{"id":47232,"date":"2019-11-03T17:26:08","date_gmt":"2019-11-03T16:26:08","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-mcadams-thom-correlacao-de-chen-ebulicao-de-nucleados-definicao\/"},"modified":"2020-01-22T17:01:48","modified_gmt":"2020-01-22T16:01:48","slug":"o-que-e-mcadams-thom-correlacao-de-chen-ebulicao-de-nucleados-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-mcadams-thom-correlacao-de-chen-ebulicao-de-nucleados-definicao\/","title":{"rendered":"O que \u00e9 McAdams – Thom – Correla\u00e7\u00e3o de Chen – Ebuli\u00e7\u00e3o de nucleados – Defini\u00e7\u00e3o"},"content":{"rendered":"
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McAdams – Thom – Correla\u00e7\u00e3o de Chen – Ebuli\u00e7\u00e3o Nucleada.\u00a0Essa correla\u00e7\u00e3o pode ser usada para c\u00e1lculos de transfer\u00eancia de calor na ebuli\u00e7\u00e3o do fluxo (ou na ebuli\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada).\u00a0Engenharia T\u00e9rmica<\/div>\n<\/div>\n
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Ebuli\u00e7\u00e3o Nucleada – Ebuli\u00e7\u00e3o por Fluxo<\/h2>\n

\"Ebuli\u00e7\u00e3o<\/a>Na\u00a0ebuli\u00e7\u00e3o do fluxo<\/strong>\u00a0(ou\u00a0ebuli\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada<\/strong>\u00a0), o fluxo de fluido \u00e9 for\u00e7ado sobre uma superf\u00edcie por meios externos, como uma bomba, bem como por efeitos de flutuabilidade.\u00a0Portanto, a ebuli\u00e7\u00e3o do fluxo \u00e9 sempre acompanhada por outros efeitos de convec\u00e7\u00e3o.\u00a0As condi\u00e7\u00f5es dependem fortemente da geometria, que pode envolver fluxo externo sobre placas e cilindros aquecidos ou fluxo interno (duto).\u00a0Nos reatores nucleares, a maioria dos regimes de ebuli\u00e7\u00e3o \u00e9 apenas fervura de convec\u00e7\u00e3o for\u00e7ada.\u00a0A ebuli\u00e7\u00e3o do fluxo tamb\u00e9m \u00e9 classificada como ebuli\u00e7\u00e3o externa e interna, dependendo de o fluido ser for\u00e7ado a fluir sobre uma superf\u00edcie aquecida ou dentro de um canal aquecido.<\/p>\n

A ebuli\u00e7\u00e3o do fluxo interno \u00e9 muito mais complicada por natureza do que a ebuli\u00e7\u00e3o do fluxo externo, porque n\u00e3o h\u00e1 superf\u00edcie livre para o vapor escapar e, portanto, o l\u00edquido e o vapor s\u00e3o for\u00e7ados a fluir juntos.\u00a0O fluxo bif\u00e1sico em um tubo exibe diferentes regimes de ebuli\u00e7\u00e3o do fluxo, dependendo das quantidades relativas das fases l\u00edquida e de vapor.\u00a0Portanto, a ebuli\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada interna \u00e9 comumente referida como\u00a0fluxo bif\u00e1sico<\/strong>\u00a0.<\/p>\n<\/div>\n<\/div>\n

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Correla\u00e7\u00f5es de ebuli\u00e7\u00e3o de nucleados – ebuli\u00e7\u00e3o por fluxo<\/h2>\n<\/div>\n<\/div>\n
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Correla\u00e7\u00e3o de McAdams<\/h2>\n

Na ebuli\u00e7\u00e3o de nucleados totalmente desenvolvida com refrigerante saturado, a temperatura da parede \u00e9 determinada pelo fluxo de calor e press\u00e3o locais e depende apenas ligeiramente do\u00a0n\u00famero de Reynolds<\/a>\u00a0.\u00a0Para \u00e1gua sub-resfriada a press\u00f5es absolutas entre 0,1 – 0,6 MPa, a\u00a0correla\u00e7\u00e3o de McAdams<\/strong>\u00a0fornece:<\/p>\n

\"ebuli\u00e7\u00e3o<\/a><\/p>\n<\/div>\n<\/div>\n

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Correla\u00e7\u00e3o de Thom<\/span><\/h2>\n

A\u00a0<\/span>correla\u00e7\u00e3o de Thom<\/span><\/strong>\u00a0\u00e9 para a ebuli\u00e7\u00e3o do fluxo (sub-resfriado ou saturado a press\u00f5es de at\u00e9 cerca de 20 MPa) sob condi\u00e7\u00f5es em que a contribui\u00e7\u00e3o da ebuli\u00e7\u00e3o nucleada predomina sobre a convec\u00e7\u00e3o for\u00e7ada.\u00a0Essa correla\u00e7\u00e3o \u00e9 \u00fatil para a estimativa aproximada da diferen\u00e7a de temperatura esperada, dado o fluxo de calor:<\/span><\/p>\n

\"ebuli\u00e7\u00e3o<\/a><\/p>\n<\/div>\n<\/div>\n

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Correla\u00e7\u00e3o de Chen<\/span><\/h2>\n

Em 1963,\u00a0<\/span>Chen<\/span><\/strong>\u00a0prop\u00f4s a primeira correla\u00e7\u00e3o de ebuli\u00e7\u00e3o do fluxo para a evapora\u00e7\u00e3o em tubos verticais, a fim de obter amplo uso.\u00a0<\/span>A correla\u00e7\u00e3o de Chen<\/span><\/strong>\u00a0inclui os\u00a0<\/span>coeficientes de transfer\u00eancia de calor<\/span><\/a>\u00a0devido \u00e0\u00a0<\/span>ebuli\u00e7\u00e3o dos nucleados<\/span><\/strong>\u00a0, bem como os\u00a0<\/span>mecanismos convectivos for\u00e7ados<\/span><\/strong>.\u00a0Deve-se notar que, em fra\u00e7\u00f5es de vapor mais altas, o coeficiente de transfer\u00eancia de calor varia fortemente com a vaz\u00e3o.\u00a0A velocidade do fluxo em um n\u00facleo pode ser muito alta, causando turbul\u00eancias muito altas.\u00a0Esse mecanismo de transfer\u00eancia de calor foi referido como “evapora\u00e7\u00e3o for\u00e7ada por convec\u00e7\u00e3o”.\u00a0Nenhum crit\u00e9rio adequado foi estabelecido para determinar a transi\u00e7\u00e3o da ebuli\u00e7\u00e3o nucleada para a vaporiza\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada.\u00a0No entanto, Chen desenvolveu uma correla\u00e7\u00e3o \u00fanica v\u00e1lida para a ebuli\u00e7\u00e3o nucleada e a vaporiza\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada, para condi\u00e7\u00f5es de ebuli\u00e7\u00e3o saturada e estendida para incluir a ebuli\u00e7\u00e3o sub-resfriada por outros.\u00a0Chen prop\u00f4s uma correla\u00e7\u00e3o em que o coeficiente de transfer\u00eancia de calor \u00e9 a\u00a0<\/span>soma<\/span><\/strong>\u00a0de um\u00a0componente de\u00a0<\/span>convec\u00e7\u00e3o for\u00e7ada<\/span><\/strong>\u00a0e uma\u00a0<\/span>ebuli\u00e7\u00e3o nucleada<\/span><\/strong>componente.\u00a0Deve-se observar que a correla\u00e7\u00e3o de ebuli\u00e7\u00e3o de nucleados de Forster e Zuber (1955) \u00e9 usada para calcular o coeficiente de transfer\u00eancia de calor em ebuli\u00e7\u00e3o de nucleados, h\u00a0<\/span>FZ<\/span><\/sub>\u00a0e a correla\u00e7\u00e3o de fluxo turbulento de Dittus-Boelter (1930) \u00e9 usada para calcular a fase l\u00edquida coeficiente de transfer\u00eancia de calor por convec\u00e7\u00e3o, h\u00a0<\/span>l<\/span><\/sub>\u00a0.<\/span><\/p>\n

\"Correla\u00e7\u00e3o<\/a><\/p>\n

O fator de supress\u00e3o de ebuli\u00e7\u00e3o dos nucleados, S, \u00e9 a raz\u00e3o entre o superaquecimento efetivo e o superaquecimento da parede.\u00a0\u00c9 respons\u00e1vel pela diminui\u00e7\u00e3o da transfer\u00eancia de calor em ebuli\u00e7\u00e3o porque o superaquecimento efetivo na camada limite \u00e9 menor que o superaquecimento com base na temperatura da parede.\u00a0O multiplicador bif\u00e1sico, F, \u00e9 uma fun\u00e7\u00e3o do par\u00e2metro Martinelli \u03c7\u00a0<\/span>tt<\/span><\/sub>\u00a0.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

……………………………………………………………………………………………………………………………….<\/p>\n

Este artigo \u00e9 baseado na tradu\u00e7\u00e3o autom\u00e1tica do artigo original em ingl\u00eas. Para mais informa\u00e7\u00f5es, consulte o artigo em ingl\u00eas. Voc\u00ea pode nos ajudar. Se voc\u00ea deseja corrigir a tradu\u00e7\u00e3o, envie-a para: translations@nuclear-power.com ou preencha o formul\u00e1rio de tradu\u00e7\u00e3o on-line. Agradecemos sua ajuda, atualizaremos a tradu\u00e7\u00e3o o mais r\u00e1pido poss\u00edvel. Obrigado.<\/p>\n","protected":false},"excerpt":{"rendered":"

McAdams – Thom – Correla\u00e7\u00e3o de Chen – Ebuli\u00e7\u00e3o Nucleada.\u00a0Essa correla\u00e7\u00e3o pode ser usada para c\u00e1lculos de transfer\u00eancia de calor na ebuli\u00e7\u00e3o do fluxo (ou na ebuli\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada).\u00a0Engenharia T\u00e9rmica Ebuli\u00e7\u00e3o Nucleada – Ebuli\u00e7\u00e3o por Fluxo Na\u00a0ebuli\u00e7\u00e3o do fluxo\u00a0(ou\u00a0ebuli\u00e7\u00e3o por convec\u00e7\u00e3o for\u00e7ada\u00a0), o fluxo de fluido \u00e9 for\u00e7ado sobre uma superf\u00edcie por meios externos, … Ler mais<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[14],"tags":[],"yoast_head":"\nO que \u00e9 McAdams - Thom - Correla\u00e7\u00e3o de Chen - Ebuli\u00e7\u00e3o de nucleados - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"McAdams - Thom - Correla\u00e7\u00e3o de Chen - Ebuli\u00e7\u00e3o de Nucleados. 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