Thesis PlanB (M.S.)--University of Wisconsin--Stout, 2008. / Includes bibliographical references.

Orientador: Jose Vicente Hallak d'Angelo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-15T03:30:00Z (GMT). No. of bitstreams: 1 Lobosco_RaquelJahara_M.pdf: 1406343 bytes, checksum: 34dc2d91be7e56471efaccf2dae92582 (MD5) Previous issue date: 2009 / Resumo: Este trabalho apresenta a proposta de uma função para avaliação do desempenho de ciclos de refrigeração, do ponto de vista termodinâmico e ambiental, através da análise estatística dos resultados da simulação computacional de um ciclo de refrigeração por compressão a vapor. A função proposta representa um índice global de avaliação da eficiência termodinâmica e dos critérios ambientais e foi desenvolvida com o intuito de facilitar a combinação de critérios utilizados na avaliação de ciclos termodinâmicos e envolve a análise exergética do ciclo, valores do COP (coefficient of performance), do ODP (ozone depletion potencial) e do GWP (Global Warming Potential). Para a simulação computacional foi utilizado o software Hysys versão 3.2 da Aspen Technology. As simulações permitiram testar diferentes combinações de misturas de refrigerantes. As equações de estado de Peng-Robinson e Peng-Robison Stryjek-Vera (PRSV) foram comparados entretanto a equação de estado Peng-Robinson foi utilizada neste trabalho para estimar as propriedades termodinâmicas. Foram consideradas neste trabalho duas eficiências do compressor, 55% e 75%. Nas simulações foram avaliados diversos refrigerantes puros (R134a, R290, R152a e R600a) e misturas binárias dos mesmos em três proporções mássicas: 75%, 50% e 25%. O desempenho do ciclo termodinâmico foi avaliado com uma variação de 10% e 20% das pressões da região de alta pressão e de baixa pressão e através dessa avaliação foi possível sugerir nova faixa de atuação das pressões visando uma otimização do ciclo. Através do índice da função de desempenho foi possível determinar que o R600a e suas misturas são os refrigerantes mais adequados para o ciclo proposto / Abstract: This work presents a proposal function to vapor compression refrigerator cycle performance from environmental and thermodynamic point of view. The function was developed through the statistic analysis of a refrigerator cycle computational results. The proposal function represents an evaluation indice of efficiency and environment criterions and was developed to make the analysis of combining criterions evaluations easier in thermodynamics cycles. It includes an exergetic analysis, COP (Coefficient of Performance), ODP (Ozone Depletion Potencial) and GWP (Global Warming Potential). Software Hysys version 3.2 from Aspen Technology was used for computational simulation development. The simulations allowed testing several combinations of refrigerants. The thermodynamic packages Peng-Robison and Peng-Robison Stryjek and Vera was compared however Peng-Robinson equation of state, was used to estimate thermodynamic properties of proposed cycle in this work. Two different efficiencies for the compressor were considered, 55% and 75%. The mixtures of refrigerants tested were pair's combinations of: R134a, R290, R152a and R600a. The variation of these mixtures was in the following proportions: 75, 50 e 25% and it was compared with the own refrigerant. In order to evaluate the performance of refrigerant mixtures, the pressure of high pressure region and low pressure region suffered a change of 10%. With this analysis was possible to suggest a new pressure range for cycle optimization. Considering the values of performance function, it was possible to conclude that R600a and its mixtures are the most indicated ones to be used in the proposed cycle / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

This thesis is based on eight articles all related to the characteristics of the cooling system and plate evaporator of a household refrigerator. Through these articles, knowledge is provided that can be used to increase the operational efficiency in household refrigeration. Papers A, B and C focus on heat transfer and pressure drop in a commonly used free convection evaporator – the plate evaporator. Applicable correlations are suggested on how to estimate the air side heat transfer, the refrigerant side pressure drop and the refrigerant side heat transfer. Papers D, E and F hold a unique experimental study of the refrigerant charge distribution in the cooling system at transient and steady state conditions. From this cyclic losses are identified and estimated and ways to overcome them are suggested. In paper G the topic “charging and throttling” is investigated in an unparalleled experimental study based on more than 600 data points at different quantities of charge and expansions device capacities. It results in recommendations on how to optimize the capillary tube length and the quantity of refrigerant charge. Finally, Paper H holds a thermographic study of the overall cooling system operating at transient conditions. Overall, a potential to lower the energy use by as much as 25 % was identified in the refrigerator studied. About 10 % was found on the evaporator’s air side. 1-2 % was identified as losses related to the edge effect of the evaporator plate. About 8 % was estimated to be cyclic losses. About 5 % was found in cycle length optimization.  It is believed that most of these findings are of general interest for the whole field of household refrigeration even though the results come from one type of refrigerator. Suggestions of simple means to reduce the losses without increasing the unit price are provided within the thesis / <p>QC 20120411</p>

The newly discovered iron based superconductors have captivated the attention of the scientific community due to the unusual mechanism behind their superconductivity and their promise as the next generation high temperature superconductors. After a century of superconductor research, the physical mechanism behind high temperature superconductivity is still not understood. These new materials bring renewed hope in elucidating the pairing mechanism responsible with high temperature superconductors and achieving the ultimate goal of the field, room temperature superconductivity. Consequently, a deeper understanding of the intriguing properties of iron based materials is essential. A great deal about the pairing mechanism of Cooper electron pairs can be inferred from the symmetry of their pairing wave function or order parameter. One of the most involved probes for studying the pairing symmetry is the London penetration depth. The low temperature behavior of London penetration depth in superconductors is directly related to the density of states and provides a powerful tool for investigating low-lying quasiparticle energy and, for this very reason, can give valuable hints on superconducting gap symmetry. The work presented focuses on investigating the pairing symmetry in the Fe1+y(Te1−xSex) system using a radio-frequency tunnel diode oscillator (TDO) technique for precise measurements of the temperature dependence of their in-plane penetration depth. The TDO technique, based on an original concept involving the use of planar inductors in an novel configuration, was implemented on a dilution refrigerator to investigate a significant number of single crystal samples, with nominal Se concentrations of 36%, 40%, 43% and 45% respectively, down to temperatures as low as 50 mK. A systematic study together with a comprehensive analysis regarding the order parameter symmetry in the Fe1+y(Te1−xSex) system is presented. In many cases we found that London penetration depth shows an upturn below at low temperatures, indicative of a paramagnetic-type contribution. Also the low-temperature behavior of penetration depth is best described by a quadratic power law with no systematic dependence on the Se concentration. Most importantly, in the limit of T → 0, in some samples we observed a narrow region of linear temperature dependence, suggestive of nodes in the superconducting gap of Fe1+y(Te1−xSex).

The United States Environmental Protection Agency has used environmental information provision as a policy tool to take advantage of consumer preferences for products that meet higher environmental standards. Such environmental programs include a variety of policies ranging from eco-labeling programs to voluntary environmental agreements between governments and manufacturers. This study analyzes the effects of two such programs - the ENERGY STAR program, an eco-labeling program, and the Climate Leaders program, a voluntary environmental agreement program - on consumer preferences for a household appliance. The study estimates consumer willingness to pay (WTP) for the two programs and examines factors that motivate WTP. A particular interest for the ENERGY STAR program is in determining how the offer of a mail-in rebate affects these preferences. Data used for this study was collected from an online survey conducted in the United States during March and April, 2009. Conditional and random parameter logit models, with product attributes only and with demographic and other individual characteristics as interaction terms, are used to analyze the data. Findings from this study imply that consumers are willing to pay a premium equivalent to a significant portion of the purchase prices for the products approved by either program. Also, it is found that consumers who are more concerned about environmental issues, such as global climate change, and who have confidence in the effects of collective action, are more likely to engage in the purchase of such environmentally friendly products. These results should help government agencies and manufacturers evaluate the effectiveness of environmental information provision programs.

Performance of a refrigerator can be characterized with its ability to maintain a preset low temperature by spending the least amount of electricity. It is important to understand natural convection inside a refrigerator for optimizing its design for performance. Computational Fluid Dynamics (CFD) together with experiments is a very powerful tool for visualizing flow and temperature fields that are essential for understanding a phenomenon that involves both fluid and heat flow. In this aspect, simulations are performed for compartment and total refrigerator models using the package program Fluent which is based on finite volume method. An experimental study is performed to determine the constant wall temperature boundary conditions for the numerical models. Effect of radiation is also investigated by comparing the numerical study of a different full refrigerator model with a similar one in literature. While evaluating the radiation effect, convection boundary condition is selected by defining overall heat transfer coefficient between the ambient room air at a constant temperature and the inner surfaces of the walls. Based on assumptions, related heat transfer analyses are done using compartment and total refrigerator model analyses. Performing CFD simulations of a refrigerator cabinet for visualizing the flow and temperature fields which is the aim of the study is achieved and some observations that can be useful in design optimization are made.

This study aims to simulate a vapor compression refrigeration cycle, working with either butane (R-600) or isobutane (R-600a). For this purpose a computer program is written to design a household refrigerator, by modeling a steady-state, vapor compression cycle, with user defined input data. Each refrigerator component can be designed separately, as well as parts of a single refrigeration system in the program. In order to determine the refrigerant thermophysical properties at different states, least squares polynomial equations for different properties of R-600 and R-600a have been developed. Computer program is used for refrigeration cycle analysis, variable speed compressor design and calculating coefficient of performance (COP) and irreversibility of the cycle. Sample-preliminary designs have been carried out for different refrigeration loads, room and cold space temperatures with the program, to compare the performance characteristics of the refrigerants. Designs have been performed at different refrigeration loads, room and cold space temperatures. It is observed that for the same conditions R-600 has slightly better performance characteristics than those of R-600a.

This thesis is to study the feasibility of using river water from Gavleån in the cooling system of University of Gävle. The project is proposed by the campus service manager Akademiska Hus AB which intended to replace the current cooling production system with the water cooling system to reduce the electricity cost in cooling production. The river by direct distance is 600 meters from the university, the river water is to be extracted from the river via a pump house, flow through pipeline buried underground and delivered to the equipment house of Akademiska Hus.   Most water source cooling prefer water body with decent depth which contain low temperature water to use as free cooling source, but the issue that limits the practice is, the decent depth is not a very common feature of most water body near or within urban area. Like Gavleån which has an average depth of not over five meters while the sufficient depth is over 50 meters for the least or 70 meters to 100 meters often. So study the potential of using rather high temperature water from shallow water body can be of high interest for most cooling consumers.   The thesis progressed through the work in five parts. To introduce cooling in general starting with literature review, the concept, the mechanism, the device for end use and production, the demand of cooling and the reason behind it. Followed by case studies of water source cooling projects worldwide, which is mostly deep water source cooling, and another case of the local hospital cooling system that extract water from Gavleån, demonstrate the use of shallow water body in assisting cooling production, it gives some insights how the potential if similar system is to be implemented in the campus, which is mounted on the same river. Several tours to the hospital were taken to acquire data and understanding of the system.   Then the water temperature measurement from Gavleån in 2014 summer is presented. The measurement was carried out at a small dock by the river side during July to September of 2014. The measurements show the temperature of river water has been increasing which limits free cooling throughout the year, additional refrigerator is required to produce chilled water. The river water, in the hot seasons is used as cooler for the refrigerator and in cold season can be used for free cooling directly. Simulation of IDA-ICE gives the cooling demand of modelled building blocks, the output of cooling production season (consistent with the hot seasons) matches the cooling consumption data from Akademiska Hus by an error of 1% (414743 kWh of simulated result to 415270 kWh in documentation of Akademiska Hus).   To meet the demand of cooling and select more cost-effective refrigerator type, consumption and COP (COP: Coefficient of Performance) are calculated for compressor chiller and absorption chiller with basic cooling cycle for both. The results shown compressor chiller has much better performance but also higher consumption in electricity, while absorption chiller has rather low COP value in comparison but the need of energy input is much less given by its major consumption of energy is heat from hot water, already a purchased item by the university from district heating network. Cost-effectiveness wise speaking absorption chiller is a more optional choice. Reasonable values of assumption are largely employed in the calculation to select the better candidate and bring certain errors, which is then exam in sensitivity analysis to weigh the alternative parameter and the outcome from it.   The last part is to estimate the cost of chillers and pipeline, for the concern of minimizing errors due to uncertainty the operation cost, labor cost and future energy price are not included. As the calculation turns out the payback year of the new system can range from 7 to 12 years by different refrigerator setup and pipeline routine design, which is considered within the life time of the chiller and pipeline, also lower than the current cooling cost of the university and therefore concluded as promising investment.   Discussion and conclusion exam and finalize the whole thesis work. For the uncertainties of the calculation, the lack of information and data, which are improvements, can be done in future work. Also the improvements in other perspectives noted in terms of better load management for the cooling production units so the cost of equipment can be reduced, changes in building attachment and cooling device to reduce the demand of cooling, etc. But mostly draw the conclusion that with proper system configuration shallow water body can be helpful in reducing cooling consumption, and be a promising option for cities that have access to such water body.

Cette thèse concerne le développement de nouvelles stratégies de contrôle d’unréfrigérateur cryogénique soumis à de fortes variations de charge thermique. De telles perturbationsvont se rencontrer lors du refroidissement des aimants supraconducteurs des futurs réacteurs defusion (tokamak JT-60SA par exemple).La modélisation d’un réfrigérateur de test, offrant une capacité de refroidissement de 800Wà 4.5K, a été effectuée sous le logiciel Matlab/Simulink. Celle-ci est basée sur les équationsthéoriques de la thermodynamique, de la thermique et de l’hydraulique et prend en compte lespropriétés non linéaire de l’hélium à basse température.A partir de ce modèle, une stratégie de contrôle multivariable a été proposée sur les deuxparties du réfrigérateur : la station de compression et la boîte froide. Les résultats expérimentauxmontrent de nettes améliorations et une plus grande stabilité du réfrigérateur en présence decharges pulsées par rapport à la stratégie initiale (PI).Un observateur de la charge thermique du bain d’hélium liquide a également été développé.Le modèle utilisé est construit par identification à partir de mesures internes au réfrigérateur. Ilpourrait servir comme outil de surveillance aux opérateurs. / This thesis is concerned with the development of a novel control scheme on a heliumrefrigerator subject to high pulsed loads. Such disturbance will happen during the cooling of thesuperconductive magnet, used in tokamak configuration.A dynamical model of a cryogenic station, which offers a cooling capacity of 800W at4.5K, has been produced. The modelling is based on the theoretical equations of thermodynamics,thermal physics and hydraulics and takes into account the non linear properties of helium at lowtemperature.Based on this model, a new control strategy has been developed for each of the two parts ofthe refrigerator: the warm compression system and the cold box. Experimental results showsignificant improvement with multivariable controllers as compared with the PIDs in the presenceof high pulsed loads.An observer of the thermal load of the helium bath has also been developed. The model isconstructed by identification using internal measures of the refrigerator. It can be used as conditionmonitoring tool for operators.

Nowadays, many electrical appliances are used daily. The refrigerator is one of them. Consequently, by affecting the energy used by the refrigerator, a huge amount of energy, greenhouse gases (GHG) emissions and money can be saved. It is what this thesis tries to do by applying a concept: using the cold from outside. Indeed, this report exposes the process to answer the following question: How much energy, GHG emissions and money can be saved by using the cold from outside on the refrigerating appliances? To do so, measurements have been done on a refrigerator placed in a climate chamber. The experiment procedure is inspired by the Swedish standard of energy consumption testing in order to have the most relevant results as possible. The results of the measures were then used to create a mathematical modelling. And finally, by applying the modelling at different climate of the world represented by chosen cities, calculations were made to estimate the energy, GHG emissions and money savings which can be done thanks to this concept.