Hydrofluorocarbon Refrigerants Research Articles

Estimating the viscosity of pure refrigerants and their mixtures by free-volume theory

In this work, the free-volume theory (FVT) was extended to modeling the viscosities of 24 hydrofluorocarbon refrigerants, and applied to predict the viscosities for the mixtures of hydrofluorocarbon refrigerants. It is the first time to apply the FVT to the viscosities of ternary mixtures of hydrofluorocarbon refrigerants. Hydrofluoro-olefins (HFOs) are a new class of refrigerants, which are identified as promising refrigerants because they have low global warming potential, were studied in this paper. For the viscosity of pure refrigerants, the average absolute relative deviations between the FVT calculation and experiment are less than 1.5%. When calculating the viscosities of the mixtures of hydrofluorocarbon refrigerants, three mixing rules without more parameters were tested and compared, the average absolute relative deviations between the FVT coupled with the best mixing rule and experiment are less than 6.5%.

A Review on Solar Powered Air Conditioning System

The twenty first century is rapidly becoming the perfect energy storm, modern society is faced with volatile energy prices and growing environmental concerns as well as energy supply and security issues. One of the greatest challenges facing mankind in the twenty first century is energy. Fossil fuels such as coal, petroleum and natural gas have been the main energy resources for everything vital for human society. The burning of fossil fuels has caused and is causing damage to the environment of earth. By 2050 the demand for energy could double or even triple as the global population grows and developing countries expand their economies. This has already raised concerns over potential supply difficulties, depletion of energy resources and expediting environmental impacts like ozone layer depletion, global warming and climate change etc. The most abundant energy resource available to human society is solar energy. The utilization of solar energy is as old as human history. Among various types of renewable energy resources, solar energy is the least utilized. Air conditioning is essential for maintaining thermal comfort in indoor environments, particularly for hot and humid climates. Today, air conditioning comprising cooling and dehumidification has become a necessity in commercial and residential buildings and industrial processes. During the summer, the demand for electricity greatly increases because of the extensive use of air-conditioning systems. This is a source of major problems in the country's electricity supply and contributes to an increase of CO2 emissions causing the environmental pollution and global warming. On the other hand, vapour compression air conditioning systems have impacts on stratospheric ozone depletion because of the chlorofluorocarbons (CFC) and the hydro fluorocarbon (HCFC) refrigerants. The use of solar energy to drive cooling cycles is attractive since the cooling load is roughly in phase with solar energy availability. To cool with solar thermal energy, one solution is to use an absorption chillier using water and lithium bromide solution. Solar air conditioning systems help to minimize fossil fuel energy use. Among the evolving energy efficient air conditioning technologies are liquid desiccant air conditioning (LDAC) systems, which have showed promising performance during the past decades and are believed to be a strong competitor with the widely used conventional air conditioning systems (CAC). Desiccant evaporation cooling technology is environmental friendly and can be used to condition the indoor environment of buildings. Unlike conventional air conditioning systems, the desiccant air conditioning systems can be driven by low grade heat sources such as solar energy and industrial waste heat. In this study, a focus is made on reduction in Air Conditioning capacity, fuel savings and emission reductions attainable through the use of solar energy.

Performance investigation of some hydro-fluorocarbon refrigerants with low global warming as substitutes to R134a in refrigeration systems

In this study, the performances of R152a, R161, and R1234yf with very low global warming potential were investigated theoretically as alternatives to R134a in vapor compression refrigeration systems. The results obtained showed that the saturation vapor pressures for R152a and R1234yf are very close to that of R134a, which indicates similar properties, while that of R161, between the temperature range of −30 to 40°C, deviated significantly by 49.2%. R152a emerged as the most energy efficient of the investigated refrigerants with average power per ton of refrigeration (PPTR) of 30.5% less than that of R134a. R152a and R161 exhibited a higher volumetric refrigerating capacity (VRC) and coefficient of performance (COP) than R134a. The highest COP was obtained using R152a in the system with an average value of 43.5% higher than that of R134a, while the average COPs for R161 and R1234yf are 4.8% higher and 7.1% lower, respectively. Generally, R152a performed better than the other two alternatives as R134a substitute in that it has similar saturation pressure as R134a, exhibited lowest PPTR, very high VRC, and highest COP. Major system redesign will be required before R161 can be employed as R134a substitute. Also, low performance of R1234yf in terms of PPTR, VRC and COP will increase its indirect contributions to global warming.

Experimental and theoretical analysis of a heat pipe heat exchanger operating with a low global warming potential refrigerant

In the present paper the experimental and theoretical analysis of a Heat Pipe Heat Exchanger (HPEH) is reported. The HPHE consists of 54 horizontal 12.7 mm micro-fin copper tubes 700 mm in length and aluminium continuous fins 0.115 mm in thickness with 3 mm of fin spacing. The HPHE presents an evaporator section of 270 mm, a condenser section of 270 mm and adiabatic section of 160 mm. The performance of the heat exchanger operating with the well-known hydrofluorocarbon refrigerant HFC134a is compared with the results obtained using the new low global warming potential hydrofluoro-olefin HFO1234ze(E). Tests were run in a double wind channel with air operating conditions typical for air-conditioning in European countries for both summer and winter seasons. The consistency of the experimental results is proved by the comparison with a semi-empirical model of the heat exchanger based on heat transfer correlations available in literature.

Theoretical analysis of the energy performance of three low global warming potential hydro-fluorocarbon refrigerants as R134a alternatives in refrigeration systems

In this study, the energy performances of low global warming potential R152a, R161 and R1234yf refrigerants were investigated theoretically as alternatives to R134a in vapour compression refrigeration system. The results obtained showed that the saturation vapour pressures for R152a and R1234yf are very close to the pressure of R134a, which indicates similar properties, while that of R161, between the temperatures range of −30℃ and 40℃, deviated significantly by being 49.2% higher than that of R134a. R152a emerged as the most energy efficient of the investigated refrigerants with average power per ton of refrigeration being 30.5% less than that of R134a. R152a and R161 exhibited higher volumetric refrigerating capacity and coefficient of performance than did R134a. The highest coefficient of performance was obtained using R152a in the system, with average value being 43.5% higher than that of R134a, while the average coefficient of performances for R161 and R1234yf are 4.8% higher and 7.1% lower, respectively. Generally, R152a performed better than other two alternatives, except that it is mildly flammable refrigerant. Major system redesign will be required before R161 can be employed as substitute for R134a. Also, R1234yf showed slightly low energy performance in terms of power per ton of refrigeration, volumetric refrigerating capacity and coefficient of performance.

Issues to improve ground source heat pump units in Korea: Refrigerant application and hot water generation

There is a need for hot water generation in a more efficient and environmentally friendly way for heating, ventilating, and air conditioning systems, and the heat pump is a great candidate for that. In this paper, hot water temperatures generated by ground source heat pump (GSHP) systems in Korea are analysed. It is also important to minimize the use and emission of refrigerants with high global warming potential (GWP) and ozone depletion potential (ODP) to reduce their impact on the environment. In this regard, refrigerants that are used in GSHP units in Korea are investigated. The database is composed of 86 GSHP units certified in Korea according to governmental regulation. The GSHP units are divided into three types: water-to-water, water-to-air, and water-to-air multi heat pump units. The average hot water temperature generated by the certified GSHP units is 43.8 °C with the Korean standard test conditions (NR GT 101). Temperature difference 3.8 °C between inlet and outlet of condenser is less than 5 °C as presented by the European Standard (NF EN standard). In order to replace the boiler and the conventional air conditioning unit with a highly efficient GSHP system, there is the need to increase the hot water generation temperature. With the refrigerants, 53.8% of the 78 water-to-water GSHP units use the hydro chlorofluorocarbon (HCFC) refrigerant, R22, while the others use the hydrofluorocarbon (HFC) refrigerants, R410A, R407C, and R134a. All water-to-air and water-to-air multi heat pump units use R410A refrigerant. Because R22 is a HCFC and has high GWP and ODP, it is being replaced with HFC and natural refrigerants. However, HFC refrigerants also have high GWP. It is therefore recommended to encourage the responsible use or replacement of HFC refrigerants with natural and other alternative refrigerants in Korea.

Experimental Study on the Replacement of HFC-R134a by Hydrocarbons in Automotive Air Conditioning System

The HFC-R134a and hydrocarbon refrigerant (HCR) will be evaluated on the automotive air conditioning (AAC) experimental test rig which completed with the AAC system including the blower, evaporator, condenser, radiator, electric motor, compressor, alternator and equipped with the simulation room acting (equipped with internal heat load) as the passenger compartment. The electric motor operated as a car’s engine and will drive the compressor simultaneously to the alternator to recharge the battery. The tests have been performed by varying the motor speed; 1000, 2000 and 3000 rpm, temperature set-point; 21 and 230C, and internal heat loads; 0, 500, 700 and 1000 W. The results of the performance characteristics of the HCR indicate the encouraging enhancement of the AAC system compared to Hydrofluorocarbon refrigerant (HFC-R134a).

Design and Performance Evaluation of a Cooler Refrigerating System Working with Ozone Friendly Refrigerant

In this study, a cooler refrigerating system was designed, constructed and tested with various charge quantities of an ozone friendly hydro-fluorocarbon refrigerant (R134a) as working fluid. The results obtained showed that the design temperature and pull-down time set by International Standard Organisation (ISO) for small refrigerator were early achieved with refrigerant charges of 100 and 120 g than with 60 and 80 g charges. Approximately the same pull-down time and minimum temperature of -14°C were obtained with refrigerant charges of 100 and 120 g. Discharge pressure is about the same for 60, 80 and 100 g refrigerant charges, but significant increase in discharge pressure was observed as the refrigerant charge increased to 120 g. The rate of increase in the refrigerating capacity and the COP with respect to evaporator temperature for refrigerant charge of 60 g to 100 g are higher than that for refrigerant charge of 120 g. Highest refrigerating capacity and COP of 4.404 kW and 3.1, respectively, were obtained in the cooler refrigerator with 100 g charge. Generally, the best performance of the cooler was obtained with refrigerant charge of 100 g and increase in the charge beyond 100 g affected the performance of the cooler negatively.

Theoretical and experimental investigation on the flame-retarding characteristic of R245fa

Some binary mixtures comprised of R245fa and flammable refrigerant were expected to be a drop-in replacement for R11 or R22. The flame-inhibiting characteristic of R245fa had great significance on evaluating the security of that binary mixture. This paper analyzed the retardant mechanism of R245fa on flammable refrigerants, and the influence factors on flammable limits of refrigerants. With two different ignition styles, an electric igniter and a common lighter, the flame-retarding characteristics of R245fa on some hydrocarbons (HCs) and hydrofluorocarbons (HFCs) refrigerants were studied experimentally. A new index (flame-retarding coefficient) that could be used to evaluate the flame-retarding effect of fire retardants was put forward. The test results showed that the flammable limits of refrigerants were greatly affected by ignition power and ignition mode, and the flame-retarding effect of R245fa on HCs was worse, and was a little better on HFCs, but both worse than that of R134a, R125 and R227ea.

Absorption Heat Pump/Refrigeration System Utilizing Ionic Liquid and Hydrofluorocarbon Refrigerants

The ionic liquid butylmethylimidazolium hexafluorophosphate (bmim)(PF6) and five different hydrofluorocarbon refrigerants were investigated as the working fluid pairs for a waste-heat driven absorption heat pump system for possible applications in electronics thermal management. A significant amount of the energy consumed in large electronic systems is used for cooling, resulting in low grade waste heat, which can be used to drive an absorption refrigeration system if a suitable working fluids can be identified. The Redlich–Kwong-type equation of state was used to model the thermodynamic conditions and the binary mixture properties at the corresponding states. The effects of desorber and absorber temperatures, waste-heat quality, and system design on the heat pump performance were investigated. Supporting experiments using R134a/(bmim)(PF6) as the working fluid pair were performed. Desorber and absorber outlet temperatures were varied by adjusting the desorber supply power and the coolant temperature at the evaporator inlet, respectively. For an evaporator temperature of 41 °C, which is relevant to electronics cooling applications, the maximum cooling-to-total-energy input was 0.35 with the evaporator cooling capability of 36 W and the desorber outlet temperature in the range of 50 to 110 °C.

Lubricity of environmentally friendly HFO-1234yf refrigerant

Global warming concerns have triggered the interest in alternative refrigerants for air-conditioning and refrigeration compressors. Newly developed refrigerant HFO-1234yf is an attractive and environmentally friendly candidate to replace existing hydrofluorocarbon refrigerants, such as R-134a. Herein, the tribological compatibility of gray cast iron material with this new refrigerant was investigated under aggressive unlubricated conditions. HFO-1234yf exhibits excellent performance compared to R-134a due to the formation of a fluorine-containing protective tribolayer on the topmost surface as X-ray photoelectron spectroscopy (XPS) analysis, inside and outside the wear tracks, revealed. The morphology of the layer was also studied using scanning electron microscopy (SEM) studies.

Lubricity effect of carbon dioxide used as an environmentally friendly refrigerant in air-conditioning and refrigeration compressors

Abstract Environmental concerns have increased the interest in alternative natural refrigerants for air-conditioning and refrigeration compressors. Carbon dioxide (CO2) or R744 is an attractive candidate to replace harmful hydrofluorocarbon refrigerants, which will need to be replaced in the near future due to their high global warming potential. In this paper the tribological behavior of gray cast iron in the presence of CO2 under unlubricated conditions was investigated. Specifically different regions of the CO2 pressure–temperature (P–T) phase diagram were studied to understand the role of pressure, temperature, CO2 mass, and the chemical interaction of gray cast iron with CO2, focusing on their impact on the friction and wear behavior. It was found that friction decreases significantly when CO2 pressure and temperature approach the gas–liquid transition in the P–T phase diagram, thus exhibiting a form of “superlubricity.” Through X-ray photoelectron spectroscopy it was found that an increase in CO2 pressure causes partial transformation of iron oxides into iron carbonates which have a positive effect on the tribological performance. The thickness of the tribolayer film, formed in the contact zone, was evaluated using Focus Ion Beam and it was found to be of the order of 0.5 μm.

Use of nanoparticles to make mineral oil lubricants feasible for use in a residential air conditioner employing hydro-fluorocarbons refrigerants

The application of nano-fluids in refrigerating systems is considered to be a potential way to improve the energy efficiency and reliability of HVAC&R facilities and to make economic the use of environment-friendly refrigerants. In this paper, we report a method that uses nanoparticles to enhance the energy efficiency of retrofitted residential air conditioners (RAC) employing HFCs as alternative refrigerants. The reliability and performance of RAC with nanoparticles in the working fluid have been investigated experimentally. A new mineral-based nano-refrigeration oil (MNRO), formed by blending some nanoparticles (NiFe 2O 4) into naphthene based oil B32, was employed in the RAC using R410a as refrigerant. A method showing how to disperse the NiFe 2O 4 nanoparticles in the mineral oil refrigeration lubricants is presented together with an investigation of their stability. The solubilities of the new MNRO in R134a, R407C, R410a and R425a were measured. The performances of the RAC, such as the cooling/heating capacity, the power input and the energy efficiency ratio, were determined. The results indicate that the mixture of R410a/MNRO works normally in the RAC. The cooling/heating EER of the RAC increased about 6% by replacing the Polyol-Easter oil VG 32 lubricant with MNRO.

Comparative scuffing performance and chemical analysis of metallic surfaces for air-conditioning compressors in the presence of environmentally friendly CO 2 refrigerant

Carbon dioxide (CO 2) has received significant interest as an alternative refrigerant for air-conditioning compressors due to its environmental benefits. These environmental benefits include zero ozone depletion potential and minimal global warming potential compared to commonly used hydrochlorofluorocarbon and hydrofluorocarbon refrigerants. This study presents results for three typical metallic tribopairs commonly found in air conditioning compressors, namely, Al390-T6, gray cast iron, and Mn–Si brass against 52,100 steel pins. The experiments were performed using a specialized tribometer capable of simulating compressor conditions, and in the presence of CO 2 and polyalkylene glycol lubricant. It was found that the scuffing resistance of gray cast iron and Mn–Si brass was similar and both materials performed better than Al390-T6. Through scanning electron microscopy and energy dispersive spectroscopy it was found that lead in Mn–Si brass melted during scuffing, and prevented sudden catastrophic failure of Mn–Si brass, unlike gray cast iron and Al390-T6 which failed abruptly. X-ray photoelectron spectroscopy conducted on the worn surfaces showed that chemically different species were present on the surfaces and their lubricious effect, originating from different metal oxides, could explain the scuffing behavior of the investigated alloys.

Phase equilibria of imidazolium ionic liquids and the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a)

A number of applications with ionic liquids (ILs) and hydrofluorocarbon gases have recently been proposed. Detailed phase equilibria and modeling are needed for their further development. In this work, vapor–liquid equilibrium, vapor–liquid–liquid equilibrium, and mixture critical points of imidazolium ionic liquids with the hydrofluorocarbon refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a) was measured at temperatures of 25 °C, 50 °C, 75 °C and pressure up to 143 bar. The ionic liquids include 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf 2N]), 1-hexyl-3-methyl-imidazolium hexafluorophosphate ([HMIm][PF 6]), and 1-hexyl-3-methyl-imidazolium tetrafluoroborate ([HMIm][BF 4]). The effects of the anion and cation on the solubility were investigated with the anion having greatest impact. [HMIm][Tf 2N] demonstrated the highest solubility of R-134a. The volume expansion and molar volume were also measured for the ILs and R-134a. The Peng–Robinson Equation of State with van der Waals 2-parameter mixing rule with estimated IL critical points were employed to model and correlate the experimental data. The models predict the vapor–liquid equilibrium and vapor–liquid–liquid equilibrium pressure very well. However, the mixture critical points predictions are consistently lower than experimental values.

Performance of Vane-Type CO2 Expander and Characteristics of Transcritical Expansion Process

Carbon dioxide (CO2) is one candidate for alternatives to hydrofluorocarbon refrigerants for refrigeration or heat-pump cycles. Since the inherent COP of an air-cooled CO2 cycle is lower than that of HFCs, the use of an expander as an expansion device is recommended to improve the cycle performance of the CO2 cycle. The performance of the expander greatly influences the improvement of the cycle performance. Moreover, an expansion process is complicated, since the expansion process occurring in the expander operated under a typical condition proceeds from supercritical to subcritical. Therefore, it is important to clarify both the expander performance and the expansion process in the expander. In this study, a small vane-type expander is developed, and the performance of the expander is measured. The prototype vane expander has a large leakage loss, and the performance is improved by changing the way of supplying a vane back pressure. Additionally, the expansion process in the expander is examined experimentally and analytically. The transcritical expansion process is also investigated in detail by using a simple piston-cylinder expansion mechanism with a glass window. It is shown that an inflection point of the pressure change under the transcritical expansion process appears with a certain time delay in comparison with an ideal case when the inlet temperature is less than about 40°C. A cluster structure of a CO2 molecule remains for a long time after entering the subcritical region.

Autocascade refrigeration system: Experimental results in achieving ultra low temperature

In this paper the experimental results of an autocascade refrigeration system for achieving ultra low temperature are presented. The plant is used to preserve tissue and cells. When the air temperature is equal to −150°C in 0.25 m3 space, the required refrigeration power is about 250 W. The influence of the most meaningful variables is discussed with regard to the design of the plant. The experimental results show an acceptable time to reach the steady state in dependence of the finality of the plant. The working substance is a non-azeotropic mixture consisting of hydrofluorocarbon (HFC) refrigerants in addition to argon and methane. Copyright © 2009 John Wiley & Sons, Ltd.

Tribological Study Comparing PAG and POE Lubricants Used in Air-Conditioning Compressors under the Presence of CO2

Polyalkylene glycol (PAG) and polyolester (POE) synthetic lubricants are good candidates for air-conditioning systems that work with alternative refrigerants such as carbon dioxide (CO2). Both synthetic lubricants are widely used in air-conditioning compressors and have been optimized for use with hydrofluorocarbon (HFC) refrigerants. However, it is still not clear which lubricant is more suitable for use in compressors operating with CO2 as a refrigerant. This study compares the performance of PAG and POE lubricants of the same viscosity (ISO VG 68) used in air-conditioning compressors. The materials used were Al390-T6 disks and hardened steel SAE 52100 pins. The tests were performed using a high pressure tribometer (pin-on-disk configuration) in the presence of CO2. The results showed that scuffing and wear resistance of Al390-T6 tested with PAG were superior compared to the samples tested with the POE lubricant. Chemical analysis using X-ray photoelectron spectroscopy showed that PAG tends to promote the formation of carbonate layers on the surface, leading to improvement in the tribological performance of the interface.

Tribological performance of PTFE-based coatings for air-conditioning compressors

Research on coatings in environments simulating compressor conditions, especially in a carbon dioxide (CO 2) environment, has been limited. In this study, polymeric, PTFE-based coatings were investigated for use in air-conditioning compressors. Tribological experiments were performed to simulate piston-type compressors as well as swash plate compressors. Specifically, the tribological contact at the connecting “rod-wrist” pin interface of a piston-type compressor and the “shoe-disk” interface of a swash plate compressor were simulated. Machined 52100 steel wrist pins from a piston-type compressor and 52100 rounded steel pins, referred to as shoes, from a swash plate compressor were used. In both cases the counterparts were gray cast iron disks coated with three commercially available PTFE-based coatings, namely, DuPont® 958-303, DuPont® 958-414 and Whitford Xylan® 1052. These coatings were tested in CO 2 environment, while testing was also performed in ambient air, and R410a, a common hydrofluorocarbon refrigerant, and the results were compared with a diamond-like-carbon (DLC) coating. The PTFE-based coatings showed low friction characteristics and high load carrying capacity and it was found that unlike the DLC coating they were not greatly affected by the testing environment. There was a significant increase in wear of the coatings under high contact pressures, however, it was shown that the wear debris generated acted as a third-body lubricant with a beneficial role in the overall wear performance. Due to their excellent tribological behavior under a range of experimental conditions, the coatings tested in this work could find use in compressor systems and other engineering applications.

Viscosity Measurements of Compressed Liquid Refrigerant Blend R-507A, Using a Vibrating-Wire Technique

The refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydrofluorocarbon refrigerants, 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125). The paper reports viscosity measurements, performed with a vibrating-wire viscometer, of the refrigerant blend R-507A, at five temperatures in the range (253 to 293) K. The measurements were carried out at pressures from slightly above saturation up to 10 MPa, except for the isotherms at 253.26 K where the maximum pressure was 7.52 MPa and at 263.23 K where the maximum pressure was 7.09 MPa. The overall uncertainty of these measurements is estimated to be ± 1.0 %. The data obtained were correlated by means of a modified hard-sphere based correlation technique. The root-mean-square deviation, rmsd, of the experimental results from the correlation equations is 0.23 %, and their bias is not significant. This correlation method has also been used to interpolate and extrapolate the present results to enable comparisons with measurements performed by other authors of the viscosity of liquid R-507A at different temperatures and pressures.