Low Global Warming Potential Refrigerants Research Articles

Experimental investigation on combustion characteristics of flammable refrigerant R290/R1234yf leakage from heat pump system for electric vehicles.

Concerning the issues regarding driving mileage reduction for electric vehicles (EVs) in cold climates, a heat pump system with low global warming potential refrigerant R290/R1234yf is employed as one of the promising solutions. Different from the widely used mobile refrigerant R134a, R290 and R1234yf are both flammable or explosive. The application of R290/R1234yf in the mobile heat pump system is hindered by unexpected refrigerant leakage with the existence of fire and explosion risk. In this study, the combustion characteristics of R290/R1234yf in a potential leakage process from an air-conditioning heat pump system for EVs were investigated. Firstly, thermodynamic behaviours of R290/R1234yf used in a typical heat pump system were analysed based on a special experimental facility designed for EVs. Then the leakage and combustion characteristics of R290/R1234yf including flame shape, temperature, radiation etc. were obtained by the experimental method under different initial temperature and mass flow rate conditions. It was found that R290/R1234yf leaked is difficult to ignite at low temperatures, while the blow-off phenomenon of the jet flame would occur at high temperature with high leakage mass flow rate. In addition, the results showed that combustion intensity would be enhanced by the leakage mass flow rate between 30 and 60°C. These results could provide guidance for fire detection and rescue system design for new energy vehicles.

Energy and environment options of working fluid alternative for different refrigeration configurations

Hydrofluorocarbons, currently used as refrigerants, in air-conditioning systems, for high-temperature heat pump systems in industrial applications are potent greenhouse gases. Their contribution to climate change is to increase. Future use of the hydrofluorocarbons as the hydrochlorofluorocarbons will be phased down. There are very different options to replace them and only a few pure fluids possess the combination of chemical, environmental, thermodynamic, and safety properties necessary for a working fluid. Low global warming potential refrigerants are anticipated to be the refrigerants of choice in industrial applications.

Exergy and energy analysis of low GWP refrigerants in the perspective of replacement of HFC-134a in a home refrigerator

The present work focusses on comparison of several low Global warming potential (GWP) refrigerants in search of possible alternatives to a refrigerant HFC-134a of a home refrigerator without any modifications. A computational mathematical model is developed and thermodynamic analysis has been carried out to investigate the influence of Evaporator temperature on the performance characteristics like Volumetric Cooling Capacity (VCC), Compressor power consumption, COP, and Compressor discharge temperature at two different Condenser temperatures (25°C and 45°C). By exergy analysis Exergetic efficiency, Exergy destruction ratio, and Efficiency defect across different components of the Vapour compression refrigeration system are also evaluated. Comparison is made between different refrigerants mentioned above. Results obtained revealed that the refrigerants HFO- 1234yf and HFC-152a can be a good replacement of HFC-134a refrigerant without any modifications. Condenser and Liquid suction heat exchanger (LSHX) have the highest and the lowest Efficiency defect respectively, among all the system components of a home refrigerator.

Exergy, exergoeconomic and exergoenvironmental studies and optimization of a novel triple-evaporator refrigeration cycle with dual-nozzle ejector using low GWP refrigerants

In this work, a novel dual-nozzle ejector enhanced triple-evaporator refrigeration cycle (DETRC) without separator is proposed to improve the performance of the conventional ejector one (CETRC). The performance of DETRC is analyzed and compared with CETRC in term of energy coefficient of performance (COPen). Under given operating conditions, the COPen improvement of the novel cycle could reach about 24.35% which shows the excellent energy-saving potential of DETRC in comparison with CETRC. Then, a comprehensive comparison between R717, R600a, R1234yf and R290 as low global warming potential (GWP) refrigerants of DETRC is conducted from the energy, exergy, economic and environmental impact (EI) aspects. It is observed that R717 gives better energetic and exergetic performances by 3.21 and 0.583 and R1234yf causes the lowest total product cost and EI rates of 8.186 $/h and 0.665 Pts/h, respectively for DETRC. Moreover, increasing the high evaporating temperature improves all desired performances of DETRC, simultaneously due to the reduction of compressor consumed power. Finally, a multi-objective optimization based on an evolutionary algorithm and LINMAP decision making are carried out to ascertain the optimum exergetic, economic and EI performances of DETRC for each refrigerant.

Laminar burning speeds and flame instabilities of isobutane carbon dioxide air mixtures at high pressures and temperatures

Liquefied petroleum gases (LPGs), such as isobutane and propane, find applications as working fluids in refrigeration and as fuels in internal combustion engines. Isobutane is typically used as a precursor molecule in the synthesis of isooctane, a component of gasoline. It can also be used as a natural low global warming potential (GWP) refrigerant, however, there are fire safety concerns. This work investigated the effects of adding carbon dioxide (CO2) to isobutane (iC4H10) to evaluate its effects on flammability and flame propagation. This paper also compared isobutane results with propane (the major LPG component) results, which were adapted from a previous study. The laminar burning speeds of blends of iC4H10/CO2/air were measured in a constant volume spherical chamber. The flame stability/instability was evaluated in a cylindrical chamber where the flame propagation was captured with a high-speed camera in a Z-shaped Schlieren system. A power law correlation was developed to determine laminar burning speeds for blends of iC4H10/CO2/air at CO2 mole fractions of 0–80%, equivalence ratios of 0.8–1.2, temperatures of 298–580 K, and pressures of 0.5–4.2 atm. Results were compared with experimental studies from the literature and numerical data obtained using 1–D premixed flame code from CANTERA. Both experiments and numerical predictions showed that the laminar burning speeds of iC4H10/CO2 mixtures decreased with increasing CO2 mole fraction, and that the maximum laminar burning speed shifted towards stoichiometric mixture. Carbon dioxide acted as an inhibitor of flame instability, as verified both experimentally by photography and theoretically by calculating the critical Peclet number.

Performance comparison of heat pumps using low global warming potential refrigerants with optimized heat exchanger designs

The objective of this study is to analyze the performance improvement of heat pumps with low global warming potential (GWP) refrigerants over conventional R-410A heat pumps by optimizing the heat exchanger designs. A simulation model is developed for heat pumps with low GWP refrigerants and validated by comparing the predicted and measured data for R-410A and R-32. Based on the developed model, the diameter of the tube and the number of paths in the indoor and outdoor heat exchangers are optimized for each alternative refrigerant using the genetic algorithm. The performances of the optimized heat pumps with the low GWP refrigerants are compared with that of the R-410A heat pump to provide a selection guide for alternative refrigerants. The average performance improvements of the heat pumps with optimized heat exchanger designs were estimated to be 6.0%, 3.4%, and 2.4% for R-32, DR-5, and L-41a, respectively, compared with that of the baseline system. Thus, the R-32 heat pump delivered the highest performance improvement with the optimized heat exchanger designs.

Modelling of Refrigerant Distribution in an Oil-Free Refrigeration System using R134a

Increasing number of refrigeration units has led to an increase of CO2 emissions and the destruction of the ozone layer. Using low global warming potential (GWP) refrigerants, improving the efficiency of vapour compression refrigeration (VCR) units, and minimising refrigerant leakages can reduce the global warming effect. Investigating the refrigerant distribution under varied operating conditions can provide a deeper understanding of refrigerant charge optimization. This study proposed a model of refrigerant mass distribution in a prototype oil-free VCR system using a linear compressor with variable strokes and R134a. The absence of the oil lubricant allows the adoption of compact heat exchangers, such as micro-channels, so that the total refrigerant charge can be reduced significantly. The predicted total refrigerant charge has a Mean Absolute Percentage Error (MAPE) of 3.7%. The simulation results indicate that refrigerant distributed in the condenser is most sensitive to operating conditions and total refrigerant charges. The refrigerant accumulated in the condenser is 6.8% higher at a total refrigerant charge of 0.33 kg than that of 0.22 kg. For a total refrigerant charge of 0.33 kg, 72.1% of the total refrigerant can accumulate in the condenser. At a fixed pressure ratio, the refrigerant as a two-phase form in the condenser decreases slightly with the increase of compressor strokes, resulting in a larger mass flow rate, thus cooling capacity. The present model can be adapted for optimization of a refrigeration unit and its components.

2,3,3,3‐Tetrafluoropropene (HFO‐1234yf) as a CF3‐Building Block: Synthesis of Enol Ethers and Vinyl Sulfides

2,3,3,3‐Tetrafluoropropene (HFO‐1234yf) is an inexpensive and readily available fluorinated building block, owing to its growing use as a low global warming potential 4th generation refrigerant, but there have so far been few reported uses of this fluoroalkene in organic synthesis. Herein, we report our investigations into nucleophilic substitution reactions of HFO‐1234yf with alkoxide and thiolate derivatives. The regiochemistry of these transformations varies with conditions and we propose these reactions proceed through addition–elimination with reversible formation of a carbanion intermediate. The regioselectivity is dictated by hard/soft nucleophile/electrophile control. This is supported by deuterium trapping of the proposed reactive intermediate. The effect of solvent and base choice was examined and the substrate scope for the synthesis of α‐trifluoromethyl enol ethers was expanded.

Thermodynamic Analysis of Low GWP Refrigerant Mixtures in a Refrigerator as Replacement to R-134A

Abstract Chlorofluorocarbons and hydro chlorofluorocarbons (HCFCs) are replaced by hydroflourocarbons (HFCs) which is not harmful to the ozone layer. However, few of HFCs have a relatively high global warming potential (GWP) and are subject to further examination due to growing concerns about global climate change. The goal now is to find the next generation of environmentally sustainable work fluids with an insignificant direct environmental impact in terms of ozone depletion and global warming potential. This document introduces the mixture of low-GWP refrigerants like R440A, R430A, R1234ze (E)/152a (50:50 by mass), R290/600a (40/60), R290/600(60/40), R290/600(50/50), ARM 42,ARM 42a and AC5 are used to replace R-134a in a domestic refrigeration system without doing any modifications to the system. The performance of the refrigerator was observed in terms of volumetric cooling capacity, blower discharge temperature, and coefficient of performance, refrigeration effect and energy consumption of a blower.

Environmental Fate and Transport Analysis of Low Global Warming Potential (GWP) Refrigerant, R-514A

Environmental Fate and Transport Analysis of Low Global Warming Potential (GWP) Refrigerant, R-514A

Comparison of Flammability of Low-GWP Refrigerants Using 1.76-m3 Combustion Chamber

ABSTRACT The transition to low global-warming potential (GWP) refrigerants is ongoing. Since a large part of Low-GWP refrigerants is combustible, fundamental flammability parameters have been studied. However, the combustion behavior of accidentally released refrigerants is not fully understood. In this study, we studied the relationship between the flammability parameters such as lower flammability limit (LFL), the fundamental burning velocity (FBV) and the combustion behaviors of Low-GWP refrigerants including R290 (C3H8), R152a (CH3CHF2), R143a (CH3CF3), R142b (CH3CClF2), R41 (CH3F), and R32 (CH2F2). We conducted tests using three experimental configurations: static configuration, laminar and turbulent flow configuration simulating realistic refrigerant leak. Under static conditions, the burning velocities for R290, R152a (CH3CHF2), and R32 were measured in a 1.76 m3 combustion chamber. The measured values of burning velocities were in a good agreement with available literature data. Laminar refrigerant leak was studied for R290, R152a, R41(CH3F), R142b (CH3CClF2), and R32 in a 1.76 m3 combustion chamber. Flammability of turbulent flow leak of R290, R152a, R143a (CH3CF3), and R32 was analyzed using a 237 L plastic container. Experiments simulating laminar and turbulent flow refrigerant leak demonstrated a positive correlation between LFL and the time before ignition. The refrigerant concentration at ignition agreed with LFL. It was found that the combustion behavior of refrigerants under leak conditions corresponds two types of flame propagation. The first type corresponds to a flame which rapidly spreads horizontally on the floor surface from the ignition source. The second type corresponds to flame kernel irregularly appearing around the continuous spark source. The approximate boundary between two types of combustion behavior corresponds to R152a (FBV = 23.6 cm/s, unsupported flame propagation) and R143a（FBV = 7.1cm/s, combustion supported by the continuous ignition source). This result is consistent with ASHRAE 34, ISO 817 and the GHS classification revised in 2017 adopting the burning velocity of 10 cm/s as a boundary between “highly flammable” and “lower flammable” refrigerants.

Energetic and Exergetic Analysis of Low Global Warming Potential Refrigerants as Substitutes for R410A in Ground Source Heat Pumps

In the European Union (EU), buildings are responsible for about 40% of the total final energy consumption, and 36% of the European global CO2 emissions. The European Commission released directives to push for the enhancement of the buildings energy performance and identified, beside the retrofit of the current building stock, Heating, Ventilation, and Air Conditioning (HVAC) systems as the other main way to increase renewable energy sharing and overall building energy efficiency. For this purpose, Ground Source Heat Pumps (GSHPs) represent one of the most interesting technologies to provide energy for heating, cooling, and domestic water production in residential applications, ensuring a significant reduction (e.g., up to 44% compared with air-source heat pumps) of energy consumption and the corresponding emissions. At present, GSHPs mainly employ the refrigerant R410A as the working fluid, which has a Global Warming Potential (GWP) of 2087. However, following the EU Regulation No. 517/2014 on fluorinated greenhouse gases, this high GWP refrigerant will have to be substituted for residential applications in the next years. Thus, to increase the sustainability of GSHPs, it is necessary to identify short time alternative fluids with lower GWP, before finding medium-long term solutions characterized by very low GWP. This is one of the tasks of the UE project "Most Easy, Efficient, and Low-Cost Geothermal Systems for Retrofitting Civil and Historical Buildings" (acronym GEO4CIVHIC). Here, a thorough thermodynamic analysis, based on both energy and exergy analysis, will be presented to perform a comparison between different fluids as substitutes for R410A, considered as the benchmark for GSHP applications. These fluids have been selected considering their lower flammability with respect to hydrocarbons (mainly R290), that is one of the main concerns for the companies. A parametric analysis has been performed, for a reversible GSHP cycle, at various heat source and sink conditions, with the aim to identify the fluid giving the best energetic performance and to evaluate the distribution of the irreversibilities along the cycle. Considering all these factors, R454B turned out to be the most suitable fluid to use in a ground source heat pump, working at given conditions. Special attention has been paid to the compression phase and the heat transfer in evaporator and condenser.

Heat transfer and pressure drop of R1123/R32 (40/60 mass%) flow in horizontal microfin tubes during condensation and evaporation

In this study, the heat transfer coefficient (HTC) and pressure drop of the new low global warming potential refrigerant mixture R1123/R32 (40/60 mass%) in a 6.0 mm OD horizontal microfin tube during condensation at 40 °C and evaporation at 10 °C are experimentally quantified. The data are then compared to the component R32. Both the condensation HTC and pressure drop of R1123/R32 (40/60 mass%) are somewhat lower than those of R32. Similarly, the pressure drop of R1123/R32 during the evaporation process at 10 °C is somewhat lower than that of R32. However, the evaporation HTC is comparable to that of R32. The lower surface tension of R1123/R32 can enhance the nucleate boiling and compensate the heat transfer degradation due to the volatility difference.

Experimental exergy and energy analysis of a novel high-temperature heat pump with scroll compressor for waste heat recovery

The industrial sector demands novel sustainable energy systems to advance in its decarbonisation and meet the targets of the Paris Agreement for the climate change mitigation. High-Temperature Heat Pumps (HTHPs) are being investigated as a feasible energy conversion technology alternative to traditional fossil fuel boilers. This paper presents the first experimental results of an HTHP prototype equipped with a modified scroll compressor and internal heat exchanger (IHX). The elements of the main and secondary circuits are presented, as well as the test methodology and heat balances are exposed. The tests have been performed using HFC-245fa at heat source temperatures between 60 and 80 °C, and heat sink temperatures between 90 and 140 °C. The heating capacity and coefficient of performance (COP) varied between 10.9 and 17.5 kW and between 2.23 and 3.41, respectively. An exergetic analysis indicated that the expansion valve was the component with the worst second law efficiency and the compressor presented the highest potential improvement over the other cycle components. A computational analysis of low global warming potential (GWP) refrigerant alternatives was carried out, which confirmed the benefits of using an internal heat exchanger (IHX) and the good performances of the low-GWP refrigerants: HCFO-1224yd(Z), HCFO-1233zd(E), and HFO-1336mzz(Z). Finally, we proved that the proposed system can save up to 57% of the equivalent CO2 emissions of a natural gas boiler. This paper provides a reference for the high-temperature heat pump recovery of the low-grade waste heat from industrial energy processes.

Options for low-global-warming-potential and natural refrigerants Part 2: Performance of refrigerants and systemic irreversibilities

There is growing interest in substituting existing refrigerants with low global warming potential (GWP) refrigerants, including naturally occurring fluids, to reduce the impact of human activities on climate change. In the Part I of the study, we examined 13 refrigerants from the perspective of the characteristic shape of their respective temperature–entropy (T–S) and the logarithm of the pressure versus inverse absolute temperature (log P vs. T−1) phase boundary. In Part 2, we are evaluating prospective low-GWP refrigerants in four distinct heat pump cycles using the First and Second Laws of thermodynamics. The essence of the study is to establish the performance of the low-GWP refrigerants when deployed in a heat pump system. Exergy analysis provides a true measure of lost work, or systemic inefficiencies, vividly quantifying areas of improvement and identifying the preferred cycle for a refrigerant. The combined knowledge of the properties of the phase boundary on either side of the critical point, and exergy analysis of prospective cycles is necessary for a better perspective on discriminating among refrigerants as hydrochlorofluorocarbons are phased out and replacement refrigerants must be found.

Performance analysis of low GWP refrigerants mixture as a substitute for R410A in residential air conditioner in tropical region

The issue of global warming has triggered more critical issues, and today’s refrigerants with high global warming potential (GWP) are facing the challenges of being phased out. According to 2014 Assessment Report of the Refrigeration, Air-Conditioning and Heat Pumps Technical Options Committee (RTOC Assessment Report 2014), the R410A has GWP of 2100 and is widely used in residential air-conditioning and heat pump systems. Currently, in the market, the potential refrigerant that can be used to replace R410A in the air-conditioning system is R32. The purpose of this project is to create a new refrigerant mixture using low GWP refrigerant as a base that can replace for R410A in an air-cooled split air conditioner. Simulation works have been developed using Refprop software to simulate the refrigeration cycle with the operating conditions of the air-cooled split air conditioner, in the tropical region. The chosen cycle was an ideal vapour compression cycle with the evaporating and condensing temperatures of 5 °C and 47 °C, respectively. Through this study, two potential refrigerants mixture was found to be suitable to replace the R410A. The two refrigerant mixtures, R32/R1234ze and R32/R600a, both based on R32, were found to have similar thermodynamic properties as the R410A. They were found to be able to produce the coefficient of performance (COP) very close to the R410A when used in an air-cooled split air-conditioning system. Hence, the use of this refrigerants will avoid significant modifications on the present air-conditioning system configurations. Refrigerant R32/R1234ze has the potential to reduce the GWP of R410A by 70 % while refrigerant R32/R600a by 73 %. At the end of the equipment lifespan, refrigerant R32/R1234ze would reduce the direct of Total Equivalent Warming Impact (TEWI) by 23 % while refrigerant R32/R600a by 20 %.in constructing both.

Experimental Investigation of Low GWP Refrigerants Applied to Split Air Conditioner

In this work, the thermal and environmental investigations for split air conditioner using low global warming potential (LGWP) refrigerants as alternatives to the present R22 are examined experimentally. Two alternative refrigerants of R290 (GWP=20) and R152a (GWP=133) are examined instead of R22 (GWP=1700). The experiments are carried out at different range of evaporator air velocities and evaporator air inlet temperatures. The experiments are conducted at evaporator air inlet temperatures of 31oC, 38oC and 48oC, the air passes over evaporator coil with velocity of 0.5 to 1.6 m/s. The study parameters such as different evaporator air temperature, discharge temperature, cooling load, electrical compressor power, coefficient of performance, indirect global warming parameter and total equivalent warming parameter are investigated. The experimental results indicate that refrigerant R152a has the higher thermal performance than R22 and R290 and produces the lowest total equivalent warming parameter. At a certain evaporator air velocity is 1.2 m/s and the evaporator air inlet temperature is 31°C, the coefficient of performance of R152a is higher than that of R22 by 44.92%. The Total Equivalent Warming Impact of R290 and R152a are lower than that of R22 by 8.2 % and 30.03 %; respectively

Standard Rating Charts for Low Global Warming Potential Refrigerants Flowing Through Adiabatic Helical Capillary Tube

The present research work is undertaken to develop ASHRAE like standard rating charts for currently used refrigerants R-134a and R-410A and their potential low global warming potential (GWP) substitutes R-1234yf and R-32, respectively. A self-adjustable mass prediction algorithm has been developed using an averaging technique. Based on this, a matlab code dynamically linked to refprop v. 9.0 software has been developed that solves governing equations of mass, momentum, and energy. Two-phase flow inside the capillary tube is assumed homogeneous and metastability is ignored in the proposed model. The proposed numerical models are in good agreement with the available experimental data with overall percentage mean deviation is less than 6%. Coil diameter plays an important role in adjusting the mass flow rate in the helical capillary tube. Coiling of capillary tube causes an increase in friction pressure drop and a reduction in refrigerant mass flow rate. It has been found that the mass flow rate reduces by about 5% as coil diameter is reduced from 120 to 20 mm.

Experimental investigation of in-tube condensation of low GWP refrigerant R450A using a fiber optic distributed temperature sensor

Heat transfer coefficients and frictional pressure drop values are experimentally measured during condensation of R134a and its proposed low global warming potential (GWP) replacement, R450A. R450A is a non-flammable zeotropic mixture of R134a and R1234ze (42/58% by mass). Experiments were conducted in a horizontal tube (ID = 4.7 mm) for a range of mass fluxes (100 kg m−2 s−1 to 550 kg m−2 s−1) and saturation conditions (45 ∘C and 55 ∘C). The measured pressure drop values and heat transfer coefficients were compared with established literature correlations. Good agreement indicates that existing correlations can be used for design of condensers with R450A as the working fluid. Additionally, this study evaluates the viability of using distributed fiber optic temperature sensors during refrigerant condensation experiments. The fiber sensor is installed in the annulus of a tube-in-tube heat exchanger and is used to obtain the axial temperature profile of the cooling water. The measurements from the distributed temperature sensors are compared with conventional RTD measurements co-located within the test section. The results (Average Deviation = ±0.26 ∘C, Maximum Deviation = ±1.11 ∘C) suggest that fiber optic measurement techniques can provide temperature data with accuracy and high spatial resolution (equal to 0.65 mm).

Molecular modeling of the solubility of low global warming potential refrigerants in polyol ester lubricants

Pentaerythritol esters (PECs) act as the main precursors in polyol ester (POE) lubricants. The solubility of low global warming potential (GWP) refrigerants in linear chained PECs was studied in this work using the perturbed chain form of the statistical associating fluid theory (PC-SAFT). The effect of PEC alkyl tail length on the solubility of various refrigerants was investigated. Results showed that the solubility of HFO refrigerants is weakly dependent on PEC molecular structure. On contrary, the solubility of other natural and paraffin refrigerants significantly increased with increasing the alkyl tail length. Within the SAFT framework, pure component and binary interaction parameters were found to correlate linearly with PEC molecular weight. These correlations were used to predict the solubility of refrigerants in a predefined PEC blend through component lumping. Sensitivity analyses showed that the latter simplification could adequately describe the mixture phase behavior. The proposed model was then applied to fully and accurately predict the solubility of carbon dioxide in commercial POE lubricants. Results demonstrate that the proposed model can be used as a fully predictive tool to determine the solubility of refrigerants in commercial POE oils, provided that the lubricant molecular weight is known, a clear step forward developing adequate low GWP refrigerants-lubricant pairs.