{"id":52881,"date":"2020-02-26T14:48:01","date_gmt":"2020-02-26T13:48:01","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/quest-ce-que-la-pression-physique-definition\/"},"modified":"2020-02-26T14:50:14","modified_gmt":"2020-02-26T13:50:14","slug":"quest-ce-que-la-pression-physique-definition","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/fr\/quest-ce-que-la-pression-physique-definition\/","title":{"rendered":"Qu&#8217;est-ce que la pression &#8211; Physique &#8211; D\u00e9finition"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">Quelle est la pression. La pression est une propri\u00e9t\u00e9 intensive de la mati\u00e8re. L&#8217;unit\u00e9 standard de pression dans le syst\u00e8me SI est le Newton par m\u00e8tre carr\u00e9 ou pascal (Pa). G\u00e9nie thermique<\/div>\n<\/div>\n<div><\/div>\n<div><\/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>Quelle est la pression<\/span><\/h2>\n<p><strong><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Manometer-Pressure-Measurement.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-16368 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Manometer-Pressure-Measurement-235x300.png\" alt=\"manom\u00e8tre-pression-mesure\" width=\"235\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Manometer-Pressure-Measurement-235x300.png\" \/><\/a><span>La pression<\/span><\/strong><span>\u00a0est une mesure de la\u00a0<\/span><strong><span>force exerc\u00e9e<\/span><\/strong><span>\u00a0par unit\u00e9 de surface sur les limites d&#8217;une substance.\u00a0L&#8217;unit\u00e9 standard de\u00a0<\/span><strong><span>pression<\/span><\/strong><span>\u00a0dans le syst\u00e8me SI est le\u00a0<\/span><strong><span>Newton par m\u00e8tre carr\u00e9 ou pascal (Pa)<\/span><\/strong><span>\u00a0.\u00a0Math\u00e9matiquement:<\/span><\/p>\n<p><strong><span>p = F \/ A<\/span><\/strong><\/p>\n<p><span>o\u00f9<\/span><\/p>\n<ul>\n<li><strong><span>p est la pression<\/span><\/strong><\/li>\n<li><strong><span>F est la force normale<\/span><\/strong><\/li>\n<li><strong><span>A est l&#8217;aire de la fronti\u00e8re<\/span><\/strong><\/li>\n<\/ul>\n<p><span>Pascal est d\u00e9fini comme la force de 1N qui s&#8217;exerce sur la surface unitaire.<\/span><\/p>\n<ul>\n<li><strong><span>1 Pascal = 1 N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<\/ul>\n<\/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\"><span>Cependant, pour la plupart des probl\u00e8mes d&#8217;ing\u00e9nierie, il s&#8217;agit d&#8217;une unit\u00e9 assez petite, il est donc pratique de travailler avec des multiples du pascal: le\u00a0<\/span><strong><span>kPa<\/span><\/strong><span>\u00a0, la\u00a0<\/span><strong><span>barre<\/span><\/strong><span>\u00a0et le\u00a0<\/span><strong><span>MPa<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<ul>\n<li><strong><span>1 MPa 10\u00a0<\/span><sup><span>6<\/span><\/sup><span>\u00a0N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<li><strong><span>1 bar 10\u00a0<\/span><sup><span>5<\/span><\/sup><span>\u00a0N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<li><strong><span>1 kPa 10\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<\/ul>\n<p><span>En g\u00e9n\u00e9ral, la pression ou la force exerc\u00e9e par unit\u00e9 de surface sur les limites d&#8217;une substance est caus\u00e9e par les\u00a0<\/span><strong><span>collisions<\/span><\/strong><span>\u00a0des\u00a0<\/span><strong><span>mol\u00e9cules<\/span><\/strong><span>\u00a0de la substance avec les limites du syst\u00e8me.\u00a0Lorsque les mol\u00e9cules frappent les murs, elles exercent des forces qui tentent de pousser les murs vers l&#8217;ext\u00e9rieur.\u00a0Les forces r\u00e9sultant de toutes ces collisions provoquent la\u00a0<\/span><strong><span>pression<\/span><\/strong><span>\u00a0exerc\u00e9e par un syst\u00e8me sur son environnement.\u00a0La pression en tant que\u00a0<\/span><a title=\"Propri\u00e9t\u00e9s \u00e9tendues et intensives\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/extensive-and-intensive-properties\/\"><strong><span>variable intensive<\/span><\/strong>\u00a0<\/a><span>est constante dans un syst\u00e8me ferm\u00e9.\u00a0Il n&#8217;est vraiment pertinent que dans les syst\u00e8mes liquides ou gazeux.<\/span><\/p>\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\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/What-is-Pressure.png\"><img loading=\"lazy\" class=\"aligncenter size-medium wp-image-16371 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/What-is-Pressure-300x129.png\" alt=\"Quelle est la pression\" width=\"300\" height=\"129\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/What-is-Pressure-300x129.png\" \/><\/a><\/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>\u00c9chelles de pression &#8211; Unit\u00e9s de pression<\/span><\/h2>\n<h2><span>Pascal &#8211; Unit\u00e9 de pression<\/span><\/h2>\n<p><span>Comme nous l&#8217;avons vu, l&#8217;\u00a0<\/span><strong><span>unit\u00e9 SI<\/span><\/strong><span>\u00a0de\u00a0<\/span><strong><span>pression<\/span><\/strong><span>\u00a0et de contrainte est le\u00a0<\/span><strong><span>pascal<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<ul>\n<li><strong><span>1 pascal 1 N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0= 1 kg \/ (ms\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0)<\/span><\/strong><\/li>\n<\/ul>\n<p><a title=\"Pascal - Unit\u00e9 de pression\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-pressure-physics\/pascal-unit-of-pressure\/\"><span>Pascal<\/span><\/a><span>\u00a0est d\u00e9fini comme un newton par m\u00e8tre carr\u00e9.\u00a0Cependant, pour la plupart des probl\u00e8mes d&#8217;ing\u00e9nierie, il s&#8217;agit d&#8217;une unit\u00e9 assez petite, il est donc pratique de travailler avec des multiples du pascal: le\u00a0<\/span><strong><span>kPa<\/span><\/strong><span>\u00a0, la\u00a0<\/span><strong><span>barre<\/span><\/strong><span>\u00a0et le\u00a0<\/span><strong><span>MPa<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<ul>\n<li><strong><span>1 MPa 10\u00a0<\/span><sup><span>6<\/span><\/sup><span>\u00a0N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<li><strong><span>1 bar 10\u00a0<\/span><sup><span>5<\/span><\/sup><span>\u00a0N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<li><strong><span>1 kPa 10\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0N \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<\/ul>\n<p><span>L&#8217;unit\u00e9 de mesure appel\u00e9e\u00a0<\/span><strong><span>atmosph\u00e8re standard<\/span><\/strong><span>\u00a0(\u00a0<\/span><strong><span>atm<\/span><\/strong><span>\u00a0) est d\u00e9finie comme:<\/span><\/p>\n<ul>\n<li><strong><span>1 atm = 101,33 kPa<\/span><\/strong><\/li>\n<\/ul>\n<p><span>L&#8217;atmosph\u00e8re standard se rapproche de la pression moyenne au niveau de la mer \u00e0 45 \u00b0 de latitude N. Notez qu&#8217;il y a une diff\u00e9rence entre l&#8217;\u00a0<\/span><strong><span>atmosph\u00e8re standard<\/span><\/strong><span>\u00a0(atm) et l&#8217;\u00a0<\/span><strong><span>atmosph\u00e8re technique<\/span><\/strong><span>\u00a0(at).<\/span><\/p>\n<p><span>Une atmosph\u00e8re technique est une unit\u00e9 de pression non SI \u00e9gale \u00e0 un kilogramme de force par centim\u00e8tre carr\u00e9.<\/span><\/p>\n<ul>\n<li><strong><span>1 \u00e0 = 98,67 kPa<\/span><\/strong><\/li>\n<\/ul>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Pressure-Units-pascal-bar-psi-atmosphere.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-16280 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Pressure-Units-pascal-bar-psi-atmosphere.png\" alt=\"Tableau - Conversion entre unit\u00e9s de pression - pascal, bar, psi, atmosph\u00e8re\" width=\"659\" height=\"289\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Pressure-Units-pascal-bar-psi-atmosphere.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<h2><strong><b><span>Livres par pouce carr\u00e9 &#8211; psi<\/span><\/b><\/strong><\/h2>\n<p><span>L&#8217;unit\u00e9 standard dans le syst\u00e8me anglais est la\u00a0<\/span><strong><span>livre-force par pouce carr\u00e9 (psi)<\/span><\/strong><span>\u00a0.\u00a0C&#8217;est la pression r\u00e9sultant d&#8217;une force d&#8217;une livre-force appliqu\u00e9e \u00e0 une zone d&#8217;un pouce carr\u00e9.<\/span><\/p>\n<ul>\n<li><strong><span>1 psi 1 lbf \/ in\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0= 4,45 N \/ (0,0254 m)\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0\u2248 6895 kg \/ m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><\/li>\n<\/ul>\n<p><span>Par cons\u00e9quent, une livre par pouce carr\u00e9 \u00e9quivaut \u00e0 environ 6895 Pa.<\/span><\/p>\n<p><span>L&#8217;unit\u00e9 de mesure appel\u00e9e atmosph\u00e8re standard (atm) est d\u00e9finie comme:<\/span><\/p>\n<ul>\n<li><strong><span>1 atm = 14,7 psi<\/span><\/strong><\/li>\n<\/ul>\n<p><span>L&#8217;atmosph\u00e8re standard se rapproche de la pression moyenne au niveau de la mer \u00e0 45 \u00b0 de latitude N. Notez qu&#8217;il y a une diff\u00e9rence entre l&#8217;\u00a0<\/span><strong><span>atmosph\u00e8re standard<\/span><\/strong><span>\u00a0(atm) et l&#8217;\u00a0<\/span><strong><span>atmosph\u00e8re technique<\/span><\/strong><span>\u00a0(at).<\/span><\/p>\n<p><span>Une atmosph\u00e8re technique est une unit\u00e9 de pression non SI \u00e9gale \u00e0 un kilogramme de force par centim\u00e8tre carr\u00e9.<\/span><\/p>\n<ul>\n<li><strong><span>1 at = 14,2 psi<\/span><\/strong><\/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<h2><b><span>Bar &#8211; Unit\u00e9 de pression<\/span><\/b><\/h2>\n<p><span>La\u00a0<\/span><strong><span>barre<\/span><\/strong><span>\u00a0est une unit\u00e9 de\u00a0<\/span><strong><span>pression<\/span><\/strong><span>\u00a0m\u00e9trique\u00a0.\u00a0Il ne fait pas partie du Syst\u00e8me international d&#8217;unit\u00e9s (SI).\u00a0La\u00a0<\/span><strong><span>barre<\/span><\/strong><span>\u00a0est couramment utilis\u00e9e dans l&#8217;\u00a0<\/span><strong><span>industrie<\/span><\/strong><span>\u00a0et la\u00a0<\/span><strong><span>m\u00e9t\u00e9orologie<\/span><\/strong><span>\u00a0, et un instrument utilis\u00e9 en m\u00e9t\u00e9orologie pour mesurer la pression atmosph\u00e9rique est appel\u00e9 barom\u00e8tre.<\/span><\/p>\n<p><span>Une barre \u00e9quivaut exactement \u00e0\u00a0<\/span><strong><em><span>100 000 Pa<\/span><\/em><\/strong><span>\u00a0et est l\u00e9g\u00e8rement inf\u00e9rieure \u00e0 la pression atmosph\u00e9rique moyenne sur Terre au niveau de la mer (\u00a0<\/span><em><span>1 bar = 0,9869 atm).\u00a0<\/span><\/em><span>La pression atmosph\u00e9rique est souvent indiqu\u00e9e en millibars, o\u00f9 la pression standard au niveau de la mer est d\u00e9finie comme 1013 mbar, 1,013 bar ou 101,3 (kPa).<\/span><\/p>\n<p><span>Parfois, \u00abBar (a)\u00bb et \u00abbara\u00bb sont utilis\u00e9s pour indiquer les pressions absolues et \u00abbar (g)\u00bb et \u00abbarg\u00bb pour les pressions manom\u00e9triques.<\/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>Pression absolue vs pression manom\u00e9trique<\/span><\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/absolute-vs.-gauge-pressure.png\"><img loading=\"lazy\" class=\"alignright size-full wp-image-16281 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/absolute-vs.-gauge-pressure.png\" alt=\"pression absolue vs manom\u00e9trique\" width=\"388\" height=\"247\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/absolute-vs.-gauge-pressure.png\" \/><\/a><span>La pression d\u00e9crite ci-dessus est appel\u00e9e\u00a0<\/span><strong><span>pression absolue<\/span><\/strong><span>\u00a0.\u00a0Souvent ,\u00a0il est important de\u00a0faire la\u00a0distinction entre\u00a0<\/span><strong><span>pression absolue<\/span><\/strong><span>\u00a0et la\u00a0<\/span><strong><span>pression de la\u00a0jauge<\/span><\/strong><span>\u00a0.\u00a0Dans cet article, le terme pression fait r\u00e9f\u00e9rence \u00e0 la pression absolue, sauf indication contraire explicite.\u00a0Mais en ing\u00e9nierie, nous avons souvent affaire \u00e0 des pressions, qui sont\u00a0<\/span><strong><span>mesur\u00e9es<\/span><\/strong><span>\u00a0par certains appareils.\u00a0Bien que les pressions absolues doivent \u00eatre utilis\u00e9es dans les relations thermodynamiques,\u00a0<\/span><strong><span>les<\/span><\/strong><span>\u00a0appareils de\u00a0<strong>mesure de pression<\/strong>\u00a0indiquent souvent la\u00a0<\/span><strong><span>diff\u00e9rence<\/span><\/strong><span>\u00a0entre la pression absolue dans un syst\u00e8me et la pression absolue de l&#8217;atmosph\u00e8re existant \u00e0 l&#8217;ext\u00e9rieur de l&#8217;appareil de mesure.\u00a0Ils mesurent la\u00a0<\/span><strong><span>pression manom\u00e9trique<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<ul>\n<li><strong><span>Pression absolue.\u00a0<\/span><\/strong><span>Lorsque la pression est mesur\u00e9e par rapport \u00e0 un vide parfait, elle est appel\u00e9e pression absolue (psia).\u00a0Les livres par pouce carr\u00e9 absolu (psia) sont utilis\u00e9es pour indiquer clairement que la pression est relative \u00e0 un vide plut\u00f4t qu&#8217;\u00e0 la pression atmosph\u00e9rique ambiante.\u00a0\u00c9tant donn\u00e9 que la pression atmosph\u00e9rique au niveau de la mer est d&#8217;environ 101,3 kPa (14,7 psi), cela s&#8217;ajoutera \u00e0 toute lecture de pression effectu\u00e9e dans l&#8217;air au niveau de la mer.<\/span><\/li>\n<li><strong><span>Pression manom\u00e9trique.\u00a0<\/span><\/strong><span>Lorsque la pression est mesur\u00e9e par rapport \u00e0 la pression atmosph\u00e9rique (14,7 psi), elle est appel\u00e9e pression manom\u00e9trique (psig).\u00a0Le terme pression relative est appliqu\u00e9 lorsque la pression dans le syst\u00e8me est sup\u00e9rieure \u00e0 la pression atmosph\u00e9rique locale, p\u00a0<\/span><sub><span>atm<\/span><\/sub><span>\u00a0.\u00a0Cette derni\u00e8re \u00e9chelle de pression a \u00e9t\u00e9 d\u00e9velopp\u00e9e car presque tous les manom\u00e8tres enregistrent z\u00e9ro lorsqu&#8217;ils sont ouverts sur l&#8217;atmosph\u00e8re.\u00a0Les pressions manom\u00e9triques sont positives si elles sont sup\u00e9rieures \u00e0 la pression atmosph\u00e9rique et n\u00e9gatives si elles sont inf\u00e9rieures \u00e0 la pression atmosph\u00e9rique.<\/span><\/li>\n<\/ul>\n<p><em><sub><span>jauge<\/span><\/sub><\/em><span><em>\u00a0p\u00a0<\/em><\/span><em><span>= p\u00a0<\/span><\/em><em><sub><span>absolu<\/span><\/sub><\/em><em><span>\u00a0&#8211; p\u00a0<\/span><\/em><em><sub><span>absolu;\u00a0au m<\/span><\/sub><\/em><\/p>\n<ul>\n<li><strong><span>Pression atmosph\u00e9rique.\u00a0<\/span><\/strong><span>La pression atmosph\u00e9rique est la pression dans l&#8217;air ambiant \u00e0 la surface de la Terre &#8211; ou \u00abpr\u00e8s\u00bb de celle-ci.\u00a0La pression atmosph\u00e9rique varie avec la temp\u00e9rature et l&#8217;altitude au-dessus du niveau de la mer.\u00a0La\u00a0<\/span><strong><span>pression atmosph\u00e9rique standard se<\/span><\/strong><span>\u00a0rapproche de la pression moyenne au niveau de la mer \u00e0 45 \u00b0 de latitude nord. La\u00a0<\/span><strong><span>pression atmosph\u00e9rique standard<\/span><\/strong><span>\u00a0est d\u00e9finie au niveau de la mer \u00e0\u00a0<\/span><em><span>273\u00a0<\/span><\/em><em><sup><span>o<\/span><\/sup><\/em><em><span>\u00a0K (0\u00a0<\/span><\/em><em><sup><span>o<\/span><\/sup><\/em><em><span>\u00a0C)<\/span><\/em><span>\u00a0et est:<\/span>\n<ul>\n<li><strong><em><span>101325 Pa<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>1.01325 bar<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>14,696 psi<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>760 mmHg<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>760 torr<\/span><\/em><\/strong><\/li>\n<\/ul>\n<\/li>\n<li><strong><span>Pression manom\u00e9trique n\u00e9gative &#8211; Pression de vide.\u00a0<\/span><\/strong><span>Lorsque la pression atmosph\u00e9rique locale est sup\u00e9rieure \u00e0 la pression dans le syst\u00e8me, le terme\u00a0<\/span><strong><span>pression de vide<\/span><\/strong><span>\u00a0est utilis\u00e9.\u00a0Un vide parfait correspondrait \u00e0 une pression nulle absolue.\u00a0Il est certes possible d&#8217;avoir une pression manom\u00e9trique n\u00e9gative, mais pas possible d&#8217;avoir une pression absolue n\u00e9gative.\u00a0Par exemple, une pression absolue de 80 kPa peut \u00eatre d\u00e9crite comme une pression manom\u00e9trique de -21 kPa (c&#8217;est-\u00e0-dire 21 kPa en dessous d&#8217;une pression atmosph\u00e9rique de 101 kPa).<\/span><\/li>\n<\/ul>\n<p><em><span>p\u00a0<\/span><\/em><em><sub><span>vide<\/span><\/sub><\/em><em><span>\u00a0= p\u00a0<\/span><\/em><em><sub><span>absolu;\u00a0atm<\/span><\/sub><\/em><em><span>\u00a0&#8211; p\u00a0<\/span><\/em><em><sub><span>absolu<\/span><\/sub><\/em><\/p>\n<p><span>Par exemple, un pneu de voiture pomp\u00e9 jusqu&#8217;\u00e0 2,5 atm (36,75 psig) au-dessus de la pression atmosph\u00e9rique locale (disons 1 atm ou 14,7 psia localement), aura une pression absolue de 2,5 + 1 = 3,5 atm (36,75 + 14,7 = 51,45 psia ou 36,75 psig).<\/span><\/p>\n<p><span>En revanche, les\u00a0<\/span><span>turbines<\/span><span>\u00a0\u00e0\u00a0vapeur\u00a0\u00e0 condensation\u00a0\u00a0(dans\u00a0<a title=\"Centrale nucl\u00e9aire\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power-plant\/\">les centrales nucl\u00e9aires<\/a>\u00a0) \u00e9vacuent la\u00a0<a title=\"Propri\u00e9t\u00e9s de Steam - Qu'est-ce que Steam\" href=\"https:\/\/www.thermal-engineering.org\/fr\/quest-ce-que-steam-proprietes-de-steam-definition\/\">vapeur<\/a>\u00a0\u00e0 une pression bien inf\u00e9rieure \u00e0 la pression atmosph\u00e9rique\u00a0<\/span><span>(par exemple \u00e0 0,08 bar ou 8 kPa ou 1,16 psia)\u00a0<\/span><span>et dans un \u00e9tat partiellement condens\u00e9.\u00a0En unit\u00e9s relatives, il s&#8217;agit d&#8217;une pression manom\u00e9trique n\u00e9gative d&#8217;environ &#8211; 0,92 bar, &#8211; 92 kPa ou &#8211; 13,54 psig.<\/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>Loi du gaz parfait<\/span><\/h2>\n<p><span>Toute \u00e9quation qui relie la pression, la temp\u00e9rature et le volume sp\u00e9cifique d&#8217;une substance est appel\u00e9e une\u00a0<\/span><strong><span>\u00e9quation d&#8217;\u00e9tat<\/span><\/strong><span>\u00a0.\u00a0L&#8217;\u00a0\u00e9quation d&#8217;\u00e9tat la\u00a0plus simple et la\u00a0<\/span><strong><span>plus connue<\/span><\/strong><span>\u00a0pour les substances en phase gazeuse est l&#8217;\u00a0<\/span><strong><span>\u00e9quation<\/span><\/strong><span>\u00a0d&#8217;\u00e9tat du\u00a0<strong>gaz parfait<\/strong>\u00a0.\u00a0\u00c9mile Clapeyron l&#8217;a d\u00e9clar\u00e9 pour la premi\u00e8re fois en 1834 comme une combinaison de la loi empirique de Boyle, de la loi de Charles et de la loi d&#8217;Avogadro.\u00a0Cette \u00e9quation pr\u00e9dit le\u00a0<\/span><strong><span>comportement pvT<\/span><\/strong><span>\u00a0d&#8217;un gaz de fa\u00e7on assez pr\u00e9cise pour les gaz dilu\u00e9s ou \u00e0 basse pression.\u00a0Dans un gaz parfait, les mol\u00e9cules n&#8217;ont pas de volume et n&#8217;interagissent pas.\u00a0Selon la loi du gaz parfait, la pression varie lin\u00e9airement avec la\u00a0<\/span><strong><span>temp\u00e9rature<\/span><\/strong><span>\u00a0et la\u00a0<\/span><strong><span>quantit\u00e9<\/span><\/strong><span>\u00a0, et inversement avec le\u00a0<\/span><strong><span>volume<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><strong><i><span>pV = nRT<\/span><\/i><\/strong><\/p>\n<p><span>o\u00f9:<\/span><\/p>\n<ul>\n<li><strong><em><span>p<\/span><\/em><\/strong><span>\u00a0est la<\/span><strong><span>\u00a0pression absolue<\/span><\/strong><span>\u00a0du gaz<\/span><\/li>\n<li><strong><em><span>n<\/span><\/em><\/strong><span>\u00a0est la<\/span><strong><span>\u00a0quantit\u00e9<\/span><\/strong><span>\u00a0de substance<\/span><\/li>\n<li><strong><em><span>T<\/span><\/em><\/strong><span>\u00a0est la<\/span><strong><span>\u00a0temp\u00e9rature absolue<\/span><\/strong><\/li>\n<li><strong><em><span>V<\/span><\/em><\/strong><span>\u00a0est le<\/span><strong><span>\u00a0volume<\/span><\/strong><\/li>\n<li><strong><em><span>R<\/span><\/em>\u00a0<\/strong><span>\u00a0est la<\/span><strong><span>\u00a0constante de gaz<\/span><\/strong><span>\u00a0id\u00e9ale ou universelle,\u00e9gale au produit de la constante de Boltzmann et de la constante d&#8217;Avogadro,<\/span><\/li>\n<\/ul>\n<p><span>Dans cette \u00e9quation, le symbole R est une constante appel\u00e9e constante de\u00a0<\/span><strong><span>gaz universelle<\/span><\/strong><span>\u00a0qui a la m\u00eame valeur pour tous les gaz, \u00e0 savoir\u00a0<\/span><strong><span>R = 8,31 J \/ mol K.<\/span><\/strong><\/p>\n<p><span>La puissance de la loi du gaz parfait r\u00e9side dans sa\u00a0<\/span><strong><span>simplicit\u00e9<\/span><\/strong><span>\u00a0.\u00a0Lorsque\u00a0<\/span><strong><span>deux<\/span><\/strong><span>\u00a0variables thermodynamiques, p, v et T\u00a0<\/span><strong><span>sont\u00a0<\/span><\/strong><strong><span>donn\u00e9es<\/span><\/strong><span>\u00a0, la\u00a0<\/span><strong><span>troisi\u00e8me<\/span><\/strong><span>\u00a0peut\u00a0<\/span><strong><span>\u00eatre facilement trouv\u00e9e<\/span><\/strong><span>.\u00a0Un gaz parfait est d\u00e9fini comme celui dans lequel toutes les collisions entre atomes ou mol\u00e9cules sont parfaitement \u00e9lastiques et o\u00f9 il n&#8217;y a pas de forces d&#8217;attraction intermol\u00e9culaires.\u00a0Un gaz parfait peut \u00eatre visualis\u00e9 comme une collection de sph\u00e8res parfaitement dures qui entrent en collision mais qui, autrement, n&#8217;interagissent pas entre elles.\u00a0En r\u00e9alit\u00e9, aucun gaz r\u00e9el n&#8217;est comme un gaz parfait et donc aucun gaz r\u00e9el ne suit compl\u00e8tement la loi ou l&#8217;\u00e9quation du gaz parfait.\u00a0\u00c0 des temp\u00e9ratures proches d&#8217;un point d&#8217;\u00e9bullition des gaz, une augmentation de la pression provoquera de la condensation et une diminution drastique du volume.\u00a0A des pressions tr\u00e8s \u00e9lev\u00e9es, les forces intermol\u00e9culaires d&#8217;un gaz sont importantes.\u00a0Cependant, la plupart des gaz sont en accord approximatif \u00e0 des pressions et des temp\u00e9ratures sup\u00e9rieures \u00e0 leur point d&#8217;\u00e9bullition.<\/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>Pressions typiques en ing\u00e9nierie &#8211; Exemples<\/span><\/h2>\n<p><span>Le\u00a0<\/span><strong><span>pascal (Pa) en<\/span><\/strong><span>\u00a0tant qu&#8217;unit\u00e9 de mesure de pression est largement utilis\u00e9 dans le monde et a largement remplac\u00e9 l&#8217;\u00a0<\/span><strong><span>unit\u00e9 de livres par pouce carr\u00e9 (psi)<\/span><\/strong><span>\u00a0, sauf dans certains pays qui utilisent encore le syst\u00e8me de mesure imp\u00e9rial, y compris les \u00c9tats-Unis.\u00a0Pour la plupart des probl\u00e8mes d&#8217;ing\u00e9nierie, le pascal (Pa) est une unit\u00e9 assez petite, il est donc pratique de travailler avec des multiples du pascal: le kPa, le MPa ou la barre.\u00a0La liste suivante r\u00e9sume quelques exemples:<\/span><\/p>\n<ul>\n<li><span>La plupart des\u00a0<\/span><strong><span>centrales nucl\u00e9aires<\/span><\/strong><span>\u00a0exploitent g\u00e9n\u00e9ralement\u00a0<\/span><strong><span>des turbines \u00e0 vapeur \u00e0 condensation \u00e0 plusieurs \u00e9tages<\/span><\/strong><span>\u00a0.\u00a0Ces turbines \u00e9vacuent la\u00a0<\/span><a title=\"Propri\u00e9t\u00e9s de Steam - Qu'est-ce que Steam\" href=\"https:\/\/www.thermal-engineering.org\/fr\/quest-ce-que-steam-proprietes-de-steam-definition\/\"><span>vapeur<\/span><\/a><span>\u00a0\u00e0 une pression bien inf\u00e9rieure \u00e0 la pression atmosph\u00e9rique (par exemple \u00e0 0,08 bar ou 8 kPa ou 1,16 psia) et dans un \u00e9tat partiellement condens\u00e9.\u00a0En unit\u00e9s relatives, il s&#8217;agit d&#8217;une pression manom\u00e9trique n\u00e9gative d&#8217;environ &#8211; 0,92 bar, &#8211; 92 kPa ou &#8211; 13,54 psig.<\/span><\/li>\n<li><span>La\u00a0<\/span><strong><span>pression atmosph\u00e9rique standard se<\/span><\/strong><span>\u00a0rapproche de la pression moyenne au niveau de la mer \u00e0 45 \u00b0 de latitude nord. La\u00a0<\/span><strong><span>pression atmosph\u00e9rique standard<\/span><\/strong><span>\u00a0est d\u00e9finie au niveau de la mer \u00e0\u00a0<\/span><em><span>273\u00a0<\/span><\/em><em><sup><span>o<\/span><\/sup><\/em><em><span>\u00a0K (0\u00a0<\/span><\/em><em><sup><span>o<\/span><\/sup><\/em><em><span>\u00a0C)<\/span><\/em><span>\u00a0et est:<\/span>\n<ul>\n<li><strong><em><span>101325 Pa<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>1.01325 bar<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>14,696 psi<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>760 mmHg<\/span><\/em><\/strong><\/li>\n<li><strong><em><span>760 torr<\/span><\/em><\/strong><\/li>\n<\/ul>\n<\/li>\n<li><span>La surpression des pneus de voiture est d&#8217;environ 2,5 bars, 0,25 MPa ou 36 psig.<\/span><\/li>\n<li><span>Chaudi\u00e8re \u00e0 tube de fum\u00e9e de locomotive \u00e0 vapeur: 150\u2013250 psig<\/span><\/li>\n<li><span>Un \u00e9tage haute pression de turbine \u00e0 vapeur \u00e0 condensation dans une centrale nucl\u00e9aire fonctionne \u00e0 l&#8217;\u00e9tat d&#8217;\u00e9quilibre avec des conditions d&#8217;entr\u00e9e de 6 MPa (60 bar ou 870 psig), t = 275,6 \u00b0 C, x = 1<\/span><\/li>\n<li><span>Un\u00a0<\/span><a title=\"BWR - R\u00e9acteur \u00e0 eau bouillante\" href=\"https:\/\/www.nuclear-power.com\/bwr-boiling-water-reactor\/\"><strong><span>r\u00e9acteur \u00e0 eau bouillante<\/span><\/strong><\/a><span>\u00a0est refroidi et mod\u00e9r\u00e9 par de l&#8217;\u00a0<\/span><a title=\"Propri\u00e9t\u00e9s de l'eau\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-of-water\/\"><span>eau<\/span><\/a><span>\u00a0comme un REP, mais \u00e0 une\u00a0<\/span><strong><span>pression inf\u00e9rieure<\/span><\/strong><span>\u00a0(par exemple 7 MPa, 70 bars ou 1015 psig), ce qui permet \u00e0 l&#8217;eau de bouillir \u00e0 l&#8217;int\u00e9rieur du r\u00e9cipient sous pression, produisant la vapeur qui fait fonctionner les turbines.<\/span><\/li>\n<li><a title=\"PWR - R\u00e9acteur \u00e0 eau sous pression\" href=\"https:\/\/www.nuclear-power.com\/pwr-pressurized-water-reactor\/\"><strong><span>Les r\u00e9acteurs \u00e0 eau sous pression<\/span><\/strong><\/a><span>\u00a0sont refroidis et mod\u00e9r\u00e9s par<\/span><a title=\"Liquide satur\u00e9 et sous-refroidi\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/saturated-and-subcooled-liquid\/\"><span>\u00a0de l&#8217;eau liquide \u00e0 haute pression<\/span><\/a><span>\u00a0(par exemple 16 MPa, 160 bars ou 2320 psig).\u00a0\u00c0 cette pression, l&#8217;eau bout \u00e0 environ 350 \u00b0 C (662 \u00b0 F), ce qui fournit une marge de sous-refroidissement d&#8217;environ 25 \u00b0 C.<\/span><\/li>\n<li><span>Le\u00a0<\/span><a title=\"R\u00e9acteur \u00e0 eau supercritique - SCWR\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power-plant\/reactor-types\/supercritical-water-reactor-scwr\/\"><strong><span>r\u00e9acteur \u00e0 eau supercritique (SCWR)<\/span><\/strong><\/a><span>\u00a0fonctionne \u00e0\u00a0<\/span><strong><span>pression supercritique<\/span><\/strong><span>\u00a0.\u00a0Le terme supercritique dans ce contexte se r\u00e9f\u00e8re au\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-of-water\/critical-point-of-water\/\"><strong><span>point critique<\/span><\/strong><\/a><span>\u00a0thermodynamique\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-of-water\/critical-point-of-water\/\"><strong>de l&#8217;eau<\/strong><\/a>\u00a0(T\u00a0<\/span><sub><span>CR<\/span><\/sub><span>\u00a0= 374 \u00b0 C; p\u00a0<\/span><sub><span>CR<\/span><\/sub><span>\u00a0= 22,1 MPa)<\/span><\/li>\n<li><strong><span>Injection directe de carburant \u00e0 rampe commune:<\/span><\/strong><span>\u00a0sur les moteurs diesel, elle est dot\u00e9e d&#8217;une\u00a0<strong>rampe d&#8217;alimentation<\/strong>\u00a0haute pression (sup\u00e9rieure \u00e0 1 000 bar ou 100 MPa ou 14500 psi).<\/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>Perte de pression &#8211; Fluides<\/span><\/h2>\n<p><span>R\u00e9sum\u00e9 de:\u00a0<\/span><a title=\"Perte de t\u00eate - Perte de pression\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/head-loss\/\"><span>Perte de charge &#8211; Perte de pression<\/span><\/a><\/p>\n<ul>\n<li><strong><span>La perte de charge<\/span><\/strong><span>\u00a0ou\u00a0<\/span><strong><span>la perte de pression<\/span><\/strong><span>\u00a0\u00a0sont la r\u00e9duction de la charge\u00a0<\/span><a title=\"T\u00eate hydraulique\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/hydraulic-head\/\"><strong><span>totale<\/span><\/strong><\/a><span>\u00a0(somme de la charge\u00a0<\/span><a title=\"T\u00eate d'\u00e9l\u00e9vation\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/elevation-head-2\/\"><span>potentielle<\/span><\/a><span>\u00a0, de la\u00a0<\/span><a title=\"T\u00eate de vitesse\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/velocity-head\/\"><span>vitesse<\/span><\/a><span>\u00a0et de la\u00a0<\/span><a title=\"T\u00eate de pression\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/bernoullis-equation-bernoullis-principle\/pressure-head-2\/\"><span>pression<\/span><\/a><span>\u00a0) d&#8217;un fluide caus\u00e9e par la\u00a0<\/span><strong><span>friction<\/span><\/strong><span>\u00a0pr\u00e9sente dans le mouvement du fluide.<\/span><\/li>\n<li><strong><span>La perte de charge et la perte de charge<\/span><\/strong><span>\u00a0repr\u00e9sentent le m\u00eame ph\u00e9nom\u00e8ne &#8211; les\u00a0<\/span><strong><span>pertes par frottement<\/span><\/strong><span>\u00a0dans les tuyaux et les pertes dans les composants hydrauliques, mais elles sont exprim\u00e9es en\u00a0<\/span><strong><span>unit\u00e9s diff\u00e9rentes<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>La perte de charge du syst\u00e8me hydraulique est divis\u00e9e en\u00a0<\/span><strong><span>deux cat\u00e9gories principales<\/span><\/strong><span>\u00a0:<\/span>\n<ul>\n<li><a title=\"Perte de t\u00eate majeure - Perte par friction\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/\"><strong><span>Perte de charge importante<\/span><\/strong><\/a><span>\u00a0&#8211; due au frottement dans des tuyaux droits<\/span><\/li>\n<li><a title=\"Perte de t\u00eate mineure - Pertes locales\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/minor-head-loss-local-losses\/\"><strong><span>Perte de charge mineure<\/span><\/strong><\/a><span>\u00a0&#8211; due \u00e0 des composants comme des valves, des coudes\u2026<\/span><\/li>\n<\/ul>\n<\/li>\n<li>\n<figure id=\"attachment_14429\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-14429\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Moody-chart-min.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-14429 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Moody-chart-min-300x188.jpg\" alt=\"Diagramme Moody\" width=\"300\" height=\"188\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Moody-chart-min-300x188.jpg\" \/><\/a><figcaption id=\"caption-attachment-14429\" class=\"wp-caption-text\"><span>Source: Donebythesecondlaw sur Wikip\u00e9dia en anglais, CC BY-SA 3.0,<\/span><br \/>\n<span>https:\/\/commons.wikimedia.org\/w\/index.php?curid=4681366<\/span><\/figcaption><\/figure>\n<p><a title=\"\u00c9quation de Darcy-Weisbach\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/darcy-weisbach-equation\/\"><strong><span>L&#8217;\u00e9quation de Darcy<\/span><\/strong><\/a><span>\u00a0peut \u00eatre utilis\u00e9e pour calculer<\/span><strong><span>\u00a0les pertes majeures<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Une\u00a0<\/span><strong><span>forme sp\u00e9ciale de l&#8217;\u00e9quation de Darcy<\/span><\/strong><span>\u00a0peut \u00eatre utilis\u00e9e pour calculer\u00a0<\/span><strong><span>les pertes mineures<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Le\u00a0<\/span><a title=\"Facteur de friction Darcy\" href=\"https:\/\/www.thermal-engineering.org\/fr\/quest-ce-que-le-facteur-de-friction-de-darcy-definition\/\"><strong><span>facteur de friction<\/span><\/strong><\/a><span>\u00a0pour l&#8217;\u00e9coulement du fluide peut \u00eatre d\u00e9termin\u00e9 \u00e0 l&#8217;aide d&#8217;un\u00a0<\/span><a title=\"Diagramme Moody\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/moody-diagram\/\"><strong><span>diagramme de Moody<\/span><\/strong><\/a><span>\u00a0.<\/span><\/li>\n<li><strong><span>Le\u00a0<\/span><a title=\"Facteur de friction pour le flux laminaire\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/friction-factor-for-laminar-flow\/\"><span>facteur de friction<\/span><\/a><\/strong><a title=\"Facteur de friction pour le flux laminaire\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/friction-factor-for-laminar-flow\/\"><span>\u00a0\u00a0pour l&#8217;\u00e9coulement laminaire<\/span><\/a><span>\u00a0est\u00a0<\/span><strong><span>ind\u00e9pendant de la rugosit\u00e9<\/span><\/strong><span>\u00a0de la surface int\u00e9rieure du tuyau.\u00a0<\/span><strong><span>f = 64 \/ Re<\/span><\/strong><\/li>\n<li><strong><span>Le\u00a0<\/span><a title=\"Facteur de friction pour \u00e9coulement turbulent - \u00c9quation de Colebrook\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/friction-factor-turbulent-flow-colebrook\/\"><span>facteur de frottement<\/span><\/a><\/strong><a title=\"Facteur de friction pour \u00e9coulement turbulent - \u00c9quation de Colebrook\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/major-head-loss-friction-loss\/friction-factor-turbulent-flow-colebrook\/\"><span>\u00a0\u00a0pour un \u00e9coulement turbulent<\/span><\/a><span>\u00a0\u00a0d\u00e9pend fortement de la\u00a0<\/span><strong><span>rugosit\u00e9 relative.\u00a0<\/span><\/strong><span>Elle est d\u00e9termin\u00e9e par l&#8217;\u00e9quation de Colebrook.\u00a0Il faut noter\u00a0<\/span><strong><span>qu&#8217;aux tr\u00e8s grands nombres de Reynolds<\/span><\/strong><span>\u00a0, le facteur de friction est ind\u00e9pendant du nombre de Reynolds.<\/span><\/li>\n<\/ul>\n<ul>\n<li><span>Les\u00a0<\/span><strong><span>pertes mineures<\/span><\/strong><span>\u00a0sont \u00e0\u00a0peu pr\u00e8s proportionnelle \u00e0 la\u00a0<\/span><strong><span>place du d\u00e9bit<\/span><\/strong><span>\u00a0et par\u00a0cons\u00e9quent ,\u00a0ils peuvent \u00eatre int\u00e9gr\u00e9s facilement dans l&#8217;\u00e9quation de\u00a0Darcy-Weisbach par\u00a0<\/span><a title=\"M\u00e9thode du coefficient de r\u00e9sistance - M\u00e9thode K - T\u00eate exc\u00e9dentaire\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/minor-head-loss-local-losses\/resistance-coefficient-method-k-method-excess-head\/\"><strong><span>coefficient de r\u00e9sistance K<\/span><\/strong><\/a><span>\u00a0.<\/span><\/li>\n<li><span>En tant que perte de pression locale,\u00a0<\/span><a title=\"Acc\u00e9l\u00e9ration du fluide - Perte de pression\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/fluid-dynamics\/minor-head-loss-local-losses\/fluid-acceleration-pressure-loss\/\"><strong><span>l&#8217;acc\u00e9l\u00e9ration du fluide dans un canal chauff\u00e9<\/span><\/strong><\/a><span>\u00a0peut \u00e9galement \u00eatre envisag\u00e9e.<\/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>Pression critique de l&#8217;eau<\/span><\/h2>\n<figure id=\"attachment_14172\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-14172\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Boiling-point-of-water.png\"><img loading=\"lazy\" class=\"size-medium wp-image-14172 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Boiling-point-of-water-300x255.png\" alt=\"Diagramme de phase de l'eau\" width=\"300\" height=\"255\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Boiling-point-of-water-300x255.png\" \/><\/a><figcaption id=\"caption-attachment-14172\" class=\"wp-caption-text\"><span>Diagramme de phase de l&#8217;eau.<\/span><br \/>\n<span>Source: wikipedia.org CC BY-SA<\/span><\/figcaption><\/figure>\n<p><span>\u00c0 une pression\u00a0\u00a0<\/span><strong><span>sup\u00e9rieure \u00e0 la pression critique, l&#8217;\u00a0\u00a0<\/span><\/strong>\u00a0<a title=\"Propri\u00e9t\u00e9s de l'eau\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-of-water\/\"><span>eau<\/span><\/a><span>\u00a0est dans un \u00e9tat sp\u00e9cial, appel\u00e9\u00a0<\/span><a title=\"Fluide supercritique - Eau supercritique\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/supercritical-fluid-supercritical-water\/\"><strong><span>\u00e9tat fluide supercritique<\/span><\/strong><\/a><span>\u00a0.\u00a0Un fluide supercritique est un fluide qui est \u00e0 des pressions sup\u00e9rieures \u00e0 ses valeurs critiques thermodynamiques.\u00a0Aux pressions critiques et supercritiques, un fluide est consid\u00e9r\u00e9 comme une\u00a0<\/span><strong><span>substance monophas\u00e9e<\/span><\/strong><span>\u00a0malgr\u00e9 le fait que toutes les propri\u00e9t\u00e9s thermophysiques subissent\u00a0<\/span><strong><span>des changements importants<\/span><\/strong><span>\u00a0dans les r\u00e9gions critiques et pseudocritiques.<\/span><\/p>\n<p><span>Pour l&#8217;eau, les param\u00e8tres critiques sont les suivants:<\/span><\/p>\n<ul>\n<li><strong><span>P\u00a0<\/span><sub><span>cr<\/span><\/sub><span>\u00a0= 22,09 MPa<\/span><\/strong><\/li>\n<li><strong><span>T\u00a0<\/span><sub><span>cr<\/span><\/sub><span>\u00a0= 374,14 \u00b0 C (ou 647,3 K)<\/span><\/strong><\/li>\n<li><strong><span>v\u00a0<\/span><sub><span>cr<\/span><\/sub><span>\u00a0= 0,003155 m3 \/ kg<\/span><\/strong><\/li>\n<li><strong><span>u\u00a0<\/span><sub><span>f<\/span><\/sub><span>\u00a0= u\u00a0<\/span><sub><span>g<\/span><\/sub><span>\u00a0= 2014 kJ \/ kg<\/span><\/strong><\/li>\n<li><strong><span>h\u00a0<\/span><sub><span>f<\/span><\/sub><span>\u00a0= h\u00a0<\/span><sub><span>g<\/span><\/sub><span>\u00a0= 2084 kJ \/ kg<\/span><\/strong><\/li>\n<li><strong><span>s\u00a0<\/span><sub><span>f<\/span><\/sub><span>\u00a0= s\u00a0<\/span><sub><span>g<\/span><\/sub><span>\u00a0= 4,406 kJ \/ kg K<\/span><\/strong><\/li>\n<\/ul>\n<p><span>Voir aussi:\u00a0<\/span><a title=\"Point critique de l'eau\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-of-water\/critical-point-of-water\/\"><span>Point critique de l&#8217;eau<\/span><\/a><\/p>\n<p><span>Voir aussi:\u00a0<\/span><a title=\"Fluide supercritique - Eau supercritique\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/supercritical-fluid-supercritical-water\/\"><span>Fluide supercritique<\/span><\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n<div><\/div>\n<div><\/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>Cet article est bas\u00e9 sur la traduction automatique de l&#8217;article original en anglais. Pour plus d&#8217;informations, voir l&#8217;article en anglais. Pouvez vous nous aider Si vous souhaitez corriger la traduction, envoyez-la \u00e0 l&#8217;adresse: translations@nuclear-power.com ou remplissez le formulaire de traduction en ligne. Nous appr\u00e9cions votre aide, nous mettrons \u00e0 jour la traduction le plus rapidement possible. Merci<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Quelle est la pression. La pression est une propri\u00e9t\u00e9 intensive de la mati\u00e8re. L&#8217;unit\u00e9 standard de pression dans le syst\u00e8me SI est le Newton par m\u00e8tre carr\u00e9 ou pascal (Pa). G\u00e9nie thermique Quelle est la pression La pression\u00a0est une mesure de la\u00a0force exerc\u00e9e\u00a0par unit\u00e9 de surface sur les limites d&#8217;une substance.\u00a0L&#8217;unit\u00e9 standard de\u00a0pression\u00a0dans le syst\u00e8me &#8230; <a title=\"Qu&#8217;est-ce que la pression &#8211; Physique &#8211; D\u00e9finition\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/fr\/quest-ce-que-la-pression-physique-definition\/\" aria-label=\"En savoir plus sur Qu&#8217;est-ce que la pression &#8211; Physique &#8211; D\u00e9finition\">Lire la suite<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[8],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v15.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Qu&#039;est-ce que la pression - Physique - D\u00e9finition<\/title>\n<meta name=\"description\" content=\"Quelle est la pression. 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