{"id":47116,"date":"2019-11-03T07:36:19","date_gmt":"2019-11-03T06:36:19","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-isolamento-termico-isolador-termico-definicao\/"},"modified":"2020-01-22T14:07:06","modified_gmt":"2020-01-22T13:07:06","slug":"o-que-e-isolamento-termico-isolador-termico-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-isolamento-termico-isolador-termico-definicao\/","title":{"rendered":"O que \u00e9 isolamento t\u00e9rmico &#8211; Isolador t\u00e9rmico &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">O isolamento t\u00e9rmico \u00e9 o processo de redu\u00e7\u00e3o da transfer\u00eancia de calor entre os objetos em contato t\u00e9rmico ou na faixa de influ\u00eancia radiativa.\u00a0Isolamento t\u00e9rmico<\/div>\n<\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Isolamento t\u00e9rmico<\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-insulation-expanded-polystyrene.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-21147 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-insulation-expanded-polystyrene-167x300.png\" alt=\"isolamento t\u00e9rmico - poliestireno expandido\" width=\"167\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-insulation-expanded-polystyrene-167x300.png\" \/><\/a><strong>O isolamento t\u00e9rmico<\/strong>\u00a0\u00e9 o processo de redu\u00e7\u00e3o da\u00a0<a title=\"Transfer\u00eancia de calor\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-transferencia-de-calor-definicao\/\">transfer\u00eancia<\/a>\u00a0de\u00a0<a title=\"Transfer\u00eancia de calor\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-transferencia-de-calor-definicao\/\">calor<\/a>\u00a0entre os objetos em contato t\u00e9rmico ou na faixa de influ\u00eancia radiativa.\u00a0<strong>Os isolamentos t\u00e9rmicos<\/strong>\u00a0consistem em\u00a0<strong>materiais<\/strong>\u00a0de baixa condutividade t\u00e9rmica combinados para obter uma\u00a0<a title=\"O que \u00e9 condutividade t\u00e9rmica - Defini\u00e7\u00e3o\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/thermal-conduction\/thermal-conductivity\/what-is-thermal-conductivity-definition\/\">condutividade t\u00e9rmica do<\/a>\u00a0sistema ainda mais baixa\u00a0.\u00a0O isolamento t\u00e9rmico pode ser alcan\u00e7ado com m\u00e9todos ou processos especialmente projetados, bem como com formas e materiais de objetos adequados.<\/p>\n<p>Veja tamb\u00e9m:\u00a0<a title=\"Condutividade t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-condutividade-termica-definicao\/\">Condutividade t\u00e9rmica<\/a><\/p>\n<p>Do ponto de vista microsc\u00f3pico, o transporte de\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-energia-interna-energia-termica-definicao\/\">energia t\u00e9rmica<\/a>\u00a0em s\u00f3lidos pode geralmente ser devido a dois efeitos:<\/p>\n<ul>\n<li><strong>a migra\u00e7\u00e3o de el\u00e9trons livres<\/strong><\/li>\n<li><strong>ondas vibracionais em treli\u00e7a (\u00a0<a title=\"O que \u00e9 Phonon - Defini\u00e7\u00e3o\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-phonon-definicao\/\">f\u00f4nons<\/a>\u00a0)<\/strong><\/li>\n<\/ul>\n<p>Quando el\u00e9trons e f\u00f4nons transportam energia t\u00e9rmica, levando \u00e0 transfer\u00eancia de calor por condu\u00e7\u00e3o em um s\u00f3lido, a condutividade t\u00e9rmica pode ser expressa como:<\/p>\n<p>k = k\u00a0<sub>e<\/sub>\u00a0+ k\u00a0<sub>ph<\/sub><\/p>\n<p><strong>Os metais<\/strong>\u00a0em geral t\u00eam\u00a0<strong>alta condutividade el\u00e9trica<\/strong>\u00a0e\u00a0<strong>alta condutividade t\u00e9rmica<\/strong>\u00a0.\u00a0Essas propriedades se originam especialmente\u00a0<strong>do<\/strong>\u00a0fato de seus\u00a0<strong>el\u00e9trons externos (el\u00e9trons livres) serem deslocalizados<\/strong>\u00a0.\u00a0Sua contribui\u00e7\u00e3o para a condutividade t\u00e9rmica \u00e9 muito alta e \u00e9 chamada de\u00a0<strong>condutividade t\u00e9rmica eletr\u00f4nica, k\u00a0<\/strong><strong><sub>e<\/sub><\/strong>\u00a0.\u00a0Como resultado, os metais s\u00e3o muito bons condutores t\u00e9rmicos em vez de isoladores t\u00e9rmicos.<\/p>\n<p>Para\u00a0<strong>s\u00f3lidos n\u00e3o met\u00e1licos<\/strong>\u00a0,\u00a0<strong>k<\/strong>\u00a0\u00e9 determinado principalmente por\u00a0<strong>k\u00a0<\/strong><strong><sub>ph<\/sub><\/strong>\u00a0, que aumenta \u00e0 medida que a frequ\u00eancia de intera\u00e7\u00f5es entre os \u00e1tomos e a rede diminui.\u00a0De fato, a condu\u00e7\u00e3o t\u00e9rmica em rede \u00e9 o mecanismo dominante de condu\u00e7\u00e3o t\u00e9rmica em n\u00e3o-metais, se n\u00e3o o \u00fanico.\u00a0Nos s\u00f3lidos, os \u00e1tomos vibram sobre suas posi\u00e7\u00f5es de equil\u00edbrio (estrutura cristalina).\u00a0As vibra\u00e7\u00f5es dos \u00e1tomos n\u00e3o s\u00e3o independentes uma da outra, mas s\u00e3o fortemente acopladas aos \u00e1tomos vizinhos.\u00a0A regularidade do arranjo de treli\u00e7a tem um efeito importante no\u00a0<strong>k\u00a0<\/strong><strong><sub>ph<\/sub><\/strong>\u00a0, com materiais cristalinos (bem ordenados), como o\u00a0<strong>quartzo,<\/strong>\u00a0com uma condutividade t\u00e9rmica mais alta que os materiais amorfos, como o vidro.<\/p>\n<p>\u00c9 preciso acrescentar que o\u00a0<strong>isolamento t\u00e9rmico<\/strong>\u00a0se baseia principalmente na\u00a0<strong>condutividade t\u00e9rmica muito baixa dos gases<\/strong>\u00a0.\u00a0Os gases possuem m\u00e1s propriedades de condu\u00e7\u00e3o t\u00e9rmica em compara\u00e7\u00e3o com l\u00edquidos e s\u00f3lidos e, portanto, s\u00e3o um bom material para isolamento se puderem ser presos (por exemplo, em uma\u00a0<strong>estrutura semelhante<\/strong>\u00a0a\u00a0<strong>espuma<\/strong>\u00a0).\u00a0Ar e outros gases geralmente s\u00e3o bons isolantes.\u00a0Mas o principal benef\u00edcio \u00e9 na\u00a0<strong>aus\u00eancia de convec\u00e7\u00e3o<\/strong>\u00a0.\u00a0Portanto, muitos materiais isolantes (por exemplo, poliestireno) funcionam simplesmente com um grande n\u00famero de\u00a0<strong>bolsas cheias<\/strong>\u00a0de\u00a0<strong>g\u00e1s<\/strong>\u00a0que\u00a0<strong>impedem a convec\u00e7\u00e3o em grande escala<\/strong>.\u00a0A altern\u00e2ncia entre bolsa de g\u00e1s e material s\u00f3lido faz com que o calor seja transferido atrav\u00e9s de muitas interfaces, causando uma r\u00e1pida diminui\u00e7\u00e3o no coeficiente de transfer\u00eancia de calor.<\/p>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<p><span>Deve-se notar que as perdas de calor de objetos mais quentes ocorrem por tr\u00eas mecanismos (individualmente ou em combina\u00e7\u00e3o):<\/span><\/p>\n<ul>\n<li><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conducao-termica-conducao-termica-definicao\/\"><strong><span>Condu\u00e7\u00e3o de calor<\/span><\/strong><\/a><\/li>\n<li><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conveccao-transferencia-de-calor-por-conveccao-definicao\/\"><strong><span>Convec\u00e7\u00e3o de calor<\/span><\/strong><\/a><\/li>\n<li><a title=\"Transfer\u00eancia de calor por radia\u00e7\u00e3o\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/radiation-heat-transfer\/thermal-radiation-radiant-heat\/\"><strong><span>Radia\u00e7\u00e3o t\u00e9rmica<\/span><\/strong><\/a><\/li>\n<\/ul>\n<p><span>At\u00e9 agora, n\u00e3o discutimos\u00a0<\/span><strong><span>a radia\u00e7\u00e3o t\u00e9rmica<\/span><\/strong><span>\u00a0como um modo de\u00a0<\/span><strong><span>perda<\/span><\/strong><span>\u00a0de\u00a0<strong>calor<\/strong>\u00a0.\u00a0<\/span><strong><span>A transfer\u00eancia de calor<\/span><\/strong><span>\u00a0por\u00a0<\/span><strong><span>radia\u00e7\u00e3o<\/span><\/strong><span>\u00a0\u00e9 mediada por\u00a0<strong>radia\u00e7\u00e3o eletromagn\u00e9tica<\/strong>\u00a0e, portanto, n\u00e3o requer nenhum meio para a transfer\u00eancia de calor.\u00a0De fato, a transfer\u00eancia de energia pela radia\u00e7\u00e3o \u00e9 mais r\u00e1pida (na velocidade da luz) e n\u00e3o sofre atenua\u00e7\u00e3o no v\u00e1cuo.\u00a0Qualquer material que tem uma temperatura acima\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-temperature-physics\/absolute-zero-temperature\/\"><span>do zero absoluto<\/span><\/a><span>\u00a0emite alguma\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/radiant-energy\/\"><strong><span>energia radiante<\/span><\/strong><\/a><span>\u00a0.\u00a0A maior\u00a0parte dessa\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/\"><span>energia<\/span><\/a><span>\u00a0est\u00e1 na regi\u00e3o\u00a0<\/span><strong><span>infravermelha<\/span><\/strong><span>\u00a0do espectro eletromagn\u00e9tico, embora parte dela esteja na regi\u00e3o vis\u00edvel.\u00a0Para diminuir esse tipo de transfer\u00eancia de calor, materiais com baixa emissividade devem ser usados.\u00a0o<\/span><strong><a title=\"Emissividade - Emissividade de Materiais\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/radiation-heat-transfer\/emissivity-emissivity-of-materials\/\"><span>A emissividade<\/span><\/a><span>\u00a0, \u03b5<\/span><\/strong><span>\u00a0, da superf\u00edcie de um material \u00e9 sua efic\u00e1cia na emiss\u00e3o de energia como<\/span><strong><span>\u00a0radia\u00e7\u00e3o t\u00e9rmica<\/span><\/strong><span>\u00a0e varia entre 0,0 e 1,0.\u00a0Em geral, os metais polidos t\u00eam emissividade muito baixa e, portanto, s\u00e3o amplamente utilizados para refletir a energia radiante de volta \u00e0 sua fonte, como no caso de<\/span><strong><span>\u00a0mantas<\/span><\/strong><span>\u00a0de<strong>\u00a0primeiros socorros<\/strong>\u00a0.<\/span><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Isolante t\u00e9rmico<\/span><\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Thermal-Insulators-Parameters.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-21157 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Thermal-Insulators-Parameters-225x300.png\" alt=\"Isoladores t\u00e9rmicos - Par\u00e2metros\" width=\"225\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Thermal-Insulators-Parameters-225x300.png\" \/><\/a><span>Como foi escrito, o\u00a0<\/span><strong><span>isolamento t\u00e9rmico<\/span><\/strong><span>\u00a0\u00e9 baseado no uso de subst\u00e2ncias com\u00a0<\/span><strong><span>condutividade t\u00e9rmica muito baixa<\/span><\/strong><span>\u00a0.\u00a0Estes materiais s\u00e3o conhecidos como\u00a0<\/span><strong><span>isoladores t\u00e9rmicos<\/span><\/strong><span>\u00a0.\u00a0Os isoladores t\u00e9rmicos comuns s\u00e3o l\u00e3, fibra de vidro, l\u00e3 de rocha, poliestireno, poliuretano e plumas de ganso etc. Esses materiais s\u00e3o condutores muito fracos de calor e, portanto, s\u00e3o bons isolantes t\u00e9rmicos.<\/span><\/p>\n<p><span>\u00c9 preciso acrescentar que o isolamento t\u00e9rmico se baseia principalmente na condutividade t\u00e9rmica muito baixa dos gases.\u00a0Os gases possuem m\u00e1s propriedades de condu\u00e7\u00e3o t\u00e9rmica em compara\u00e7\u00e3o com l\u00edquidos e s\u00f3lidos e, portanto, s\u00e3o um bom material para isolamento se puderem ser presos (por exemplo, em uma\u00a0<\/span><strong><span>estrutura semelhante<\/span><\/strong><span>\u00a0a\u00a0<strong>espuma<\/strong>\u00a0).\u00a0Ar e outros gases geralmente s\u00e3o bons isolantes.\u00a0Mas o principal benef\u00edcio \u00e9 na\u00a0<\/span><strong><span>aus\u00eancia de convec\u00e7\u00e3o<\/span><\/strong><span>\u00a0.\u00a0Portanto, muitos materiais isolantes (por exemplo, poliestireno) funcionam simplesmente tendo um grande n\u00famero de\u00a0<\/span><strong><span>bolsas cheias<\/span><\/strong><span>\u00a0de\u00a0<strong>g\u00e1s<\/strong>\u00a0que\u00a0<\/span><strong><span>impedem a convec\u00e7\u00e3o em grande escala<\/span><\/strong><span>\u00a0.\u00a0Em todos os tipos de isolamento t\u00e9rmico, a evacua\u00e7\u00e3o do ar no espa\u00e7o vazio reduzir\u00e1 ainda mais a condutividade t\u00e9rmica geral do isolador.<\/span><\/p>\n<p><span>A altern\u00e2ncia de bolsa de g\u00e1s e material s\u00f3lido faz com que o calor seja transferido atrav\u00e9s de\u00a0<\/span><strong><span>muitas interfaces,<\/span><\/strong><span>\u00a0causando uma r\u00e1pida diminui\u00e7\u00e3o no coeficiente de transfer\u00eancia de calor.<\/span><\/p>\n<p><span>No caso de\u00a0<\/span><strong><span>isolamento t\u00e9rmico por radia\u00e7\u00e3o<\/span><\/strong><span>\u00a0, podem ser utilizados isolamentos refletivos.\u00a0Os isolamentos refletivos geralmente s\u00e3o compostos de folhas paralelas multicamadas de alta refletividade, espa\u00e7adas para refletir a radia\u00e7\u00e3o t\u00e9rmica de volta \u00e0 sua fonte.<\/span><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Exemplo &#8211; Perda de calor atrav\u00e9s de uma parede<\/span><\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/heat-loss-through-wall-example-calculation.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-21148 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/heat-loss-through-wall-example-calculation-169x300.png\" alt=\"perda de calor atrav\u00e9s da parede - exemplo - c\u00e1lculo\" width=\"169\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/heat-loss-through-wall-example-calculation-169x300.png\" \/><\/a><span>Uma das principais fontes de\u00a0<\/span><strong><span>perda<\/span><\/strong><span>\u00a0de\u00a0<strong>calor<\/strong>\u00a0de uma casa \u00e9 atrav\u00e9s das paredes.\u00a0Calcule a taxa de\u00a0<\/span><a title=\"Densidade do fluxo de calor - Fluxo t\u00e9rmico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/introduction-to-heat-transfer\/heat-flux-density-thermal-flux\/\"><span>fluxo<\/span><\/a><span>\u00a0de\u00a0<a title=\"Densidade do fluxo de calor - Fluxo t\u00e9rmico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/introduction-to-heat-transfer\/heat-flux-density-thermal-flux\/\">calor<\/a>\u00a0atrav\u00e9s de uma parede com 3 mx 10 m de \u00e1rea (A = 30 m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0).\u00a0A parede tem 15 cm de espessura (L\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0) e \u00e9 feita de tijolos com\u00a0<\/span><a title=\"Condutividade t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-condutividade-termica-definicao\/\"><span>condutividade t\u00e9rmica<\/span><\/a><span>\u00a0de k\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0= 1,0 W \/ mK (isolador t\u00e9rmico ruim).\u00a0Suponha que as\u00a0<\/span><a title=\"O que \u00e9 temperatura - F\u00edsica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-temperatura-fisica-definicao\/\"><span>temperaturas<\/span><\/a><span>\u00a0interna e externa\u00a0sejam 22 \u00b0 C e -8 \u00b0 C, e os\u00a0<\/span><a title=\"Coeficiente de transfer\u00eancia de calor por convec\u00e7\u00e3o\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-coeficiente-de-transferencia-de-calor-por-conveccao-definicao\/\"><span>coeficientes de transfer\u00eancia de calor por convec\u00e7\u00e3o<\/span><\/a><span>\u00a0nos lados interno e externo sejam h\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0= 10 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0K e h\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0= 30 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>K, respectivamente.\u00a0Observe que esses coeficientes de convec\u00e7\u00e3o dependem muito das condi\u00e7\u00f5es ambientais e interiores (vento, umidade etc.).<\/span><\/p>\n<ol>\n<li><span>Calcule o fluxo de calor (\u00a0<\/span><a title=\"Perdas de calor\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/heat-losses\/\"><strong><span>perda de calor<\/span><\/strong><\/a><span>\u00a0) atrav\u00e9s desta parede n\u00e3o isolada.<\/span><\/li>\n<li><span>Agora assuma o\u00a0<\/span><strong><span>isolamento t\u00e9rmico<\/span><\/strong><span>\u00a0no lado externo desta parede.\u00a0Use\u00a0<\/span><strong><span>isolamento de poliestireno<\/span><\/strong><span>\u00a0expandido com\u00a010 cm de espessura (L\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0) com a condutividade t\u00e9rmica de k\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0= 0,03 W \/ mK e calcule o fluxo de\u00a0<\/span><a title=\"Perdas de calor\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/heat-losses\/\"><strong><span>calor<\/span><\/strong><\/a><span>\u00a0(\u00a0<a title=\"Perdas de calor\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/heat-losses\/\"><strong>perda de calor<\/strong><\/a>\u00a0) atrav\u00e9s dessa parede composta.<\/span><\/li>\n<\/ol>\n<p><strong><span>Solu\u00e7\u00e3o:<\/span><\/strong><\/p>\n<p><span>Como foi escrito, muitos dos processos de transfer\u00eancia de calor envolvem sistemas compostos e at\u00e9 envolvem uma combina\u00e7\u00e3o de\u00a0<\/span><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conducao-termica-conducao-termica-definicao\/\"><span>condu\u00e7\u00e3o<\/span><\/a><span>\u00a0e\u00a0<\/span><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conveccao-transferencia-de-calor-por-conveccao-definicao\/\"><span>convec\u00e7\u00e3o<\/span><\/a><span>\u00a0.\u00a0Com estes sistemas compostos, muitas vezes \u00e9 conveniente trabalhar com um\u00a0<\/span><strong><a title=\"Coeficiente geral de transfer\u00eancia de calor - fator U\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-coeficiente-geral-de-transferencia-de-calor-fator-u-definicao\/\"><span>coeficiente de transfer\u00eancia total de calor<\/span><\/a><span>\u00a0,<\/span><\/strong><span>\u00a0conhecido como um\u00a0<\/span><strong><span>factor-L<\/span><\/strong><span>\u00a0.\u00a0O fator U \u00e9 definido por uma express\u00e3o an\u00e1loga \u00e0\u00a0<\/span><a title=\"Lei de Newton de resfriamento\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-a-lei-do-resfriamento-de-newton-definicao\/\"><strong><span>lei do resfriamento de Newton<\/span><\/strong><\/a><span>\u00a0:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/u-factor-overall-heat-transfer-coefficient.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-20390 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/u-factor-overall-heat-transfer-coefficient.png\" alt=\"fator u - coeficiente geral de transfer\u00eancia de calor\" width=\"314\" height=\"136\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/u-factor-overall-heat-transfer-coefficient.png\" \/><\/a><\/p>\n<p><span>O\u00a0<\/span><strong><span>coeficiente geral de transfer\u00eancia de calor<\/span><\/strong><span>\u00a0est\u00e1 relacionado \u00e0\u00a0<\/span><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-resistencia-termica-resistividade-termica-definicao\/\"><span>resist\u00eancia t\u00e9rmica total<\/span><\/a><span>\u00a0e depende da geometria do problema.<\/span><\/p>\n<ol>\n<li><strong><span>parede nua<\/span><\/strong><\/li>\n<\/ol>\n<p><span>Assumindo a transfer\u00eancia de calor unidimensional atrav\u00e9s da parede plana e desconsiderando a radia\u00e7\u00e3o, o\u00a0<\/span><strong><span>coeficiente geral de transfer\u00eancia de calor<\/span><\/strong><span>\u00a0pode ser calculado como:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/overall-heat-transfer-coefficient-heat-loss-calculation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-21160 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/overall-heat-transfer-coefficient-heat-loss-calculation.png\" alt=\"coeficiente geral de transfer\u00eancia de calor - c\u00e1lculo da perda de calor\" width=\"343\" height=\"200\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/overall-heat-transfer-coefficient-heat-loss-calculation.png\" \/><\/a><\/p>\n<p><span>O\u00a0<\/span><strong><span>coeficiente geral de transfer\u00eancia de calor<\/span><\/strong><span>\u00a0\u00e9 ent\u00e3o:<\/span><\/p>\n<p><span>U = 1 \/ (1\/10 + 0,15 \/ 1 + 1\/30) = 3,53 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0K<\/span><\/p>\n<p><span>O fluxo de calor pode ser calculado simplesmente como:<\/span><\/p>\n<p><span>q = 3,53 [W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0K] x 30 [K] = 105,9 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/p>\n<p><span>A perda total de calor atrav\u00e9s desta parede ser\u00e1:<\/span><\/p>\n<p><span>q\u00a0<\/span><sub><span>perda<\/span><\/sub><span>\u00a0= q.\u00a0A = 105,9 [W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0] x 30 [m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0] = 3177W<\/span><\/p>\n<ol start=\"2\">\n<li><strong><span>parede comp\u00f3sita com isolamento t\u00e9rmico<\/span><\/strong><\/li>\n<\/ol>\n<p><span>Assumindo a transfer\u00eancia de calor unidimensional atrav\u00e9s da parede composta plana, sem resist\u00eancia ao contato t\u00e9rmico e sem considerar a radia\u00e7\u00e3o, o\u00a0<\/span><strong><span>coeficiente geral de transfer\u00eancia de calor<\/span><\/strong><span>\u00a0pode ser calculado como:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/overall-heat-transfer-coefficient-thermal-insulation-calculation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-21159 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/overall-heat-transfer-coefficient-thermal-insulation-calculation.png\" alt=\"coeficiente geral de transfer\u00eancia de calor - c\u00e1lculo de isolamento t\u00e9rmico\" width=\"423\" height=\"211\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/overall-heat-transfer-coefficient-thermal-insulation-calculation.png\" \/><\/a><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-insulation-expanded-polystyrene.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-21147 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-insulation-expanded-polystyrene-167x300.png\" alt=\"isolante t\u00e9rmico - poliestireno expandido\" width=\"167\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-insulation-expanded-polystyrene-167x300.png\" \/><\/a><span>O\u00a0<\/span><strong><span>coeficiente geral de transfer\u00eancia de calor<\/span><\/strong><span>\u00a0\u00e9 ent\u00e3o:<\/span><\/p>\n<p><span>U = 1 \/ (1\/10 + 0,15 \/ 1 + 0,1 \/ 0,03 + 1\/30) = 0,276 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0K<\/span><\/p>\n<p><span>O fluxo de calor pode ser calculado simplesmente como:<\/span><\/p>\n<p><span>q = 0,276 [W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0K] x 30 [K] = 8,28 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/p>\n<p><span>A perda total de calor atrav\u00e9s desta parede ser\u00e1:<\/span><\/p>\n<p><span>q\u00a0<\/span><sub><span>perda<\/span><\/sub><span>\u00a0= q.\u00a0A = 8,28 [W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0] x 30 [m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0] = 248 W<\/span><\/p>\n<p><span>Como pode ser visto, uma adi\u00e7\u00e3o de isolador t\u00e9rmico causa uma diminui\u00e7\u00e3o significativa nas perdas de calor.\u00a0Deve ser adicionado, uma adi\u00e7\u00e3o da pr\u00f3xima camada de isolador t\u00e9rmico n\u00e3o causa economias t\u00e3o altas.\u00a0Isso pode ser visto melhor no m\u00e9todo de resist\u00eancia t\u00e9rmica, que pode ser usado para calcular a transfer\u00eancia de calor atrav\u00e9s de\u00a0<\/span><strong><span>paredes compostas<\/span><\/strong><span>\u00a0.\u00a0A taxa de transfer\u00eancia constante de calor entre duas superf\u00edcies \u00e9 igual \u00e0 diferen\u00e7a de temperatura dividida pela\u00a0<\/span><a title=\"Resist\u00eancia t\u00e9rmica - Resistividade t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-resistencia-termica-resistividade-termica-definicao\/\"><span>resist\u00eancia t\u00e9rmica<\/span><\/a><span>\u00a0total\u00a0entre essas duas superf\u00edcies.<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-resistance-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-20128 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-resistance-equation.png\" alt=\"resist\u00eancia t\u00e9rmica - equa\u00e7\u00e3o\" width=\"601\" height=\"73\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-resistance-equation.png\" \/><\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n<p>&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<\/p>\n<p>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":"<p>O isolamento t\u00e9rmico \u00e9 o processo de redu\u00e7\u00e3o da transfer\u00eancia de calor entre os objetos em contato t\u00e9rmico ou na faixa de influ\u00eancia radiativa.\u00a0Isolamento t\u00e9rmico Isolamento t\u00e9rmico O isolamento t\u00e9rmico\u00a0\u00e9 o processo de redu\u00e7\u00e3o da\u00a0transfer\u00eancia\u00a0de\u00a0calor\u00a0entre os objetos em contato t\u00e9rmico ou na faixa de influ\u00eancia radiativa.\u00a0Os isolamentos t\u00e9rmicos\u00a0consistem em\u00a0materiais\u00a0de baixa condutividade t\u00e9rmica combinados para obter &#8230; <a title=\"O que \u00e9 isolamento t\u00e9rmico &#8211; Isolador t\u00e9rmico &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-isolamento-termico-isolador-termico-definicao\/\" aria-label=\"More on O que \u00e9 isolamento t\u00e9rmico &#8211; Isolador t\u00e9rmico &#8211; Defini\u00e7\u00e3o\">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":"<!-- This site is optimized with the Yoast SEO plugin v15.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>O que \u00e9 isolamento t\u00e9rmico - Isolador t\u00e9rmico - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"O isolamento t\u00e9rmico \u00e9 o processo de redu\u00e7\u00e3o da transfer\u00eancia de calor entre os objetos em contato t\u00e9rmico ou na faixa de influ\u00eancia radiativa. 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