Journal articles: 'Transcritical CO2'

1

Liu, Ying Fu, Chun Jing Geng, and Guang Ya Jin. "Vortex Tube Expansion Transcritical CO2 Heat Pump Cycle." Applied Mechanics and Materials 190-191 (July 2012): 1340–44. http://dx.doi.org/10.4028/www.scientific.net/amm.190-191.1340.

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The application of natural refrigerant CO2 is of great significance to reduce the greenhouse effect and ozone depletion. Transcritical CO2 heat pump cycle is presently an important aspect of natural refrigerant alternatives research. In this paper, a vortex tube expansion transcritical CO2 heat pump cycle is established and compared to that of the transcritical CO2 refrigeration cycle with throttle valve. Thermodynamic analysis results indicate that the system performance of vortex tube expansion transcritical CO2 heat pump cycle is better than the transcritical CO2 heat pump cycle with throttle valve, and the COPh improvement is 5.8%~13.9% at given conditions. The gas-cooler outlet temperature has a great impact on the system performance, there is a higher COPh improvement when the cycle at lower evaporation temperature or higher gas-cooler outlet temperature.

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Yang, Dazhang, Yang Li, Jing Xie, and Jinfeng Wang. "Research and application progress of transcritical CO2 refrigeration cycle system: a review." International Journal of Low-Carbon Technologies 17 (December 8, 2021): 245–56. http://dx.doi.org/10.1093/ijlct/ctab086.

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Abstract CO2 refrigerant and its transcritical cycle system have become the research focus in the refrigeration field due to their advantages of environmentally friendly, safe and low environmental temperature adaptability. This paper summarizes the research progress on the modified methods for the defects of basic transcritical CO2 refrigeration cycle system in recent years. Meanwhile, the technical status of transcritical CO2 refrigeration technology in commercial supermarket refrigeration, heat pump system, automobile air conditioning and artificial ice rink is discussed in detail. Finally, the development of transcritical CO2 refrigeration cycle system is prospected and the key problems to be solved are put forward.

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Yang, Dazhang, Yang Li, Jing Xie, and Jinfeng Wang. "Research and application progress of transcritical CO2 refrigeration cycle system: a review." International Journal of Low-Carbon Technologies 17 (December 8, 2021): 245–56. http://dx.doi.org/10.1093/ijlct/ctab086.

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Abstract CO2 refrigerant and its transcritical cycle system have become the research focus in the refrigeration field due to their advantages of environmentally friendly, safe and low environmental temperature adaptability. This paper summarizes the research progress on the modified methods for the defects of basic transcritical CO2 refrigeration cycle system in recent years. Meanwhile, the technical status of transcritical CO2 refrigeration technology in commercial supermarket refrigeration, heat pump system, automobile air conditioning and artificial ice rink is discussed in detail. Finally, the development of transcritical CO2 refrigeration cycle system is prospected and the key problems to be solved are put forward.

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4

Belman-Flores, J. M., V. H. Rangel-Hernández, V. Pérez-García, A. Zaleta-Aguilar, Qingping Fang, and D. Méndez-Méndez. "An Advanced Exergoeconomic Comparison of CO2-Based Transcritical Refrigeration Cycles." Energies 13, no. 23 (December 6, 2020): 6454. http://dx.doi.org/10.3390/en13236454.

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CO2-based transcritical refrigeration cycles are currently gaining significant research attention, as they offer a viable solution to the use of natural refrigerants (e.g., CO2). However, there are almost no papers that offer an exergoeconomic comparison between the different configurations of these types of systems. Accordingly, the present work deals with a comparative exergoeconomic analysis of four different CO2-based transcritical refrigeration cycles. In addition, the work is complemented by an analysis of the CO2 abatement costs. The influences of the variation of the evaporating temperature, the gas cooler outlet temperature, and the pressure ratio on the exergy efficiency, product cost rate, exergy destruction cost rate, exergoeconomic factor, and CO2 penalty cost rate are compared in detail. The results show that the transcritical cycle with the ejector has the lowest exergetic product cost and a low environmental impact.

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Feng, Fan, Ze Zhang, Xiufang Liu, Changhai Liu, and Yu Hou. "The Influence of Internal Heat Exchanger on the Performance of Transcritical CO2 Water Source Heat Pump Water Heater." Energies 13, no. 7 (April 8, 2020): 1787. http://dx.doi.org/10.3390/en13071787.

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The characteristics of the transcritical CO2 heat pump water heater (HPWH) system are; a lower inlet hot water temperature (Ti-hw) (sometimes this is lower than the water source temperature), and an outlet gas cooler temperature (To-gc) which is affected by the Ti-hw and often lower than the critical temperature. In order to study the effects of the internal heat exchanger (IHX) on the operational performance of the transcritical CO2 HPWH when To-gc is low, a transcritical CO2 water source HPWH experiment platform is established to conduct experimental research and comparative analysis on the operational performance of the transcritical CO2 water source HPWH, with or without IHX. It is found that, if only the coefficient of performance (COP) and heating at the optimal exhaust pressure of the transcritical CO2 water source HPWH were considered, COP and the heating of the non-IHX system would be slightly higher than those of the IHX system at the lower hot water flow and water source temperature, and this increase was not obvious. At the higher hot water flow rate and water source temperature, COP and the heating of the non-IHX system were also higher than those of the IHX system, and the increase was obvious. The experiment results showed that, near the optimal exhaust pressure, the variation range of COP and heating of the IHX system is relatively small, and the system has a relatively high stability.

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Sarkar, Jahar. "Performance improvement of double-tube gas cooler in CO2 refrigeration system using nanofluids." Thermal Science 19, no. 1 (2015): 109–18. http://dx.doi.org/10.2298/tsci120702121s.

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The theoretical analyses of the double-tube gas cooler in transcritical carbon dioxide refrigeration cycle have been performed to study the performance improvement of gas cooler as well as CO2 cycle using Al2O3, TiO2, CuO and Cu nanofluids as coolants. Effects of various operating parameters (nanofluid inlet temperature and mass flow rate, CO2 pressure and particle volume fraction) are studied as well. Use of nanofluid as coolant in double-tube gas cooler of CO2 cycle improves the gas cooler effectiveness, cooling capacity and COP without penalty of pumping power. The CO2 cycle yields best performance using Al2O3-H2O as a coolant in double-tube gas cooler followed by TiO2-H2O, CuO-H2O and Cu-H2O. The maximum cooling COP improvement of transcritical CO2 cycle for Al2O3-H2O is 25.4%, whereas that for TiO2-H2O is 23.8%, for CuO-H2O is 20.2% and for Cu-H2O is 16.2% for the given ranges of study. Study shows that the nanofluid may effectively use as coolant in double-tube gas cooler to improve the performance of transcritical CO2 refrigeration cycle.

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Liu, Ying Fu, and Guang Ya Jin. "Vortex Tube Expansion Two-Stage Transcritical CO₂ Refrigeration Cycle." Advanced Materials Research 516-517 (May 2012): 1219–23. http://dx.doi.org/10.4028/www.scientific.net/amr.516-517.1219.

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Use of vortex tube as an expansion device in transcritical CO2 cycle could reduce the throttle loss and improve the coefficient of performance. In this paper, a vortex tube expansion two-stage transcritical CO2 refrigeration cycle(VTTC) is established and compared to that of the two-stage transcritical CO2 refrigeration cycle with throttle valve(TVTC). Thermodynamic analysis results indicate that there is also an optimum heat rejection pressure for the vortex tube cycle, and the COP improvement is 2.4%~16.3% at given conditions. Decrease in evaporation temperature or increase in gas-cooler outlet temperature decrease the COP, but the COP improvement will increase. The effect of cold mass fraction on the COP is negligible, but the COP improvement will increase fast with the increase of cold mass fraction.

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Fukuta, Mitsuhiro, Yuki Nakamura, and Tadashi Yanagisawa. "Characteristics of CO2 transcritical expansion process." HVAC&R Research 19, no. 7 (August 19, 2013): 767–78. http://dx.doi.org/10.1080/10789669.2013.833544.

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SARKAR, JAHAR. "TRANSCRITICAL CO2 REFRIGERATION SYSTEMS: COMPARISON WITH CONVENTIONAL SOLUTIONS AND APPLICATIONS." International Journal of Air-Conditioning and Refrigeration 20, no. 04 (December 2012): 1250017. http://dx.doi.org/10.1142/s2010132512500174.

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Carbon dioxide (CO2) is one of the natural refrigerants which can be used as working fluid in various refrigeration applications along with the ammonia and hydrocarbons due to its eco-friendliness, higher volumetric capacity, good heat transfer properties, etc. The present article consists of two parts: A detailed comparative study of CO2 -based transcritical refrigeration systems with conventional refrigerants-based systems in terms of both thermodynamic and heat transfer performances, and review of both theoretical and experimental researches on transcritical CO2 vapor compression cycle for various refrigeration applications including commercial product status. Suitability of the CO2 system in specific refrigeration application is also discussed.

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Verma, Abhishek, S. C. Kaushik, and S. K. Tyagi. "Thermodynamic Analysis of a Combined Single Effect Vapour Absorption System and tc-CO2 Compression Refrigeration System." HighTech and Innovation Journal 2, no. 2 (June 1, 2021): 87–98. http://dx.doi.org/10.28991/hij-2021-02-02-02.

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Transcritical CO2 refrigeration system is coupled with the single effect vapour absorption with LiBr-water as a working pair having an objective to enhance the performance of low temperature transcritical refrigeration system while using natural working pair and to reduce the electricity consumption to produce low temperature refrigeration. The high grade waste heat rejected in the gas cooler of tc-CO2 compression refrigeration system (TCRS) is utilized to run the single effect vapour absorption system (SEVAR) to enhance the energy efficiency of the system. The gas cooler in the transcritical CO2 system is having heat energy at high temperature and pressure, which is utilized to run the vapour absorption system, while the other refrigerant heat exchanger provides subcooling to further enhance the performance. The combined cycle can provide refrigeration temperature at different levels, to use it for different applications. Energetic and exergetic analysis have been done to analyze the combined system to compute the performance parameters and the irreversibilities occurring in different components to further increase the performance. The combined system is optimized for various heat rejection and refrigeration temperatures. The COP of the combined system has been enhanced by to 24.88% while the enhancement in exergetic efficiency (ηex) is observed as 10.14% respectively over tradition transcritical CO2 compression refrigeration system, with -10°C as an evaporation (TCRS cooling) temperature and exit temperature of gas cooler T4 being 40°C. Doi: 10.28991/HIJ-2021-02-02-02 Full Text: PDF

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11

Bellos, Evangelos, and Christos Tzivanidis. "CO2 Transcritical Refrigeration Cycle with Dedicated Subcooling: Mechanical Compression vs. Absorption Chiller." Applied Sciences 9, no. 8 (April 18, 2019): 1605. http://dx.doi.org/10.3390/app9081605.

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The objective of this paper is the comparison of two dedicated subcooling methods, after the gas cooler, in a CO2 transcritical refrigeration system. The use of vapor compression refrigeration with R134a for subcooling is the first method, and the second is the use of an absorption chiller that operates with a LiBr-H2O working pair. The examined systems are compared energetically and exegetically with the reference transcritical CO2 refrigeration cycle without subcooling. The analysis is conducted for different operating scenarios and in every case, the system is optimized by selecting the proper temperature and pressure levels. The analysis is performed with a developed and validated model in Engineering Equation Solver. According to the final results, the use of the absorption chiller is able to decrease the system electricity consumption by about 54% compared to the simple transcritical cycle, while the decrease with the mechanical subcooling is 41%. Both systems with dedicated subcooling are found to have an important increase in the system exergy performance compared to the simple transcritical cycle. However, the system with the mechanical subcooling is found to be the best choice exegetically, with a small difference from the system with the absorption chiller.

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12

Belusko, Martin, Raymond Liddle, Alemu Alemu, Edward Halawa, and Frank Bruno. "Performance Evaluation of a CO2 Refrigeration System Enhanced with a Dew Point Cooler." Energies 12, no. 6 (March 20, 2019): 1079. http://dx.doi.org/10.3390/en12061079.

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Dew point cooling (DPC) is a novel indirect evaporative cooling concept capable of delivering air temperatures approaching the dew point. Coupling this technology with CO2 refrigeration is well suited to minimising transcritical operation when the coefficient of performance (COP) is dramatically reduced in hot climates. A substantial experimental program was conducted to characterise this combination by testing a 20 kW CO2 refrigeration system subject to ambient temperatures above 40 °C. It was demonstrated that DPC operation not only avoided transcritical operation during such weather conditions, but also increased the COP by up to 140% compared to the conventional system. The combination of these technologies was successfully mathematically modelled, from which the optimum condenser inlet air temperature was identified for each condenser temperature. Using this optimum condition, it was possible to maximise the COP for a range of conditions applicable to the psychometric chart. An annual case study for Adelaide, Australia was conducted which demonstrated that optimally coupling DPC with CO2 refrigeration can reduce the annual energy consumption and peak demand by 16% and 47%, respectively, compared to a conventional CO2 booster system. Furthermore, the number of hours of transcritical operation was reduced from 3278 to 27.

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Rony, Rajib, Huojun Yang, Sumathy Krishnan, and Jongchul Song. "Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review." Energies 12, no. 3 (January 31, 2019): 457. http://dx.doi.org/10.3390/en12030457.

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Heat pump (HP) is one of the most energy efficient tools for address heating and possibly cooling needs in buildings. Growing environmental concerns over conventional HP refrigerants, chlorofluorocarbons (CFCs), and hydrofluorocarbons (HFCs) have forced legislators and researchers to look for alternatives. As such, carbon dioxide (R744/CO2) has come to light due to its low global warming potential (GWP) and zero ozone depleting characteristics. Even though CO2 is environmentally benign, the performance of CO2 HP has been of concern since its inception. To improve the performance of CO2 HP, research has been playing a pivotal role in developing functional designs of heat exchangers, expansion devices, and compressors to suit the CO2 transcritical cycle. Different CO2 HP cycles coupled with auxiliary components, hybrid systems, and refrigerant mixtures along with advanced control strategies have been applied and tested. This paper presents a complete overview of the most recent developments of transcritical CO2 HPs, their components, and applications.

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Ning, Jing Hong, and Sheng Chun Liu. "Design and Performance Analysis on CO₂ Combined System in Supermarket." Advanced Materials Research 433-440 (January 2012): 1219–25. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.1219.

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This paper reports a combined space cooling, space heating, water heating and food refrigeration system (named CO2 combined system) in supermarket. This system using CO2 as the working fluid consists of a two-stage CO2 transcritical cycle used for food refrigeration, a single-stage CO2 transcritical cycle for space cooling in summer and space heating in winter. The waste heat emitted from the CO2 gas cooling in food refrigeration cycle and space cooling and space heating cycles is recovered by heat recover exchanger and is used to provide hot water for space heating and for general usage, such as the catering, the washing and the toilet facilities in the supermarket. So this CO2 combined system improves the coefficient of performance, decreases the energy consumption as well as reduces the heat pollution. Moreover, this CO2 combined system is compared with typical conventional supermarket technology, the results show that the energy consumption of CO2 combined system is reduced largely and energy efficiency is increased obviously. It can be concluded that the CO2 combined system has a good future for protecting environment and saving energy.

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Wu, Zhongkai, Feifei Bi, Jiyou Fei, Zecan Zheng, Yulong Song, and Feng Cao. "The Collaborative Optimization of the Discharge Pressure and Heat Recovery Rate in a Transcritical CO2 Heat Pump Used in Extremely Low Temperature Environment." Energies 16, no. 4 (February 20, 2023): 2059. http://dx.doi.org/10.3390/en16042059.

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Considering the excellent environmental properties and heating capability under wide running conditions of the natural fluid CO2, the transcritical CO2 heat pump system has widely been used in the application of water heaters, commercial heating and cooling, electric vehicle thermal management, etc. Since the performance was highly affected by the discharge pressure and heat recovery rate in a transcritical CO2 system, the collaborative optimization of these two parameters was analyzed in detail in this study. The results showed that the optimal value of the system heating COP, which was the ration of heating capacity to power consumption, was better under a higher heat recovery rate and relatively lower discharge pressure, which is why these kinds of operating conditions are highly recommended from the perspective of collaborative optimization. Additionally, the heat recovery rate had a positive effect on the system performance when the discharge pressure was lower than its optimal value, while the heat recovery rate would present a passive effect on the system performance when the discharge pressure was higher than its optimal value. The relevant conclusions of this study provide a good theoretical basis for the efficient and stable operation of the transcritical CO2 heat pump technology under the conditions of a wide ambient temperature range.

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Ji, Hongzeng, Jinchen Pei, Jingyang Cai, Chen Ding, Fen Guo, and Yichun Wang. "Review of Recent Advances in Transcritical CO2 Heat Pump and Refrigeration Cycles and Their Development in the Vehicle Field." Energies 16, no. 10 (May 10, 2023): 4011. http://dx.doi.org/10.3390/en16104011.

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Refrigerant substitution is an urgent need in the context of reducing carbon emissions and slowing global warming. CO2 is now being proposed as a promising solution based on its excellent properties and system performance, especially in low-temperature environments. This paper presents an overview of recent advances in system configuration and operation characteristics to improve the performance of transcritical CO2 heat pump and refrigeration systems. The paper first introduces the basic research background, system cycle, and thermodynamic characteristics. Secondly, CO2 cycle improvements with single modifications and modification combinations are reviewed. Then, some important operation characteristics and control methods are discussed. Additionally, the paper provides a detailed description of the development of transcritical CO2 heat pump and refrigeration systems in the vehicle field. At the end of this review, conclusions and opportunities for future work in this field are presented.

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Liu, Ying Fu, Peng Yu Shen, and Guang Ya Jin. "Experimental Investigation on Transcritical CO₂ Refrigeration System." Advanced Materials Research 516-517 (May 2012): 1156–59. http://dx.doi.org/10.4028/www.scientific.net/amr.516-517.1156.

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The application of natural refrigerant CO2 is of great significance to reduce the greenhouse effect and ozone depletion. Transcritical CO2 refrigeration cycle is presently an important aspect of natural refrigerant alternatives research. In this paper, the transcritical CO2 refrigeration cycle system is experimentally studied, effect on performance of heat rejection pressure, gas-cooler outlet temperature and evaporation temperature is analyzed. The experimental results show that there is an optimum high pressure to achieve the maximum COP, the evaporation temperature and gas-cooler exit temperature have great impact on the COP. Increase of gas-cooler outlet temperature led to a rapid increase in the optimal high pressure, but effect of evaporation temperature is not obvious. So in order to obtain the optimum performance, the influence of heat rejection pressure, evaporating temperature and gas-cooler outlet temperature should be considered during the designing and operating CO2 refrigeration cycle system.

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Zhang, Chun-Lu, and Liang Yang. "Modeling of Supercritical CO2 Flow Through Short Tube Orifices." Journal of Fluids Engineering 127, no. 6 (July 11, 2005): 1194–98. http://dx.doi.org/10.1115/1.2060738.

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The transcritical cycle of carbon dioxide (CO2) is a promising alternative approach to heat pumps and automobile air conditioners. As an expansion device, the short tube orifice in a transcritical CO2 system usually receives supercritical fluid at the entrance and discharges a two-phase mixture at the exit. In this work, a two-fluid model (TFM) is developed for modeling the flow characteristics of supercritical CO2 through the short tube orifice. The deviations between the TFM predictions and the measured mass flow rates are within ±20%. Meanwhile, the TFM predicts reasonable pressure, temperature, and velocity distributions along the tube length. The small values of interphase temperature difference and velocity slip indicate that the nonequilibrium characteristics of the two-phase flow of CO2 in the short tube orifice are not significant. Consequently, the homogeneous equilibrium model reduced from the TFM gives a good prediction of the mass flow rate as well.

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Li, Daqing, and Eckhard A. Groll. "Transcritical CO2 refrigeration cycle with ejector-expansion device." International Journal of Refrigeration 28, no. 5 (August 2005): 766–73. http://dx.doi.org/10.1016/j.ijrefrig.2004.10.008.

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Barroca, Pierre, Armin Hafner, Bart Verlaat, Paolo Petagna, Wojciech Hulek, Lukasz Zwalinski, Pierre Hanf, Michele Battistin, Loic Davoine, and Daniella Teixeira. "An Ultra-Low Temperature Transcritical R744 Refrigeration System for Future Detectors at CERN LHC." Applied Sciences 11, no. 16 (August 11, 2021): 7399. http://dx.doi.org/10.3390/app11167399.

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The cooling systems of the future tracking detectors of the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN will be entirely based on CO2 refrigeration technology. The system is a booster refrigeration system, composed of a two stage primary part with transcritical R744 equipment and a low temperature secondary CO2 pumped loop. The primary refrigeration sub-system installed on surface provides cold R744 at −53∘C to the CO2 pumped loops installed 100 m underground and rejects the heat exchanged. The process must be reliable and remain stable regardless of the amount of heat exchanged, which will amount to hundreds of kilowatts and is expected to vary throughout the lifetime of the detectors. The paper discusses the concept adopted for the innovative transcritical R744 cycle and describes the technical details of the first prototype built.

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Wang, Yikai, Yifan He, Yulong Song, Xiang Yin, Feng Cao, and Xiaolin Wang. "Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid." Energies 14, no. 15 (July 23, 2021): 4470. http://dx.doi.org/10.3390/en14154470.

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Given the large demand nowadays for domestic hot water, and its impact on modern building energy consumption, air source transcritical CO2 heat pumps have been extensively adopted for hot water production. Since their system efficiency is limited by significant irreversibility, a CO2-based mixture could offer a promising drop-in technology to overcome this deficiency without increasing system complexity. Although many CO2 blends have been studied in previously published literature, little has been presented about the CO2/R32 mixture. Therefore, a proposed mixture for use in transcritical CO2 heat pumps was analyzed using energy and exergy analysis. Results showed that the coefficient of performance and exergy efficiency variation displayed an “M” shape trend, and the optimal CO2/R32 mixture concentration was determined as 0.9/0.1 with regard to flammability and efficiency. The irreversibility of the throttling valve was reduced from 0.031 to 0.009 kW⋅kW−1 and the total irreversibility reduction was more notable with ambient temperature variation. A case study was also conducted to examine domestic hot water demand during the year. Pure CO2 and the proposed CO2 blend were compared with regard to annual performance factor and annual exergy efficiency, and the findings could provide guidance for practical applications in the future.

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Fazelpour, Farivar. "Energetic and exergetic analyses of carbon dioxide transcritical refrigeration systems for hot climates." Thermal Science 19, no. 3 (2015): 905–14. http://dx.doi.org/10.2298/tsci121007026f.

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In the last two decades many scientific papers and reports have been published in the field of the application of the carbon dioxide as a refrigerant for refrigeration systems and heat pumps. Special attention has been paid to the transcritical cycle. However, almost no papers discussed such cycles for hot climates, i.e., when the temperature of the environment is higher than 40?? during a long period of time. This paper deals with the energetic and exergetic evaluation of a CO2 refrigeration system operating in a transcritical cycle under hot climatic conditions. The performance and exergy efficiency of the CO2 refrigeration system depend on the operation conditions. The effect of varying these conditions is also investigated as well as the limitations associated with these conditions.

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Bai, Wanjin, and Xiaoxiao Xu. "Comparative analyses of two improved CO2 combinated cooling, heating, and power systems driven by solar energy." Thermal Science 22, Suppl. 2 (2018): 693–700. http://dx.doi.org/10.2298/tsci171008054b.

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To make use of solar energy fully and efficiently, the two improved combined cooling, heating, and power systems (CCHP) are proposed by adding a gas heater and an extraction turbine, based on the transcritical CO2 ejector refrigeration system. A relatively high pressure fluid is extracted by the extraction turbine as a primary stream of ejector to improve the ejector performance. In the meantime, the gas heater absorbs low temperature exhaust heat to increase the extraction turbine?s output work. Comparative studies on the thermal efficiency and exergy efficiency of the two improved systems show they are more efficient alternatives for the transcritical CO2 ejector refrigeration system. The CCHP-B system has relatively broad working condition, higher thermal efficiency and exergy efficiency than that of CCHP-A system.

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Catalán-Gil, J., L. Nebot-Andrés, D. Sánchez, R. Llopis, R. Cabello, and D. Calleja-Anta. "Improvements in CO2 Booster Architectures with Different Economizer Arrangements." Energies 13, no. 5 (March 9, 2020): 1271. http://dx.doi.org/10.3390/en13051271.

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CO2 transcritical booster architectures are widely analyzed to be applied in centralized commercial refrigeration plants in consonance with the irrevocable phase-out of HFCs. Most of these analyses show the limitations of CO2 cycles in terms of energy efficiency, especially in warm countries. From the literature, several improvements have been proposed to raise the booster efficiency in high ambient temperatures. The use of economizers is an interesting technique to reduce the temperature after the gas cooler and to improve the energy efficiency of transcritical CO2 cycles. The economizer cools down the high pressure’s line of CO2 by evaporating the same refrigerant extracted from another point of the facility. Depending on the extraction point, some configurations are possible. In this work, different booster architectures with economizers have been analyzed and compared. From the results, the combination of the economizer with the additional compressor allows obtaining energy savings of up to 8.5% in warm countries and up to 4% in cold countries with regard to the flash-by-pass arrangement and reduce the volumetric displacement required of the MT compressors by up to 37%.

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Ayub, Abubakr, Costante M. Invernizzi, Gioele Di Marcoberardino, Paolo Iora, and Giampaolo Manzolini. "Carbon Dioxide Mixtures as Working Fluid for High-Temperature Heat Recovery: A Thermodynamic Comparison with Transcritical Organic Rankine Cycles." Energies 13, no. 15 (August 4, 2020): 4014. http://dx.doi.org/10.3390/en13154014.

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This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO2-R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO2-R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical carbon dioxide cycle efficiency of 0.1274, obtained at the comparatively high maximum pressure of 300 bars. Steam cycles, owing to their larger number of required turbine stages and lower power output, did not prove to be a suitable option in this application.

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Liu, Liuchen, Qiguo Yang, and Guomin Cui. "Supercritical Carbon Dioxide(s-CO2) Power Cycle for Waste Heat Recovery: A Review from Thermodynamic Perspective." Processes 8, no. 11 (November 15, 2020): 1461. http://dx.doi.org/10.3390/pr8111461.

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Supercritical CO2 power cycles have been deeply investigated in recent years. However, their potential in waste heat recovery is still largely unexplored. This paper presents a critical review of engineering background, technical challenges, and current advances of the s-CO2 cycle for waste heat recovery. Firstly, common barriers for the further promotion of waste heat recovery technology are discussed. Afterwards, the technical advantages of the s-CO2 cycle in solving the abovementioned problems are outlined by comparing several state-of-the-art thermodynamic cycles. On this basis, current research results in this field are reviewed for three main applications, namely the fuel cell, internal combustion engine, and gas turbine. For low temperature applications, the transcritical CO2 cycles can compete with other existing technologies, while supercritical CO2 cycles are more attractive for medium- and high temperature sources to replace steam Rankine cycles. Moreover, simple and regenerative configurations are more suitable for transcritical cycles, whereas various complex configurations have advantages for medium- and high temperature heat sources to form cogeneration system. Finally, from the viewpoints of in-depth research and engineering applications, several future development directions are put forward. This review hopes to promote the development of s-CO2 cycles for waste heat recovery.

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Tao, Yong Qing, Yang Shi, Si Min Zhang, Xi Yao Dong, Pan Pan Gao, Jin Han Wang, Nan Zhao, Hai Hua Ruan, and Hui Zhao. "One-Step Effective Segregation of Ginger Essential Oil and Gingerol in Oleoresin Ginger via Transcritical CO₂." Advanced Materials Research 699 (May 2013): 207–11. http://dx.doi.org/10.4028/www.scientific.net/amr.699.207.

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We developed a supercritical CO2 extraction procession and determinated ginger essential oil contents from the ginger oleoresin to explore the effects of temperatures or pressures on the supercritical CO2 extraction. Our research indicated that pressures had little effect on the liquid CO2 extraction capacity. However, supercritical CO2 extraction capacity was affected dramatically by the variant pressures. Additionally, changing pressures or temperature pushed the CO2 into transcritical isolation state. Under this circumstance, we not only ensured the yield of ginger oleoresin, but also did we obtain the ginger essential oil and gingerol simultaneously.

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KADAM, ASHISH, ATUL PADALKAR, and S. MARTÍNEZ-BALLESTER. "EFFECT OF CONTROL OPTIMIZATION OF CO2 TRANSCRITICAL SPLIT AIR CONDITIONER ON THERMAL COMFORT OF OCCUPANTS IN SINGLE ZONE ROOM." International Journal of Air-Conditioning and Refrigeration 22, no. 01 (March 2014): 1450006. http://dx.doi.org/10.1142/s2010132514500060.

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Energy, environment and economics are considered as very vital parameters for the evaluation of an air conditioning system and associated indoor environment. The cooling performance of an air conditioner has an effect on the thermal comfort of occupants in the room. Transcritical CO 2 air conditioner (System B) with a control for gas cooler pressure has better energy performance than a transcritical CO 2 air conditioner (System A) without any control on the gas cooler pressure. An experimental technique is used for generating performance equations to define transcritical CO 2 air conditioners in the EnergyPlus program. EnergyPlus simulates combined model of a transcritical CO 2 air conditioner and room for known yearly weather data for an effect on thermal comfort in the room. Thermal comfort in the room is evaluated using the Fanger thermal comfort model and the Pierce two node model. The better energy performance of System B results in improved indoor room environment of the room. The total cooling of System B is 15.78–20.2% higher than that of System A. The Fanger thermal comfort model shows that 95% to 133% people are more dissatisfied with an indoor thermal environment during the morning and 85% to 127% people during the afternoon for a room coupled with System A vis-à-vis room with System B.

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29

Okasha, Ahmed, Norbert Müller, and Kalyanmoy Deb. "Bi-objective optimization of transcritical CO2 heat pump systems." Energy 247 (May 2022): 123469. http://dx.doi.org/10.1016/j.energy.2022.123469.

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30

Bush, John, Mohamed Beshr, Vikrant Aute, and Reinhard Radermacher. "Experimental evaluation of transcritical CO2 refrigeration with mechanical subcooling." Science and Technology for the Built Environment 23, no. 6 (April 5, 2017): 1013–25. http://dx.doi.org/10.1080/23744731.2017.1289056.

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31

Sarkar, Jahar. "Optimization of ejector-expansion transcritical CO2 heat pump cycle." Energy 33, no. 9 (September 2008): 1399–406. http://dx.doi.org/10.1016/j.energy.2008.04.007.

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32

Yang, Jun Lan, Yi Tai Ma, Min Xia Li, and Jun Hua. "Modeling and simulating the transcritical CO2 heat pump system." Energy 35, no. 12 (December 2010): 4812–18. http://dx.doi.org/10.1016/j.energy.2010.09.007.

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33

Ersoy, H. Kursad, and Nagihan Bilir. "Performance characteristics of ejector expander transcritical CO2 refrigeration cycle." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 226, no. 5 (May 9, 2012): 623–35. http://dx.doi.org/10.1177/0957650912446547.

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34

Sarkar, J., Souvik Bhattacharyya, and M. Ram Gopal. "Irreversibility minimization of heat exchangers for transcritical CO2 systems." International Journal of Thermal Sciences 48, no. 1 (January 2009): 146–53. http://dx.doi.org/10.1016/j.ijthermalsci.2008.02.007.

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35

Cen, Jiwen, Pei Liu, and Fangming Jiang. "A novel transcritical CO2 refrigeration cycle with two ejectors." International Journal of Refrigeration 35, no. 8 (December 2012): 2233–39. http://dx.doi.org/10.1016/j.ijrefrig.2012.07.001.

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36

Fartaj, Amir, David S. K. Ting, and Wendy W. Yang. "Second law analysis of the transcritical CO2 refrigeration cycle." Energy Conversion and Management 45, no. 13-14 (August 2004): 2269–81. http://dx.doi.org/10.1016/j.enconman.2003.07.001.

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37

Hwang, Yunho, Jun-Pyo Lee, and Reinhard Radermacher. "Oil distribution in a transcritical CO2 air-conditioning system." Applied Thermal Engineering 27, no. 14-15 (October 2007): 2618–25. http://dx.doi.org/10.1016/j.applthermaleng.2007.01.019.

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38

Shao, Liang-Liang, Zi-Yang Zhang, and Chun-Lu Zhang. "Constrained optimal high pressure equation of CO2 transcritical cycle." Applied Thermal Engineering 128 (January 2018): 173–78. http://dx.doi.org/10.1016/j.applthermaleng.2017.09.023.

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39

Song, Yulong, Haidan Wang, and Feng Cao. "Investigation of the Impact Factors on the Optimal Intermediate Temperature in a Dual Transcritical CO2 System with a Dedicated Transcritical CO2 Subcooler." Energies 13, no. 2 (January 8, 2020): 309. http://dx.doi.org/10.3390/en13020309.

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As a natural fluid with superior environment advantages, CO2 is used to constitute a dual transcritical system to reduce performance deterioration under high gas-cooler outlet temperature. Aiming at the system configuration, improvement potential, and optimization, the proposed system is deeply analyzed, and corresponding coupling models are presented in detail. First, the veracity of simulation models is completely verified by comparing with previous measurements. Then, the existence of the optimal intermediate temperature is validated, while the optimal values are found to increase with the augmentation in ambient and water-feed temperatures. Moreover, the negative effects of the pinch point on the heat transfer inside the gas cooler could be greatly reduced by using the dual gas cooler. Finally, a predictive correlation for optimal intermediate temperature determination with ambient and water-feed temperature as independent variables is proposed, which provides a theoretical basis for the proposed system to realize efficient control in the industrialization process.

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40

Elbarghthi, Anas F. A., and Václav Dvořák. "Evaluation of Various Ejector Profiles on CO2 Transcritical Refrigeration System Performance." Entropy 24, no. 9 (August 23, 2022): 1173. http://dx.doi.org/10.3390/e24091173.

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This study examines the potential impact of the different ejector profiles on the CO2 transcritical cooling system to highlight the contribution of the multi-ejector in the system performance improvement. The research compares the implementation of an ejector-boosted CO2 refrigeration system over the second-generation layout at a motive flow temperature of 35 °C and discharge pressure of 90 bar to account for the transcritical operation mode. The result revealed a significant energy saving by reducing the input power to the maximum of 8.77% when the ejector was activated. Furthermore, the multi-ejector block could recover up to 25.4% of the expansion work losses acquired by both ejector combinations VEJ1+2. In addition, the behavior of the multi-ejector geometries and operation conditions greatly influence the system exergy destruction. The analysis shows a remarkable lack of exergy destruction during the expansion process by deploying the ejector in parallel with the HPV.

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41

Liu, Jinghang, Aofang Yu, Xinxing Lin, Wen Su, and Shaoduan Ou. "Performances of Transcritical Power Cycles with CO2-Based Mixtures for the Waste Heat Recovery of ICE." Entropy 23, no. 11 (November 21, 2021): 1551. http://dx.doi.org/10.3390/e23111551.

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In the waste heat recovery of the internal combustion engine (ICE), the transcritical CO2 power cycle still faces the high operation pressure and difficulty in condensation. To overcome these challenges, CO2 is mixed with organic fluids to form zeotropic mixtures. Thus, in this work, five organic fluids, namely R290, R600a, R600, R601a, and R601, are mixed with CO2. Mixture performance in the waste heat recovery of ICE is evaluated, based on two transcritical power cycles, namely the recuperative cycle and split cycle. The results show that the split cycle always has better performance than the recuperative cycle. Under design conditions, CO2/R290(0.3/0.7) has the best performance in the split cycle. The corresponding net work and cycle efficiency are respectively 21.05 kW and 20.44%. Furthermore, effects of key parameters such as turbine inlet temperature, turbine inlet pressure, and split ratio on the cycle performance are studied. With the increase of turbine inlet temperature, the net works of the recuperative cycle and split cycle firstly increase and then decrease. There exist peak values of net work in both cycles. Meanwhile, the net work of the split cycle firstly increases and then decreases with the increase of the split ratio. Thereafter, with the target of maximizing net work, these key parameters are optimized at different mass fractions of CO2. The optimization results show that CO2/R600 obtains the highest net work of 27.43 kW at the CO2 mass fraction 0.9 in the split cycle.

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42

Song, Yulong, Qinfei Sun, Shuo Yang, Qijing Xing, Ling Cheng, and Feng Cao. "The theoretical and experimental research on the thermodynamic process in transcritical carbon dioxide piston compressor." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 2 (June 3, 2018): 267–79. http://dx.doi.org/10.1177/0954408918777172.

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The general mathematical model of the transcritical CO2 compressor was presented to assess the compressor efficiencies including isentropic efficiency and volumetric efficiency based on the thermodynamic theories and compressor structures. Furthermore, the prototype of the transcritical CO2 system was established and relative measurements were carried out to evaluate the precision of the simulation. Results showed that the volumetric efficiency of the compressor kept decreasing while the isentropic efficiency increased first and then kept almost constant and even declined with the increase in the pressure ratio. Besides, the indicated efficiency and volumetric efficiency declined slightly with the decrease in the suction density corresponding to the increase in suction superheating. As for the effects of compressor structures on the performances, the indicated efficiency increased sharply and then decreased gradually, while the volumetric efficiency kept declining with the increase in the cylinder diameter-to-height ratio, respectively.

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43

Sarkar, Jahar, and Dnyanesh Joshi. "Extended Exergy Analysis Based Comparison of Subcritical and Transcritical Refrigeration Systems." International Journal of Air-Conditioning and Refrigeration 24, no. 02 (June 2016): 1650009. http://dx.doi.org/10.1142/s2010132516500097.

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The main purpose of this study is to apply advanced exergy analysis to the transcritical CO2 vapor compression refrigeration system, and compare with the analysis of subcritical cycle using ammonia and R404a. Endogenous, exogenous, avoidable and unavoidable exergy destructions are determined for each component of these systems. For CO2 system, compressor contributes highest avoidable endogenous exergy destruction and gas cooler contributes highest avoidable exogenous exergy destruction. It is concluded that compressor is the first component for CO2 and R404a, and evaporator is the first component for NH3 to be improved. System improvement options to reduce the exergy destruction are discussed as well.

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44

Nebot-Andrés, Laura, Daniel Calleja-Anta, Daniel Sánchez, Ramón Cabello, and Rodrigo Llopis. "Thermodynamic Analysis of a CO2 Refrigeration Cycle with Integrated Mechanical Subcooling." Energies 13, no. 1 (December 18, 2019): 4. http://dx.doi.org/10.3390/en13010004.

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Different alternatives are being studied nowadays in order to enhance the behavior of transcritical CO2 refrigeration plants. Among the most studied options, subcooling is one of the most analyzed methods in the last years, increasing cooling capacity and Coefficient Of Performance (COP), especially at high hot sink temperatures. A new cycle, called integrated mechanical subcooling cycle, has been developed, as a total-CO2 solution, to provide the subcooling in CO2 transcritical refrigeration cycles. It corresponds to a promising solution from the point of view of energy efficiency. The purpose of this work is to present, for the first time, thermodynamic analysis of a CO2 refrigeration cycle with integrated mechanical subcooling cycle from first and second law approaches. Using simplified models of the components, the optimum operating conditions, optimum gas-cooler pressure, and subcooling degree are determined in order to obtain the maximum COP. The main energy parameters of the system were analyzed for different evaporation levels and heat rejection temperatures. The exergy destruction was analyzed for each component, identifying the elements of the system that introduce more irreversibilities. It has been concluded that the new cycle could offer COP improvements from 11.7% to 15.9% in relation to single-stage cycles with internal heat exchanger (IHX) at 35 °C ambient temperature.

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45

Kozioł, Joachim, Wiesław Gazda, and Łukasz Wilżyński. "Energy efficiency for the transcritical compression CO2 cycle with the use of the ejector as the first stage of the compression." Archives of Thermodynamics 31, no. 4 (October 1, 2010): 61–69. http://dx.doi.org/10.2478/v10173-010-0028-3.

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Energy efficiency for the transcritical compression CO2cycle with the use of the ejector as the first stage of the compressionAn analysis of energy efficiency for transcritical compression unit with CO2 (R744) as the refrigerant has been carried out using empirical operating characteristics for the two-phase ejector. The first stage of the refrigerant compression is carried out in the ejector. The criterion adopted for the estimation of energy efficiency for the cycle is the coefficient of performance COP. The analysis is performed for the heat pump and refrigeration systems. The results of COP for the systems with the ejector has been compared with the COPLvalues for the single stage Linde cycle.

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46

Zhou, Tang, Zhang, and Li. "Thermodynamic Analysis of the Air-Cooled Transcritical Rankine Cycle Using CO2/R161 Mixture Based on Natural Draft Dry Cooling Towers." Energies 12, no. 17 (August 29, 2019): 3342. http://dx.doi.org/10.3390/en12173342.

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Heat rejection in the hot-arid area is of concern to power cycles, especially for the transcritical Rankine cycle using CO2 as the working fluid in harvesting the low-grade energy. Usually, water is employed as the cooling substance in Rankine cycles. In this paper, the transcritical Rankine cycle with CO2/R161 mixture and dry air cooling systems had been proposed to be used in arid areas with water shortage. A design and rating model for mixture-air cooling process were developed based on small-scale natural draft dry cooling towers. The influence of key parameters on the system’s thermodynamic performance was tested. The results suggested that the thermal efficiency of the proposed system was decreased with the increases in the turbine inlet pressure and the ambient temperature, with the given thermal power as the heat source. Additionally, the cooling performance of natural draft dry cooling tower was found to be affected by the ambient temperature and the turbine exhaust temperature.

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47

Taslimi Taleghani, Sahar, Mikhail Sorin, and Sébastien Poncet. "Analysis and Optimization of Exergy Flows inside a Transcritical CO2 Ejector for Refrigeration, Air Conditioning and Heat Pump Cycles." Energies 12, no. 9 (May 4, 2019): 1686. http://dx.doi.org/10.3390/en12091686.

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In this study, the exergy analysis of a CO2 (R744) two-phase ejector was performed using a 1D model for both single and double choking conditions. The impact of the back pressure on the exergy destruction and exergy efficiencies was presented to evaluate the exergy performance under different working conditions. The results of two exergy performance criteria (transiting exergy efficiency and Grassmann exergy efficiency) were compared for three modes of an ejector functioning: Double choking, single choking and at the critical point. The behavior of three thermodynamic metrics: Exergy produced, exergy consumed and exergy destruction were evaluated. An important result concerning the ejector’s design was the presence of a maximum value of transiting exergy efficiency around the critical point. The impact of the gas cooler and evaporator pressure variations on the different types of exergy, the irreversibilities and the ejector global performance were investigated for a transcritical CO2 ejector system. It was also shown that the transiting exergy flow had an important effect on the exergy analysis of the system and the Grassmann exergy efficiency was not an appropriate criterion to evaluate a transcritical CO2 ejector performance.

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48

Mu, Deying, Yuanlong Liu, Ruhong Li, Quanxin Ma, and Changsong Dai. "Transcritical CO2 extraction of electrolytes for lithium-ion batteries: optimization of the recycling process and quality–quantity variation." New Journal of Chemistry 41, no. 15 (2017): 7177–85. http://dx.doi.org/10.1039/c7nj00771j.

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49

GOMRI, Rabah. "Energy and Exergy Analyses of Different Transcritical CO2 Refrigeration Cycles." El-Cezeri Fen ve Mühendislik Dergisi 5, no. 2 (May 31, 2018): 425–36. http://dx.doi.org/10.31202/ecjse.402904.

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50

Naveen, Michael Roger. "Experimental Investigation of a Combined Power Refrigeration Transcritical CO2 Cycle." Indian Journal of Science and Technology 8, no. 1 (January 20, 2015): 1–4. http://dx.doi.org/10.17485/ijst/2015/v8i31/84313.

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Journal articles on the topic 'Transcritical CO2'

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