{"id":387990,"date":"2024-10-03T14:03:58","date_gmt":"2024-10-03T14:03:58","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/mass-conservation-issue-in-methane-pyrolysis-shock-tube-simulation\/"},"modified":"2024-10-03T14:03:58","modified_gmt":"2024-10-03T14:03:58","slug":"mass-conservation-issue-in-methane-pyrolysis-shock-tube-simulation","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/mass-conservation-issue-in-methane-pyrolysis-shock-tube-simulation\/","title":{"rendered":"Mass Conservation Issue in Methane Pyrolysis Shock Tube Simulation"},"content":{"rendered":"<p>&lt;p&gt;Dear ANSYS Support Team,&lt;\/p&gt;&lt;p&gt;I am working on replicating a shock tube experiment for methane pyrolysis in ANSYS Fluent. To simplify the process, I initially set up a basic simulation before incorporating a complex kinetic model. The reaction I&#8217;m modeling is methane pyrolysis using a one-step kinetic reaction with the following parameters:&lt;\/p&gt;<\/p>\n<ul>\n<li>Reaction: CH\u2084 &rarr; 2H\u2082 + C<\/li>\n<li>Pre-exponential factor: 606800<\/li>\n<li>Activation Energy (J\/kmol): 1.852e+8<\/li>\n<li>Temperature exponent: 0.1<\/li>\n<\/ul>\n<p>&lt;p&gt;&nbsp;&lt;\/p&gt;&lt;h3&gt;Problem Overview:&lt;\/h3&gt;&lt;p&gt;For the initial conditions, I set the driver gas at 100 bar and 2500K and the driven gas at 1 bar and 723K. My domain is defined as a simple shock tube with driver and driven sections, surrounded by walls. I utilized mesh adaptation to track the shock, based on a&nbsp;curvature of&nbsp;pressure.&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/10\/03-10-2024-1727964218-mceclip3.png\" \/>&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/10\/03-10-2024-1727963980-mceclip2.png\" \/>&lt;\/p&gt;&lt;p&gt;&nbsp;&lt;\/p&gt;&lt;p&gt;My first run was done without including the kinetic reaction to ensure the basics&mdash;such as mesh, mass conservation, and shock behavior&mdash;were functioning correctly. All basic checks appeared successful.&lt;\/p&gt;&lt;p&gt;However, upon testing different driver gases [CH\u2084,CO\u2082 or H\u2082] and applying the following conditions:&lt;\/p&gt;<\/p>\n<ul>\n<li>Driver: gas at 2500K and 100 bar<\/li>\n<li>Driven: CH\u2084 at 723K and 1 bar<\/li>\n<\/ul>\n<p>&lt;p&gt;I encountered an issue with mass conservation in the closed system. &lt;\/p&gt;&lt;h3&gt;Issue:&lt;\/h3&gt;&lt;p&gt;Despite trying various numerical parameters, I continue to experience mass conservation errors over time, as shown in the attached figure. I&#8217;m surprised by this result, particularly since the residuals for continuity seem to converge (with values below 0.001 absolute). Note that the simulation with CH\u2084 as driver has no mass issue.&lt;\/p&gt;&lt;p&gt;<img decoding=\"async\" src=\"https:\/\/innovationspace.ansys.com\/forum\/wp-content\/uploads\/sites\/2\/2024\/10\/03-10-2024-1727963770-mceclip1.png\" \/>&lt;\/p&gt;&lt;h3&gt;Question:&lt;\/h3&gt;&lt;p&gt;Could you please provide guidance on the appropriate numerical parameters or settings I should use to resolve this mass conservation issue? Any insights into why the continuity residual converges but mass conservation errors persist would be greatly appreciated.&lt;\/p&gt;&lt;p&gt;Thank you for your assistance!&lt;\/p&gt;&lt;p&gt;Best regards,&lt;br&gt;Ghislain&lt;\/p&gt;<\/p>\n","protected":false},"template":"","class_list":["post-387990","topic","type-topic","status-publish","hentry","topic-tag-massconservationcheck"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_author_ip":["142.58.196.172"],"_btv_view_count":["808"],"_bbp_topic_status":["unanswered"],"_bbp_notification_enabled":["39651"],"_bbp_subscription":["101181","39651"],"_bbp_topic_id":["387990"],"_bbp_forum_id":["27792"],"_bbp_engagement":["39651","101181"],"_bbp_voice_count":["2"],"_bbp_reply_count":["8"],"_bbp_last_reply_id":["393554"],"_bbp_last_active_id":["393554"],"_bbp_last_active_time":["2024-11-11 10:21:10"]},"test":"ghislain_madiotsfu-ca"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/387990","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\/387990\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=387990"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}