{"id":161689,"date":"2023-01-25T07:16:40","date_gmt":"2023-01-25T07:16:40","guid":{"rendered":"\/knowledge\/forums\/topic\/why-is-the-cell-data-not-available-in-the-define_specific_heat-udf\/"},"modified":"2023-07-31T12:35:43","modified_gmt":"2023-07-31T12:35:43","slug":"why-is-the-cell-data-not-available-in-the-define_specific_heat-udf","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/why-is-the-cell-data-not-available-in-the-define_specific_heat-udf\/","title":{"rendered":"Why is the cell data not available in the DEFINE_SPECIFIC_HEAT UDF?"},"content":{"rendered":"<p>The UDF for specific heat is called as part of the material definition in the solver where the cell is not available. This is a limitation for this macro and its Real Gas equivalent.   Cp is by definition \u2202H\/\u2202T, so for it to have other dependencies is not expected by the solver. Since Cp and enthalpy definitions are critical to the stability of the energy equation, a strict format has to be defined so that the UDF doesn&#8217;t cause instabilities.  The only way to vary the Cp at the cell level is via the variation of the mass fractions of a mixture. This is what most users are trying to emulate when they are using a UDS, UDM or similar value to vary Cp. They should instead add a new species (which is not much more expensive than a UDS) to follow the material flow. The species could be a copy of the original species, but with a different Cp. Then, the Cp can be varied by varying the proportions of the species, potentially via source terms driven by UDM values.<\/p>\n","protected":false},"template":"","class_list":["post-161689","topic","type-topic","status-publish","hentry","topic-tag-4424","topic-tag-fluent","topic-tag-fluid-dynamics","topic-tag-general-fluent"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_wp_page_template":["default"],"_bbp_forum_id":["27796"],"_bbp_author_ip":["23.56.168.180"],"_bbp_last_active_time":["1-24-2023  20:20:10"],"_btv_view_count":["866"],"siebel_km_number":["2032638"],"product_version":["16"],"km_published_date":["2013-09-16T12:19:39.000Z"],"family":["Fluid Dynamics"],"application_name":["FLUENT"]},"test":"articlesansys-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/161689","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/161689\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/media?parent=161689"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}