{"id":47124,"date":"2019-11-03T08:12:42","date_gmt":"2019-11-03T07:12:42","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-a-principal-propriedade-dos-materiais-de-isolamento-definicao\/"},"modified":"2020-01-22T14:10:49","modified_gmt":"2020-01-22T13:10:49","slug":"o-que-e-a-principal-propriedade-dos-materiais-de-isolamento-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-a-principal-propriedade-dos-materiais-de-isolamento-definicao\/","title":{"rendered":"O que \u00e9 a principal propriedade dos materiais de isolamento &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">As principais propriedades dos materiais de isolamento s\u00e3o: condutividade t\u00e9rmica, valor R, valor U, emissividade da superf\u00edcie e resist\u00eancia ao fogo.\u00a0Propriedades e caracter\u00edsticas dos materiais de isolamento<\/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>Propriedades dos materiais de isolamento<\/h2>\n<p><strong>O isolamento t\u00e9rmico<\/strong>\u00a0\u00e9 baseado no uso de subst\u00e2ncias com baixa condutividade t\u00e9rmica e baixa emissividade superficial.\u00a0\u00c9 importante observar que os fatores que influenciam o desempenho podem variar ao longo do tempo, \u00e0 medida que a idade do material ou as condi\u00e7\u00f5es ambientais mudam.\u00a0As principais\u00a0<strong>propriedades dos materiais de isolamento<\/strong>\u00a0s\u00e3o:<\/p>\n<ul>\n<li><strong><a title=\"Condutividade t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-condutividade-termica-definicao\/\">Condutividade t\u00e9rmica<\/a>\u00a0.\u00a0A condutividade t\u00e9rmica,<\/strong>\u00a0\u00a0medida em W \/ mK, descreve como um material conduz o calor.\u00a0Observe que<strong>\u00a0a lei de Fourier<\/strong>aplica-se a toda mat\u00e9ria, independentemente de seu estado (s\u00f3lido, l\u00edquido ou g\u00e1s); portanto, tamb\u00e9m \u00e9 definida para l\u00edquidos e gases.\u00a0\u00c9 a quantidade de calor (em watts) transferida atrav\u00e9s de uma \u00e1rea quadrada de material de determinada espessura (em metros) devido a uma diferen\u00e7a de temperatura.\u00a0Quanto menor a condutividade t\u00e9rmica do material, maior a capacidade do material de resistir \u00e0 transfer\u00eancia de calor e, portanto, maior a efic\u00e1cia do isolamento.\u00a0Em geral, os gases t\u00eam baixa condutividade t\u00e9rmica (por exemplo, o ar tem 0,025 W \/ mK), enquanto os metais t\u00eam valores altos (por exemplo, o cobre tem 400 W \/ mK).\u00a0Os isolantes comumente usados \u200b\u200btendem a ter uma condutividade t\u00e9rmica entre 0,019 W \/ mK e 0,046 W \/ mK.<\/li>\n<li><strong><a title=\"Valor R - Fator de isolamento t\u00e9rmico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/thermal-conduction\/thermal-resistance-thermal-resistivity\/r-value-thermal-insulance-factor\/\">Valor R &#8211; Resist\u00eancia t\u00e9rmica<\/a>\u00a0.\u00a0<\/strong>O valor R (fator de isolamento t\u00e9rmico) \u00e9 uma medida de resist\u00eancia t\u00e9rmica.\u00a0Quanto maior o valor R, maior a efic\u00e1cia do isolamento.\u00a0A isola\u00e7\u00e3o t\u00e9rmica possui as unidades [(m<sup>\u00a02<\/sup>\u00a0.K) \/ W] em unidades SI ou [(p\u00e9s<sup>\u00a02<\/sup>\u00a0\u00b0 F \u00b7 h) \/ Btu] em unidades imperiais.\u00a0\u00c9 a resist\u00eancia t\u00e9rmica da \u00e1rea unit\u00e1ria de um material.\u00a0O valor R depende do tipo de isolamento, sua espessura e densidade.\u00a0\u00c9 necess\u00e1ria uma diferen\u00e7a de \u00e1rea e temperatura para resolver o calor transferido.\u00a0A ind\u00fastria da constru\u00e7\u00e3o utiliza unidades como o<strong>\u00a0valor R (resist\u00eancia)<\/strong>, que \u00e9 expressa como a espessura do material normalizado para a condutividade t\u00e9rmica e, em condi\u00e7\u00f5es uniformes, \u00e9 a raz\u00e3o da diferen\u00e7a de temperatura entre um isolador e a densidade do fluxo de calor atrav\u00e9s dele: R (x) = \u2206T \/ q.\u00a0Quanto maior o valor R, mais um material impede a transfer\u00eancia de calor.\u00a0Como pode ser visto, a resist\u00eancia depende da espessura do produto.<\/li>\n<li><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\/\">Valor U &#8211; transmit\u00e2ncia t\u00e9rmica<\/a>\u00a0.\u00a0<\/strong>\u00a0<strong>A transmit\u00e2ncia t\u00e9rmica<\/strong>\u00a0descreve como o material conduz o calor. \u00a0<strong>A transmit\u00e2ncia t\u00e9rmica<\/strong>\u00a0\u00e9 o inverso do valor R (ou seja, 1 \/ R) e quanto menor o valor U, melhor o isolamento.\u00a0O valor U \u00e9 definido por uma express\u00e3o an\u00e1loga \u00e0<strong>\u00a0lei do resfriamento de Newton.<\/strong><\/li>\n<li><strong><a title=\"Emissividade - Emissividade de Materiais\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/radiation-heat-transfer\/emissivity-emissivity-of-materials\/\">Emissividade de superf\u00edcie<\/a>\u00a0.\u00a0<\/strong>Como foi escrito, a transfer\u00eancia de calor atrav\u00e9s de qualquer um desses sistemas de isolamento pode incluir v\u00e1rios modos: condu\u00e7\u00e3o atrav\u00e9s dos materiais s\u00f3lidos, condu\u00e7\u00e3o ou convec\u00e7\u00e3o atrav\u00e9s do ar nos espa\u00e7os vazios e troca de radia\u00e7\u00e3o entre as superf\u00edcies da matriz s\u00f3lida.\u00a0Portanto, a emissividade de um material tamb\u00e9m desempenha papel muito importante.\u00a0A<strong>\u00a0emissividade, \u03b5<\/strong>\u00a0, da superf\u00edcie de um material \u00e9 sua efic\u00e1cia na emiss\u00e3o de energia como<strong>\u00a0radia\u00e7\u00e3o t\u00e9rmica<\/strong>e varia entre 0,0 e 1,0.\u00a0A emissividade \u00e9 simplesmente um fator pelo qual multiplicamos a transfer\u00eancia de calor do corpo negro para levar em conta que o corpo negro \u00e9 o caso ideal.\u00a0A superf\u00edcie de um corpo negro emite radia\u00e7\u00e3o t\u00e9rmica a uma taxa de aproximadamente 448 watts por metro quadrado em temperatura ambiente (25 \u00b0 C, 298,15 K).\u00a0Objetos reais com emissividades inferiores a 1,0 (por exemplo, papel alum\u00ednio) emitem radia\u00e7\u00e3o a taxas correspondentemente mais baixas (por exemplo, 448 x 0,07 = 31,4 W \/ m\u00a0<sup>2<\/sup>\u00a0).<\/li>\n<li><strong>Resist\u00eancia ao fogo<\/strong>\u00a0.\u00a0Os materiais de isolamento t\u00e9rmico devem ter uma classifica\u00e7\u00e3o de resist\u00eancia ao fogo.\u00a0Essa classifica\u00e7\u00e3o \u00e9 importante porque pode ter influ\u00eancia na aplica\u00e7\u00e3o de materiais isolantes.\u00a0Normalmente, a classifica\u00e7\u00e3o de resist\u00eancia ao fogo \u00e9 seguida como um limite de tempo nos minutos 15, 30, 45, 60, 90, 120, 180, 240 ou 360, que mostra o tempo em que os crit\u00e9rios de desempenho s\u00e3o cumpridos durante um teste de fogo padronizado.<\/li>\n<\/ul>\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>Materiais de isolamento<\/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>Como foi escrito, o\u00a0<strong>isolamento t\u00e9rmico<\/strong>\u00a0\u00e9 baseado no uso de subst\u00e2ncias com\u00a0<strong>condutividade t\u00e9rmica muito baixa<\/strong>\u00a0.\u00a0Esses materiais s\u00e3o conhecidos como\u00a0<strong>materiais de isolamento<\/strong>\u00a0.\u00a0Os materiais de isolamento comuns s\u00e3o l\u00e3, fibra de vidro, l\u00e3 de rocha, poliestireno, poliuretano e penas de ganso, etc. Esses materiais s\u00e3o condutores de calor muito fracos e, portanto, s\u00e3o bons isolantes t\u00e9rmicos.<\/p>\n<p>\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<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 de isolamento (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>\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.<\/p>\n<p>A altern\u00e2ncia de bolsa de g\u00e1s e material s\u00f3lido faz com que o calor seja transferido atrav\u00e9s de\u00a0<strong>muitas interfaces,<\/strong>\u00a0causando 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\u00a0<\/span><strong><span>a radia\u00e7\u00e3o t\u00e9rmica<\/span><\/strong><span>\u00a0\u00a0como um modo de\u00a0<\/span><strong><span>perda<\/span><\/strong><span>\u00a0de\u00a0\u00a0<strong>calor<\/strong>\u00a0.\u00a0<\/span><strong><span>A transfer\u00eancia de calor\u00a0<\/span><\/strong><span>\u00a0por\u00a0<\/span><strong><span>radia\u00e7\u00e3o<\/span><\/strong><span>\u00a0\u00e9 mediada por\u00a0\u00a0<strong>radia\u00e7\u00e3o eletromagn\u00e9tica\u00a0<\/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\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\u00a0<\/span><\/a><span>\u00a0emite alguma\u00a0\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\u00a0\u00a0\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 do\u00a0\u00a0<\/span><strong><span>infravermelho<\/span><\/strong><span>\u00a0do espectro eletromagn\u00e9tico, embora parte dele esteja na regi\u00e3o vis\u00edvel.\u00a0Para diminuir esse tipo de transfer\u00eancia de calor, materiais com baixa emissividade (alta refletividade) devem ser utilizados.\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.\u00a0A\u00a0\u00a0<\/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>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\u00a0\u00a0<\/span><strong><span>radia\u00e7\u00e3o t\u00e9rmica<\/span><\/strong><span>\u00a0\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 energia radiante de volta \u00e0 sua fonte, como no caso de\u00a0<\/span><strong><span>mantas<\/span><\/strong><span>\u00a0de\u00a0\u00a0<strong>primeiros 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>Espessura cr\u00edtica da isola\u00e7\u00e3o<\/span><\/h2>\n<p><strong><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Critical-Thickness-Insulation-Figure.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20276 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Critical-Thickness-Insulation-Figure-300x202.png\" alt=\"Isolamento de espessura cr\u00edtica\" width=\"300\" height=\"202\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Critical-Thickness-Insulation-Figure-300x202.png\" \/><\/a><span>Em uma parede plana,<\/span><\/strong><span>\u00a0\u00a0a \u00e1rea perpendicular \u00e0 dire\u00e7\u00e3o do fluxo de calor, adicionando mais isolamento a uma parede sempre diminui a transfer\u00eancia de calor.\u00a0Quanto\u00a0\u00a0<\/span><strong><span>mais espessa a isola\u00e7\u00e3o<\/span><\/strong><span>\u00a0,\u00a0\u00a0<\/span><strong><span>menor a<\/span><\/strong><span>\u00a0\u00a0taxa de\u00a0<strong>transfer\u00eancia de calor<\/strong>\u00a0.\u00a0Isso se deve ao fato de a\u00a0\u00a0<\/span><strong><span>superf\u00edcie externa ter sempre a mesma \u00e1rea<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><strong><span>Mas nas coordenadas cil\u00edndricas e esf\u00e9ricas, a adi\u00e7\u00e3o de isolamento tamb\u00e9m aumenta a superf\u00edcie externa<\/span><\/strong><span>\u00a0, o que diminui a resist\u00eancia de convec\u00e7\u00e3o na superf\u00edcie externa.\u00a0Al\u00e9m disso, em alguns casos, uma diminui\u00e7\u00e3o na resist\u00eancia \u00e0 convec\u00e7\u00e3o devido ao aumento na \u00e1rea da superf\u00edcie pode ser mais importante do que um aumento na resist\u00eancia \u00e0 condu\u00e7\u00e3o devido ao isolamento mais espesso.\u00a0Como resultado, a\u00a0\u00a0<\/span><strong><span>resist\u00eancia total<\/span><\/strong><span>\u00a0\u00a0pode realmente diminuir, resultando em aumento do fluxo de calor.<\/span><\/p>\n<p><span>A\u00a0\u00a0<\/span><strong><span>espessura<\/span><\/strong><span>\u00a0\u00a0at\u00e9 a qual o fluxo de calor aumenta e ap\u00f3s o qual o fluxo de calor diminui \u00e9 denominada\u00a0\u00a0<\/span><strong><span>espessura cr\u00edtica<\/span><\/strong><span>\u00a0.\u00a0No caso de cilindros e esferas, \u00e9 chamado\u00a0\u00a0<\/span><strong><span>raio cr\u00edtico<\/span><\/strong><span>\u00a0.\u00a0Pode-se derivar que o\u00a0\u00a0<\/span><a title=\"Espessura cr\u00edtica do isolamento - raio cr\u00edtico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/thermal-conduction\/critical-thickness-of-insulation-critical-radius\/\"><strong><span>raio cr\u00edtico do isolamento<\/span><\/strong><\/a><span>\u00a0\u00a0depende da condutividade t\u00e9rmica do isolamento k e do coeficiente de transfer\u00eancia de calor por convec\u00e7\u00e3o externa h.<\/span><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0\u00a0<\/span><a title=\"Espessura cr\u00edtica do isolamento - raio cr\u00edtico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/thermal-conduction\/critical-thickness-of-insulation-critical-radius\/\"><strong><span>Raio cr\u00edtico do isolamento<\/span><\/strong><\/a><\/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 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\"><\/div>\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","protected":false},"excerpt":{"rendered":"<p>As principais propriedades dos materiais de isolamento s\u00e3o: condutividade t\u00e9rmica, valor R, valor U, emissividade da superf\u00edcie e resist\u00eancia ao fogo.\u00a0Propriedades e caracter\u00edsticas dos materiais de isolamento Propriedades dos materiais de isolamento O isolamento t\u00e9rmico\u00a0\u00e9 baseado no uso de subst\u00e2ncias com baixa condutividade t\u00e9rmica e baixa emissividade superficial.\u00a0\u00c9 importante observar que os fatores que influenciam &#8230; <a title=\"O que \u00e9 a principal propriedade dos materiais de isolamento &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-a-principal-propriedade-dos-materiais-de-isolamento-definicao\/\" aria-label=\"More on O que \u00e9 a principal propriedade dos materiais de isolamento &#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 a principal propriedade dos materiais de isolamento - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"As principais propriedades dos materiais de isolamento s\u00e3o: condutividade t\u00e9rmica, valor R, valor U, emissividade da superf\u00edcie e resist\u00eancia ao fogo. 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