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Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Liquid and Vapor Viscosities of Binary Refrigerant Mixtures Containing R1234yf or R1234ze(E) Masoumeh Akhfash,† Saif ZS. Al Ghafri,† Darren Rowland,† Thomas J. Hughes,‡ Tomoya Tsuji,§ Yukio Tanaka,∥ Yoshio Seiki,⊥ and Eric F. May*,†
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†
Fluid Science & Resources Division, Department of Chemical Engineering, University of Western Australia, Crawley, WA 6009, Australia ‡ Oil and Gas Engineering, Resources Engineering, Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia § Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Kuala Lumpur 54100, Malaysia ∥ Chemical Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, LTD., Hiroshima 733-8553, Japan ⊥ Global Research & Innovation Center, Mitsubishi Heavy Industries Asia Pacific PTE, LTD., Singapore 189720, Singapore ABSTRACT: Liquid and vapor viscosities are reported for the binary refrigerant mixtures (R125 + R152a), (R125 + R1234ze(E)), (R143a + R1234ze(E)), (R143a + R1234yf), and (R1234ze(E) + R1234yf). The measurements were made with a vibrating wire viscometer and span temperatures from (252 to 403) K and pressures from (0.9 to 4.0) MPa. The performance of the vibrating-wire apparatus was validated by measuring the viscosity of pure R152a in both the vapor and liquid regions. These measurements and previously published data were used to tune binary interaction parameters in the extended corresponding states equation model for viscosity implemented in the NIST software REFPROP 9.1. After tuning, deviations between the model and reported viscosities were reduced from between (−4 and 8)% to within ±2%.
1. INTRODUCTION The viscosity of mixtures of refrigerants containing hydrofluoroolefins (HFOs) are of interest as such fluids could serve as more environmentally friendly alternatives to chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs). Although pure HFOs typically have low global warming potentials (GWPs) and other environmental advantages, they are not necessarily ideal for certain refrigerant applications (e.g., air conditioning) due to their low vapor pressure and small enthalpy of vaporization1 and increased flammability.2 This means that mixtures of HFOs with HFCs are likely to be adopted for initial commercial deployment. Viscosity data for mixtures are needed to improve the accuracy of models used to design and simulate industrial processes such as refrigeration systems. Viscosity data for mixtures containing natural gas components, cryogenic gases, and refrigerants are available from various sources (see, for example, Chichester and Huber3). However, as the HFOs R1234yf and R1234ze(E) have come to attention relatively recently, viscosity data for their mixtures are comparatively rare. The data summarized in Table 1 were found during our survey of the literature. The primary motivation of this work was to measure the viscosity of binary refrigerant mixtures containing R1234yf and R1234ze(E) for which there are no data currently available. A © XXXX American Chemical Society
Table 1. Summary of Literature Sources of Viscosity Data for Binary Mixtures Containing HFOs R1234yf or R1234ze(E) system
reference
N
range (T, p, z)a
R32 + R1234ze(E) R134a + R1234ze(E)
1 4
21 (liq) 9 (liq)
R32 + R1234yf
5
20 (vap)
R32 + R1234yf R32 + R1234yf
1 5
18 (liq) 26 (liq)
R125 + R1234yf
5
20 (vap)
R125 + R1234yf
5
27 (liq)
293−348 K, psat, 0.67 293−369 K, 0.5−3.2 MPa, 0.44 278−338 K, 0.1 MPa, 0.35−0.69 293−343 K, psat, 0.52−0.79 283−320 K, 2−3 MPa, 0.48−0.84 278−338 K, 0.1 MPa, 0.19−0.69 283−320 K, 1.6−2.1 MPa, 0.29−0.69
z is the mole fraction composition of the first-named component in the binary mixture. a
vibrating wire viscometer (VWV) was used in this work to acquire the data over a wide range of temperatures and pressures relevant to their likely industrial application, in both the liquidand vapor-phase regions. Received: November 5, 2018 Accepted: January 28, 2019
A
DOI: 10.1021/acs.jced.8b01039 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Table 2. Refrigerants Studied in This Report, Chemical Supplier, and Purity ASHRAE refrigerant number 125 143a 152a 1234yf 1234ze(E)
CAS #
supplier
supplier purityc
354-33-6 420-46-2 75-37-6 754-12-1 29118-24-9
Core Gas Core Gas Core Gas Core Gas Core Gas
0.995 0.995 0.995 0.995 0.995
IUPAC name a
pentafluoroethane 1,1,1-trifluoroethanea 1,1-difluoroethanea 2,3,3,3-tetrafluoropropeneb (E)-1,3,3,3-tetrafluoropropeneb
a
HFC compound. bHFO compound. cMole fraction basis.
Figure 1. Schematic diagram of the vibrating wire viscometer assembly.
2. MATERIALS AND METHODS Binary mixtures of refrigerant components R125, R143a, R152a, R1234yf, and R1234ze(E) (Table 2) were targeted for viscosity measurements. A vibrating wire apparatus (Figure 1) was constructed to measure the viscosity of homogeneous pure fluids or mixtures. The experimental setup and measurement technique were explained in detail previously,6−9 so only a brief description is provided here. A centerless-ground tungsten wire approximately 40 mm in length and 48.4 μm diameter was clamped tautly by an assembly formed from stainless steel and polyimide. The wire holder was fabricated from nonmagnetic 316 stainless steel and was electrically isolated from the holder by cups machined from polyimide that were inserted into the stainless steel holder and served to electrically isolate the wire clamps and retaining screws from the holder. The vibrating wire was located in the field of two samarium cobalt permanent magnets producing a field of 0.45 T, all of which were housed within a high-pressure vessel. The pressure of the sample fluid was controlled with an ISCO syringe pump (operated in constant-pressure mode). The temperature of the sample was controlled by immersing the vessel in a stirred thermostatic bath containing silicone oil (for high temperatures) or ethanol (for low temperatures). The temperature was determined with a platinum resistance thermometer (PRT) that was calibrated against a standard PRT. The pressure, temperature, and the voltage response of the VWV were continuously monitored and logged using custom data acquisition software and saved for subsequent processing and analysis. The wire was operated in steady-state mode, and the amplitude of the wire’s vibration was monitored by observing the electromagnetically induced voltage (through demodulation and subtraction of the drive signal using a lock-in amplifier). The largest induced voltage occurs when the frequency of the drive
signal matches the mechanical resonance frequency of the wire. Stepping the drive signal frequency, f, through resonance allows the fluid’s viscosity to be determined by fitting the measured resonance to a hydrodynamic response function,10,11 Vhydro, given by Vhydro = u(f ) − iv(f ) =
(A1 + iA 2 )f i[f 2 (1 + β) − f02 ] + f 2 (β′ + 2Δ0)
(1)
where u(f) and v(f) are the two quadratures of the voltage; β is the dimensionless added mass owing to the fluid surrounding the wire; β′ is the dimensionless viscous damping of the fluid surrounding the wire; and Δ0 is the logarithmic decrement in vacuum (vacuum damping). The parameters β and β′ contain terms involving modified complex Bessel functions K0 and K1 that include the ratio of viscosity η to mass density ρ of the fluid, the density of the wire ρs, a dimensionless quantity closely related to the Reynolds number Ω, and the radius of the wire R: ρ ρ β = k and β′ = k′ ρS ρS (2) k = −1 + 2Im(() and k′ = 2Re(() ÄÅ ÑÉ ÅÅ 2K1(i Ω)1/2 ÑÑÑÑ Å Å ( = iÅÅ1 + ÑÑ ÅÅ (i Ω)1/2 K 0(i Ω)1/2 ÑÑÑÖ ÅÇ Ω=
2πfρR2 η
(3)
(4)
(5)
In principle, the method provides an absolute measurement of viscosity, owing to the ability to determine all parameters by independent means. In practice, greater accuracy is achieved by calibrating the apparatus with reference fluids to determine Δ0 B
DOI: 10.1021/acs.jced.8b01039 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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and R.6 However, as described recently by Czubinski et al.,12 these parameters are correlated; furthermore, Δ0 is temperature dependent, while R does not vary measurably over the temperature ranges normally accessible to a particular clamped vibrating wire viscometer. In this work, we followed the method of Czubinski et al.12 to determine R and Δ0 by conducting calibration measurements using dilute gaseous methane and liquid propane. Reference values for the densities and viscosities of methane and propane were calculated using the default models implemented in NIST REFPROP 9.1,13,14 which are stated to have relative density uncertainties of less than 0.03% and relative viscosity uncertainties of less than 0.3%. First, the temperature dependence of Δ0 was obtained using a fixed, nominal value of R by measuring the viscosity of pure methane at a pressure of 1 MPa over the temperature range (252 to 403) K. For each temperature, the vacuum damping parameter was adjusted so that the measured viscosities agreed with the reference values for methane within 0.1%. Next, the viscosity of liquid propane was measured over the temperature range (252 to 294) K and the pressure range (1.6 to 7.2) MPa. The viscosity residuals obtained for the propane measurements exhibited both an offset from zero and a small dependence on pressure. The latter was eliminated by applying a temperature-independent offset to the Δ0 function determined from the pure methane data. Then, the offset in the propane viscosity residuals was minimized by adjusting the wire radius to an optimized value of (24.2 ± 0.1) μm. The vacuum damping values determined using the method of Czubinski et al.12,15 are shown in Figure 2 for this optimized
rpm for at least 12 hours to ensure homogeneity before being injected into the apparatus (at constant pressure). The combined standard uncertainty in the synthetic mole fraction of a component is principally determined by uncertainty in the volume injected from the syringe pumps and the fluid densities at the conditions of the syringe pump. Taking this into account, and considering mixture homogeneity and uncertainties associated with mixture transfer, the standard uncertainty in the mole fraction of the prepared mixtures was estimated to be u(x) = 0.01, for all the binary mixtures prepared in this work.16 An analysis of the Type B uncertainty contributions for the viscosity measurements performed here is shown in Table 3. Table 3. Contribution to Type B Uncertainty of the Viscosities u(η) Measured in This Work source
100u(η)/η
nonlinear motion/out of plane motion wire radius calibration density of wire material mixture composition mixture density vacuum damping pressure sensor temperature sensor total contribution
0.44 0.85 0.09 0.03 0.5 0.95 0.85 0.05 1.7
Type A uncertainties of the measured viscosities were obtained from the standard deviations of repeated measurements. The combined uncertainties of the measured viscosities corresponding to a coverage factor of k = 1 were then calculated by combining the Type A values in quadrature with the Type B uncertainties. The performance of the apparatus was validated by measuring the viscosity of R152a in both the vapor and liquid regions, using densities calculated with the reference equation of state (EOS) for this fluid of Outcalt and McLinden17 implemented in the software package NIST REFPROP 9.1.13 The viscosities obtained for R152a are listed in Table 4. The relative deviations between the experimental values and the extended corresponding states (ECS) model18 implemented in NIST REFPROP 9.1 are shown in Figure 3. The relative deviations of the data measured by Assael et al.19 and by Assael and Polimatidou20 are also shown. The relative deviations of the measurements made in this work from the ECS correlation are within 3%, which is consistent with the combined uncertainty of the measurements and correlation. Moreover, the relative differences between the present measurements and the literature data are generally less than 2%. For the measurements of the binary systems, the mixture densities needed in eqs 2 to 5 were estimated using the default Helmholtz energy mixture models implemented in NIST REFPROP 9.1. (Lemmon et al.13). Al Ghafri et al.16 have recently shown that these density predictions were always within 0.5% of the measured densities for these mixtures. This upper bound in the relative differences between the measured and predicted mixture densities was taken as the uncertainty in the density when evaluating its contribution to the uncertainty in the measured mixture viscosity (Table 3). Extended Corresponding States (ECS) Model. The fundamental principles of the ECS model implemented in the software REFPROP are described in depth by Chichester and Huber.3 Reference equations are used to calculate the viscosity
Figure 2. Vacuum damping (Δ0) as a function of temperature used in this work. Error bars represent standard deviation over approximately 50 repeat measurements. The solid curve corresponds to the fitted fourth-order polynomial function.
radius over the temperature range (252 to 403) K. The observed temperature dependence of Δ0 is similar to that reported previously, and accordingly the measured values were regressed to a fourth-order polynomial function of temperature, T. The purpose of this correlation was simply to interpolate the value of Δ0 needed for application of eqs 1 to 5 when determining refrigerant viscosities from the measured resonance curve. Refrigerant binary mixtures with an approximately equimolar composition were prepared following the method described by Al Ghafri et al.16 Each pure refrigerant was loaded into separate syringe pump at room temperature and pressure above 5 MPa (ensuring a liquid phase in the pump). The two refrigerants were injected sequentially into a third pump having an in-built stirrer. The moles of each component added were calculated from the volume injected (at constant pressure) and the fluid's density at injection conditions. The mixtures were stirred at 500 or 1000 C
DOI: 10.1021/acs.jced.8b01039 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 4. Measured Viscosity Data and Combined Standard Uncertainties for Pure R152aa p/MPa
T/K
η/μPa·s
uc(η)/μPa·s
state
p/MPa
T/K
η/μPa·s
uc(η)/μPa·s
state
1.30 1.01 0.81 0.63 1.44 3.26 4.88 6.65 8.37 10.12 11.77 13.33 1.68 4.16
333.2 333.2 333.2 333.2 273.2 273.2 273.2 273.2 273.2 273.2 273.2 273.2 293.3 293.3
11.7 11.7 11.6 11.6 215.4 220.0 224.0 228.3 232.3 236.4 240.3 243.8 173.9 180.1
0.2 0.2 0.2 0.2 3.5 3.5 3.6 3.7 3.8 3.8 3.9 3.9 2.8 2.9
vapor vapor vapor vapor liquid liquid liquid liquid liquid liquid liquid liquid liquid liquid
6.42 8.49 10.92 13.21 15.53 17.70 1.96 3.81 5.55 7.21 9.45 11.27 13.14
293.3 293.3 293.3 293.3 293.3 293.3 313.2 313.2 313.2 313.2 313.2 313.2 313.2
185.4 190.2 195.2 200.4 205.2 209.7 140.0 144.7 148.7 152.5 157.6 161.6 165.3
3.0 3.0 3.1 3.2 3.3 3.4 2.2 2.3 2.4 2.4 2.5 2.6 2.6
liquid liquid liquid liquid liquid liquid liquid liquid liquid liquid liquid liquid liquid
a Standard uncertainties u are u(T) = 0.1 K and u(p) = 0.01 MPa. Fluid densities calculated from Outcalt and McLinden17 as implemented in NIST REFPROP 9.1.
Figure 3. Relative deviations of the measured viscosities for pure R152a and those reported by Assael et al.19 and Assael and Polimatidou20 (with uncertainty of 0.5%) and those calculated using the ECS model of Klein et al.18 implemented in NIST REFPROP 9.1.
of many pure refrigerants; these equations have been developed based on accurate experimental data for the pure fluids in both the dilute vapor and dense liquid regions. The expected uncertainty in viscosity values calculated with the reference equations varies typically from around (1 to 10) % (Table 5). The ECS model represents the viscosity of a pure fluid as a sum of dilute gas and residual contributions. The dilute gas term is based on a Lennard-Jones potential. When the model is extended to a mixture of fluids i and j, the collision diameter, σij, and pair-potential energy, ϵij, of the mixture are related to the constituent pure fluid parameters by combining rules (Chichester and Huber3)
Table 5. Reference Correlations in NIST REFPROP 9.1 for Viscosity and Expected Uncertainties R32 R125 R134a R143a R152a R1234yf R1234ze(E)
D
reference viscosity equation
expected uncertainty
Huber et al.21 Huber and Laesecke22 Huber et al.21 Huber et al.21 Klein et al.18 estimation method estimation method
2−5% 0.8% vap, 3% liq 0.5−5%
