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The effect of wall thermal capacity and thermal resistance in the energy efficiency of small office

Brito, Adriana Camargo de; Akutsu, Maria; Vittorino, Fulvio; Aquilino, Marcelo M; Tribess, Arlindo
Fonte: Ashrae; Doha, Qatar Publicador: Ashrae; Doha, Qatar
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
56.2%
Historically, many ancient civilizations erected buildings that happened to have high thermal inertia. In places with high daily amplitude of air temperature and intense solar radiation, buildings made of heavy elements with high thermal capacity showed improved interior thermal environment conditions. Due to environmental concerns, recent studies have taken up this concept, indicating its potential in improve thermal comfort while reducing energy consumption in HVAC in small buildings exposed to various different weather conditions. Other studies have also revealed the main factors affecting building thermal inertia. One that stands out is the position of thermal insulation in the building envelope, which provides different thermal responses of buildings for the same value of thermal resistance. In Brazil, many air-conditioned office buildings have low thermal inertia prioritizing, instead, the thermal insulation of the envelope, characterized by maximum values of thermal transmittance, in accordance with Brazilian legislation for energy efficiency.This work presents an analysis of the energy performance of a small office building located in the city of São Paulo, considering eight different kinds of walls, with the same thermal resistance...

Efeito da gordura do leite de vaca sobre o valor D65ºC do Mycobacterium fortuitum (NCTN 8573); Effect of fat ratio of whole and skim cow milk on thermal resistance of Mycobacterium fortuitum (NCTC 8573)

Nishimoto, Érica Junko
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/10/2006 Português
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O presente trabalho objetivou avaliar o efeito da gordura do leite bovino na resistência térmica do Mycobacterium fortuitum. Amostras de leite bovino integral e desnatado foram contaminadas com inóculo padronizado de M. fortuitum, atingindo a concentração de aproximadamente 107 UFC/mL de leite, e submetidas à pasteurização lenta (65ºC/30mim.). Foi realizada a contagem do agente nos tempos 0, 5, 10, 15, 20, 25 e 30 minutos de pasteurização (em meio Lowenstein-Jensen, incubação a 37ºC/5 dias), e os resultados, em logarítmo, foram plotados em diagrama de dispersão com posterior regressão linear para construção da curva de sobreviventes (ou curva de morte térmica). Foram obtidas 3 curvas para o leite integral e 3 para o leite desnatado, porém, para o cálculo do valor D65ºC, utilizou-se a melhor reta obtida para cada tipo de leite. Encontraram-se valores D65ºC do Mycobacterium fortuitum iguais a 18,02 minutos para o leite integral e 7,82 minutos para o desnatado; a gordura do leite influenciou no padrão da curva de morte térmica e teve efeito protetor sobre o M. fortuitum. Conclui-se que a pasteurização lenta é capaz de reduzir 3,85 log de M. fortuitum em leite desnatado e 1,67 log em leite integral, resultando em diferentes níveis de segurança ao consumidor.; This study aimed to evaluate the effect of cow milk fat on the thermal resistance of Mycobacterium fortuitum. Samples of whole and skim cow milk were contaminated with a standardized inoculum of M. fortuitum...

Inativação térmica (75ºC) de Mycobacterium bovis (isolados de origem bovina) em leite integral experimentalmente inoculado; Thermal inactivation (75ºC) of Mycobacterium bovis (isolated from bovine) in whole milk experimentally contaminated

Ribeiro, Leandro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/12/2009 Português
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46.12%
A pasteurização do leite destinado ao consumo é obrigatória no Brasil e o sistema rápido (75ºC/15 a 20 segundos) é o mais empregado no país. O processo visa eliminar. Os parâmetros de tempo e temperatura empregados no mundo foram definidos após estudos sobre a resistência térmica do Mycobacterium tuberculosis e da Coxiella burnetti, reconhecidos como os microrganismos patogênicos, não formadores de esporos e que eventualmente podem estar presentes no leite cru, que apresentam a maior resistência térmica. Entretanto, não há estudos sobre a resistência térmica do M. bovis que circula nos bovinos no Brasil. Este estudo propôs-se a avaliar a resistência térmica (75ºC) de cinco espoligotipos de M. bovis, isolados de bovinos abatidos no estado de São Paulo, em leite integral experimentalmente contaminado. Leite UHT foi contaminado com M. bovis e, então, submetido a tratamento térmico em banho-maria a 75ºC por 20 segundos. Cada espoligotipo foi testado 3 vezes. As amostras foram retiradas do banho nos tempos 0 (o momento em que o leite atingiu 75ºC), 5, 10, 15 e 20, correspondendo ao tempo, em segundos, de tratamento térmico. O leite contaminado também foi analisado, para quantificação da carga inicial. O controle do processo envolveu o acompanhamento da temperatura do leite (um tubo com termômetro) e análise das enzimas fosfatase alcalina e peroxidase ao final do tratamento; para tal...

Determinação dos parâmetros cinéticos de resistência térmica da Proteína Verde Fluorescente recombinante (GFPuv); Determination of kinetic parameters of thermal resistance of the Green Fluorescent Protein (GFPuv)

Ishii, Marina
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/04/2003 Português
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66.13%
Células transformadas de E.coli DH5-α expressando a proteína verde fluorescente (GFPuv, pico de excitação e emissão de 394nm e 509nm) foram submetidas a extração pelo método de partição de três fases (TPP) e o extrato obtido purificado por cromatografia de interação hidrofóbica (HIC). O objetivo principal deste trabalho foi estudar a termoestabilidade da GFPuv extraída, para avaliar a sua possível utilização como indicador biológico econômico, de resposta rápida e precisa para processos térmicos de esterilização utilizando o calor úmido. A estabilidade térmica da proteína foi estudada em diferentes soluções-tampão (acetato, fosfato e tris-HCI 10mM) no intervalo de valor de pH de 5,O a 9,0 e, em temperaturas entre 75° e 95°C. Os parâmetros de resistência térmica determinados foram: o tempo de redução decimal (Valor D - min), valor z (°C), coeficiente Q10 e valor de energia de ativação (kcal/mol). A termoestabilidade da GFPuv, expressa em valor D, mostrou correlação linear para valores de pH ≥ 5,50, em tampão acetato. Em tampão fosfato, para valores de pH ≥ 7,50 a estabilidade térmica da proteína foi independente do valor de pH da solução. Em tampão tris-HCI...

Avaliação da cinética de crescimento, resistência ácida e resistência térmica de Salmonella enteritidis envolvida em surtos alimentares ocorridos no Rio Grande do Sul e comparação com outros sorovares; Growth kinetics, acid and thermal resistance of Salmonella enteritidis involved in foodborne outbreaks occurred in the Rio Grande do Sul state and comparation with other serovars

Malheiros, Patricia da Silva
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
66.14%
No período de 1999 a 2002, uma linhagem de Salmonella Enteritidis esteve envolvida em mais de 90% das salmoneloses ocorridas no RS. Este trabalho teve por objetivo avaliar a cinética de crescimento, a resistência ácida e a resistência térmica dessa linhagem e compará-la com S. Typhimurium e S. Bredeney não envolvidas em surtos alimentares, porém isoladas na mesma região. Em uma primeira etapa, a cinética de crescimento foi avaliada semeando-se cada sorovar em caldo nutriente (CN) e em salada de batata com maionese caseira (SMC), os quais foram mantidos a 30°C e 9,5°C. Em CN, a cinética de crescimento a 30°C foi semelhante para todos os sorovares, porém, em SMC a S. Enteritidis apresentou maior quantidade de células nas primeiras 6 horas de crescimento, sendo que somente depois de 12 horas todos os sorovares atingiram quantidades semelhantes de células. Em CN e em SMC, na temperatura de 9,5°C, não foi detectado crescimento de nenhum dos sorovares de Salmonella durante as primeiras 24 horas, sugerindo que essa temperatura foi suficiente para controlar a multiplicação desses microrganismos. Em uma segunda etapa, avaliou-se a resistência ácida e térmica dos diferentes sorovares de Salmonella. Para tanto, os três sorovares foram inoculados separadamente em CN e CN enriquecido com 1% de glicose (CNG)...

Stagnant effective thermal conductivity of agro-industrial residues for solid-state fermentation

Casciatori, Fernanda Perpétua; Laurentino, Carmem Lúcia; Magdaleno Lopes, Karen Christine; Gonçalves de Souza, André; Thoméo, João Cláudio
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1578-1593
Português
Relevância na Pesquisa
56.02%
The stagnant effective thermal conductivities (K0) of sugar cane bagasse (SCB), wheat bran (WB), orange pulp and peel (OPP) and their combination (weight proportion 1:2:2 SCB/OPP/WB) were obtained using the line heat source method. These solid materials were applied to pectinase production via solid-state fermentation. The moisture content ranged from 4 to 80% (w.b.). A conduction mechanism through the porous media was observed, along with conduction through a liquid film and contact thermal resistance between the samples and the probe. K0 was low for intermediate moisture contents and approached the molecular conductivity of water for high moisture contents. © 2013 Copyright Taylor and Francis Group, LLC.

Aumento da resistencia termica da borracha SIS atraves da adição de poli (oxido fenileno); To increase of SIS rubber thermal resistance with polioxyde phenilene addition

Anatoli Ivanov Junior
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 24/04/2009 Português
Relevância na Pesquisa
46.12%
A utilização de borracha SIS (copolímero em bloco estireno/isopreno/estireno) em diversas aplicações tais como solados de sapatos, artefatos de vedação, adesivos com baixa resistência térmica (até 40º C). No entanto, neste trabalho apresentam -se os resultados obtidos com a incorporação de PPO (polioxidofenileno) a borracha SIS, o que resulta o aumento de resistência térmica da borracha, ampliando assim suas aplicações. Neste trabalho estudou-se a melhor condição em massa dos materiais SIS e PPO. De acordo com análises físico-químicas encontrou-se a composição de 50% de cada material uma condição onde se tem um incremento na resistência térmica da borracha de até 70° C, o que então era de -51º C. No sentido de apresentar uma aplicação, realizou-se a confecção de um laminado auto-adesivo com resistência térmica até 70º C; The rubber use SIS (block copolymer) in several such applications as shoes, technical engines, stickers with low thermal resistance (up to 40º C). However, in this work they come the results obtained with the incorporation of PPO (polioxide phenilene) on rubber SIS, with results the increase of thermal resistance of the rubber, increase the applications. In this work it was studied the best condition in mass of material SIS and PPO. In agreement with analyses it met the composition of 50% of each material a condition where an increment is had in the thermal resistance of the rubber of up to 70° C...

Modelamento matematico da transferencia de calor durante o tratamento termico de alimentos liquidos embalados; Mathematical modelling of heart transfer in in-package liquid food thermal process

Pedro Esteves Duarte Augusto
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/05/2009 Português
Relevância na Pesquisa
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A crescente busca por alimentos mais seguros e de melhor qualidade nutricional e sensorial cria a necessidade de melhor entendimento dos processos envolvidos na produção dos mesmos. O tratamento térmico é um dos métodos mais utilizados na conservação de alimentos, sendo o processamento dentro da embalagem um dos mais seguros. A utilização de modelamento matemático da transferência de calor na avaliação de tratamentos térmicos vem se mostrando uma poderosa ferramenta na garantia da segurança sem comprometimento da qualidade nutricional e sensorial dos alimentos. A fluidodinâmica computacional (CFD) vem sendo utilizada em diversos trabalhos para melhor entendimento de processos térmicos de alimentos líquidos. Entretanto, a falta de consistência e uniformidade nas modelagens, aliadas as raras avaliações experimentais das simulações, criam a necessidade de avaliações entre metodologias utilizadas e validações criteriosas. O presente trabalho estudou a transferência de calor durante tratamentos térmicos de alimentos líquidos embalados em garrafas comerciais através de modelagem matemática por CFD. Determinou-se o coeficiente convectivo de transferência de calor (h) para duas garrafas comerciais em um sistema de aquecimento e um de resfriamento em imersão em água. Observou-se que mesmo pequenas diferenças entre geometrias de embalagens resultaram em considerável diferença nos valores de h entre embalagens e sistemas...

Characterization of Fatty Acid Composition, Spore Germination, and Thermal Resistance in a Nisin-Resistant Mutant of Clostridium botulinum 169B and in the Wild-Type Strain†

Mazzotta, Alejandro S.; Montville, Thomas J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /02/1999 Português
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The membrane fatty acids, thermal resistance, and germination of a nisin-resistant (Nisr) mutant of Clostridium botulinum 169B were compared with those of the wild-type (WT) strain. In the membranes of WT cells, almost 50% of the total fatty acids were unsaturated, but in those of Nisr cells, only 23% of the fatty acids were unsaturated. WT and Nisr spores contained similar amounts (approximately 23%) of unsaturated fatty acids, but the saturated straight-chain/branched-chain ratio was significantly higher in Nisr spores than in WT spores. These fatty acid differences suggest that Nisr cell and spore membranes may be more rigid, a characteristic which would interfere with the pore-forming ability of nisin. Nisr C. botulinum did not produce an extracellular nisin-degrading enzyme, nor were there any differences in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of coat proteins extracted from WT and Nisr spores, eliminating these as possible reasons for nisin resistance. Nisr spores had thermal resistance parameters similar to those of WT spores. In WT spores, but not in Nisr spores, nisin caused a 40% reduction in thermal resistance and a twofold increase in the germination rate. Because the nisin-induced increase in the germination rate of WT spores occurred only in the presence of a germinant (a molecule that triggers germination)...

Changes in Membrane Fatty Acid Composition of Pediococcus sp. Strain NRRL B-2354 in Response to Growth Conditions and Its Effect on Thermal Resistance

Annous, Bassam A.; Kozempel, Michael F.; Kurantz, Michael J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /07/1999 Português
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Membrane fatty acid composition and thermal resistance (D value) of Pediococcus sp. were determined for mid-exponential-phase (ME) and stationary-phase (ST) cells grown in tryptic soy broth (TSB) and tryptone-glucose-yeast extract (TGY) at 28 and 37°C. As the cells entered the stationary phase of growth, the unsaturated fatty acid, C18:1 n11c, produced during the exponential phase of growth was converted to its cyclic form, C19:0 Δ9c. This shift in membrane fatty acid composition was accompanied by an increase in the D values of this bacterium. Data from this study suggest that the membrane fatty acid composition of Pediococcus sp. is dependent on the growth conditions and that membrane fatty acid composition plays a critical role in thermal resistance. Thermal inactivation curves of Pediococcus sp. cells grown in TGY at 28°C indicated the presence of a cell population that is heterogeneous in thermal resistance. The growth of this bacterium in TGY at 37°C and in TSB at 28 and 37°C resulted in cell populations that were uniform in thermal resistance with a lag time for thermal inactivation. Thermal inactivation curves of ME and ST cultures were similar. The data presented here suggest that the cell population’s uniformity of thermal inactivation is independent of the growth phase of the culture.

Osmotically induced increase in thermal resistance of heat-sensitive, dipicolinic acid-less spores of Bacillus cereus Ht-8.

Bhothipaksa, K; Busta, F F
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1978 Português
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46.18%
Thermal resistance in heat-sensitive, dipicolinic acid (DPA)-less spores of Bacillus cereus Ht-8 heated in sucrose solutions increased at and above a concentration of 2 M sucrose. The decimal reduction times at 75 degrees C for spores heated in 0.0, 1.8, 2.2, and 2.6 M sucrose were 2.0, 2.8, 4.5, and 12 min, respectively. Maltose, fructose, and glucose increased heat resistance above that observed in water but did not elevate resistance to the level observed with sucrose at the same osmolality. Cation-induced loss of thermal resistance in chemically sensitized spores was reversed in the presence of sucrose. Spores germinated in brain heart infusion were resistant when heated in sucrose. In the presence of sucrose, spores exhibited an increase in optical density at 700 nm. Electron micrographs of the DPA-less spores suspended in 2.2 M sucrose revealed a shrinkage of outer coats and exosporium membranes. The results suggested that the osmotic property of sugars increased thermal resistance in DPA-less spores. The osmotic pressure exerted by sugars may be similar to the pressure that usually exists within the cortex of normal spores containing DPA and may cause the dehydration of the protoplast and the consequent thermal resistance. The role of dehydration and the nonessential nature of DPA for thermal resistance in spores were confirmed.

Morphological Changes and Antibiotic-Induced Thermal Resistance in Vegetative Cells of Bacillus subtilis

Dul, Michael J.; McDonald, William C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1971 Português
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46.24%
The morphology and thermal resistance of vegetative cells of Bacillus subtilis W168 were examined after growth at 37 and 53 C. Vegetative cells grown at 37 C exhibited a typical trilaminar morphology, whereas cells grown at 53 C exhibited a cell wall which was apparently thicker and more loosely organized and had a poorly defined periphery. A concurrent increase in thermal resistance to a heat shock of 60 C occurs with the change in cell wall morphology. The change to the aberrant cell wall form, or its reversal to the normal form, is always accompanied by the gain or the loss of thermal resistance, respectively. The inhibition of protein synthesis by chloramphenicol has little effect upon the acquisition of thermal resistance at 53 C. Addition of the disaccharide pentapeptide subunit to the cell wall peptidoglycan is apparently essential to growth at 53 C and the acquisition of thermal resistance, since both growth and thermal resistance are inhibited by bacitracin. Two antibiotics, penicillin and cycloserine, which inhibit the final cross-linking of the cell wall peptidoglycan at two separate points, do not affect the acquisition of thermal resistance at 53 C. These same antibiotics induce a high degree of thermal resistance at 37 C. It is proposed that a change in the cell wall structure is related to an increased thermal resistance.

Thermal Resistance of Staphylococcus aureus in Milk, Whey, and Phosphate Buffer1

Walker, G. C.; Harmon, L. G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1966 Português
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46.1%
The thermal resistance of four strains of coagulase-positive Staphylococcus aureus was determined in phosphate buffer, whole milk, skim milk, and Cheddar cheese whey. The logarithmic order of death prevailed until about 99.99 to 99.999% of the organisms were destroyed, after which there was a decline in the rate of destruction. The organisms were more resistant in skim milk and Cheddar cheese whey than in phosphate buffer and whole milk. Thermal resistance varied among strains of S. aureus but was consistent with individual strains. As the age of cultures of strain B-120 increased from 12 to 228 hr, the D55 values increased from 0.95 to 3.0. The thermal resistance of cultures obtained from survivors to partial thermal destruction was similar to that of the parent cultures.

Effect of functionalized MWCNTs/water nanofluids on thermal resistance and pressure fluctuation characteristics in oscillating heat pipe

Tanshen, R.; Batmunkh, M.; Nine, M.; Chung, H.; Jeong, H.
Fonte: Pergamon-Elsevier Science Ltd Publicador: Pergamon-Elsevier Science Ltd
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
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66.12%
An influence of multi-walled carbon nanotube (MWCNT) based aqueous nanofluids with different concentrations on the heat transport and the relevant pressure distribution in oscillating heat pipe (OHP) has been investigated. The present paper describes the heat transfer phenomena in terms of thermal resistance, pressure and frequency of pressure fluctuation in multi-loop oscillating heat pipe (OHP) charged by aqueous nanofluids with MWCNT loadings of 0.05 wt.%, 0.1 wt.%, 0.2 wt.% and 0.3 wt.%. The multi-loop OHP with 3 mm inner diameter has been conducted in the experiment at 60% filling ratio. Experimental results show that thermal characteristics are significantly inter-related with pressure distribution and strongly depend upon the number of pressure fluctuations with time. The investigation shows that the 0.2 wt.% MWCNTs based aqueous nanofluids obtain maximum number of the fluctuation frequency and low thermal resistance at any evaporator power input. Based on the experimental results, we discuss the reasons for enhancement and decrement of thermal characteristics of the nanofluids.; Md. Riyad Tanshen, B. Munkhbayar, Md. J. Nine, Hanshik Chung, Hyomin Jeong

Report of NPSAT1 battery thermal contact resistance testing, modeling and simulation

Sakoda, Daniel; Phelps, Ronald; Donovan, Bryce
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório
Português
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The report entitled “Report of NPSAT1 Battery Thermal Contact Resistance Testing, Modeling and Simulation” was prepared for the Naval Postgraduate School Space Systems Academic Group.; Thermal modeling is an important part of spacecraft design, especially where critical components have narrow operating temperature limits. For the Naval Postgraduate School’s NPSAT1 spacecraft, the lithium ion battery is the spacecraft component with the smallest temperature range of 0°C to 45°C during operation. Thermal analysis results, however, can only provide adequate results if there is sufficient fidelity in thermal modeling. Arguably, the values used in defining thermal coupling for components are the most difficult to estimate because of the many variables that define them. This document describes the work performed by the authors starting in the 2012 winter quarter as part of the SS3900 directed study course. The objectives of the study were to determine an adequate thermal model of the NPSAT1 battery as a lumped capacitance model, and an appropriate value of thermal resistance between the battery and its mounting surface for three thermal interfaces: metal-to-metal (bolted interface), Kapton®, and Chotherm® 1671. These objectives were performed through testing in a thermal-vacuum chamber with controlled boundary conditions. Modeling and simulation using the NX I-DEAS Thermal Model Generator software was performed to duplicate the test results in simulation. Agreement between the simulations and testing was achieved with differences ranging between +4°C and -8°C for the metal-to-metal interface...

Thermal characterization of the SiO2-Ge2Sb2Te5 interface from room temperature up to 400 °C

BATTAGLIA, Jean-Luc; KUSIAK, Andrzej; SCHICK, Vincent; CAPPELLA, Andrea; WIEMER, Claudia; LONGO, Massimo; VARESI, Enrico
Fonte: American Institute of Physics Publicador: American Institute of Physics
Português
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46.09%
The thermal conductivity of Ge2Sb2Te5 (GST) layers, as well as the thermal boundary resistance at the interface between the GST and amorphous SiO2, was measured using a photothermal radiometry experiment. The two phase changes in the Ge2Sb2Te5 were retrieved, starting from the amorphous and sweeping to the face centered cubic (fcc) crystalline state at 130 °C and then to the hexagonal crystalline phase (hcp) at 310 °C. The thermal conductivity resulted to be constant in the amorphous phase, whereas it evolved between the two crystalline states. The thermal boundary resistance at the GST-SiO2 interface was estimated to be higher for the hcp phase than for the amorphous and fcc ones.

Study of the thermal resistance of alpha-phase aluminum oxide (alpha-Al2O3) films deposited on the paper substrate

Lisboa, A. J. T.; Vasconcelos, N. S. L. S.; Rangel, J. H. G.; Oliveira, M. M. O.; Longo, E.; Varela, J. A.; Vasconcelos, J. S.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 9509-9516
Português
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66.17%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); The purpose of this study was to increase the thermal resistance of a cellulose substrate, using films (a mixture of corundum-phase aluminum oxide, (x-Al2O3, and a PVA solution). The corundum phase, which was chosen due to its high thermal resistance, was obtained using an adaptation of Pechini's polymeric precursor method. A polyvinyl alcohol (PVA) solution was used as a medium for mixing the oxide for subsequent deposition on a paper substrate. The materials were characterized by X-ray diffraction (XRD) and field emission gun scanning electron microscopy (BEG-SEM) coupled with energy dispersive X-ray spectrometry (EDS). The thermal behavior of the material was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The EDS results indicate that all the samples with deposited a-phase aluminum oxide contain the chemical elements (Al and O) originating from the a-phase, while the surface analysis indicated that the paper substrates were completely coated with the films. The TG and DSC analyses of the thermal resistance of the film-coated substrate indicate that it was impossible to increase the thermal resistance of the paper substrate because the events that occurred (decomposition of cellulose and pyrolysis of lignin...

Thermal and structural performances of insulated cavity rammed earth wall houses.

Dong, Xiang
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2015 Português
Relevância na Pesquisa
46.08%
Rammed earth (RE) wall construction is perceived to carry extremely low embodied energy and have desirable thermal performance without much energy input for heating and cooling due to the thermal mass effect. In Australia, however, because of the low thermal resistance (R-value) of RE material, it is very difficult for houses constructed with only solid RE walls to comply with the Deemed-to-Satisfy Provision provided in the National Construction Code (NCC) by the Building Code of Australia, which specifies the minimum R-value for external walls. The NCC provides an alternative provision, named the Energy Efficiency Provision, which states a maximum allowance of energy use by a residential house. As houses have the potential to consume little energy load particularly when passive design strategies are implemented, houses built with RE walls may still be able to comply with the Energy Efficiency Provision of the NCC. Adding thermal insulation to the wall construction is one way to ensure that RE wall houses comply with NCC. Normally, rigid board foam insulation can be inserted in the middle of RE walls to maintain the aesthetics of the wall surfaces and part of the thermal mass effect. The result of this solution is an insulated cavity rammed earth (ICRE) wall system. This solution...

Thermally driven classical Heisenberg chain with a spatially varying magnetic field: Thermal rectification and Negative differential thermal resistance

Bagchi, Debarshee
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/11/2014 Português
Relevância na Pesquisa
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Thermal rectification and negative differential thermal resistance are two important features that have direct technological relevance. In this paper, we study the classical one dimensional Heisenberg model, thermally driven by heat baths attached at the two ends of the system, and in presence of an external magnetic field that varies monotonically in space. Heat conduction in this system is studied using a local energy conserving dynamics. It is found that, by suitably tuning the spatially varying magnetic field, the homogeneous symmetric system exhibits both thermal rectification and negative differential thermal resistance. Thermal rectification, in some parameter ranges, shows interesting dependences on the average temperature T and the system size N - rectification improves as T and N is increased. Using the microscopic dynamics of the spins we present a physical picture to explain the features observed in rectification as exhibited by this system and provide supporting numerical evidences. Emergence of NDTR in this system can be controlled by tuning the external magnetic field alone which can have possible applications in the fabrication of thermal devices.; Comment: 7 pages, 20 eps figures (comments/suggestions/criticism will be appreciated)

Thermal resistance of the nanoscale constrictions between carbon nanotubes and solid substrates

Maune, Hareem; Chiu, Hsin-Ying; Bockrath, Marc
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 03/07/2006 Português
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We have determined the thermal resistance for transferring heat between individual single-walled carbon nanotube devices and solid substrates. Using sapphire and comparing our results to previous results obtained from SiO2, we find that the resistance is dominated by interfacial resistance rather than the spreading resistance of heat for diffusing into the substrate. Our results are in agreement to a recent model for the thermal resistance of nanoscale constrictions. Our results suggest that relatively short contact lengths (~10–30 nm) to a typical solid should be sufficient to transfer heat efficiently into carbon nanotubes, underscoring the potential of carbon nanotubes for nanoscale thermal management.