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Refrigeration Lubricants
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Mark R. Baker, Michael G. Foster
The Montreal Protocol led to the phaseout of ozone-depleting CFC and HCFC refrigerants and the introduction of refrigerants with zero ODP. The Kigali amendment to the Montreal Protocol in 2016 will phase down HFC refrigerants to reduce global warming potential. Once it was realized that CFC usage needed to be phased out, other chemicals had to be found to replace them in essential applications. Many substances can be used as refrigerants. Most commonly used refrigerants are substances that can be changed easily from liquid to a gas and back again. These substances can be split into five main groups: “Natural refrigerants” such as carbon dioxide, isobutane, and ammonia.CFCs, which are composed of the elements chlorine, fluorine, and carbon only; for example, R-12.Hydrochlorofluorocarbons (HCFCs), which contain hydrogen in addition to chlorine, fluorine, and carbon; for example, R-22.Hydrofluorocarbons (HFCs), which contain hydrogen, fluorine, and carbon but no chlorine; for example, R-134a.Hydrofluoroolefins (HFOs), which contain hydrogen, fluorine, carbon, no chlorine, and a double bond; for example, R-1234yf. This is a low GWP refrigerant developed originally primarily for the automotive sector.
Refrigerants
Published in Vasile Minea, Industrial Heat Pump-Assisted Wood Drying, 2018
Hydrofluoroolefins (HFOs) are synthetic refrigerants that promise to be a part of solution to the environmental problems. Among them, there are pure compound refrigerants such as HFO-1234yf (2,3,3,3-tetrafluoropropene) and HFO-1234ze(E) (trans 1,3,3,3-tetrafluoropropene) (Calm 2008; Brown et al. 2009) as promising low-GWP substitutes to HFC-134a with minimal modifications of existing heat pump systems.
Refrigeration Cycles
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
Heat ventilation, air-conditioning, and refrigeration (HVAC&R) equipments have been primarily using high-GWP HFC refrigerants since the 1990s. To comply with the global HFC phasedown targets and proposals, the industry started developing equipment that uses low-GWP alternative refrigerants. As per those regulations, an ideal refrigerant should (i) be non-toxic, (ii) be non-flammable, (iii) have zero ozone depletion potential (ODP), (iv) have zero GWP, (v) have acceptable operating pressures, and (vi) have volumetric capacity appropriate to the application. Low-GWP HFCs include hydrocarbons, ammonia, carbon dioxide, and hydrofluoroolefins (HFOs). Hydrocarbons: The three most viable hydrocarbon refrigerants include propane, isobutane, and propylene. These hydrocarbons have GWP values of 3, and they are classified as A3 refrigerants due to their high flammability.Ammonia: It is classified as B2 refrigerant and has a GWP value of 0. Refrigeration systems in industrial applications often use ammonia as a refrigerant. Due to its class B toxicity rating, ammonia cannot make itself as a suitable candidate for comfort conditioning applications or indoor commercial refrigeration applications.Carbon dioxide (CO2): It is classified as A1 (non-flammable, non-toxic) and has a GWP of 1. CO2 has been proved to be a viable alternative for several applications including heat pumps, water heaters, commercial refrigerated vending machines, supermarket refrigeration, secondary expansion systems, and industrial and transport refrigeration systems. Carbon dioxide is also a technically viable option in mobile vehicle air-conditioning (MVAC) systems.Hydrofluoroolefins (HFOs): These are emerging as the most viable alternative refrigerants. Refrigerant manufacturers have developed several HFO blends specifically to some applications. HFO-1234yf and HFO1234ze are a step ahead along in development. HFO-1234yf and HFO-1234ze are both classified as A2L and have GWP values less than 1. Moreover, the performance of HFO-1234yf is almost close to that of HFC-134a. HFO-1234yf has been extensively used outside the USA for future MVAC systems, and one automobile manufacturing company based in the USA has been dedicated to using HFO-1234yf since 2013. HFO-1234yf also shows the potential as a refrigerant in chillers and commercial refrigeration applications that are currently using HFC-134a. Table 12.1 shows the ozone depletion and global warming potential of various refrigerants.
Experiments and Correlations for Single-Phase Convective Heat Transfer in Brazed Plate Heat Exchangers
Published in Heat Transfer Engineering, 2023
Angela Mutumba, Francesco Coletti, Alex Reip, Mohamed M. Mahmoud, Tassos G. Karayiannis
A literature survey shows that there has been a lot of experimental work on Plate Heat Exchangers (PHEs) focused on refrigerant applications. Common working fluids included the use of both pure fluids and mixtures. However, the use of such substances was found to affect the ozone layer and contributed to greenhouse effects. Consequently, international environmental regulations promoted the development of alternative and suitable refrigerants such as Hydrofluoroolefins (HFOs) with both low Global Warming Potential (GWP) and Ozone Depletion Potential (ODP). However, their performance in energy conversion systems such as the Organic Rankine Cycles (ORCs) is yet to be determined. ORCs are particularly well-suited to converting low- to medium-grade heat (below 100 °C to 300-400 °C) to power. Recently, HFOs like R1233zd(e) and R1336mzz(z) have shown to be a promising replacement for R245fa; commonly used in ORCs. For example, Moles et al. [2] evaluated the performance of R1233zd(e) and R1336mzz(z) as potential substitutes for R245fa in an ORC for waste heat recovery. Throughout the range of operating conditions and configurations examined, the alternative refrigerants consumed lower pumping power and could therefore achieve higher values of net cycle efficiency. This study showed that R1233zd(e) required 10.3%−17.3% less pumping power and produced up to 10.6% higher net cycle efficiencies than R245fa, over the range of cycle conditions examined. The possibility of replacing R245fa with R1233zd(e) is also supported by the similar thermo-physical properties as shown in Table 1. The values reported in Table 1 are based on Engineering Equation Solver (EES) software and reference [3].
Numerical and experimental investigation of liquid blowing agent and pentane blowing agent effects on the insulation of a household refrigerator
Published in Science and Technology for the Built Environment, 2021
Gizem Duru, Dilek Kumlutaş, Hasan Avci, Utku Alp Yücekaya, Özgün Özer
Hydrofluoroolefins (HFOs) are the new generation of blowing agents, which have zero ODP and near-zero GWP. There is no significant risk presented in the literature for HFOs (Hydrofluoroolefins) apart from data that elevated levels could act as irritants (Naldzhiev et al., 2020).
Optimum fin geometries on condensation heat transfer and pressure drop of R1234ze(E) in 4-mm outside diameter horizontal microfin tubes
Published in Science and Technology for the Built Environment, 2019
Masataka Hirose, Daisuke Jige, Norihiro Inoue
Moreover, the Kigali Amendment to the Montreal Protocol requires an 85% reduction in hydrofluorocarbons (HFCs) by 2036 in developed countries and by 2047 in developing countries. Hydrofluoroolefin (HFO) refrigerants are attracting attention as refrigerants with low GWPs, because regulations regarding HFC refrigerants are expected to become increasingly stringent. R1234yf and R1234ze(E) are the most popular HFO refrigerants in commercial use. Table 1 show the GWP values for conventional HFCs and HFOs (Myhre and Shindell 2013). Some researchers have reported on the condensation heat transfer and pressure drop characteristics of HFO refrigerants. Hossain et al. (2012) investigated the condensation heat transfer coefficients of R1234ze(E) in a 4.35-mm inside diameter (ID) smooth tube within a saturation temperature range of 35 °C–45 °C and a mass velocity range of 200–400 kg m−2 s−1. Kondou et al. (2013) investigated the condensation heat transfer characteristics for R1234ze(E) inside two kinds of microfin tubes with 5.3-mm equivalent ID at a saturation temperature of 40 °C and a mass velocity range of 130–400 kg m−2 s−1. Del Col et al. (2015) reported the condensation heat transfer of R1234ze(E) inside a 0.96-mm ID minichannel at a saturation temperature of 40 °C and a mass velocity range of 100–800 kg m−2 s−1. Diani et al. (2017) investigated the condensation heat transfer coefficient and pressure drop of R1234yf in a microfin tube with a fin-tip diameter of 3.4 mm at saturation temperatures of 30 °C and 40 °C and a mass velocity range of 100–1000 kg m−2 s−1. Longo et al. (2018) measured the condensation heat transfer coefficients of R1234yf and R1234ze(E) inside 4.0-mm ID smooth tubes at saturation temperatures of 30 °C, 35 °C, and 40 °C. Gu et al. (2018) investigated the condensation flow pattern and model assessment of R1234ze(E) for minichannels with IDs of 4.57, 1, and 0.49 mm. Hirose, Fujima, et al. (2018) investigated the condensation heat transfer coefficient and pressure drop of R1234ze(E) in two kinds of microfin tubes with 3.5-mm equivalent ID. Studies on the condensation characteristics inside small-diameter microfin tubes have been reported by Diani et al. (2017) and Hirose, Fujima, et al. (2018). However, their studies on the condensation heat transfer and pressure drop characteristics of HFO refrigerants inside small-diameter microfin tubes are limited to IDs of 3–5 mm and less than 100 kg m−2 s−1. In particular, they have not extensively evaluated the influence of fin geometries on the heat transfer and pressure drop characteristics.