Apparatus for Low-Temperature Investigations: Phase Equilibrium

Article pubs.acs.org/jced

Apparatus for Low-Temperature Investigations: Phase Equilibrium Measurements for Systems Containing Ammonia Yanxing Zhao,†,‡ Xueqiang Dong,*,† Maoqiong Gong,† Hao Guo,† Jun Shen,† and Jianfeng Wu† †

Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, P.O. Box 2711, Beijing 100190, China ‡ University of Chinese Academy of Sciences, Beijing 100039, China ABSTRACT: In this paper, a low-temperature apparatus was designed to measure vapor−liquid and vapor−liquid−liquid equilibria for binary systems containing ammonia. The standard combined uncertainties of the temperature, pressure, and the mole fraction are less than ±5 mK, ±0.0008 MPa, and ±0.005, respectively. The saturated vapor pressures of the ammonia, n-butane, and 1-butene were measured, and there were quantitative similarities between the experimental data and the data from Refprop 9.1, with differences less than 0.0007 MPa. The reliability of the experimental setup was verified. The experimental data of the (ammonia + n-butane) system and the (ammonia + 1-butene) system were presented. The homogeneous azeotropic behavior was shown at T = (293.150 and 283.150) K and a heterogeneous azeotropic was found at 273.150 K for the (ammonia + 1-butene) system. Besides, a heterogeneous azeotropic was found at T = (273.150 and 263.150) K for the (ammonia + n-butane) system. All the experimental data were correlated with the PR-MHV2-NRTL model. The maximum root mean square deviations in temperature, pressure, liquid mole fraction, and vapor mole fraction for the systems concerned are 0.010 K, 0.0035 MPa, 0.011, and 0.011, respectively.

1. INTRODUCTION Ammonia is an unique substance by virtue of its excellent thermodynamic properties as a refrigerant and the benefits it brings to the environment,1−3 and it has remained in continuous use as a refrigerant since its introduction around 1870. However, the toxicity and flammability of ammonia limited its civil application. Moreover, ammonia is immiscible with conventional lubricating oil. In most cases, flow boiling heat transfer is affected by the presence of lubricating oil entering the flow from the compressor. Immiscible oil forms a layer with a poor conductivity, thus causing a strong reduction of the heat transfer coefficient.4−6 To take the advantages of ammonia and minimize its disadvantages, one of the most perspective directions is a search for new mixture refrigerants based on ammonia. Khmelnyuk and Shevchenko7 demonstrated that adding some of the hydrocarbons to pure ammonia can improve energy efficiency, reduce discharge temperature of the compressor, and provide solubility of working agents. Meanwhile, several research projects in Europe using the mixture of ammonia and dimethyl ether have proven the concept of low charge systems for domestic heating.1 Nevertheless, the fundamental (vapor + liquid) equilibrium (VLE) data of binary systems consisting of ammonia and other environment-friendly refrigerants were rarely reported in the literature. In Kay and Fisch’s work,8 the p−v−T−x relations of the ammonia + n-butane system were determined at the © XXXX American Chemical Society

liquid−vapor phase boundaries from 100 to 269.5 F. Ammonia and n-butane form an azeotrope whose composition varies from 81.7 mol ammonia at 300 psi to 86.3 mol at 1295 psi. Noda et al.9 reported the VLE data of the (ammonia + propane) system and (ammonia + propene) system, and the azeotropic behaviors of both systems were shown. Wilding et al.10 performed the phase equilibrium measurement on the (ammonia + n-butane) system. A large immiscibility region was found at 273.15 K and a strong positive deviation resulting in a maximum-boiling azeotrope was shown at 323.15 K. The nonrandom two-liquid (NRTL)11 activity coefficient equation was used to regress the data. Kao et al.12 observed the double azeotropy behavior in the (ammonia + pentafluoroethane) system. Using the original two-parameter Peng-Robinson equation of state (PR13 EoS) with the three-parameter mixing rule similar to one proposed by Schwartzentruber and Renon,14 a good VLE description was achieved. However, as pointed out by Michelsen and Kistenmacher,15 it is not invariant to divide a mixture component into a number of identical subcomponents. In their later work,16 the peculiar VLE behavior of the (ammonia + pentafluoroethane) mixture was further studied using a modified three-parameter PR EoS with a nonquadratic Received: July 12, 2016 Accepted: October 19, 2016

A

DOI: 10.1021/acs.jced.6b00623 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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are exposed in ambient environment. Therefore, the setup may not be used when the temparature of the fluids are higher than the environment temperature due to the potential condensation of the vapor phase. 2.1. Temperature and Pressure Measurement. The measurements were implemented in a cylindrical equilibrium cell, which is made of stainless steel 316. The chamber is equipped with two sapphire glasses and immersed in an isothermal alcohol liquid bath. The volumes of the cell and the bath are about 0.15 and 6.5 L, respectively. To accelerate the equilibrium time and decrease the temperature gradient in the liquid bath, two magnetic stirrers and a specially designed diversion trench were installed. A self-made magnetic pump was connected to the top and bottom of the cylindrical chamber to drive the vapor phase into the liquid phase. The temperatures were measured with a 25 Ω standard platinum resistance thermometer (PT25), which is connected to a FLUKE 1594A superthermometer with an uncertainty of 0.24 ppm, and were continuously recorded using the data acquisition software LABVIEW. The uncertainty of the thermometer is less than ±3 mK which was calibrated by the Cryogenic Metrology Station of the Chinese Academy of Sciences based on the 1990 International Temperature Scale (ITS90). The temperature of the isothermal liquid bath was controlled by matching heat loads from a mixed-gases JouleThomson refrigerator (MJTR) and an electric heater. The output power of the electric heater was adjusted by the LABVIEW program. A long-term temperature stability of ±3 mK can be achieved within at least 30 min. The combined standard uncertainty of the temperature measurement was calculated as

mixing rule. They indicated the unusual shapes of the bubble point pressure are due to the intermolecular complex formation in the liquid phase. Moreover, Shiflett and Yokozeki17 reported the azeotropic or azeotrope-like compositions of ammonia and hydrofluorocarbons in their patent. It is noteworthy that only in the work from Noda et al.9 were the vapor and liquid mole fractions determined by means of a gas chromatograph. The other values12,16,17 were calculated with the material balance equations. Because of the strong polarity and hydrogen bonding of ammonia, it is interesting to study the suitable thermodynamic model for anmmonia and its mixtures. A three parameter fit of the isothermal VLE data for (ammonia + pentafluoroethane) system using the WS18 mixing rules and the NRTL model was performed by Shiflett and Sandler19 and the experimental data were well reproduced. Grandjean et al.20 applied GC-PPC-SAFT EoS to ammonia and its mixtures. Predictions on ammonia + n-alkanes systems have shown good quality with n-alkanes ranging from propane to n-hexadecane. To study the vapor−liquid and vapor−liquid−liquid equilibria for systems containing ammonia, a noncopper experimental device was designed. In this paper, we will describe the apparatus and the experimental procedure first. Then the saturated vapor pressures of ammonia, n-butane, and 1-butene at temperatures from (243.150 to 293.150) K were presented, and the experimental data were compared with REFPROP 9.1.21 Finally, the VLE data of (ammonia + nbutane) and (ammonia +1-butene) systems were shown, and they were correlated by the Peng−Robinson (PR) equation of state with the modified Huron−Vidal second-order (MHV2)22,23 mixing rule combining the NRTL activity coefficient model (PR-MHV2-NRTL).

u(T ) =

2. EXPERIMENTAL SETUP The apparatus is based on vapor−liquid recirculation method. The experimental system is schematically shown in Figure 1. (Vapor + liquid) and (vapor + liquid + liquid) equilibrium can be studied for multicomponent systems at temperatures ranging from (173 to 303) K and for pressures up to 6 MPa. These multicomponent systems can contain ammonia and other refrigerants, since no copper was used in the experimental device. The pipelines for sampling and pressure measurement

=

uPT25(T )2 + uFLUKE(T )2 + u fluctuation(T )2 (3)2 + 0 + (3/ 3 )2 (1)

≈ 3.5 mK

Considering some unknown factors that may be not included in above equation, the combined standard uncertainty is estimated to be less than ±5 mK. The pressures in the equilibrium cell were measured by a Mensor Series 6000 digital pressure transducer with an accuracy of 0.020%FS at two full scales of (3.0 and 6.0) MPa. In this work, the full scale of 3.0 MPa was used and the uncertainty of the pressure transducer is 0.0006 MPa. The pressure stability of ±0.0001 MPa can be achieved within at least 30 min. The combined standard uncertainty of the pressure measurement was calculated as u(p) = =

utransducer(p)2 + u fluctuation(p)2 (0.0006)2 + (0.0001/ 3 )2

≈ 0.0006MPa.

(2)

Considering the effect of impurities of the samples on the pressure and other unknown factors that may be not included in above equation, the combined standard uncertainty is estimated as less than ±0.0008 MPa. 2.2. Sampling. Four capillaries with an internal diameter of 0.35 mm at different levels in the chamber were employed for vapor and liquid phases sampling. The sample was taken from the equilibrium cell with a needle valve (SS-31RS4, Swagelok) connected to a six-port-automatic-sample-injection (SPASI) valve. Figure 2 shows a schematic diagram of the SPASI value.

Figure 1. Schematic diagram of the experimental system: 1, vacuum pump; 2, isothermal liquid bath; 3, view windows; 4, cooling coil; 5, refrigerating machine; 6, vacuum vessel; 7, motor; 8, gas chromatograph; 9, feed system; 10, magnetic pump; 11, thermometer; 12, pressure transducer; 13, stabilized voltage supply; 14, pressure and temperature indicator; 15, diversion trench; 16, equilibrium cell; 17, stirrer; 18, electric heater. B



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at first to remove the residual impurities. Small amounts of the mixture to be studied were introduced into the cell and then degassed by activating the vacuum pump to evacuate the cell and the whole circuit. The degassing process was repeated three times, then each component was charged with the refrigerating machine working. After the desired temperature arrived and the temperature fluctuation in the cell was less than ±3 mK and the pressure fluctuation was less than ±100 Pa for at least 30 min, the equilibrium state was considered to be established. Then the vapor and liquid mole fractions were measured by the gas chromatograph at least three times respectively to make sure the deviation among them was less than ±0.001, and the average value was recorded. Successive isothermal vapor pressure measurements for the binary mixture are made over roughly one-half of the composition range by adding one component to the equilibrium cell containing a fixed amount of the second component. At last, the cell was evacuated again, and the saturated vapor pressure data of each component were measured.

Figure 2. A schematic diagram of the six-port-automatic-sampleinjection valve: (a) position A; (b) position B.

At position A, the sample is loaded in the quantitative loop with a volume of 0.5 mL. At position B, the sample in the loop is injected in the chromatographic column by rotation of the rotor 60°. Small amount of the sample was discharged from the cell in this method. Since it is negligible compare to the volume of the cell, the equilibrium state was hardly affected when the temperature of the cell return. The compositions of both phases were analyzed by a gas chromatograph (Beifen, model SP3400) equipped with a thermal conductivity detector (TCD) with an estimated uncertainty of ±0.001 in the mole fraction. The column packing was Porapack Q with a length of three meters, and the column temperature was 373.15 K. The carrier gas was highpurity helium with the mole purity of 0.99999 at 20 mL/min. The gas chromatograph was calibrated by the mixtures with known compositions gravimetrically. At least three analyses were performed for each sample to ensure deviations in mole fractions within ±0.0005. Then a standard curve was drawn with the multipoint calibration method. Figure 3 gives the

3. MATERIALS Ammonia, n-butane, and 1-butene were supplied by Beijing AP BAIF Gases Industry Co., Ltd. with mole purities of 0.99999, 0.995, and 0.995, respectively. All chemicals were found to be within acceptable purity specifications by GC analysis (>0.999) and were used without further purification. The mole fraction purities, critical parameters, and acentric factors for ammonia, n-butane, and 1-butene were shown in Table 1. Table 1. CAS Number, Mole Fraction Purities, Critical Parameters (Tc, pc) and Acentric Factors ω for Ammonia, nButane, and 1-Butene components a

ammonia n-butanea 1-butenea a

CAS No.

mole fraction purity

Tc/Kb

pc/MPab

ωb

7664-41-7 106-97-8 106-98-9

0.99999 0.999 0.995

405.40 425.13 419.29

11.333 3.796 4.005

0.256 0.201 0.192

Supplied by Beijing AP BAIF Gases Industry Co., Ltd. bReference 21.

4. THERMODYNAMICS MODELS The conventional mixing rules, such as van der Waals mixing rules, cannot precisely reproduce the expeimental VLE data of mixtures containing ammonia due to the strong polarity of ammonia. In this paper, the PR-MHV2-NRTL model was employed to correlate the experimental data. The PR EoS is expressed in the following form:

Figure 3. Standard curve for (ammonia + n-butane) and (ammonia +1-butene) systems with the multipoint calibration method. blue +, (ammonia + n-butane); red ●: (ammonia + 1-butene).

p=

standard curve for (ammonia + n-butane) and (ammonia + 1butene) systems. Taking into account the uncertainties from the calibration, the dispersion of analyses and the uncertainty of the gas chromatograph, the uncertainty on the vapor and liquid mole fractions is estimated to be within ±0.005 over the whole range of concentration. 2.3. Experimental Procedure. The procedure consists of three steps: filling the mixtures in the cell, setting up the experimental conditions, and then taking the measurements at equilibrium. The cell and the recirculation lines were evacuated

a(T ) RT − v−b v(v + b) + b(v − b)

a(T ) = 0.457235

b = 0.077796

RTc pc

R2Tc2α(T ) pc

(3)

(4)

(5)

α (T ) = [1 + (0.37464 + 1.54226ω − 0.26992ω 2)(1 − Tr0.5)]2 (6) C


Journal of Chemical & Engineering Data Tr =

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T Tc

Table 2. Experimental (pexp) and Calculated Vapor Pressure (pref) from REFPROP 9.1 and the Deviation (Δp) between pexp and pref of Ammonia, n-Butane and 1-Butenea

(7)

where p is the pressure in Pa, T is the temperature in K, vis the mole volume in m3/mol, R is the gas constant in J/(mol·K), pc and Tc are the critical pressure and temperature, respectively, and ω is the acentric factor of the pure component. The excess molar Gibbs energy GE was calculated by the NRTL activity coefficient model using a reference pressure of zero, which is given by GE = RT

∑ xi

∑l Glixl

(8)

Gji = exp( −αjiτji)

(9)

where τji and τij are adjustable parameters with τii = 0. The parameter αji was set to 0.3 in this work with αji = αij. The PR EoS and NRTL activity coefficient model was combined by the modified Huron−Vidal second-order mixing rule, which can be rewritten as n

q1(αm − =

n

∑ xiαii) + q2(αm2 − ∑ xiαii2)

i=1 E Gm,0

RT

+

i=1

∑ xi ln( b ) i

bii

(10)

n

b=

∑ xibi

(11)

i=1

αm = am /bmRT

(12)

f Vi

293.150 288.150 283.150 278.150 273.150 268.150 263.150 258.150 253.150 248.150 243.150

0.8572 0.7287 0.6148 0.5156 0.4297 0.3550 0.2910 0.2359 0.1902 0.1520 0.1200

293.150 283.150 273.150 263.150 253.150 243.150

0.2075 0.1482 0.1030 0.0698 0.0451 0.0283

293.150 283.150 273.150 263.150 253.150 243.150

0.2553 0.1834 0.1287 0.0874 0.0573 0.0362

pref Ammonia 0.8575 0.7285 0.6150 0.5157 0.4294 0.3548 0.2907 0.2362 0.1901 0.1515 0.1194 n-Butane 0.2077 0.1485 0.1032 0.0696 0.0452 0.0282 1-Butene 0.2546 0.1835 0.1287 0.0875 0.0575 0.0362

MPa

pexp

0.0002 −0.0002 0.0002 0.0002 −0.0004 −0.0002 −0.0003 0.0003 −0.0002 −0.0005 −0.0006

0.03 −0.03 0.04 0.03 −0.08 −0.06 −0.09 0.13 −0.08 −0.35 −0.48

0.0002 0.0003 0.0002 −0.0002 0.0001 −0.0001

0.07 0.17 0.22 −0.35 0.16 −0.33

−0.0007 0.0001 0.0000 0.0001 0.0001 0.0000

−0.27 0.06 0.00 0.14 0.24 0.09

differences less than 0.0007 MPa. The reliability of the experimental setup was verified. 5.2. VLE Measurements. The experimental data of (ammonia + n-butane) at T = (273.150 and 263.150) K are shown in Table 3 and Figure 4. This binary system has a large immiscibility region. The data from the literature10 are also presented in Figure 4. The data in this work exhibit good

(13)

f Li

where and represent the fugacity of the vapor phase and liquid phase, respectively. The binary interaction coefficients in eqs 9 were obtained by regressing the VLE data based on the minimum of the following objective function OF:

Table 3. Experimental Pressures (p), Mole Fractions of Liquid Phase (x) and Vapor Phase (y) of Ammonia for the Ammonia (1) + n-Butane (2) Binary Systema

2 N ⎡ ⎛ Tcal, i − Texp, i ⎞2 ⎛ pcal, i − pexp, i ⎞ ⎢ ⎜ ⎟ OF = ∑ ⎜ ⎟ +⎜ ⎟ ⎢ δT δp ⎠ ⎝ ⎠ i ⎣⎝

p/MPa

2⎤

⎛ x1cal, i − x1exp, i ⎞2 ⎛ y1cal, i − y1exp, i ⎞ ⎟⎟ ⎥ +⎜ ⎟ + ⎜⎜ δx δ ⎝ ⎠ ⎝ ⎠ ⎥⎦ y

100Δp b

a Standard uncertainties u are u(T) = 0.005 K and u(p) = 0.0008 MPa. Declared mole fraction purities: ammonia (0.99999), n-butane (0.995), 1-butene (0.995). bΔp = pref − pexp.

where n is the number of the components, q1 = −0.478 and q2 = −0.0047. The thermodynamic condition for the VLE is the equality of the fugacities of each component in each phase, which is expressed as

fiV = fiL

pexp

K

∑j τjiGjixj

i

Δp

T

0.1032 0.1626 0.2090 0.3012 0.4015 0.4514 0.5262b 0.5262b 0.4297

(14)

where N is the number of the experiment points, δ is the estimated variance of each of the measured variances, and δT = 0.005 K, δp = 0.0008 MPa, and δx = δy = 0.005. 2

5. RESULTS AND DISCUSSION 5.1. Saturated Vapor Pressures. The vapor pressures of the ammonia, n-butane, and 1-butene were measured, as shown in Table 2. There were quantitative similarities between the experimental data and the data from Refprop 9.1, with

x1 T = 273.150 K 0.000 0.011 0.018 0.048 0.084 0.098 0.157 0.992 1.000

y1 0.000 0.359 0.488 0.650 0.745 0.779 0.814 0.814 1.000

p/MPa 0.0696 0.1634 0.1225 0.2374 0.3186 0.3433 0.3562b 0.3562b 0.2907

x1 T = 263.150 K 0.000 0.020 0.028 0.042 0.100 0.129 0.146 0.995 1.000

y1 0.000 0.577 0.435 0.705 0.786 0.804 0.815 0.815 1.000

a Standard uncertainties u are u(T) = 0.005 K and u(p) = 0.0008 MPa and u(x) = u(y) = 0.005. Declared mole fraction purities: ammonia (0.99999), n-butane (0.995). b(Liquid + liquid) equilibrium.

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Figure 4. VLE data of ammonia (1) + n-butane (2) system at 273.150 and 263.150 K and ammonia (1) + propane (2) system at 293.150 and 273.150 K: ●, liquid phase; ○, vapor phase; ▲ and △ are data from literature;10 □, VLE data of ammonia + propane system reported by Noda and Inoue.9 Solid lines are predicted by the PR-MHV2-NRTL model.

Figure 5. VLE data of ammonia (1) + 1-butene (2) binary system at 293.150, 283.150, and 273.150 K and ammonia (1) + propylene (2) system at 293.150, 273.150, and 263.150 K: ●, liquid phase; ○, vapor phase; □, VLE data of ammonia + propylene system reported by Noda and Inoue.9 Solid lines are predicted by the PR-MHV2-NRTL model.

alkenes may have better miscibility with ammonia than alkanes do. Table 5 lists the parameters and the root-mean-square deviations in total pressure, temperature, and liquid and vapor compositions. The thermodynamic consistency test was passed by the area test. Table 5 and Figure 3 and 4 show that the calculated values represent the experimental ones fairly well, although further development is needed for more precise agreement in the (vapor + liquid + liquid) phase region. Table 6 gives the estimated homogeneous or heterogeneous azeotropic pressure p and mole fractions x, y for (ammonia +

agreement with the literature data at 273.150 K, although the measuring methods are different. Table 4 and Figure 5 give the expeimental data of (ammonia + 1-butene) at T = (293.150, 283.150, and 273.150) K. A homogeneous azeotropic behavior was shown at T = (293.150 and 283.150) K and a heterogeneous azeotropic was found at 273.150 K. Besides, the VLE data of (ammonia + propane) and (ammonia + propylene) systems9 were shown in Figure 4 and Figure 5, respectively. Similar behaviors were exhibited as compared to the systems studied in the present work, which implies that

Table 4. Experimental Pressures (p), Mole Fractions of Liquid Phase (x) and Vapor Phase (y) of Ammonia for the Ammonia (1) + 1-Butene (2) Binary Systema p/MPa

x1

0.2553 0.3577 0.5548 0.7034 0.9518 1.0039 1.0141 1.0172 1.0196 1.0202 1.0206 1.0210 1.0209 1.0197 1.0064 0.9160 0.8572

T = 293.150 K 0.000 0.049 0.130 0.214 0.450 0.604 0.632 0.659 0.748 0.767 0.786 0.802 0.831 0.846 0.912 0.983 1.000

y1 0.000 0.282 0.552 0.653 0.766 0.793 0.797 0.801 0.803 0.804 0.807 0.809 0.816 0.818 0.836 0.931 1.000

p/MPa

x1

0.1834 0.3658 0.4848 0.5626 0.6570 0.6892 0.7270 0.7322 0.7363 0.7416 0.7441 0.7468 0.7469 0.7470 0.7467 0.7465 0.7463 0.7446 0.7430 0.7356 0.7261 0.6689 0.6148

T = 283.150 K 0.000 0.101 0.194 0.272 0.407 0.464 0.537 0.540 0.551 0.564 0.565 0.656 0.817 0.836 0.873 0.885 0.894 0.911 0.922 0.945 0.957 0.976 1.000

y1 0.000 0.519 0.665 0.716 0.769 0.786 0.802 0.803 0.805 0.808 0.810 0.812 0.814 0.813 0.809 0.809 0.810 0.813 0.818 0.830 0.842 0.902 1.000

p/MPa 0.1287 0.2512 0.3743 0.4270 0.4910 0.5240b 0.5240b 0.5040 0.4297

x1 T = 273.150 K 0.000 0.075 0.157 0.217 0.313 0.404 0.945 0.972 1.000

y1 0.000 0.487 0.680 0.735 0.778 0.812 0.812 0.853 1.000

a

Standard uncertainties u are u(T) = 0.005 K and u(p) = 0.0008 MPa and u(x) = u(y) = 0.005. Declared mole fraction purities: ammonia (0.99999), 1-butene (0.995). b(Liquid + liquid) equilibrium. E



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Table 5. Regressed Binary Interaction Coefficients τij and Root Mean Square Deviations (RMS)a in Temperature (T), Pressure (p), Liquid Mole Fraction (x) and Vapor Mole Fraction (y) for Ammonia (1) + n-Butane (2) System and Ammonia (1) + 1-Butene (2) System T/K

a

τ12

RMS (T)/K

τ21

273.150 263.150

4.626 5.068

293.150 283.150 273.150

3.249 3.511 3.430

RMS (p)/MPa

Ammonia + n-Butane 1.908 0.004 0.0014 2.033 0.010 0.0027 Ammonia + 1-Butene 0.341 0.009 0.0022 0.365 0.009 0.0035 0.711 0.008 0.0018

RMS (x1)

RMS (y1)

0.003 0.006

0.007 0.005

0.005 0.011 0.011

0.011 0.007 0.009

Notes

The authors declare no competing financial interest.

■

Abbreviations

AARD AZ PR RMS VDW VLE a b f L N p R s T x y

N

RMS(w) = [∑ (wcal − wexp)2 /N ]0.5 i=1

Table 6. Estimated Homogeneous or Heterogeneous Azeotropic Pressure p and Mole Fractions x(L1 Denotes the First Liquid Phase and L2 Denotes the Second Liquid Phase), y for (Ammonia + n-Butane) and (Ammonia +1Butene) Systems

a

pcal

273.150 263.150

0.5371a 0.3608a

293.150 283.150 273.150

1.0112b 0.7402b 0.5247a

x1,az = y1,az

xL1

Ammonia + n-Butane 0.166 0.158 Ammonia + 1-Butene 0.814 0.815 0.455

xL2

y

0.994 0.995

0.804 0.809

attractive parameter in the EoS covolume in the EoS fugacity liquid phase number of components pressure, MPa universal gas constant, J·mol−1·K−1 entropy, J·mol−1·K−1 temperature, K liquid phase composition vapor phase composition

Greek letters

μ chemical potential τij binary interaction parameter between components i and j Subscripts

i, j component index m mixture Superscripts 0.947

0.799

V vapor phase L liquid phase

Heterogeneous azeotropy. bHomogeneous azeotropy.

■

n-butane) and (ammonia + 1-butene) systems. the maximum root mean square deviations in temperature, pressure, liquid mole fraction, and vapor mole fraction for the systems concerned are 0.010 K, 0.0035 MPa, 0.011, and 0.011, respectively.

REFERENCES

(1) Pearson, A. Ammonia’s future. ASHRAE J. 2008, 50, 30−37. (2) Pearson, A. Refrigeration with ammonia. Int. J. Refrig. 2008, 31, 545−551. (3) Palm, B. Ammonia in low capacity refrigeration and heat pump systems. Int. J. Refrig. 2008, 31, 709−715. (4) Shah, M. Visual observations in an ammonia evaporator. ASHRAE Trans. 1975, 81, 295−306. (5) Chaddock, J. Film coefficients for in-tube evaporation of ammonia and R-502 with and without small percentages of mineral oil. ASHRAE Trans. 1986, 92, 22−40. (6) Boyman, T.; Aecherli, P.; Wettstein, A. S. W. Flow Boiling of Ammonia in Smooth Horizontal Tubes in the Presence of Immiscible Oil; International Refrigeration and Air Conditioning Conference, Purdue, IL, 2004. (7) Khmelnyuk, M.; Shevchenko, V. Experimental research of the refrigerating machine working on mixes on the basis of ammonia. International Conference on Ammonia Refrigeration Technology for Today and Tomorrow. International Institute of Refrigeration. Ohrid, Republic of Macedonia, April 19−21, 2007. (8) Kay, W. B.; Fisch, H. A. Phase relations of binary systems that form azeotropes: I. The ammonia−n − Butane system. AIChE J. 1958, 4, 293−296. (9) Noda, K.; Inoue, K.; Asai, T.; Ishida, K. Isothermal vapor-liquid and liquid-liquid equilibria for the propane-ammonia and propyleneammonia systems. J. Chem. Eng. Data 1993, 38, 9−11. (10) Wilding, W. V.; Giles, N. F.; Wilson, L. C. Phase equilibrium measurements on nine binary mixtures. J. Chem. Eng. Data 1996, 41, 1239−1251.

6. CONCLUSIONS In this paper, the statured vapor pressures of the ammonia, nbutane, and 1-butene and the VLE data of (ammonia + nbutane) and (ammonia +1-butene) systems were measured using an apparatus based on vapor−liquid recirculation method. The vapor pressures of the ammonia, n-butane and 1-butene were compared with Refprop 9.1, and the maxmium deviation of pressure is 0.0007 MPa. The PR-MHV2-NRTL can reproduce the VLE data of the (ammonia + n-butane) and (ammonia +1-butene) systems. The homogeneous or heterogeneous azeotropic behavior was found for the systems studied over the temperature ranges investigated.

■

average absolute relative deviation azeotropic Peng−Robinson root mean square deviations van der Waals vapor liquid equilibrium

Symbols

Root mean square deviations are calculated as

T/K

NOMENCLATURE

AUTHOR INFORMATION

Corresponding Author

*Tel./Fax: +86 10 82543736. Email: [email protected]. Funding

This work is financially supported by the National Natural Sciences Foundation of China under Contract No. 51376188 and Youth Innovation Promotion Association CAS (No. 2015021). F



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Apparatus for Low-Temperature Investigations: Phase Equilibrium

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