ASHRAE Journal - August 2009 - 26

Refrigerant6 Molecular Formula6 NBP °F (°C) 5.019 (–15.0) –3.921 (–20.0) –7.218 (–21.8) –7.520 (–22.0) –18.322 (–28.0) –2.122 (–19.0) 48.322 (9.0) –13.39 (–25.2) Tc °F (°C) 236.5 (113.6) 223.1 (106.1) 218.2 (103.4) 224.1 (106.7) 205.1 (96.1) 232.2 (111.2) 308.5 (153.6) 222.0 (105.5) Pc psia (kPa) 493.3 (3401) 483.8 (3335) 480.4 (3312) 512.6 (3534) 498.2 (3435) 518.7 (3576) 575.8 (3970) 542.5 (3740) rc lbm/ft3 (kg/m3) 32.3 (517) 32.3 (517) 32.3 (517) 29.6 (473) 29.6 (473) 29.6 (473) 29.6 (473) 26.4 (423) o cp at Tr = 0.8 Btu/lbm ∙ °R (kJ/kg1 ∙ K) w R-1225ye(E) R-1125ye(Z) R-1225zc R-1234ye(E) R-1234yf R-1234ze(E) R-1234ze(Z) R-1243zf CF3CF = CHF CF3CF = CHF CF3CH = CF2 CHF2CF = CHF CF3CF = CH2 CF3CH = CHF CF3CH = CHF CF3CH = CH2 0.189 (0.789) 0.186 (0.778) 0.185 (0.774) 0.198 (0.828) 0.202 (0.845) 0.200 (0.836) 0.217 (0.906) 0.223 (0.934) 0.313 0.305 0.303 0.290 0.280 0.295 0.333 0.274 Table 3: Estimated fundamental thermodynamic parameters for eight fluorinated propene isomers based only on the refrigerants’ measured NBPs and their structural formulae.13 for condensation. PF is a concept developed by Cavallini15 for comparing the relative heat transfer performance potentials—at least for condensation—of refrigerants. In particular, the PF is a product of two local energy penalization terms, both of which negatively affect the amount of required compressor work: the first penalization term is associated with the frictional pressure drop of the condensing refrigerant, and the second penalization term is associated with the driving temperature difference for the heat transfer process. These two penalization terms can be shown to be equivalent to the more traditional concepts of exergy losses or entropy generation: the first one being related to fluid flow (pressure drop) and the second one to heat transfer. For a specified refrigerant, saturation temperature and tube geometry, Cavallini showed that the product of the two penalization components can be expressed as a function of the heat transfer coefficient (a). When the PF is computed for the same value of a for a given pipe geometry, it can be directly used as a quantitative criterion to rank the heat transfer performance potentials of different working fluids: the smaller the PF, the better the performance potential of the refrigerant. Figure 3 shows the PFs for the eight fluorinated propene isomers being considered in this article, together with several additional more conventional refrigerants. One can see from the figure that from among the eight fluorinated propene isomers being considered in this paper, the lowest pressure refrigerant, R-1234ze(Z), has the highest PF (i.e., its heat transfer performance potential is the lowest) and the highest pressure refrigerant, R-1243zf, has the lowest PF (i.e., its heat transfer performance potential is the greatest), being similar to that of R-134a. Potential Performance for Several Applications 100 12 R3 ea 36 R-2 0 60 R- a 13 R4a 15 R0 29 R- 2a Plain Tube Ts = 39°C x =0.5 d = 7.69 mm PF (K2) 10 22 R- 41 R- 0A 3 R- 2 1 3,000 40 R- 4A 4,000 5,000 7,000 a (W m–2 K–1) R-1225ye(E) R-1225ye(Z) R-1225zc R-1234ye(E) R-1234yf R-1234ze(E) R-1234ze(Z) R-1243zf 7 71 R- 10,000 15,000 20,000 Figure 3: Penalty factor (PF) for condensation versus heat transfer coefficient () for eight fluorinated propene isomers and several additional refrigerants. When evaluating a refrigerant as a potential substitute in a particular application, a good starting point is to evaluate the 26 ASHRAE Journal refrigerant’s performance (COP and volumetric capacity) in an idealized vapor compression refrigeration cycle. The advantage of this approach is that one can quickly and easily screen many possible candidate refrigerants by evaluating their performance potentials without having to resort to time-consuming and expensive experimentation or detailed system modeling. In this way, one can limit more detailed investigations to a few select refrigerants from among the most promising candidates. The goal of this subsection is to evaluate the performance potentials of the eight fluorinated propene isomers being considered in this article, together with several additional more conventional refrigerants, in idealized vapor compression refrigeration cycles for three different applications: (1) unitary air conditioning, (2) automotive air conditioning, and (3) ashrae.org August 2009
ASHRAE Journal - August 2009

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