Navegando por Assunto "Calor"

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Acesso aberto (Open Access)
Análise da convecção natural no escoamento laminar em cavidades parcialmente preenchidas com meios porosos utilizando transformadas integrais
(Universidade Federal do Pará, 2016-04-15) QUARESMA, Sil Franciley dos Santos; MACÊDO, Emanuel Negrão; http://lattes.cnpq.br/8718370108324505; QUARESMA, João Nazareno Nonato; http://lattes.cnpq.br/7826389991864785
A numerical study is performed to analyze the natural convection in a vertical rectangular enclosure that is partially filled with a porous medium, by the Generalized Integral Transform Technique (GITT). The first studies concerning flow transient in a channel partially filled with porous medium without the effect of natural convection in order to understand the technical solution or problems with interfaces. Two different formulations were studied: the two-domain approach and the single-domain approach. Subsequently a numerical study is performed to analyze the steady-state thermal natural convection fluid flow and heat transfer in a vertical rectangular enclosure that is partially filled with a porous medium. The flow is modeled using the Brinkman- Forchheimer extended Darcy and energy conservation equation was used to predict the heat transfer. The mathematical description of the problem is based on a one-domain formulation of the conservation equations. Finally it carried out the study of double diffusive natural convection, also nominated thermosolutal natural convection in partially porous enclosures. The validity of the so-called one-domain approach used in this case compared to existing results in the literature. A particular class of problems dealing with thermal and double diffusive natural convection mechanisms in partially porous enclosures is presented, and it is shown that this configuration exhibits specific features in terms of the heat and mass transfer characteristics.
Acesso aberto (Open Access)
Correlação entre condições de solidificação, microestrutura a resistência mecânica
(Universidade Estadual de Campinas, 1999-02-02) QUARESMA, José Maria do Vale; GARCIA, Amauri; http://lattes.cnpq.br/1721691084829002
Correlation among solidification conditions, microstructure and mechanical behavior / The imposition of a wide range of operational conditions in foudry and static casting generates, as a direct consequence, a diversity of solidification structures. Structural parameters such as grain size and interdendrictic spacings are highly influenced by the thermal behavior of the metal/mold system. during solidification, consequently imposing a close correlation between the described system and the resulting microstructure. The mechanical properties of an alIoy in its crude state of solidification depend on the microstructural arrangement defined in the solidification process. Under the circumstances, the mechanical behavior of the alIoy, represented by stresses and/or strains, wilI be defined by grain size, interdendritic spacings, casual porosities, segregated products and other phases. Expressions correlating the mechanical behavior with microstructural parameters are very useful in order to search for a type of previous planning of the solidification conditions in terms of a determined leveI of mechanical resistance which is intended to be attained, e.g. to settle a way of programming the microstructure and the mechanical properties as well. Particularly, the literature in this field presents relations between the yield strength of the material and the grain size, such as the renowned HalI-Petch's equation. The present work advances in that direction, in search of relations among mechanical behavior in the plastic field, secondary dendritic spacings and solidification conditions. In order to analyze an important variable of solidification in molds with good heat diffusivity, like the metal/mold heat transfer coefficient, alloys of the Sn-Pb system - with compositions Sn- 5%Pb, Sn- 10%Pb, Sn- 20%Pb, Sn- 38,1%Pb (eutectic) - besides the element tin, were chosen. The choice was made because such alloys are easily handled in laboratory and chiefly because their thermophysical properties are well known. Particularly the influences of the following operational conditions on hi were investigated: mold thickness, liquid metal superheating and magnitude of the solidification range. Experimental results related to the distribution of temperatures in metal and mold during solidification, as compared with the results of simulation with a numerical model, made it possible to attain of expressions, for each case, by relating hi in terms of time. Heat transfer from the external surface of the mold to the environment was also analyzed; in the same manner, expressions were developed correlating the mold/environment heat transfer coefficient hAmb in terms of time as well. To correlate parameters of dendritic structures and mechanical properties, the following alloys of the Al-Cu system were chosen: Al- 4,5%Cu; Al- 15%Cu. The same aforementioned analysis referring to hi and hAmb was extended to those alloys including the one of eutectic composition (Al- 33%Cu) and pure aluminum. Based upon results of standardized solidification tests, secondary dendritic spacing ( EDS ) and upon mathematical models of heat transfer and dendritic growth, expressions were developed correlating the ultimate tensile strength (σu) and specific elongation (δ) as a function of variables of the metallmold system. Thus it was a way towards the programming of the dendritic structure and the leveI of resistance as a function of preestablished operational conditions in the solidification process.
Acesso aberto (Open Access)
Obstáculos epistemológicos no estudo do calor
(Universidade Federal do Pará, 2004-10-30) RIBEIRO, Elinete Oliveira Raposo; BRITO, Licurgo Peixoto de; http://lattes.cnpq.br/5100592138044970
The intention of this work is to identify epistemological obstacles in the process of construction of related physical concepts to the heat, from the epistemology of Gaston Bachelard. The research was developed, having as public target, students of third series in the average education of a public school of Belém. For the identification of epistemological obstacles, a questionnaire of opened answers was elaborated, which was applied, first in a group, objectifying the validation of the inquiry instrument. This test, guided the reformulation of the questionnaire for future application in other groups. The answers make possible three different strategies of analysis: in the first one it was focused presence of epistemological obstacles without restricting students or questions, from which it was identified the presence of substantiality obstacle, first experience, verbal, realistic and animistic common knowledge; second it was guided to detect epistemological obstacles disclosed by each student, in all the set of questions, where we verify the presence of at least one epistemological obstacle in the set of answers of each student; third it searched to relate each question (topical) with the corresponding epistemological obstacles, where we verify that the obstacles of the first and substantiality experience were present in answers of almost all the boarded topics, and the obstacles of, verbal, realistic and animistic the common knowledge, are present in lesser frequency. In the attempt to contribute with the improvement of Physics Education, the work shows some suggestions to the theacher, searching the overcoming of these obstacles for the students.
Acesso aberto (Open Access)
Transferência de calor com mudança de fase em processos de borbulhamento
(Universidade Estadual de Campinas, 1986-04-25) SOUZA, Célio Augusto Gomes de; ANDRADE, Alberto Luiz de; http://lattes.cnpq.br/5905831095854831
Heat transfer fenomena with phase change is analyed in a bubbling process, where heated gas hubbies pass through a liquid. The experimental evaporation rate is measured with an equipment which operates with gas feed temperatures in the range of 70 to 285°C, A diffusive transient model is presented in which the simultaneous transfer effects and surface bubble superheating are taken into account to calculate heat and mass transfer coefficients and flow rates. The modeling equations are presented in the explicit form thus permitting the direct calculations of heat and mass transfer rates during the evaporation of a liquid and the testing the predicted values with experimental results. A comparison between the simultaneous and the superheating models showed that at higher gas temperatures and higher residence times , both modeIs reproduce satisfactorily the operational conditions. in order to verify the equipment performance to obtain the bubbling time needed for the attainment of steady state, the liquid equilibrium temperature was theoretically calculated taking into a account the simultaneous and the superheating effects, being these results compared with the experimental values.