{"id":47412,"date":"2019-11-04T08:39:21","date_gmt":"2019-11-04T07:39:21","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-circulacao-natural-definicao\/"},"modified":"2020-01-23T13:20:08","modified_gmt":"2020-01-23T12:20:08","slug":"o-que-e-circulacao-natural-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-circulacao-natural-definicao\/","title":{"rendered":"O que \u00e9 Circula\u00e7\u00e3o Natural &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">Circula\u00e7\u00e3o natural \u00e9 a circula\u00e7\u00e3o de fluido dentro de sistemas de tubula\u00e7\u00e3o ou piscinas abertas devido \u00e0s altera\u00e7\u00f5es de densidade causadas por diferen\u00e7as de temperatura.\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>Circula\u00e7\u00e3o Natural<\/h2>\n<figure id=\"attachment_20639\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-20639\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Natural-Circulation-schema.png\"><img loading=\"lazy\" class=\"size-medium wp-image-20639 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Natural-Circulation-schema-300x219.png\" alt=\"Circula\u00e7\u00e3o Natural - esquema\" width=\"300\" height=\"219\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Natural-Circulation-schema-300x219.png\" \/><\/a><figcaption id=\"caption-attachment-20639\" class=\"wp-caption-text\">Circula\u00e7\u00e3o natural em circuito fechado<\/figcaption><\/figure>\n<p><strong>Circula\u00e7\u00e3o natural<\/strong>\u00a0\u00e9 a circula\u00e7\u00e3o de fluido dentro de\u00a0<strong>sistemas de tubula\u00e7\u00e3o<\/strong>\u00a0ou\u00a0<strong>piscinas abertas<\/strong>\u00a0devido \u00e0s\u00a0<strong>altera\u00e7\u00f5es de densidade<\/strong>\u00a0causadas por diferen\u00e7as de temperatura.\u00a0<strong>A circula\u00e7\u00e3o natural<\/strong>\u00a0n\u00e3o requer dispositivos mec\u00e2nicos para manter o fluxo.<\/p>\n<p>Esse fen\u00f4meno tem natureza semelhante \u00e0 convec\u00e7\u00e3o natural, mas, neste caso, o coeficiente de transfer\u00eancia de calor n\u00e3o \u00e9 um objeto de estudo.\u00a0Nesse caso, o\u00a0<strong>fluxo em<\/strong>\u00a0massa\u00a0<strong>atrav\u00e9s do loop<\/strong>\u00a0\u00e9 o objeto de estudo.\u00a0Esse fen\u00f4meno \u00e9 mais um\u00a0<strong>problema hidr\u00e1ulico do<\/strong>\u00a0que um problema de transfer\u00eancia de calor, embora, como resultado, a circula\u00e7\u00e3o natural remova o calor da fonte e o transporte para o dissipador de calor e seja da maior import\u00e2ncia na seguran\u00e7a do reator.<\/p>\n<\/div>\n<\/div>\n<p>&nbsp;<\/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<h2><span>Condi\u00e7\u00f5es necess\u00e1rias para a circula\u00e7\u00e3o natural<\/span><\/h2>\n<p><span>Da mesma forma que na\u00a0<\/span><strong><span>convec\u00e7\u00e3o natural<\/span><\/strong><span>\u00a0,\u00a0<\/span><strong><span>a circula\u00e7\u00e3o natural<\/span><\/strong><span>\u00a0n\u00e3o opera essencialmente na \u00f3rbita da Terra.\u00a0A circula\u00e7\u00e3o natural ocorre em um loop apenas sob condi\u00e7\u00f5es espec\u00edficas.\u00a0Mesmo ap\u00f3s o in\u00edcio da circula\u00e7\u00e3o natural, a remo\u00e7\u00e3o de qualquer uma dessas condi\u00e7\u00f5es far\u00e1 com que a\u00a0<\/span><strong><span>circula\u00e7\u00e3o natural pare<\/span><\/strong><span>\u00a0.\u00a0As condi\u00e7\u00f5es para circula\u00e7\u00e3o natural s\u00e3o as seguintes:<\/span><\/p>\n<ul>\n<li><strong><span>Presen\u00e7a de acelera\u00e7\u00e3o adequada.\u00a0<\/span><\/strong><span>A circula\u00e7\u00e3o natural s\u00f3 pode ocorrer em um campo gravitacional ou na presen\u00e7a de outra acelera\u00e7\u00e3o adequada, como acelera\u00e7\u00e3o, for\u00e7a centr\u00edfuga.<\/span><\/li>\n<li><strong><span>Presen\u00e7a de fonte de calor e dissipador de calor<\/span><\/strong><span>\u00a0.\u00a0Fonte de calor e dissipador de calor s\u00e3o necess\u00e1rios, porque\u00a0<\/span><strong><span>a circula\u00e7\u00e3o natural<\/span><\/strong><span>\u00e9 gerado pela diferen\u00e7a de densidade no fluido que ocorre devido \u00e0 diferen\u00e7a de temperatura.\u00a0O fluido que entra em uma fonte de calor recebe calor e, por expans\u00e3o t\u00e9rmica, torna-se menos denso e sobe.\u00a0A expans\u00e3o t\u00e9rmica do fluido desempenha um papel crucial.\u00a0O processo em um canto de calor \u00e9 oposto, o canto de calor recebe calor e o fluido se torna mais denso.\u00a0A diferen\u00e7a de densidade \u00e9 a for\u00e7a motriz do fluxo de circula\u00e7\u00e3o natural.\u00a0A diferen\u00e7a de temperatura deve ser mantida para que a circula\u00e7\u00e3o natural continue.\u00a0A adi\u00e7\u00e3o de calor por uma fonte de calor deve existir na \u00e1rea de alta temperatura.\u00a0A remo\u00e7\u00e3o cont\u00ednua de calor por um dissipador de calor deve existir na \u00e1rea de baixa temperatura.\u00a0Caso contr\u00e1rio, as temperaturas acabariam se igualando, e nenhuma circula\u00e7\u00e3o adicional ocorreria.<\/span><\/li>\n<li><strong><span>Geometria adequada<\/span><\/strong><span>.\u00a0A presen\u00e7a e magnitude da circula\u00e7\u00e3o natural tamb\u00e9m dependem da geometria do problema.\u00a0A presen\u00e7a de um gradiente de densidade de fluido em um campo gravitacional n\u00e3o garante a exist\u00eancia de correntes de convec\u00e7\u00e3o naturais.\u00a0A circula\u00e7\u00e3o natural em um circuito fechado cheio de fluido \u00e9 estabelecida pela localiza\u00e7\u00e3o de um dissipador de calor no circuito a uma eleva\u00e7\u00e3o mais alta que a fonte de calor.\u00a0O fluido circulante remove o calor da fonte e o transporta para a pia.\u00a0O fluxo pode ser monof\u00e1sico ou bif\u00e1sico, em que o vapor flui ao longo do l\u00edquido.\u00a0A diferen\u00e7a de temperatura deve ser mantida para que a circula\u00e7\u00e3o natural continue.\u00a0A adi\u00e7\u00e3o de calor por uma fonte de calor deve existir na \u00e1rea de alta temperatura.\u00a0A remo\u00e7\u00e3o cont\u00ednua de calor por um dissipador de calor deve existir na \u00e1rea de baixa temperatura.\u00a0Caso contr\u00e1rio, as temperaturas eventualmente se igualariam,\u00a0e n\u00e3o ocorreria mais circula\u00e7\u00e3o.\u00a0\u00c9 poss\u00edvel que a circula\u00e7\u00e3o natural ocorra em fluxo bif\u00e1sico, mas geralmente \u00e9 mais dif\u00edcil manter o fluxo.<\/span><\/li>\n<li><strong><span>Fluidos em contato<\/span><\/strong><span>\u00a0.\u00a0As duas \u00e1reas devem estar em contato para que o fluxo entre as \u00e1reas seja poss\u00edvel.\u00a0Se o caminho do fluxo estiver obstru\u00eddo ou bloqueado, a circula\u00e7\u00e3o natural n\u00e3o poder\u00e1 ocorrer.<\/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\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Circula\u00e7\u00e3o Natural &#8211; Vaz\u00e3o<\/span><\/h2>\n<p><strong><span>A<\/span><\/strong><span>\u00a0taxa de fluxo de\u00a0<strong>circula\u00e7\u00e3o natural<\/strong>\u00a0no circuito, em estado estacion\u00e1rio, \u00e9 determinada a partir do\u00a0<\/span><strong><span>equil\u00edbrio<\/span><\/strong><span>\u00a0entre as\u00a0<strong>for\u00e7as\u00a0<\/strong><\/span><strong><span>motriz<\/span><\/strong><span>\u00a0e\u00a0<\/span><strong><span>resist\u00eancia<\/span><\/strong><span>\u00a0.\u00a0A for\u00e7a motriz resulta da diferen\u00e7a de densidade entre a perna quente e a perna fria do circuito.\u00a0O cabe\u00e7ote necess\u00e1rio para compensar as perdas de cabe\u00e7ote \u00e9 criado por gradientes de densidade e altera\u00e7\u00f5es de eleva\u00e7\u00e3o.<\/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>Cabe\u00e7a de condu\u00e7\u00e3o t\u00e9rmica<\/span><\/h2>\n<p><strong><span>Cabe\u00e7a de acionamento t\u00e9rmico<\/span><\/strong><span>\u00a0\u00e9 a for\u00e7a que causa\u00a0<\/span><strong><span>a circula\u00e7\u00e3o natural<\/span><\/strong><span>\u00a0.\u00a0\u00c9 causada pela diferen\u00e7a de\u00a0<\/span><a title=\"O que \u00e9 densidade - F\u00edsica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-density-physics\/\"><span>densidade<\/span><\/a><span>\u00a0entre dois corpos ou \u00e1reas de fluido.\u00a0Considere dois volumes iguais do mesmo tipo de fluido.\u00a0Se os dois volumes n\u00e3o estiverem na mesma\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>temperatura<\/span><\/a><span>\u00a0, o\u00a0<\/span><a title=\"O que \u00e9 volume - F\u00edsica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-volume-physics\/\"><span>volume<\/span><\/a><span>\u00a0com a temperatura mais alta tamb\u00e9m ter\u00e1 uma densidade mais baixa e, portanto, menos massa.\u00a0Sabe-se que a densidade de gases e l\u00edquidos depende da temperatura, geralmente diminuindo (devido \u00e0 expans\u00e3o do fluido) com o aumento da temperatura.\u00a0Como o volume a uma temperatura mais alta ter\u00e1 uma\u00a0<a title=\"O que \u00e9 massa\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-mass-and-weight\/what-is-mass\/\">massa<\/a>\u00a0menor<\/span><span>, tamb\u00e9m ter\u00e1 menos for\u00e7a exercida sobre ele pela gravidade.\u00a0Essa diferen\u00e7a na for\u00e7a da gravidade exercida sobre o fluido tender\u00e1 a fazer com que o fluido mais quente suba e o fluido mais frio afunde.\u00a0<\/span><strong><span>A cabe\u00e7a de acionamento t\u00e9rmico<\/span><\/strong><span>\u00a0pode ser simplesmente calculada usando a diferen\u00e7a de press\u00f5es hidrost\u00e1ticas:<\/span><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-driving-head-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-20658 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-driving-head-equation.png\" alt=\"cabe\u00e7a de condu\u00e7\u00e3o t\u00e9rmica - equa\u00e7\u00e3o\" width=\"377\" height=\"58\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-driving-head-equation.png\" \/><\/a><\/p>\n<p><span>Como pode ser visto, quanto maior a diferen\u00e7a de temperatura entre as \u00e1reas quentes e frias do fluido, maior a\u00a0<\/span><strong><span>cabe\u00e7a de acionamento t\u00e9rmico<\/span><\/strong><span>\u00a0e a vaz\u00e3o resultante.<\/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>For\u00e7a de resist\u00eancia hidr\u00e1ulica<\/span><\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/PLC-Pressure-loss-coefficient-equations.png\"><img loading=\"lazy\" class=\"alignright size-full wp-image-20526 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/PLC-Pressure-loss-coefficient-equations.png\" alt=\"CLP - Coeficiente de perda de press\u00e3o - equa\u00e7\u00f5es\" width=\"339\" height=\"375\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/PLC-Pressure-loss-coefficient-equations.png\" \/><\/a><span>Como foi escrito,\u00a0<\/span><strong><span>a taxa de fluxo de circula\u00e7\u00e3o natural<\/span><\/strong><span>\u00a0, V, no circuito fechado, em condi\u00e7\u00f5es de estado estacion\u00e1rio, \u00e9 determinada a partir do equil\u00edbrio entre a cabe\u00e7a motriz e as for\u00e7as resistentes.\u00a0Como o atrito do tubo, as\u00a0<\/span><strong><span>perdas de press\u00e3o gerais<\/span><\/strong><span>\u00a0s\u00e3o\u00a0<\/span><strong><span>proporcionais ao quadrado da vaz\u00e3o<\/span><\/strong><span>\u00a0e, portanto, podem ser facilmente integradas na\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/darcy-weisbach-equation\/\"><strong><span>equa\u00e7\u00e3o de Darcy-Weisbach<\/span><\/strong><\/a><span>\u00a0.\u00a0Os engenheiros costumam usar o\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/head-loss\/pressure-loss-coefficient-plc\/\"><strong><span>coeficiente de perda de press\u00e3o<\/span><\/strong><\/a><span>\u00a0,\u00a0<\/span><strong><span>CLP<\/span><\/strong><span>\u00a0.\u00a0Nota-se K ou\u00a0<\/span><strong><span>\u03be<\/span><\/strong><span>\u00a0(pronunciado \u201cxi\u201d).\u00a0Este coeficiente caracteriza a\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/head-loss\/\"><span>perda de press\u00e3o<\/span><\/a><span>de um determinado sistema hidr\u00e1ulico ou de uma parte de um sistema hidr\u00e1ulico.\u00a0Pode ser facilmente medido em loops hidr\u00e1ulicos.\u00a0O coeficiente de perda de press\u00e3o pode ser definido ou medido para tubos retos e especialmente para\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/minor-head-loss-local-losses\/\"><strong><span>perdas locais (menores)<\/span><\/strong><\/a><span>\u00a0.\u00a0Como o\u00a0<\/span><a title=\"Fator de atrito de Darcy\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-fator-de-atrito-de-darcy-definicao\/\"><span>fator de atrito de Darcy<\/span><\/a><span>\u00a0\u00e9 uma fun\u00e7\u00e3o da velocidade (no n\u00famero de Reynolds), o c\u00e1lculo do coeficiente de perda de press\u00e3o \u00e9 um processo iterativo.<\/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>Circula\u00e7\u00e3o Natural em Engenharia de Reatores<\/span><\/h2>\n<figure id=\"attachment_20639\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-20639\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Natural-Circulation-schema.png\"><img loading=\"lazy\" class=\"size-medium wp-image-20639 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Natural-Circulation-schema-300x219.png\" alt=\"Circula\u00e7\u00e3o Natural - esquema\" width=\"300\" height=\"219\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Natural-Circulation-schema-300x219.png\" \/><\/a><figcaption id=\"caption-attachment-20639\" class=\"wp-caption-text\"><span>Circula\u00e7\u00e3o natural em circuito fechado<\/span><\/figcaption><\/figure>\n<p><span>Na\u00a0<\/span><a title=\"Engenharia nuclear\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/\"><span>engenharia de reatores<\/span><\/a><span>\u00a0,\u00a0<\/span><strong><span>a circula\u00e7\u00e3o natural<\/span><\/strong><span>\u00a0\u00e9 um fen\u00f4meno muito desejado, pois \u00e9 capaz de fornecer\u00a0<\/span><a title=\"Arrefecimento do reator\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/reactor-operation\/reactor-cooling\/\"><strong><span>resfriamento do n\u00facleo do reator<\/span><\/strong><\/a><span>\u00a0ap\u00f3s a perda de\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/reactor-coolant-pump\/\"><strong><span>RCPs<\/span><\/strong><\/a><span>\u00a0(por exemplo, ap\u00f3s perda de energia\u00a0<a href=\"https:\/\/www.nuclear-power.com\/reactor-coolant-pump\/\"><strong>externa<\/strong><\/a>\u00a0&#8211; LOOP).\u00a0Em PWRs, o projeto da planta fornece uma\u00a0<\/span><strong><span>diferen\u00e7a de eleva\u00e7\u00e3o<\/span><\/strong><span>\u00a0,\u00a0<\/span><strong><span>h<\/span><\/strong><span>\u00a0, de aproximadamente\u00a0<\/span><strong><span>12 metros<\/span><\/strong><span>\u00a0entre a linha central do\u00a0<\/span><a title=\"Gerador de vapor\" href=\"https:\/\/www.nuclear-power.com\/steam-generator\/\"><span>gerador de vapor<\/span><\/a><span>\u00a0e a linha central do\u00a0<\/span><a title=\"N\u00facleo do reator\" href=\"https:\/\/www.reactor-physics.com\/what-is-reactor-core-definition\/\"><span>n\u00facleo<\/span><\/a><span>\u00a0do\u00a0<a title=\"N\u00facleo do reator\" href=\"https:\/\/www.reactor-physics.com\/what-is-reactor-core-definition\/\">reator<\/a>\u00a0.\u00a0O layout do sistema deve garantir a capacidade de circula\u00e7\u00e3o natural ap\u00f3s uma perda de fluxo para permitir a recarga sem superaquecer o n\u00facleo.\u00a0Al\u00e9m disso, a tubula\u00e7\u00e3o de interconex\u00e3o do\u00a0<a title=\"Embarca\u00e7\u00e3o de Press\u00e3o do Reator\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power-plant\/nuclear-reactor\/reactor-pressure-vessel\/\">vaso de press\u00e3o<\/a>\u00a0do\u00a0<\/span><a title=\"Embarca\u00e7\u00e3o de Press\u00e3o do Reator\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power-plant\/nuclear-reactor\/reactor-pressure-vessel\/\"><span>reator<\/span><\/a><span>Os geradores de vapor devem estar intactos, livres de obstru\u00e7\u00f5es, como gases n\u00e3o condens\u00e1veis \u200b\u200b(por exemplo, bolsas de vapor).\u00a0Dessa forma, a circula\u00e7\u00e3o natural garantir\u00e1 que o fluido continue fluindo enquanto o reator estiver mais quente que o dissipador de calor, mesmo quando a energia n\u00e3o puder ser fornecida \u00e0s bombas.<\/span><\/p>\n<p><a title=\"Bomba de refrigera\u00e7\u00e3o do reator\" href=\"https:\/\/www.nuclear-power.com\/reactor-coolant-pump\/\"><span>Os RCPs<\/span><\/a><span>\u00a0geralmente n\u00e3o s\u00e3o &#8220;sistema de seguran\u00e7a&#8221;, conforme definido.\u00a0Ap\u00f3s a perda de RCPs (por exemplo, ap\u00f3s perda de energia externa &#8211; LOOP), o reator deve ser desligado imediatamente, pois os RCPs diminuem lentamente at\u00e9 a vaz\u00e3o zero.\u00a0A remo\u00e7\u00e3o de calor residual suficiente e segura \u00e9 ent\u00e3o assegurada por um\u00a0fluxo de\u00a0<\/span><strong><span>circula\u00e7\u00e3o natural<\/span><\/strong><span>\u00a0atrav\u00e9s do reator.\u00a0Sem fluxo for\u00e7ado, o l\u00edquido de arrefecimento no n\u00facleo come\u00e7a a aquecer.\u00a0O aumento da temperatura do refrigerante causa uma redu\u00e7\u00e3o na densidade do refrigerante, que por sua vez move o refrigerante para o gerador de vapor.\u00a0Deve-se notar que a circula\u00e7\u00e3o natural n\u00e3o \u00e9 suficiente para remover o calor gerado quando o reator est\u00e1 na pot\u00eancia.<\/span><\/p>\n<p><span>Os projetos modernos de reatores usam a circula\u00e7\u00e3o natural, um\u00a0<\/span><strong><span>recurso de seguran\u00e7a<\/span><\/strong><span>\u00a0muito importante\u00a0.\u00a0Muitos sistemas de seguran\u00e7a passiva em projetos modernos de reatores operam sem o uso de bombas, o que cria maior seguran\u00e7a, integridade e confiabilidade do projeto, reduzindo simultaneamente o custo geral do reator.<\/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>Indicadores de circula\u00e7\u00e3o natural<\/span><\/h2>\n<p><span>Nos PWRs, v\u00e1rios par\u00e2metros podem ser usados \u200b\u200bpara indicar ou verificar a circula\u00e7\u00e3o natural.\u00a0Isso depende do tipo e dos sistemas da planta.\u00a0Por exemplo, para um PWR, os par\u00e2metros selecionados que podem ser usados \u200b\u200bs\u00e3o os seguintes:<\/span><\/p>\n<ul>\n<li><span>Idealmente, a\u00a0<\/span><strong><span>taxa de fluxo<\/span><\/strong><span>\u00a0pode ser medida em cada um dos loops.<\/span><\/li>\n<li><strong><span>\u0394T<\/span><\/strong><span>\u00a0(\u00a0<\/span><strong><span>T\u00a0<\/span><sub><span>quente<\/span><\/sub><span>\u00a0&#8211; T\u00a0<\/span><sub><span>frio<\/span><\/sub><\/strong><span>\u00a0).\u00a0A diferen\u00e7a de temperatura entre as pernas quentes e as frias deve ser de 25 a 80% do valor total da pot\u00eancia e estar constante ou diminuir lentamente.\u00a0Isso indica que o calor de decomposi\u00e7\u00e3o est\u00e1 sendo removido do sistema a uma taxa adequada para manter ou reduzir as temperaturas do n\u00facleo.<\/span><\/li>\n<li><span>As temperaturas quentes e frias das pernas devem estar est\u00e1veis \u200b\u200bou diminuindo lentamente.\u00a0Novamente, isso indica que o calor est\u00e1 sendo removido e a carga de calor do decaimento est\u00e1 diminuindo conforme o esperado.<\/span><\/li>\n<li><span>A press\u00e3o do vapor do gerador de vapor (press\u00e3o lateral secund\u00e1ria) deve estar seguindo a temperatura do sistema de refrigera\u00e7\u00e3o do reator.\u00a0Isso verifica se o gerador de vapor est\u00e1 removendo o calor do l\u00edquido de arrefecimento RCS.<\/span><\/li>\n<\/ul>\n<p><span>Refer\u00eancia especial: Circula\u00e7\u00e3o natural em usinas nucleares resfriadas a \u00e1gua, IAEA-TECDOC-1474.\u00a0IAEA, 2005. ISBN 92\u20130\u2013110605 \u2013 X.<\/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-accordion\">\n<div class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\">\n<div class=\"su-spoiler-content su-clearfix\"><\/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<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Circula\u00e7\u00e3o natural \u00e9 a circula\u00e7\u00e3o de fluido dentro de sistemas de tubula\u00e7\u00e3o ou piscinas abertas devido \u00e0s altera\u00e7\u00f5es de densidade causadas por diferen\u00e7as de temperatura.\u00a0Engenharia T\u00e9rmica Circula\u00e7\u00e3o Natural Circula\u00e7\u00e3o natural em circuito fechado Circula\u00e7\u00e3o natural\u00a0\u00e9 a circula\u00e7\u00e3o de fluido dentro de\u00a0sistemas de tubula\u00e7\u00e3o\u00a0ou\u00a0piscinas abertas\u00a0devido \u00e0s\u00a0altera\u00e7\u00f5es de densidade\u00a0causadas por diferen\u00e7as de temperatura.\u00a0A circula\u00e7\u00e3o natural\u00a0n\u00e3o requer dispositivos &#8230; <a title=\"O que \u00e9 Circula\u00e7\u00e3o Natural &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-circulacao-natural-definicao\/\" aria-label=\"More on O que \u00e9 Circula\u00e7\u00e3o Natural &#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 Circula\u00e7\u00e3o Natural - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"Circula\u00e7\u00e3o natural \u00e9 a circula\u00e7\u00e3o de fluido dentro de sistemas de tubula\u00e7\u00e3o ou piscinas abertas devido \u00e0s altera\u00e7\u00f5es de densidade causadas pelas diferen\u00e7as de temperatura. 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