{"id":51437,"date":"2020-01-27T13:07:36","date_gmt":"2020-01-27T12:07:36","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-processo-isotermico-e-processo-adiabatico-definicao\/"},"modified":"2020-01-27T13:16:56","modified_gmt":"2020-01-27T12:16:56","slug":"o-que-e-processo-isotermico-e-processo-adiabatico-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-processo-isotermico-e-processo-adiabatico-definicao\/","title":{"rendered":"O que \u00e9 processo isot\u00e9rmico e processo adiab\u00e1tico – defini\u00e7\u00e3o"},"content":{"rendered":"
\n
Um processo adiab\u00e1tico n\u00e3o \u00e9 necessariamente um processo isot\u00e9rmico, nem um processo isot\u00e9rmico \u00e9 necessariamente adiab\u00e1tico. Caracter\u00edsticas dos processos adiab\u00e1ticos e isot\u00e9rmicos. Engenharia T\u00e9rmica<\/div>\n<\/div>\n
<\/div>\n
\n

Processo isot\u00e9rmico<\/h2>\n

Um\u00a0<\/span>processo isot\u00e9rmico<\/span><\/strong>\u00a0\u00e9 um\u00a0<\/span>processo termodin\u00e2mico<\/span><\/strong><\/a>\u00a0, no qual a\u00a0<\/span>temperatura<\/span><\/strong>\u00a0do sistema\u00a0<\/span>permanece constante<\/span><\/strong>\u00a0(T = const).\u00a0A transfer\u00eancia de calor para dentro ou para fora do sistema geralmente deve ocorrer a uma taxa t\u00e3o lenta, a fim de se ajustar continuamente \u00e0 temperatura do reservat\u00f3rio atrav\u00e9s da troca de calor.\u00a0Em cada um desses estados, o\u00a0<\/span>equil\u00edbrio t\u00e9rmico<\/span><\/strong><\/a>\u00a0\u00e9 mantido.<\/span><\/p>\n

Para um\u00a0<\/span>g\u00e1s ideal<\/span><\/strong><\/a>e um processo politr\u00f3pico, o caso\u00a0<\/span>n = 1<\/span><\/em><\/strong>\u00a0corresponde a um processo\u00a0<\/span>isot\u00e9rmico<\/span><\/strong>\u00a0(temperatura constante).\u00a0Ao contr\u00e1rio do\u00a0<\/span>processo adiab\u00e1tico<\/span><\/strong><\/a>\u00a0, no qual\u00a0<\/span>n = \u03ba<\/span><\/i><\/strong>\u00a0\u00a0 e\u00a0<\/span><\/em>um sistema n\u00e3o trocam calor com o ambiente (Q = 0;\u00a0<\/span><\/em>\u2206T \u2260 0\u00a0<\/span><\/em>)\u00a0<\/span><\/em>, em um processo isot\u00e9rmico n\u00e3o h\u00e1 altera\u00e7\u00e3o na energia interna (devido a \u2206T = 0 ) e, portanto,\u00a0<\/span><\/em>\u0394U = 0 (para gases ideais) e Q \u2260 0.<\/span><\/em>\u00a0Um processo adiab\u00e1tico n\u00e3o \u00e9 necessariamente um processo isot\u00e9rmico, nem um processo isot\u00e9rmico \u00e9 necessariamente adiab\u00e1tico.<\/span><\/p>\n

Na engenharia, mudan\u00e7as de fase, como evapora\u00e7\u00e3o ou fus\u00e3o, s\u00e3o processos isot\u00e9rmicos quando, como geralmente ocorre, ocorrem a press\u00e3o e temperatura constantes.<\/span><\/p>\n

<\/div>\n

Processo isot\u00e9rmico e a primeira lei<\/span><\/h2>\n

A forma cl\u00e1ssica da\u00a0<\/span>primeira lei da termodin\u00e2mica<\/span><\/a>\u00a0\u00e9 a seguinte equa\u00e7\u00e3o:<\/span><\/p>\n

dU = dQ – dW<\/span><\/strong><\/p>\n

Nesta equa\u00e7\u00e3o, dW \u00e9 igual a\u00a0<\/span>dW = pdV<\/span><\/strong>\u00a0e \u00e9 conhecido como\u00a0<\/span>trabalho de fronteira<\/span><\/a>\u00a0.<\/span><\/p>\n

No\u00a0<\/span>processo isot\u00e9rmico<\/span><\/strong>\u00a0e no\u00a0<\/span>g\u00e1s ideal<\/span><\/strong><\/a>\u00a0, todo o calor adicionado ao sistema ser\u00e1 usado para realizar o trabalho:<\/span><\/p>\n

Processo isot\u00e9rmico (dU = 0):<\/span><\/strong><\/p>\n

dU = 0 = Q – W \u2192 W = Q \u00a0\u00a0<\/span><\/strong>(para g\u00e1s ideal)<\/span><\/em><\/p>\n

O\u00a0<\/span>processo isot\u00e9rmico\u00a0<\/span><\/strong>\u00a0pode ser expresso com a\u00a0<\/span>lei do g\u00e1s ideal<\/span><\/strong>\u00a0como:<\/span><\/p>\n

pV = constante<\/span><\/em><\/strong><\/p>\n

ou<\/span><\/p>\n

p\u00a0<\/span>1<\/span><\/sub>\u00a0V\u00a0<\/span>1<\/span><\/sub>\u00a0\u00a0= p\u00a0<\/span>2<\/span><\/sub>\u00a0V\u00a0<\/span>2<\/span><\/sub><\/strong><\/em><\/p>\n

Em um diagrama pV, o processo ocorre ao longo de uma linha (chamada uma isot\u00e9rmica) que tem a equa\u00e7\u00e3o\u00a0<\/span>p = constante \/ V.<\/span><\/strong><\/p>\n<\/div>\n

 <\/p>\n

Processo Adiab\u00e1tico<\/span><\/h2>\n

Um\u00a0<\/span>processo adiab\u00e1tico<\/span><\/strong>\u00a0\u00e9 um\u00a0<\/span>processo termodin\u00e2mico<\/span><\/a>\u00a0, no qual n\u00e3o\u00a0<\/span>h\u00e1 transfer\u00eancia de calor para<\/span><\/strong>\u00a0dentro ou para fora do sistema (Q = 0).\u00a0O sistema pode ser considerado\u00a0<\/span>perfeitamente isolado<\/span><\/strong>\u00a0.\u00a0Em um processo adiab\u00e1tico, a energia \u00e9 transferida apenas como trabalho.\u00a0A suposi\u00e7\u00e3o de que n\u00e3o h\u00e1 transfer\u00eancia de calor \u00e9 muito importante, pois podemos usar a aproxima\u00e7\u00e3o adiab\u00e1tica apenas em\u00a0<\/span>processos muito r\u00e1pidos<\/span><\/strong>\u00a0.\u00a0Nesses processos r\u00e1pidos, n\u00e3o h\u00e1 tempo suficiente para que a transfer\u00eancia de energia como calor ocorra de ou para o sistema.<\/span><\/p>\n

Em dispositivos reais (como turbinas, bombas e compressores)\u00a0ocorrem\u00a0<\/span>perdas<\/span><\/strong>\u00a0e\u00a0perdas de calor<\/strong>\u00a0no processo de combust\u00e3o, mas essas perdas s\u00e3o geralmente baixas em compara\u00e7\u00e3o com o fluxo geral de energia e podemos aproximar alguns processos termodin\u00e2micos pelo processo adiab\u00e1tico.<\/span><\/p>\n

<\/div>\n

Processo Adiab\u00e1tico e a Primeira Lei<\/span><\/h2>\n

Para um sistema fechado, podemos escrever a\u00a0\u00a0<\/span>primeira lei da termodin\u00e2mica em termos de entalpia<\/span><\/a><\/strong>\u00a0:<\/span><\/p>\n

dH = dQ + Vdp<\/span><\/strong><\/p>\n

Nesta equa\u00e7\u00e3o, o termo\u00a0<\/span>Vdp<\/span><\/strong>\u00a0\u00e9 um\u00a0<\/span>trabalho de processo de fluxo<\/span><\/a>\u00a0.\u00a0<\/span><\/strong>Este trabalho, Vdp, \u00e9 usado para sistemas de fluxo aberto, como uma turbina ou uma bomba na qual existe um “dp”, ou seja, mudan\u00e7a de press\u00e3o.\u00a0Como pode ser visto, essa forma de lei\u00a0<\/span>simplifica a descri\u00e7\u00e3o da transfer\u00eancia de energia<\/span><\/strong>\u00a0.\u00a0No processo adiab\u00e1tico, a\u00a0<\/span>mudan\u00e7a de entalpia<\/span><\/strong>\u00a0\u00e9 igual ao\u00a0<\/span>trabalho do processo de fluxo<\/span><\/strong>\u00a0realizado no ou pelo sistema:<\/span><\/p>\n

Processo adiab\u00e1tico (dQ = 0):<\/span><\/strong><\/p>\n

dH = Vdp \u2192 W = H\u00a0<\/span><\/strong>2<\/span><\/sub><\/strong>\u00a0– H\u00a0<\/span><\/strong>1<\/span><\/sub><\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u2192 H\u00a0<\/span><\/strong>2<\/span><\/sub><\/strong>\u00a0– H\u00a0<\/span><\/strong>1<\/span><\/sub><\/strong>\u00a0=\u00a0<\/span>C\u00a0<\/span><\/em><\/strong>P<\/span><\/sub><\/em><\/strong>\u00a0(T\u00a0<\/span><\/em><\/strong>2<\/span><\/sub><\/em><\/strong>\u00a0– T\u00a0<\/span><\/em><\/strong>1<\/span><\/sub><\/em><\/strong>\u00a0) \u00a0\u00a0\u00a0<\/span><\/em><\/strong>\u00a0(para um\u00a0\u00a0<\/span>g\u00e1s ideal<\/span><\/a>\u00a0)<\/span><\/em><\/p>\n

 <\/p>\n

\n
\n

Expans\u00e3o Adiab\u00e1tica<\/span><\/h2>\n
\"Diagrama<\/a>
Assuma uma expans\u00e3o adiab\u00e1tica de h\u00e9lio (3 \u2192 4) em uma turbina a g\u00e1s (ciclo de Brayton).<\/span><\/figcaption><\/figure>\n<\/div>\n<\/div>\n
\n
\n
<\/div>\n

Expans\u00e3o Livre – Expans\u00e3o Joule<\/span><\/h2>\n

Esses s\u00e3o\u00a0<\/span>processos adiab\u00e1ticos<\/span><\/strong><\/a>\u00a0nos quais\u00a0<\/span>nenhuma transfer\u00eancia de calor<\/span><\/strong>\u00a0ocorre entre o sistema e seu ambiente e\u00a0<\/span>nenhum trabalho \u00e9 realizado<\/span><\/strong>\u00a0no sistema.\u00a0Esses tipos de processos adiab\u00e1ticos s\u00e3o chamados de\u00a0<\/span>expans\u00e3o livre<\/span><\/strong>\u00a0.\u00a0\u00c9 um\u00a0<\/span>processo irrevers\u00edvel<\/span><\/strong>\u00a0no qual um g\u00e1s se expande para uma c\u00e2mara evacuada isolada.\u00a0\u00c9 tamb\u00e9m chamado de\u00a0<\/span>expans\u00e3o Joule<\/span><\/strong>\u00a0.\u00a0Para um g\u00e1s ideal, a temperatura n\u00e3o muda\u00a0<\/span>(isso significa que o processo tamb\u00e9m \u00e9\u00a0<\/span>isot\u00e9rmico<\/span>\u00a0)<\/span><\/strong>\u00a0; no entanto, os gases reais sofrem uma mudan\u00e7a de temperatura durante a expans\u00e3o livre.\u00a0Na expans\u00e3o livre Q = W = 0, e a primeira lei exige que:<\/span><\/p>\n

dE\u00a0<\/span><\/strong>int<\/span><\/sub><\/strong>\u00a0= 0<\/span><\/strong><\/p>\n

Uma expans\u00e3o livre n\u00e3o pode ser plotada em um diagrama PV, porque o processo \u00e9 r\u00e1pido, n\u00e3o quase est\u00e1tico.\u00a0Os estados intermedi\u00e1rios n\u00e3o s\u00e3o estados de equil\u00edbrio e, portanto, a press\u00e3o n\u00e3o est\u00e1 claramente definida.<\/span><\/p>\n<\/div>\n<\/div>\n

 <\/p>\n

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……………………………………………………………………………………………………………………………….<\/div>\n
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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<\/div>\n","protected":false},"excerpt":{"rendered":"

Um processo adiab\u00e1tico n\u00e3o \u00e9 necessariamente um processo isot\u00e9rmico, nem um processo isot\u00e9rmico \u00e9 necessariamente adiab\u00e1tico. Caracter\u00edsticas dos processos adiab\u00e1ticos e isot\u00e9rmicos. Engenharia T\u00e9rmica Processo isot\u00e9rmico Um\u00a0processo isot\u00e9rmico\u00a0\u00e9 um\u00a0processo termodin\u00e2mico\u00a0, no qual a\u00a0temperatura\u00a0do sistema\u00a0permanece constante\u00a0(T = const).\u00a0A transfer\u00eancia de calor para dentro ou para fora do sistema geralmente deve ocorrer a uma taxa t\u00e3o lenta, … 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 processo isot\u00e9rmico e processo adiab\u00e1tico - defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"Um processo adiab\u00e1tico n\u00e3o \u00e9 necessariamente um processo isot\u00e9rmico, nem um processo isot\u00e9rmico \u00e9 necessariamente adiab\u00e1tico. Caracter\u00edsticas dos processos adiab\u00e1ticos e isot\u00e9rmicos. 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