{"id":51910,"date":"2020-02-01T17:44:14","date_gmt":"2020-02-01T16:44:14","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-o-numero-de-reynolds-definicao\/"},"modified":"2020-02-01T17:46:53","modified_gmt":"2020-02-01T16:46:53","slug":"o-que-e-o-numero-de-reynolds-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-numero-de-reynolds-definicao\/","title":{"rendered":"O que \u00e9 o n\u00famero de Reynolds &#8211; defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">O n\u00famero de Reynolds \u00e9 a raz\u00e3o de for\u00e7as inerciais para for\u00e7as viscosas e \u00e9 um par\u00e2metro conveniente para prever se uma condi\u00e7\u00e3o de fluxo ser\u00e1 laminar ou turbulenta. Engenharia T\u00e9rmica<\/div>\n<\/div>\n<div><\/div>\n<div><\/div>\n<div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-60 lgc-tablet-grid-60 lgc-mobile-grid-100 lgc-equal-heights  lgc-first\">\n<div class=\"inside-grid-column\">\n<h2><span>N\u00famero de Reynolds<\/span><\/h2>\n<p><strong><span>O n\u00famero de Reynolds<\/span><\/strong><span>\u00a0\u00e9 a propor\u00e7\u00e3o de\u00a0<\/span><strong><span>for\u00e7as de in\u00e9rcia<\/span><\/strong><span>\u00a0para\u00a0<\/span><strong><span>as for\u00e7as viscosas<\/span><\/strong><span>\u00a0e \u00e9 um par\u00e2metro conveniente para prever se uma condi\u00e7\u00e3o de escoamento vai ser\u00a0<\/span><strong><span>laminar ou turbulento<\/span><\/strong><span>\u00a0.\u00a0Pode-se interpretar que quando as\u00a0<\/span><strong><span>for\u00e7as viscosas<\/span><\/strong><span>\u00a0s\u00e3o dominantes (fluxo lento, Re baixo) s\u00e3o suficientes o suficiente para manter todas as part\u00edculas de fluido alinhadas, ent\u00e3o o fluxo \u00e9 laminar.\u00a0Mesmo Re muito baixo indica movimento de rastejamento viscoso, onde os efeitos de in\u00e9rcia s\u00e3o desprez\u00edveis.\u00a0Quando as\u00a0<\/span><strong><span>for\u00e7as inerciais dominam<\/span><\/strong><span>\u00a0sobre as for\u00e7as viscosas (quando o fluido est\u00e1 fluindo mais r\u00e1pido e Re \u00e9 maior), ent\u00e3o o fluxo \u00e9 turbulento.<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-Number.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14465 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-Number.png\" alt=\"N\u00famero de Reynolds\" width=\"563\" height=\"284\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-Number.png\" \/><\/a><\/p>\n<p><strong><span>\u00c9 um n\u00famero sem dimens\u00e3o<\/span><\/strong><span>\u00a0composto pelas caracter\u00edsticas f\u00edsicas do fluxo.\u00a0Um n\u00famero crescente de Reynolds indica uma crescente turbul\u00eancia do fluxo.<\/span><\/p>\n<p><span>\u00c9 definido como:<\/span><br \/>\n<a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14445 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-formula.png\" alt=\"N\u00famero de Reynolds\" width=\"229\" height=\"82\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-formula.png\" \/><\/a><\/p>\n<p><span>em que:<\/span><br \/>\n<span>V \u00e9 a velocidade do fluxo,<\/span><br \/>\n<span>D \u00e9 uma\u00a0<\/span><strong><span>dimens\u00e3o linear caracter\u00edstica<\/span><\/strong><span>\u00a0(comprimento percorrido do fluido;\u00a0<\/span><a title=\"Di\u00e2metro hidr\u00e1ulico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/internal-flow\/hydraulic-diameter-2\/\"><span>di\u00e2metro hidr\u00e1ulico<\/span><\/a><span>\u00a0etc.)<\/span><br \/>\n<span>\u03c1 densidade do fluido (kg \/ m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0),<\/span><br \/>\n<span>\u03bc viscosidade din\u00e2mica (Pa.s),<\/span><br \/>\n<span>\u03bd viscosidade cinem\u00e1tica ( m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0\/ s);\u00a0\u03bd = \u03bc \/ \u03c1.<\/span><\/p>\n<div class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\"><\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-40 lgc-tablet-grid-40 lgc-mobile-grid-100 lgc-equal-heights  lgc-last\">\n<div class=\"inside-grid-column\">\n<h2><span>Fluxo Laminar vs. Turbulento<\/span><\/h2>\n<p><strong><span>Fluxo laminar:<\/span><\/strong><\/p>\n<ul>\n<li><strong><span>Re &lt;2000<\/span><\/strong><\/li>\n<li><span>velocidade &#8216;baixa&#8217;<\/span><\/li>\n<li><span>Part\u00edculas fluidas se movem em\u00a0<\/span><strong><span>linhas retas<\/span><\/strong><\/li>\n<li><span>Camadas de \u00e1gua fluem umas sobre as outras em velocidades diferentes,\u00a0<\/span><strong><span>praticamente sem mistura<\/span><\/strong><span>\u00a0entre as camadas.<\/span><\/li>\n<li><span>O perfil da velocidade do fluxo para o fluxo laminar em tubos circulares \u00e9 parab\u00f3lico, com um fluxo m\u00e1ximo no centro do tubo e um fluxo m\u00ednimo nas paredes do tubo.<\/span><\/li>\n<li><span>A velocidade m\u00e9dia do fluxo \u00e9 aproximadamente metade da velocidade m\u00e1xima.<\/span><\/li>\n<li><span>\u00c9 poss\u00edvel uma an\u00e1lise matem\u00e1tica simples.<\/span><\/li>\n<li><strong><span>Raro na pr\u00e1tica em sistemas de \u00e1gua<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<\/ul>\n<p><strong><span>Fluxo turbulento:<\/span><\/strong><\/p>\n<ul>\n<li><strong><span>Re&gt; 4000<\/span><\/strong><\/li>\n<li><span>&#8216;alta velocidade<\/span><\/li>\n<li><span>O fluxo \u00e9 caracterizado pelo\u00a0<\/span><strong><span>movimento irregular<\/span><\/strong><span>\u00a0de part\u00edculas do fluido.<\/span><\/li>\n<li><span>O movimento m\u00e9dio est\u00e1 na dire\u00e7\u00e3o do fluxo<\/span><\/li>\n<li><span>O perfil de velocidade do fluxo para turbul\u00eancia \u00e9 bastante plano atrav\u00e9s da se\u00e7\u00e3o central de um tubo e cai rapidamente extremamente perto das paredes.<\/span><\/li>\n<li><span>A velocidade m\u00e9dia do fluxo \u00e9 aproximadamente igual \u00e0 velocidade no centro do tubo.<\/span><\/li>\n<li><span>A an\u00e1lise matem\u00e1tica \u00e9 muito dif\u00edcil.<\/span><\/li>\n<li><strong><span>Tipo mais comum de fluxo<\/span><\/strong><span>\u00a0.<\/span><\/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\"><\/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<h2><span>Regimes num\u00e9ricos de Reynolds<\/span><\/h2>\n<p><strong><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Flow-Regime.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-14393 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Flow-Regime-300x175.png\" alt=\"Regime de fluxo\" width=\"300\" height=\"175\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Flow-Regime-300x175.png\" \/><\/a><span>Fluxo laminar.\u00a0<\/span><\/strong><span>Para fins pr\u00e1ticos, se o n\u00famero de Reynolds for\u00a0<\/span><strong><span>menor que 2000<\/span><\/strong><span>\u00a0, o fluxo ser\u00e1 laminar.\u00a0O n\u00famero de Reynolds de transi\u00e7\u00e3o aceito para o fluxo em um tubo circular \u00e9\u00a0<\/span><strong><span>Re\u00a0<\/span><sub><span>d, crit<\/span><\/sub><span>\u00a0= 2300.<\/span><\/strong><\/p>\n<p><strong><span>Fluxo de transi\u00e7\u00e3o.\u00a0<\/span><\/strong><span>Nos n\u00fameros de Reynolds\u00a0<\/span><strong><span>entre 2000 e 4000,<\/span><\/strong><span>\u00a0o fluxo \u00e9 inst\u00e1vel como resultado do in\u00edcio da turbul\u00eancia.\u00a0Esses fluxos \u00e0s vezes s\u00e3o chamados de fluxos de transi\u00e7\u00e3o.<\/span><\/p>\n<p><strong><span>Fluxo turbulento.\u00a0<\/span><\/strong><span>Se o n\u00famero de Reynolds for\u00a0<\/span><strong><span>maior que 3500<\/span><\/strong><span>\u00a0, o fluxo ser\u00e1 turbulento.\u00a0A maioria dos sistemas de fluidos em instala\u00e7\u00f5es nucleares opera com fluxo turbulento.<\/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>N\u00famero de Reynolds e fluxo interno<\/span><\/h2>\n<figure id=\"attachment_14394\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-14394\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Internal-Flow.png\"><img loading=\"lazy\" class=\"size-medium wp-image-14394 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Internal-Flow-300x269.png\" alt=\"Fluxo Interno\" width=\"300\" height=\"269\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Internal-Flow-300x269.png\" \/><\/a><figcaption id=\"caption-attachment-14394\" class=\"wp-caption-text\"><span>Fonte: White Frank M., Mec\u00e2nica dos Fluidos, McGraw-Hill Education, 7\u00aa edi\u00e7\u00e3o, fevereiro de 2010, ISBN: 978-0077422417<\/span><\/figcaption><\/figure>\n<p><a title=\"Fluxo Interno\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/internal-flow\/\"><strong><span>A<\/span><\/strong><\/a><span>\u00a0configura\u00e7\u00e3o de<a title=\"Fluxo Interno\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/internal-flow\/\"><strong>\u00a0fluxo interno<\/strong><\/a>\u00a0(por exemplo, fluxo em um tubo) \u00e9 uma geometria conveniente para fluidos de aquecimento e resfriamento usados \u200b\u200bem tecnologias de convers\u00e3o de energia, como<\/span><a title=\"Usina nuclear\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power-plant\/\"><span>\u00a0usinas nucleares<\/span><\/a><span>\u00a0.<\/span><\/p>\n<p><span>Em geral, esse regime de fluxo \u00e9 importante na engenharia, porque os tubos circulares podem suportar altas press\u00f5es e, portanto, s\u00e3o usados \u200b\u200bpara transportar l\u00edquidos.\u00a0Dutos n\u00e3o circulares s\u00e3o usados \u200b\u200bpara transportar gases de baixa press\u00e3o, como ar em sistemas de refrigera\u00e7\u00e3o e aquecimento.<\/span><\/p>\n<p><span>Para\u00a0<\/span><a title=\"Fluxo Interno\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/internal-flow\/\"><span>o regime de fluxo interno,<\/span><\/a><span>\u00a0uma\u00a0<\/span><strong><span>regi\u00e3o de entrada<\/span><\/strong><span>\u00a0\u00e9 t\u00edpica.\u00a0Nesta regi\u00e3o, um fluxo a montante quase inviscido a montante converge e entra no tubo.\u00a0Para caracterizar esta regi\u00e3o, o\u00a0<\/span><strong><span>comprimento da entrada hidrodin\u00e2mica<\/span><\/strong><span>\u00a0\u00e9 introduzido e \u00e9 aproximadamente igual a:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/hydrodynamic-entrance-length.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14416 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/hydrodynamic-entrance-length.png\" alt=\"comprimento hidrodin\u00e2mico da entrada\" width=\"365\" height=\"69\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/hydrodynamic-entrance-length.png\" \/><\/a><\/p>\n<p><span>O comprimento m\u00e1ximo de entrada hidrodin\u00e2mica, em\u00a0<\/span><strong><span>Re\u00a0<\/span><sub><span>D, crit<\/span><\/sub><span>\u00a0\u00a0= 2300<\/span><\/strong><span>\u00a0(\u00a0<\/span><strong><span>fluxo laminar<\/span><\/strong><span>\u00a0), \u00e9 L\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0= 138d, onde D \u00e9 o di\u00e2metro do tubo.\u00a0Esse \u00e9 o maior comprimento de desenvolvimento poss\u00edvel.\u00a0Em\u00a0<\/span><strong><span>escoamento turbulento<\/span><\/strong><span>\u00a0, as camadas limite crescer mais rapidamente, e L\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0\u00a0\u00e9 relativamente mais curto.\u00a0Para qualquer problema,\u00a0<\/span><strong><span>L\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0\u00a0\/ D<\/span><\/strong><span>\u00a0deve ser\u00a0<\/span><strong><span>verificado<\/span><\/strong><span>\u00a0para ver se L\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0\u00a0\u00e9 insignificante quando comparado ao comprimento do tubo.\u00a0A uma dist\u00e2ncia finita da entrada, os efeitos da entrada podem ser negligenciados, porque as camadas de fronteira se fundem e o n\u00facleo inv\u00edscido desaparece.\u00a0O fluxo do tubo \u00e9 ent\u00e3o\u00a0<\/span><strong><span>totalmente desenvolvido<\/span><\/strong><span>\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\"><\/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<h2><span>Di\u00e2metro hidr\u00e1ulico<\/span><\/h2>\n<p><span>Como a\u00a0<\/span><strong><span>dimens\u00e3o caracter\u00edstica<\/span><\/strong><span>\u00a0de um tubo circular \u00e9 um di\u00e2metro comum D e, principalmente, os reatores cont\u00eam canais n\u00e3o circulares, a dimens\u00e3o caracter\u00edstica deve ser generalizada.<\/span><\/p>\n<p><span>Para esses fins, o\u00a0<\/span><strong><span>n\u00famero de Reynolds<\/span><\/strong><span>\u00a0\u00e9 definido como:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-hydraulic-diameter.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14472 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-hydraulic-diameter.png\" alt=\"N\u00famero de Reynolds - di\u00e2metro hidr\u00e1ulico\" width=\"207\" height=\"63\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-hydraulic-diameter.png\" \/><\/a><\/p>\n<p><span>onde D\u00a0<\/span><sub><span>h<\/span><\/sub><span>\u00a0\u00e9\u00a0<\/span><a title=\"Di\u00e2metro hidr\u00e1ulico\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/internal-flow\/hydraulic-diameter-2\/\"><strong><span>o di\u00e2metro hidr\u00e1ulico<\/span><\/strong><\/a><span>\u00a0:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Hydraulic-Diameter-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14418 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Hydraulic-Diameter-equation.png\" alt=\"Di\u00e2metro hidr\u00e1ulico - equa\u00e7\u00e3o\" width=\"99\" height=\"70\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Hydraulic-Diameter-equation.png\" \/><\/a><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Hydraulic-Diameter-non-circular-tubes.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-14421 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Hydraulic-Diameter-non-circular-tubes-232x300.png\" alt=\"Di\u00e2metro hidr\u00e1ulico\" width=\"232\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Hydraulic-Diameter-non-circular-tubes-232x300.png\" \/><\/a><strong><span>O di\u00e2metro hidr\u00e1ulico, D\u00a0<\/span><sub><span>h<\/span><\/sub><\/strong><span>\u00a0, \u00e9 um termo comumente usado ao manipular o fluxo em\u00a0<\/span><strong><span>tubos e canais n\u00e3o circulares<\/span><\/strong><span>\u00a0.\u00a0O di\u00e2metro hidr\u00e1ulico transforma dutos n\u00e3o circulares em tubos de\u00a0<\/span><strong><span>di\u00e2metro equivalente<\/span><\/strong><span>\u00a0.\u00a0Usando este termo, pode-se calcular muitas coisas da mesma maneira que para um tubo redondo.\u00a0Nesta equa\u00e7\u00e3o, A \u00e9 a\u00a0<\/span><strong><span>\u00e1rea da se\u00e7\u00e3o transversal<\/span><\/strong><span>\u00a0e P \u00e9 o\u00a0<\/span><strong><span>per\u00edmetro \u00famido<\/span><\/strong><span>\u00a0da se\u00e7\u00e3o.\u00a0O per\u00edmetro \u00famido de um canal \u00e9 o per\u00edmetro total de todas as paredes do canal que est\u00e3o em contato com o fluxo.<\/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>N\u00famero de Reynolds e fluxo externo<\/span><\/h2>\n<p><strong><span>O n\u00famero de Reynolds tamb\u00e9m<\/span><\/strong><span>\u00a0descreve naturalmente o\u00a0<\/span><a title=\"Fluxo externo\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/external-flow\/\"><span>fluxo externo<\/span><\/a><span>\u00a0.\u00a0Em geral, quando um fluido flui sobre uma\u00a0<\/span><strong><span>superf\u00edcie estacion\u00e1ria<\/span><\/strong><span>\u00a0, por exemplo, a placa plana, o leito de um rio ou a parede de um tubo, o fluido que toca a superf\u00edcie \u00e9 interrompido pela\u00a0<\/span><strong><span>tens\u00e3o de cisalhamento<\/span><\/strong><span>\u00a0na parede.\u00a0A regi\u00e3o na qual o fluxo se ajusta da velocidade zero na parede at\u00e9 o m\u00e1ximo na corrente principal do fluxo \u00e9 denominada\u00a0<\/span><a title=\"Camada limite\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-camada-de-limite-definicao\/\"><strong><span>camada limite<\/span><\/strong><\/a><span>\u00a0.<\/span><\/p>\n<p><span>As caracter\u00edsticas b\u00e1sicas de todas\u00a0<\/span><strong><span>as camadas limite laminar e turbulenta<\/span><\/strong><span>\u00a0s\u00e3o mostradas no fluxo em desenvolvimento sobre uma placa plana.\u00a0Os est\u00e1gios da forma\u00e7\u00e3o da camada limite s\u00e3o mostrados na figura abaixo:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Boundary-layer-on-flat-plate.png\"><img loading=\"lazy\" class=\"aligncenter size-large wp-image-14390 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Boundary-layer-on-flat-plate-1024x357.png\" alt=\"Camada limite na placa plana\" width=\"669\" height=\"233\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Boundary-layer-on-flat-plate-1024x357.png\" \/><\/a><\/p>\n<p><strong><span>As camadas de limite<\/span><\/strong><span>\u00a0podem ser\u00a0<\/span><strong><span>laminares<\/span><\/strong><span>\u00a0ou\u00a0<\/span><strong><span>turbulentas,<\/span><\/strong><span>\u00a0dependendo do valor do\u00a0<\/span><strong><span>n\u00famero de Reynolds<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><span>Tamb\u00e9m aqui o n\u00famero de Reynolds representa a raz\u00e3o entre for\u00e7as de in\u00e9rcia e for\u00e7as viscosas e \u00e9 um par\u00e2metro conveniente para prever se uma condi\u00e7\u00e3o de fluxo ser\u00e1 laminar ou turbulenta.\u00a0\u00c9 definido como:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14445 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-formula.png\" alt=\"N\u00famero de Reynolds\" width=\"229\" height=\"82\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Reynolds-number-formula.png\" \/><\/a><\/p>\n<p><span>em que V \u00e9 a velocidade m\u00e9dia do fluxo, D uma dimens\u00e3o linear caracter\u00edstica, \u03c1 densidade do fluido, \u03bc viscosidade din\u00e2mica e \u03bd viscosidade cinem\u00e1tica.<\/span><\/p>\n<p><span>Para\u00a0<\/span><strong><span>n\u00fameros mais baixos de Reynolds<\/span><\/strong><span>\u00a0, a camada limite \u00e9 laminar e a velocidade no sentido do fluxo muda uniformemente \u00e0 medida que se afasta da parede, conforme mostrado no lado esquerdo da figura.\u00a0<\/span><strong><span>\u00c0 medida que o n\u00famero de Reynolds aumenta<\/span><\/strong><span>\u00a0(com x), o\u00a0<\/span><strong><span>fluxo se torna inst\u00e1vel<\/span><\/strong><span>\u00a0e, finalmente, para n\u00fameros mais altos de Reynolds, a camada limite \u00e9 turbulenta e a velocidade do fluxo \u00e9 caracterizada por fluxos inst\u00e1veis \u200b\u200b(mudando com o tempo) dentro da camada limite.<\/span><\/p>\n<p><strong><span>A transi\u00e7\u00e3o da<\/span><\/strong><span>\u00a0camada limite\u00a0<strong>laminar para a turbulenta<\/strong>\u00a0ocorre quando o n\u00famero de Reynolds em x excede\u00a0<\/span><strong><span>Re\u00a0<\/span><sub><span>x<\/span><\/sub><span>\u00a0~ 500.000<\/span><\/strong><span>\u00a0.\u00a0A transi\u00e7\u00e3o pode ocorrer mais cedo, mas depende principalmente da\u00a0<\/span><strong><span>rugosidade<\/span><\/strong><span>\u00a0da\u00a0<strong>superf\u00edcie<\/strong>\u00a0.\u00a0A camada limite turbulenta espessa mais rapidamente do que a camada limite laminar como resultado do aumento da tens\u00e3o de cisalhamento na superf\u00edcie do corpo.<\/span><\/p>\n<p><span>O fluxo externo reage \u00e0 borda da camada limite, assim como faria \u00e0 superf\u00edcie f\u00edsica de um objeto.\u00a0Portanto, a camada limite fornece a qualquer objeto uma forma &#8220;efetiva&#8221; que geralmente \u00e9 ligeiramente diferente da forma f\u00edsica.\u00a0Definimos a\u00a0<\/span><strong><span>espessura<\/span><\/strong><span>\u00a0da camada limite como a dist\u00e2ncia da parede at\u00e9 o ponto em que a velocidade \u00e9 99% da velocidade do &#8220;fluxo livre&#8221;.<\/span><\/p>\n<p><span>Para tornar as coisas mais confusas, a camada limite pode decolar ou se &#8220;separar&#8221; do corpo e criar uma forma eficaz muito diferente da forma f\u00edsica.\u00a0Isso acontece porque o fluxo na fronteira tem energia muito baixa (em rela\u00e7\u00e3o \u00e0 corrente livre) e \u00e9 mais facilmente impulsionado por mudan\u00e7as na press\u00e3o.<\/span><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a title=\"Espessura da camada limite\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/boundary-layer\/boundary-layer-thickness\/\"><span>Espessura da camada limite<\/span><\/a><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a title=\"Fluxo externo\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/external-flow\/\"><span>Tubo em fluxo cruzado &#8211; fluxo externo<\/span><\/a><\/p>\n<p><strong><span>Refer\u00eancia especial:<\/span><\/strong><span>\u00a0Schlichting Herrmann, Gersten Klaus.\u00a0Teoria da camada limite, Springer-Verlag Berlin Heidelberg, 2000, ISBN: 978-3-540-66270-9<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<div><\/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 n\u00famero de Reynolds \u00e9 a raz\u00e3o de for\u00e7as inerciais para for\u00e7as viscosas e \u00e9 um par\u00e2metro conveniente para prever se uma condi\u00e7\u00e3o de fluxo ser\u00e1 laminar ou turbulenta. Engenharia T\u00e9rmica N\u00famero de Reynolds O n\u00famero de Reynolds\u00a0\u00e9 a propor\u00e7\u00e3o de\u00a0for\u00e7as de in\u00e9rcia\u00a0para\u00a0as for\u00e7as viscosas\u00a0e \u00e9 um par\u00e2metro conveniente para prever se uma condi\u00e7\u00e3o de &#8230; <a title=\"O que \u00e9 o n\u00famero de Reynolds &#8211; defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-numero-de-reynolds-definicao\/\" aria-label=\"More on O que \u00e9 o n\u00famero de Reynolds &#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 o n\u00famero de Reynolds - defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"O n\u00famero de Reynolds \u00e9 a raz\u00e3o de for\u00e7as inerciais para for\u00e7as viscosas e \u00e9 um par\u00e2metro conveniente para prever se uma condi\u00e7\u00e3o de fluxo ser\u00e1 laminar ou turbulenta. 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