical instability, hygroscopicity, lubricity, and high cost. In contrast, AB lubricant oil has excellent chemical stability, low hygroscopicity, and high lubricity.27−29 Thus, the aim of this work is to study the solubility and miscibility of the mixture of HFC-161 + AB lubricant oil. The comparisons are developed between the results for the mixture (HFC-161 + AB lubricant oil) and the mixture (HFC-161 + POE lubricant oil). All research will supply a valuable reference for the selection of the lubricant oils about HFC-161.

Table 2. Typical Properties of the AB Lubricant Oil property ρ (293.15 K)/kg·m−3 vk (313.15 K)/mm2·s−1 vk (373.15 K)/mm2·s−1 viscosity index pour point/K flash point/K total acid number/mg(KOH)·g−1 moisture/ppm

test method ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM

D1298 D445 D445 D2270 D97 D92 D974 D4928

AB lubricant oil 883 15.14 3.218 60 218.15 459.15 0.005 0.9974. The AB lubricant oil (nhexadecylbenzene, C6H5(CH2)15CH3, CAS Registry No. 1459-09-2) used in the experiment was supplied by Cognis (Shanghai, China) with a mass fraction purity of > 0.9200. The basic information on the samples used is shown in Table 1, and the typical physical properties of AB lubricant oil are shown in Table 2. In Table 2, ρ is the density, and vk is the kinematic viscosity. All samples were used without any further purification. 2.2. Experimental Apparatus and Procedure. The apparatus used for the solubility measurement is shown in Figure 1, similar to the one described in detail by Han et al.26,30 The mixture (HFC-161 (1) + AB lubricant oil (2)) was put into a stainless steel cell with its volume of about 80 mL. A visual observation of the solution in the cell can be made by the glass windows. The vapor phase was cycled from vapor to liquid

wR = 1637

mR − mRV mR + mAB − mRV

(1)

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Table 3. Experimental Data (pexp), Calculated Results (pcal), and Relative Pressure Deviation (δp) for the Mixture (HFC-161 (1) + AB (2)) in Various Mass Fractions (w1) from (278.15 to 348.15) Ka T/K

w1

pexp/kPa

pcal/kPa

δpb/%

T/K

w1

pexp/kPa

pcal/kPa

δpb/%

278.15 278.15 278.15 278.15 278.15 278.15 278.15 278.15

0.1379 0.2361 0.4118 0.4966 0.6300 0.7324 0.8512 0.8996

329.07 416.35 490.06 504.55 509.70 510.18 511.45 512.37

320.18 432.39 495.47 500.96 501.49 501.53 504.41 506.78

−2.70 3.85 1.10 −0.71 −1.61 −1.70 −1.38 −1.09

288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15 288.15

0.1350 0.2331 0.2919 0.4107 0.4955 0.6293 0.7318 0.8509 0.8994

424.20 561.04 598.86 646.16 672.21 691.87 692.54 693.80 695.02

420.10 564.10 607.72 647.93 658.64 666.70 672.29 681.24 685.87

−0.97 0.55 1.48 0.27 −2.02 −3.64 −2.92 −1.81 −1.32

318.15 318.15 318.15 318.15 318.15 318.15 318.15 318.15 318.15 318.15

0.1310 0.2273 0.2828 0.4042 0.4871 0.5343 0.6207 0.7253 0.8477 0.8971

785.75 1057.72 1152.20 1281.66 1338.70 1365.21 1406.83 1449.69 1493.69 1510.18

788.65 1056.42 1149.63 1278.52 1336.04 1362.93 1405.27 1448.87 1493.45 1510.07

−0.23 2.28 2.50 1.35 1.69 −0.06 −1.12 −0.75 −0.57 −0.85

298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15 298.15

0.1339 0.2315 0.2889 0.4093 0.4942 0.6283 0.7310 0.8505 0.8992

534.09 713.21 777.11 835.21 881.54 908.62 914.51 918.84 921.29

540.44 716.84 771.00 828.92 849.16 870.19 884.25 901.48 909.02

1.19 0.51 −0.79 −0.75 −3.67 −4.23 −3.31 −1.89 −1.33

328.15 328.15 328.15 328.15 328.15 328.15 328.15 328.15 328.15

0.1282 0.1728 0.2818 0.4006 0.4860 0.6171 0.7223 0.8461 0.8956

902.14 1084.33 1373.55 1555.79 1645.58 1748.99 1814.21 1878.57 1901.57

905.28 1084.72 1370.10 1551.89 1642.36 1747.12 1813.24 1878.29 1901.44

−1.54 −1.12 2.16 2.07 1.08 −1.42 −0.93 −0.58 −0.62

308.15 308.15 308.15 308.15 308.15 308.15 308.15 308.15 308.15

0.1326 0.2296 0.2868 0.4075 0.4897 0.6264 0.7283 0.8494 0.8985

657.36 867.98 980.21 1045.96 1069.28 1143.21 1166.04 1179.65 1197.46

664.14 881.02 952.20 1038.28 1073.14 1115.05 1141.08 1170.05 1181.54

1.03 1.50 −2.86 −0.73 0.36 −2.46 −2.14 −0.81 −1.33

338.15 338.15 338.15 338.15 338.15 338.15 338.15 338.15 338.15

0.1262 0.1675 0.2792 0.3983 0.4820 0.6127 0.7188 0.8437 0.8937

1016.05 1223.31 1610.92 1866.75 1994.86 2146.14 2241.02 2331.87 2363.51

1019.21 1223.87 1607.52 1862.93 1991.71 2144.31 2240.08 2331.60 2363.39

−0.45 −1.59 2.51 1.99 −0.34 −1.53 −0.91 −0.58 −0.91

348.15 348.15 348.15 348.15 348.15 348.15 348.15 348.15 348.15 348.15

0.1245 0.1697 0.2788 0.3955 0.4806 0.5277 0.6071 0.7117 0.8406 0.8912

1124.03 1395.64 1873.70 2213.81 2395.70 2479.92 2601.82 2733.07 2861.94 2905.03

1127.51 1396.97 1871.97 2211.50 2393.73 2478.22 2600.62 2732.43 2861.75 2904.95

−0.19 −1.42 2.18 2.28 1.01 −0.53 −1.87 −0.99 −0.02 −0.44

Uncertainties u are u(T) = ± 0.01 K, u(w1) = ± 0.002, and u(pexp) = ± 1.45 kPa. bδp is the relative pressure deviation, and it is defined as δp = ((pcal − pexp)/(pexp))·100 %. a

where m stands for the mass, and subscripts R and AB stand for the refrigerant and AB lubricant oil, respectively. The superscript V stands for vapor phase. The mass of refrigerant in the vapor phase was obtained by the following equation

mRV = ρRV V V

purged with alcohol and the refrigerant HFC-161, respectively, and was evacuated for 1 h. These steps were done alternately more than once before each experiment. After the purge, the system was evacuated. A specific amount of AB lubricant oil was directly charged into the equilibrium cell. Before the desired amount of HFC-161 was charged into the equilibrium cell, the system was evacuated again. Then, the entire equilibrium cell was submerged in a thermostatic bath, and the refrigeration system and the temperature controller were turned on. When the system was cooled down to 283.15 K or so, the desired amount of HFC-161 was charged into the cell (the equilibrium cell with the low temperature is helpful to accelerate the charging of HFC-161). In the experiment, the equilibrium cell was almost filled according to a certain ratio; thus the composition in the equilibrium cell was approximately

(2)

ρVR

where is the density of refrigerant in the vapor phase, given by REFPROP.31 The volume of vapor phase refrigerant VV, which consists of stainless steel pipe volume V1 and the upper vapor space volume V2 in the equilibrium cell, has an uncertainty of ± 1.15 cm3. The total uncertainty of wR is within ± 0.002. The experimental procedures are as follows. To ensure the purities in the system, the equilibrium cell was first intensely 1638

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the composition of the liquids. Afterward, the recycle pump began working, and the mixture was stirred continuously. When the system temperature was in the set temperature for 2 h or more, the pressure fluctuation was very small; at this time, it was believed that the system was in the vapor−liquid equilibrium state, and the experimental data (temperature, pressure, and mass fraction of HFC-161 in the liquid phase) were recorded. The above procedures were conducted repeatedly, and afterwards the temperature (the two adjacent temperature intervals were 10 K) was set to the required value again.

Table 4. Second Virial Coefficient (B1), Molar Volume as Saturated Liquid (vL1 ), and Saturation Vapor Pressure (ps1) for HFC-161 in the Correction Factor Equation (eq 5) Calculated by REFPROP32

3. RESULTS AND DISCUSSION Isothermal solubility measurements of the mixture (HFC161(1) + AB lubricant oil (2)) were performed at (278.15, 288.15, 298.15, 308.15, 318.15, 328.15, 338.15, and 348.15) K. The experimental data are listed in Table 3 (where w1 is the mass fraction of HFC-161 in the liquid phase and pexp is the experimental pressure). During the whole experiment, the samples in the equilibrium cell were observed, and there was no stratification and no sediment generation; the color of the samples had no change. All suggested that the mixture (HFC161 + AB lubricant oil) in the different ratios should be miscible. In addition, the vapor phase of the mixture was analyzed using the chromatography (model: GC112A from China) at 70 °C at each composition; the results suggested that no chemical reactions occurred and there is almost no lubricant oil in the vapor phase of the mixture. The vapor−liquid equilibrium (VLE) data were correlated by the NRTL model. When the mixture (HFC-161 (1) + AB lubricant oil (2)) was in the vapor−liquid equilibrium, the basic correlation equation for VLE can be given by eq 3 yi Φip = xiγipis

Φi ≡

⎡ exp⎢ − ⎢⎣ ϕi

ϕî

s

−

RT

pis ) ⎤ ⎥

⎡ (B − − i = exp⎢ ⎥⎦ ⎢⎣ RT viL)(p

m−3·mol−1

P1S/kPa

278.15 288.15 298.15 308.15 318.15 328.15 338.15 348.15

−0.48002 −0.42656 −0.38194 −0.34429 −0.31219 −0.28457 −0.26058 −0.23959

0.063 75 0.065 20 0.066 80 0.068 62 0.070 70 0.073 16 0.076 17 0.080 10

514.14 697.45 925.65 1205.14 1542.78 1946.12 2423.84 2986.56

2 ⎡ ⎤ τ21G21 τ12G12 ⎥ ln γ1 = x 22⎢ + (x 2 + x1G12)2 ⎦ ⎣ (x1 + x 2G21)2

(6)

2 ⎡ ⎤ τ12G12 τ21G21 ⎥ ln γ2 = x12⎢ + 2 2 (x1 + x 2G21) ⎦ ⎣ (x 2 + x1G12)

(7)

G12 = exp( −ατ12)

(8)

G21 = exp( −ατ21)

(9)

τ12 = τ12(0) exp(T /τ12(1)) + τ12(2)

(10)

(0) (1) (2) τ21 = τ21 exp(T /τ21 ) + τ21

τ(0) 12 ,

pis ) ⎤ ⎥

τ(1) 12 ,

τ(2) 12 ,

τ(0) 21 ,

τ(1) 21 ,

(11)

τ(2) 21

where and are the parameters of eqs (1) 10 and 11, respectively. The values of the parameters τ(0) 12 , τ12 , (2) (0) (1) (2) τ12 , τ21 , τ21 , τ21 , and α are obtained by fitting the experimental data; the objective function (OBF) is

⎥⎦

(4)

N

where is the vapor phase fugacity coefficient for the ith component, ϕsi is the fugacity coefficient for the pure ith component as saturated vapor, Bi is the second virial coefficient for the ith component at the system temperature T, vLi is the molar volume for the ith component as saturated liquid at T, and R is the universal gas constant. For the mixture (HFC-161 (1) + AB lubricant oil (2)), the vapor phase was mainly composed of HFC-161 vapor due to the negligible volatility of AB lubricant oil, and y1 is considered as 1 within the temperature ranges in this work. Thus, eq 3 can be rewritten as p exp{[(B1 − v1L)(p − p1s )]/RT } pΦ1 = x1p1s x1p1s

m−3·mol−1

where α, τ12, and τ21 are the parameters of NRTL equation. τ12 and τ21 are considered as the function dependent on the temperature; their expressions were written as

ϕ̂ Vi

γ1 =

T/K

where γ1 and γ2 are the activity coefficients for the first and second component, respectively. x1 and x2 are the mole fractions for the first and second components, respectively. G12 and G21 are defined as follows

(3)

viL(p

v1L·103

γ1 can be calculated by lots of activity coefficient models. Here, the NRTL33 equations are used, and they can be expressed as

where psi is the saturated vapor pressure of the ith component, p is the system pressure, and xi, yi, and γi are the liquid phase mole fraction, the vapor phase mole fraction, and the activity coefficient for the ith component, respectively. Φi is the correction factor for the ith component, which can be expressed as follows32 V

B1·103

OBF =

∑ (ln γ1,exp − ln γ1,cal)i2 i=1

(12)

where N is the number of experimental points, γ1,exp is the experimental activity coefficient for the first component, and γ1,cal is the calculated activity coefficient for the first component. In the above correlation, the molecular weight of HFC-161 is 48.06 g·mol −1 , and its saturated pressures are from REFPROP.31 The molecular weight of AB lubricant oil is 310.95 g·mol−1. The results calculated by the NRTL model for the mixture (HFC-161 (1) + AB lubricant oil (2)) are listed in Table 3 (where pcal is the calculated pressure) and shown in Figures 2 (1) (2) (0) and 3. The optimized values of parameters τ(0) 12 , τ12 , τ12 , τ21 , (1) (2) τ21 , τ21 , and α are tabulated in Table 5. From Table 3 and Figures 2 and 3, it can be found that the average relative pressure deviation between experimental and

(5)

In the equation, B1, v1L, and p1s can be calculated by REFPROP,31 and the responding values are listed in Table 4. 1639

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Meanwhile, the comparisons were developed between the experimental results of the mixtures (HFC-161 + AB lubricant oil, HFC-161 + POE lubricant oil) shown in Figure 4. The

Figure 2. Pressure of the mixture (HFC-161 (1) + AB lubricant oil (2)) for system versus mass fraction of HFC-161 (w1) in VLE. ★, T = 278.15 K; ⧫, T = 288.15 K; ▼, T = 298.15 K; ●, T = 308.15 K; ▲, T = 318.15 K; ■, T = 328.15 K; ▶, T = 338.15 K; ◀, T = 348.15 K. , calculated value.

Figure 4. Pressure of the mixtures (HFC-161 (1) + AB lubricant oil (2); HFC-161 (1) + POE lubricant oil (2)) for the system versus mass fraction of HFC-161 (w1) in VLE. ★, T = 278.15 K (for HFC-161 + AB lubricant oil); ☆, T = 278.15 K (for HFC-161 + POE lubricant oil); ⧫, T = 288.15 K (for HFC-161 + AB lubricant oil); ◊, T = 288.15 K (for HFC-161 + POE lubricant oil); ▼, T = 298.15 K (for HFC-161 + AB lubricant oil); ▽, T = 298.15 K (for HFC-161 + POE lubricant oil); ●, T = 308.15 K (for HFC-161 + AB lubricant oil); ○, T = 308.15 K (for HFC-161 + POE lubricant oil); ▲, T = 318.15 K (for HFC-161 + AB lubricant oil); △, T = 318.15 K (for HFC-161 + POE lubricant oil); ■, T = 328.15 K (for HFC-161 + AB lubricant oil); □, T = 328.15 K (for HFC-161 + POE lubricant oil). , calculated value for the mixture (HFC-161 (1) + AB lubricant oil (2)).

compared results showed that HFC-161 was miscible with AB lubricant oil and POE lubricant oil in different ratios. But from the pressures of the two mixtures (the experimental data for HFC-161 + POE lubricant oil mixture are cited in the literature26) in VLE, it can be analyzed that the solubility for the two mixtures was different; this is because, compared to the mixture (HFC-161 + POE lubricant oil), the pressures of the mixture (HFC-161 + AB lubricant oil) for the system in VLE were closer to the saturated pressures of pure HFC-161 at a given mass fraction of HFC-161 under the same temperature. The analysis obtained by the literature18,34 showed that the closer the pressures of the mixture (refrigerant + lubricant oil) for the system in VLE and the saturation pressures of pure HFC-161 were, the smaller the solubility of the mixture (refrigerant + lubricant oil) was. Therefore, it can be derived in this work that the solubility of the mixture (HFC-161 + POE lubricant oil) was larger than that of the HFC-161 + AB lubricant oil mixture. It is well-known through some research that the solubility of the refrigerant and lubricant oil mixture has an effect on the evaporator performance.18,34 At the outlet end of the evaporator, the operated fluid is usually composed of a vapor phase (refrigerant and little oil) and a liquid phase. The liquid phase is an oil-rich phase which dissolves some refrigerant. The dissolved refrigerant does not take part in the evaporation. Some research revealed that one of the important factors was the solubility of refrigerant and lubricant oil, which had a direct effect on the quantity of nonevaporated refrigerant. The orders of magnitude for the quantity of nonevaporated refrigerant may be very different with the change of the solubility for refrigerant and lubricant oil, and the

Figure 3. Relative pressure deviations (δp) of experimental data from the calculated values with NRTL model for the mixture (HFC-161 (1) + AB lubricant oil (2)). (1) (2) (0) (1) (2) Table 5. Constant Values (τ(0) 12 , τ12 , τ12 , τ21 , τ21 , τ21 , α) Derived by Fitting the Experimental Dataa

constant valuesb τ(0) 12

τ(1) 12

τ(2) 12

τ(0) 21

τ(1) 21

τ(2) 21

α

74.54

−113.09

−2.395

0.007 40

111.0

−0.9931

0.4

a (1) (2) Uncertainties u are u(τ(0) 12 ) = ± 0.03, u(τ12 ) = ± 0.01, u(τ12 ) = ± (1) (2) 0.001, u(τ(0) 21 ) = ± 0.00002, u(τ21 ) = ± 0.1, and u(τ21 ) = ± 0.0005. b Experimental measurement range: T/ K: 278.15 to 348.15, mole fraction: 0.12 to 0.90.

calculated values was 1.4 %, and the maximum relative pressure deviation was 4.2 % , which showed that the calculated results had a good agreement with the experimental results. Also, it can be seen from Figure 2 that the pressure of the mixture (HFC161 (1) + AB lubricant oil (2)) for the system in VLE was lower than the saturated pressure of pure substance HFC-161 at different temperatures. At the same temperature, the vapor pressure of the mixture (HFC-161 (1) + AB lubricant oil (2)) for the system in VLE decreased with the increase of the mass fraction of the lubricant oil, and this trend was more obvious as the increase of the temperature. 1640

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bigger solubility of refrigerant and lubricant oil was, the larger the quantity of nonevaporated refrigerant was, which made the cooling capacity decrease, the reason for which being the latent heat of nonevaporated refrigerant trapped in the lubricant oil could not be used fully.18,34 From the above analyses, AB lubricant oil may be more suitable for HFC-161 than POE lubricant oil; this is because the AB lubricant oil has excellent chemical stability, low hygroscopicity, and high lubricity, and the solubility of HFC161 + POE lubricant oil mixture is larger than that of the HFC161 + AB lubricant oil mixture.

4. CONCLUSIONS In this paper, the solubility measurements of the mixture (HFC-161 + AB lubricant oil) are presented in a temperature range from (278.15 to 348.15) K. For the mixture, the vapor pressure decreases with the increase of oil concentration. The experimental data were correlated with the NRTL model. The average relative deviation for pressures between experimental and calculated values is 1.4 %, and the maximum relative pressure deviation is 4.2 %. The calculated results showed a good agreement with the experimental data, which suggested that the model obtained by this work has a good prediction capability. Meanwhile, the experimental results in this work were compared with those of the HFC-161 + POE lubricant oil mixture in the temperature range of (278.15 to 328.15) K. The comparison results reveal that both POE lubricant oil and AB lubricant oil have good miscibility with HFC-161, but the solubility of HFC-161 in POE lubricant oil is larger than that of HFC-161 in AB lubricant oil. Based on the analyses of this work, AB lubricant oil may be a better choice than POE lubricant oil for HFC-161. However, there may be other factors which affected the selection of lubricant oil besides the solubility of the mixture (refrigerant + lubricant oil). Beyond this work, more research for the mixture (HFC-161 + lubricant oil) needs to be developed for a comprehensive consideration for the selection of suitable lubricant oil.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Telephone: +86 571 8795 3944. Fax: +86 571 8795 3944. Funding

This work has been supported by the Nation Natural Science Foundation of China (No. 51176166), and the Fundamental Research Funds for the Central Universities (2013QNA4014) are gratefully acknowledged. Notes

The authors declare no competing financial interest.

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REFERENCES

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