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Potential R-114 replacement refrigerants.

INTRODUCTION

In the introduction to his 2007 paper published in HVAC&R Research, Brown (2007b) states
  Even though CFCs are scheduled for phase-out, many will still be used
  for some time in the future. For example, R-11, R-12, R-113 and R-114
  are presently used in industrial processes operating under high
  ambient conditions and in high-temperature heat pumps, with R-114
  being the most widely used refrigerant in these applications.
  However, as this equipment is being considered for replacement or for
  new applications, alternative heating technologies are being
  considered since no known and viable non-CFC retrofit refrigerants
  are available. Moreover, with the recent run-up in primary energy
  costs and expected price pressures for primary energy persisting into
  the near- and mid-term future, it is anticipated that there will be
  renewed interest in high-temperature heat pumps for many possible
  applications. Therefore, a strong need exists to identify and develop
  new refrigerants and technologies to allow for the continued
  application of and expanded use of high-temperature heat pumps
  despite the scheduled phase-out of CFC refrigerants.


The goal of this paper, therefore, is to contribute to the search for suitable R-114 replacement refrigerants. In particular, this paper uses the methodology for evaluating the thermodynamic performance potentials of alternative refrigerants described in, for example, Reid et al. (1987) and Poling et al. (2001)--and illustrated in recent publications by Brown (2007a, 2007b, 2008)--to evaluate 56 potential R-114 replacement refrigerants for high-temperature heat-pumping applications. In particular, 36 pure fluids and 20 near-azeotropes are considered.

This paper describes the general methodologies used to establish a list of R-114 substitute refrigerants and their performance potential and suitability for high-temperature heat-pumping applications. Results are presented for each refrigerant, including a list of the important thermodynamic parameters (Brown 2007b), a list of simulation results for an idealized ideal vapor compression refrigeration cycle, and a discussion of the relative merits of the various refrigerants. Finally, conclusions are drawn and presented.

METHODOLOGY

Establishing a List of Potential Replacement Refrigerants

The methodology used to generate the list of potential R-114 replacement refrigerants consists of an extensive literature search of the following publications:

* every issue of the International Journal of Refrigeration dating back to 1988

* every issue of the IIR Bulletin dating back to 1994

* every issue of ASHRAE Transactions dating back to 1998

* every issue of HVAC&R Research

* US patents dating back to 1976

* US patent applications dating back to 2002

* extensive online database searches

The initial (though nondefinitive) approach used to screen the literature quickly to determine if a refrigerant was to be considered a potential R-114 replacement refrigerant consisted of one or more of the following criteria: (1) its critical temperature was between 120[degrees]C and 200[degrees]C (248[degrees]F and 392[degrees]F), (2) its normal boiling point temperature was between -5[degrees]C and 15[degrees]C (23[degrees]F and 59[degrees]F), (3) its vapor pressure at 25[degrees]C (77[degrees]F) was within [+ or -]10% that of R-114 at the same temperature, and (4) the reference source claimed the refrigerant to be an R-1 14 replacement. A refrigerant was eliminated from this list if it: (1) had an ODP > 0.05 or was a banned substance per the Montreal Protocol, (2) had a GWP greater than 2000, (3) was an ASHRAE Class 3 flammable refrigerant, or (4) was a zeotrope with a temperature glide greater than 5[degrees]C (9[degrees]F). This approach generated 56 preliminary refrigerants-36 pure fluids and 20 near-azeotropes.

Evaluation of Refrigerant Performance Potential

There are many ways that one can estimate or establish the thermodynamic performance potential (heating coefficient of performance [[COP.sub.H]] and volumetric heating capacity [VHC]) of a refrigerant for high-temperature heat-pumping applications. For example, one could resort to experimental investigation or detailed system modeling. However, at least two drawbacks to these types of approaches are that they can be expensive and time-consuming, particularly when evaluating a large number of refrigerants. Perhaps a more effective starting point--the one used in this paper--for estimating the thermodynamic performance potential of a large number of potential replacement refrigerants, would be to estimate COPH and VHC in an idealized vapor compression refrigeration cycle. The advantages of this approach are: (1) it avoids unnecessary, expensive, and time-consuming experimentation and detailed system modeling for refrigerants that, in the end, will prove not to be suitable replacements and (2) it easily and quickly can be used to narrow a large list of potential replacement refrigerants to a much shorter and more focused list, which then can be investigated more in depth using experimentation or detailed system modeling.

Standard Evaluation Cycle

Since the particular interest of this paper is high-temperature heat-pumping applications, each refrigerant was evaluated in a standard cycle typical of such applications. In particular, the cycle consists of an idealized vapor compression refrigeration cycle composed of a constant evaporation temperature of 26.7[degrees]C (80[degrees]F), a constant condensation temperature of 85[degrees]C (185[degrees]F), a condenser subcooling of 11.1[degrees]C (20[degrees]F), a compressor isentropic efficiency of 85%, and the minimum amount of evaporator superheat that ensures saturated or superheated vapor at the compressor outlet.

Simulation Model

A beta version of the National Institute for Standards and Technology's CYCLE_D model (Brown et al. 2007c) was used to model the thermodynamic performance of each refrigerant in the idealized vapor compression refrigeration cycle described above. The commercially available CYCLE_D Version 3.0 (Domanski et al. 2003) is a thermo-dynamic cycle model representing eleven state points, composed of an evaporator, a compressor, a condenser, a liquid-line suction-line heat exchanger, and an expansion device, which uses REFPROP 7.0 (Lemmon et al. 2002) to model the thermodynamic properties of 37 pure fluids and five mixtures of various combinations of these pure fluids. The beta version of CYCLE_D has all the capabilities of Version 3.0 but, in addition, contains several features and thermodynamic cycles not contained in Version 3.0. For the purposes of this paper, the relevant capabilities of the beta version are: (1) it is based on REFPROP 8.0 (Lemmon et al. 2007) and (2) it contains a database of 93 pure fluids. Of these 93 pure fluids, 61 of them are contained in REFPROP 8.0. Their thermodynamic properties are calculated using the default, high-accuracy equations of state contained in REFPROP 8.0; whereas, the thermodynamic properties of the remaining 32 fluids are calculated using the Peng-Robinson equation of state, as implemented in REFPROP 8.0, where the required fundamental thermodynamic parameters are estimated using the methodology as described in, for example, Reid et al. (1987) and Poling et al. (2001). (See Brown [2008] for a detailed discussion of this methodology.)

RESULTS AND DISCUSSION

Determination of Thermodynamic Parameters

The literature survey described above generated 36 pure fluids and 20 near-azeotropes as potential R-114 replacement refrigerants. Table 1 lists the 36 pure fluids and Table 2 lists the 20 near-azeotropes. In addition to the fluids listed in Tables 1 and 2, Table 3 contains another seven pure fluids, which, though not directly potential R-114 replacements, are used to form some of the 20 near-azeotropes listed in Table 2. In all, there are 63 potential replacement refrigerants, of which 16 of the pure fluids and six of the near-azeotropes are contained in the database REFPROP 8.0 database (Lemmon et al. 2007), leaving a total of 41 refrigerants whose thermodynamic parameters need to be estimated using the approach illustrated in Brown (2008). The thermodynamic parameters required for this approach are normal boiling point temperature (NBP), critical temperature ([T.sub.c]), critical pressure ([P.sub.c]), critical density ([[rho].sub.c]), ideal gas specific heat at constant pressure ([c.sub.p.sup.o]), and acentric factor ([omega]), which are all provided in Tables 1, 2, and 3 in nondimensional terms (referenced to R-114 values). In particular, the respective nondimensional terms are [[tau].sub.NBP] (relative normal boiling point temperature), [[tau].sub.c] (relative critical temperature), [[PI].sub.c] (relative critical pressure), [[delta].sub.c] (relative critical density), CP (relative ideal gas specific heat at constant pressure), and AF (relative acentric factor). (Note, temperature ratios must be made using an absolute scale of Rankine or Kelvin.) Finally, to allow one to convert easily the nondimensional values of Tables 1, 2, and 3 to dimensional terms, Table 4 provides the values of NBP, [T.sub.c], [P.sub.c], [[rho].sub.c], [c.sub.p.sup.o], and co in both SI and I-P units for R-114.
Table 1. Nondimensional Thermodynamic Parameters for Thirty-Six Pure
Fluids that are Potential R-114 Replacements (Note: Superscripts
Indicate Data Source)

Refrigerant                   Formula                 [[tau].sub.NBP]

HFE7100               [CH.sub.3]O-3 ([F.sub.2])-          1.207 (1)
                      [CH.sub.3]

R-601                 [CH.sub.3]-3 ([CF.sub.2])-          1.117 (3)
                      [CH.sub.3]

R-E347mmc             [CH.sub.3] [OCF.sub.2]              1.114 (4)
                      ([CF.sub.2])- [CH.sub.3]

HFE7000               [CH.sub.3] [OCF.sub.2]              1.110 (1)
                      [CF.sub.2] [CF.sub.3]

R-E347mmy1            [CH.sub.3] [OCF.sub.2]              1.093 (5)
                      [CF.sub.2] [CF.sub.3]

R-E236ca              [CHF.sub.2] [OCF.sub.2]             1.090 (9)
                      [CHF.sub.2]

TMS                   Si[([CH.sub.3]).sub.4]              1.083 (7)

R-601a                [([CH.sub.3]).sub.2]                1.088 (3)
                      [CHCH.sub.2] [CH.sub.3]

R-356mff              [CF.sub.3][CH.sub.2]                1.077 (6)
                      [CH.sub.2][CF.sub.3]

R-245eb               [CH.sub.2][FCHFCF.sub.3]            1.070 (8)

R-245ca               [CHF.sub.2] [CF.sub.2]              1.078 (3)
                      [CH.sub.2]F

R-338mf               [CF.sub.3] [CH.sub.2]               1.052 (6)
                      [CF.sub.2] [CF.sub.3]

[SF.sub.5]            [SF.sub.5] [C.sub.2] [F.sub.5]      1.034 (9)
[C.sub.2]
[F.sub.5]

N                     N[([CF.sub.3]).sub.2]               1.025 (9)
[([CF.sub.3]).sub.2]  ([CH.sub.3])
([CH.sub.3])

R-245fa               [CF.sub.3] [CH.sub.2]               1.042 (3)
                      [CHF.sub.2]

R-631                 [CH.sub.3] [CH.sub.2]               1.047 (10)
                      [(NH.sub.2)]

[SF.sub.5]            [SF.sub.5] [CF.sub.2]H              1.005 (9)
[CF.sub.2]H

R-E236fa              [CF.sub.3] [OCH.sub.2]              1.007 (9)
                      [CF.sub.3]

R-272fb               [CH.sub.3] [CH.sub.2]               1.017 (6)
                      [CHF.sub.2]

R-E245cb 1            [CH.sub.3] [OCF.sub.3]              1.007 (11)
                      [CF.sub.2]

R-E263fb              [CF.sub.3] [OCH.sub.2]              1.009 (9)
                      [CH.sub.3]

R-236ca               [CF.sub.3] [CF.sub.2]               1.005 (13)
                      [CHF.sub.2]

R-E161                [CH.sub.2] [FOCH.sub.3]             1.023 (9)

R-236ea               [CHF.sub.2] [CHFCF.sub.3]           1.009 (3)

R-CE225e              [CF.sub.2] [CHFCF.sub.2]            0.999 (9)
                      O-cyclo

R-143                 [CH.sub.2] [FCHF.sub.2]            1.005 (13)

R-E134                [CHF.sub.2] [OCHF.sub.2]           1.009 (14)

R-236cb               [CH.sub.2] [FCF.sub.2]             0.983 (13)
                      [CF.sub.3]

R-254cb               [CHF.sub.2] [CF.sub.2]             0.984 (13)
                      [CH.sub.3]

R-1311                [CF.sub.3]I                        0.908 (3)

R-630                 [CH.sub.3] [NH.sub.2]              0.964 (10)

R-764                 [SO.sub.2]                         0.951 (3)

R-E170                [CH.sub.3][OCH.sub.3]              0.897 (3)

R-152a                [CHF.sub.2] [CH.sub.3]             0.900 (3)

R-C270                [CH.sub.2] [CH.sub.2]              0.873 (3)
                      [CH.sub.2]-cyclo

R-171                 [NH.sub.3]                         0.867 (3)

Refrigerant                         [[tau].sub.c]  [[PHI].sub.c]

HFE7100                                1.118(1)       0.685 (1)

R-601                                  1.121 (3)      1.035 (3)

R-E347mmc                              1.045 (4)      0.760 (4)

HFE7000                                1.046 (1)      0.761 (1)

R-E347mmy1                             1.036 (5)      0.783 (5)

R-E236ca                               1.040 (2)      0.816 (2)

TMS                                    1.071 (7)      0.866 (7)

R-601a                                 1.099 (3)      1.037 (3)

R-356mff                               1.028 (2)      0.765 (2)

R-245eb                                1.051 (2)      0.905 (2)

R-245ca                                1.069 (3)      1.205 (3)

R-338mf                                0.990 (2)      0.677 (2)

[SF.sub.5][C.sub.2][F.sub.5]           0.981 (2)      0.698 (2)

N [([CF.sub.3]).sub.2]([CH.sub.3])     0.985 (2)      0.804 (2)

R-245fa                                1.020 (3)      1.121 (3)

R-631                                  1.089 (10)     1.723 (10)

[SF.sub.5][CF.sub.2]H                  0.997 (2)      0.952 (2)

R-E236fa                               0.961 (2)      0.816 (2)

R-272fb                                1.026(2)       1.149 (2)

R-E245cb 1                             0.971 (12)     0.886 (12)

R-E263fb                               0.986 (2)      1.028 (2)

R-236ca                                0.984 (13)     1.013 (13)

R-E161                                 1.044 (2)      1.427 (2)

R-236ea                                0.985 (3)      1.075 (3)

R-CE225e                               0.961 (2)      0.865 (2)

R-143                                  1.029 (13)     1.300 (13)

R-E134                                 1.003 (14)     1.298 (14)

R-236cb                                0.963 (13)     0.957 (13)

R-254cb                                1.001 (13)     1.152 (13)

R-1311                                 0.947 (3)      1.214 (3)

R-630                                  1.028 (10)     2.338 (10)

R-764                                  1.028 (3)      2.421 (3)

R-E170                                 0.960 (3)      1.633 (3)

R-152a                                 0.923 (3)      1.387 (3)

R-C270                                 0.951 (3)      1.713 (3)

R-171                                  0.968 (3)      3.480 (3)

Refrigerant                   [[delta].sub.c]     CP           AF

HFE7100                          0.654 (1)     2.0602 (2)  1.714 (2)

R-601                            0.948 (3)     1.261 (3)   0.995 (3)

R-E347mmc                        0.781 (4)     1.774(2)    1.600 (2)

HFE7000                          0.815 (1)     1.590 (2)   1.571 (2)

R-E347mmy1                       0.779 (2)     1.581 (2)   1.519 (2)

R-E236ca                         0.953 (2)     1.245 (2)   1.459 (2)

TMS                              0.814 (7)     1.312 (7)   0.977 (7)

R-601a                           0.964 (3)     1.245 (3)   0.901 (3)

R-356mff                         0.856 (2)     1.379 (2)   1.354 (2)

R-245eb                          1.070 (2)     1.085 (2)   1.152 (2)

R-245ca                          1.151 (3)     1.128 (3)   1.402 (3)

R-338mf                          0.791 (2)     1.494 (2)   1.400 (2)

[SF.sub.5][C.sub.2][F.sub.5]     0.854 (2)     1.472 (2)   1.312 (2)

N [([CF.sub.3]).sub.2]           0.923 (2)     1.300 (2)   1.316 (2)
([CH.sub.3])

R-245fa                          1.135 (3)     1.051 (3)   1.500 (3)

R-631                            1.619 (10)    0.724 (10)  1.146 (2)

[SF.sub.5][CF.sub.2]H            1.188 (2)     1.033 (2)   1.075 (2)

R-E236fa                         0.953 (2)     1.214 (2)   1.459 (2)

R-272fb                          1.263 (2)     0.855 (2)   1.074 (2)

R-E245cb 1                       0.999 (11)    1.158 (2)   1.417 (2)

R-E263fb                         1.103 (2)     1.022 (2)   1.417 (2)

R-236ca                          1.051 (2)     1.103 (2)   1.368 (2)

R-E161                           1.600 (2)     0.679 (2)   1.221 (2)

R-236ea                          1.091 (3)     1.117 (3)   1.504 (3)

R-CE225e                         0.998 (2)     1.021 (2)   1.422 (2)

R-143                            1.289 (2)     0.695 (2)   1.044 (2)

R-E134                           1.321 (14)    0.874 (2)   1.495 (2)

R-236cb                          1.015 (2)     1.109 (2)   1.274 (2)

R-254cb                          1.175 (2)     0.985 (2)   0.980 (2)

R-1311                           1.306 (3)     0.536 (3)   0.720 (3)

R-630                            1.907 (10)    0.460 (10)  1.157 (2)

R-764                            2.415 (3)     0.322 (3)   1.013 (3)

R-E170                           1.656 (3)     0.585 (3)   0.763 (3)

R-152a                           1.642 (3)     0.586 (3)   1.091 (3)

R-C270                           1.810 (3)     0.554 (3)   0.517 (3)

R-171                            3.894 (3)     0.281 (3)   1.015 (3)

(1.) 3M (2007); (2.) Reid et al (1987) and Poling et al. (2001); (3.)
Lemmon et al. (2007); (4.) Ohta et al. (2001); (5.) Calm and Hourahan
(2007); (6.) Minor (2007); (7.) NIST (2007); (8.) ABCR (2007); (9.)
Bivens and Minor (1998); (10.) CHERIC (2007); (11.) Yoshii et al.
(2000); (12.) Yasumoto et al. (1996); (13.) Devotta and Penyala (1994);
(14.) Defibaugh et al. (1992)

Table 2. Nondimensional Thermodynamic Parameters for Twenty Near-
Azeotropes that are Potential R-114 Replacements

Binary Mixture          Mass      Reference Source  [[tau].sub.c]
                      Fractions    (US Patent #)

R-245fa/methanol     0.955/0.005      5,683,974        1.024
R-245fa/cyclopetane  0.950/0.050      5,672,294        1.038
R-245fa/n-hexane     0.980/0.020      5,672,294        1.026
R-245fa/ethanol      0.998/0.002      5,683,974        1.021
R-245fa/i-hexane     0.980/0.020      5,672,294        1.025
R-245fa/n-propanol   0.999/0.001      5,683,974        1.020
R-245fa/i-propanol   0.999/0.001      5,683,974        1.020
R-245fa/R-601        0.950/0.050      5,866,029        1.029
R-245fa/R-601a       0.950/0.050      5,866,029        1.027
R-245fa/TMS          0.780/0.220      5,854,296        1.035
R-272fb/R-E236fa     0.177/0.823      6,905,630        0.982
R-236ea/R-E170       0.993/0.007      6,013,194        0.984
R-236ea/R-CE225e     0.085/0.915      6,905,630        0.963
R-236ea/R-E134       0.472/0.528      6,905,630        0.996
R-356mff/R-E134      0.029/0.971      6,905,630        1.004
R-143/R-E236ca       0.880/0.120      6,905,630        1.030
R-143/R-E134         0.621/0.379      6,905,630        1.021
R-338mf/R-E134       0.345/0.655      6,905,630        1.000
R-236cb/R-CE225e     0.833/0.167      6,905,630        0.963
R-E134/R-CE225e      0.356/0.644      5,607,616        0.979

Binary Mixture       [[pi].sub.c]  [[delta].sub.c]    CP

R-245fa/methanol         1.135            1.148      1.041
R-245fa/cyclopetane      1.208            1.135      1.052
R-245fa/n-hexane         1.134            1.120      1.066
R-245fa/ethanol          1.124            1.137      1.050
R-245fa/i-hexane         1.136            1.120      1.066
R-245fa/n-propanol       1.122            1.135      1.051
R-245fa/i-propanol       1.122            1.135      1.051
R-245fa/R-601            1.172            1.115      1.068
R-245fa/R-601a           1.185            1.117      1.067
R-245fa/TMS              1.242            1.015      1.131
R-272fb/R-E236fa         0.958            1.032      1.104
R-236ea/R-E170           1.041            1.101      1.105
R-236ea/R-CE225e         0.919            1.005      1.029
R-236ea/R-E134           1.202            1.216      0.973
R-356mff/R-E134          1.313            1.306      0.884
R-143/R-E236ca           1.280            1.261      0.730
R-143/R-E134             1.300            1.299      0.751
R-338mf/R-E134           1.340            1.141      1.021
R-236cb/R-CE225e         0.972            1.012      1.094
R-E134/R-CE225e          1.190            1.109      0.962

Table 3. Nondimensional Thermodynamic Parameters for Seven Additional
Pure Fluids Used to Create some of the Near-Azeotropes Listed in Table
2 (Note: Superscripts Indicate Data Source [see Table 1])

Refrigerant    Formula                 [[tau].sub.NBP]  [[tau].sub.c]

Ethanol        [C.sub.2] [H.sub.6]O       1.2703 (3)       1.227 (3)

n-hexane       [CH.sub.3]                 1.235 (3)        1.212 (3)
               CH[[(CH.sub.2)].sub.2]
               [CH.sub.3]

i-hexane       [[(CH.sub.3)].sub.2        1.205 (3)        1.188 (3)
               CH[[(CH.sub.2)].sub.2]
               [CH.sub.3]

Methanol       [CH.sub.3]OH               1.220 (3)        1.226 (3)

cyclo-pentane  5[(CH.sub.2)]-cyclo        1.165 (10)       1.222 (10)

n-propanol     [CH.sub.3] [CH.sub.2]      1.338 (10)       1.282 (10)
               [CH.sub.2]OH

i-propanol     [[(CH.sub.3)].sub.2]       1.284 (10)       1.214 (10)
               CHOH

Refrigerant    Formula                 [[PHI].sub.c]  [[delta].sub.c]

Ethanol        [C.sub.2] [H.sub.6]O        1.888 (3)      1.766 (3)

n-hexane       [CH.sub.3]                  0.932 (3)      0.797 (3)
               CH[[(CH.sub.2)].sub.2]
               [CH.sub.3]

i-hexane       [[(CH.sub.3)].sub.2]        0.933 (3)      0.800 (3)
               CH[[(CH.sub.2)].sub.2]
               [CH.sub.3]

Methanol       [CH.sub.3]OH                2.523 (3)      2.589 (3)

cyclo-pentane  5[(CH.sub.2)]-cyclo         1.385 (10)     1.138 (10)

n-propanol     [CH.sub.3] [CH.sub.2]       1.587 (10)     1.352 (10)
               [CH.sub.2] OH

i-propanol     [[(CH.sub.3)].sub.2]        1.463 (10)     1.328 (10)
               CHOH

Refrigerant               Formula                    CP        AF

Ethanol        [C.sub.2] [H.sub.6]O                 0.743  2.553 (3)
                                                    (3)

n-hexane       [CH.sub.3] CH[[(CH.sub.2)].sub.2]    1.595  1.185 (3)
               [CH.sub.3]                           (3)

i-hexane       [[(CH.sub.3)].sub.2]                 1.588  1.109 (3)
               CH[[(CH.sub.2)].sub.2] [CH.sub.3]    (3)

Methanol       [CH.sub.3]OH                         0.440  2.229 (3)
                                                    (3)

cyclo-pentane  5[(CH.sub.2)]-cyclo                  1.113  0.777 (10)
                                                    (10)

n-propanol     [CH.sub.3][CH.sub.2] [CH.sub.2] OH   0.973  2.469 (10)
                                                    (10)

i-propanol     [[(CH.sub.3)].sub.2] CHOH            0.960  2.636 (10)
                                                    (10)

Table 4. Thermodynamic Parameter Values for R-114 in SI and I-P Units
(Lemmon et al. 2007)

         NBP         [T.sub.c]        [P.sub.c]  [[rho].sub.c]

SI       276.74K     418.83K          3257 kPa   3.393 kmol.
Units                                            [m.sup.-3]

English  498.1       753.9[degrees]R  472.4      0.2118
Units    [degrees]R                   psia       lbmol.[ft.sup.-3]

                     [c.sub.p.sup.o]                         w

SI Units       137.9 KJ9*[kmol.sup.-1][K.sup.-1]            0.2523

English Units  33.0 Btu*[Ibmol.sup.-1][degrees][R.sup.-1]  0.2523


A few further comments are in order regarding Tables 1-3: (1) the superscripts in Tables 1 and 3 provide references for the data sources, and the third column of Table 2 provides the reference where the near-azeotrope was found; (2) the refrigerants of Tables 1 and 2 are listed in the same ascending order as in Tables 5 and 6--that is, they are listed from the lowest VHC ratio ([VHC.sub.refrig]/[VHC.sub.R-114]) to the highest VHC ratio, which will is explained in more detail below; (3) the mixture properties of Table 2, as well as the mixture properties used to calculate the values in Table 6, are estimated using Lemmon and Jacobsen's method (1999).
Table 5. Nondimensional Cycle Simulation Results and Environmental and
Safety Characteristics for Thirty-Six Pure Fluids that Are Potential R-
114 Replacements (Note: Superscripts Indicate Data Source)

              Refrigerant           [COP.sub.H] Ratio  VHC Ratio

HFE7100                                   1.061          0.179

R-601                                     1.054          0.403

R-E347mcc                                 1.034          0.420

HFE7000                                   1.033          0.422

R-E347mmy1                                1.028          0.483

R-E236ca                                  1.030          0.501

TMS                                       1.039          0.504

R-601a                                    1.045          0.504

R-356mff                                  1.022          0.539

R-245eb                                   1.038          0.584

R-245ca                                   1.040          0.599

R-338mf                                   0.996          0.637

[SF.sub.5][C.sub.2] [F.sub.5]             0.987          0.721

N[[(CF.sub.3)].sub.2] [(CH.sub.3)]        0.990          0.811

R-245fa                                   1.019          0.824

R-631                                     1.086          0.887

[SF.sub.5][CF.sub.2]H                     0.992          0.935

R-E236fa                                  0.969          0.946

R-272fb                                   1.036          0.954

R-E245cb1                                 0.981          0.971

R-E263fb                                  1.000          1.017

R-236ca                                   0.992          1.023

R-E161                                    1.068          1.023

R-236ea                                   0.992          1.027

R-CE225e                                  0.977          1.038

R-143                                     1.060          1.113

R-E134                                    1.026          1.124

R-236cb                                   0.969          1.153

R-254cb                                   1.007          1.158

R-13I1                                    1.000          2.063

R-630                                     1.066          2.082

R-764                                     1.052          2.355

R-E170                                    1.007          2.521

R-152a                                    0.984          2.628

R-C270                                    1.009          3.038

R-717                                     1.019          5.462

              Refrigerant          [V.sub.comp]  [T.sub.comp,disch]
                                       Ratio           Ratio

HFE7100                                5.599           1.000

R-601                                  2.483           1.000

R-E347mcc                              2.385           1.000

HFE7000                                2.374           1.000

R-E347mmy1                             2.069           1.000

R-E236ca                               1.995           1.000

TMS                                    1.986           1.000

R-601a                                 1.982           1.000

R-356mff                               1.856           1.000

R-245eb                                1.712           1.001

R-245ca                                1.672           1.000

R-338mf                                1.570           1.000

[SF.sub.5][C.sub.2] [F.sub.5]          1.386           1.000

N[[(CF.sub.3)].sub.2][(CH.sub.3)]      1.234           1.000

R-245fa                                1.214           1.000

R-631                                  1.129           1.049

[SF.sub.5][CF.sub.2]H                  1.069           1.000

R-E236fa                               1.057           1.000

R-272fb                                1.048           1.003

R-E245cb1                              1.031           1.000

R-E263fb                               0.984           1.000

R-236ca                                0.977           1.000

R-E161                                 0.978           1.046

R-236ea                                0.975           1.000

R-CE225e                               0.963           1.000

R-143                                  0.897           1.033

R-E134                                 0.891           1.004

R-236cb                                0.868           1.000

R-254cb                                0.864           1.000

R-13I1                                 0.485           1.050

R-630                                  0.480           1.136

R-764                                  0.425           1.198

R-E170                                 0.397           1.045

R-152a                                 0.381           1.051

R-C270                                 0.329           1.051

R-717                                  0.183           1.205

      Refrigerant      [T.sub.evap,sup]    Environmental and Safety
                             Ratio             Characteristics

HFE7100                      2.605       GWP = 390 (2) and nonflam (4)

R-601                        1.000               LFL = 1.4% (1)

R-E347mcc                    2.447               GWP = 480 (2)

HFE7000                      2.105       GWP = 370 (4) and nonflam (4)

R-E347mmy1                   2.174               GWP = 343 (1)

R-E236ca                     1.421

TMS                          1.816

R-601a                       1.000                   A3 (1)

R-356mff                     1.789            LT = 7.9 [y.sup.2]

R-245eb                      1.000

R-245ca                      0.684       LFL = 7.1% (1), GWP = 640 (2)

R-338mf                      2.118             GWP probably high

[SF.sub.5][C.sub.2]          2.253
[F.sub.5]

N[[(CF.sub.3)].sub.2]        1.663
[(CH.sub.3)]

R-245fa                      0.421          B1 (1), GWP = 950 (2)

R-631                        0.000              LFL = 3.5% (1)

[SF.sub.5][CF.sub.2]H        1.000

R-E236fa                     1.400               GWP = 470 (2)

R-272fb                      0.000             F/(F + H) = 0.25

R-E245cb1                    1.211       flammable (1) GWP = 580 (2)

R-E263fb                     0.684             F/(F + H) = 0.38

R-236ca                      1.000

R-E161                       0.000             F/(F + H) = 0.17

R-236ea                      1.000              GWP = 1200 (2)

R-CE225e                     0.484             LT = 2 6 [y.sup.3]

R-143                        0.000       F/(F+H) = 0.5, GWP = 330 (2)

R-E134                       0.000             GWP = 6100 (2)

R-236cb                      1.053             GWP = 1300 (2)

R-254cb                      0.789              F/(F+H) = 0.5

R-13I1                       0.000       ODP < 0.018 (1), GWP = 1 (2)

R-630                        0.000             LFL = 4.9% (1)

R-764                        0.000            B11, GWP = 300 (1)

R-E170                       0.000                  A3 (1)

R-152a                       0.000          A2 (1), GWP = 120 (2)

R-C270                       0.000              LFL = 2.4% (1)

R-717                        0.000            B2 (1), GWP <1 (1)

1. Calm and Hourahan (2007); 2, IPCC (2001); 3. Bivens and Minor
 (1998); 4.3m (2007)

Note: Al ... A3 and B1 ... B3 = ASHRAE safety classifications; F/(F+H)
 = number of fluorine atoms relative to the warming potential; ODP =
ozone depletion potential; LFL = lower flammability limit; LT =
atmospheric life

Table 6. Nondimensional Cycle Simulation Results for Twenty
Near-Azeotropes that are Potential R-114 Replacements

Binary Mixture            Mass       [COP.sub.H]   VHC   [V.sub.comp]
                       Fractions        Ratio     Ratio      Ratio

R-245fa/methanol      0.995/0.005      0.989      0.748      1.337

R-245fa/cyclopentane  0.950/0.050      1.020      0.773      1.293

R-245fa/n-hexane      0.980/0.020      1.011      0.776      1.289

R-245fa/ethanol       0.998/0.002      1.003      0.790      1.266

R-245fa/i-hexane      0.980/0.020      1.017      0.797      1.255

R-245fa/n-propanol    0.999/0.001      1.005      0.797      1.255

R-245fa/i-propanol    0.999/0.001      1.012      0.808      1.237

R-245fa/R-601         0.950/0.050      1.020      0.817      1.224

R-245fa/R-601a        0.950/0.050      1.014      0.840      1.191

R-245fa/TMS           0.780/0.220      1.006      0.870      1.150

R-272fb/R-E236fa      0.177/0.823      0.986      0.965      1.037

R-236ea/R-E170        0.993/0.007      0.988      1.040      0.962

R-236ea/R-CE225e      0.085/0.915      0.973      1.062      0.942

R-236ea/R-E134        0.472/0.528      1.007      1.094      0.915

R-356mff/R-E134       0.029/0.971      1.022      1.122      0.892

R-143/R-E236ca        0.880/0.120      1.062      1.122      0.891

R-143/R-E134          0.621/0.379      1.052      1.135      0.881

R-338mf/R-E134        0.345/0.655      0.984      1.136      0.880

R-236cb/R-CE225e      0.833/0.167      0.967      1.159      0.863

R-E134/R-CE225e       0.356/0.644      0.979      1.207      0.829

   Binary Mixture      [T.sub.evap,sup] Ratio/  [T.sub.evap,glide]/
                      [T.sub.comp,disch] Ratio  [T.sub.cond,glide],
                                                     [degrees]C

R-245fa/methanol             0.237/1.002              2.57/1.27

R-245fa/cyclopentane         0.405/1.002              0.93/1.36

R-245fa/n-hexane             0.474/1.002              1.20/1.34

R-245fa/ethanol              0.358/1.001              1.18/0.49

R-245fa/i-hexane             0.489/1.001              0.47/0.69

R-245fa/n-propanol           0.384/1.0                1.0/0.4

R-245fa/i-propanol           0.411/1.0                0.54/0.24

R-245fa/R-601                0.511/1.0                0.01/0.13

R-245fa/R-601a               0.505/1.0                0.22/0.05

R-245fa/TMS                  0.921/1.0                0.0/0.23

R-272fb/R-E236fa             1.074/1.0                0.02/0.04

R-236ea/R-E170               0.947/1.001              0.27/0.42

R-236ea/R-CE225e             0.521/1.0                0.14/0.22

R-236ea/R-E134               0.389/1.0                0.0/0.01

R-356mff/R-E134              0.0/1.003                0.06/0.01

R-143/R-E236ca               0.0/1.017                0.03/0.17

R-143/R-E134                 0.0/1.019                0.0/0.07

R-338mf/R-E134               0.568/1.0                0.25/0.0

R-236cb/R-CE225e             1.005/1.0                0.0/0.0

R-E134/R-CE225e              0.211/1.0                0.02/0.15



Simulation Results

A beta version of CYCLE_D (Brown et al. 2007c) was used in the standard cycle described above to simulate the thermodynamic performance (CO[P.sub.H] and VHC) of the 36 pure fluids listed in Table 1 and the 20 near-azeotropes listed in Table 2. The simulation results are given for the pure fluids in Table 5 and for the near-azeotropes in Table 6. The results in the tables are listed in ascending order from the smallest VHC ratio to the highest. Table 5 additionally provides: (1) [V.sub.comp] ratio, which is the relative compressor volumetric flow rate (V.sub.comp,refrig]/[V.sub.comp,R-114]) required to achieve the same heating capacity; (2) [T.sub.comp,disch], which is the relative compressor discharge temperature ratio ([T.sub.evap,sup,refrig]/[T.sub.evap,sup,R-114); (3) [T.sub.evap,sup] which is the relative evaporator superheat temperature ratio ([T.sub.evap,sup,refrig]/[T.sub.evap,sup,R-114]); and (4) some environmental (ODP and/or GWP) and safety (toxicity or flammability) characteristics. (Note, for R-114 the evaporator superheat value is 10.56[degrees]C [19[degrees]F], and the compressor discharge temperature is 85[degrees]C [185[degrees]F]). In addition to CO[P.sub.H] ratio (CO[P.sub.H,refrig]/CO[P.sub.H,R114]), Table 6 provides VHC ratio and items 1 and 2 listed above, the temperature glides in the evaporator and condenser. In some instances in Table 5, the ratio F/(F + H) is given to indicate the probable degree of flammability. (Note, F is the number of fluorine atoms in the molecule and H is the number of hydrogen atoms in the molecule.) Bivens and Minor (1998) provide the rule-of-thumb that if F/(F + H) < 0.67, then the fluid is likely to be flammable.

The fluids shaded in darker gray in Tables 5 and 6 clearly violate one of the environmental or safety characteristics established as elimination criteria, namely: ODP > 0.05 (or a banned substance per the Montreal Protocol), GWP > 2000, or an ASHRAE Class 3 (or highly flammable fluid). The fluids shaded in lighter gray in the tables most likely violate one of the elimination criteria. Therefore, the twelve shaded pure fluids and the six shaded near-azeotropes are eliminated from further consideration.

The pure fluids, HFE7100, R-E347mcc, HFE7000, R-E347mmy1, R-E236ca, TMS, R-356mff, [SF.sub.5][C.sub.2][F.sub.5], and N[(C[F.sub.3]).sub.2]([CH.sub.3]), are all eliminated from further consideration because they are lower pressure fluids than R-114, indicating the need for much larger systems (small VHC ratio or high [V.sub.comp] ratio), and they all require much larger evaporator superheat values in order to avoid two-phase compression. Therefore, of the original thirty-six pure fluids, fifteen remain as potential R-114 replacements. Of these, R-245ca, R-E245cb1, R-152a, and R-717, are somewhat flammable and, most likely, so are R-245eb (based on its molecular structure, it is probably less flammable than R-245ca), R-143 (based on its molecular structure, it is probably less flammable than R-143a), and R-254cb. Furthermore, based on their molecular structures and other isomers, R-236ca probably has a GWP [approximately equal to]1000, R-245eb probably has 640 < GWP < 950, and, based on its molecular structure, R-254cb probably has an acceptable GWP.

Table 7 provides evaporator and condenser operating pressures and compressor pressure ratios for the 15 pure fluids in nondimensional terms and includes the values for R-114 in dimensional terms in order to allow one to convert the non-dimensional values easily to dimensional terms. Of the remaining 15 pure fluids, R-13I1 and R-152a have relatively low critical temperatures--123.5[degrees]C (254.3[degrees]F) and 113.4[degrees]C (236.2[degrees]F), respectively--making them less attractive than the others for high-temperature heat-pumping applications, where the operating temperatures can approach 120[degrees]C (248[degrees]F) in some instances. Therefore, of the original 36 pure fluids, 13 of them should receive further consideration as potential R-114 replacement refrigerants. As for the remaining near-azeotropes (six have already been eliminated for safety and/or environmental reasons), the ten near-azeotropes containing R-245fa and the near-azeotrope R-236ea/R-E170 are all eliminated from further consideration since the relative fractions of the refrigerants other than R-245fa and R-236ea are small enough not to warrant the additional complexity of the mixtures. Therefore, of the original 20 near-azeotropes, only three remain: R-272fb/R-E236fa, R-143/R-E236ca, and R-236cb/R-CE225e. However, none of these is particularly attractive since they do not significantly add any benefits beyond those of the pure fluids.
Table 7. Additional Nondimensional Cycle Simulation Results for the
Fifteen Most Promising Pure Fluids as Potential R-114 Replacements

Refrigerant            [P.sub.evap]  [P.sub.cond]  [P.sub.comp,ratio]
                          Ratio          Ratio            Ratio

R-245eb                    0.502         0.582            1.158

R-245ca                    0.475         0.623            1.311

R-245fa                    0.697         0.859            1.233

[SF.sub.5][CF.sub.2]H      0.938         0.960            1.024

R-E236fa                   0.953         1.030            1.081

R-E245cb1                  0.953         1.036            1.087

R-236ca                    0.981         1.075            1.010

R-236ea                    0.964         1.085            1.124

R-143                      0.957         1.025            1.071

R-236cb                    1.198         1.229            1.026

R-254cb                    1.148         1.148            1.000

R-13I1                     2.254         1.914            0.849

R-764                      1.834         1.940            1.058

R-152a                     2.770         2.502            0.903

R-717                      4.669         4.438            0.950

R-114:

SI Units                 226.1 kPa     1038.8 kPa         4.59

English Units            32.8 psia     150.7 psia         4.59


CONCLUSIONS

This paper uses the methodology for evaluating the thermodynamic performance potentials of alternative refrigerants described in, for example, Reid et al. (1987) and Poling et al. (2001)--and illustrated in recent publications by Brown (2007a, 2007b, 2008)--to evaluate 56 potential R-114 replacement refrigerants for high-temperature heat-pumping applications. In particular, the 56 refrigerants consist of 36 pure fluids and 20 near-azeotropes. An idealized vapor compression refrigeration cycle is used to estimate the performance potentials (COP and VHC) of the 56 refrigerants. In addition to the COP and VHC, other basic cycle data are provided for each refrigerant. Furthermore, some other relevant data (e.g., global warming potential, flammability, and toxicity) are provided.

In the opinion of the author, of the 56 refrigerants considered, 23 of the pure fluids and all 20 of the near-azeotropes do not merit further detailed investigations. These conclusions are based on the refrigerants' thermodynamic parameters, their safety characteristics, their environmental measures, and/or their thermodynamic performance.

Therefore, of the original 56 refrigerants, 13 should receive further consideration as potential R-114 replacement refrigerants. Three--R-245eb, R245ca, and R-245fa--are lower-pressure fluids (implying larger systems); eight--[SF.sub.5][CF.sub.2]H, R-E236fa, R-E245cb1, R-236ca, R-236ea, R-143, R-236cb, and R-254cb--have similar operating pressures as R-114 (implying similarly sized systems); and two-R-764 and R-717-are higher-pressure fluids (implying smaller systems) with high compressor discharge temperatures.

NOMENCLATURE

AF = relative acentric factor, [[omega].sub.refrig]/[[omega].sub.R-114]

CO[P.sub.H] = heating coefficient of performance

CO[P.sub.H] ratio = CO[P.sub.H,refrig]/CO[P.sub.H,R-114]

[C.sub.o.sup.p] = ideal gas specific heat at constant pressure evaluated at [T.sub.c] kJ.k[mol.sup.-1].[K.sup.-1] (Btu*lb[mol.sup.-1]*[degrees][R.sup.-1])

CP = relative ideal gas specific heat at constant pressure, [([C.sub.p.sup.o]).sub.refrig]/[([C.sub.p.sup.o]).sub.R-114]

GWP = global warming potential

NBP = normal boiling point temperature, [degrees]C ([degrees]F)

ODP = ozone depletion potential

P = pressure, kPa (psia)

T = temperature, [degrees]C ([degrees]F)

[T.sub.comp,disch] ratio = relative compressor discharge temperature ratio, [T.sub.cond,disch,refrig/[T.sub.cond,disch,R-114]

[T.sub.evap,sup] ratio = relative evaporator superheat temperature ratio, [T.sub.evap,sup,refrig/[T.sub.evap,sup,R-114]

[V.sub.comp] ratio = relative required compressor volumetric flow rate, ([V.sub.comp,refrig/[V.sub.comp,R-114)

VHC = volumetric heating capacity, kJ.[m.sup.-3](Btu*[ft.sup.-3] )

VHC ratio = [VHC.sub.refrig]/[VHC.sub.R-114]

[delta] = relative density, [[rho].sub.refrig]/[P.sub.R-114]

[PI] = relative pressure, [P.sub.refrig]/[P.sub.R-114]

[rho] = density, kg.[m.sup.-3] (lbm*[ft.sup.-3])

[tau] = relative temperature, [T.sub.refrig]/[T.sub.R-114]

[omega] = acentric factor

Subscripts

c = critical

comp = compressor

cond = condenser

disch = discharge

evap = evaporator

refrig = refrigerant

sup = superheat

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J. Steven Brown, PhD, PE

Member ASHRAE

J. Steven Brown is an associate professor and chair of the Department of Mechanical Engineering, Catholic University of America, Washington, DC.
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