Isobaric Heat Capacity Measurements for Dimethyl Ether and 1,1

Jul 30, 2014 - The isobaric heat capacity of dimethyl ether and 1,1-difluoroethane in liquid phase were measured at temperatures from 305 K to 365 K a...
1 downloads 0 Views 713KB Size
Download PDF
Article pubs.acs.org/jced

Isobaric Heat Capacity Measurements for Dimethyl Ether and 1,1Difluoroethane in the Liquid Phase at Temperatures from 305 K to 365 K and Pressures up to 5 MPa Yijian He, Neng Gao,* Yunyun Jiang, Bin Ren, and Guangming Chen Institute of Refrigeration and Cryogenics, Zhejiang University, 38 Zheda Road, Hangzhou 310027, P. R. China ABSTRACT: The isobaric heat capacity of dimethyl ether and 1,1-difluoroethane in liquid phase were measured at temperatures from 305 K to 365 K and pressures up to 5 MPa. A heat conduction calorimeter was applied in the measurements and a total of 81 data points for dimethyl ether and 78 data points for 1,1-difluoroethane were obtained. The uncertainties of measured heat capacity were estimated to be 2.1% for dimethyl ether and 1.8% for 1,1-difluoroethane, respectively. To reproduce the experimental data, a uniform equation was proposed. The equation showed average absolute deviations of 0.17 % for dimethyl ether and 0.30 % for 1,1-difluoroethane from the experimental values. Saturated liquid heat capacities for both experimental subjects were also obtained by extrapolating the equation to saturated pressures. Finally, comparisons have been done between our experimental data and literature data and fundamental equation of states.

■

INTRODUCTION Dimethyl ether (DME), also known as methoxymethane, is the simplest ether and is a useful precursor to other organic compounds. A thousand tons of DME are annually consumed as the feedstock for the production of the methylating agent, dimethyl sulfate. It is also considered to be a potential green refrigerant owing to its zero ozone depletion potential and its global warming potential (GWP) of 0.1 (100 years), with ASHRAE refrigerant designation RE170.1 Thermophysical property measurements of DME have been carried out at different aspects, such as critical parameters, densities, vapor pressures, and so on.2−4 A fundamental equation of state was also established upon the basis of the experimental property data.1 However, the latest equation of state does not show satisfactory behavior for the isobaric heat capacity, which might be a result of the lack of experimental isobaric heat capacity data points. As a matter of fact, only Tanaka and Higashi5 reported isobaric heat capacity measurements for DME in the liquid phase, and their results showed positive deviations of 6.5 % from the equation of state. More experimental data points are needed both for the modification of the equation of state and the application in engineering calculations. 1,1-Difluoroethane (R152a) is a promising alternative to 1,1,1,2-tetrafluoroethane (R134a) in automobile applications and a commonly used blend component in many refrigerant blends. It has a zero ozone depletion and a relatively low GWP of 124 (100 years) compared with a GWP of 1430 for R134a.6 In addition to serving as a refrigerant, R152a is also used widely as an aerosol propellant. In this study, the isobaric heat capacities of DME and R152a in the liquid phase were measured. The experimental © 2014 American Chemical Society

temperatures ranged from 305 K to 365 K for DME and 305 K to 360 K for R152a. The experimental pressures ranged from 1.5 MPa to 5 MPa.

■

EXPERIMENTAL APPARATUS The experimental system and method used in this study was introduced in our former work.7 As shown in Figure 1, the key part of the system is a Calvet type calorimeter, which works on the Calvet−Tian principle. The calorimeter can be used from the ambient temperature to 300 K above ambient with a temperature accuracy of 0.05 K and calorimetric accuracy of 0.1 %. Coupled with a specialized sample cell and a pressure balance container, the calorimeter was capable of isobaric heat capacity measurements of liquids at elevated pressures. Two identically manufactured cells were placed symmetrically inside the calorimeter chamber. One of the cells was filled with experimental sample and the other remained empty as a reference. The calorimeter chamber was surrounded by heating elements and could be heated at a constant temperature increasing rate. Because of the temperature difference, heat was transferred from the chamber to the cells through the thermopiles around the outside surface of the cells. The resulting voltage signals in the thermopiles were acquired as the original signals of the heat transferred. To measure the heat capacity of a sample, three tests were required under the same experimental conditions: The first test is a blank test carried out with the sample cell empty (vacuum). The second test is carried out with the sample cell filled with a Received: June 7, 2014 Accepted: July 22, 2014 Published: July 30, 2014 2885

dx.doi.org/10.1021/je500512f | J. Chem. Eng. Data 2014, 59, 2885−2890

Journal of Chemical & Engineering Data

Article

Figure 1. Schematic diagram of the experimental system.

reference sample in our experiments on DME and R152a. The property data of R134a, including heat capacity and density, were taken from the NIST REFPROP database,8 and so were the liquid densities of DME and R152a. The accuracy of the experimental system and the method has been tested with typical materials.7 The deviations between the experimental results and the suggested values were within the experimental uncertainties.

reference sample. The heat capacity equation of the reference sample is known and reliable. The third test is carried out with the sample cell filled with the sample to be measured. The heat capacities of the reference sample and the sample were given by Cpref =

Cps =

(HFref − HFblank ) mref (dT /dt )ref

(1)

■

(HFsample − HFblank ) ms(dT /dt )s

EXPERIMENTAL RESULTS AND DISCUSSION Information of the sample DME and R152a as well as the R134a used as reference sample in this study is shown in Table 1. No further purification was done before the experiments.

(2)

where Cpref was the heat capacity of the reference sample, Cps was the heat capacity of the sample (kJ·kg−1·K−1). HFref, HFsample and HFblank were the heat flow signals detected during the three tests with the reference sample, sample, and blank cells (W). mref and ms were the masses of the reference sample and the sample in the cell (kg). (dT/dt)ref and (dT/dt)s were the rates of temperature increase of the reference sample and the sample (K·s−1). A comparison of eq 1 and eq 2 shows that the heat capacity of the sample could be obtained as Cps =

(HFsample − HFblank ) mref (dT /dt )ref (HFref − HFblank )

ms (dT /dt )s

Table 1. Source and Purity of the Experimental Compounds chemical name DMEa R152ab

Cpref

(3)

R134ac

Since the sample cell was completely filled with liquids throughout the tests, the masses could be obtained as mref = ρrefV for the reference sample and ms = ρsV for the sample. ρref and ρs are the densities of the reference sample and the sample (kg·m−3). V is the volume of the cell (m3). Thus, eq 3 could be reduced as (HFsample − HFblank ) ρref (dT /dt )ref Cps = Cpref (HFref − HFblank ) ρs (dT /dt )s

source Zhejiang Quhua Fluorochemstry Co. Ltd. (China) Zhejiang Research Institute of Chemical Industry (China) Honeywell (China) Co., Ltd.

mass fraction purity

purification method

water content (w/w %)

0.995

none

0.005

0.998

none

0.001

0.999

none

0.001

a DME = methoxymethane. bR152a = 1,1-difluoroethane. cR134a = 1,1,1,2-tetrafluoroethane.

The isobaric heat capacity of DME in the liquid phase was measured at temperatures from 305 K to 365 K and pressures up to 5 MPa. A total of 81 data points were obtained and they are listed in Table 2; 78 data points were obtained for R152a at temperatures from 305 K to 360 K and pressures up to 5 MPa, and the values are listed in Table 3. Figure 2 and Figure 3 showed the pressure dependence of the heat capacity for DME and R152a along different isotherms. The overall uncertainties of the heat capacity in Table 2 and Table 3 could be estimated according to the propagation law of uncertainty. For DME, the

(4)

From eq 4, it could be found out that with acquired experimental signals and known property information on the samples, the heat capacity of the measured sample could be obtained. Considering its widely accepted property information and its representativeness as a refrigerant, R134a was chosen to be the 2886

dx.doi.org/10.1021/je500512f | J. Chem. Eng. Data 2014, 59, 2885−2890

Journal of Chemical & Engineering Data

Article

Table 2. Heat Capacities Cp of Liquid DME at Temperatures T from 305.15 K to 365.15 K and Pressures P up to 5 MPaa

Table 3. Heat Capacities Cp of Liquid R152a at Temperatures T from 305.15 K to 360.15 K and Pressures P up to 5 MPaa

T

P

Cp

T

P

Cp

K

MPa

kJ·kg−1·K−1

K

MPa

kJ·kg−1·K−1

T

2.457 2.449 2.434 2.439 2.431 2.421 2.415 2.410 2.463 2.451 2.438 2.441 2.425 2.414 2.419 2.416 2.492 2.477 2.466 2.463 2.448 2.434 2.441 2.436 2.523 2.506 2.497 2.494 2.475 2.461 2.465 2.459 2.558 2.538 2.532 2.519 2.503 2.487 2.489 2.481 2.580

330.15 330.15 330.15 330.15 330.15 330.15 335.15 335.15 335.15 335.15 335.15 335.15 335.15 340.15 340.15 340.15 340.15 340.15 340.15 345.15 345.15 345.15 345.15 345.15 345.15 350.15 350.15 350.15 350.15 350.15 355.15 355.15 355.15 355.15 360.15 360.15 360.15 365.15 365.15 365.15

2.572 2.556 2.540 2.519 2.519 2.509 2.634 2.623 2.608 2.589 2.562 2.561 2.548 2.690 2.672 2.650 2.619 2.616 2.601 2.773 2.747 2.721 2.690 2.684 2.667 2.836 2.803 2.773 2.761 2.741 2.897 2.864 2.845 2.820 2.970 2.945 2.912 3.126 3.089 3.048

K

MPa

305.15 305.15 305.15 305.15 305.15 305.15 305.15 305.15 310.15 310.15 310.15 310.15 310.15 310.15 310.15 310.15 315.15 315.15 315.15 315.15 315.15 315.15 315.15 315.15 320.15 320.15 320.15 320.15 320.15 320.15 320.15 320.15 325.15 325.15 325.15 325.15 325.15 325.15 325.15

1.49 2.07 2.54 2.95 3.44 4.01 4.60 5.03 1.49 2.07 2.54 2.95 3.44 4.01 4.60 5.03 1.49 2.07 2.54 2.95 3.44 4.01 4.60 5.03 1.49 2.07 2.54 2.95 3.44 4.01 4.60 5.03 1.49 2.07 2.54 2.95 3.44 4.01 4.60

305.15 305.15 305.15 305.15 305.15 305.15 305.15 305.15 310.15 310.15 310.15 310.15 310.15 310.15 310.15 310.15 315.15 315.15 315.15 315.15 315.15 315.15 315.15 315.15 320.15 320.15 320.15 320.15 320.15 320.15 320.15 320.15 325.15 325.15 325.15 325.15 325.15 325.15 325.15 325.15 330.15

1.46 2.03 2.52 2.93 3.54 4.06 4.58 5.02 1.46 2.03 2.52 2.93 3.54 4.06 4.58 5.02 1.46 2.03 2.52 2.93 3.54 4.06 4.58 5.02 1.46 2.03 2.52 2.93 3.54 4.06 4.58 5.02 1.46 2.03 2.52 2.93 3.54 4.06 4.58 5.02 2.03

2.52 2.93 3.54 4.06 4.58 5.02 2.03 2.52 2.93 3.54 4.06 4.58 5.02 2.52 2.93 3.54 4.06 4.58 5.02 2.52 2.93 3.54 4.06 4.58 5.02 2.93 3.54 4.06 4.58 5.02 3.54 4.06 4.58 5.02 4.06 4.58 5.02 4.06 4.58 5.02

Cp −1

kJ·kg ·K 1.832 1.834 1.829 1.821 1.806 1.810 1.801 1.794 1.844 1.840 1.833 1.829 1.818 1.813 1.807 1.803 1.875 1.866 1.859 1.854 1.844 1.835 1.826 1.823 1.910 1.896 1.889 1.881 1.873 1.862 1.848 1.844 1.953 1.932 1.923 1.914 1.906 1.892 1.875

−1

T

P

Cp

K

MPa

kJ·kg−1·K−1

325.15 330.15 330.15 330.15 330.15 330.15 330.15 330.15 335.15 335.15 335.15 335.15 335.15 335.15 335.15 340.15 340.15 340.15 340.15 340.15 340.15 345.15 345.15 345.15 345.15 345.15 345.15 350.15 350.15 350.15 350.15 350.15 355.15 355.15 355.15 355.15 360.15 360.15 360.15

5.03 2.07 2.54 2.95 3.44 4.01 4.60 5.03 2.07 2.54 2.95 3.44 4.01 4.60 5.03 2.54 2.95 3.44 4.01 4.60 5.03 2.54 2.95 3.44 4.01 4.60 5.03 2.95 3.44 4.01 4.60 5.03 3.44 4.01 4.60 5.03 4.01 4.60 5.03

1.869 1.978 1.965 1.955 1.945 1.929 1.909 1.902 2.032 2.017 2.004 1.990 1.971 1.950 1.942 2.078 2.060 2.043 2.021 1.997 1.988 2.148 2.125 2.105 2.079 2.049 2.038 2.212 2.181 2.148 2.111 2.097 2.281 2.234 2.187 2.168 2.347 2.287 2.258

a

Standard uncertainties u are u (T) = 0.05 K, ur (P) = 0.002 and ur (Cp) = 0.018.

a

Standard uncertainties u are u (T) = 0.05 K, ur (P) = 0.002 and ur (Cp) = 0.021.

Pc and Tc are critical parameters, their values for DME were taken from the report by Wu et al.,1 while the values for R152a were from the work by Higashi et al.9 The dimensionless coefficients ai, bi, ci (i = 0, 1, 2) are listed in Table 4. The average absolute deviation (AAD %) and maximum absolute deviation (MAD %) between the experimental data and eq 5 were 0.17 % and 0.61 % for DME and 0.30 % and 1.0 % for R152a respectively, which showed good representation of the empirical equation to experimental results. Experimental data points in the present work were compared with literature reports. For liquid dimethyl ether, only two data sets were available for the isobaric heat capacity, which were reported by Kennedy et al.4 and Tanaka and Higashi.5 The work by Kennedy et al. was carried out in the temperature range of 137 K to 245 K along the saturation line, and there was

estimated uncertainty of Cp was 2.1 % and for R152a it was 1.8 %. To reproduce the experimental data, a uniform equation was used for both DME and R152a as below: CpM /R = A + BPr + CPr 0.5

P

(5)

A = a0 + a1(1 − Tr) + a 2(1 − Tr)−1 B = b0(1 − Tr)−3.5 C = c0(1 − Tr)−1.5 + c1(1 − Tr)−2

where Cp is the heat capacity (kJ·kg−1·K−1), M is the molar mass (g·mol−1), R = 8.31451 J·mol−1·K−1, Pr = P/Pc, Tr = T/Tc. 2887

dx.doi.org/10.1021/je500512f | J. Chem. Eng. Data 2014, 59, 2885−2890

Journal of Chemical & Engineering Data

Article

Figure 2. Heat capacities of DME at temperatures from 305 K to 365 K. □, present experimental points at T = 305 K; ×, 315 K; ○, 325 K; +, 335 K; △, 340 K; ▽, 345 K; ◇, 350 K; ☆, 355 K; ▷, 360 K; ◁, 365 K; ●, calculated saturated points; solid lines, eq 5

Figure 4. Comparison of the isobaric heat capacity of DME between the present data and experimental data from Tanaka and Higashi5 and equation of state by Wu et al.1 ▷, present work at T = 310 K; ◁, 320 K; ▽, 330 K; △, 340 K; ○, 350 K; □, 360 K; ▶, Tanaka and Higashi at T = 310 K; ◀, 320 K; ▼, 330 K; ▲, 340 K; ●, 350 K; ■, 360 K; solid lines, equation of state by Wu et al.

deviations from the equation of state and the deviations were considerable (about 6.5 %). Figure 5 showed the deviation plot

Figure 3. Heat capacities of R152a at temperatures from 310 K to 360 K. □, present experimental points at T = 310 K; +, 320 K; ○, 330 K; ×, 335 K; ☆, 340 K; △, 345 K; ▽, 350 K; ◇, 355 K; ◁, 360 K; ●, calculated saturated points; solid lines, eq 5 Figure 5. Deviations of the isobaric heat capacity of DME between the present experimental data and calculated values from the fundamental equation of state by Wu et al.1

no data in the liquid state. Tanaka and Higashi obtained 29 data points from 310 K to 360 K using a metal-bellows calorimeter. Besides, the latest fundamental equation of state for DME proposed by Wu et al.1 was also compared. As shown in Figure 4, data points in this work deviated negatively from the equation of state and agreed well with it at higher temperatures. Alternately, the points by Tanaka and Higashi showed positive

between our data and the equation of state. The average absolute deviation was 1.7 % and the maximum deviation was within 3 %. As claimed in Wu’s report, the correlated

Table 4. Parameters in Equation 5 for DME and R152a Tc/K Pc/MPa M/(g·mol−1) R/(J·mol−1·K−1) a0 a1 a2 b0 c0 c1 AAD %b MAD %b no. of points

DME

R152a

400.38 5.3368 46.068 8.31451 1.2510·10−03 (3.2531·10−05)a 2.1319·10−02 (1.5488·10−03) 1.7966·10−03 (9.6340·10−05) 6.4640·10−07 (1.4166·10−07) 2.1648·10−04 (4.5050·10−05) −1.4125·10−04 (2.2022·10−05) 0.17 0.61 81

386.41 4.5198 66.051 8.31451 2.5862·10−03 (8.3005·10−05) 2.2174·10−02 (2.5562·10−03) 1.6492·10−03 (1.0747·10−04) 2.8308·10−07 (8.4327·10−08) 1.2484·10−04 (4.4047·10−05) −9.5119·10−05 (1.9276·10−05) 0.30 1.0 78

The standard errors of the fitting coefficients are shown in the parentheses. bAAD % = (∑iN= 1|(Cpcal − Cpexp)/Cpcal|·100)/N, MAD % = max(|(Cpcal − Cpexp)/Cpcal|·100)N. a

2888

dx.doi.org/10.1021/je500512f | J. Chem. Eng. Data 2014, 59, 2885−2890

Journal of Chemical & Engineering Data

Article

Helmholtz free energy equation of state does not work well for the isobaric heat capacity for dimethyl ether; one possible reason might be that the available experimental data were very scattered and not usable in the development of the equation. Better agreement could be expected if the data points obtained in this work were to be used in the parameter correlating of the equation of state. Compared with the DME, R152a has a relatively more abundant property database, especially in heat capacity. Porichanskii et al.10 reported their experimental data for isobaric heat capacity of liquid R152a in a wide temperature range from 181 K to 386 K and a pressure range from 2 MPa to 20 MPa. Nakagawa et al.11 carried out measurements at temperatures from 275 K to 360 K and pressures up to 3 MPa with a flow calorimeter. Molar heat capacities of R152a at constant volume were also investigated by Magee in 1998.12 Outcalt and McLinden proposed a modified Benedict−Webb− Rubin (MBWR) equation of state for R152a,13 and with carefully correlated parameters from experimental data sets, the equation gives a good representation for the heat capacity of R152a. The comparison between our data and literature data is shown in Figure 6. Data points in this work agreed well with

Figure 7. Deviations of the isobaric heat capacity of R152a between the present experimental data and the fundamental equation of state by Outcalt and McLinden.13

Table 5. Saturated Liquid Heat Capacity Cpsat of DME at Different Temperatures T and Saturated Pressures Psat T

Psat

Cpsat

K

MPa

kJ·kg−1·K−1

305.15 310.15 315.15 320.15 325.15 330.15 335.15 340.15 345.15 350.15 355.15 360.15 365.15

0.716 0.819 0.933 1.059 1.196 1.346 1.510 1.688 1.881 2.089 2.315 2.558 2.820

2.465 2.481 2.504 2.533 2.569 2.613 2.667 2.731 2.807 2.895 2.997 3.115 3.249

Table 6. Saturated Liquid Heat Capacity Cpsat of R152a at Different Temperatures T and Saturated Pressures Psat

Figure 6. Comparison of the isobaric heat capacity of R152a between present data and literature data and the equation of state by Outcalt and McLinden.13 Present work at T = ▷, 310 K; ◁, 320 K; ◇, 330 K; ▽, 340 K; △, 350 K; ○, 355 K; □, 360 K; Nakagawa et al.11 at T = ▶, 310 K; ◀, 320 K; ◆, 330 K; ▼, 340 K; ▲, 350 K; ●, 355 K; ■, 360 K. The symbols half filled represent data from Porichanskii et al.10 at T = right pointing triangle, 310 K; left pointing triangle, 320 K; diamond, 330 K; down pointing triangle, 340 K; circle, 350 K; up pointing triangle, 355 K; square, 360 K; solid lines, equation of state by Outcalt and McLinden.

the equation of state while the points by Nakagawa et al. showed slightly negative deviations. Few data points by Porichanskii et al. were located in this region, and they trended to show positive deviations at higher pressures. The deviation plot between our data and the equation of state were further shown in Figure 7, the average absolute deviation was 0.52 % and the maximum deviation was within 1 %. With more data points obtained and better agreements with the fundamental equation of state, this work confirmed the reliability and accuracy of the existing equation of state to be used in isobaric heat capacity calculations for liquid R152a at elevated pressures. An extrapolation of eq 5 to saturated pressures along isotherms gives the saturated liquid heat capacities for DME and R152a. These values are listed in Table 5 and Table 6, respectively. Comparisons of saturated heat capacity were also carried out between our results and the literature reports, which

T

Psat

Cpsat

K

MPa

kJ·kg−1·K−1

305.15 310.15 315.15 320.15 325.15 330.15 335.15 340.15 345.15 350.15 355.15 360.15

0.727 0.835 0.955 1.087 1.233 1.393 1.567 1.758 1.965 2.191 2.435 2.700

1.858 1.875 1.898 1.928 1.965 2.011 2.066 2.133 2.211 2.302 2.403 2.512

are shown in Figure 8 for DME and Figure 9 for R152a. For DME, our results were much closer to the equation of state compared with the results by Tanaka and Higashi. The average absolute deviation and maximum deviation between our results and the equation of state were 1.3 % and 2.0 %. As for R152a, all the experimental points, our results as well as the results by Nakagawa et al., were close to the MBWR equation of state. The average absolute deviation and maximum deviation 2889

dx.doi.org/10.1021/je500512f | J. Chem. Eng. Data 2014, 59, 2885−2890

Journal of Chemical & Engineering Data

Article

and the National Basic Research Program of China, Project No. 2010CB227304. Notes

The authors declare no competing financial interest.

■

(1) Wu, J.; Zhou, Y.; Lemmon, E. W. An Equation of State for the Thermodynamic Properties of Dimethyl Ether. J. Phys. Chem. Ref. Data 2011, 40, 023104. (2) Ihmels, E. C.; Lemmon, E. W. Experimental Densities, Vapor Pressures, and Critical Point, and a Fundamental Equation of State for Dimethyl Ether. Fluid Phase Equilib. 2007, 260, 36−48. (3) Wu, J.; Liu, Z.; Wang, F.; Ren, C. Surface Tension of Dimethyl Ether from (213 to 368) K. J. Chem. Eng. Data 2003, 48, 1571−1573. (4) Kennedy, R. M.; Sagenkahn, M.; Aston, J. G. The Heat Capacity and Entropy, Heats of Fusion and Vaporization, and the Vapor Pressure of Dimethyl Ether. The Density of Gaseous Dimethyl Ether. J. Am. Chem. Soc. 1941, 63, 2267−2272. (5) Tanaka, K.; Higashi, Y. Measurements of the Isobaric Specific Heat Capacity and Density for Dimethyl Ether in the Liquid State. J. Chem. Eng. Data 2010, 55, 2658−2661. (6) Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K. B., Tignor, M., Miller, H. L. Eds. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change; Cambridge University Press: Cambridge, 2007. (7) Gao, N.; Jiang, Y.; Wu, J.; He, Y.; Chen, G. Measurements of the Isobaric Heat Capacity of R1234yf in Liquid Phase at Temperatures from 305 K to 355 K and Pressures up to 5 MPa. Fluid Phase Equilib. 2014, http://dx.doi.org/10.1016/j.fluid.2014.05.029. (8) Lemmon, E. W.; Huber, M. L.; Mclinden, M. O. NIST Standard Reference Database 23, NIST Reference Fluid Thermodynamic and Transport Properties - REFPROP, version 9.0; Standard Reference Data Program; National Institute of Standards and Technology: Gaithersburg, MD, 2010. (9) Higashi, Y.; Ashizawa, M.; Kabata, Y.; Majima, T.; Uematsu, M.; Watanabe, K. Measurements of Vapor−Pressure, Vapor Liquid Coexistence Curve and Critical Parameters of Refrigerant 152a. JSME Int. J. 1987, 30, 1106−1112. (10) Porichanskii, E. G.; Ponomareva, O. P.; Svetlichnyi, P. I. Study of the Isobaric Heat Capacity of Freon 152A in a Wide Range of Parametric Conditions. Izv. Vyash. Uchebo. Zaved Energy 1982, 3, 122− 125. (11) Nakagawa, S.; Hori, T.; Sato, H.; Watanabe, K. Isobaric Heat Capacity for Liquid 1-Chloro-1,1-difluoroethane and 1,1-Difluoroethane. J. Chem. Eng. Data 1993, 38, 70−74. (12) Magee, J. W. Molar Heat Capacity at Constant Volume of 1,1Difluoroethane (R152a) and 1,1,1-Trifluoroethane (R143a) from the Triple-Point Temperature to 345 K at Pressures to 35 MPa. Int. J. Thermophys. 1998, 19, 1397−1420. (13) Outcalt, S. L.; McLinden, M. O. A Modified Benedict−Webb− Rubin Equation of State for the Thermodynamic Properties of R152a (1,1-Difluoroethane). J. Phys. Chem. Ref. Data 1996, 25, 605−636.

Figure 8. Saturated liquid heat capacities of DME: ■, present work; ▲, Tanaka and Higashi;5 solid line, equation of state by Wu et al.1

Figure 9. Saturated liquid heat capacities of R152a: ■, present work; ▲, Nakagawa et al.;11 solid line, equation of state by Outcalt and McLinden.13

between our results and the equation of state were 0.53 % and 2.4 %, respectively.

■

CONCLUSIONS Measurements of the isobaric heat capacity in the liquid phase were carried out at temperatures from 305 K to 365 K for dimethyl ether and 305 K to 360 K for 1,1-difuoroethane. A total of 81 data points for DME and 78 data points for R152a were obtained. Based on the experimental results, a uniform equation was used to reproduce the data for DME and R152a. The equation showed good agreements with the experimental data with correlated parameters. Heat capacity of saturated liquid DME and R152a were obtained by extrapolating the correlated equation to saturated pressures along different isotherms. For the isobaric heat capacity for DME, experimental data in this work include more data points at wider conditions than the existing literature and could be useful in the modification of fundamental equation of states. As for R152a, experimental data in this work agreed well with the existing MBWR equation of state, which could confirm the reliability of the equation of state to be used in isobaric heat capacity calculations for liquid R152a at higher pressures.

■

REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel./fax: +86 571 87952464. Funding

This work is financially supported by the National Natural Science Foundation of China, under Contract No. 51206140, 2890

dx.doi.org/10.1021/je500512f | J. Chem. Eng. Data 2014, 59, 2885−2890