{"id":47104,"date":"2019-11-03T06:42:59","date_gmt":"2019-11-03T05:42:59","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-perda-de-calor-definicao\/"},"modified":"2020-01-22T14:02:11","modified_gmt":"2020-01-22T13:02:11","slug":"o-que-e-perda-de-calor-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-perda-de-calor-definicao\/","title":{"rendered":"O que \u00e9 perda de calor &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">As perdas de calor de objetos mais quentes ocorrem por tr\u00eas mecanismos.\u00a0N\u00e3o h\u00e1 material que possa impedir completamente as perdas de calor, elas podem ser minimizadas apenas.\u00a0Engenharia T\u00e9rmica<\/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>Perdas de calor<\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Zeroth-Law-of-Thermodynamics-heat.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-16452 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Zeroth-Law-of-Thermodynamics-heat-300x158.png\" alt=\"zeroth-lei-da-termodin\u00e2mica-calor\" width=\"300\" height=\"158\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Zeroth-Law-of-Thermodynamics-heat-300x158.png\" \/><\/a>Enquanto\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-energia-interna-energia-termica-definicao\/\"><strong>energia t\u00e9rmica<\/strong><\/a>\u00a0se refere \u00e0 energia total de todas as mol\u00e9culas dentro do objeto, o\u00a0<a title=\"Calor na Termodin\u00e2mica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-calor-na-fisica-calor-definicao\/\"><strong>calor<\/strong><\/a>\u00a0\u00e9 a quantidade de energia que\u00a0<strong>flui<\/strong>\u00a0de um corpo para outro espontaneamente devido \u00e0 diferen\u00e7a de temperatura.\u00a0<strong>O calor<\/strong>\u00a0\u00e9 uma forma de energia, mas \u00e9\u00a0<strong>energia em tr\u00e2nsito<\/strong>\u00a0.\u00a0O calor n\u00e3o \u00e9 propriedade de um sistema.\u00a0No entanto, a transfer\u00eancia de energia como calor ocorre no n\u00edvel molecular como resultado de uma\u00a0<strong>diferen\u00e7a de temperatura<\/strong>\u00a0.\u00a0Quando\u00a0existe\u00a0uma\u00a0<strong>diferen\u00e7a de\u00a0<\/strong><strong><a title=\"O que \u00e9 temperatura - F\u00edsica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-temperatura-fisica-definicao\/\">temperatura<\/a><\/strong>\u00a0, o calor flui espontaneamente\u00a0<strong>do sistema mais quente para o sistema mais frio<\/strong>\u00a0, nunca o contr\u00e1rio.\u00a0Essa dire\u00e7\u00e3o dos\u00a0<a title=\"Processos termodin\u00e2micos\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-processo-termodinamico-definicao\/\">processos termodin\u00e2micos<\/a>\u00a0\u00e9 dada pela<a title=\"Segunda Lei da Termodin\u00e2mica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-a-segunda-lei-da-termodinamica-definicao\/\">segunda lei da termodin\u00e2mica<\/a>\u00a0.<\/p>\n<p>Como resultado, qualquer objeto mais quente que o ambiente deve perder continuamente parte de sua energia t\u00e9rmica.\u00a0Este \u00e9 um comportamento natural de todos os objetos.\u00a0Quando o\u00a0<strong>fluxo de calor p\u00e1ra<\/strong>\u00a0, \u00e9 dito que eles est\u00e3o na\u00a0<strong>mesma temperatura<\/strong>\u00a0.\u00a0Dizem que eles est\u00e3o em\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-temperature-physics\/thermal-equilibrium\/\"><strong>equil\u00edbrio t\u00e9rmico<\/strong><\/a>\u00a0.\u00a0<strong>As perdas<\/strong>\u00a0de calor de objetos mais quentes ocorrem por tr\u00eas mecanismos (individualmente ou em combina\u00e7\u00e3o):<\/p>\n<ul>\n<li><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conducao-termica-conducao-termica-definicao\/\"><strong>Condu\u00e7\u00e3o de calor<\/strong><\/a><strong>\u00a0.\u00a0<\/strong>A condu\u00e7\u00e3o de calor, tamb\u00e9m chamada difus\u00e3o, ocorre dentro de um corpo ou entre dois corpos em contato.\u00a0\u00c9 a troca microsc\u00f3pica direta de energia cin\u00e9tica de part\u00edculas atrav\u00e9s da fronteira entre dois sistemas.\u00a0Quando um objeto est\u00e1 a uma temperatura diferente de outro corpo ou de seus arredores<\/li>\n<li><a href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conveccao-transferencia-de-calor-por-conveccao-definicao\/\"><strong>Convec\u00e7\u00e3o por Calor<\/strong><\/a><strong>\u00a0.\u00a0<\/strong>A convec\u00e7\u00e3o de calor depende do movimento de massa de uma regi\u00e3o do espa\u00e7o para outra.\u00a0A convec\u00e7\u00e3o de calor ocorre quando o fluxo a granel de um fluido (g\u00e1s ou l\u00edquido) transporta calor junto com o fluxo de mat\u00e9ria no fluido.<\/li>\n<li><strong><a title=\"Radia\u00e7\u00e3o T\u00e9rmica - Calor Radiante\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-radiacao-termica-calor-radiante-definicao\/\">Radia\u00e7\u00e3o t\u00e9rmica<\/a>\u00a0.\u00a0<\/strong>A radia\u00e7\u00e3o \u00e9 a transfer\u00eancia de calor por radia\u00e7\u00e3o eletromagn\u00e9tica, como a luz do sol, sem a necessidade de que a mat\u00e9ria esteja presente no espa\u00e7o entre os corpos.<\/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>Perdas de calor &#8211; vestu\u00e1rio<\/h2>\n<p>O objetivo da roupa \u00e9 semelhante.\u00a0As propriedades isolantes da roupa prov\u00eam das\u00a0<strong>propriedades isolantes do ar<\/strong>\u00a0.\u00a0Os gases possuem m\u00e1s\u00a0propriedades de\u00a0<a title=\"Condutividade t\u00e9rmica de fluidos - gases e l\u00edquidos\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/heat-transfer\/thermal-conduction\/thermal-conductivity\/thermal-conductivity-of-fluids-gases-and-liquids\/\">condu\u00e7\u00e3o t\u00e9rmica em<\/a>\u00a0compara\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 estrutura semelhante a espuma).\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.\u00a0Sem roupas, nossos corpos no ar parado aqueciam o ar em contato direto com a pele e logo se tornavam razoavelmente confort\u00e1veis \u200b\u200bporque o ar \u00e9 um isolante muito bom.\u00a0Deve ser adicionado, tamb\u00e9m neste caso o ar estar\u00e1 fluindo devido \u00e0\u00a0<a title=\"Convec\u00e7\u00e3o Natural - Convec\u00e7\u00e3o Livre\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-conveccao-natural-definicao\/\">convec\u00e7\u00e3o natural<\/a>\u00a0.\u00a0Em\u00a0<strong>convec\u00e7\u00e3o natural<\/strong>, o ar ao redor de um corpo recebe calor e, por\u00a0<strong>expans\u00e3o t\u00e9rmica,<\/strong>\u00a0torna-se menos denso e sobe.\u00a0A expans\u00e3o t\u00e9rmica do ar desempenha um papel crucial.\u00a0Em outras palavras, componentes mais pesados \u200b\u200b(mais densos) cair\u00e3o, enquanto componentes mais leves (menos densos) subir\u00e3o, levando ao movimento do ar a granel.<\/p>\n<p>No vento, o ar quente ao redor do nosso corpo seria substitu\u00eddo pelo ar frio, aumentando assim a diferen\u00e7a de temperatura e a\u00a0<strong>perda de calor<\/strong>\u00a0do corpo.\u00a0As roupas constituem uma barreira para esse ar em movimento.\u00a0O principal benef\u00edcio \u00e9 na aus\u00eancia de convec\u00e7\u00e3o em larga escala.\u00a0Al\u00e9m disso, as roupas s\u00e3o feitas de materiais, que geralmente s\u00e3o bons isolantes.\u00a0Muitos materiais isolantes (por exemplo, l\u00e3) funcionam simplesmente com um grande n\u00famero de\u00a0<strong>bolsas cheias<\/strong>\u00a0de\u00a0<strong>g\u00e1s, o<\/strong>\u00a0que diminui significativamente a condutividade t\u00e9rmica do material.\u00a0A altern\u00e2ncia de 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>\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<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<h2><span>Perdas de Calor &#8211; Isolamento T\u00e9rmico<\/span><\/h2>\n<figure id=\"attachment_21154\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-21154\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/expanded-polystyrene-thermal-insulation.png\"><img loading=\"lazy\" class=\"size-medium wp-image-21154 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/expanded-polystyrene-thermal-insulation-300x180.png\" alt=\"poliestireno expandido - isolamento t\u00e9rmico\" width=\"300\" height=\"180\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/expanded-polystyrene-thermal-insulation-300x180.png\" \/><\/a><figcaption id=\"caption-attachment-21154\" class=\"wp-caption-text\"><span>Isolante em poliestireno expandido<\/span><\/figcaption><\/figure>\n<p><span>Para minimizar as\u00a0<\/span><strong><span>perdas de calor<\/span><\/strong><span>\u00a0na ind\u00fastria e tamb\u00e9m na constru\u00e7\u00e3o de edif\u00edcios, o\u00a0<\/span><strong><span>isolamento t\u00e9rmico<\/span><\/strong><span>\u00a0\u00e9 amplamente utilizado.\u00a0O objetivo do isolamento t\u00e9rmico \u00e9 reduzir o\u00a0<\/span><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 geral de transfer\u00eancia de calor<\/span><\/a><span>\u00a0adicionando material com baixa\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>\u00a0. \u00a0<\/span><strong><span>O isolamento t\u00e9rmico<\/span><\/strong><span>\u00a0em edif\u00edcios \u00e9 um fator importante para obter conforto t\u00e9rmico para seus ocupantes.\u00a0O isolamento t\u00e9rmico reduz a\u00a0<\/span><strong><span>perda de calor<\/span><\/strong><span>\u00a0indesejada\u00a0e tamb\u00e9m reduz o\u00a0<\/span><strong><span>ganho de calor<\/span><\/strong><span>\u00a0indesejado\u00a0.\u00a0Portanto, o isolamento t\u00e9rmico pode diminuir as demandas de energia dos sistemas de aquecimento e refrigera\u00e7\u00e3o.\u00a0Deve ser adicionado, n\u00e3o h\u00e1 material que possa impedir completamente as perdas de calor, as perdas de calor s\u00f3 podem ser minimizadas.<\/span><\/p>\n<p><span>Da mesma forma que no vestu\u00e1rio, o isolamento t\u00e9rmico \u00e9 baseado em materiais de baixa condutividade t\u00e9rmica e em sua geometria (por exemplo, janelas de painel duplo).\u00a0As propriedades isolantes desses materiais s\u00e3o provenientes das propriedades isolantes do ar.\u00a0Muitos materiais isolantes (por exemplo, l\u00e3 de vidro) funcionam simplesmente com 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>evitam a convec\u00e7\u00e3o em grande escala<\/span><\/strong><span>\u00a0.\u00a0A geometria desses materiais tamb\u00e9m desempenha papel crucial.\u00a0Por exemplo, aumentar a largura da camada de ar, como usar dois pain\u00e9is de vidro separados por um espa\u00e7o de ar, reduzir\u00e1 a perda de calor mais do que simplesmente aumentar a espessura do vidro, uma vez que a condutividade t\u00e9rmica do ar \u00e9 muito menor que a do vidro .<\/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 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 janela<\/span><\/h2>\n<p><strong><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Example-Heat-Flux-Thermal-Conduction.png?36a14b\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-20047 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Example-Heat-Flux-Thermal-Conduction-300x280.png?36a14b\" alt=\"Exemplo - Fluxo de Calor - Condu\u00e7\u00e3o T\u00e9rmica\" width=\"300\" height=\"280\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Example-Heat-Flux-Thermal-Conduction-300x280.png?36a14b\" \/><\/a><span>Perda de calor atrav\u00e9s das janelas<\/span><\/strong><\/p>\n<p><span>Uma das principais fontes de perda de calor de uma casa \u00e9 atrav\u00e9s das janelas.\u00a0Calcule a taxa de fluxo de calor atrav\u00e9s de uma janela de vidro com 1,5 mx\u00a0<\/span><strong>\u00a0<\/strong><span>1,0 m de \u00e1rea e 3,0 mm de espessura, se as temperaturas nas superf\u00edcies interna e externa forem de 14,0 \u00b0 C e 13,0 \u00b0 C, respectivamente.\u00a0Calcule o fluxo de calor atrav\u00e9s desta janela.<\/span><\/p>\n<p><strong><span>Solu\u00e7\u00e3o:<\/span><\/strong><\/p>\n<p><span>Neste ponto, conhecemos as temperaturas nas superf\u00edcies do material.\u00a0Essas temperaturas s\u00e3o dadas tamb\u00e9m pelas condi\u00e7\u00f5es dentro e fora da casa.\u00a0Nesse caso, o calor flui por condu\u00e7\u00e3o atrav\u00e9s do vidro da temperatura interna mais alta para a temperatura externa mais baixa.\u00a0Usamos a equa\u00e7\u00e3o de condu\u00e7\u00e3o de calor:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Heat-loss-through-window-equation.png?36a14b\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-20027 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Heat-loss-through-window-equation.png?36a14b\" alt=\"Perda de calor atrav\u00e9s da janela - equa\u00e7\u00e3o\" width=\"259\" height=\"145\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Heat-loss-through-window-equation.png?36a14b\" \/><\/a><\/p>\n<p><span>Assumimos que a condutividade t\u00e9rmica de um vidro comum \u00e9 k = 0,96 W \/ mK<\/span><\/p>\n<p><span>O fluxo de calor ser\u00e1 ent\u00e3o:<\/span><\/p>\n<p><span>q = 0,96 [W \/ mK] x 1 [K] \/ 3,0 x 10\u00a0<\/span><sup><span>-3<\/span><\/sup><span>\u00a0\u00a0[m] = 320 W \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/p>\n<p><span>A perda total de calor atrav\u00e9s desta janela ser\u00e1:<\/span><\/p>\n<p><span>q\u00a0<\/span><sub><span>perda<\/span><\/sub><span>\u00a0\u00a0= q.\u00a0A = 320 x 1,5 x 1,0 = 480W<\/span><\/p>\n<p><span>Deve ser adicionado, 15 \u00b0 C n\u00e3o \u00e9 muito quente para a sala de uma casa.\u00a0Mas esta temperatura n\u00e3o corresponde \u00e0 temperatura interior, mas corresponde \u00e0 temperatura da superf\u00edcie.\u00a0Devido ao coeficiente de transfer\u00eancia de calor por convec\u00e7\u00e3o finita, sempre h\u00e1 uma queda consider\u00e1vel de temperatura entre a temperatura interna e a temperatura da superf\u00edcie da janela.\u00a0Observe que os dois coeficientes de convec\u00e7\u00e3o dependem fortemente, especialmente das condi\u00e7\u00f5es ambientais e interiores (vento, umidade, etc.).<\/span><\/p>\n<p><span>Vide tamb\u00e9m:\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>Coeficiente de transfer\u00eancia de calor por convec\u00e7\u00e3o<\/span><\/a><\/p>\n<p><span>Da mesma forma que no vestu\u00e1rio, o isolamento t\u00e9rmico \u00e9 baseado em materiais de baixa condutividade t\u00e9rmica e em sua geometria (por exemplo, janelas de painel duplo).\u00a0As propriedades isolantes desses materiais s\u00e3o provenientes das propriedades isolantes do ar.\u00a0Muitos materiais isolantes (por exemplo, l\u00e3) funcionam simplesmente com 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.\u00a0A geometria desses materiais tamb\u00e9m desempenha papel crucial.\u00a0Por exemplo, aumentar a largura da camada de ar, como usar dois pain\u00e9is de vidro separados por um espa\u00e7o de ar, reduzir\u00e1 a perda de calor mais do que simplesmente aumentar a espessura do vidro, uma vez que a condutividade t\u00e9rmica do ar \u00e9 muito menor que a do vidro .<\/span><\/p>\n<\/div>\n<\/div>\n<figure id=\"attachment_21154\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-21154\"><figcaption id=\"caption-attachment-21154\" class=\"wp-caption-text\">&#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<\/figcaption><\/figure>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>As perdas de calor de objetos mais quentes ocorrem por tr\u00eas mecanismos.\u00a0N\u00e3o h\u00e1 material que possa impedir completamente as perdas de calor, elas podem ser minimizadas apenas.\u00a0Engenharia T\u00e9rmica Perdas de calor Enquanto\u00a0energia t\u00e9rmica\u00a0se refere \u00e0 energia total de todas as mol\u00e9culas dentro do objeto, o\u00a0calor\u00a0\u00e9 a quantidade de energia que\u00a0flui\u00a0de um corpo para outro espontaneamente &#8230; <a title=\"O que \u00e9 perda de calor &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-perda-de-calor-definicao\/\" aria-label=\"More on O que \u00e9 perda de calor &#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 perda de calor - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"As perdas de calor de objetos mais quentes ocorrem por tr\u00eas mecanismos. 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