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Previous issue date: 2017-03-27 / Canais compostos s?o caracterizados por possu?rem canais principais, regi?es mais
largas onde o fluido escoa axialmente com maior facilidade, e canais secund?rios
(fendas) que s?o regi?es mais estreitas onde o fluido ? desacelerado devido aos
efeitos viscosos. Para determinar os coeficientes de transfer?ncia de calor e de atrito
nos canais compostos ? necess?rio entender o comportamento dos escoamentos
turbulentos que ocorrem neles, por?m isto continua sendo um desafio para a
engenharia. Estes canais apresentam, al?m do fluxo axial paralelo ao canal,
flutua??es na velocidade transversal que est?o associadas a estruturas de grande
escala denominadas de estruturas coerentes. Assim, neste trabalho buscou-se
analisar os efeitos do aparecimento dessas estruturas e as suas consequ?ncias para
o escoamento, tanto na parte din?mica como na t?rmica. Para isto foi utilizado uma
geometria empregada em trabalhos experimentais, que ? composta por um canal
retangular com um tubo interno, de di?metro D, que est? a uma dist?ncia W/D da
parede inferior do canal. O fluido escoa axialmente apenas na parte externa do tubo.
No total foram analisados cinco casos, modificando apenas a rela??o W/D
(espa?amento da fenda). Para examinar as caracter?sticas do escoamento turbulento
no interior deste canal, empregou-se o pacote ANSYS CFX 13 com o modelo de
turbul?ncia SAS-SST. Os resultados mostraram que quanto maior a rela??o W/D,
mais elevados foram os valores do Fator de Desempenho T?rmico. Este fator ? uma
rela??o entre o n?mero de Nusselt e o fator de atrito e, quanto maior seu valor,
melhor ? o desempenho t?rmico do canal. Em rela??o as estruturas coerentes, nos
canais em que surgiram, elas t?m uma grande influ?ncia sobre os escoamentos, j?
que essas estruturas acabam elevando os valores locais dos coeficientes de
transfer?ncia de calor e de atrito superficial, o que torna esse fen?meno
indispens?vel nos projetos e an?lises de seguran?a de equipamentos que possuem
fendas. / Compound channels are characterized by having main channels, wider regions
where the fluid flows axially more easily, and narrower regions (gaps) where the fluid
is decelerated due to the viscous effects. In order to determine the heat transfer
coefficients in these channels it is necessary to understand the behavior of the
turbulent flows in them, but this remains a challenge for engineering. These channels
have, in addition to axial flow parallel to the channel, a cross flow velocity in the gap
region that are associated with large scale structures called coherent structures.
Thus, the goal of this work is to compare the effects on the appearance of coherent
structures of large scale and its consequences for the flow in dynamic and thermal
characteristics. To accomplish this, the same geometry used in the experimental
works was applied, which is composed of a rectangular channel with an internal tube
of diameter D and it is located at a distance W/D from the lower wall of the channel.
The fluid flows axially only on the outside of the tube. In total, five different cases
were analyzed, modifying only the W/D ratio (gap distance). To examine the
characteristics of the turbulent flow inside this channel, ANSYS CFX13 with SASSST
turbulence model was applied. The results showed that the W/D ratio increase
also caused an increase in the values of the Thermal Performance Factor. This factor
is a relationship between the Nusselt number and the friction factor, and the higher
its value, better is the thermal performance of the channel. In relation to the coherent
structures, in the channels in which they arise, they have a great influence on the
flows, since these structures end up raising the local values of heat transfer and
friction coefficients, making this phenomenon indispensable in projects and safety
analyzes of equipment with gap.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/23691 |
| Date | 27 March 2017 |
| Creators | Aoyama, Guilherme Keiti |
| Contributors | 42635926034, http://lattes.cnpq.br/7400466085627528, Sanches, F?bio Dalmazzo, 70244472300, http://lattes.cnpq.br/2231659567413659, Goulart, Jhon Nero Vaz, 77808711004, http://lattes.cnpq.br/7863382021033244, Bessa, Kleiber Lima de, 01864959436, http://lattes.cnpq.br/3825553608740400, Souza, Sandi Itamar Schafer de |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM ENGENHARIA MEC?NICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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