Relevant bibliographies by topics / Transcritical CO2

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers

Academic literature on the topic 'Transcritical CO2'

Author: Grafiati
Published: 6 September 2023

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Journal articles on the topic "Transcritical CO2"

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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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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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Dissertations / Theses on the topic "Transcritical CO2"

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Yang, Chen. "Thermodynamic Cycles using Carbon Dioxide as Working Fluid : CO2 transcritical power cycle study." Doctoral thesis, KTH, Tillämpad termodynamik och kylteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-50261.

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The interest in utilizing the energy in low‐grade heat sources and waste heat is increasing. There is an abundance of such heat sources, but their utilization today is insufficient, mainly due to the limitations of the conventional power cycles in such applications, such as low efficiency, bulky size or moisture at the expansion outlet (e.g. problems for turbine blades). Carbon dioxide (CO2) has been widely investigated for use as a working fluid in refrigeration cycles, because it has no ozonedepleting potential (ODP) and low global warming potential (GWP). It is also inexpensive, non‐explosive, non‐flammable and abundant in nature. At the same time, CO2 has advantages in use as a working fluid in low‐grade heat resource recovery and energy conversion from waste heat, mainly because it can create a better matching to the heat source temperature profile in the supercritical region to reduce the irreversibility during the heating process. Nevertheless, the research in such applications is very limited. This study investigates the potential of using carbon dioxide as a working fluid in power cycles for low‐grade heat source/waste heat recovery. At the beginning of this study, basic CO2 power cycles, namely carbon dioxide transcritical power cycle, carbon dioxide Brayton cycle and carbon dioxide cooling and power combined cycle were simulated and studied to see their potential in different applications (e.g. low‐grade heat source applications, automobile applications and heat and power cogeneration applications). For the applications in automobile industries, low pressure drop on the engine’s exhaust gas side is crucial to not reducing the engine’s performance. Therefore, a heat exchanger with low‐pressure drop on the secondary side (i.e. the gas side) was also designed, simulated and tested with water and engine exhaust gases at the early stage of the study (Appendix 2). The study subsequently focused mainly on carbon dioxide transcritical power cycle, which has a wide range of applications. The performance of the carbon dioxide transcritical power cycle has been simulated and compared with the other most commonly employed power cycles in lowgrade heat source utilizations, i.e. the Organic Rankin Cycle (ORC). Furthermore, the annual performance of the carbon dioxide transcritical power cycle in utilizing the low‐grade heat source (i.e. solar) has also been simulated and analyzed with dynamic simulation in this work. Last but not least, the matching of the temperature profiles in the heat exchangers for CO2 and its influence on the cycle performance have also been discussed. Second law thermodynamic analyses of the carbon dioxide transcritical power systems have been completed. The simulation models have been mainly developed in the software known as Engineering Equation Solver (EES)1 for both cycle analyses and computer‐aided heat exchanger designs. The model has also been connected to TRNSYS for dynamic system annual performance simulations. In addition, Refprop 7.02 is used for calculating the working fluid properties, and the CFD tool (COMSOL) 3 has been employed to investigate the particular phenomena influencing the heat exchanger performance.
QC 20111205
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Mureddu, Alessandro. "Thermodynamic analysis of an ORC plant and a transcritical CO2 plant for low temperature waste heat recovery." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

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La domanda di energia nel mondo è in continuo aumento e, contemporaneamente, l'aumento dell'inquinamento ambientale spinge verso una diminuzione dell'utilizzo di combustibili fossili. Per questo motivo, oggi è fondamentale sia lo sviluppo di nuove fonti energetiche pulite, sia il recupero di calore di scarto da varie applicazioni che, in passato, veniva perso. Lo scopo di questo lavoro è un'analisi termodinamica di impianti ORC e impianti a CO2 transcritica, entrambi usati per il recupero di calore di scarto industriale a bassa temperatura (=200°C). In particolare, verranno analizzati due diversi layout per ogni tipologia di impianto: il layout semplice e quello recuperato. Le quattro simulazioni son state sviluppate in Matlab, implementando le equazioni di bilancio entalpico per ogni ciclo, in modo tale da poter calcolare le performance termodinamiche e, dunque, poter confrontare i diversi layout, in modo da scegliere quello che assicura le migliori prestazioni. Le quattro simulazioni son state svolte considerando un set di parametri di progetto, in linea con lo stato dell'arte attuale, e per diversi valori della pressione massima del ciclo, in modo tale da trovarne il valore che massimizzi l'efficienza termodinamica. In seguito, son stati confrontati tutti i valori calcolati, così da scegliere l'impianto più adatto al recupero di calore di scarto a bassa temperatura. Successivamente, le simulazioni son state svolte con un diverso valore della temperatura di uscita dei fumi e della temperatura di uscita dell'acqua di raffreddamento, per motivi di impatto ambientale. In seguito, i cicli son stati valutati per diversi valori della temperatura di ingresso dei fumi caldi e per diversi valori del rendimento isoentropico di turbina, così da valutare l'effetto di una variazione di tali parametri sul rendimento termodinamico di ogni ciclo.
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Bouteiller, Paul. "Etude expérimentale de cycles de pompe à chaleur utilisant des mélanges à base de CO2." Thesis, Paris, CNAM, 2017. http://www.theses.fr/2017CNAM1089/document.

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Cette étude consiste en l’expérimentation de mélanges de fluides frigorigènes à base de CO2 dans les applications de pompes à chaleur domestiques. L’objectif est l’obtention de performances supérieures à une pompe à chaleur au CO2 double-service (eau chaude sanitaire et chauffage). L’ajout d’autres composés au CO2 déplace le point critique et de façon plus générale modifie les lignes d’équilibre de phases. On peut alors s’attendre à la réduction des pressions de fonctionnement et à une augmentation du rendement énergétique du cycle thermodynamique. Une pompe à chaleur mono-étagée au CO2 est utilisée comme référence, et les conditions de température externes à la boucle thermodynamique sont invariantes. Deux scénarii sont considérés : La production d’eau chaude sanitaire (ECS), où l’eau est chauffée de 10 °C à 65 °C ; la production d’eau de chauffage (CH) où l’au est chauffée de 30 °C à 35 °C. Dans les deux cas, l’eau glycolée en l’entrée de l’évaporateur est régulée à 7 °C. Afin de pouvoir analyser le comportement des cycles thermodynamiques avec mélanges, il est essentiel de connaitre la composition du fluide frigorigène en circulation. Pour ce faire, nous avons mis au point une technique de mesure statistique et non-intrusive de la composition: Des cellules optiques installées sur les tubes de la boucle permettent de recueillir les spectres d’absorption du fluide en circulation, grâce à un spectromètre proche infrarouge à transformée de Fourier. Un étalonnage méticuleux est effectué via l’acquisition de nombreux spectres d’échantillons ayant des compositions connues. Un modèle statistique est alors créé pour lier les concentrations aux données spectrales. Les compositions peuvent ensuite être estimées à partir de nouveau spectres, dont l’acquisition rapide permet l’analyse de la composition du fluide même en fonctionnement dynamique de la pompe à chaleur. Des mélanges de CO2 & propane, et CO2 & R-1234yf ont été testés, montrant des potentiels d’amélioration des performances de la pompe à chaleur pour les applications de chauffage des locaux
The aim of this work is to experiment CO2 based mixtures as working fluids for heat pump applications in buildings, in order to enhance their performances compared to pure CO2 dual services heat pumps. Since adding other chemicals to CO2 moves the critical point and generally equilibrium lines, it is expected that lower operating pressures as well as higher global efficiencies can be reached. A simple stage pure CO2 cycle is used as reference, with fixed external conditions. Two scenarios are considered: water is heated from 10 °C to 65 °C for Domestic Hot Water (DHW) scenario and from 30 °C to 35 °C for Central Heating (CH) scenario. In both cases, water at the evaporator inlet is set at 7 °C to account for such outdoor temperature conditions. In order to understand the dynamic behaviour of thermodynamic cycles with mixtures, it is essential to measure the fluid circulating composition. To this end, we have developed a non intrusive method. Online optical flow cells allow the recording of infrared spectra by means of a Fourier Transform Infra Red spectrometer. A careful calibration is performed by measuring a statistically significant number of spectra for samples of known composition. Then, a statistical model is constructed to relate spectra to compositions. After calibration, compositions are obtained by recording the spectrum in few seconds, thus allowing for a dynamic analysis. Mixtures of CO2 & propane and CO2 & R-1234yf have been tested and showed great potential on enhancing performances of the heat pump for central heating applications
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Bouzrara, Ali. "Etude expérimentale des éjecteurs : Application à la récupération de l'énergie de détente des machines frigorifiques au CO2." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI065/document.

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Les fluides naturels employés en réfrigération et en conditionnement d’air possèdent de faibles PRG et sont de ce fait une véritable alternative aux HFC. Cependant, leur généralisation se heurte à des limites provenant de leur caractère toxique (NH3), inflammable (hydrocarbures, NH3) ou de leurs caractéristiques thermodynamiques défavorables (CO2). Leur utilisation accrue nécessite la mise en œuvre de composants spécifiques (échangeurs de chaleur intermédiaire, éjecteur) qui sans qui les performances seraient inférieures à celles obtenues avec les HFC (COPCO2 = 55 % du COPHFC-134a pour des températures de sources de 0 °C et 40 °C). L’utilisation d’un éjecteur comme organe de détente est une solution envisagée pour réduire les irréversibilités. Les éjecteurs diphasiques constituent une alternative intéressante pour les dispositifs de détente classiques utilisés depuis plusieurs décennies. Le principal avantage de l’éjecteur est de récupérer une partie de l’énergie cinétique du processus de détente de la haute pression à la basse pression pour augmenter la pression d’aspiration du compresseur. Ceci entraîne une diminution du travail consommé par ce dernier et, par suite, une augmentation du coefficient de performance du système. Néanmoins, une bonne conception d’un éjecteur diphasique nécessite une analyse détaillée en termes de simulations numériques et travaux expérimentaux. Ainsi, l’objectif de ce travail est d’apporter une contribution expérimentale à l’étude des machines frigorifiques au CO2 transcritique équipées d’éjecteur diphasique. Des efforts importants ont été investis dans la conception d’un éjecteur diphasique avec diverses géométries pour évaluer les principales caractéristiques à savoir le facteur d’entraînement et le rapport de compression. Les essais effectués ont permis de mettre en évidence l’influence des différents paramètres géométriques sur les performances de la machine (différents diamètres au col des tuyères primaires, différents diamètres de mélangeurs, longueurs de mélangeurs, distance entre le plan de sortie de la tuyère primaire et l’entrée du mélangeur, l’angle de divergent des tuyères primaires…) ainsi que les paramètres thermodynamiques (température d’évaporation, température à l’entrée de la tuyère primaire)
Natural refrigerants used in refrigeration and air conditioning have low GWP and are therefore a real alternative to HFCs. However, their generalization comes up against limits due to their toxic (NH3), flammable (hydrocarbons, NH3) or their unfavorable thermodynamic characteristics (CO2). Their increased use requires the implementation of specific components (intermediate heat exchangers, ejector) which without performance would be lower than those obtained with HFCs (COPCO2 = 55% of COPHFC-134a for temperatures source of 0 °C and 40 °C). The use of an ejector as an expansion device is a solution considered to reduce irreversibility. Two-phase ejector has been an interesting alternative for conventional expansion devices for several decades. The main advantage of the ejector is to recover some of the kinetic energy of the process of expansion from high pressure to low pressure to increase the suction pressure of the compressor. This results in a reduction of the work consumed by the latter and, consequently, an increase in the coefficient of performance of the system. Nevertheless, a good design of a two-phase ejector requires a detailed analysis in terms of numerical simulations and experimental work. Thus, the objective of this work is to make an experimental contribution to the study of transcritical CO2refrigeration machines equipped with two-phase ejector. Significant efforts have been invested in the design of a two-phase ejector with various geometries to evaluate the main characteristics namely the entrainment ratio and the compression ratio. The tests carried out made it possible to highlight the influence of the various geometrical parameters on the performances of the machine (different diameters of the throat of the primary nozzle, different mixers diameters and lengths, distance between the exit of the primary nozzle and the inlet of the mixer, the divergence angle of the primary nozzles ...) as well as the thermodynamic parameters (evaporation temperature, temperature at the inlet of the primary nozzle)
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Goodman, Christopher L. "Modeling, validation and design of integrated carbon dioxide heat pumps and water heaters." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22560.

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SANTINI, FABRIZIO. "Impianti di refrigerazione a CO2 transcritici Caratterizzazione sperimentale ed analisi teoriche per l’ottimizzazione energetica." Doctoral thesis, Università degli Studi dell'Aquila, 2020. http://hdl.handle.net/11697/148279.

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L’adozione di refrigeranti a basso impatto ambientale sintetici, HFO, o naturali, CO2 e NH3, in sostituzione dei refrigeranti tradizionali potrebbe ridurre le emissioni dirette in atmosfera. Il settore della refrigerazione commerciale sta progressivamente sostituendo i refrigeranti tradizionali con l’anidride carbonica, R744. La CO2, come refrigerante, presenta delle proprietà termodinamiche che collimano con i fabbisogni commerciali, essendo un fluido non infiammabile, non esplosivo, non tossico e con GWP ed ODP rispettivamente pari ad 1 e a 0. Le problematiche impiantistiche relative all’adozione dell’anidride carbonica sono dovute alle elevate pressioni di lavoro spesso maggiori della pressione critica pari a 73,8 bar infatti, per la realizzazione del ciclo frigorifero, la pressione massima tende ad incrementarsi ad elevate temperature esterne, peggiorando l’efficienza e le condizioni operative. Nonostante gli impianti transcritici abbiano delle prestazioni energetiche maggiori degli impianti tradizionali a basse temperature esterne, la loro efficienza, in termini di COP, si degrada sensibilmente con temperature crescenti. Il miglioramento del COP potrebbe contribuire alla promozione ed all’adozione della CO2 in aree che hanno generalmente condizioni climatiche sfavorevoli, riducendo le emissioni indirette e l’impatto ambientale degli impianti tradizionali. Nella sala motori “C. Caputo” dell’Università degli Studi dell’Aquila, in collaborazione con la società Epta Refrigeration S.p.A., è stata installata, collaudata ed avviata una centrale transcritica a CO2 con una potenza nominale agli evaporatori di 18 kWt ed ai compressori di 17 kWe. La possibilità di sperimentare questo sistema di refrigerazione innovativo consente di monitorare la variazione dei principali parametri termodinamici a diverse temperature esterne, permettendo il calcolo del COP e la ricostruzione modellistica dei cicli frigoriferi transcritici. L’estesa campagna sperimentale effettuata rappresenta la situazione di riferimento su cui implementare modelli teorici di efficientamento energetico, supportati dal software di calcolo NIST-RefProp. I modelli riportano incrementi percentuali del COP fino al 50%, giustificando una validazione sperimentale delle configurazioni proposte.
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Samakai, Elsie. "TRANSCRIPTIONAL CONTROL OF Ca2+ SIGNALING IN T CELLS." Diss., Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/466164.

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Biochemistry
Ph.D.
Antigen presentation to T cells results in their activation through T Cell Receptor (TCR) stimulation, resulting in sustained elevation of cytosolic Ca2+ concentration critical for T cell activation. Sustained Ca2+ signals are important for the activation of Nuclear Factor of Activated T cells (NFAT), which is a key regulator of T cell activation through its transcriptional control of genes in multiple process including cytokine production, proliferation and differentiation(Rao, Luo, & Hogan, 1997). Recently it was shown that Stromal Interaction Molecule 1 (STIM1) inhibits plasma membrane Ca2+/ATPase 4 (PMCA4) function during T cell activation resulting in sustained elevation of Ca2+ signals(Ritchie, Samakai, & Soboloff, 2012). This interaction requires upregulation of both STIM1 and PMCA4. In this thesis, I hypothesize that changes in Ca2+ signals arising from transcriptional changes of STIM1 and PMCA are important for the efficient activation of T cells. In the first part of this thesis, I assess the transcriptional regulation of STIM1 and PMCA4. My in vitro studies show that expression of both proteins is regulated by the EGR family members, EGR1 and EGR4. Additionally, transcriptional regulation of PMCA inhibition by EGR1 and EGR4 is required for efficient activation of T cells. Interestingly, whereas significant roles for EGR1, EGR2 and EGR3 in T cell development and function have been established, a role for EGR4 has not, hitherto been elucidated. In the second half of this thesis, using qPCR, I reveal that EGR4 expression is stimulated by TCR engagement in primary double positive, CD4 and CD8 positive murine T cells. Further, EGR4-null mice exhibit shifts in early thymic development, although this does not affect the relative number of double or single positive T cells in the thymus. Interestingly, EGR4-null primary T cells exhibit normal Ca2+ entry, but fail to exhibit activation-induced inhibition of Ca2+ clearance. Although not all subsets of EGR1 and EGR4 null primary T cells exhibited decreased STIM1 expression, significant defects in proliferation, migration and/or cytokine production were observed upon stimulation in all populations, albeit to different extents. These findings reveal a two-faceted role in which EGRs regulate T cell development and function through both Ca2+-dependent and independent methods. I believe that these findings have important implications towards the general understanding of transcriptional control of Ca2+ signaling, as well as having a possible impact in the quest to advance therapies targeting immunological disorders.
Temple University--Theses
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Rocha, Tomás Pinto de Freitas Teixeira da. "Modelling of a transcritical CO2 ejector with variable geometry." Master's thesis, 2021. https://hdl.handle.net/10216/135891.

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Rocha, Tomás Pinto de Freitas Teixeira da. "Modelling of a transcritical CO2 ejector with variable geometry." Dissertação, 2021. https://hdl.handle.net/10216/135891.

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Avila, Rony Andre Sian, and 羅翔安. "Modeling and Simulation of Transcritical CO2 for Heat Pump and Dryer Applications." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/t85ag4.

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Abstract:
博士
國立交通大學
機械工程系所
107
In this thesis, a constrains-free transcritical CO2 heat pump model for medium and large system applications and a transient heat pump for clothes drying applications are developed. On each model, the detailed geometric characteristics of the major component are taken into account and, unlike existing models existing in literature applicable for CO2 system, the developed models do not impose constraints upon simulation, such as fixed operating pressures and constant temperatures. Yet, pressure optimization is also addressed and heat rejection pressure is modulated through a recent sophisticated generalized dimensionless log-linear correlation of the Poisson type. The models are tested against experimental data for a wide range of operating conditions and the results accurately reflected an actual system with a maximum error of 9.6% and 3.9% for the coefficient of performance and heating capacity, respectively. Moreover, the simulation results of both models are discussed and substantiated in the context of experimental results reported in literature. Yet, the generalized correlation employed for pressure optimization is also tested, validated and discussed thorough comparison to experimental data and other correlations available from literature. The correlation can accurately predict heat rejection pressure with an average error of 1.31% and a standard deviation of 4.26 bar, with a valid range of applicability for ambient temperatures from -18 to 50 °C, and within -7 to 15 °C and 10 to 50 °C for the evaporator and gas cooler outlet, respectively. Once the transcritical heat pump model, pressure optimization method and heat pump dryer models are validated, a fully transient heat pump dryer model is developed and simulated using CO2 and then R-134a, for comparison purposes. A standard performance test is carried out and employed later as the reference case when investigating the influence of relevant parameters affecting the overall performance of the system for both refrigerants. Subsequently, comprehensive parametric studies are conducted to identify relevant parameters influencing system performance. In this regard, simulations for both systems (CO2 and R-134a) are conducted for comparison purposes. Additionally, guidelines and control strategies to optimize system performance and highlight the advantages of transcritical CO2 systems are provided.
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Books on the topic "Transcritical CO2"

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Yamaguchi, Hiroshi, and Xin-Rong Zhang. Transcritical CO2 Heat Pump: Fundamentals and Applications. Wiley & Sons, Incorporated, John, 2021.

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Yamaguchi, Hiroshi, and Xin-Rong Zhang. Transcritical CO2 Heat Pump: Fundamentals and Applications. Wiley & Sons, Incorporated, John, 2021.

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Book chapters on the topic "Transcritical CO2"

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Wang, Yi-Zhou, Yi-Kun He, and Xin-Rong Zhang. "Transcritical CO2 Refrigeration Cycle and Systems." In Lecture Notes in Energy, 35–53. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-22512-3_3.

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Wang, Hongli, Jingrui Tian, and Huiqin Liu. "Performance Analysis of Transcritical CO2 Compression Cycle." In Communications in Computer and Information Science, 730–36. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-34041-3_101.

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Feng, Xu, Zhenying Zhang, Jianjun Yang, and Dingzhu Tian. "Numerical Study on Two-Phase Flow of Transcritical CO2 in Ejector." In Environmental Science and Engineering, 385–93. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-13-9524-6_41.

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Karacayli, Ibrahim, and Ozay Akdemir. "Exergetic Performance Assessment of a Two–Stage Compression Transcritical CO2 Refrigeration Cycle." In Springer Proceedings in Energy, 835–44. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-30171-1_87.

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Zeng, Min-Qiang, Xin-Rong Zhang, Xue-Lai Zhang, and Yi-Wei Yan. "Theoretical Analysis of Expansion Process and Components in CO2 (Transcritical) Refrigeration System." In Lecture Notes in Energy, 55–90. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-22512-3_4.

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Manju Lata, Ashish Kumar Yadav, and Dileep Kumar Gupta. "Thermodynamic Analysis of Transcritical CO2 Booster Systems with Flooded Evaporator for Supermarket Application." In Renewable Energy and Climate Change, 293–304. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-32-9578-0_27.

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Wang, Hongli, Huiqin Liu, and Jingrui Tian. "Performance Analysis of Transcritical CO2 Sewage Source Heat Pump by Visual Basic Program." In Communications in Computer and Information Science, 630–37. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-34038-3_87.

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Date, Abhijit, and Neeraj Agrawal. "Capillary Tube Flow Characterization of a Transcritical CO2 Cycle Using Separated Two-Phase Flow Model." In Advances in Air Conditioning and Refrigeration, 111–18. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-6360-7_11.

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Mondal, P., S. Samanta, S. Ghosh, and S. N. Barman. "Bio-Waste Fired Gas Turbine and Transcritical Co2 Cycle Based Combined Power Plant: Thermodynamic, Economic and Environmental Performance Assessment." In Lecture Notes in Mechanical Engineering, 287–301. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-3497-0_22.

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Sengupta, Ayan, and Mani Sankar Dasgupta. "Thermodynamic Analysis of a Novel Dual-Ejector Multi-Compressor Transcritical-CO2 Refrigeration System for Supermarket Applications in Warm Climates." In Lecture Notes in Mechanical Engineering, 625–30. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-6270-7_104.

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Conference papers on the topic "Transcritical CO2"

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Huang, Meibin, Wensheng Lin, Hongming He, and Anzhong Gu. "A Transcritical CO2 Rankine Cycle With LNG Cold Energy Utilization and Liquefaction of CO2 in Gas Turbine Emission." In ASME 2008 2nd International Conference on Energy Sustainability collocated with the Heat Transfer, Fluids Engineering, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/es2008-54050.

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A novel transcritical Rankine cycle is presented in this paper. This cycle adopts CO2 as its working fluid, with exhaust from a gas turbine as its heat source and LNG as its cold sink. With CO2 working transcritically, large temperature difference for the Rankine cycle is realized. Moreover, the CO2 in the gas turbine exhaust is further cooled and liquefied by LNG after transferring heat to the Rankine cycle. In this way, not only the cold energy is utilized, but also a large part of the CO2 from burning of the vaporized LNG is recovered. In this paper, the system performance of this transcritical cycle is calculated. The influences of the highest cycle temperature and pressure to system specific work, exergy efficiency and liquefied CO2 mass flow rate are analyzed. The exergy loss in each of the heat exchangers is also discussed. It turns out that this kind of CO2 cycle is energy-conservative and environment-friendly.
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Hwang, Yunho, Hans-Joachim Huff, Marcus Preissner, and Reinhard Radermacher. "CO2 Transcritical Cycles for High Temperature Applications." In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/aes-23630.

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Abstract A breadboard CO2 prototype heat pump for stationary applications was designed, constructed, and tested. Test results of the CO2 prototype showed about 12% lower cooling capacity but a similar cooling Coefficient of Performance (COP) at 40°C (104°F) ambient temperature as compared to R-22 environmental control units (ECU). However the projected COP of the CO2 prototype at 52°C (125°F) is lower than that of the original R-22 ECU. Therefore it is necessary to investigate methods to improve the efficiency while considering the design issues especially for high temperature operation. As means to improve the performance of the CO2 cycle at higher ambient conditions, four methods were investigated: a suction-line heat exchanger, an expander, an evaporatively cooled gas cooler, and a two-stage split cycle. It is expected that a suction-line heat exchanger can increase the high temperature capacity and COP of a CO2 system by approximately 10% and 20%, respectively. For an expander inlet temperature of 52 °C (125°F), the COP improvement is about 27% with an expander efficiency of 50%. An improvement in COP of 17% to 24% is achieved by using an evaporatively cooled gas cooler while the system cooling capacity improved by 6% to 8% at ambient temperatures of 35°C (95°F) and 45°C (113°F), respectively. The two-stage split cycle with intercooling offers 38% to 63% COP improvement at 30 to 50°C (86 to 122°F) ambient conditions. If one of these methods are implemented, the performance of the CO2 system can compete with R-22 ECUs. If two or more of above methods are implemented, the benefits may be higher than each one of them. However the benefit cannot be simply superpositioned due to the counteract effects. Therefore, the benefits of the implementation of two or more of above methods remain as a further study.
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Wang, Jinggang, Ligai Kang, and Jie Liu. "CO2 Transcritical Cycle for Ground Source Heat Pump." In 2009 WRI World Congress on Computer Science and Information Engineering. IEEE, 2009. http://dx.doi.org/10.1109/csie.2009.235.

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Xia, Jiaxi, Jiangfeng Wang, Pan Zhao, and Dai Yiping. "Performance Analysis and Comparison Study of Transcritical Power Cycles Using CO2-Based Mixtures as Working Fluids." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57132.

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CO2 in a transcritical CO2 cycle can not easily be condensed due to its low critical temperature (304.15K). In order to increase the critical temperature of working fluid, an effective method is to blend CO2 with other refrigerants to achieve a higher critical temperature. In this study, a transcritical power cycle using CO2-based mixtures which blend CO2 with other refrigerants as working fluids is investigated under heat source. Mathematical models are established to simulate the transcritical power cycle using different CO2-based mixtures under MATLAB® software environment. A parametric analysis is conducted under steady-state conditions for different CO2-based mixtures. In addition, a parametric optimization is carried out to obtain the optimal design parameters, and the comparisons of the transcritical power cycle using different CO2-based mixtures and pure CO2 are conducted. The results show that a raise in critical temperature can be achieved by using CO2-based mixtures, and CO2-based mixtures with R32 and R22 can also obtain better thermodynamic performance than pure CO2 in transcritical power cycle. What’s more, the condenser area needed by CO2-based mixture is smaller than pure CO2.
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Jinggang Wang, Ligai Kang, Jie Liu, and Zhenjiang Yin. "A combination of CO2 transcritical cycle with desiccant cooling." In 2009 Chinese Control and Decision Conference (CCDC). IEEE, 2009. http://dx.doi.org/10.1109/ccdc.2009.5191649.

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LI, MINXIA, YITAI MA, WENJIN GONG, and WEICHENG SU. "TWO-STAGE DRYING OF CO2 TRANSCRITICAL CYCLE HEAT PUMP." In The Proceedings of the 5th Asia-Pacific Drying Conference. World Scientific Publishing Company, 2007. http://dx.doi.org/10.1142/9789812771957_0057.

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Yingfu, Liu, Xiao Jian, and Jin Guangya. "Influence of External Heat Source on Transcritical CO2 Refrigeration System." In 2012 Third International Conference on Digital Manufacturing and Automation (ICDMA). IEEE, 2012. http://dx.doi.org/10.1109/icdma.2012.256.

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Wang, Xurong, Yi Wu, Jiangfeng Wang, Yiping Dai, and Danmei Xie. "Thermo-Economic Analysis of a Recompression Supercritical CO2 Cycle Combined With a Transcritical CO2 Cycle." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42033.

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The transcritical CO2 cycle (TCO2 cycle) exhibits good performance in low-grade waste heat recovery area. In this study, a TCO2 cycle was employed as a bottoming cycle to recover the waste heat in the topping recompression supercritical CO2 Brayton cycle (SCO2 cycle). A detailed system analysis was performed of a recompression SCO2 cycle combined with a TCO2 cycle to improve the efficiency of energy conversion. Thermodynamic analysis, calculation of heat exchangers’ area and economic analysis were considered. The SCO2 turbine expansion ratio, TCO2 turbine inlet pressure, high temperature recuperator (HTR) effectiveness and condensation temperature were studied to investigate their effect on the system performance. For the basic analysis, SCO2 turbine inlet temperature was conservatively selected to be 550 °C and the compressor outlet pressure set at 20 MPa. For these operating conditions the proposed combined SCO2-TCO2 cycle yielded about 46% thermal efficiency at a SCO2 turbine expansion ratio of 2.7 and TCO2 turbine inlet pressure of 10 MPa. Similarly, the capital cost per net power output of the combined cycle was found as 6.6 k$/kW, which was ∼ 6% more expensive than that of the recompression SCO2 cycle without the bottoming cycle under the same operating condition. An optimum TCO2 turbine inlet pressure and an optimum SCO2 turbine expansion ratio existed where the system thermal efficiency reached the maximum value. Furthermore, the system thermal efficiency was very sensitive to the changes in the condensation temperature and the HTR effectiveness. The HTR effectiveness also had a strong effect on the ratio of heat exchangers’ cost to the plant capital cost. Additionally, increasing SCO2 turbine inlet temperature would significantly improve the cycle overall thermal efficiency and decrease the plant capital cost per net power output.
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McLean, D., K. Pope, and Y. Muzychka. "Thermal energy from transcritical CO2 heat pumps for small marine applications." In OCEANS 2014. IEEE, 2014. http://dx.doi.org/10.1109/oceans.2014.7003256.

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Noeding, Michael, Wilhelm Tegethoff, and Juergen Koehler. "Decoupling Control for Sub- and Transcritical Operation of CO2 Refrigeration Cycles." In 2018 IEEE Conference on Control Technology and Applications (CCTA). IEEE, 2018. http://dx.doi.org/10.1109/ccta.2018.8511423.

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