Thermal energy storage in Swedish single family houses : a case study

In a Nordic climate, space heating (SH) and domestic hot water (DHW) used in buildings constitute a considerable part of the total energy use in the country. For 2010, energy used for SH and DHW amounted to almost 90 TWh in Sweden which corresponds to 60 % of the energy used in the residential and service sector, or almost 24 % of the total final energy use for the country. Storing heat and cold with the use of thermal energy storage (TES) can be one way of increasing the energy efficiency of a building by opening up possibilities for alternative sources of heat or cold through a reduced mismatch between supply and demand. Thermal energy storage without the use of specific control systems are said to be passive and different applications using passive TES have been shown to increase energy efficiency and/or reduce power peaks of systems supplying the heating and cooling needs of buildings, as well as having an effect on the indoor climate. Results are however not consistent between studies and focus tend to be on the reduction of cooling energy or cooling power peaks. In this paper, passive TES introduced through an increased thermal mass in the building envelope to two single family houses with different insulation standard is investigated with building energy simulations. A Nordic climate is used and the focus of this study is both on the reduction of space heating demand and space heating power, as well as on reduction of excess temperatures in residential single family houses without active cooling systems. Care is taken to keep the building envelope characteristics other than the thermal mass equal for all cases so that any observations made can be derived to the change in thermal mass. Results show that increasing the sensible thermal mass in a single family house can reduce the heating demand only slightly (1-4 %) and reduce excess temperatures (temperatures above 24 degrees C) by up to 20 %. Adding a layer of PCM (phase change materials) to the light building construction can give similar reduction in heating demand and excess temperatures, however the phase change temperature is important for the results.

Ser do tempo em Bergson

O artigo apresenta a concepção bergsoniana de duração. Pretende-se mostrar que, segundo Bergson, o tempo dos filósofos e cientistas é um tempo fictício, um esquema espacial que oculta a natureza do tempo real, o qual não pode ser separado dos acontecimentos físicos e psicológicos. Para Bergson, o tempo real é sucessão, continuidade, mudança, memória e criação.

Modelagem numérica de escoamento em padrão anular com transferência de calor e massa

Annular flow is the prevailing pattern in transport and energy conversion systems and therefore, one of the most important patterns in multiphase flow in ducts. The correct prediction of the pressure gradient and heat transfer coefficient is essential for optimizing the system s capacity. The objective of this work is to develop and implement a numerical algorithm capable of predicting hydrodynamic and thermal characteristics for upflow, vertical, annular flow. The numerical algorithm is then complemented with the physical modeling of phenomena that occurs in this flow pattern. These are, turbulence, entrainment and deposition and phase change. For the development of the numerical model, axial diffusion of heat and momentum is neglected. In this way the time-averaged equations are solved in their parabolic form obtaining the velocity and temperature profiles for each axial step at a time, together with the global parameters, namely, pressure gradient, mean film thickness and heat transfer coefficient, as well as their variation in the axial direction. The model is validated for the following conditions: fully-developed laminar flow with no entrainment; fully developed laminar flow with heat transfer, fully-developed turbulent flow with entrained drops, developing turbulent annular flow with entrained drops, and turbulent flow with heat transfer and phase change

A sustainable alternative for cooling the machining processes using a refrigerant fluid in recirculation inside the toolholder

This article presents a cooling system for cutting tool in turning based in a toolholder with cooling fluid flowing inside its body being that this fluid must necessarily be able to phase change due to heat generated from machining processes. In this way, the fluid evaporates just under the cutting tool allowing a heat transfer more efficient than if were used a fluid without phase change once the latent heat of evaporation is beneficial for removal heat. Following, the cooling fluid evaporated passes through a condenser located out of the toolholder where it is condensated and returns to the toolholder again and a new cycle is started. In this study, the R-123, a hydrochlorofluorocarbon (HCFC) fluid, was selected for the turning of a Cr-Ni-Nb-Mn-N austenitic steel of hard machinability. The machining tests were carried out under three different machining conditions: dry machining, external cutting fluid (conventional method), and with the toolholder proposed. As result, the developed system allows a surface roughness up to 10% better than dry machining and a tool life close to the conventional method, but 32% superior to dry machining; moreover, there are environmental and economics advantages once the cooling fluid is maintained in a loop circuit.

Pressure drop correlation for oil-refrigerant R134a mixture flashing flow in a small diameter tube

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

ZERO SOUND-VELOCITY IN PI, RHO-MESON GASES

Sharp transitions are perhaps absent in QCD, so that one looks for physical quantities which may reflect the phase change. One such quantity is the sound velocity which was shown in lattice theory to become zero at the transition point for pure glue. We show that even in a simple bag model the sound velocity goes to zero at temperature T = T(v) not-equal 0 and that the numerical value of this T(v) depends on the nature of the meson. The average thermal energy of mesons goes linearly with T near T(v), with much smaller slope for the pion. The T(v) - s can be connected with the Boltzmann temperatures obtained from transverse momentum spectrum of these mesons in heavy-ion collision at mid-rapidity. It would be interesting to check the presence of different T(v) - s in present day finite T lattice theory.

PCM thermal insulation in buildings

This paper presents the results of a numerical and experimental study of phase change material (PCM) filled walls and roofs under real operational conditions to achieve passive thermal comfort. The numerical part of the study was based on a one-dimensional model for the phase change problem controlled by pure conduction. Real radiation data was used to determine the external face temperature. The numerical treatment was based upon using finite difference approximations and the ADI scheme. The results obtained were compared with field measurements. The experimental set-up consisted of a small room with movable roof and side wall. The roof was constructed in the traditional way but with the phase change material enclosed. Thermocouples were distributed across the cross section of the roof. Another roof, identical but without the PCM, was also used during comparative tests. The movable wall was also constructed as is done traditionally but with the PCM enclosed. Again, thermocouples were distributed across the wall thickness to enable measurement of the local temperatures. Another wall, identical but without the PCM, was also used during comparative tests. The PCM used in the numerical and experimental tests was composed of a mixture of two commercial grades of glycol in order to obtain the required fusion temperature range. Comparison between the simulation results and the experiments indicated good agreement. Field tests also indicated that the PCM used was adequate and that the concept was effective in maintaining the indoor temperature very close to the established comfort limits. Further economical analysis indicated that the concept could effectively help in reducing the electric energy consumption and improving the energy demand pattern. © 1997 by John Wiley & Sons, Ltd.

Design studies of the magnetic properties of structural materials affecting the magnetic field of high-homogeneity superconducting magnets

Austenitic stainless steel presents phase changes caused by heat treatment and welding processes. Because it represents a problem in the design of high-homogeneity magnets, we have been studying the magnetic properties of Ti alloys for their use instead of stainless steel as structural material for superconducting magnet construction. In this work, we present the comparative study of the influence of magnetic properties of steel and Ti alloys on the magnetic-field homogeneity of a superconducting coil through numerical calculation using the measured magnetic properties. © 2001 Elsevier Science B.V. All rights reserved.

Carbon dioxide evaporation in a single microchannel

Despite its importance for designing evaporators and condensers, a review of the literature shows that heat transfer data during phase change of carbon dioxide is very limited, mainly for microchannel flows. In order to give a contribution on this subject, an experimental study of CO 2 evaporation inside a 0.8 mm-hydraulic diameter microchannel was performed in this work. The average heat transfer coefficient along the microchannel was measured and visualization of the flow patterns was conducted. A total of 67 tests were performed at saturation temperature of 23.3°C for a heat flux of 1800 W/(m2°C). Vapor qualities ranged from 0.005 to 0.88 and mass flux ranged from 58 to 235 kg/(m2s). An average heat transfer coefficient of 9700 W/(m2°C) with a standard deviation of 35% was obtained. Nucleate boiling was found to characterize the flow regime for the test conditions. The dryout of the flow, characterized by the sudden reduction in the heat transfer coefficient, was identified at vapor qualities around 0.85. Flow visualization results showed three flow patterns. For low vapor qualities (up to about 0.25), plug flow was predominant, while slug flow occurred at moderated vapor qualities (from about 0.25 to 0.50). Annular flow was the flow pattern for higher vapor qualities. Copyright © 2006 by ABCM.

Análise do fenômeno de cavitação em bomba centrífuga

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Simulação do escoamento bifásico da mistura óleo-refrigerante através da folga radial de compressores rotativos de pistão rolante

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Portaferramentas para torneamento com refrigeração interna baseada na mudança de fase do fluido

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Professoras aposentadas em território rural/ribeirinho: identidades e práticas socioculturais

O presente trabalho dedica-se a analisar os sentidos que professoras aposentadas, docentes da Educação Básica, e outros moradores atribuem às identidades e às práticas desenvolvidas por essas mulheres nas vilas Moiraba e Carmo do Tocantins, em especial, na interação com a nova geração de professores. Para dar conta dessa investigação, realizamos 03 movimentos de inserção naquelas comunidades para coleta das narrativas dos sujeitos envolvidos, a saber: a 1ª fase, em que foi realizada a pesquisa Exploratória; a 2ª fase, em que foram realizadas as entrevistas com os diferentes grupos de moradores; a 3ª fase, em que foram construídas as Oficinas de Memória, essas fazes ocorreram em 2009, 2011 e 2012, respectivamente. Assim, fizemos uso dos pressupostos da História Oral, em especial, na organização das Oficinas de Memória. As narrativas foram analisadas, a partir das temáticas que envolveram os saberes da experiência, a profissionalidade, o trabalho, a ciclo profissional e o saber docente associadas ao dialogismo bakhtiniano e à perspectiva da cultura enquanto modos de vida. Tais encaminhamentos foram importantes para compreendermos que essas aposentadas ao chegarem na Idade Madura e na Velhice deparam-se com o evento da aposentadoria e em direção oposta ao que se poderia esperar diante dos estereótipos criados a respeito do aposentado como um sujeito que não tem mais condições de contribuir com a sociedade, elas ressignificam a lógica de que a aposentadoria é o fim de projetos de vida. Desse modo, as aposentadas dão continuidade ao investimento em outros tipos de atividades produtivas e se colocam à disposição para vivenciarem novas experiências mostrando que em determinadas comunidades da Amazônia Paraense ainda é recorrente a imbricação entre escola, igreja, lideranças comunitárias e esse grupo que não atua sob exigências político-administrativas, mas por relações afetivas, de respeito e valorização de experiências partilhadas, principalmente com os docentes da Educação Básica, contribuindo assim com sua formação intelectual e humana. Elas colocam em prática novos projetos de vida e procuram manter o status que as mesmas possuem, isto é, trata-se de mulheres aposentadas que ainda se colocam à disposição para exercer determinadas funções nas diferentes esferas públicas, especial, na igreja e na escola. Tais encaminhamentos garantem a elas não apenas reconhecimento social, mas também bem-estar, aspecto interessante na construção de uma velhice bem-sucedida. Por conta disso, a aposentadoria não representa um fim, mas uma fase de avaliação e preparação de projetos de vida que se apoiam em projetos mais coletivos para dar novos sentidos à vida.

Análise experimental de um trocador de calor por mudança de fase e desenvolvimento de um modelo numérico simplificado

Pós-graduação em Engenharia Mecânica - FEIS

Magnetic Tuning of All-Organic Binary Alloys between Two Stable Radicals

Mixtures of 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzi-midazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN.) crystallize as solid solutions (alloys) across a wide range of binary compositions. (F4BImNN)(x)(BImNN)((1-x)) with x < 0.8 gives orthorhombic unit cells, while x >= 0.9 gives monoclinic unit cells. In all crystalline samples, the dominant intermolecular packing is controlled by one-dimensional (1D) hydrogen-bonded chains that lead to quasi-1D ferromagnetic behavior. Magnetic analysis over 0.4-300 K indicates ordering with strong 1D ferromagnetic exchange along the chains (J/k = 12-22 K). Interchain exchange is estimated to be 33- to 150-fold weaker, based on antiferromagnetic ordered phase formation below Neel temperatures in the 0.4-1.2 K range for the various compositions. The ordering temperatures of the orthorhombic samples increase linearly as (1 - x) increases from 0.25 to 1.00. The variation is attributed to increased interchain distance corresponding to decreased interchain exchange, when more F4BImNN is added into the orthorhombic lattice. The monoclinic samples are not part of the same trend, due to the different interchain arrangement associated with the phase change.