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1
Haile-Michael, Getu. « Cascade and secondary coolant supermarket refrigeration systems : modelling and new frost correlations ». Thesis, University of Auckland, 2011. http://hdl.handle.net/2292/6846.
Texte intégralRésumé :
Nowadays traditional (direct expansion) supermarket refrigeration systems are mostly employed in supermarket establishments for refrigerating food products and beverages in the store. However, the installations of long piping system, fittings and joints in traditional systems are causing substantial refrigerant losses. The refrigerant losses in turn bring about cost and high environmental damage in terms of ozone layer depletion and global warming potential. Additionally, defrosting of air-coils is one of the most energy consuming processes in supermarket refrigeration systems due to susceptibility of the air-coils to moisture. Hence, the frost forming on air-coils as a result of moisture transfer should be removed to keep display cabinets under the required temperature. Various studies, though limited in scope, have been conducted both numerically and experimentally by several researchers in order to provide efficient and environmentally friendly supermarket refrigeration technologies. Empirical and mathematical expressions have also been continuously developed to quantify frost characteristics on flat plates and round tubes thereby determining the appropriate defrost periods. Cascade and secondary coolant refrigeration systems are the potential candidates to replace traditional ones due to the fact that the former can work on natural refrigerants and the latter essentially eliminates long connecting lines and environmentally damaging refrigerants. Development of empirical correlations for frost characteristics on real heat exchangers could also provide accurate prediction of defrost periods thereby eliminating unnecessary waste of energy and deterioration of food products. The current study, therefore, presents (a) mathematical expressions for carbon dioxide-ammonia (R744-R717) cascade refrigeration system; (b) mathematical expressions for frost property and air pressure drop; and (c) a numerical model for medium-temperature secondary coolant system incorporating the new frost property correlations. The thermodynamic analysis of the cascade refrigeration system is useful for the supermarket refrigeration industry to optimize the design and operating parameters of the system. The development of the frost property correlations from experiments on a lab-scale flat-finned-tube heat exchanger is also useful for the supermarket refrigeration industry for better prediction and control of defrost periods and duration for medium temperature air-coils. The medium-temperature secondary coolant model adopted the most appropriate heat transfer, mass transfer and pressure drop correlations obtained from the open literature. The system components such as air-coil, plate heat exchangers, distribution lines, coolant pump and compressor were modeled independently. Each component model was validated and linked to form a complete overall medium-temperature secondary coolant refrigeration system model. The experimental results showed that COP of the Monopropylene glycol/water based medium temperature secondary coolant refrigeration system could be 1.33, whereas the simulated results on a typical supermarket showed that COP of the system could be as high as 1.75. The fundamental difference between the existing secondary coolant models and the current one is that frost characteristics have been incorporated in the air-coil model. In addition to this, complete independent models have been developed for plate heat exchangers based on their respective applications. Hence, the main advantage of the current medium-temperature secondary coolant refrigeration system model is that defrost periods and time span required to defrost frosted air-coils can be accurately determined to achieve energy savings and prevent product deterioration in the display cabinets. The plate heat exchanger models can also enable one to reasonably determine pressure drops thereby leading to an appropriate coolant pump selection. Finally, a step-by-step exercise of the application of the secondary coolant model, which has been included in this project, can be used to completely design, select, evaluate and install such systems or retrofit the existing traditional direct expansion refrigeration systems in supermarkets.
2
Schutte, Abraham Jacobus. « Demand-side energy management of a cascade mine surface refrigeration system / A.J. Schutte ». Thesis, North-West University, 2007. http://hdl.handle.net/10394/1843.
Texte intégralRésumé :
The investigations focus on load shifting, load clipping and energy efficiency through control strategies. Load shifting is achieved by increasing the amount of work done in the Eskom non-peak period. This then results in a decrease in the Eskom peak time work load.
The mine refrigeration system is modelled and verified with the data. A simulation is made from the model and the simulation is used to develop the new control strategy and new operational parameters. Predicted results are verified to be within production operational constraints.
A case study was carried out to prove the effectiveness of the newly developed control strategy and operational parameters. Firstly the cascade mine surface refrigeration system is automated to allow remote viewing and control of the system from a central point. The control strategy is tested through implementation on automated mine refrigeration systems.
The real-time energy management system (REMS) is set up and the communication with the SCADA is tested through observing dam level temperatures and stopping and starting refrigeration machines. The decisions the controllers make are monitored until the system is fully automated.
The results of the new control system on the flows, temperatures, dam levels, thermal energy and electrical energy are validated and verified. An assessment of the case study proved that DSM can be done on cascade mine refrigeration systems. A 4.2 MW load shift was predicted and research found an over performance of 0.3 MW. It is clear from the results that utilising the thermal storage in cascade mine surface refrigeration systems, will allow DSM load shifting.
In general, this dissertation proved DSM can be done on refrigeration systems and it is recommended that further studies be done on underground mine refrigeration systems.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2008.
3
Sawalha, Samer. « Carbon Dioxide in Supermarket Refrigeration ». Doctoral thesis, Stockholm : Energiteknik, Energy Technology, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4753.
Texte intégral
4
Queiroz, Marcus Vinícius Almeida. « Avaliação experimental de um sistema de refrigeração cascata subcrítico com HFCs/C02 ». Universidade Federal de Uberlândia, 2017. https://repositorio.ufu.br/handle/123456789/19110.
Texte intégralRésumé :
Este estudo avalia o desempenho de um sistema em cascata em operação subcrítica utilizando o par R134a/R744, como uma opção a sistemas convencionais em supermercados que normalmente utilizam R404A ou R22. O aparato experimental consiste em um compressor alternativo de velocidade variável para R744 e uma válvula de expansão eletrônica que promove a evaporação direta do CO2 dentro de uma câmara fria (2,3m x 2,6m x 2,5m) para manter a temperatura interna do ar estável. O ciclo de alta temperatura consiste em um compressor alternativo para R134a, uma válvula de expansão eletrônica, e um condensador a ar. Um trocador de calor de placas, que é ao mesmo tempo, o condensador para o R744 e o evaporador para R134a completa a configuração. Durante os testes experimentais, dois parâmetros foram manipulados: o grau de superaquecimento do R744, 515 K, e a frequência de operação do compressor R744, 45-65 Hz. Os valores da capacidade de refrigeração, para R134a/R744 variaram entre 4,30 ± 0,01 e 5,57 ± 0,02 kW, demonstrando a aplicabilidade desse sistema cascata em condições de carga térmica variável. Essa flexibilidade operacional também se estendeu aos valores estabelecidos para a temperatura do ar dentro da câmara fria, sendo o menor valor de -17,7 °C e o mais alto -0,8 °C. A fim de contribuir para a melhoria dos processos de refrigeração, principalmente no que se refere à eficiência energética, foi feito um drop-in no ciclo de alta temperatura, cuja carga de R134a foi substituída por R438A. A comparação foi feita de forma que os sistemas proporcionem capacidades de refrigeração e valores de temperatura do ar dentro da câmara fria semelhantes. Como resultado, o consumo de compressor com R438A foi maior em todos os testes. Os valores de COP para o sistema R134a/R744 variaram de 1,81 ± 0,01 a 2,09 ± 0,01, enquanto no sistema R438A/R744, de 1,41 ± 0,01 a 1,66 ± 0,01. O impacto total equivalente de aquecimento global para o sistema R438A/R744 foi maior em relação ao sistema original, devido ao maior potencial de aquecimento global do fluido R438A e ao maior consumo de potência elétrica do compressor do ciclo de alta temperatura. Logo, o refrigerante proposto no drop-in do sistema de alta temperatura de R134a por R438A provou-se uma alternativa menos eficiente, para as aplicações específicas.This study evaluates the performance of a cascade system in subcritical operation using the pair R134a/R744, as an option to conventional systems in supermarkets, which usually uses R404A, or R22. The experimental apparatus consists of a variable speed reciprocating compressor for R744 and an electronic expansion valve that promotes direct evaporation of the CO2 inside a cold room (2,3m x 2,6m x 2,5m) to maintain the internal air temperature stable. The high-temperature cycle consists of a reciprocating compressor for R134a, an electronic expansion valve, and an air-cooled condenser. A plate heat exchanger, which is at the same time, the condenser for the R744 and evaporator to R134a completes the setup. During the experimental tests, two parameters were manipulated: The superheating degree of the R744, 5-15 K, and the R744 compressor operation frequency, 45-65 Hz. The cooling capacity values for R134a/R744 ranged between 4,30 ± 0,01 and 5,57 ± 0,02 kW, demonstrating an application to the cascade system under variable thermal load conditions. This operational flexibility also extends to the air temperature values established inside the cold room, being the lower value of -17,7 ° C and higher -0,8 ° C. In order to contribute to the improvement of the cooling processes, mainly about the energy efficiency, a drop-in has been made at the high- temperature cycle, which R134a refrigerant charge has been replaced by R438A. The comparison was done regard both systems providing similar cooling capacities and air temperature values inside the cold room. As a result, the consumption of the compressor operating with R438A was higher in all tests. The COP values for the R134a/R744 system ranged from 1,81 ± 0,01 to 2,09 ± 0,01, while with the R438A/R744 system, from 1,41 ± 0,01 to 1,66 ± 0,01. The total equivalent warming impact for the R438A/R744 system was higher compared to the original system, as a result of the higher GWP for the R438A and higher electrical power consumptions. It has been proven the proposed drop-in, at the high temperature cycle from R134a by R438A, is a less efficient choice for such specific applications.
Dissertação (Mestrado)
5
Coggins, Charles Lee. « Single- and Multiple-Stage Cascaded Vapor Compression Refrigeration for Electronics Cooling ». Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16283.
Texte intégralRésumé :
The International Technology Roadmap for Semiconductors (ITRS) predicts that microprocessor power consumption will continue to increase in the foreseeable future. It is also well known that microprocessor performance can be improved by lowering the junction temperature: recent analytical studies show that for a power limited chip, there is a non-linear scaling effect that offers a 4.3x performance enhancement at -100 °C, compared to 85 °C operation. Vapor Compression Refrigeration (VCR) is a sufficiently compact, low cost, and power efficient technology for reducing the junction temperature of microprocessors below ambient, while removing very high heat fluxes via phase change.
The current study includes a scaling analysis of single- and multiple-stage VCR systems for electronics cooling and an experimental investigation of small-scale, two-stage cascaded VCR systems. In the scaling analysis, a method for estimating the size of single- and multiple-stage VCR systems is described, and the resulting trends are presented. The compressor and air-cooled condenser are shown to be by far the largest components of the system, dwarfing the evaporator, expansion device, and inter-stage heat exchanger. For systems utilizing off-the-shelf components and removing up to 200 W at evaporator temperatures as low as 173 K, compressor size dominates the system and scales with the compressor s motor. The air-cooled condenser is the second largest component, and its size is constrained by the air-side heat transfer coefficient. In the experimental work, a two-stage cascaded VCR system with a total volume of 60000 cm3 is demonstrated that can remove 40 W at -61 °C.
6
Скрипник, О. В., В. В. Свяцький, O. Skrypnyk et V. Sviatskyi. « Перспективні напрямки технологічного застосування гідратів двооксиду вуглецю ». Thesis, ХНТУ, 2017. http://dspace.kntu.kr.ua/jspui/handle/123456789/6869.
Texte intégralRésumé :
Наведено аналіз останніх досліджень і приклади застосування газових гідратів двооксиду вуглецю. Наведено приклад можливості заміщення двооксидом вуглецю метану у природніх гідратах, організовуючи контрольований видобуток метану із субаквальних газогідратних покладів. Розглянуто питання про обмеження викиду парникових газів за рахунок їх уловлювання і зберігання за допомогою технології CCS (Carbon Capture and Storage). Наведено приклад каскадних систем на базі аміаку з двооксидом вуглецю із сумішами вуглеводнів як основу холодильних установок для одержання глибокого холоду. Розглянуто спосіб вибухового штампування з метою підвищення безпеки та збільшення економічної ефективності технологічного процесу за рахунок використання стабільних газових компонентів, застосування більш простого технологічного обладнання. Зроблено висновок, що використання двооксиду вуглецю в складі газових гідратів дозволяє на принципово нових основах істотно покращити технологічні процеси в різних галузях промисловості, а також ефективність енерго- та ресурсозбереження. The analysis of the latest studies and application examples of gas hydrates of carbon dioxide is given. An example of the possibility of replacing methane carbon dioxide in natural hydrates by organizing controlled methane production from subaquatic gas hydrate deposits is given. The issue of limiting the emission of greenhouse gases through their capture and storage using Carbon Capture and Storage technology is considered. An example of cascade systems based on ammonia with carbon dioxide and hydrocarbon mixtures as a basis for refrigeration facilities for obtaining deep cold is given. The method of explosive stamping is considered with the purpose of increasing safety and increasing the economic efficiency of the technological process due to the use of stable gas components, the use of more simple technological equipment. It is concluded that the use of carbon dioxide in gas hydrates allows essentially new ways to improve technological processes in various industries, as well as the efficiency of energy and resource saving.
7
Cipolato, Liza. « Analise exergetica de um ciclo em cascata para liquefação de gas natural ». [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266261.
Texte intégralRésumé :
Orientador: Jose Vicente Hallak D'AngeloDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-11T14:06:54Z (GMT). No. of bitstreams: 1 Cipolato_Liza_M.pdf: 1029854 bytes, checksum: e29def5b437d5ad6a00d8fc677c63bf5 (MD5) Previous issue date: 2008
Resumo: O comércio de gás natural liquefeito apresenta um crescente interesse por parte tanto de países exportadores como dependentes desta fonte energética. Apesar de o transporte por gasoduto ser muito menos suscetível a perdas, ele se torna inviável a longas distâncias ou a demandas variáveis. A liquefação do gás natural também proporciona o armazenamento desta fonte energética numa forma estável e de alto potencial energético,evidenciando o caráter estratégico do processo. Desde a década de 60 a tecnologia para liquefação do gás natural é utilizada, porém, apenas há alguns anos os países iniciaram o comércio desta fonte energética em larga escala e isto acarretará um aumento mundial tanto no número de terminais exportadores (plantas de liquefação) quanto importadores (terminais de regaseificação). O processo de liquefação do gás natural ocorre através de uma sequência de ciclos termodinâmicos de refrigeração, e estes, por sua vez, precisam trabalhar de forma otimizada para reduzir perdas. A análise exergética é uma ferramenta muito útil para avaliar estas perdas e pode ser essencial na instalação de uma nova planta ou melhoria de uma já existente. O presente trabalho realizou uma análise exergética de um ciclo de refrigeração utilizado para a liquefação de gás natural, o qual é do tipo multiestágio em cascata, padrão utilizado atualmente, sendo o mais conhecido e difundido entre as indústrias da área. Primeiramente, o processo foi simulado em software comercial Hysys (versão 3.2 da Aspen Technology). O resultado obtido da simulação foi validado através de comparação com dados da literatura, mostrando-se adequado. Em seguida, a simulação foi testada em diferentes condições operacionais, seguindo um planejamento fatorial completo, o qual teve como objetivo verificar a influência da variação das pressões de seis pontos específicos do ciclo sobre a variável resposta, que é a taxa de exergia total destruída no processo, visando sua minimização. Os resultados obtidos levaram a uma nova condição de operação para o ciclo de refrigeração com redução de aproximadamente 48% da taxa de exergia destruída com relação aos dados do caso obtido da literatura. Tal resultado evidencia o potencial da metodologia termodinâmica utilizada, demonstrando sua aplicação em estudos de melhoria do desempenho de ciclos de refrigeração para a indústria de liquefação de gás natural
Abstract: The liquefied natural gas trade shows a growing interest either from countries which are exporters or countries which depend on this kind of energetic source. Although gas pipelines are less susceptible of transportation losses, they become impracticable when distances are too long or when demands are highly variable. The liquefaction of natural gas also enables its storage in a stable way, in which energetic potential is high, expressing the strategic purpose of the process. Since the 1960 decade natural gas liquefying technology is been used, but only a few years ago countries have started the trade of this kind of energetic source on a large scale. Consequently, the number of exporter terminals (liquefaction industries) and importer terminals (regasification plants) will increase worldwide. The natural gas liquefaction process is based on a sequence of refrigeration thermodynamics cycles, which need to work in an optimized way in order to reduce losses. The exergy analysis is a very useful tool to evaluate these losses and can be crucial in a new plant installation or in a current one improvement. This dissertation performed an exergy analysis of a multistage cascade refrigeration cycle applied in natural gas liquefaction. The multistage cascade cycle is currently the standard type, being the most known and diffused among industries. Firstly, the process was simulated in commercial software Hysys (version 3.2 of Aspen Technology). The result obtained from the simulation was validated by comparison with the literature data and showed a very adequate similarity. After that, the simulation was checked in different operational conditions, according to the complete factorial design of experiments. The design of experiments¿ objective was to verify the pressure influence of six specific points of the cycle over the response variable, which is the rate of total exergy destroyed in the cycle, in order to reach its minimal value. The results showed a new operational condition to the refrigeration cycle, in which the destroyed exergy rate was reduced by approximately 48% in comparison with literature data. This result provides evidence of the high potential of the thermodynamic tool used, showing its application in studies of performance improvements for refrigeration cycles in industries of natural gas liquefaction
Mestrado
Sistemas de Processos Quimicos e Informatica
Mestre em Engenharia Química
8
Goloubev, Dmitri. « Kühlung eines resistiven HTSL-Kurzschlussstrombegrenzers mit einer Gemisch-Joule-Thomson-Kältemaschine ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1095838519812-78347.
Texte intégralRésumé :
Die vorliegende Arbeit beschäftigt sich nach der Analyse und Optimierung der Stromzuführungen auf Flüssigstickstoff-Temperaturniveau, hauptsächlich mit der Untersuchung einer Gemisch-Stickstoff-Kaskade als Kälteversorgungssystem eines resistiven HTSL-Kurzschlussstrombegrenzers. Unter einem Kurzschlussstrombegrenzer versteht man einen veränderlichen elektrischen Widerstand, welcher, gegebenenfalls in Serie mit konventionellen, mechanischen Stromunterbrechern, direkt in den zu schützenden Stromkreis eingebaut ist. Als veränderlicher elektrischer Widerstand kann z.B. ein supraleitendes Element verwendet werden. Im normalen Betriebsfall setzt dieser dem fließenden Strom praktisch keinen Widerstand entgegen. Die Dimensionierung wird so gewählt, dass im Falle eines Überstroms ein rascher Übergang in den normalleitenden Zustand erfolgt. Durch den nun vorhandenen Widerstand wird der Stromfluss sehr effektiv begrenzt, bis beispielsweise nachgeschaltete mechanische Schutzeinrichtungen ansprechen. Sobald dies erfolgt ist, kann der Supraleiter regenerieren und in den Ausgangszustand zurückkehren. Die Verwendung von HTSL-Material als Supraleiter erscheint hier höchst vorteilhaft, da damit ein Arbeiten auf Flüssigstickstoff-Temperaturniveau erlaubt wird. Ein entscheidender Punkt für die erfolgreiche Einführung der HTSL-FCL ist die Bereitstellung einer geeigneten Kälteversorgung. Dies kann entweder durch regelmäßiges Nachfühlen mit flüssigem Stickstoff oder durch den Einsatz einer Kältemaschine zur Stickstoffrekondensation realisiert werden. Beim Einsatz einer Kältemaschine hat man einen von der Stickstoffnachlieferung unabhängigen Betrieb mit geschlossenem Kühlsystem. Die Energiedissipation in dem HTSL-Element selbst ist unter Normalbedingungen vernachlässigbar klein. Für die Auslegung des Kühlsystems ist von Bedeutung, dass der größte Teil der Wärmelast durch die metallischen Stromzuführungen verursacht wird. Die Auslegung des Kühlsystems muss sich daher an der thermodynamischen Analyse der Stromzuführungen orientieren. Das Ziel dieser Arbeit bestand in der Analyse von Kühlmethoden für solche Stromzuführungen hinsichtlich ihrer Effektivität und Wirtschaftlichkeit. Ein neues Kühlsystem auf der Basis einer Gemisch-Stickstoff-Kaskade wird vorgeschlagen als Alternative zu den derzeit in Frage kommenden Kühltechniken. Es wurde folgende Vorgehensweise gewählt: 1. Verschiedene Kühlmethoden zur Kühlung von SZF werden aufgeführt und thermodynamisch bewertet. 2. Kühlsysteme, basierend auf einer Gemisch-Stickstoff-Kaskade, werden vorgeschlagen und deren Charakteristika mittels numerischer Simulation bestimmt. 3. Ein auf der Basis einer Gemisch-Kältemaschine gebauter Stickstoffverflüssiger wird in Betrieb genommen und getestet. 4. Die Funktion und die Effektivität der Gemisch-Stickstoff-Kaskade zur Kühlung der Stromzuführungen werden bewertet. 5. Zugehörige Kühlsysteme auf der Basis verschiedener Kühltechniken werden analysiert 6. In einer Wirtschaftlichkeitsbetrachtung werden die Kühlsysteme einander gegenübergestellt Insgesamt kann als Ergebnis festgehalten werden, dass der Einsatz der vorgestellten Gemisch-Stickstoff-Kaskadenanlagen zur Kälteversorgung im vorgestellten Anwendungsfall eine durchaus wettbewerbsfähige, voraussichtlich sogar überlegene Alternative zu den sonst verfügbaren Methoden darstellt.
9
Goloubev, Dmitri. « Kühlung eines resistiven HTSL-Kurzschlussstrombegrenzers mit einer Gemisch-Joule-Thomson-Kältemaschine ». Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24374.
Texte intégralRésumé :
Die vorliegende Arbeit beschäftigt sich nach der Analyse und Optimierung der Stromzuführungen auf Flüssigstickstoff-Temperaturniveau, hauptsächlich mit der Untersuchung einer Gemisch-Stickstoff-Kaskade als Kälteversorgungssystem eines resistiven HTSL-Kurzschlussstrombegrenzers. Unter einem Kurzschlussstrombegrenzer versteht man einen veränderlichen elektrischen Widerstand, welcher, gegebenenfalls in Serie mit konventionellen, mechanischen Stromunterbrechern, direkt in den zu schützenden Stromkreis eingebaut ist. Als veränderlicher elektrischer Widerstand kann z.B. ein supraleitendes Element verwendet werden. Im normalen Betriebsfall setzt dieser dem fließenden Strom praktisch keinen Widerstand entgegen. Die Dimensionierung wird so gewählt, dass im Falle eines Überstroms ein rascher Übergang in den normalleitenden Zustand erfolgt. Durch den nun vorhandenen Widerstand wird der Stromfluss sehr effektiv begrenzt, bis beispielsweise nachgeschaltete mechanische Schutzeinrichtungen ansprechen. Sobald dies erfolgt ist, kann der Supraleiter regenerieren und in den Ausgangszustand zurückkehren. Die Verwendung von HTSL-Material als Supraleiter erscheint hier höchst vorteilhaft, da damit ein Arbeiten auf Flüssigstickstoff-Temperaturniveau erlaubt wird. Ein entscheidender Punkt für die erfolgreiche Einführung der HTSL-FCL ist die Bereitstellung einer geeigneten Kälteversorgung. Dies kann entweder durch regelmäßiges Nachfühlen mit flüssigem Stickstoff oder durch den Einsatz einer Kältemaschine zur Stickstoffrekondensation realisiert werden. Beim Einsatz einer Kältemaschine hat man einen von der Stickstoffnachlieferung unabhängigen Betrieb mit geschlossenem Kühlsystem. Die Energiedissipation in dem HTSL-Element selbst ist unter Normalbedingungen vernachlässigbar klein. Für die Auslegung des Kühlsystems ist von Bedeutung, dass der größte Teil der Wärmelast durch die metallischen Stromzuführungen verursacht wird. Die Auslegung des Kühlsystems muss sich daher an der thermodynamischen Analyse der Stromzuführungen orientieren. Das Ziel dieser Arbeit bestand in der Analyse von Kühlmethoden für solche Stromzuführungen hinsichtlich ihrer Effektivität und Wirtschaftlichkeit. Ein neues Kühlsystem auf der Basis einer Gemisch-Stickstoff-Kaskade wird vorgeschlagen als Alternative zu den derzeit in Frage kommenden Kühltechniken. Es wurde folgende Vorgehensweise gewählt: 1. Verschiedene Kühlmethoden zur Kühlung von SZF werden aufgeführt und thermodynamisch bewertet. 2. Kühlsysteme, basierend auf einer Gemisch-Stickstoff-Kaskade, werden vorgeschlagen und deren Charakteristika mittels numerischer Simulation bestimmt. 3. Ein auf der Basis einer Gemisch-Kältemaschine gebauter Stickstoffverflüssiger wird in Betrieb genommen und getestet. 4. Die Funktion und die Effektivität der Gemisch-Stickstoff-Kaskade zur Kühlung der Stromzuführungen werden bewertet. 5. Zugehörige Kühlsysteme auf der Basis verschiedener Kühltechniken werden analysiert 6. In einer Wirtschaftlichkeitsbetrachtung werden die Kühlsysteme einander gegenübergestellt Insgesamt kann als Ergebnis festgehalten werden, dass der Einsatz der vorgestellten Gemisch-Stickstoff-Kaskadenanlagen zur Kälteversorgung im vorgestellten Anwendungsfall eine durchaus wettbewerbsfähige, voraussichtlich sogar überlegene Alternative zu den sonst verfügbaren Methoden darstellt.
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KUMAR, PRAKASH. « CASCADE REFRIGERATION CYCLE ». Thesis, 2017. http://dspace.dtu.ac.in:8080/jspui/handle/repository/16002.
Texte intégralRésumé :
A thermodynamic analysis is done for cascade cycle which is a combination of vapour compression system with vapour absorption system. The objective of the work is to determine the effects of different parameters on the performance of the cycle. Equations used follow the first law of thermodynamics. Capacity of the cascade cycle is taken as 50 kw. Refrigerants used in the cycle are lithium bromide-water in the absorption cycle and R134a in the vapour compression cycle. EES has been used to find out the results through doing simulation in it. The result of the simulation is to study the relationship between different components of the cycle such as generator, condenser, heat exchanger evaporator on the cop of the cycle. The outcome can be used to enhance the performance and determine the parameters for better working of the cascade cycle.
11
Tsung-Chiuan, Chen陳宗權, et 陳宗權. « Research of Cascade Refrigeration System ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/gtmpzu.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
100
The Cryogenic systems use cascade system, thus reducing the compression ratio. As the volume of the compressors in two stages is decreased, the wasted work is reduced relatively, so that the energy can be saved, and the system operating temperature can be reached easily. Therefore, this study used the cascade refrigeration system available on the market for hardware design, control strategy and refrigerant collocation, in order to meet the appropriate operating conditions of this system design. Due to the faults of the original system compressor and control circuit, the compressor with similar discharge capacity was used instead, and the board circuit was replaced by traditional circuit. The hot section refrigerant A+B and cold section refrigerant A+B were filled in, so that the cascade system could meet the required temperature and stability. After the refrigeration system was completed. The chamber temperature was cooled to setting value, and then tested the performance of the system under the stable and maintained chamber temperature. The load was increased at the chamber temperature of -60℃, -70℃, -80℃ and -80℃ for testing. Afterwards, the temperature and pressure data in two hours stable operation were taken and the pressure-enthalpy chart was drawn to calculate the performance of refrigeration system. The results showed that the performance of cascade system in operation at -60℃ was 2.31, the performance at -70℃ was 1.07, the performance at -80℃ was 0.84 and the performance with additional load at -80℃ was 1.78, however, considering the time required in the process of cooling to -80℃ the cascade system performance was 0.33.
12
Chiang, Fu-Lin, et 江富麟. « Cascade Refrigeration System Reaearch of Freeze Dryer ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/5xyjg9.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
97
Refrigeration system has a long history, and vacuum freeze-drying is a technology used for drying, color protection, fresh keeping, or nutrition preservation of food, biologics, biomaterials, or micro/nano materials, So Freeze-drying systems to be used for some time. But most operating temperature to the systems are -50℃, besides, old machines have only one cold trap chamber, if we want to remove the ice on cold trap, we will shutdown the machines, then Production process will be delayed. This thesis is focused on improving the cascade vacuum Freeze-drying Development, and this operating temperature can reach to -80℃,it is more favorable for specific high-tech products process and will not have a negative impact on production time. In experiments, freeze-drying system had a best evaporative temperature.
13
Lin, Shian-Tzong, et 林憲宗. « Performance Analysis of R717/HC Cascade Refrigeration System ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/sme3j6.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
98
Low-temperature storage refrigeration system is vital for much industry range. The traditional single-stage vapor compressor system is not suitable for low-temperature system; therefore, it should be used through cascade refrigeration system. For many years, as a result of environmental protection issue related global warning and depletion of ozone layer caused by the use of synthetic refrigerants (CFC’s, HCFC’s and HFC’s), the return to the use of harmless natural substances is a must to alternative refrigerants in refrigeration systems. Ammonia (R717) and Hydrocarbon refrigerant have excellent thermodynamic and thermo-physical properties; they can be used in a wide range of refrigeration system. In this paper, a cascade refrigeration system with Ammonia (R717) and Hydrocarbon refrigerant (HC) as working fluids in the low and high temperature stages, respectively, has been analysed and compared with R22 and R134a of traditional refrigerant. Further to research and analysis the relation of COP and mass flow ratio versus operating and design parameters of 6 group’s refrigerant in order to get optimization of parameter and analysed refrigerant in cascade low-temperature refrigeration system.
14
Hsieh, Cheng-Chih, et 謝承志. « Study of Expansion Valve on Cascade Refrigeration System Performance ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/442s6p.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
102
The cascade refrigeration systems are widely applied in Taiwan, for use in air conditioning, refrigeration and food processing, pharmaceuticals, chemicals, machinery, etc. More attention recently, So this thesis refrigeration components easily available in the market to buy the dual refrigeration system developed for conducted to explore various expansion valve of the refrigerant flow. The system of high and low temperature circulation system individually in four A, B, C and D expansion valve testing, in order to best binary refrigerating system expansion valve and the coefficient of performance. Results in a high temperature due to the circulatory system A, B, C the expansion valve of the refrigerant flow rate is too small, resulting in low temperature startup cycle, temperature cycle system can,t be stabilized at the intercooler below -30 ℃, the system also due to temperature cycling and A the flow of refrigerant expansion valve B is too small, the evaporator can,t reach -80 ℃, and start C expansion valve of the evaporator inlet temperature difference is too large, said it could not achieve a good cooling effect, this thesis high binary refrigeration system, hypothermic circulatory system are available starting D expansion valve coefficient of 0.45 for the best performance.
15
Cheng, Po-Jen, et 鄭博仁. « Analysis of Improving the Performance of Cascade Refrigeration System ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/rx22f2.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
102
This paper examines how the common refrigerant R-134a and the non-azeotropic refrigerant R-404A perform in a binary refrigeration with the addition of a refrigerant precooler and a desuperheater and the changes in the system with the added refrigerants before and after subcooling through experiments and comparison. Inferences are made on the viability of installing a ‘refrigerant precooler’ in the refrigerant system through theoretical analysis of changes in the coefficient of performance (COP) of the system in the subcooled and superheated states. The purpose is to understand how the binary refrigeration system performs in terms of actual operation and system performance in the different models designed for this study and examine the possibility to optimize the ‘refrigerant precooler and desuperheater combination’ developed in this study based on the data obtained. Analysis of the data obtained from this experiment reveals that the addition of a heat receiver at the outlet of the compressor in a refrigerated vehicle can effectively control the degree of subcooling of the drainage pipe in the condenser at below 38℃ and the addition of a refrigerant precooler improves problems such as unstable refrigerant temperature rise in the refrigerated vehicle after evaporator pump-down and shutdown, thereby increasing the refrigeration speed. An analysis that compares the model in which both additional components are synchronized with the basic model shows that with the power consumption of the binary refrigeration system as the baseline, adding only the desuperheater, only the precooler, and the desuperheater and precooler combination achieves energy efficiency of 24%, 54.3% and 57.8%, respectively. Therefore, the addition of the desuperheater and precooler combination to the binary refrigeration system can effectively improve overall performance and reduce carbon emissions.
16
Liu, Po-Wen, et 劉博文. « Thermodynamic Analysis of Optimum Condensing Temperature of Cascade-Condenser for CO2/NH3 Cascade Refrigeration Systems ». Thesis, 2005. http://ndltd.ncl.edu.tw/handle/726c3g.
Texte intégralRésumé :
碩士國立臺北科技大學
冷凍空調工程系所
93
For the low-temperature applications, such as quick freezing and frozen storage of food, the required evaporating temperature of refrigeration system ranges from -40°C to -55°C, in which a single-stage vapor-compression refrigeration system is inadequate. Considering global environmental protection, the use of natural refrigerants in refrigeration systems has been revealed to be a complete solution to permanent alternative for fluorocarbon-based refrigerants. A cascade refrigeration system applying the natural refrigerants CO2 and NH3 fulfills these requirements for low-temperature applications of industry refrigeration systems. Although studies on carbon dioxide as a refrigerant are now gaining attention, the works on CO2/NH3 cascade refrigeration system are still lacking. This study applied thermodynamic analysis to find the optimum condensing temperature of the cascade-condenser in a cascade refrigeration system utilizing carbon dioxide and ammonia as refrigerants, in which the system attained the maximum COP. The design parameters for this paper is：High temperature circuit condensing temperature (Tc= 30, 35, 40℃), low temperature circuit evaporating temperature (TE= -45, -50, -55℃), cascade condenser difference temperature (△T= 3, 4, 5℃). The analysis result show：For condensing temperature is 35℃and evaporating temperature is -50℃of CO2/NH3 cascade system. The cascade condenser optimum condensing temperature TMC is -15℃. Under this condition, optimal TMC will increase by the raise of TE, Tc and △T.
17
Chiou, Chi-Han, et 邱祈翰. « Study of an Auto - Cascade Refrigeration System with Refrigerant Mixtures ». Thesis, 2001. http://ndltd.ncl.edu.tw/handle/83760711606136132132.
Texte intégralRésumé :
碩士國立交通大學
機械工程系
89
The objective of this research is to design a auto-cascade refrigeration system with zeotropic refrigerant mixtures R-32/R-134a（30/70 wt％）, which might reach a low temperature —40℃. This system utilizes only one single compressor with a phase separator in order to shift the concentration contents of the refrigerant mixtures .The vapor phase flows through a cascade heat exchanger and exchanges latent heat with the low temperature liquid phase after expansion. Then, the mixture rich with higher boiling component flows into the evaporator to create the low temperature cooling, and merges with the mixture rich with lower boiling component, which leads finally back to the compressor and thus completes a cycle. This system have two advantages. First, utilization of the temperature glide of zeotropic refrigerant mixtures can reduce heat transfer irreversibility in the heat exchangers. Secondly, the phase separator shifts the concentration percentages of the components by the temperature difference of the boiling points. Thus, this system can raise the cooling capacity and can reduce the power consumption. Test results for a R-32/R-134a (30/70 wt %) cascade loop, compared with a baseline loop, indicates the increase of only 6％ in the power consumption and degradation of 10％ in the COP. In conclusion, this system can raise the evaporating pressure, can reduce the pressure ratio with one single compressor, and can achieve the designed low temperature.
18
Tsai, Meng-Ying, et 蔡孟穎. « The application of cascade refrigeration system in the development for refrigeration, hot water and steam in convenience shops ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/pmzb25.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
100
The study aims at providing convenient stores with the required energy for cooling, freezing, and supply of hot water and steam through acascade refrigeration system composed of HFC-134a and HFC-245fa refrigerants. In the experiment, the paper makes use of the feasibility of producing hot water and steam and raising the coefficient of performance (COP) of low temperature system by the high temperature feature of HFC-245fa refrigerant. Through planning of static and dynamic testing conditions, the paper designs the complete experimental methods and procedures, analyzes the effects of each experimental parameter on the performance of the system, and further studies and develops a refrigeration system with environmental protection concept and energy-saving effect. Experimental results show that when the evaporation temperature of HFC-245fa is 45oC and the effluent water temperature is 90oC, the COPH (COP as a heater) of heat-sensitive expansion valve is 1.81, being 4.6% more than the manual expansion valve; and the COPL (COP as a heating load) is 1.64, being 19.4% more than the manual expansion valve. Use of the heat pump system of binary refrigeration system for heating can save energy by 41% when compared to heating by natural gas, 92.5% when compared to heating by liquid petroleum gas, 98.5% when compared to heating by diesel boiler, and 122% when compared to heating by electric heater. Through cascade system, the study can offer compression again to condensing heat by the low-temperature side, achieving the effects of making high-temperature heat and saving energy.
19
Kuo, Ming-Chang, et 郭銘昌. « Optimum Allocation of Heat-Exchanger Thermal Conductance in CO2/NH3 Cascade Refrigeration System ». Thesis, 2006. http://ndltd.ncl.edu.tw/handle/3b649q.
Texte intégralRésumé :
碩士國立臺北科技大學
冷凍空調工程系所
94
This study mainly discusses the optimum allocation of heat-exchanger thermal conductance in CO2/NH3 cascade refrigeration systems, such as evaporative, cascade condenser, condenser. Using cold-water temperature, chillier fluid temperature, cool capacity and total thermal conductance as conditional parameters, this research built three models of Reversed Carnot Cycle and Ideal Vapour Compressor Refrigeration Cycle and Real Vapour Compressor Refrigeration Cycle, which followed thermo dynamics analysis and Klein thermal conductance equation. The system produced Heat-exchanger thermal conductance optimum allocation by analyzing calculated maximum COP with different parameters and thermal conductance allocation. The result of this research articulated that the principle of three heat-exchangers optimum allocation in CO2/NH3 cascade refrigerator system: 1.Heat-exchanger thermal conductance optimum allocation in Reversed Carnot Cycle is 1：1：1. 2.Heat-exchanger thermal conductance optimum allocation would be 1：1.0625：1.0625 in Ideal Vapour Compressor Refrigeration Cycle and Real Vapour Compressor Refrigeration Cycle, of which restricted conditions are that average chiller fluid temperature is from -42℃ to -46℃, average cold water temperature range is from 31℃ to 32℃, total thermal conductance is from 120kW/K to 140kW/K, and cool capacity between 120kW to 160kW. If Total thermal conductance is over 170kW/K, then Heat-exchanger thermal conductance optimum allocation should approach 1：1：1.
20
Chung, Jenn Chyi, et 鐘震麒. « Study on Energy Saving of Appling Cascade System on Walk-in Refrigeration Show Cabinet ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/51912954238237127949.
Texte intégralRésumé :
碩士國立臺北科技大學
冷凍與低溫科技研究所
91
Refrigerated display cabinets are widely used in 24-hr convenience store in Taiwan. In this research, we built a 5 in 1 closed type walk-in refrigerated display cabinet and its compression refrigeration system, which including traditional single stage compression system and cascade refrigeration system, to evaluate their system performance. The results of the performance test showed that the cascade refrigeration system adopting R134a and R507 combination has better system performance than the combination of R134a and R404A, and the power consumption test also showed 5 ~ 7% energy saving improved comparing with the single stage compression refrigeration system adopting R404A under the testing condition of 40℃ condensing temperature.
21
Yen, Chia-Houng, et 顏家宏. « Study of two Auto-Cascade Refrigeration System with Refrigerant Mixture R-32/R-134a ». Thesis, 2004. http://ndltd.ncl.edu.tw/handle/3umbv7.
Texte intégralRésumé :
碩士國立交通大學
機械工程系所
92
The objective of this research is to design a two auto-cascades refrigeration system with refrigerant mixture R-32/R-134a in which two phase separators and two heat exchangers are used to raise the concentration of the richer R-32 mixture flow through the evaporator in order to achieve the low temperature cooling , only utilize a 1.5HP compressor to support system power consumption. In comparison with the one-cascade system , test results for a R-32/R-134a(30/70 wt%) two cascades loop , showed an increase of only 2.14 % in the power consumption , and a cop valve 2.21 with an increment of 4.25% , as well as evaporator temperature of -51℃ . Also the condensation pressure and evaporation pressure in this two-cascade loop were much lower than those in one-cascade loop . The advantage of this system is that it needs only one 1.5 hp compressor to fulfil all the foregoing achievements .
22
Wang, Pei-Yi, et 王姵懿. « Study on Low-Temperature Auto-Cascade Refrigeration Systems Operating with Zeotropic HC Refrigerant Mixtures ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/7p3xg7.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
99
The temperature of the freezer ranging from -40 to -160℃ is widely used in cryomedicine, energy, biotechnology as cryopreservation. The system used to zeotropic refrigerant mixtures and single compressor, through zeotropic refrigerant mixture in the high boiling point and low boiling point in order to achieve the natural separation between the multi-level series with the stack method, to take the system from -40 to -160℃ temperature purposes. The feature of the auto-cascade refrigeration systems is affected by zeotropic refrigerant mixtures therefore the composition of the refrigerant and mass fraction are the key factors.The purpose of this study is to investigate auto-cascade refrigeration systems as the object of study, use simulation to look into the application of zeotropic HC refrigerant mixtures of R170/R290, R170/R1270, R170/R600 and 170/R600a to coefficient of performance (COP), and do a comprehensive appraisal of the composition of refrigerant. According to the research, in the same design conditions, R170/R290, R170/R1270, R170/R600, and R170/R600a zeotropic refrigerants mixture the best performance value and size of the sequence is: R170/R600(COP=1.34)>R170/R600a(0.82)>R170/R290(0.36)>R170/R1270(0.34), and the corresponding ratio of the best refrigerants composition were: 0.16,0.22,0.34,0.31. To R170/R1270 mixed refrigerant as a benchmark, the benchmark value of 1, R170/R600, R170/R600a, R170/R290 mixed refrigerant composition with the ratio of 3.92:2.41:1.06:1.
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Tang, Hsin-Chuan, et 唐欣傳. « Study on Low-Temperature Auto-Cascade Refrigeration Systems with Regenerator and Zeotropic Refrigerant Mixtures ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/tb5w4p.
Texte intégralRésumé :
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
100
With the development of technology, the requirement for cryogenic freezing is getting stricter in the scope of energy, military, bio-tech, and medical. Especially in medical, the cell preservation technique is the key of graft. Auto-cascade system uses zeotropic mixture as refrigerant to implement the natural separation and multi-stage cascade through the temperature glide for getting low temperature of -60°C to -160°C. The performance of Auto-cascade system is mainly affected by the zeotropic refrigerant, so the key point is to select the composition and fraction. The major issue of this study is to probe into the best fraction and COP of R1150/R290, R1150/R1270, R1150/R600, and R1150/R600a mixtures in Auto-cascade system with Regenerator through the theoretical analyzing. The study shows that 1). R1150/R600 mixture has the best COP 2.01 with R1150 mass fraction of 0.11, 2). The best COP 2.01 of R1150/R600 mixture is greater than the best COP 1.34 of R170/R600 mixture, 3). The best COP of R1150/R600 Auto-cascade with Regenerator has COP 2.21, which is greater than the value 2.01 of COP without Regenerator.
24
Chiang, Chi Feng, et 江奇峰. « Cascade Refrigeration System with Refrigerant Mixtures using a Liquid Over Feeding Accumulator Heat Exchanger ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/07922647873631590883.
Texte intégralRésumé :
碩士國立交通大學
機械工程系
91
The objective of this research is to design and improve the efficiency of the cascade refrigeration system with zeotropic refrigerant mixtures. This system utilizes a single compressor with R-32/R-134a refrigerant mixtures. Phase separator is put in this system in order to change the concentration of refrigerant mixtures. The vapor phase flows through a cascade heat exchanger and exchanges latent heat with the low temperature liquid phase after expansion. Then, the higher-boiling-component mixture flows into the evaporator to create the low temperature cooling, and merges with the lower-boiling-component mixture, which leads finally back to the compressor and thus completes a cycle. Furthermore we design a Liquid Over Feeding Accumulator Heat Exchanger（LOF-AHX）between the outlet of the evaporator and condenser in order to make the high pressure liquid refrigerant exchange heat with the low pressure vapor refrigerant. This design enables the refrigerant: (1) to get super heat before sucking into compressor in order to protect compressor from liquid compression; (2) to get subcooling before entering expansion; (3) to increase the mass flow rate; (4) to raise the cooling capacity; (5) to reduce the pressure ratio and exit temperature. Due to the concentration shift effect of cascade loop of refrigerant mixtures, using LOF can raise cooling capacity substantially. Therefore, the optimal COP can reach 2.126, as well as the lowest temperature can reach —38.35oC. All of those results occur in cascade loop of refrigerant mixtures with LOF.
25
ANAND, SAURABH. « COMPARATIVE ANALYSIS OF THERMODYNAMICS PERFORMANCE OF CASCADE REFRIGERATION SYSTEM FOR REFRIGERANT COUPLE R23/R290 AND R23/R600A ». Thesis, 2019. http://dspace.dtu.ac.in:8080/jspui/handle/repository/16950.
Texte intégralRésumé :
This study presents a comparative analysis of thermodynamic performance of cascade refrigeration systems (CRSs) for refrigerant couples R23/R290 and R23/R600A to discover whether R600A is a suitable substitute for R290. The discharge temperature, input power of the compressor, coefficient of performance (COP), exergy loss (X) and exergy efficiency (g) are chosen as the objective functions. The operating parameters considered in this thesis include condensing temperature, evaporating temperature in both high-temperature cycle i.e HTC and lower cycle i.e LTC and Temperature difference in the cascade heat exchanger. Under the same operation condition, the input power of R23/R600A CRS is lower than that of R23/R290 CRS, and COP opt is higher than that of R23/R290 CRS. The theoretical analysis indicates that R23/R600A is a more potential refrigerant couple than R23/R290 in Cascade Refrigeration System (CRS).
26
KUMAR, RAHUL. « EXERGY AND ENERGY ANALYSIS OF THREE STAGE CASCADE REFRIGERATION SYSTEM FOR BIOMEDICAL APPLICATION USING NATURAL REFRIGRANTS ». Thesis, 2016. http://dspace.dtu.ac.in:8080/jspui/handle/repository/14475.
Texte intégralRésumé :
ABSTRACT
Biomedical preservation requires the temperature for the storage of stem cell, blood, sperm & organs at a storage temperature of below -80°C.We can achieve effectively cooling of about -35°C with the help of simple vapour compression refrigeration system. With the help of compound vapour compression refrigeration system, temperature up to – 50 °C is achievable.
The cascade refrigeration system is widely used where low temperatures are needed. The natural refrigerant CO2 makes it possible to achieve temperatures as low as -54°C in the low temperature stage. In this case propene is the refrigerant for the upper cascade stage.Using other refrigerants (e.g. ethane) in low temperature circuit temperatures as low as -88oC can be realized.
So the required evaporating temperature below -80 °C can be achieved by cascade refrigeration system.
Present work deals with thermodynamic analysis of cascade refrigeration system using ozone friendly hydrocarbon refrigerants Iso-butane (R-600a), Propane(R-290) & Ethane (R-170). Iso-butane (R-600a), Propane (R-290) & Ethane (R-170) are the natural refrigerants. These are hydrocarbons. These refrigerants are used as replacement to CFC refrigerant in low temperature applications. These refrigerants have zero ozone depletion potential and less global warming potential. Hydrocarbons are flammable but non toxic. System with charge mass sizes of 0.15 kg or less can be installed in any size of room. Since these refrigerants are pure natural gases, there is no problem of temperature glide as it occurs in azeotropic mixture.
This study deals thermodynamically analysis of R-600a, R-290 & R-170, three stage cascade refrigeration system to optimize the operating parameters of the system. The operating parameters include: Condensing, evaporating, sub cooling and superheating temperatures in the high temperature circuit, temperature difference in the cascade heat exchanger, Condensing, evaporating, sub cooling and superheating temperatures in the low & medium temperature circuit.
This article presents a thermodynamic analysis to optimize a cascade refrigeration system to be used for biomedical cold-storage application. It can also be used successfully for rapid freezing and storage of frozen food and liquidification of petroleum vapor. A combination of hydrocarbon refrigerants i.e. Isobutene, Propane and Ethane–(R600a, R290 & R170) cascade system has been promoted as a prospective alternative solution to the use of HFC refrigerants.
27
KUMAR, RAHUL. « EXERGY & ; ENERGY ANALYSIS OF THREE STAGE CASCADE REFRIGERATION SYSTEM FOR BIOMEDICAL APPLICATION USING NATURAL REFRIGERANTS ». Thesis, 2013. http://dspace.dtu.ac.in:8080/jspui/handle/repository/14204.
Texte intégralRésumé :
Biomedical preservation requires the temperature for the storage of stem cell, blood, sperm & organs at a storage temperature of below -80°C.We can achieve effectively cooling of about -35°C with the help of simple vapour compression refrigeration system. With the help of compound vapour compression refrigeration system, temperature up to – 50 °C is achievable.
The cascade refrigeration system is widely used where low temperatures are needed. The natural refrigerant CO2 makes it possible to achieve temperatures as low as -54°C in the low temperature stage. In this case propene is the refrigerant for the upper cascade stage.Using other refrigerants (e.g. ethane) in low temperature circuit temperatures as low as -88oC can be realized.
So the required evaporating temperature below -80 °C can be achieved by cascade refrigeration system.
Present work deals with thermodynamic analysis of cascade refrigeration system using ozone friendly hydrocarbon refrigerants Iso-butane (R-600a), Propane(R-290) & Ethane (R-170). Iso-butane (R-600a), Propane (R-290) & Ethane (R-170) are the natural refrigerants. These are hydrocarbons. These refrigerants are used as replacement to CFC refrigerant in low temperature applications. These refrigerants have zero ozone depletion potential and less global warming potential. Hydrocarbons are flammable but non toxic. System with charge mass sizes of 0.15 kg or less can be installed in any size of room. Since these refrigerants are pure natural gases, there is no problem of temperature glide as it occurs in azeotropic mixture.
This study deals thermodynamically analysis of R-600a, R-290 & R-170, three stage cascade refrigeration system to optimize the operating parameters of the system. The operating parameters include: Condensing, evaporating, sub cooling and superheating temperatures in the high temperature circuit, temperature difference in the cascade heat exchanger, Condensing, evaporating, sub cooling and superheating temperatures in the low & medium temperature circuit.
This article presents a thermodynamic analysis to optimize a cascade refrigeration system to be used for biomedical cold-storage application. It can also be used successfully for rapid freezing and storage of frozen food and liquidification of petroleum vapor. A combination of hydrocarbon refrigerants i.e. Isobutene, Propane and Ethane–(R600a, R290 & R170) cascade system has been promoted as a prospective alternative solution to the use of HFC refrigerants.
28
Yang, Kai-Chiuan, et 楊凱全. « Design of Fuzzy Temperature Controller with Cascade Refrigerator System ». Thesis, 2009. http://ndltd.ncl.edu.tw/handle/71541170759503129601.
Texte intégralRésumé :
碩士中原大學
機械工程研究所
97
In general, the refrigeration system controls the temperature by turning on or turning off the fixed-frequency compressor, or installing the heating device, but these methods waste too much electricity. The main method of controlling low temperature is using compressor system. Compressor system has a high energy efficiency and large refrigeration capacity in the general environment. However, when the evaporation temperature is lower, the efficiency of refrigeration device will decrease significantly. Therefore, we try to work this compressor system with other devices under the range of ultra-low temperature (-40 ℃ below) to maintain the low temperature. In this study, we design a cascade system which is controlled by fuzzy, and operate the compressor system with Thermoelectric Cooler. We try to economize energy by" inputting different heat energy to change the speed of compressor." On the other hand, we also cool down the surface of the Thermoelectric Cooler by using of the cascade, and reducing the difference temperature of the hot and cold surface substantially. Therefore, it is cold enough to achieve the target output temperature, -40 ℃, in second times. According to the simulation results, the speeds of the compressor are different with operating the cascade refrigeration system at 65 watts, 30 watts and 10 watts respectively, and the power consumption is also reduced with lower load. Finally, the water temperature remains at -40 ℃ stably with our investigation.
29
Gupta, Ankush 1986. « Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration System ». Thesis, 2012. http://hdl.handle.net/1969.1/148111.
Texte intégralRésumé :
The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves.