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HFC-365mfc-Fluoroketone Mixtures as Organic Rankine Cycle Working Fluids

IP.com Disclosure Number: IPCOM000206692D
Publication Date: 2011-May-02
Document File: 4 page(s) / 77K

Publishing Venue

The IP.com Prior Art Database

Abstract

Binary mixtures of HFC-365mfc (1,1,1,3,3-Pentafluorobutane) and fluorinated ketones are shown to be suitable for use as working fluids for organic Rankine cycle systems. These mixtures possess desirable thermophysical properties, are non-flammable and result in working fluids with lower global warming potential compared to HFC-365mfc. Rankine cycle calculations for a condenser temperature of 50oC and boiler temperature of 150oC show efficiencies of 0.144, 0.109 and 0.130 for HFC-365mfc, C2F5C(O)CF(CF3)2 and the HFC-365mfc (48.3% by weight)/ C2F5C(O)CF(CF3)2 (51.7% by weight) respectively.

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HFC-365mfc-Fluoroketone Mixtures as Organic Rankine Cycle Working Fluids

Binary mixtures of HFC-365mfc (1,1,1,3,3-Pentafluorobutane) and fluorinated ketones are shown to be suitable for use as working fluids for organic Rankine cycle systems. These mixtures possess desirable thermophysical properties, are non-flammable and result in working fluids with lower global warming potential compared to HFC-365mfc. Rankine cycle calculations for a condenser temperature of 50oC and boiler temperature of 150oC show efficiencies of 0.144, 0.109 and 0.130 for HFC-365mfc, C2F5C(O)CF(CF3)2 and the HFC-365mfc (48.3% by weight)/ C2F5C(O)CF(CF3)2 (51.7% by weight) respectively.

The organic Rankine cycle (ORC) converts low-grade heat energy to mechanical power, which may be used to drive processes or electrical generators to produce electricity. Typically, Rankine cycles powered by heat from fossil fuels operate with steam as the working fluid. In such cases, the available heat is of high enough temperature to superheat the steam, thus giving good efficiencies and leading to economical systems. However, for low-grade heat sources, organic fluids are preferred for their better efficiencies as well as other benefits[1][2][3].

For a given heat source and sink, the efficiency of the ORC is largely dependant on the thermodynamic properties of the chosen working fluid. However, aside from the thermodynamic properties, it is generally desirable to employ working fluids that are non-flammable and have low impact on the environment i.e. fluids that are non-ozone depleting and possess low global warming potential (GWP).

Hydrofluorocarbons (HFCs), such as HFC-245fa (1,1,1,3,3-Pentafluoropropane) are known to possess thermodynamic properties that lead to good performance in ORC's. HFC-245fa has been used in systems that are currently commercially available[4], even though, like most HFCs, it has relatively high GWP.

Some HFCs have other disadvantages that limit their use as working fluids in ORCs. For instance, HFC-365mfc (1,1,1,3,3-Pentafluorobutane) has suitable thermodynamic properties and would generally perform well as a working fluid, but, in addition to it's relatively high GWP of 890 (100 yr. time horizon), it is also flammable[5].


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A potential alternative is the use of mixtures of HFC-365mfc and non-flammable, low GWP fluids. Ideally, such mixtures would have acceptable Rankine cycle performance, be non-flammable and have lower, resultant GWPs compared to HFC-365mfc. Fluorinated ketones with GWPs ~1 (100 yr. time horizon) have been considered as working fluids for ORCs[6]. Compositions of some azeotropic mixtures of fluorinated ketones and HFC-365mfc have also been previously disclosed[7]. Examples are:

The mixture of C6 Fluoroketone {C2F5C(O)CF(CF3)2} and HFC-365mfc
(51.7%:48.3% w/w).

The mixture of i, i C7 Fluoroketone {(CF3)2CFC(O)CF(CF3)2} and HFC- 365mfc (21.0%:79.0% w/w).

The mixture of n, i-C7 Fluoroketone {C3F7C(O)CF(CF3)2} and HFC...