Halogenated hydrocarbons with high ozone depletion potential (ODP) were banned under Montreal Protocol (1987) due to their detrimental effects on ozone layer that shields the planet against ultraviolet radiations. The greenhouse gases (GHG) used in modern refrigeration, air conditioning, and heat pumping systems, are under Kyoto Protocol (1997)’s time-barred permission period. In order to reduce the depletion of ozone and reverse the climate change effects, the European Union legislation (2014) and Paris Accord (2016) are strongly emphasizing the phasing out of the use of harmful synthetic refrigerants. Choice of natural refrigerants makes no net addition of the greenhouse gases (GHG) in the environment. To retrofit and modify existing cooling and heating systems using natural refrigerants, extensive investigations are in progress worldwide. This work reviews timeworn, current and the next-generation refrigerants using Refrigerant Qualitative Parametric (RQP) quantification model to assist the refrigerant choice decision process. It is based on the ratio of arithmetic sums of actual parametric values of refrigerants normalized to equivalent ideal values. This model can help in choosing alternative refrigerants to replace CFCs by HCFCs or HFCs provisionally and finally replacing HCFCs or HFC to low GWP and ODP synthetic and natural refrigerants. A set of 16 refrigerants, both natural and synthetic, as an example, is computed for the standard Vapour Compression Cycle (VCC) based on the proposed model using REFPROP (NIST- 23 standard). The techno-economic parametric values of chosen refrigerants are taken from cited literature, ASHREA safety standards and international environmental legislations, laws and protocols. This paper reports the environment benign natural (CO2, NH3, HCs) and a few synthetic (R-152a, R-1234yf) refrigerants to be the optimal options.

Natural and synthetic refrigerants, global warming: A review

The current European F-gas regulation establishes restrictions in the use of fluoride refrigerants with a high global warming potential (GWP) in applications of refrigeration and air conditioning (RAC) systems. Moreover, a gradual limitation on the GWP weight of the fluoride refrigerants placed on the market is ongoing and will end with approximately one-fifth of today's offer. In this context, many of the RAC systems operate with refrigerants R134a, R404A, and R410A that have GWP values of 1300, 3943 and 2088, respectively, are being forced to be replaced by environmentally friendly alternatives, like hydrofluoroolefin (HFO) refrigerants and their mixtures with hydrofluorocarbons (HFC), which can be designed to present intermediate characteristics and become the ideal candidate many RAC applications. This work presents the most recent HFC/HFO/HC/R744 refrigerant mixture options for an alternative to the refrigerants mentiond above and compares their energetic and performance with the early developed mixture prototypes.

Overview of low GWP mixtures for the replacement of HFC refrigerants: R134a, R404A and R410A

A review of refrigerant R1234ze(E) recent investigations

Two alternative correlations are presented for heat transfer during condensation in plain conventional channels as well as mini/micro channels in all orientations. These have been validated by comparison with a database that includes 33 fluids, diameters 0.10 to 49.0 mm, reduced pressures 0.0008 to 0.946, mass flux from 1.1 to 1400 kgm −2 s −1 , various shapes (round, rectangular, triangular, etc.), all orientations (horizontal, vertical up and down, and angles in between). The data are from 136 data sets from 67 sources. While both correlations predict the 4063 data points with mean absolute deviation (MAD) of about 17%, their accuracy varies somewhat in different ranges. The same data are also compared to other correlations.

Comprehensive correlations for heat transfer during condensation in conventional and mini/micro channels in all orientations

A review of water heating technologies: An application to the South African context

R1234ze(E), trans-1, 3, 3, 3-tetrafluoropropene, is a fluorinated propene isomer which may be a substitute of R134a for refrigeration applications. R1234ze(E) has a much lower GWP100-years than that of R134a. In this paper, the local heat transfer coefficient during condensation of R1234ze(E) is investigated in a single minichannel, horizontally arranged, with hydraulic diameter equal to 0.96 mm. Since the saturation temperature drop directly affects the heat transfer rate, the pressure drop during adiabatic two phase flow of R1234ze(E) is also measured. Predictive models are assessed both for condensation heat transfer and pressure drop. A comparative analysis is carried out among several fluids (R1234ze(E), R32, R134a and R1234yf) starting from experimental data collected at the same conditions and using the Performance Evaluation Criteria (PEC) named Penalty Factor (PF) and Total Temperature Penalization (TTP) to rank the tested refrigerants in forced convective condensation.

Condensation heat transfer and two-phase frictional pressure drop in a single minichannel with R1234ze(E) and other refrigerants

Much attention has been paid in the recent years to the possible use of fluorinated propene isomers for the substitution of high global warming potential refrigerants. Among the fluorinated propene isomers, R1234ze(E) may be a substitute of R134a for refrigeration applications. R1234ze(E) has a global warming potential lower than 1 (considering a period time of 100 years), and it is receiving some attention also as a component of low global warming potential mixtures. In this article, a mixture of R1234ze(E) and R32 has been investigated at two different mass compositions (23/77% and 46/54% by mass) with regard to the performance at the condenser. The local heat transfer coefficients during condensation in a single microchannel with 0.96 mm diameter are measured and analyzed. The frictional two-phase pressure drop in the same channel is also investigated. The present tests are carried out on the experimental apparatus available at the Two-Phase Heat Transfer Lab of the University of Padova. The new experi...

Two-phase pressure drop and condensation heat transfer of R32/R1234ze(E) non-azeotropic mixtures inside a single microchannel

Effect of inclination during condensation inside a square cross section minichannel

The condensation heat transfer coefficient and two-phase frictional pressure drop of ternary zeotropic mixtures R455A (R32, R1234yf and R744 at 21.5/75.5/3.0% by mass composition) and R452B (R32, R1234yf and R125 at 67.0/26.0/7.0% by mass composition) have been measured inside a minichannel (0.96 mm diameter) and a conventional tube (8.0 mm diameter). The effects of tube diameter, mass velocity, vapor quality and saturation-to-wall temperature difference have been investigated. A comparison between the experimental data of the tested mixtures and the condensation heat transfer of the pure components R32 and R1234yf has been performed. The two-phase pressure drop and condensation heat transfer data are compared to predictions of correlations available in the literature. In the prediction of the heat transfer coefficient, the models are adapted to account for the additional mass transfer resistance occurring during condensation of zeotropic mixtures.

Condensation of ternary low GWP zeotropic mixtures inside channels

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2341&context=iracc

Marco Azzolin

Papers

Condensation heat transfer and two-phase frictional pressure drop in a single minichannel with R1234ze(E) and other refrigerants

Two-phase pressure drop and condensation heat transfer of R32/R1234ze(E) non-azeotropic mixtures inside a single microchannel

Effect of inclination during condensation inside a square cross section minichannel

Condensation of ternary low GWP zeotropic mixtures inside channels

Energy efficiency in a ground source heat pump with variable speed drives