{"id":369991,"date":"2024-06-05T20:45:57","date_gmt":"2024-06-05T20:45:57","guid":{"rendered":"\/forum\/forums\/topic\/vacuum-chamber-air-extraction-from-1-atm-to-vacuum-in-a-closed-geometry\/"},"modified":"2024-06-05T20:45:57","modified_gmt":"2024-06-05T20:45:57","slug":"vacuum-chamber-air-extraction-from-1-atm-to-vacuum-in-a-closed-geometry","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/vacuum-chamber-air-extraction-from-1-atm-to-vacuum-in-a-closed-geometry\/","title":{"rendered":"Vacuum chamber &#8211; air extraction, from 1 atm to vacuum in a closed geometry"},"content":{"rendered":"<p>Hello there,<\/p>\n<p>I&#8217;m having a troubles with my simulation. I want to simulate the behaviour pressure over time of a parallelepiped vessel attached to a vacuum pump (which is just described by a mass flow outlet on the vessel). At the beginning of the experiment, there&#8217;s 1 atm of air inside the volume.<\/p>\n<p>The decrease in pressure I get is way less than what&#8217;s observed with the experiments and the analytical estimation.&nbsp;<br \/>&#8212;<br \/>My simulation is a watertight geometry with only one outlet.<\/p>\n<p>I use the Density based solver. The fluid is air from the material fluid list, and I changed &#8220;Density&#8221; parameter from constant to ideal gas, so density can vary, accordingly to P and T. (I tried other real gasses models as well, and tried many viscous models)<\/p>\n<p>My mesh has a good quality, I kept the number of nodes around 1M beceause it&#8217;s taking too long otherwise. (even as I&#8217;m computing on a Calculator)<\/p>\n<p>Transient simulation, time steps of 1e-4 s. The Solution is converging properly, with 20 it\/time step at the beginning and then reducing it to 3.&nbsp;<\/p>\n<p>From experimental and analytical pov, we know that we should observe a drop in pressure of about 5800 Pa in the volume after 10 seconds. However, The simulation only gives me a 10 Pa pressure drop. I&#8217;m attaching images here : https:\/\/www.swisstransfer.com\/d\/d29e23d6-0a70-48e6-923d-76c0e16e8a54 as i can&#8217;t attach them down here, idk why.&nbsp;<\/p>\n<p>What am I missing ?&nbsp;<br \/>Thanks for your time reading me <img decoding=\"async\" class=\"inlineimg\" title=\"Smile\" src=\"https:\/\/www.cfd-online.com\/Forums\/images\/smilies\/smile.gif\" alt=\"\" border=\"0\"><\/p>\n","protected":false},"template":"","class_list":["post-369991","topic","type-topic","status-closed","hentry","topic-tag-pressure-drop","topic-tag-vacuum-chamber-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["350472"],"_bbp_author_ip":["184.24.96.177"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["520"],"_bbp_topic_status":["unanswered"],"_bbp_topic_id":["369991"],"_bbp_forum_id":["27792"],"_bbp_engagement":["199","350472"],"_bbp_voice_count":["2"],"_bbp_reply_count":["1"],"_bbp_last_reply_id":["370126"],"_bbp_last_active_id":["370126"],"_bbp_last_active_time":["2024-07-02 13:32:17"]},"test":"gilles-butikofehes-so-ch"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/369991","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\/369991\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=369991"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}