Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 50-51).

Cost-effective liquefaction of gases at cryogenic temperatures requires a combined approach of designing efficient refrigeration cycles to generate cooling capacity and designing efficient liquefaction processes to utilize that capacity. This dissertation addresses both approaches for improvement of the liquefaction process. Magnetic refrigeration employing the magnetocaloric effect of ferromagnetic materials has been identified as potentially more efficient and cost-effective than conventional refrigeration systems. One magnetic cycle that shows promise for efficiently achieving cooling over large temperature spans is active magnetic regenerative refrigeration (AMRR). In this cycle the magnetic material serves the dual functions of work input and thermal regeneration, however the operation is complex with coupled fluid, thermal, and magnetic phenomena and a clearer understanding of the regenerative operation is required. Models to elucidate the flow characteristics of the regenerative heat exchangers of rotary AMRR and Gifford-McMahon (GM) systems using a commercially available computational fluid dynamics (CFD) software package are described. Theoretical results are presented to qualify and quantify the effect of maldistributed flow within regenerators. Experimental results of an improved regenerator for the GM system based on the CFD flow simulations are presented. Efforts to develop an improved AMRR thermal model using the commercial package are also described. The second approach for the design of efficient liquefiers addresses a drawback of the usual embodiment of the AMRR cycle, namely, the provision of cooling at a single temperature which necessitates that cryogenic designs have multiple stages providing cooling over a range of discrete temperatures for an efficient liquefaction process. Use of multiple stages leads to increased expense and complexity. A simple, inexpensive plumbing change of the flow through the regenerator of a single-stage device can significantly increase the overall liquefaction capacity compared to the usual flow configuration making additional staging unnecessary. This dissertation describes the alternative flow arrangement, known variously as “bypass flow,” “permanent flow,” or “DC flow,” which is suitable for all passive and active regenerative refrigeration cycles used as liquefiers. Theoretical results showing increased liquefaction capacity when bypass flow is employed are given for active magnetic regenerative and Gifford-McMahon systems. Experimental results are presented for a single-stage GM refrigerator modified for bypass flow which demonstrates increased liquefaction capacity. / Graduate

This research paper studies the concept of developing a different type of freezer rather than vapor-compression for Dippin' Dots, a company who sells frozen goods. The freezer in question is a magnetic freezer that works by removing the compressor and bringing in magnetocaloric materials, which provide cooling by being subjected to a magnetic field. Many possibilities for improvements are available from this technology including a safer more environmentally benign fluid, a higher efficiency, and a possible cost savings. A theoretical model was designed and efficiency calculations and a cost analysis were both performed to determine if there were any improvements and if constructing a prototype freezer was feasible. The coefficient of performance of the designed freezer had the theoretical capability of being up to 5 times that of the vapor-compression freezer, but with the pumps found to complete the design this high number fell significantly short. The price to build a prototype was calculated to be around $7,050. After considering the data building a magnetic freezer prototype does not seem feasible. Although this freezer does not seem reasonable, the magnetic refrigerator technology seems applicable for other uses and is capable of developing in the future.

Orientador: Flavio Vasconcelos da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T18:18:51Z (GMT). No. of bitstreams: 1 Pinelli_ThiagoGomes_M.pdf: 3499061 bytes, checksum: 0b7fc1ffa57b990b43362b82cb12bb54 (MD5) Previous issue date: 2008 / Resumo: Nos últimos anos ocorreu um excessivo aumento da demanda elétrica no Brasil devido principalmente a um aumento significativo do consumo industrial e comercial. Sabe-se que os sistemas de refrigeração são grandes consumidores de energia elétrica e este setor sofreu um grande impacto com o racionamento de energia. Além disso, o problema da destruição da camada de ozônio pelos refrigerantes CFC's utilizados nos ciclos frigoríficos proporcionaram uma preocupação adicional quanto os seus efeitos sobre o meio ambiente. Estes dois fatores têm motivado não só o setor produtivo como a comunidade científica a estudar formas de melhorar o desempenho energético dos sistemas de refrigeração. A eficiência energética em equipamentos de refrigeração é cada vez mais importante para indústrias, comércio e residências, devido à magnitude que tais equipamentos representam no consumo de energia elétrica. O processo de melhoria energética em um sistema de refrigeração, inicia-se na fase de projeto, com análise de eficiência exergética de seus componentes e a implementação de controladores nas variáveis do processo. Neste contexto propôs-se, a montagem de um protótipo de resfriamento de líquido completamente automatizado que possibilite a monitoração das variáveis do processo e a análise do consumo de energia elétrica. Os ensaios foram realizados com variações de carga térmica e freqüência do motor em 1800, 1500, 1200 e 900 W e 40, 50, 60 e 70 Hz utilizando condensação à água e condensação a ar. Foram feitas análises dos comportamentos da temperatura de descarga, COP Total, COP Útil e potência consumida. Foram observados, melhores resultados para o sistema com condensação a ar. Observou-se também que para temperaturas de condensação menores, e temperaturas de evaporação maiores, tem-se um aumento no COP total, COP útil e uma redução na temperatura de descarga e no consumo de energia. / Abstract: In the latest years occurred an excessive rise in the electric demand in Brazil due mainly to a significant growth in the commercial and industrial consumption. It is known that cooling systems are big electric energy consumers and that this sector suffered a big impact because of the energy rationing. Besides that the destruction of the ozone layer problems caused by refrigerant fluids (CFC's) created an additional concern ragarding its efects over the environment. Both of these factors have motivated not only the productive sector but also the scientific community to try to develop ways of improving the cooling systems energetic performance. The concern with the energy efficiency in cooling equipments is growing in the industry, commerce and private residence due to the magnitude that these equipments represent in the electric consumption. The procedures to improve the cooling systems in energetic matters are started during the project development, through its components energy efficiency analysis and through the implementation of controllers in the process variables. Within this context it was suggested the assembly of a fully automatic liquid cooling prototype that permit the process variables to be monitored and the electric energy to be analyzed. The condensing temperature, evaporating temperature, discharge temperature, coefficient of performance, (COP), useful coefficient of performance, (useful COP), and power consumption were analyzed. The tests were made using water condenser and air condenser. The compressor frequency was varied from 40 to 70 Hz and the cooling capacity in 1800, 1500, 1200, and 900 W. The best observed results were the ones that used air condensation. It was also noticed that for lower condensing temperatures and higher evaporating temperatures there was a rise in the total COP, useful COP and a reduction in the discharge temperature and in the electrical energy consumption. / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

Bibliography: pages 205-209. / An extensive literature study on the subject of absorption refrigeration has revealed that there is no proven methodology that can be used to design, optimise and size a plant. On the contrary there are numerous methods which analyse the performance of an existing plant from collected data. These methods however, do not provide any means of predicting how the analysed plant would perform if one or more of its working conditions should change. This work provides a complete design for an ammonia-water absorption refrigeration plant. The ranges of the working conditions in the evaporator and condenser are from -5°C to -55°C and from 5°C to 45°C respectively. For any combination of temperatures within these ranges, the temperature of the generator is optimised for maximum performance of the plant. Depending on the refrigeration capacity, the components are sized and designed. The proper design of the various components takes into account both heat and mass transfer correlations, something which has not been considered in the past as a necessary step for absorption refrigeration machines. Literature indicates that there is a vast amount of research into the absorption of gases into liquids and two-phase flows through tubes of various sections. The correlations cited in these studies have been used in designing the absorption column, evaporator and generator. The proposed optimisation method is a novel approach in designing a plant and stems from the fact that the performance of the absorption refrigerator reaches a maximum at a specific generator temperature. For this, optimisation curves have been developed, which for a particular combination of evaporator and cooling environment temperatures, both the optimum generator temperature and the maximum performance of the plant are predicted. The equations used in the computerised simulation procedure are based on the well-established enthalpy-concentration chart for the ammonia-water mixtures. Thus the properties of the mixture at various points in the plant are accurately predicted. Published computerised procedures in the past have been proven inaccurate in predicting the properties of the mixtures at near pure-ammonia concentrations. The validity of the simulation model is verified by tests performed on a laboratory size absorption plant. The plant was built from design parameters predicted by the simulation model for a refrigeration capacity of 1 kW at -l5°C evaporator coil and 25°C condensate temperatures. Thereafter the unit was operated for a range of evaporator conditions while the generator temperature was varied.

In this master thesis project, conventional supermarket refrigeration systems using R404A are compared with refrigeration system solutions using natural refrigerants such as carbon dioxide and ammonia. This systems analysis considers the behavior of those systems in floating condensing and heat recovery mode. System heating and cooling COP have been calculated by using computer simulation with the calculation software EES (Engineering Equation Solver). The impact of important parameters such as sub-cooling, external superheating and compressor discharge was also determined through the computer models.The estimation of the system annual energy consumptions shows that systems using natural refrigerant can compete with systems using artificial refrigerant by using heat recovery system such as heat pump cascade, heat pump cascade for sub-cooling, fixed pressure system and de-superheater. If the indirect emission of systems using natural refrigerant and artificial refrigerant is approximately similar, the direct emission for carbon dioxide systems and ammonia systems can be estimated to be 10000 times less important than R404A systems.Multi-unit refrigeration systems have also been studied in this project; it appears that in theory COP improvement of 10% is possible if the condensing temperature of each unit is controlled adequatelly. / B

Indiana University-Purdue University Indianapolis (IUPUI) / Optical refrigeration in quantum dots was carried out in this research. Zinc-blende crystalline CdSe/CdS (core/shell structure) QDs with complete surface passivation were synthesized and been used as the cooling substance. Phonon-assisted up-conversion photoluminescence driven by sub-band gap laser excitation was utilized as the cooling mechanism in the QD samples. A net cooling efficiency was predicted by a semi-empirical model developed during the research, within a range of the laser excitation energy, even after taking into account possible parasitic heating processes. To observe the cooling effect, the experiment was carried out in a thermally isolated environment, which temperature was also monitored. By using an optical thermometry technique developed for this research, a maximum temperature drop around 0.68 K was observed in the experiment. This development paves the way to use QDs' cooling in new industrial and fundamental research approaches.

No description available.

Magnetic refrigeration is an alternative cooling technology to vapour compression. Due to the large operating space of magnetic refrigeration devices, modelling is critical to predict results, optimize device parameters and regenerator design, and understand the physics of the system. Modeling requires accurate material data including specific heat, magnetization and adiabatic temperature change, . For a reversible material can be attained directly from measurement or indirectly through calculation from specific heat and magnetization data. Data sets of nine MnFeP1-xAsx alloys are used to compare calculated against measured . MnFeP1-xAsx is a promising first order material because of a tunable transition temperature, low material cost and large magnetocaloric properties. Because MnFeP1-xAsx alloys exhibit thermal hysteresis there are four possible calculation protocols for adiabatic temperature change; , , and . deviates the most from measured data and therefore it is assumed that this case is not representative of the material behavior. Results show and align with measured data as well as . The three protocols that align best with measured data have two consistent errors including a colder peak and a larger . With more data sets and analysis a preferred calculation protocol may be found. / Graduate

Ammonia refrigeration systems are widely used in industry. Demand of these systems is expected to increase due to the advantages of ammonia as refrigerant and because ammonia is considered a green refrigerant. Therefore, it is important to evaluate the risks in existing and future ammonia refrigeration systems to ensure their safety. LOPA (Layer of Protection Analysis) is one of the best ways to estimate the risk. It provides quantified risk results with less effort and time than other methods. LOPA analyses one cause-consequence scenario per time. It requires failure data and PFD (Probability of Failure on Demand) of the independent protection layers available to prevent the scenario. Complete application of LOPA requires the estimation of the severity of the consequences and the mitigated frequency of the initiating event for risk calculations. Especially in existing ammonia refrigeration systems, information to develop LOPA is sometimes scarce and uncertain. In these cases, the analysis relies on expert opinion to determine the values of the variables required for risk estimation. Fuzzy Logic has demonstrated to be useful in this situation allowing the construction of expert systems. Based on fuzzy logic, the LOPA method was adapted to represent the knowledge available in standards and good industry practices for ammonia refrigeration. Fuzzy inference systems were developed for severity and risk calculation. Severity fuzzy inference system uses the number of life threatening injuries or deaths, number of injuries and type of medical attention required to calculate the severity risk index. Frequency of the mitigated scenario is calculated using generic data for the initiating event frequency and PFD of the independent protection layers. Finally, the risk fuzzy inference system uses the frequency and severity values obtained to determine the risk of the scenario. The methodology was applied to four scenarios. Risk indexes were calculated and compared with the traditional approach and risk decisions were made. In conclusion, the fuzzy logic LOPA method provides good approximations of the risk for ammonia refrigeration systems. The technique can be useful for risk assessment of existing ammonia refrigeration systems.