{"id":354538,"date":"2024-02-29T12:23:20","date_gmt":"2024-02-29T12:23:20","guid":{"rendered":"\/forum\/forums\/topic\/define-mass-diffusion-coefficients-for-porous-media-and-multiphase\/"},"modified":"2024-02-29T12:23:20","modified_gmt":"2024-02-29T12:23:20","slug":"define-mass-diffusion-coefficients-for-porous-media-and-multiphase","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/define-mass-diffusion-coefficients-for-porous-media-and-multiphase\/","title":{"rendered":"define mass diffusion coefficients for porous media and multiphase"},"content":{"rendered":"<p>Hi all<br \/>I am trying to use an UDF to define mass diffusion coefficients for fluid in the system.<br \/>I am attempting to redefine the fluid diffusion coefficient using `DEFINE_DIFFUSIVITY`, but I am encountering issues. My goal is to modify the diffusion coefficient based on a pressure condition using a scaling factor, and I am using `C_DIFF_EFF(c,t,i)` to retrieve the diffusion coefficient. However, when storing this value in a User-Defined Memory (UDMI) variable, it remains 0. Can you help me identify the issue? Below is my UDF.<br \/>DEFINE_DIFFUSIVITY(DD, c, t,i)\/*two-phase fluid*\/<br \/>{<br \/>real Kg;\/*diffusion coefficient*\/<\/p>\n<p>if (C_P(c, t) &lt; 20e+05)<br \/>{<br \/>Kg = 10e-20*C_DIFF_EFF(c, t, 1);<\/p>\n<p>}<\/p>\n<p>else if (C_P(c, t) &gt; 20e+05)<br \/>{<br \/>Kg = C_DIFF_EFF(c, t, 1);<\/p>\n<p>}<br \/>C_UDMI(c, t, 0) = C_DIFF_EFF(c, t, 1);<\/p>\n<p>return Kg;<\/p>\n<p>}<\/p>\n","protected":false},"template":"","class_list":["post-354538","topic","type-topic","status-closed","hentry","topic-tag-multiphaseudfevaporationdpmspeciestransportdefinesourcesourcetermeulerianlagrangian-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["340242","15180"],"_bbp_author_ip":["23.52.43.10"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_edit_lock":["1709211807:38756"],"_btv_view_count":["125"],"_bbp_topic_status":["unanswered"],"_bbp_topic_id":["354538"],"_bbp_forum_id":["27792"],"_bbp_engagement":["15180","340242"],"_bbp_voice_count":["2"],"_bbp_reply_count":["1"],"_bbp_last_reply_id":["355142"],"_bbp_last_active_id":["355142"],"_bbp_last_active_time":["2024-03-04 12:38:59"]},"test":"gsy990410mail-shiep-edu-cn"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/354538","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\/354538\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=354538"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}