{"id":48521,"date":"2019-11-11T00:14:33","date_gmt":"2019-11-10T23:14:33","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-entalpia-em-unidades-extensivas-definicao\/"},"modified":"2020-01-29T13:36:23","modified_gmt":"2020-01-29T12:36:23","slug":"o-que-e-entalpia-em-unidades-extensivas-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-entalpia-em-unidades-extensivas-definicao\/","title":{"rendered":"O que \u00e9 entalpia em unidades extensivas – Defini\u00e7\u00e3o"},"content":{"rendered":"
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A entalpia \u00e9 uma quantidade extensa, depende do tamanho do sistema ou da quantidade de subst\u00e2ncia que ele cont\u00e9m.\u00a0A unidade SI de entalpia \u00e9 o joule (J).\u00a0Engenharia T\u00e9rmica<\/div>\n<\/div>\n
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Entalpia em unidades extensivas<\/h2>\n
\"Propriedades<\/a>
Propriedades extensivas e intensivas do meio no pressurizador.<\/figcaption><\/figure>\n

H = U + pV<\/strong><\/em><\/p>\n

A entalpia<\/strong><\/a>\u00a0\u00a0\u00e9 uma quantidade extensa, depende do tamanho do sistema ou da quantidade de subst\u00e2ncia que ele cont\u00e9m.\u00a0A unidade SI de entalpia \u00e9 o joule (J).\u00a0\u00c9 a energia contida no sistema, excluindo a energia cin\u00e9tica do movimento do sistema como um todo e a energia potencial do sistema como um todo devido a campos de for\u00e7a externos.\u00a0\u00c9 a quantidade termodin\u00e2mica equivalente ao\u00a0conte\u00fado total de calor<\/strong>\u00a0de um sistema.<\/p>\n

Por outro lado, a energia pode ser armazenada nas liga\u00e7\u00f5es qu\u00edmicas entre os \u00e1tomos que comp\u00f5em as mol\u00e9culas.\u00a0Esse armazenamento de energia no n\u00edvel at\u00f4mico inclui energia associada a estados orbitais de el\u00e9trons, rota\u00e7\u00e3o nuclear e for\u00e7as de liga\u00e7\u00e3o no n\u00facleo.<\/p>\n

A entalpia<\/strong>\u00a0\u00e9 representada pelo s\u00edmbolo\u00a0H<\/strong>\u00a0, e a altera\u00e7\u00e3o na entalpia em um processo \u00e9\u00a0H\u00a02<\/sub>\u00a0– H\u00a01<\/sub><\/strong>\u00a0.<\/p>\n

Existem express\u00f5es em termos de vari\u00e1veis \u200b\u200bmais familiares, como\u00a0temperatura<\/a>\u00a0e\u00a0press\u00e3o<\/a>\u00a0:<\/p>\n

dH = C\u00a0p<\/sub>\u00a0dT + V (1-aT) dp<\/strong><\/em><\/p>\n

Onde\u00a0C\u00a0p<\/sub><\/strong>\u00a0\u00e9 a\u00a0capacidade calor\u00edfica a press\u00e3o constante<\/strong>\u00a0e\u00a0\u03b1<\/em><\/strong>\u00a0\u00e9 o coeficiente de expans\u00e3o t\u00e9rmica (c\u00fabico).\u00a0Para o g\u00e1s ideal \u03b1T = 1 e, portanto:<\/p>\n

dH = C\u00a0p<\/sub>\u00a0dT<\/em><\/strong><\/p>\n<\/div>\n<\/div>\n

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Exemplo: Pist\u00e3o sem atrito – Calor – Entalpia<\/span><\/h2>\n
\"Entalpia<\/a>
Calcule a temperatura final, se 3000 kJ de calor forem adicionados.<\/span><\/figcaption><\/figure>\n

Um pist\u00e3o sem atrito \u00e9 usado para proporcionar uma press\u00e3o constante de\u00a0<\/span>500 kPa<\/span><\/strong>\u00a0num cilindro contendo vapor (\u00a0<\/span>vapor sobreaquecido<\/span><\/a>\u00a0) de um volume de\u00a0<\/span>2 m\u00a0<\/span>3<\/span><\/sup><\/strong>\u00a0\u00a0a\u00a0<\/span>500 K<\/span><\/strong>\u00a0.\u00a0Calcule a temperatura final, se\u00a0<\/span>3000 kJ<\/span><\/strong>\u00a0de\u00a0<\/span>calor<\/span><\/strong>\u00a0forem adicionados.<\/span><\/p>\n

Solu\u00e7\u00e3o:<\/span><\/strong><\/p>\n

Usando\u00a0<\/span>tabelas de vapor<\/span><\/a>\u00a0, sabemos que a\u00a0<\/span>entalpia espec\u00edfica<\/span><\/strong>\u00a0desse vapor (500 kPa; 500 K) \u00e9 de cerca de\u00a0<\/span>2912 kJ \/ kg<\/span><\/strong>\u00a0.\u00a0Como nessa condi\u00e7\u00e3o o vapor possui densidade de 2,2 kg \/ m\u00a0<\/span>3<\/span><\/sup>\u00a0, sabemos que h\u00e1 cerca de\u00a0<\/span>4,4 kg de vapor<\/span><\/strong>\u00a0no pist\u00e3o na entalpia de 2912 kJ \/ kg x 4,4 kg =\u00a0<\/span>12812 kJ<\/span><\/strong>\u00a0.<\/span><\/p>\n

Quando usamos simplesmente\u00a0<\/span>Q = H\u00a0<\/span>2<\/span><\/sub>\u00a0– H\u00a0<\/span>1<\/span><\/sub><\/strong>\u00a0, a entalpia resultante do vapor ser\u00e1:<\/span><\/p>\n

H\u00a0<\/span>2<\/span><\/sub>\u00a0= H\u00a0<\/span>1<\/span><\/sub>\u00a0+ Q =\u00a0<\/span>15812 kJ<\/span><\/strong><\/p>\n

Nas\u00a0<\/span>tabelas de vapor<\/span><\/strong>\u00a0, esse vapor superaquecido (15812 \/ 4,4 = 3593 kJ \/ kg) ter\u00e1 uma temperatura de\u00a0<\/span>828 K (555 \u00b0 C)<\/span><\/strong>\u00a0.\u00a0Uma vez que nesta entalpia do vapor tem a densidade de 1,31 kg \/ m\u00a0<\/span>3<\/span><\/sup>\u00a0, \u00e9 \u00f3bvio que se expandiu em cerca de 2,2 \/ 1,31 = 1,67 (+ 67%).\u00a0Portanto, o volume resultante \u00e9 de 2 m\u00a0<\/span>3<\/span><\/sup>\u00a0x 1,67 = 3,34 m\u00a0<\/span>3<\/span><\/sup>\u00a0e \u2206V = 3,34 m\u00a0<\/span>3<\/span><\/sup>\u00a0– 2 m\u00a0<\/span>3<\/span><\/sup>\u00a0= 1,34 m\u00a0<\/span>3<\/span><\/sup>\u00a0.<\/span><\/p>\n

A\u00a0parte\u00a0<\/span>p\u2206V<\/span><\/strong>\u00a0da entalpia, ou seja, o trabalho realizado \u00e9:<\/span><\/p>\n

W = p\u2206V = 500 000 Pa x 1,34 m\u00a0<\/span>3<\/span><\/sup>\u00a0= 670 kJ<\/span><\/strong><\/p>\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<\/figcaption><\/figure>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

A entalpia \u00e9 uma quantidade extensa, depende do tamanho do sistema ou da quantidade de subst\u00e2ncia que ele cont\u00e9m.\u00a0A unidade SI de entalpia \u00e9 o joule (J).\u00a0Engenharia T\u00e9rmica Entalpia em unidades extensivas Propriedades extensivas e intensivas do meio no pressurizador. H = U + pV A entalpia\u00a0\u00a0\u00e9 uma quantidade extensa, depende do tamanho do sistema … 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 entalpia em unidades extensivas - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"A entalpia \u00e9 uma quantidade extensa, depende do tamanho do sistema ou da quantidade de subst\u00e2ncia que ele cont\u00e9m. A unidade SI de entalpia \u00e9 o joule (J). 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