{"id":457290,"date":"2026-04-28T14:36:23","date_gmt":"2026-04-28T14:36:23","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/difference-between-thermal-radiation-of-shell-faces\/"},"modified":"2026-04-28T14:36:23","modified_gmt":"2026-04-28T14:36:23","slug":"difference-between-thermal-radiation-of-shell-faces","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/difference-between-thermal-radiation-of-shell-faces\/","title":{"rendered":"Difference between thermal radiation of shell faces"},"content":{"rendered":"<p>&lt;p&gt;Hello, all. I hope you had a good day.&lt;\/p&gt;&lt;p&gt;I&#8217;m trying to understand how thermal radiation is set up for thin shells. I am having unintuitive results that I will explain.&lt;\/p&gt;<\/p>\n<ul>&lt;li style=&#8221;font-weight: bold;&#8221;&gt;<strong>Initial setup<\/strong><\/li>\n<\/ul>\n<p>&lt;p&gt;-I have a cylindrical shell. It is set at 300K &lt;span style=&#8221;text-decoration: underline;&#8221;&gt;as an initial temperature&lt;\/span&gt;. It does not touch any other solid. It is floating inside a big cylinder &lt;span style=&#8221;text-decoration: underline;&#8221;&gt;forced at 300K&lt;\/span&gt; (also defined by shells). The mesh looks like this on a slice view:&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2026\/04\/28-04-2026-1777384371-mceclip0.png\" \/>&lt;br&gt;-I set thermal radiation for the outer to be this way:&lt;br&gt;Surface to surface, emissivity = 1, ambiant temperature = 200K, open enclosure, enclosure number 1, &lt;span style=&#8221;text-decoration: underline;&#8221;&gt;radiation from above. (&lt;\/span&gt;the &#8220;above&#8221; being directed towards the interior of the system).&lt;br&gt;-I set thermal radiation for the cylindrical shell to be this way:&lt;br&gt;Surface to surface, emissivity = 1, ambiant temperature = 200K, open enclosure, enclosure number 1. &lt;span style=&#8221;text-decoration: underline;&#8221;&gt;radiation from above&lt;\/span&gt;.&lt;br&gt;-The normals of all faces are oriented inwards. By setting &#8220;radiation from above&#8221; I then direct the radiation inward too. See below:&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2026\/04\/28-04-2026-1777385136-mceclip1.png\" \/>&lt;br&gt;-No other thermal transfer occurs.&lt;\/p&gt;<\/p>\n<ul>&lt;li style=&#8221;font-weight: bold;&#8221;&gt;<strong>Expectation<\/strong><\/li>\n<\/ul>\n<p>&lt;p&gt;As you can see, my shell starts out at 300K. It is fully encased within a cylinder which is forced at 300K. In theory, the shell can only exchange radiation with either itself or the cylinder. In theory, t&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;here is no view towards the &#8220;ambiant&#8221; defined at 200K&lt;\/span&gt;. So, we only have 300K facets that radiate with other 300K facets. No other thermal transfer occurs. Therefore, I then run a&nbsp;<strong>static thermal analysis. <\/strong>I expect the whole system to stay at 300K. Maybe, due to small numerical inaccuracies in view factor computation, it might be possible for the shell to &#8220;see&#8221; the ambiant &#8220;through&#8221; the outer cylinder, so maybe I will be a bit below 300K.&lt;\/p&gt;<\/p>\n<ul>&lt;li style=&#8221;font-weight: bold;&#8221;&gt;<strong>Result<\/strong><\/li>\n<\/ul>\n<p>&lt;p&gt;With&nbsp;&lt;span style=&#8221;text-decoration: underline;&#8221;&gt;radiation from above&lt;\/span&gt;, the shell is mostly radiating with itself. The temperature profile of the shell is not too far off what I expect: we are standing at around 299,985K (or 26,835&deg;C) instead of 300K (or 26,850&deg;C)&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2026\/04\/28-04-2026-1777385336-mceclip2.png\" \/>&lt;\/p&gt;&lt;p&gt;With &lt;span style=&#8221;text-decoration: underline;&#8221;&gt;radiation from below&lt;\/span&gt;, that means the shell is now radiating outwards, so mostly with the outer cylinder. We lose 0,005K so it&#8217;s mostly OK.&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2026\/04\/28-04-2026-1777386477-mceclip3.png\" \/>&lt;\/p&gt;&lt;p&gt;With radiation from both sides, as I understand it, radiation is emitted from both sides of the shell. And now, the temperature profile looks baffling to me. (I&#8217;ll edit to show a picture). It is significantly colder, as if the shell now had a larger view factor towards the &#8220;ambiant&#8221;.&lt;\/p&gt;&lt;p&gt;My question is: <strong>what is happening here?<\/strong>&lt;\/p&gt;&lt;p&gt;Best regards,&lt;\/p&gt;&lt;p&gt;R&eacute;mi&lt;\/p&gt;&lt;p&gt;&nbsp;&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-457290","topic","type-topic","status-publish","hentry","topic-tag-SurfaceTemperature-1","topic-tag-thermal-radiation-1","topic-tag-mechanical"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27790"],"_bbp_topic_id":["457290"],"_bbp_subscription":["90439"],"_bbp_author_ip":["194.9.100.101"],"_bbp_last_reply_id":["0"],"_bbp_last_active_id":["457290"],"_bbp_last_active_time":["2026-04-28 14:36:23"],"_bbp_reply_count":["0"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["1"],"_btv_view_count":["12"],"_bbp_topic_status":["unanswered"],"_bbp_engagement":["90439"]},"test":"remi-gerard-marzansafrangroup-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/457290","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/457290\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=457290"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}