Preliminary selection of R-114 replacement refrigerants using fundamental thermodynamic parameters (RP-1308).INTRODUCTION
Over the last 25 or so years, the Years, The
the seven decades of Eleanor Pargiter’s life. [Br. Lit.: Benét, 1109]
See : Time worldwide phase-out of chlorofluorocarbons chlorofluorocarbons (klōr'əflr`əkär'bənz, klôr'–) (CFCs), organic compounds that contain carbon, chlorine, and fluorine atoms. (CFCs) and hydrofluorochlorocarbons (HCFCs HCFCs: see chlorofluorocarbons. ) has led to active research and development programs by the HVAC&R industry, manufacturers, universities, and governments with the aim of identifying and developing new fluids and equipment. The most commonly pursued short-term solution is to retrofit ret·ro·fit
v. ret·ro·fit·ted or ret·ro·fit, ret·ro·fit·ting, ret·ro·fits
1. To provide (a jet, automobile, computer, or factory, for example) with parts, devices, or equipment not in CFC CFC
See: Controlled foreign corporation applications with appropriate HCFCs and hydrofluorocarbons hydrofluorocarbons: see under chlorofluorocarbons. (HFCs), and longer-term solutions include replacing CFC and HCFC Noun 1. HCFC - a fluorocarbon that is replacing chlorofluorocarbon as a refrigerant and propellant in aerosol cans; considered to be somewhat less destructive to the atmosphere
hydrochlorofluorocarbon applications with appropriate HFCs or "natural" (e.g., water, air, ammonia, carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. , hydrocarbon) refrigerants Chemical refrigerants are assigned an R number(sometimes the label replaces it with the word Freon) which is determined systematically according to molecular structure. The following is a list of refrigerants with their R numbers, IUPAC chemical name, molecular formula, and CAS number. and/or to develop new equipment and cycles. The twin environmental concerns of ozone depletion Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions and global warming global warming, the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution. are the principal driving forces behind these changes. While the Montreal Protocol Montreal Protocol, officially the Protocol on Substances That Deplete the Ozone Layer, treaty signed on Sept. 16, 1987, at Montreal by 25 nations; 168 nations are now parties to the accord. and its amendments have addressed the ozone depletion problem, more recent initiatives (for example, the Kyoto Protocol Kyoto Protocol: see global warming. ) are attempting to address the global warming problem. As a response, the industry has developed measures that account not only for a refrigerant's direct contribution but also a refrigerant's indirect contribution to global warming. The total equivalent warming impact Total equivalent warming impact or TEWI is besides global warming potential measure used to express contributions to global warming.
It is defined as sum of the direct (chemical emissions) and indirect (energy use) emissions of greenhouse gases. (TEWI TEWI Total Equivalent Warming Impact ) is one such measure that accounts for a refrigerant's direct contribution through leakage of the refrigerant re·frig·er·ant
1. Cooling or freezing; refrigerating.
2. Reducing fever.
1. A substance, such as air, ammonia, water, or carbon dioxide, used to provide cooling either as the working substance of into the atmosphere and its indirect effect related to the amount of carbon dioxide generated from burning fossil fuels fossil fuel: see energy, sources of; fuel.
Any of a class of materials of biologic origin occurring within the Earth's crust that can be used as a source of energy. Fossil fuels include coal, petroleum, and natural gas. to power the refrigeration refrigeration, process for drawing heat from substances to lower their temperature, often for purposes of preservation. Refrigeration in its modern, portable form also depends on insulating materials that are thin yet effective. system. Another similar measure is the life-cycle climate performance (LCCP LCCP Light (Forces) Contingency Communications Package
LCCP Life-Cycle Climate Performance
LCCP Lexmark Cartridge Collection Program (recycling)
LCCP Louisiana Cancer Control Partnership ), which, in addition to including the effects captured by TEWI, also attempts to account for other indirect effects related to the manufacturing, transporting, recycling, etc., of the refrigerant.
Even though CFCs are scheduled for phase-out, many will still be used for some time. 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 heat pump: see air conditioning.
Device for transferring heat from a substance or space at one temperature to another at a higher temperature. , 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 increase in primary energy costs and expected price pressures for primary energy persisting into the near future, it is anticipated that there will be a 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 and expanded use of high-temperature heat pumps despite the scheduled phase-out of CFC refrigerants. The scope of this paper, however, is somewhat more limited than finding direct replacements for these CFC refrigerants. In particular, what is addressed is this question: What should be the thermodynamic ther·mo·dy·nam·ic
1. Characteristic of or resulting from the conversion of heat into other forms of energy.
2. Of or relating to thermodynamics. parameters of a replacement refrigerant for R-114 in high-temperature heat pumping applications?
When considering replacement refrigerants, either for existing or new applications, a good starting point Noun 1. starting point - earliest limiting point
terminus a quo
commencement, get-go, offset, outset, showtime, starting time, beginning, start, kickoff, first - the time at which something is supposed to begin; "they got an early start"; "she knew from the for the performance potential of the various alternative refrigerants in an idealized i·de·al·ize
v. i·de·al·ized, i·de·al·iz·ing, i·de·al·iz·es
1. To regard as ideal.
2. To make or envision as ideal.
1. vapor-compression refrigeration Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, private residences, hotels, hospitals, theaters, restaurants and cycle. This approach avoids unnecessary, costly, and time-consuming experimentation and detailed system modeling. In particular, simplified analytical approaches (see, for example, Brown ) can indicate a few promising refrigerants from a much longer list of potential refrigerants. This shortened list can then be investigated in depth using conventional approaches such as experimentation or detailed system modeling. Regardless of which approach one chooses to pursue, typical measures of performance potential for heat pumping applications include the heating coefficient of performance The coefficient of performance, or COP (sometimes CP), of a heat pump is the ratio of the output heat to the supplied work or ([COP.sub.H]) and the volumetric volumetric /vol·u·met·ric/ (vol?u-met´rik) pertaining to or accompanied by measurement in volumes.
Of or relating to measurement by volume. heating capacity (VHC VHC Virginia Horse Center (Lexington, Virginia)
VHC Vermont Humanities Council
VHC Very High Compression (General Motors)
VHC Valdez Heli-Camps (Valdez, AK) ), where [COP.sub.H] is a measure of energy efficiency (operating costs operating costs npl → gastos mpl operacionales [Didion 1999]) and VHC indicates equipment size (capital costs [Didion 1999]).
It is known from previous studies (e.g., McLinden , Morrison , Didion ) that properties and characteristics such as cost, stability, toxicity, flammability flam·ma·ble
Easily ignited and capable of burning rapidly; inflammable.
[From Latin flamm , environmental impact, liquid viscosity, liquid thermal conductivity, materials compatibility, solubility solubility
Degree to which a substance dissolves in a solvent to make a solution (usually expressed as grams of solute per litre of solvent). Solubility of one fluid (liquid or gas) in another may be complete (totally miscible; e.g. with lubricants lubricants
preparations for the lubrication of passages to reduce frictional injury, e.g. oily preparations, including petroleum jelly, lanolin or water-soluble preparations such as methyl cellulose. , etc., are all extremely important. As a first-cut approximation, however, the thermodynamic properties Here is a partial list of thermodynamic properties of fluids:
1. pertaining to a mole of a substance.
2. a measure of the concentration of a solute, expressed as the number of moles of solute per liter of solution. Symbol M, , or mol/L. heat capacity can provide an indication of how a particular refrigerant will perform in an idealized vapor-compression refrigeration cycle. In particular, increasing the critical point temperature implies a higher [COP.sup.H] and a lower VHC; conversely, decreasing the critical point temperature implies a lower [COP.sup.H] and a higher VHC. Furthermore, molecular complexity provides an indication of the value of the vapor molar heat capacity and thus the shape of the refrigerant's two-phase saturation lines, i.e., its vapor dome. As the vapor molar heat capacity increases, expansion-side losses increase and the likelihood of wet compression increases (to avoid this detrimental effect, larger superheats are required).
In the sections that follow, these previous studies are expanded and it is shown that the critical temperature, the ideal gas specific heat at constant pressure, and the acentric factor In thermodynamics, the acentric factor is a factor originally used by K.S. Pitzer and coworkers as an expression in an equation for the compressibility factor. It is defined as largely determine the [COP.sub.H] and VHC in an idealized vapor-compression refrigeration cycle. Simulation results are presented and acceptable ranges for the above-listed thermodynamic parameters are provided for refrigerants operating in typical R-114 heat pumping applications.
OVERALL MODELING APPROACH
As a first step in evaluating the performance potential of a refrigerant in a particular application, one could calculate its [COP.sub.H] and VHC in an idealized vapor-compression refrigeration cycle (see Figure 1), which includes two irreversibilities--one due to superheating
In physics, superheating (sometimes referred to as boiling retardation, or boiling delay of the refrigerant prior to and during compression and one due to a fully irreversible expansion process leading to both lost work potential and lost refrigeration capacity. Careful observation of Figure 1 further shows that the shape of the temperature-entropy (T-s) state diagram state diagram - state transition diagram and the locations of the application temperatures relative to the critical temperature determine the [COP.sub.H] and VHC (for more detailed discussions, see, for example, Morrison  or Didion ). This idealized vapor-compression refrigeration cycle does not capture all the irreversibilities of a real cycle, e.g., irreversible heat transfers and pressure losses in the heat exchangers. It does, however, provide a good indication of how a particular refrigerant will perform in an actual cycle, particularly if one accounts for compressor compressor, machine that decreases the volume of air or other gas by the application of pressure. Compressor types range from the simple hand pump and the piston-equipped compressor used to inflate tires to machines that use a rotating, bladed element to achieve irreversibilities via isentropic is·en·tro·pic
Without change in entropy; at constant entropy.
[is(o)- + entrop(y) + -ic.]
is efficiency. Therefore, one could calculate [COP.sub.H] and VHC in an idealized vapor-compression refrigeration cycle in order to select a few promising refrigerants from a much longer list of potential refrigerants. This shortened list could then be investigated in depth via experimentation and detailed system modeling.
[FIGURE 1 OMITTED]
In a recent paper, Brown (2007) successfully used the Peng-Robinson Equation of State (P-R EoS) to accurately simulate [COP.sub.H] and VHC for a wide range of refrigerants, including R-114, in an idealized vapor-compression refrigeration cycle. In this paper, the P-R EoS implemented in REFPROP 8.0 (Lemmon et al. 2007) is used. In order to use the process described in Brown (2007), one must know several fundamental thermodynamic parameters, namely, the refrigerant's critical temperature [(T.sub.c)], critical pressure [(P.sub.c)], critical density [([rho].sub.c)], acentric factor ([omega]), molecular weight (M), one saturated liquid density [([rho].sub.f)] data point, and the ideal gas specific heat at constant pressure (C.sub.p.sup.o]) as a function of temperature. Brown showed that with these known inputs, one could predict the [COP.sup.H] and the VHC for a group of 24 refrigerants (Table A1) with absolute errors of 1.5% and 2.7%, respectively, compared to the values calculated using the default, high-accuracy equations in REFPROP (Lemmon et al. 2007). It was further shown that for new and alternative refrigerants, where these input data may not be well known, one could (1) use the group contribution methods of Ambrose (see Reid et al. [1987a]) and Joback (see Reid et al. [1987b]) to predict [T.sub.c], [P.sub.c], [[rho].sub.c], and [c.sub.p.sup.0] and (2) use the method of Reid et al. (1987c) to predict [omega]. Following this approach, Brown showed that for the same group of 24 refrigerants, knowing only their normal boiling point boiling point, temperature at which a substance changes its state from liquid to gas. A stricter definition of boiling point is the temperature at which the liquid and vapor (gas) phases of a substance can exist in equilibrium. (NBP NBP Narodowy Bank Polski (Polish: National Bank of Poland)
NBP Name Binding Protocol
NBP National Braille Press
NBP National Bank of Pakistan
NBP National Biosolids Partnership
NBP Nathaniel B. ) temperatures and their molecular structures, one could predict the [COP.sub.H] and VHC with absolute errors of 2% and 10%, respectively, compared to the values calculated using default equations in REFPROP (Lemmon et al. 2007).
Here, the approach of Brown (2007) is used to answer the question what should be the fundamental thermodynamic parameters of a replacement refrigerant for R-114 in high-temperature heat pumping applications? (Note: McLinden  used a somewhat similar approach to the one reported in this paper to find "optimum" refrigerants for non-ideal cycles. In particular, McLinden used the principle of corresponding states The principle (law) of corresponding states can, most generally, be summarized as unity in diversity. Material constants that vary for each type of material are eliminated, in a recast reduced form of a constitutive equation. to determine the optimum [T.sub.c] and optimum [c.sub.p.sub.0] for refrigerator applications.) In this paper, the approach is to parametrically study the effects of [T.sub.c], [c.sub.p.sup.0], and [omega] on [COP.sub.H] and VHC using the P-R EoS, which then allows one to determine the "ideal" R-114 replacement refrigerant. Note: in the following discussion, it should become clearer why [P.sub.c],[[rho].sub.c], M, and [[rho].sub.f] also do not need to be parametrically studied.
In particular, the parametric space is defined by the nondimensional value [[tau].sub.c] of the critical temperature ranging from 0.89 to 1.42, the nondimensional value CP of the ideal gas specific heat at constant pressure ranging from 0.18 to 1.45, and the nondimensional value AF of the acentric factor ranging from 0.59 to 2.14. Note: [[tau].sub.c] = [([T.sub.refrig]/[T.sub.R-114]).sub.c], CP = [([c.sub.p.sup.0]).sub.refrig]/[(['c.sub.p.sup.0]).sub.R-114] calculated at [T.sub.c], and AF = [[omega].sub.refrig]/[[omega].sub.R-114], and Table 1 provides some relevant thermodynamic parameters for R-114.
As previously suggested, it is not necessary to parametrically study M and [[rho].sub.f] since [COP.sub.H] and VHC calculations are independent of them. Therefore, in addition to [T.sub.c], [c.sub.p.sup.0], and [omega], one only needs to consider the possible effects [P.sub.c] and[[rho].sub.c] might have on [COP.sup.H] and VHC. First, [T.sub.c], [P.sub.c], and[[rho].sub.c] are not unrelated but can be related by the compressibility factor The compressibility factor (Z) is used to alter the ideal gas equation to account for the real gas behaviour. The compressibility factor is usually obtained from the compressibility chart. :
[Z.sub.c] = [[P.sub.c]/[[[rho].sub.c]R[T.sub.c]]] (1)
where the compressibility factor [z.sub.c] is a function of [T.sub.c], [P.sub.c], and M, and R is the universal gas constant universal gas constant: see gas laws. . [z.sub.c] typically ranges in value from 0.22 to 0.30 for a wide range of fluids (Wark 1995). To verify this for refrigerants, 42 typical refrigerants (Table A2) and their known values of [T.sub.c], [P.sub.c], and[[rho].sub.c] were used to calculate [z.sub.c], resulting in a mean value of 0.27, a minimum value of 0.24, a maximum value of 0.28, and a standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.
(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. of 0.012. Second, since[[rho].sub.c] can be correlated with [c.sub.p.sup.0], the same group of 42 refrigerants was used to develop a power law correlation in [c.sub.p.sup.0]. In terms of nondimensional quantities, the resulting fit having an R-squared value of 0.92 is
[[delta].sub.c] = 1.083[CP.sup.[ - 0.723]], (2)
where [[delta].sub.c] = [([[rho].sub.refrig]/[rho]R-114).sub.c].
Figures 2 and 3 show, for the 42 refrigerants, the actual versus the predicted critical densities and critical pressures, respectively, calculated from Equation 1 with [z.sub.c] = 0.27 and Equation 2 in conjunction with their known critical temperatures. The figures include labels for refrigerants not falling within the [+ or -]10% band and for some typical refrigerants, namely, R-22, R-32, R-114, R-125, R-134a, and R-290. While the predictions show some scatter, they are generally within [+ or -]10%. Therefore, since [P.sub.c] and[[rho].sub.c] can be calculated using Equation 1 with [z.sub.c] = 0.27 and Equation 2, it should now be clearer why only [T.sub.c], [omega], and [c.sub.p.sup.0] need to be parametrically studied.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
RESULTS AND DISCUSSION
As previously discussed, the three variables that affect the shape of the T-s state diagram, and thus ultimately affect [COP.sub.H] and VHC, are [T.sub.c], [c.sub.p.sup.0], and [omega]. First, as [T.sub.c] increases for fixed [c.sub.p.sup.0] and [omega], the shape of the T-s state diagram does not change, but the critical point moves further from the application temperatures (Figure 4a). Second, [c.sub.p.sup.0] is the variable that has the most dramatic effect on the shape of the T-s state diagram. In particular, as [c.sub.p.sup.0] increases for fixed [T.sub.c] and [omega], the magnitude of the slope of the saturated liquid line decreases, whereas the magnitude of the slope of the saturated vapor line increases, eventually becoming infinite and finally decreasing as [c.sub.p.sup.0] increases further. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke"
put differently , as [c.sub.p.sup.0] increases, the vapor dome "leans over" to the right (Figure 5a). Third, as [omega] increases for fixed [T.sub.c] and [c.sub.p.sup.0] , the T-s state diagram broadens and the slope of the saturated liquid line decreases slightly (Figure 6a). Figures 4-6 show T-s and P-h state diagrams where each of the nondimensional quantities [[tau].sub.c], CP, and AF, which correspond to the variables [T.sub.c], [c.sub.p.sup.0], and [omega], respectively, are changed parametrically, while the other two are held constant.
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
In order to obtain a sense of the performance potentials of generic replacement fluids, [[tau].sub.c], CP, and AF were parametrically varied, where [[tau].sub.c] ranged from approximately 0.89 to 1.42, CP ranged from approximately 0.18 to 1.45, and AF ranged from approximately 0.59 to 2.14. Note: the simulated cycle had a constant evaporation evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity temperature of 26.7[degrees]C (80[degrees]F), a constant condensation temperature of 85[degrees]C (185[degrees]F), a condenser condenser
Device for reducing a gas or vapour to a liquid. Condensers are used in power plants to condense exhaust steam from turbines and in refrigeration plants to condense refrigerant vapours, such as ammonia and Freons. subcooling of 5.56[degrees]C (10[degrees]F), a compressor isentropic efficiency of 85%, and an evaporator evaporator
Industrial apparatus for converting liquid into gas or vapour. The single-effect evaporator consists of a container or surface and a heating unit; the multiple-effect evaporator uses the vapour produced in one unit to heat a succeeding unit. superheat su·per·heat
tr.v. su·per·heat·ed, su·per·heat·ing, su·per·heats
1. To heat excessively; overheat.
2. that ensured saturated or superheated su·per·heat
tr.v. su·per·heat·ed, su·per·heat·ing, su·per·heats
1. To heat excessively; overheat.
2. vapor at the condenser inlet (however, the minimum evaporator superheat was 11.11[degrees]C [20[degrees]F]). Some of the simulation points are shown in Figures 7 and 8 for [COP.sub.H] and VHC, respectively. Note: each of the curves represents parametric changes in only one of the three variables [[tau].sub.c], CP, or AF, while the other two parameters remain constant with values of 1. Figure 7 shows that (1) [COP.sub.H] increases as a strong function of increasing [[tau].sub.c], (2) [COP.sub.H] reaches a maximum at a CP value of approximately 0.5, and (3) [COP.sub.H] increases somewhat as a relatively weak function of increasing AF. Figure 8 shows that (1) VHC decreases as a strong function of increasing [[tau].sub.c], (2) VHC decreases with increasing CP, and (3) VHC decreases somewhat as a relatively weak function of increasing AF. These results suggest that one could choose an optimum arrangement of the parameters [[tau].sub.c], CP, and AF in order, for example, to maximize [COP.sub.H] or to maximize VHC or to maximize [COP.sub.H] for a given value of VHC or to maximize VHC for a given value of [COP.sub.H]. For example, to maximize [COP.sub.H] independent of VHC, [[tau].sub.c] should have a value of 1.42, CP should have a value of approximately 0.5, and AF should have a value of 2.14. Given these parameters, the relative [COP.sub.H] ratio ([COP.sub.H,refrig]/[COP.sub.H,R-114]) is 1.09 and the relative VHC ratio ([VHC.sub.refrig]/[VHC.sub.R-114]) is 0.02. As a second example, to maximize VHC independent of [COP.sub.H], [[tau].sub.c] should have a value of 0.89, CP should have a value of 0.18, and AF should have a value of 0.59. Given these parameters, the relative [COP.sub.H] ratio is 0.86 and the relative VHC ratio is 9.47. Note: these "optimum" values are based on the parameter space In generative art people talk about parameter space as the set of possible parameters for a generative system.
In statistics one can study the distribution of a random variable. Several models exist, the most common one being the normal distribution (or Gaussian distribution). defined earlier. Figures 7 and 8, however, are less helpful when attempting to answer questions such as "What parameters would maximize [COP.sub.H] for a given value of VHC?" or "What parameters would maximize VHC for a given value of [COP.sub.H]?" To help answer these types of questions, the results are plotted in Figure 9a, with CP as a function of [[tau].sub.c] in a set of three curves, which set the bounds on the values of VHC being within [+ or -]10%, [+ or -]25%, or [+ or -]50% of the value of R-114. Figure 9a, therefore, could be used to help one locate a combination of CP and [[tau].sub.c] that would yield a desired value of VHC. One limitation of Figure 9a is that it does not include the functional dependence of AF; however, as can be seen from Figures 7 and 8, the functional dependence of AF on both [COP.sub.H] and VHC is relatively weak. Therefore, Figure 9a is a useful representation of the approximate overall functional dependence of [[tau].sub.c], CP, and AF on [COP.sub.H] and VHC.
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
Before concluding, it is useful to demonstrate another aspect of the power of the methodology, namely, not only its capability to evaluate generic replacement refrigerants but, in addition, its capability to evaluate particular refrigerants. For example, consider the potential R-114 replacements given in Devotta and Pendyala (1994) and in Bivens and Minor (1998) together with 39 fluids contained in REFPROP (Lemmon et al. 2007). Then, if the principal sorting criterion were chosen to be that [T.sub.c] must fall in the range from 110[degrees]C (230[degrees]F) to 200[degrees]C (392[degrees]F), the three cited sources would yield 21 potential replacement fluids. Note: this critical temperature range is determined from Figures 7 and 8 such that 0.5 < VHC ratio < 1.5; the critical temperature range would change if one were to impose a different VHC ratio range. (Note: this paper considers only replacement fluids cited in the three references listed above since it is not meant to be an exhaustive search for and presentation of all possible R-114 replacements but rather is an illustration of an overall selection methodology.) In addition to this primary sorting criterion there are, of course, dozens of possible secondary sorting criteria; however, in this paper, only three are applied: (1) flammability, (2) ozone depletion potential The ozone depletion potential (ODP) of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane (R-11) being fixed at an ODP of 1.0. Chlorodifluoromethane (R-22), for example, has an ODP of 0.05. (ODP ODP - Open Distributed Processing ), and (3) global warming potential Global warming potential (GWP) is a measure of how much a given mass of greenhouse gas is estimated to contribute to global warming. It is a relative scale which compares the gas in question to that of the same mass of carbon dioxide (whose GWP is by definition 1). (GWP GWP Global Warming Potential
GWP Global Water Partnership
GWP Gift With Purchase
GWP Guinea-Bissau Peso (currency code: now GNF)
GWP German Wirehaired Pointer (dog breed)
GWP Gross World Product ). Namely, fluids are considered to fail the secondary sorting criteria if (1) they are ANSI/ASHRAE Standard 34 Class 3 flammable flam·ma·ble
Easily ignited and capable of burning rapidly; inflammable.
[From Latin flamm refrigerants, (2) they have ODP > 0, and (3) they have GWP > 2000. These three secondary criteria are applied because of the strong reluctance by the industry to use highly flammable refrigerants in systems requiring large refrigerant charge and because of the ever-growing worldwide awareness and concern regarding environmental impacts. Table 2 lists the 21 refrigerants, together with values for [[tau].sub.c], CP, AF, [COP.sub.H] ratio, and VHC ratio, based on the reference cycle defined above. (Note: the sources for the property data for Table 2 are ASHRAE ASHRAE American Society of Heating, Refrigerating & Air Conditioning Engineers , Bivens and Minor , Brown , IPCC See IMS Forum. , REFPROP [Lemmon et al. 2007], and Reid et al. [1987a, 1987b, 1987c]). These 21 possible R-114 replacements also are shown on a CP vs. [[tau].sub.c] plot in Figure 9b. As previously stated, the functional dependence of AF is missing from the figure so that the VHC value predicted from locating CP and [[tau].sub.c] on the figure is only approximate. One could obtain a better estimate of VHC by "correcting" the prediction using the AF functional dependence shown in Figure 8. The power of Figures 9a and 9b is that one can obtain a reasonable estimate for VHC without having to resort to EoS modeling. For example, one could use the methods of Ambrose (see Reid et al. [1987a]) and Joback (see Reid et al. [1987b]) to easily predict [[tau].sub.c] and CP, respectively, for potential replacement fluids that are not well described, even before predicting other thermodynamic parameters with an EoS model. Finally, Figure 10 shows the [COP.sub.H] ratios and VHC ratios, listed from highest to lowest VHC ratios, for the 21 possible R-114 replacements described above.
Table 2. Twenty-One Potential R-114 Replacement Refrigerants Refrigerant [[tau].sub.c] CP AF Refrigerants Passing Secondary Criteria R-143 1.029 0.695 1.044 R-152a 0.923 0.587 1.091 R-236ca 0.984 1.103 1.369 R-236cb 0.963 1.109 1.274 R-236ea 0.989 1.117 1.504 R-245ca 1.069 1.128 1.405 R-245fa 1.020 1.052 1.476 R-254cb 1.001 0.989 0.980 R-717 0.968 0.281 1.016 RE245cb1 0.971 1.158 1.417 [SF.sub.5][CF.sub.2]H 0.997 1.035 1.075 [SF.sub.5][C.sub.2][F.sub.5] 0.980 1.475 1.313 Refrigerants Failing Secondary Criteria R-12 0.920 0.592 0.714 R-123 1.091 0.923 1.119 R-124 0.944 0.847 1.143 R-142b 0.979 0.733 0.921 R-236fa 0.950 1.087 1.496 R-C318 0.927 1.323 1.409 R-600 1.015 0.951 0.798 R-600a 0.974 0.917 0.730 RE134 1.036 0.874 1.496 Refrigerant [COP.sub.H] Ratio VHC Ratio R-143 1.064 1.139 R-152a 0.993 2.669 R-236ca 1.012 1.017 R-236cb 0.952 1.134 R-236ea 0.986 1.022 R-245ca 1.055 0.609 R-245fa 1.033 0.841 R-254cb 1.012 1.167 R-717 1.029 5.527 RE245cb1 0.969 0.957 [SF.sub.5][CF.sub.2]H 0.993 0.940 [SF.sub.5][C.sub.2][F.sub.5] 0.964 0.705 R-12 0.966 2.550 R-123 1.085 0.557 R-124 0.976 1.672 R-142b 1.032 1.603 R-236fa 0.948 1.224 R-C318 0.849 1.149 R-600 1.032 1.155 R-600a 0.991 1.475 RE134 1.048 1.155 Refrigerant Failure of Secondary Criteria R-143 - R-152a - R-236ca - R-236cb - R-236ea - R-245ca - R-245fa - R-254cb - R-717 - RE245cb1 - [SF.sub.5][CF.sub.2]H - [SF.sub.5][C.sub.2][F.sub.5] - R-12 CFC R-123 HCFC R-124 HCFC R-142b HCFC R-236fa GWP = 9,400 R-C318 GWP = 10,000 R-600 A3 R-600a A3 RE134 GWP = 6,100
[FIGURE 10 OMITTED]
The P-R EoS was used to investigate fundamental thermodynamic parameters that affect the selection of R-114 replacements in high-temperature heat pumping applications. It was shown that the critical temperature, the ideal gas specific heat at constant pressure, and the acentric factor are the three fundamental thermodynamic parameters that largely determine the performance ([COP.sub.H] and VHC) of refrigerants operating in idealized vapor-compression refrigeration cycles. It was shown that (1) the optimum range of [[tau].sub.c] depends on the desired VHC; (2) to maximize [COP.sub.H], CP should have values from approximately 0.35 to approximately 0.75, and to increase VHC, CP should be less than 1; and (3) to increase [COP.sub.H], AF should have larger values, and to increase VHC, AF should have smaller values. For the studied parametric space, the maximum achievable [COP.sub.H] ratio is 1.09 (with a corresponding VHC ratio of 0.02) and the maximum achievable VHC ratio is 9.47 (with a corresponding [COP.sub.H] ratio of 0.86). For the [COP.sub.H] ratio of 1.09, [[tau].sub.c] = 1.42, CP = 0.5, and AF = 2.14, and for the VHC ratio of 9.47, [[tau].sub.c] = 0.89, CP = 0.18, and AF = 0.59. Therefore, trade-offs become necessary due to the conflict between [COP.sub.H] and VHC. The process presented in this paper provides a framework for quickly and easily screening a large number of potential R-114 replacement refrigerants. One could easily create, from a much longer list, a focused list of potential replacements that could then be investigated in depth using the more conventional approaches of experimentation and detailed system modeling.
The author would like to thank Drs. Eric Lemmon and Mark McLinden Mark McLinden, born 8th July, 1979 in Canberra, Australia is an Australian rugby league player.
Mark McLinden plays for Harlequins RL, formerly known as London Broncos in the European Super League.
McLinden's position of choice is as a full-back. for making available a beta version A pre-shipping release of hardware or software that has gone through alpha test. A beta version of software is supposed to be very close to the final product, but, in practice, it is more a way of getting users to test the software in the first place under real conditions. of REFPROP 8.0 and for several helpful discussions. The author would also like to thank Dr. David Didion for many fruitful discussions over the past ten years, including recent ones regarding the subject of this paper.
NOMENCLATURE nomenclature /no·men·cla·ture/ (no´men-kla?cher) a classified system of names, as of anatomical structures, organisms, etc.
AF = relative acentric factor, [[omega].sub.refrig]/[[omega].sub.[R - 114]]
[COP.sub.H] = heating coefficient of performance
[COP.sub.H] ratio = [COP.sub.H,refrig]/[COP.sub.[H,R - 114]]
[c.sub.p.sup.0] = ideal gas specific heat at constant pressure evaluated at [T.sub.c], kJ [kmo1.sup.-1] [K.sup.-1] (Btu [lbmo1.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]]
h = enthalpy enthalpy (ĕn`thălpē), measure of the heat content of a chemical or physical system; it is a quantity derived from the heat and work relations studied in thermodynamics. , kJ [kg.sup.-1] (Btu [lbm.sup-1])
H* = nondimensional enthalpy, [[h.sub.refrig] - [h.sub.[f,R - 114,T = 0[degrees]C]]]/[h.sub.[fg,R - 114, T = 0[degrees]C]]
M = molecular weight, kg [kmol.sup.-1] (lbm [lbmol.sup.-1])
NBP = normal boiling point temperature, [degrees]C ([degrees]F)
P = pressure, kPa (psia)
P* = nondimensional pressure, [P.sub.refrig]/[P.sub.[c,R - 114]]
s = entropy entropy (ĕn`trəpē), quantity specifying the amount of disorder or randomness in a system bearing energy or information. Originally defined in thermodynamics in terms of heat and temperature, entropy indicates the degree to which a given , kJ [kg.sup.-1] [K.sup.-1] (Btu lbm-1 [degrees][R.sup.-1])
S* = nondimensional entropy, [[s.sub.refrig] - [s.sub.[f,R - 114,T = 0[degrees]C]]]/[s.sub.[fg,R - 114,T = 0[degrees]C]]
T = temperature, [degrees]C ([degrees]F)
T* = nondimensional temperature, [T.sub.refrig]/[T.sub.[c,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]/ [rho]R-114
[pi] = relative pressure, [[rho].sub.refrig]/[rho]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
c = critical
cond = condenser
evap = evaporator
f = saturated liquid
fg = difference between saturated vapor and saturated liquid property values
g = saturated vapor
refrig = refrigerant
ASHRAE. 2005. 2005 ASHRAE Handbook--Fundamentals, Chapters 19 and 20. Atlanta: American Society of Heating, Refrigerating re·frig·er·ate
tr.v. re·frig·er·at·ed, re·frig·er·at·ing, re·frig·er·ates
1. To cool or chill (a substance).
2. To preserve (food) by chilling. and Air-Conditioning Engineers, Inc.
Bivens, D.B., and B.H. Minor. 1998. Fluoroethers and other next generation fluids. International Journal of Refrigeration 21(7):567-76.
Brown, J.S. 2007. Predicting performance of new refrigerants using the Peng-Robinson equation of state. International Journal of Refrigeration. In press.
Devotta, S., and V.R. Pendyala. 1994. Thermodynamic screening of some HFCs and HFEs for high-temperature heat pumps as alternatives to CFC114. International Journal of Refrigeration 17(5):338-42.
Didion, D.A. 1999. How thermophysical fluid properties influence the performance of the new ozone-safe refrigerants. International Journal of Applied Thermodynamics thermodynamics, branch of science concerned with the nature of heat and its conversion to mechanical, electric, and chemical energy. Historically, it grew out of efforts to construct more efficient heat engines—devices for extracting useful work from expanding 2(1):19-35.
IPCC. 2001. IPCC Third Assessment Report The IPCC Third Assessment Report is an assessment of available scientific and socio-economic information on climate change by an intergovermental panel (IPCC) established by the United Nations Environment Programme (UNEP) and the UN's World Meteorological Organization (WMO). : Climate Change 2001. Intergovernmental Panel on Climate Change “IPCC” redirects here. For other uses, see IPCC (disambiguation).
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment , Geneva Geneva, canton and city, Switzerland
Geneva (jənē`və), Fr. Genève, canton (1990 pop. 373,019), 109 sq mi (282 sq km), SW Switzerland, surrounding the southwest tip of the Lake of Geneva. , Switzerland.
Lemmon, E.W., M.L. Huber, and M.O. McLinden. 2007. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. reference fluid thermodynamic and transport properties--REFPROP. NIST standard reference database 23, Version 8.0.
McLinden, M.O. 1990. Optimum refrigerants for non-ideal cycles: An analysis employing corresponding states. Proceedings of the 1990 USNC-11R-Purdue Refrigeration Conference and ASHRAE-Purdue CFC Conference, West Lafayette, Indiana West Lafayette (IPA: [wɛst ˈlɑ.fəˌjɛt]) is a city in Tippecanoe County, Indiana, United States, 65 miles (105km) northwest of Indianapolis. The population was 28,778 at the 2000 census. , pp. 69-79.
Morrison, G. 1994. The shape of the temperature-entropy saturation boundary. International Journal of Refrigeration 17(7):494-504.
Reid, R.C., J.M. Prausnitz, and B.E. Poling. 1987a. The Properties of Gases and Liquids, 4th ed. New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of : McGraw-Hill, p. 12-14.
Reid, R.C., J.M. Prausnitz, and B.E. Poling. 1987b. The Properties of Gases and Liquids, 4th ed. New York: McGraw-Hill, p. 154-56.
Reid, R.C., J.M. Prausnitz, and B.E. Poling. 1987c. The Properties of Gases and Liquids, 4th ed. New York: McGraw-Hill, p. 23.
Wark, K. 1995. Advanced Thermodynamics for Engineers. New York: McGraw-Hill, p. 165.
Table A1. List of Refrigerants from Brown (2007) R-11 R-41 R-134a R-152a R-236fa R-600 R-12 R-123 R-141b R-170 R-245ca R-600a R-22 R-124 R-142b R-218 R-245fa R-1270 R-32 R-125 R-143a R-227ea R-290 R-C318 Table A2. List of Refrigerants Used to Develop Equation 2 and Figures 2 and 3 R-11 R-23 R-115 R-141b R-227ea R-338mccq R-C270 R-12 R-32 R-116 R-142b R-236ea R-600 R-C318 R-13 R-41 R-123 R-143a R-236fa R-600a R-E125 R-13I1 R-50 R-124 R-152a R-245ca R-717 R-E134 R-14 R-113 R-125 R-170 R-245fa R-744 R-E245 R-22 R-114 R-134a R-218 R-290 R-1270 R-E245mc
J. Steven Brown is an associate professor and the Chair of the Department of Mechanical Engineering, The Catholic University of America Catholic University of America, at Washington, D.C.; the national university of the Roman Catholic Church in the United States; coeducational; founded 1887 and opened 1889. , Washington, DC.
J. Steven Brown, PhD, PE
Received October 25, 2006; accepted April 16, 2007
This paper is based on findings resulting from ASHRAE Research Project RP-1308.
Table 1. Some Relevant Thermodynamic Parameters of R-114 (Lemmon et al. 2007) SI NBP 276.74 K [T.sub.c] 418.83 K [P.sub.c] 3257 kPa [[rho].sub.c] 3.39 kmol [m.sup.-3] [omega] 0.2523 M 170.92 kg [kmol.sup.-1] [c.sub.p.sup.0](evaluated 137.9 at [T.sub.c]) kJ [kmol.sup.-1] [K.sup.-1] I-P NBP 498.13 [degrees]R [T.sub.c] 753.89 [degrees]R [P.sub.c] 472.4 psia [[rho].sub.c] 0.212 lbmol [ft.sub.-3] [omega] 0.2523 M 170.92 lbm [lbmol.sup.-1] [c.sub.p.sup.0](evaluated 33.0 at [T.sub.c]) Btu [lbmol.sup.-1] [degrees][R.sup.-1]