{"id":161750,"date":"2023-01-25T07:16:50","date_gmt":"2023-01-25T07:16:50","guid":{"rendered":"\/knowledge\/forums\/topic\/how-to-compute-residence-time-distribution-rtd-for-stirred-tanks-with-inlet-and-outlet\/"},"modified":"2023-07-31T12:35:50","modified_gmt":"2023-07-31T12:35:50","slug":"how-to-compute-residence-time-distribution-rtd-for-stirred-tanks-with-inlet-and-outlet","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/how-to-compute-residence-time-distribution-rtd-for-stirred-tanks-with-inlet-and-outlet\/","title":{"rendered":"How to compute Residence Time Distribution (RTD) for stirred tanks with inlet and outlet?"},"content":{"rendered":"<p>Often, Chemical Engineers need to compute the RTD of their Continuous stirred tank reactors (CSTRs). FLUENT&#8217;s DPM model is challenging to use in these systems due to difficulty in getting statistically meaningful number of particles at the outlet. A second method is to introduce passive tracer material either with species or user-defined scalars. A method with user-defined scalars (UDS) is outlined here.  Approach:  1. Solve for single-phase steady state flow field with inlets and outlets.  2. Switch to unsteady solver.  3. Introduce a UDS with mass flux as convection term and default unsteady term. The UDS represents a passive tracer that is used to determine RTD.  4. Change UDS diffusivity to zero or reasonable values. For water-water system, this is quite low ~ 1e-10 m2\/s.  5. For pulse input, patch a known amount of UDS near the inlet; for step input, make UDS value = 1 at inlet.  6. Turn on surface monitor of area-av. UDS value at the outlet. Plot, print\/ write to file.  7. Turn off all equations except the UDS equation. Run for the required flow time.  The UDS conc. at the outlet as a function of time can be used to extract the residence time distribution. If you use step input of tracer (UDS value = 1 at inlet), the outlet UDS profile when normalized (Coutlet\/Cinlet) is called F curve which is a cumulative residence time distribution. If you introduce a pulse, the normalized response is called C Curve which is the RTD function.<\/p>\n","protected":false},"template":"","class_list":["post-161750","topic","type-topic","status-publish","hentry","topic-tag-dpm","topic-tag-fluent","topic-tag-fluid-dynamics","topic-tag-general","topic-tag-other"],"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  20:20:02"],"_btv_view_count":["3824"],"siebel_km_number":["844"],"product_version":["Other"],"km_published_date":["2003-08-26T17:30:00.000Z"],"family":["Fluid Dynamics"],"application_name":["FLUENT"],"_bbp_likes_count":["1"]},"test":"articlesansys-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/topics\/161750","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\/161750\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/knowledge\/wp-json\/wp\/v2\/media?parent=161750"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}