An Experimental Study on the Capillary Tube Flow and its Effect on the Acoustic Behavior of Household Refrigerators

Since the beginning of the “artificial” refrigeration era, a great deal of effort has been applied on the development of high efficient systems. The efforts were primarily focused on the compressor, bringing its efficiency to record-high values. Simultaneously, the compressor noise was brought down to almost inaudible levels. As a consequence, sources of noise that were previously unnoticeable became audible and started to play a major role among refrigerator manufacturers. One of those new sources of noise, generally known as fluid borne noise, is now a growing field of interest in engineering. The aim of this work is to study the relationship between the capillary tube flow and the acoustic behavior of household refrigerators by investigating a particular type of fluid borne noise that only occurs during the freezer mode of dual-evaporator appliances, known as fluctuating noise. To this end a household refrigerator was carefully instrumented and firstly tested in a reverberant chamber. Very heavy sound power level oscillations were found, even with the system in thermodynamic steady-state conditions. Acceleration measurements were also taken at the inlet pipe of the evaporator showing that the refrigerant flow in that region is highly pulsating, i.e., that the refrigerant flow pattern at the discharge of the capillary tube is not steady, in contrast to the indications of the thermodynamic readings. Visualizations studies of the flow pattern at the inlet of the capillary tube were also carried out, showing the presence of vapor bubbles – caused by an unbalance between the compressor and capillary tube mass flow rates – for most of the time. A needle valve was then installed in series with the freezer capillary tube in order to increase restriction and match the compressor and the capillary tube mass flow rates. The restriction provided by the optimum pair needle valve-capillary tube was converted into an equivalent I.D. capillary tube. The original freezer capillary tube was replaced by a same length smaller I.D. capillary tube, and another appliance tests were carried out. It was found that the higher restriction capillary tube attenuate the pulsating characteristic of the refrigerant flow, almost averting the disturbing fluctuating noise

Numerical and Experimental Analysis of Heat and Mass Transfer Processes on Water Trays in Household Refrigerators

Frost formation on the cold evaporator surface is a typical problem in household refrigerators. It happens due to humidity present in the ambient air associated with frequent door openings. In addition, mass transfer from stored goods to dry internal cabinet air and moisture infiltration through door gaskets also contribute to frost formation on the evaporator surface. To prevent this, the evaporator has to be defrosted manually or automatically (as in modern refrigerators). To do so, an electrical heater is switched on at a preset time and frequency and defrosts the evaporator. During this time, defrosted water is drained through a pipe into a water tray which is usually placed at the vicinity of the compressor. There the water evaporates mainly due to heat transfer from hot compressor shell. This system of defrosting and evaporation works well in areas with low relative humidity, where the amount of defrosted water is small and the evaporation rate is higher when compared to places with high relative humidity. Moreover, the compressor shell temperatures of high efficient compressors are not usually high enough to provide the minimum evaporation rate to balance the defrosted water flow rate and thus avoid water overflow. The aim of this work is to get a better understanding of the defrosted water evaporation process and to come up with low cost, practical and more efficient designs of water trays. To this end a test facility was designed and constructed to reproduce the compressor operating conditions and the defrosted water flow rate and temperature. The test rig was placed within a climate-controlled room with a strict control of air temperature and relative humidity. A mathematical model was also developed to predict the water evaporation rate based on the fundamental conservation equations of mass and energy. Several tests were carried out under different operating conditions and with different water trays designs. The model predictions were compared to the experimental data base with most of the points falling within an error band of ?10%

Rheological behavior of wood and wood based materials

A madeira, assim como outros materiais utilizados em construção, sofre alterações em sua resistência e rigidez quando submetida a carregamentos de longa duração. Esse fenômeno tem importância considerável na avaliação da capacidade de resistência dos elementos estruturais. Mecanicamente a madeira se comporta como um sólido visco-elástico. Desta forma, com o passar do tempo os elementos estruturais de madeira submetidos a cargas permanentes ou cíclicas sofrem deformações permanentes, mesmo se o carregamento é feito dentro do regime elástico, o que caracteriza o comportamento viscoelástico. Esse comportamento depende, dentre outros fatores, principalmente da intensidade e da duração da carga. No presente estudo, foi realizada uma revisão a respeito desse fenômeno, evidenciando suas causas e efeitos, visando o seu melhor entendimento, o qual é essencial para o uso adequado e eficiente da madeira e de seus derivados como materiais estruturais. _________________________________________________________________________________ ABSTRACTThe wood, as well as other construction materials, presents changes in this stiffness and strength when submitted to a long time loading. This phenomenon is important in the analyses resistance capacity of structural materials. Mechanically, the wood behaves as a viscous-elastic solid. However, over time, the structural elements submitted to permanent or cyclic loading presents some deformation, which denotes a viscous-elastic behavior. This characteristic is influenced mainly on the intensity and duration of loading. In this study a review of rheological phenomenon is presented, showing up the causes and effects for a better understanding, which is essential for the appropriate and efficient use of the wood and wood composites as structural materials

Prediction of Evaporator Frosting in Household Refrigerators Subjected to Periodic Door Opening

This paper describes a quasi-steady-state simulation model for predicting the transient behavior of a household refrigerator subjected to periodic door opening. A semi-empirical steady-state sub-model was developed for the refrigeration loop, and a transient sub-model was devised to predict the energy and mass transfer into and within the refrigerated compartments as well as the evaporator frosting. The key empirical heat and mass transfer parameters required by the model were derived from a set of experiments carried out in a climate-controlled chamber. In general, it was found that the model predictions followed closely the experimental trends for the power consumption (deviations within ±10%) and for the compartment temperatures (deviations within ±2 K)

Utjecaj tipa ljepila na svojstva LVL ploča izrađenih od plantažnog drva paricá (Schizolobium amazonicum Huber ex. Ducke)

The work aimed at evaluating the influence of the adhesives on physical and mechanical properties of laminated veneer lumber (LVL) boards made from Schizolobium amazonicum plantation trees. This species is native from Amazonia and it is showing fast growing and low density. LVL was produced in three different treatment groups considering the type of adhesive used (Polyvinyl Acetate Crosslinking – PVAc, phenol-formaldehyde – PF and polyurethane – PU). For each treatment, pieces with dimensions of 25 cm x 2.2 cm x 50 cm were produced. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (EM), modulus of rupture (fM), compression strength parallel to grain (fc,0), shear strength parallel to glue-line (fv,0), shear strength perpendicular to glue-line (fv,90), water absorption and thickness swelling for 2 and 24 h of water immersion. The adhesives used in this study significantly influenced the performance of LVL. Polyurethane adhesive presented better results with respect to physical properties. Phenol-formaldehyde provided greater resistance among the adhesives tested.Rad je usmjeren na vrednovanje utjecaja ljepila na fizikalna i mehanička svojstva lameliranih furnirskih ploča (LVL) izrađenih od drva Schizolobium amazonicum iz plantažnog uzgoja. Vrsta potječe iz Amazone i ima svojstva brzog rasta i male gustoće drva. LVL ploče proizvedene su primjenom triju vrsta ljepila (polivinil acetatnoga - PVAc, fenol-formaldehidnoga - PF i poliuretanskog ljepila - PU). Dimenzije proizvedenih ploča bile su 25 cm x 2,2 cm x 50 cm. Određivana su ova mehanička i fizikalna svojstva: statički modul elastičnosti pri savijanju (EM ), modul loma (fM ), čvrstoća na tlak paralelno s vlakancima (fc,0 ), smična čvrstoća paralelno s linijom lijepljenja (fv,0 ), smična čvrstoća okomito na liniju lijepljenja (fv,90), apsorpcija vode i debljinsko bubrenje nakon 2 i 24 sata potapanja uzoraka u vodi. Istraživanje je pokazalo da ljepilo upotrijebljeno za izradu LVL ploče znatno utječe na njezina svojstva. Poliuretansko ljepilo utjecalo je na bolja fizikalna svojstva, a fenol-formaldehidno ljepilo pokazalo se najotpornijim među istraživanim ljepilima

Relatório de Estágio

O relatório de estágio surge como uma das etapas fundamentais para a obtenção do Grau de Mestre em Ensino de Educação Física nos Ensinos Básico e Secundário e resulta de uma reflexão sobre o percurso profissional do mestrando bem como das várias etapas durante a presente formação. Numa primeira fase, elaborou-se uma reflexão sobre as evidências da lecionação da disciplina e posteriormente, de acordo com o exigido, a aplicação de duas unidades didáticas – uma sobre ginástica acrobática e a segunda sobre o malabarismo, a qual seria a base da intervenção para o trabalho de investigação à posteriori. O presente estudo de investigação focaliza as Influências do malabarismo na proficiência motora de alunos com dificuldades Intelectuais e desenvolvimentais, nomeadamente Défice Intelectual e Desenvolvimental (DID), Perturbação da Hiperatividade com Défice de Atenção (PHDA), Perturbação do Espectro do Autismo (PEA) e Défice de Atenção, Motor e Perceção (DAMP). Procurou-se compreender qual a relação/influxo das atividades de malabarismo, mais concretamente, o diábolo, batons do diabo, pratos chineses e bolas de malabarismo, na proficiência motora dos alunos. De forma a quantificar, utilizou-se como instrumento o teste de proficiência motora de Bruininks e Ozeretsky (BOT2-versão reduzida). O estudo teve a participação de 30 adolescentes. A faixa etária compreendia jovens dos 13 anos aos 16 anos, do quinto ano ao nono ano de escolaridade. A intervenção preconizada obteve resultados estatisticamente significativos na medida em que se registaram melhorias pertinentes nas áreas motoras de controlo manual fino - precisão motora; na coordenação manual – destreza manual e por último, na força, sugerindo a importância das atividades com malabares como instrumento de intervenção neste tipo de população objetivando uma interferência positiva nas capacidades motoras.The internship report emerges as one of the fundamental stages for obtaining the Master's Degree in Physical Education Teaching in Basic and Secondary Education and results from a echo on the professional course of the master's degree as well as the various stages during the present formation. In a first level, a consideration on the evidences of the teaching of the discipline was elaborated and later, as required, the application of two didactic units - one on acrobatic gymnastics and the second on juggling, which would be the basis of the intervention research work. The present research study focalizes on the Influences of juggling on motor proficiency of students with intellectual and developmental disability’s, especially Intellectual and Developmental Deficit (IDD), Attention Deficit Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), Deficit of Attention, Motor and Perception (DAMP). We sought to ascertain the impact of juggling activities, as diabolo, devil lipsticks, Chinese dishes and juggling balls, in the students' motor skills., The Bruininks and Ozeretsky motor proficiency test (BOT2-brief form) were used . The study had the participation of 30 adolescents. The age range comprised young people from 13 years to 16 years, from the fifth year to the ninth year of schooling. The studied intervention yielded statistically significant results as there were relevant improvements in the fine motor control areas - motor precision; in manual coordination - manual dexterity and finally in strength, suggesting the importance of juggling activities as an intervention tool in this type of population aiming for a positive interference in motor skills

A teoria dos sistemas sociais em Niklas Luhmann

Resenha sobre a obra: (Rodrigues, Leo Peixoto; Neves, Fabrício Monteiro. Niklas Luhmann: a sociedadecomo sistema. Porto Alegre: Edipucrs, 2012, 132 p.

Noise Generation in Household Refrigerators: An Experimental Study on fluid Borne Noise

The oscillatory pressure disturbance created by the refrigerant flow through pipes and components is one of the main sources of noise in household refrigerators. This type of excitation is transmitted to the pipes and travels through the structure reaching the cabinet and other parts exposed to the air, where audible airborne sound waves are created. In order to get a better understanding of this type of noise a household refrigerator was especially instrumented with thermocouples, absolute and dynamic pressure transducers and accelerometers. Tests were carried out at different operating conditions, when it was found that the compressor was the main source of excitation, practically affecting the entire refrigeration loop. It was also found that the flow velocity at the outlet of the capillary tube was high enough to induce significant vibrations in the evaporator. Finally, it was found that the entrance of vapor bubbles in the capillary tube produces sporadic and strong excitations. However those excitations do not travel very far along the flow, being attenuated by the condenser and the evaporator, but can nevertheless be transmitted to the pipes. In view of the collected database, comments and suggestions concerning the design of household refrigerators are presented and discussed

EMPREENDEDORISMO E INOVAÇÃO: O PAPEL DA EDUCAÇÃO SUPERIOR NAS ECONOMIAS MUNDIAIS

Empreendedorismo e Inovação, principalmente em tempos de crise, são os principais pilares que sustentam o crescimento das economias em todos os países, sendo a educação superior o motor fundamental para este desenvolvimento. Tendo como base esta premissa, o objetivo do presente artigo é apresentar o Empreendedorismo e a Inovação, que nascem por meio a investimentos na educação superior, como fatores críticos de sucesso para as economias mundiais. Para se atingir este objetivo, realizou-se uma pesquisa exploratória e qualitativa. A coleta de dados se deu por meio de pesquisa documental e bibliográfica, buscando dados referentes ao papel do empreendedorismo e inovação, além dos investimentos na educação superior, com delimitação em quatro continentes: Europa, Ásia, América do Norte (com foco nos Estados Unidos) e América do Sul (com foco no Brasil). Para tanto, foram utilizados como referências artigos e relatórios a respeito deste tema publicados em todo o mundo. Os resultados apresentaram que o Empreendedorismo e a Inovação têm representado a principal arma das nações para enfrentar a crise que as assola, mas para que isto seja possível, será necessário um grande investimento na educação, sobretudo na educação superior

DEMOCRATIZAÇÃO DA EDUCAÇÃO SUPERIOR NO BRASIL: UMA ANÁLISE CRÍTICA DA UNIVERSIDADE ABERTA DO BRASIL (UAB)

A UAB tem por objetivo suprir uma demanda educacional do país, por meio da democratização da educação. Contudo, há uma discussão entre a efetividade destes programas, mais especificamente sobre os aspectos quantitativos e qualitativos do programa. Diante deste contexto, o artigo teve como objetivo apresentar uma análise critica sobre a UAB. Em relação ao método, a pesquisa foi classificada como exploratória, com uma abordagem qualitativa, sendo ainda classificada como documental e bibliográfica. Os resultados apontam que a expansão da educação superior a distância no Brasil cumpre um importante papel social, porém é necessário que esta expansão seja feita com qualidade. Além do mais, deve se conceder maior ênfase na avaliação das Tutorias e na equipe multidisciplinar responsável pela condução deste processo