Carbon Dioxide Refrigeration Research Articles

Design analysis of the novel Revolving Vane expander in a transcritical carbon dioxide refrigeration system

In this paper, four possible design variants of the Revolving Vane expander have been examined in relation to their application when using CO 2 as the working fluid in a refrigeration cycle. The detailed examination of the design components and illustrations are presented and discussed. The study shows that the Revolving Vane expander RV-I design configuration with the vane attached to the rotor and in which the rotor is also used as the driving component is the most superior design. It is found to have the highest mechanical efficiency and the most desirable variation of the power produced.

Friction and wear of the lubricated vane and roller materials in a carbon dioxide refrigerant

Due to environmental concerns, carbon dioxide (CO 2), a natural refrigerant, is an attractive alternative refrigerant to replace the current HFC refrigerants that are used in air conditioning systems. This paper investigated the friction and wear characteristics of sliding surfaces between a vane and an orbiting roller in a compressor in order to develop a new compressor, and especially a rotary type. The sliding tests were performed using various sliding speeds and refrigerant pressures. Two types of lubricants were used in these tests, namely POE (polyol ester) oil and PAG (polyalkylene glycol) oil. The PAG oil under the CO 2 refrigerant had better lubricity than did the POE oil. It is believed that the amounts of the CO 2 refrigerant dissolved in the POE oil were larger than those dissolved in the PAG oil. As a result, the viscosity of the PAG oil was less reduced than that of the POE oil due to the dissolved CO 2 refrigerant. The reduction in the oil viscosity was associated with the formation of the relatively thin lubricating films on the sliding surfaces. Therefore, this thin film was associated with higher friction forces and rates of wear. Surface damage during the CO 2/POE tests was one of the reasons that the wear volume was increased in this specimen. The formation of a thicker oxide layer caused less wear on the surface of the pin. It is possible that as the pressure increased, the viscosity of the POE oil dropped and the lubricant film on the sliding surface became thinner. As a consequence, the friction and the wear increased as the real area of the metallic contact increased. However, the friction and wear were nearly constant regardless of the CO 2 pressure in the CO 2/PAG mixture environment.

Carbon dioxide as the replacement for synthetic refrigerants in mobile air conditioning

Based on Kyoto Protocol and the decisions of European Commission R134a refrigerant, currently dominantly used in mobile air conditioning systems, needs to be phased-out. At present automotive industry looks at carbon dioxide (CO2; R744) as the refrigerant of the future. Apart from the environmental benefits discussed are the technical characteristics of carbon dioxide refrigeration cycle and mobile air-conditioning systems in comparison to R134a refrigerant. Analyzed are challenges emerged from the use of CO2 as refrigerant and improvement opportunities in regards to increase of the system performance and efficiency. Particular attention is dedicated to the advantages of CO2 utilization in prospective automotive heat pump systems.

Admission (Economizer) Port Optimization of a Voorhees Modified Reciprocating CO2 Compressor

Admission (the use of an economizer) is a well-known method to reduce the expansion losses of a refrigeration system. The alternative refrigerant carbon dioxide (CO2) has a relatively large isentropic exponent. Therefore, refrigeration systems using CO2 as a refrigerant have a high potential for raising efficiency by admission. Reciprocating piston compressors are favored for CO2 refrigeration applications due to the compression chamber's small sealing length and resulting low internal leakage rate. This paper presents a methodology to investigate the influence of the admission (economizer) port design of a reciprocating compressor on the admission process. The port's geometry—especially its cross-sectional area—has a large impact on the system efficiency at operation conditions and therefore needs to be optimized. For this purpose, an optimization process has been established. It is based on indicator diagram analysis. To exemplify, the measurements of three admission ports were compared at constant suction pressure (1.2 MPa relates to an evaporation temperature of −35°C) and varying admission pressures (1.4–2.6 MPa). Based on the results, the optimal port diameter for the targeted operation condition is obtained by interpolation.

Experimental study of throttling of carbon dioxide refrigerant to atmospheric pressure

The pressure in carbon dioxide (CO 2) refrigeration system is very high, and it is necessary to install a safety valve in the refrigeration system so as to release some amounts of CO 2 refrigerant through the valve as well as its downstream line into the atmosphere to eliminate overpressure. But solid CO 2 might be observed in the safety valve or its downstream line and disturb the expected function of the safety valve. As the releasing flow through the safety valve is very complex and difficult to be studied, a needle valve has been used to substitute the safety valve and to control the openings in the present paper. An experimental setup to simulate the refrigerant flow through the valve and its downstream line has been developed in order to reveal the influence of the upstream vapour quality and the opening of the throttle valve on the freezing and blockage of CO 2 in the safety valve and its downstream line under the upstream pressure of 5.7–6.1 MPa. The solid CO 2 will block the valve itself when the mass flow rate becomes less than 0.007 kg s −1; and it will block the downstream line when the mass flow rate is larger than 0.03 kg s −1. The blocking and de-blocking in the downstream line has shown periodic characteristics. The period increases with the upstream vapor quality, which varies from 0.7 to 16 s. And it is recommended to avoid oversize of the downstream line of the safety valve and to install a device to eliminate static electricity in the downstream line.

Operating Characteristics of Expander/Compressor Combination for Carbon Dioxide Refrigeration Cycle

Operating Characteristics of Expander/Compressor Combination for Carbon Dioxide Refrigeration Cycle

Ultra High Pressure Tribometer for Testing CO2 Refrigerant at Chamber Pressures up to 2000 psi to Simulate Compressor Conditions

The growing interest for using the natural refrigerant carbon dioxide (CO2) in refrigeration and air-conditioning applications instead of HFC refrigerants, due to environmental concerns, has led to the development of an ultra high pressure tribometer (UHPT) specifically tailored for testing in CO2 environment. The existing research on tribology related to CO2 environment has focused on investigations at relatively low chamber pressures due to equipment restrictions. The UHPT is a unique tribometer that has been custom designed and manufactured to allow testing under CO2 refrigerant at environmental pressures comparable to those found in compressors. A special housing, which surrounds the tribological surfaces subject to testing, is capable of withstanding chamber pressures up to 13.8 MPa (2000 psi) and can be temperature controlled from 0°C to 100°C via a thermal control system. A multi-axis strain gauge force transducer measures the applied load, frictional forces, and moments during friction testing, and computer control permits different loading profiles. Using this machine, experiments were performed at a range of pressures between 1.4 MPa (200 psi) and 6.9 MPa (1000 psi) of CO2 refrigerant. The results suggest a slightly better tribological performance at higher pressures compared to lower pressures.

Tribological investigation of cast iron air-conditioning compressor surfaces in CO2 refrigerant

Tribological investigations of air-conditioning compressors have been a topic of great interest in recent years and gray cast iron has been a commonly used material by various compressor manufacturers. The scope of this paper is to determine the role of oxygen and in particular carbon dioxide refrigerant (R744) in cast iron samples tribologically tested using an Ultra High Pressure Tribometer that is suitable for tribological testing of compressor contact interfaces that operate with carbon dioxide refrigerant. A series of experiments was performed in environments of air, nitrogen (N2), oxygen (O2) and carbon dioxide (CO2). While it was found that the presence of oxygen is beneficial, CO2 has a more positive effect on the surfaces than in the case of pure O2 suggesting that the use of CO2 promotes a different wear mechanism. Also, it was found that CO2 has better tribological performance over a range of pressures between 100 psi (0.69 MPa) to 600 psi (4.1 MPa), compared to lower pressures. Furthermore, CO2 was compared with tetrafluorethane (R134a), a common hydrofluorocarbon refrigerant and found to have superior tribological performance. Two surface chemical analysis techniques were utilized to examine the surfaces after tribological testing. Auger electron spectroscopy (AES) was used to track changes in the elemental composition while X-ray photoelectron spectroscopy (XPS) was utilized to detect the different chemical states resulting from compound formation on the tribologically tested surfaces. It was found that CO2 leads to better tribological performance of the interface due to the formation of carbonates on the surface, which reduce friction and prevent wear.

Construction and testing of a wet-compression absorption carbon dioxide refrigeration system for vehicle air conditioner

The environmental benefits of the transcritical carbon dioxide (CO 2) refrigeration cycle are considerable. But its application is greatly challenged by the high operation pressure, which could be as high as 120 bar. A wet-compression absorption (WCA) CO 2 refrigeration cycle was constructed by adding a non-volatile liquid into a CO 2 refrigeration cycle. CO 2 is highly soluble in the liquid and easily absorbed and desorbed by it. In the WCA CO 2 refrigeration cycle, the high side pressure was less than 35 bar, which was tremendously reduced compared to the transcritical CO 2 refrigeration cycle. In this paper, following a thermodynamic analysis of working fluid, a WCA CO 2 refrigeration demonstrator plant was constructed within the restricted physical and operational envelope of an existing vehicle refrigeration unit. This unique plant operated satisfactorily, delivering sustainable cooling for refrigerated vehicle. The relationship between system performance and the cycle ratio and IHX (internal heat exchanger) efficiency was tested. The components used in the demonstrator were entirely based on existing components and not optimized and considerable potential exists for efficiency improvements.

Performance investigation of transcritical carbon dioxide two-stage compression cycle with expander

The trend toward the energy efficiency improvement for transcritical carbon dioxide refrigeration cycles has led to the development of the two-stage compression process. Three different variations of transcritical carbon dioxide two-stage compression cycles with expanders are investigated by using thermodynamics analysis. They are the two-stage compression at optimal intermediate pressure (TCOP) cycle, two-stage compression with expander driving high-pressure stage (TCDH) cycle and two-stage compression with expander driving low-pressure stage (TCDL) cycle, respectively. The performance of the TCOP cycle and the single-stage compression with expander (SCE) cycle is mainly discussed and compared for a wide operating condition. It is found that the COP and exergy efficiency of the TCOP cycle are on average 9% higher than those of the SCE cycle. At given design points, the COP of the TCDH cycle outperforms the other options, showing 11.32%, 9.65% and 0.72% performance improvement over the TCDL cycle, SCE cycle and the TCOP cycle, respectively. If design and structure are also taken into account, the TCDH cycle is a feasible option since the expander and the auxiliary compressor are integrated into one unit; thus, the transfer loss and leakage loss can be decreased greatly. The key problem is to adopt some measures that control the operating conditions to avoid deviating from the design point.

05/02743 Exergy analysis of transcritical carbon dioxide refrigeration cycle with an expander

05/02743 Exergy analysis of transcritical carbon dioxide refrigeration cycle with an expander

Exergy analysis of transcritical carbon dioxide refrigeration cycle with an expander

In this paper, a comparative study is performed for the transcritical carbon dioxide refrigeration cycles with a throttling valve and with an expander, based on the first and second laws of thermodynamics. The effects of evaporating temperature and outlet temperature of gas cooler on the optimal heat rejection pressure, the coefficients of performance (COP), the exergy losses, and the exergy efficiencies are investigated. In order to identify the amounts and locations of irreversibility within the two cycles, exergy analysis is employed to study the thermodynamics process in each component. It is found that in the throttling valve cycle, the largest exergy loss occurs in the throttling valve, about 38% of the total cycle irreversibility. In the expander cycle, the irreversibility mainly comes from the gas cooler and the compressor, approximately 38% and 35%, respectively. The COP and exergy efficiency of the expander cycle are on average 33% and 30% higher than those of the throttling valve cycle, respectively. It is also concluded that an optimal heat rejection pressure can be obtained for all the operating conditions to maximize the COP. The analysis results are of significance to provide theoretical basis for optimization design and operation control of the transcritical carbon dioxide cycle with an expander.

Industry Genius - Inventions and People Protecting the Climate and Fragile Ozone Layer

Preface: genius for the next generation Richard H. Truly Foreword: Just when Earth needed genius Jacqueline Aloisi de Larderel Introduction Stephen O. Andersen and Durwood Zaelke 1. Alcoa Aluminum: energy in the bank 2. Aviation Partners: future is on the wing 3. DaimlerChrysler: champagne of natural refrigerants 4. Energy Star: isn't all you're saving 5. Japan's F-Center for developing greenhouse gas alternatives: living through chemistry 6. Honda: and it will happen 7. Seiko Epson: Some day all products will be made the Epson way 8. ST Microelectronics: on, plug off 9. Trane: about making green 10. Visteon: proves simple is better THE GENIUS COMPANIES Alcoa: Putting Energy in the Bank Shifting a century-old engineering paradigm from process optimization toward production with big financial and climate benefits. Aviation Partners: The Future is On the Wing A dream team of retired engineers challenged the conventional wisdom of aerodynamics with Blended Winglets that increase the fuel efficiency an astonishing 7%-now a joint venture with Boeing will retrofit the global aircraft fleet. DaimlerChrysler: The Champagne of Natural Refrigerants Engineer advocates of air conditioning with natural carbon dioxide refrigerant energized the motor vehicle industry to protect the climate with higher fuel efficiency and lower greenhouse gas emissions. Energy Star(R): Money Isn't All You're Saving State-of-the-art marketing in this government branding program promotes energy-saving appliances with empowered customers, rewarded companies, and the clout of government procurement. Japan's F-Center for Greenhouse Gas Alternatives: Sustainable Living through Chemistry Designing sustainable chemicals safe for the ozone layer, climate, and ecosystem in a collaboration of chemical industries and the Japan Ministry of Economy, Trade and Industry. Honda: Dream and It Will Happen Engineers merge cutting-edge combustion, electric, hybrid, fuel cell, advanced materials, aerodynamic, and regenerative technology for Earth-friendly products that deliver the triple bottom line. Seiko Epson: Someday All Products Will Be Made the Epson Way Striving for manufacturing and a world where the kinetic energy of keystrokes and motion powers portable computers, cell phones, and personal entertainment systems. ST Microelectronics: Turn On, Plug Out Using the power of semiconductors to eliminate energy waste in battery chargers and other consumer products-dramatically cutting electricity consumption. Trane: It's about Making Green A breakthrough in energy efficiency for building and process air conditioning chillers raises the bar on environmental performance and cost savings. Visteon: Superintegration(TM) Proves Simple Is Better A fresh design integrates flexible electronic circuits to reduce materials, space, and weight and at the same time improve the reliability and energy efficiency of automobiles.

スイング圧縮機搭載CO_2給湯機の開発(FP4 省エネルギー・小型分散・コジェネ技術)

A heat pump water heater system using carbon dioxide refrigerant can supply high temperature water efficiently. Carbon dioxide is the natural working fluid without inflammability, toxicity and environmental impact. Otherwise carbon dioxide has high operating pressure and high density. We chose a swing compressor as the solution for this system. Practically, reduction of the operating sound is important for the system to operate in the nighttime. We developed a new compact heat exchanger and a new fan for suitable operation.

Modelling and transient simulation of CO2-refrigeration systems with Modelica

This paper presents the current results of the development of a Modelica library for CO2-refrigeration systems based on the free Modelica library ThermoFluid. The development of the library is carried out in a research project of Airbus Deutschland and the TUHH and is focused on the aim to obtain a library for detailed numerical investigations of refrigeration systems with the rediscovered refrigerant carbon dioxide (CO2). A survey of the concept of an integrated on-board cooling system of airliners, the modelling language Modelica™ and the CO2-library is given and the modelling of CO2-heat exchangers is described. A comparison with steady state results of heat exchangers shows a fair agreement. The presented transient simulation results are compared with experimental data showing also a fair agreement.

Transcritical Carbon Dioxide Refrigeration Cycle Model With Visual Interface

This article presents a transcritical carbon dioxide refrigeration cycle model with a visual interface. The model is easy to use and allows both experts and novices with little experience or prior knowledge to easily model transcritical carbon dioxide refrigeration cycles for various applications. To illustrate the power of the model, we simulated a carbon dioxide-based automotive air-conditioning system. As the dominant thermodynamic losses for systems operating at moderate to high ambient temperatures are the expansion losses, we simulated both a baseline system and systems equipped with additional hardware specifically designed to reduce the expansion-side losses. The coefficient of performance (COP) and cooling capacity of the baseline system are 1.90 and 3.28 kW, respectively. The most efficient system equipped with additional hardware was one that included an isentropic expansion process with 100% work recovery. The COP and cooling capacity for this system are 3.22 and 3.57 kW, respectively, which represents a 69.5% and an 8.8% improvement in the COP and cooling capacity, respectively.

Determination of the optimum high pressure for transcritical CO 2-refrigeration cycles

Modern refrigeration systems have to fulfill many requirements, which include a rapidly growing number of environmental aspects. For compression systems, this entails demands for low energy for propulsion of the systems and a high coefficient of performance ( COP) respectively. Compression systems using the ecological refrigerant carbon dioxide (CO 2) are often run at transcritical conditions. This means that the evaporation of the refrigerant takes place at subcritical conditions, whereas the heat rejection into the environment occurs at supercritical pressures and temperatures. For such transcritical CO 2-systems with the main components compressor, gas cooler, expansion unit and evaporator, a maximum COP exists, depending on system, environmental conditions and operating conditions. The COP is influenced mainly by high pressure. A graphical method from the literature to determine the optimum high pressure is too time-consuming if several operating conditions are investigated. With a simulation model, the optimum high pressure can easily be determined for different operating conditions as a function of the refrigerant temperature at the gas cooler outlet. With these data it is possible to determine a control function. This function is used to adjust the high pressure so that the system can be run with a COP that deviates from the maximum values by less than 5.8%.

Heat Transfer from Supercritical Carbon Dioxide in Tube Flow: A Critical Review

Since the discovery that CFCs and HCFCs destroy the ozone layer and cause global warming, the need to regulate their use has been critical. In the ensuing search for new environmentally benign refrigerants, carbon dioxide has been considered due to its excellent thermophysical properties. This paper gives a review of the heat transfer and pressure drop characteristics of supercritical carbon dioxide in tube flow. This information is necessary for designing the gas cooler of a carbon dioxide refrigeration system. A comparison of the different heat transfer correlations applicable to cooling of supercritical carbon dioxide has also been made.

Theoretical Evaluation of Carbon Dioxide Refrigeration Cycle

Concerns of ozone depletion and global warming call for investigation of natural refrigerants. In this study the performance potential of the carbon dioxide refrigeration cycle is investigated theoretically. For this purpose, two cycle simulation models were developed. One is an Evans-Perkins cycle model for R-22, and the other is a transcritical cycle model for CO2. By using these models, the CO2 refrigeration cycle and heat exchangers for the CO2 refrigeration cycle were optimized. The water chilling and tap water heating performances of CO2 were compared to those of R-22. The thermophysical properties of CO2 and the proper heat exchanger design appropriate to CO2 offer the opportunity of reducing heat exchanger size and mass for tap water heating applications.

A new, efficient and environmentally benign system for car air-conditioning

There is a widespread belief that the only viable refrigerants in most applications are new fluorocarbon chemicals. This trend will result in continued emissions of several hundred thousand tonnes of alien chemicals to the atmosphere each year, involving the potential risk of unforeseen environmental effects. A number of other options exist, or may be developed. By using substances that already have a natural role in the ecosystem, some uncertainty about the critical issue of our future environment can be avoided. By development and practical testing of a laboratory prototype it has been shown that carbon dioxide is an excellent refrigerant in car air-conditioners, solving completely all environmental problems associated with such systems. General use of carbon dioxide as a refrigerant may provide a number of advantages in the present situation, both from an environmental and practical point of view. It is the authors' considered opinion that the use of the old refrigerant carbon dioxide offers a key to the complete solution of the environmental problems in many areas of refrigeration usage.