Dissertations / Theses on the topic 'Refrigeratori domestici'

2014 - 2015
The present experimental work was born from the need to expand the knowledge on the new type of refrigerant fluids, the HFO, representing the fourth generation of fluorinated refrigerants, born in response to the directives before the Kyoto Protocol and subsequently with the entry into force of the new Regulation in the European field (F-gas Regulation) requiring the reduction of greenhouse gases, including HFCs are also included. The on HFO-based technology offers interesting promises as regards energy efficiency and environmental impact. The primary characteristic of the HFO is the global warming potential (GWP) extremely low. In spite of other fluids, comparable yields of 'R134a are obtainable without significant modifications of' hardware plant, as some of the main thermodynamic properties (boiling point, critical point, the vapor density of the liquid and density) of HFO are very similar to those of R134a. In fact, the knowledge of the chemical-physical properties of a fluid refrigerant is of fundamental importance to be able to properly size the mechanical components used in the reverse cycle of the vapor compression. This allows you to assess whether or not to introduce new fluids on existing plants, and how they might be amended if necessary to make the drop-in. For both fluids and even after the two mixtures were made tests according to UNI ISO 15502 using an experimental system a refrigerating machine samsung RT 59QBPN, energy class A + two compartments, one from 342 liters for fresh food, and that for frozen from 131 l. Three types of tests are identified: pull-down, the endurance tests twenty-four hours at -18 ° C and -26 ° C. At first we have to check the performance of the 'system with R134a .All data were acquired using LabView and analyzed using a MatLab program. Once extracted the main thermodynamic properties of the cycle and performances relating to 'R134a, it was made the drop-in with the then R1234ze with R1234yf, and finally were tested mixtures. Though . performance of 'R1234yf are very similar to those of R134a performance parameters of' HFO1234ze slightly exceed those the traditional R134a, also diminish both the TEWI that 'LCCP, which is why you might think as a valid candidate for a next use in domestic refrigeration systems. Even better the performance following the drop-in first goes to a R134a HFOyf-mixture and subsequently with the R134a-HFOze. In summary, they have obtained for the first mixture a decrease in consumption (≈16%) of TEWI (≈16.5%) and LCCP (≈16%). It remains to evaluate the performance in other types of applications. [edited by author]
XIV n.s.

My dissertation emerges from a curiosity about the mundane objects and machines with which we live and it pauses in Britain’s kitchens to ask what we might learn from looking in the fridge. Considered by many to be a rather ordinary and unremarkable appliance, the refrigerator forms a virtually ubiquitous backdrop to routine activities of feeding, provisioning and storing, but rarely is it brought into explicit focus. This study traces the ‘career’ of the mechanical refrigerator and is based upon interviews and archival work in Britain. I unravel intersecting histories and geographies of cooling, discuss a global trade in ice, explore changing understanding of the nature of heat and cold and show how varied ideas and technologies contributed to achieving the creation of artificial cold. The means by which these techniques were translated into the home is central to my discussion and I show how the domestication of refrigeration also played a role in the reconfiguration of associated practices, such as freezing, shopping and eating. I consider the process of normalisation through which refrigerators shifted category from novel products to essential appliances and argue that in many ways the refrigerator has now become integral to the constitution of domestic space. My research follows the lifecourse of the refrigerator and its journeys through multiple sites and spaces, enabling me to analyse diverse refrigerator knowledges and practices from repair shops and recycling facilities to scrap yards and museums, in addition to the home. Although using a refrigerator is frequently dismissed as something ‘self-evident’ or ‘obvious,’ I argue that fridge practices are not innate but learned. I explore ways in which these knowledges travel and pay particular attention to the translation of scientific and technical knowledges into domestic contexts. The ‘reach’ of the domestic refrigerator is considerable and I use one of the more notorious moments in its career, when refrigerators were implicated in global climate change, as a way to show how day to day activities like chilling milk and lettuce can have far-reaching effects at a range of scales.

A growing global environmental awareness and the rising costs of energy are driving demand for the development of sustainable cooling technologies. Most governments worldwide have implemented minimum energy performance standards for household refrigerators and innovative new solutions are required to improve the efficiency of these appliances. This thesis investigated the design and operation of a thermal storage refrigerator. The aim was to improve the refrigerator energetic efficiency, temperature stability and extend its offcycle. The research demonstrated that larger displacement compressors are more efficient. The proposed method to exploit the superior performance of large compressors is to accumulate their high cooling capacity in a phase change material (PCM). The combination of thin phase change material with a large displacement compressor is a novel design approach with the potential to enhance the refrigerator efficiency. Theoretical modelling and experimental validation were undertaken to determine the phase change material charge and discharge rate and the corresponding refrigerator on and off cycle durations. The integration of a 5 mm PCM slab into the refrigerator allowed 3 to 5 hours of continuous operation without power supply (compared to 9 minutes without PCM) depending on the ambient temperature. A computational fluid dynamics (CFD) model was used to predict the airflow and temperature distribution within the thermal storage refrigerator. Several design options were investigated by simulation to identify the most effective PCM configuration (horizontal or vertical), the phase change temperature and the design for the refrigerator i.e. conventional door type or top opening drawer appliance. The CFD was used to select the best design options for developing a novel thermal storage refrigerator. A horizontal PCM configuration was found to be more efficient than a vertical PCM. The temperature distribution with a horizontal PCM was tested experimentally and the results were shown to be in close agreement with the CFD predictions. Both the simulation and the experimental results suggested that a eutectic with a phase change temperature below 0°C needs to be employed to maintain the compartment temperature within acceptable limits.

Orientador: Vivaldo Silveira Junior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: Os equipamentos utilizados para refrigeração e condicionamento ambiental têm um potencial significativo de redução de consumo energético, principalmente porque esta pratica utilizam quantidades significativas de energia e são encontrados em todas as residências e indústrias. Neste contexto existem numerosos estudos dirigidos para aumentar a eficiência energética dos sistemas de refrigeração domésticos, utilizando diferentes estratégias tecnológicas. O dispositivo proposto neste trabalho atua como um condensador evaporativo, substituindo o ar,, como meio de troca térmica convencional dos sistemas de refrigeração domésticos, por uma corrente vertical de água em contato com a superfície do condensador, aproveitando desta maneira o calor absorvido pela água na mudança de fase (efeito evaporativo) e diminuindo a temperatura de condensação. O protótipo foi desenvolvido, considerando o principio de funcionamento dos condensadores evaporativos industriais e adaptado numa escala menor, para que possa ser facilmente montado na estrutura de um refrigerador doméstico convencional. Com as mudanças nas condições de condensação, especificamente a temperatura, procura-se aumentar o COP (coeficiente de desempenho) que é um indicador da eficiência do sistema, dado que nessas condições de funcionamento, o efeito frigorífico torna-se maior e o trabalho do compressor torna-se menor durante o ciclo. Estas condições de funcionamento, assim como o consumo de energia elétrica, foram monitorados e comparados com os sistemas de refrigeração convencional, utilizando uma câmara especialmente condicionada para esse propósito. Assim, o desempenho do sistema com as novas condições de condensação, promovidas pelo dispositivo, teve uma maior eficiência global com um COP maior em 24% e, em consequência, um aumento da eficiência energética do sistema, com uma redução de 17% de energia em ensaios padronizados conforme norma ABNT 12888
Abstract: Los equipos utilizados para refrigeración y condicionamiento ambiental tienen gran potencial de reducción de consumo energético, principalmente porque estos aparatos utilizan cantidades significativas de energía y son encontrados en la mayoría de residencias y en las industrias. Existen numerosos estudios dedicados a aumentar la eficiencia energética de los sistemas de refrigeración domésticos utilizando diferentes estrategias tecnológicas. El dispositivo propuesto en este trabajo actuara como un condensador evaporativo, substituyendo el aire, como medio de intercambio de calor convencional de los sistemas de refrigeración domésticos, por una corriente vertical de agua en contacto con la superficie del condensador, aprovechando de esta forma el calor absorbido por el agua durante el cambio de estado (efecto evaporativo) y disminuyendo la temperatura de condensación. Este prototipo fue desarrollado considerando el principio de funcionamiento de los condensadores evaporativos industriales y fue adaptado a una escala menor, para que pueda ser fácilmente instalado en la estructura de un refrigerador domestico convencional. Con las modificaciones en las condiciones de condensación específicamente, la temperatura, se procura aumentar el COP (coeficiente de desempeño), que es un indicador de la eficiencia del sistema, en vista que en estas condiciones de funcionamiento, el efecto frigorífico se torna mayor y el compresor trabaja menos durante el ciclo. Estas condiciones de funcionamiento, así como el consumo de energía eléctrica son monitoreados e comparados con los sistemas de refrigeración convencional, utilizando una cámara especialmente condicionada para este propósito. De esta manera el desempeño del sistema con las nuevas condiciones de condensación, promovidas por el dispositivo en estudio, tuvo una mayor eficiencia global con un COP superior en 24%, y como consecuencia un aumento de la eficiencia energética del sistema, con una reducción del consumo de energía en 17% durante ensayos homogenizados según la norma Brasileña ABNT 12888
Mestrado
Mestre em Engenharia de Alimentos

Sustainable development is one of the major challenges that humanity faces today. The rational use of energy resources and the increase of systems efficiency seems to be an important task for all contexts of modern life, from industry to transport and household appliances. The interest on this subject is justified not only by the price of energy, which can potentially increase, but also by the need to reduce emissions of gases, which are thought to be responsible for global warming. This work wants to present innovative solutions for the energy efficiency improvement of household heat pump systems, with particular reference to heat pump dryers, domestic refrigerators and tap water heat pumps. Since clothes drying is a very energy-intensive process, in recent years much attention has been paid to the development of energy efficient dryers. The heat pump has been recognised as a very attractive technology for this application. Actual interest is focused on finding good alternatives to halocarbon refrigerants. Because it’s safe for domestic rooms, carbon dioxide is regarded as a possible substitute for the traditional synthetic compounds. In this research work, the CO2 transcritical cycle is compared with the traditional R134a subcritical cycle. The comparison is carried out with a theoretical analysis and experimental tests, returning a positive assessment for CO2 as working fluid. Tap water heat pumps are considered a privileged application for the employment of CO2 as refrigerant. This work presents an innovative upper cycle pressure control logic to face the optimisation problem, and also reports an experimental investigation of CO2 heat pump prototype, using a double wall plate heat exchanger gas cooler. This solution was studied as a possibility to reduce the risk of tap water contamination with lubricant oil. Here some innovative solutions for the energy efficiency improvements of household refrigerators are presented. An experimental study was carried out on a under-counter refrigerator to analyse the effect of the operating cycling frequency on the electric consumptions. The experimental results show a reduction in energy consumption when the frequency of the compressor start-up increases. To better understand these issues it was developed a dynamic simulation model for evaporators, based on the “moving boundary” scheme. Temporal integration of core variables makes the mean void fraction to be time-variant. The use of this kind of variables improves the model accuracy and speed, with respect to boundary variables, when the compressor start-up is simulated. This choice was considered suitable to simulate household refrigerators, which typically work with continuous on/off cycles. Finally it’s presented an innovative solution for the energy efficiency improvement of total no-frost combi refrigerators. In these systems the fresh food compartment is cooled by air streams coming from the freezer. Therefore, the refrigeration unit produces the cooling effect at a temperature which is suitable for the freezer, but considerably colder than what is needed for the fridge. Consequently the system works with the thermodynamic disadvantage of supplying the cooling power at the lowest level of temperature. It was studied a combined household refrigerator (fridge/freezer), which works with a single refrigeration unit, but with two different air-loops. The unit consists of a single evaporator, which is employed to cool both the compartments. The air flow, involving the heat exchanger, comes alternately from the fridge or from the freezer. In this way the system works at two different evaporating temperatures, improving the thermodynamic efficiency when the fresh food compartment requires the cooling supply.
Lo sviluppo sostenibile rappresenta una delle più importanti sfide che oggi l’umanità deve affrontare. L’uso razionale delle risorse energetiche e l’aumento dell’efficienza dei sistemi che le utilizzano, è un importante obiettivo per tutti i contesti della vita moderna, dal settore industriale, ai trasporti, agli elettrodomestici di uso quotidiano. L’interesse verso questo tema è giustificato, non solo dal prezzo dell’energia in potenziale aumento, ma anche dalla necessità di ridurre le emissioni dei gas che sono ritenuti responsabili del riscaldamento globale. Questo lavoro si inquadra nello studio di soluzioni tecnologiche innovative volte al miglioramento dell’efficienza energetica di apparecchiature domestiche, più precisamente macchine che operano con un ciclo inverso a compressione di vapore. In particolare verrà fatto riferimento ad asciugabiancheria a pompa di calore, refrigeratori domestici e pompe di calore per il riscaldamento di acqua calda sanitaria. Come è noto, le asciugatrici domestiche realizzano un processo termodinamico che richiede un elevato dispendio energetico. Per questo motivo negli ultimi anni si è dato molto spazio alla ricerca di soluzioni che ne possano ridurre i consumi elettrici, trovando nella tecnologia della pompa di calore una significativa possibilità di miglioramento. Oggi l’attenzione è rivolta a incrementarne ulteriormente l’efficienza energetica e a trovare dei sostituiti ai tradizionali fluidi refrigeranti alogenati per ridurne l’impatto sull’ambiente. Poiché non è né tossica né infiammabile, l’anidride carbonica è perfettamente compatibile con gli ambienti domestici, ed è vista come un possibile sostituto dei composti sintetici. In questo lavoro il ciclo transcritico ad anidride carbonica viene messo a confronto, sia su base teorica che sperimentale, con il ciclo subcritico a R134a. I risultati di questa indagine mostrano buone prospettive per l’impiego della CO2 in questa applicazione. Nella sezione successiva verranno approfonditi aspetti teorici e tecnologici delle pompe di calore dedicate al riscaldamento di acqua calda sanitaria, applicazione in cui il ciclo transcritico ad anidride carbonica risulta essere molto efficace. L’analisi prevede lo studio di logiche di controllo di tipo adattativo per l’ottimizzazione della pressione superiore di ciclo. Sarà inoltre presentato uno studio sperimentale di macchine operanti con gas-cooler a piastre a doppia parete, impiegato per ridurre il rischio di contaminazione del circuito idraulico. Verranno poi approfondite alcune tematiche legate al miglioramento dell’efficienza energetica dei refrigeratori domestici. Si riportano i risultati di un’indagine sperimentale condotta su un frigorifero domestico di tipo “sottotavolo”, i cui consumi elettrici sono stati monitorati al variare della frequenza ciclica di accensione del compressore. Per questa apparecchiatura è stata registrata una significativa riduzione dei consumi ad elevati frequenze. Per approfondire ulteriormente questi temi, mediante simulazione numerica, è stato sviluppato un modello per evaporatori in regime di funzionamento dinamico, seguendo uno schema di tipo “moving boundary”. Un’opportuna scelta delle variabili di stato (nello specifico, variabili corrispondenti a proprietà medie e non a grandezze di confine del modello) ha permesso di tenere conto delle variazioni nel tempo del grado di vuoto medio della zona bifase e di conseguire una maggiore velocità di simulazione dei transitori di avviamento del compressore. Questo modello è stato quindi sviluppato appositamente per la simulazione di refrigeratori domestici che operano in regime ciclico di funzionamento. Infine, nell’ottica del miglioramento dell’efficienza dei refrigeratori domestici combinati di tipo total-no-frost, viene presentata una soluzione innovativa per il ciclo termodinamico. In queste apparecchiature il vano dei prodotti freschi viene di solito raffreddato facendo circolare una piccola portata d’aria proveniente dal vano dei prodotti surgelati. Questo tipo di funzionamento è inefficiente, in quanto la potenza frigorifera viene erogata al più basso livello di temperatura. La soluzione studiata prevede, invece, di convogliare alternativamente verso l’evaporatore due flussi d’aria che raffreddano distintamente i due vani refrigerati. Così facendo è possibile differenziare due livelli di temperatura per la produzione della potenza frigorifera, conseguendo un aumento dell’efficienza energetica quando l’unità opera al raffreddamento del vano a temperatura positiva.

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Neste trabalho realizou-se um estudo numérico do escoamento em gabinetes de refrigeradores domésticos operando em regime de convecção natural, usando-se o Método de Volumes Finitos. No procedmento numérico, o problema do acoplamento pressão-velocidade foi resolvido pelo algoritmo SIMPLE - Semi Implicit Method for Pressure Linked Equations para malha desencontrada. O esquema Power-Law foi utilizado como função de interpolação para os termos convectivo-difusivos e o TDMA-Tri Diagonal Matrix Algorithm foi usado para resolver os sistemas de equações algébricas. O gabinete do refrigerador foi modelado como uma cavidade tridimensional vazia sem prateleiras e o evaporador foi modelado como uma placa plana vertical com temperatura uniforme prescrita. O código numérico foi verificado parcialmente para problemas clássicos de convecção natural encontrados na literatura. Resultados experimentais preliminares para um refrigerador doméstico comercial de 350 l também foram levantados para a validação do código numérico. Após a validação do código numérico, as influências do posicionamento e temperatura do evaporador nos campos de temperatura e velocidade foram analisadas para três configurações do gabinete: gabinete sem gaveta de verdura, gabinete com gaveta de verdura e gabinete com gaveta de verdura com aberturas laterais. O modelo de gabinete com gaveta de verdura com aberturas laterais mostrou-se o mais adequado para estudar o problema. Nove posições do evaporador foram avaliadas, mostrando que o posicionamento na direção horizontal praticamente não influencia o campo de temperatura e velocidade do escoamento, enquanto que o posicionamento na direção vertical tem uma influencia significativa. Os campos de velocidade e temperatura e a carga térmica do evaporador...
A numerical study of the flow inside cabinets of domestic refrigerators working on natural convection regime is performed in this work using the Finite Volume Method as numerical procedure for solving the governing equations. The pressure-velocity coupling was solved using the algorithm SIMPLE–Semi Implicit Method for Pressure Linked Equations applied to a staggered mesh. The Power-Law scheme was used as interpolation function for the convective-diffusive terms, and the algorithm TDMA-Tri Diagonal Matrix Algorithm was used to solve the systems of algebraic equations. The model was applied to static refrigerator working in steady state with constant and uniform evaporator temperature. The cabinet was considered as an empty three-dimensional cavity without shelves and the evaporator was modeled as a vertical flat plate with prescribed uniform temperature. The numerical code was partially verified for classical natural convection problems usually found in the literature. Preliminary experimental results for a 350 l commercial domestic refrigerator were also obtained for validating the numerical code. After validating the numerical code, the influence of the positioning and temperature of the evaporator on the temperature and velocity fields were analyzed for three cabinet configurations: cabinet without vegetable drawer, cabinet with vegetable drawer, and cabinet with vegetable drawer presenting lateral openings. The model including the vegetable drawer with lateral openings showed to be the best model to study the problem. Nine evaporator positions were evaluated, showing that the positioning in the horizontal direction practically does not affect the temperature and velocity fields of the flow, while the vertical positioning has a significant effect on the results. The temperature and velocity... (Complete abstract click electronic access below)

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

QC 20120411

Orientador: José Luiz Gasche
Banca: Cassio Roberto Macedo Maia
Banca: Sidnei José de Oliveira
Resumo: Neste trabalho realizou-se um estudo numérico do escoamento em gabinetes de refrigeradores domésticos operando em regime de convecção natural, usando-se o Método de Volumes Finitos. No procedmento numérico, o problema do acoplamento pressão-velocidade foi resolvido pelo algoritmo SIMPLE - Semi Implicit Method for Pressure Linked Equations para malha desencontrada. O esquema Power-Law foi utilizado como função de interpolação para os termos convectivo-difusivos e o TDMA-Tri Diagonal Matrix Algorithm foi usado para resolver os sistemas de equações algébricas. O gabinete do refrigerador foi modelado como uma cavidade tridimensional vazia sem prateleiras e o evaporador foi modelado como uma placa plana vertical com temperatura uniforme prescrita. O código numérico foi verificado parcialmente para problemas clássicos de convecção natural encontrados na literatura. Resultados experimentais preliminares para um refrigerador doméstico comercial de 350 l também foram levantados para a validação do código numérico. Após a validação do código numérico, as influências do posicionamento e temperatura do evaporador nos campos de temperatura e velocidade foram analisadas para três configurações do gabinete: gabinete sem gaveta de verdura, gabinete com gaveta de verdura e gabinete com gaveta de verdura com aberturas laterais. O modelo de gabinete com gaveta de verdura com aberturas laterais mostrou-se o mais adequado para estudar o problema. Nove posições do evaporador foram avaliadas, mostrando que o posicionamento na direção horizontal praticamente não influencia o campo de temperatura e velocidade do escoamento, enquanto que o posicionamento na direção vertical tem uma influencia significativa. Os campos de velocidade e temperatura e a carga térmica do evaporador... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: A numerical study of the flow inside cabinets of domestic refrigerators working on natural convection regime is performed in this work using the Finite Volume Method as numerical procedure for solving the governing equations. The pressure-velocity coupling was solved using the algorithm SIMPLE-Semi Implicit Method for Pressure Linked Equations applied to a staggered mesh. The Power-Law scheme was used as interpolation function for the convective-diffusive terms, and the algorithm TDMA-Tri Diagonal Matrix Algorithm was used to solve the systems of algebraic equations. The model was applied to static refrigerator working in steady state with constant and uniform evaporator temperature. The cabinet was considered as an empty three-dimensional cavity without shelves and the evaporator was modeled as a vertical flat plate with prescribed uniform temperature. The numerical code was partially verified for classical natural convection problems usually found in the literature. Preliminary experimental results for a 350 l commercial domestic refrigerator were also obtained for validating the numerical code. After validating the numerical code, the influence of the positioning and temperature of the evaporator on the temperature and velocity fields were analyzed for three cabinet configurations: cabinet without vegetable drawer, cabinet with vegetable drawer, and cabinet with vegetable drawer presenting lateral openings. The model including the vegetable drawer with lateral openings showed to be the best model to study the problem. Nine evaporator positions were evaluated, showing that the positioning in the horizontal direction practically does not affect the temperature and velocity fields of the flow, while the vertical positioning has a significant effect on the results. The temperature and velocity... (Complete abstract click electronic access below)
Mestre

Orientador: André Luiz Seixlack
Banca: Emanuel Rocha Woiski
Banca: José Roberto Simões Moreira
Resumo: Neste trabalho apresenta-se um modelo numérico para a simulação do escoamento transiente de fluidos refrigerantes ao longo de condensadores do tipo arame-sobre-tubo, comumente usados em refrigeradores domésticos que empregam o ciclo de compressão de vapor. A análise envolve o escoamento do fluido refrigerante no interior do tubo e a transferência de calor por convecção natural e radiação entre a superfície externa do tubo, as aletas em forma de arames cilíndricos e o ar externo. No interior do tubo o escoamento é considerado unidimensional e dividido em uma região monofásica de vapor superaquecido, uma região bifásica líquido-vapor e outra em que o refrigerante encontra-se no estado de líquido subresfriado. A queda de pressão no interior do tubo é também considerada. Na região bifásica o escoamento é considerado homogêneo, ou seja, são consideradas condições de equilíbrio térmico e hidrodinâmico entre as fases. Inicialmente, condições de regime permanente serão assumidas e posteriormente será analisada a resposta dinâmica do condensador às variações das condições de operação do sistema. A simulação do escoamento ao longo do condensador é obtida a partir da solução numérica das equações de conservação da massa, da quantidade de movimento e de conservação de energia. Para a parede do condensador, a equação de conservação de energia é resolvida para determinar a sua distribuição de temperatura. O método de Volumes Finitos é usado na discretização das equações governantes. O modelo permite a determinação, nos regimes permanente e transiente, das distribuições de pressão, título, temperatura do refrigerante e temperatura do tubo ao longo do condensador, em função da geometria do condensador e das condições de operação. O modelo proposto é analisado e os resultados obtidos são discutidos e comparados... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work presents a numerical model to simulate the unsteady refrigerant fluid flow along wire-on-tube condensers, commonly used in vapor compression cycle based domestic refrigerators. The model considers the refrigerant flow inside the tube and the heat transfer from the outer surfaces of the wires and tubes to the surrounding air by free convection and radiation. The refrigerant flow along the condenser is divided into a vapor superheated singlephase region, a two-phase liquid-vapor flow region and a subcooled liquid region. The refrigerant pressure drop is taking into account. The homogeneous model is employed for the two-phase flow region, i.e. the hydrodynamic and thermal equilibrium between the phases are considered. Initially the steady state condition is considered and later condenser unsteady behavior is analyzed. The mass conservation, momentum and energy conservation equations for the refrigerant flow are solved in order to evaluate the distributions of mass flux, pressure and temperature of the refrigerant fluid, respectively. Also, the energy conservation equation for the tube wall is solved to determine the wall temperature distribution. The system of differential equations is solved using the Finite Volume method. The model is analyzed and the obtained results are compared with data available in the open literature.
Mestre

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Neste trabalho apresenta-se um modelo numérico para a simulação do escoamento transiente de fluidos refrigerantes ao longo de condensadores do tipo arame-sobre-tubo, comumente usados em refrigeradores domésticos que empregam o ciclo de compressão de vapor. A análise envolve o escoamento do fluido refrigerante no interior do tubo e a transferência de calor por convecção natural e radiação entre a superfície externa do tubo, as aletas em forma de arames cilíndricos e o ar externo. No interior do tubo o escoamento é considerado unidimensional e dividido em uma região monofásica de vapor superaquecido, uma região bifásica líquido-vapor e outra em que o refrigerante encontra-se no estado de líquido subresfriado. A queda de pressão no interior do tubo é também considerada. Na região bifásica o escoamento é considerado homogêneo, ou seja, são consideradas condições de equilíbrio térmico e hidrodinâmico entre as fases. Inicialmente, condições de regime permanente serão assumidas e posteriormente será analisada a resposta dinâmica do condensador às variações das condições de operação do sistema. A simulação do escoamento ao longo do condensador é obtida a partir da solução numérica das equações de conservação da massa, da quantidade de movimento e de conservação de energia. Para a parede do condensador, a equação de conservação de energia é resolvida para determinar a sua distribuição de temperatura. O método de Volumes Finitos é usado na discretização das equações governantes. O modelo permite a determinação, nos regimes permanente e transiente, das distribuições de pressão, título, temperatura do refrigerante e temperatura do tubo ao longo do condensador, em função da geometria do condensador e das condições de operação. O modelo proposto é analisado e os resultados obtidos são discutidos e comparados...
This work presents a numerical model to simulate the unsteady refrigerant fluid flow along wire-on-tube condensers, commonly used in vapor compression cycle based domestic refrigerators. The model considers the refrigerant flow inside the tube and the heat transfer from the outer surfaces of the wires and tubes to the surrounding air by free convection and radiation. The refrigerant flow along the condenser is divided into a vapor superheated singlephase region, a two-phase liquid-vapor flow region and a subcooled liquid region. The refrigerant pressure drop is taking into account. The homogeneous model is employed for the two-phase flow region, i.e. the hydrodynamic and thermal equilibrium between the phases are considered. Initially the steady state condition is considered and later condenser unsteady behavior is analyzed. The mass conservation, momentum and energy conservation equations for the refrigerant flow are solved in order to evaluate the distributions of mass flux, pressure and temperature of the refrigerant fluid, respectively. Also, the energy conservation equation for the tube wall is solved to determine the wall temperature distribution. The system of differential equations is solved using the Finite Volume method. The model is analyzed and the obtained results are compared with data available in the open literature.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Neste trabalho apresenta-se um modelo distribuído para análise de condensadores do tipo parede aquecida, hot-wall, usados em refrigeradores domésticos. Nesse modelo considera-se o escoamento do fluido refrigerante no interior do tubo do condensador e a transferência de calor entre a placa de revestimento externo do refrigerador e o ar ambiente. No modelo, inclui-se também a transferência de calor ao longo da fita de alumínio, usada para fixação do tubo na placa de revestimento externo e a transferência de calor através do isolamento térmico para o interior do compartimento refrigerado. O escoamento no interior do tubo é considerado unidimensional e dividido em três regiões: região monofásica de vapor superaquecido, região bifásica líquido-vapor e região monofásica de líquido sub-resfriado. O escoamento bifásico é analisado segundo o modelo homogêneo, ou seja, considerando condições de equilíbrio térmico e hidrodinâmico entre as fases. Considera-se também a queda de pressão do escoamento no interior do tubo. A fita de alumínio e a placa de revestimento externo são consideradas como aletas com extremidades adiabáticas. As equações do escoamento do fluido refrigerante: conservação da massa, quantidade de movimento e conservação de energia, são resolvidas por integração numérica e a equação de conservação de energia ao longo da fita de alumínio é resolvida pelo método de Volumes Finitos. O sistema de equações algébricas, decorrente do processo de discretização das equações diferenciais, é solucionado iterativamente por substituições sucessivas, ponto a ponto, ao longo do tubo do condensador e da fita de alumínio. Os resultados obtidos são comparados com dados experimentais disponíveis na literatura. Considerando toda a faixa de vazão em massa do fluido refrigerante analisada, 2,52 – 4,32 kg/h, o desvio absoluto médio entre os resultados calculados e os dados experimentais de capacidade do condensador foi de 1,8 %.
This work presents a distributed model for the analysis of hot-wall condensers used in domestic refrigerators. In this model, the flow of refrigerant inside the condenser tube and the heat transfer between the outer coating plate of the refrigerator and the ambient air are considered. Also included in this model the heat transfer along the aluminum tape used to hold the tube to the outer coating plate and the heat transfer through the thermal insulation into the refrigerated compartment. The flow inside the tube is taken as one-dimensional and divided into three regions: superheated vapor region, two-phase liquid-vapor region and sub-cooled liquid region. The two-phase flow is analyzed according to the homogeneous model, that is, considering conditions of thermal and hydrodynamic equilibrium between the phases. It is also considered the pressure drop of the flow inside the tube. The aluminum tape and the outer coating plate are considered as fins with adiabatic ends. The equations of the refrigerant flow: mass conservation, momentum and energy conservation, are solved by numerical integration and the energy conservation equation along the aluminum tape is solved by the Finite Volume method. The set of algebraic equations, resulting from the discretization process of the differential equations, is solved iteratively by successive iterations, point-to-point along the condenser tube and the aluminum tape. The results obtained are compared with experimental data available in the literature. Considering whole range of refrigerant mass flow rate analyzed, 2.52 - 4.32 kg/h, the mean absolute deviation between the calculated results and the experimental condenser capacity data was 1.8%.

Orientador: André Luiz Seixlack
Resumo: Neste trabalho apresenta-se um modelo distribuído para análise de condensadores do tipo parede aquecida, hot-wall, usados em refrigeradores domésticos. Nesse modelo considera-se o escoamento do fluido refrigerante no interior do tubo do condensador e a transferência de calor entre a placa de revestimento externo do refrigerador e o ar ambiente. No modelo, inclui-se também a transferência de calor ao longo da fita de alumínio, usada para fixação do tubo na placa de revestimento externo e a transferência de calor através do isolamento térmico para o interior do compartimento refrigerado. O escoamento no interior do tubo é considerado unidimensional e dividido em três regiões: região monofásica de vapor superaquecido, região bifásica líquido-vapor e região monofásica de líquido sub-resfriado. O escoamento bifásico é analisado segundo o modelo homogêneo, ou seja, considerando condições de equilíbrio térmico e hidrodinâmico entre as fases. Considera-se também a queda de pressão do escoamento no interior do tubo. A fita de alumínio e a placa de revestimento externo são consideradas como aletas com extremidades adiabáticas. As equações do escoamento do fluido refrigerante: conservação da massa, quantidade de movimento e conservação de energia, são resolvidas por integração numérica e a equação de conservação de energia ao longo da fita de alumínio é resolvida pelo método de Volumes Finitos. O sistema de equações algébricas, decorrente do processo de discretização das equações difere... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work presents a distributed model for the analysis of hot-wall condensers used in domestic refrigerators. In this model, the flow of refrigerant inside the condenser tube and the heat transfer between the outer coating plate of the refrigerator and the ambient air are considered. Also included in this model the heat transfer along the aluminum tape used to hold the tube to the outer coating plate and the heat transfer through the thermal insulation into the refrigerated compartment. The flow inside the tube is taken as one-dimensional and divided into three regions: superheated vapor region, two-phase liquid-vapor region and sub-cooled liquid region. The two-phase flow is analyzed according to the homogeneous model, that is, considering conditions of thermal and hydrodynamic equilibrium between the phases. It is also considered the pressure drop of the flow inside the tube. The aluminum tape and the outer coating plate are considered as fins with adiabatic ends. The equations of the refrigerant flow: mass conservation, momentum and energy conservation, are solved by numerical integration and the energy conservation equation along the aluminum tape is solved by the Finite Volume method. The set of algebraic equations, resulting from the discretization process of the differential equations, is solved iteratively by successive iterations, point-to-point along the condenser tube and the aluminum tape. The results obtained are compared with experimental data available in the ... (Complete abstract click electronic access below)
Mestre

Neste trabalho, apresentamos uma proposta de ensino de Física Térmica contextualizada e integrada à formação técnica para alunos de nível médio do curso Técnico Integrado em Refrigeração e Climatização do Instituto Federal Sul-rio-grandense, Campus Venâncio Aires, RS. O trabalho foi desenvolvido com 60 alunos de duas turmas de primeiro ano, durante o segundo semestre de 2011 e, concretizou uma proposta de ementa que buscou construir um currículo integrado entre a formação geral e a técnica, com vistas a uma formação unitária e um ensino potencialmente significativo. Como instrumento motivador e desencadeador do processo de ensino/aprendizagem, utilizou-se um sistema de refrigeração doméstico montado sob a forma de uma bancada didática que, associado a um texto de apoio produzido sob o referencial das teorias da aprendizagem significativa de David Ausubel e da interação social de Lev Semyonovich Vygotsky, guiaram as atividades com os alunos. O produto educacional resultante deste trabalho de conclusão compreende um material didático impresso preparado para a aplicação desta metodologia com alunos, ficando disponível para os demais interessados em utilizar ou adaptar tal material para a sua realidade de ensino.
In this work one presents a proposal of Thermal Physics teaching contextualized and integrated to the technical formation, directed to students of high school from the Integrated Technical Course on Refrigeration and Air Conditioning (Curso Técnico Integrado em Refrigeração e Climatização) of Instituto Federal Sul-rio-grandense, Campus Venâncio Aires, RS. This work was developed with 60 students of two classes of the first year during the second semester of 2011 and it aimed at making true a draft proposal which tries to build an integrated grade, between the general and technical formation, aiming at an unitary formation and a potentially significant teaching. As a motivating and starting instrument of the teaching-learning process one used a domestic refrigeration system, mounted on a teaching table that, associated to a help text, produced based on the theories of significant learning of David Ausubel and the social interaction of Lev Semyonovich Vygotsky, guided the activities along with the students. The educational product resulting from this completion work comprehends a printed didactical material prepared to the application of this methodology with the students, being available to anyone who may be interested in using or adapt such material to their teaching reality.

碩士
華梵大學
機電工程研究所
92
Due to the demands of energy-saving and product competition, the development of a highly efficient refrigerator becomes a very urgent job at present. The objective of this research is to combine direct experimental measurements with computational fluid dynamics modeling to study the thermal fluid phenomena in a domestic refrigerator. Experiments were carried out on a real refrigerator. Thermocouples were fixed inside the refrigerator, including freezer compartment, fresh food compartment and fruit area. The output signals from the thermocouples were connected to a computer-based data acquisition system. The computational fluid dynamics model was built to simulate the thermal and flow fields of the refrigerator. Computational fluid dynamics based on the finite volume method was employed to investigate the thermal and fluid fields, which include flow velocity and temperature distributions. The simulated model included the freezer compartment, fresh food compartment, separating plates, and flow passages. For the fluid domain, equations of conservation of mass, momentum, and energy were solved to obtain the temperature, pressure and velocity distributions. Conjugate heat transfer was utilized to comprehend the thermal fields of the solid domain. Thus temperature distributions of solid segments were also computed. The parameters, which are detrimental to the overall heat transfer efficiency, such as conduction, natural and forced convection, flow passage design, and volume flow rate, were investigated. Experimental measurements have also been used to verify the CFD model and gain a better understanding of the thermal and flow fields. The CFD model have been shown to be accurate in general. However, there are areas where the accuracy is less than satisfactory. The reasons for this may be attributed to not enough information about the wall temperature. At last, five proposals for improving the outcomes of simulations are recommended.

碩士
華梵大學
機電工程研究所
94
The objective of this research is to understand the temperature and flow fields of the interior of a refrigerator. Computational fluid dynamics based on the finite volume method is employed to investigate the flow and temperature fields. The simulated model includes the freezer compartment, fresh food compartment, separating plates, and flow passages. For the fluid domain, equations of conservation of mass, momentum, and energy are solved to obtain the temperature, pressure and velocity distributions. Conjugate heat transfer is utilized to comprehend the thermal fields of the solid domain. Thus temperature distributions of solid segments are also computed. The parameters, which are detrimental to the overall heat transfer efficiency, such as flow passage design are investigated. The ultimate purpose of this study is to improve the efficiency of a domestic refrigerator through optimal interior and flow passage design.

碩士
淡江大學
國際企業學系碩士在職專班
101
Since Taiwan joined World Trade Organization (WTO for short) in 2002 and signed Economic Cooperation Framework Agreement (ECFA for short) in 2010, the difference between the prices of imported products and the prices of domestic products has narrowed. Even China household appliances have more competitive advantage than domestic products, which makes manufacturers of domestic household appliances face a difficulty of sales decline and market saturation. If the manufacturers of domestic household appliances ran their business under this disadvantageous environment, they were bound to response on the product development strategy, cater to the change of consumption environment and launch the refrigerators that market needs. Expecting to understand the market of domestic refrigerators in Taiwan, to explore the major factor for consumers while choosing the refrigerators and consumers’ lifestyle and to understand the effect of demographic variables on purchase decision and lifestyle are the goals of this study. The results of the study showed： 1. The major motivations for consumers to purchase domestic refrigerators are environmental protection, energy saving, power saving, replacing the old ones and product functionality. 2. The main sources for consumers to collect the information of refrigerators are TV commercial, past consumer experience, internet, retail advertisement, introduction of sales and introductions of colleagues, friends and relatives. 3. The primary consideration for consumers to purchase is quality guarantee. 4. Consumers’ purchase decision would change due to “gender”, “age” and “average monthly salary of family”.

碩士
淡江大學
企業管理學系碩士在職專班
96
The study via questionnaire, Kano''s Two-Dimensional Quality Model and the analysis of Quality Improvement to realize the values of the customers to quality elements to domestic refrigerator. And via participating in the research and discussion from the focus group, introducing the way of QFD, to transfer Customer''s requirement into Engineering Characteristics. By constructing the House of Quality to increase the efficiency of product development and to satisfy customer''s requirement. The integration of Kano''s Two-Dimensional Quality Model and QFD method is mainly used to introduce the result of QFD method into the customer''s requirement from the QFD method and the values of customer''s preference. This study has introduced the relationship matrix between Kano''s two-dimensional quality elements and quality improvement modes and importance of quality elements by double confirmed. According to judgement on decrement dissatisfaction more than increment satisfaction, the 3×3 matrix is composed of Kano''s two-dimensional quality elements and quality improvement modes, that have 9 sets compose，it is supplyed 1~9 score or weight dividedly. According to importance’s score or weight, which has introduced into calculation and sorting of importance of customer''s requirements for QFD, the purpose and efficiency of integrating kano''s model Into QFD have accomplished.

After World War II in the United States, the household refrigerator and freezer became interwoven into a domestic reality defined by consumption, mechanical innovation, and a tension between spatial isolation and cultural interconnectivity. This thesis positions narrative Hollywood cinema, television and print media as the dominant sites where the refrigerator and freezer’s social identities were formed and negotiated. These productions employ the devices to explore postwar family gender roles, the influence of culture industries and consumer economies within the home, and technological fantasies and fears. They also illustrate a fertile conversation between household media technologies and kitchen accessories. As a result, viewing the refrigerator and freezer through film and television representations substantially alters existing conclusions over who interacted with the objects on an everyday basis, and their effect for a culture increasingly reliant upon appliances to provide basic human needs and generate a satisfying, entertaining lifestyle.
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