HFO-1234yf Research Articles

A Novel Generator Design Utilised for Conventional Ejector Refrigeration Systems

Ejector refrigeration systems are rapidly evolving and are poised to become one of the most preferred cooling systems in the near future. CO2 transcritical refrigeration systems have inherently high working pressures and discharge temperatures, providing a large volumetric heating capacity. In the current research, the heat ejected from the CO2 gas cooler was proposed as a driving heating source for the compression ejector system, representing the energy supply for the generator in a combined cycle. The local design approach was investigated for the combined plate-type heat exchanger (PHE) via Matlab code integrated with the NIST real gas database. HFO refrigerants (1234ze(E) and 1234yf) were selected to serve as the cold fluid on the generator flowing through three different phases: subcooled liquid, a two-phase mixture, and superheated vapour. The study examines the following: the effectiveness, the heat transfer coefficients, and the pressure drop of the PHE working fluids under variable hot stream pressures, cold stream flow fluxes, and superheated temperatures. The integration revealed that the cold fluid mixture phase dominates the heat transfer coefficients and the pressure drop of the heat exchanger. By increasing the hot stream inlet pressure from 9 MPa to 12 MPa, the cold stream two-phase convection coefficient can be enhanced by 50% and 200% for R1234yf and R1234ze(E), respectively. Conversely, the cold stream two-phase convection coefficient dropped by 17% and 37% for R1234yf and R1234ze(E), respectively. The overall result supports utilising the ejected heat from the CO2 transcritical system, especially at high CO2 inlet pressures and low cold channel flow fluxes. Moreover, R1234ze(E) could be a more suitable working fluid because it possesses a lower pressure drop and bond number.

Oxygen anion (O- ) and hydroxide anion (HO- ) reactivity with a series of old and new refrigerants.

The reactivity of a series of commonly used halogenated compounds (trihalomethanes, chlorofluorocarbon, hydrochlorofluorocarbon, fluorocarbons, and hydrofluoroolefin) with hydroxide and oxygen anion is studied in a compact Fourier transform ion cyclotron resonance. O- is formed by dissociative electron attachment to N2 O and HO- by a further ion-molecule reaction with ammonia. Kinetic experiments are performed by increasing duration of introduction of the studied molecule at a constant pressure. Hydroxide anion reactions mainly proceed by proton transfer for all the acidic compounds. However, nucleophilic substitution is observed for chlorinated and brominated compounds. For fluorinated compounds, a specific elimination of a neutral fluorinated alkene is observed in our results in parallel with the proton transfer reaction. Oxygen anion reacts rapidly and extensively with all compounds. Main reaction channels result from nucleophilic substitution, proton transfer, and formal H2+ transfer. We highlight the importance of transfer processes (atom or ion) in the intermediate ion-neutral complex, explaining part of the observed reactivity and formed ions. In this paper, we present the first reactivity study of anions with HFO 1234yf. Finally, the potential of O- and HO- as chemical ionization reagents for trace analysis is discussed.

Tribological performance of environmentally friendly refrigerant HFO-1234 yf under starved lubricated conditions

Concerted research efforts have been made in the field of alternative refrigerants due to environmental concerns. Newly developed, HFO-1234 yf (2,3,3,3-Tetrafluoropropene) refrigerant has been proposed as a direct replacement solution for substituting the existing harmful hydrofluocarbon refrigerants, such as R134a (1,1,1,2-Tetrafluoroethane). This paper presents a comparative tribological study of R134a and HFO-1234 yf refrigerants. Specifically, we present scuffing resistance, friction and wear, using gray cast iron interface under starved lubricated conditions. Better tribological performance was observed with HFO-1234 yf, compared to R134a. Optical microscopy and profilometry techniques were employed to analyze wear, and scanning electron microscopy was carried out to reveal the morphological changes along with the mode of wear. Chemical composition of the substrate was studied using energy dispersive X-ray spectroscopy, which showed the presence of fluorine element in the case of HFO-1234 yf refrigerant. This result in conjunction with the X-ray photoelectron spectroscopy results (disks and pins analyses), support the presence of fluorine-containing tribolayers preventing metal–metal contact and sustaining prolonged interface functionality.

On the pressure dependence of flammability limits of CH 2=CFCF 3, CH 2F 2 and methane

Flammability limits of CH 2=CFCF 3 (HFO-1234 yf), CH 2F 2 (HFC-32), and methane were measured at pressures from ambient to 2500 kPa in a 5 l stainless-steel spherical vessel. For HFO-1234 yf, as the pressure rises from ambient, the lower flammability limit is shifted downward and the upper limit is shifted upward. The changes to the lower flammability limits are, in general, small compared to the upper flammability limits. Both the lower and upper flammability limits of this compound can be approximated by simple logarithmic functions of pressure. For HFC-32, the behavior of lower flammability limit is similar to that for HFO-1234 yf, but the behavior for the upper limit is rather complicated. As the pressure is increased, it begins to rise upward gradually. Then, as the pressure becomes larger than about 1000 kPa it begins to rise upward rapidly, and then the change becomes moderate again. This must be due to a change of combustion reaction mechanism below 1000 kPa and above 1500 kPa in the upper flammability limit region for this compound. On the other hand, both the flammability limits of methane change almost linearly with pressure, at least in the pressure region considered.