{"id":46342,"date":"2020-07-20T18:46:07","date_gmt":"2020-07-20T18:46:07","guid":{"rendered":"\/forum\/forums\/topic\/critical-heat-flux-simulation-fluent\/"},"modified":"2020-07-20T18:46:07","modified_gmt":"2020-07-20T18:46:07","slug":"critical-heat-flux-simulation-fluent","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/critical-heat-flux-simulation-fluent\/","title":{"rendered":"Critical Heat Flux Simulation – FLUENT"},"content":{"rendered":"

Hello everyone, <\/p>\n

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I am currently working on simulating the critical heat flux phenomena in FLUENT and am using experimental data from Celata et al. The geometry is a 2.5 mm ID pipe with 100 mm of pipe followed by 100 mm of heated pipe. I’m modeling a case run at 2.5 MPa pressure using the 2D axisymmetric condition with a rectangular geometry of 1.25 mm in width and 200 mm in length. The mesh has 20 radial divisions and 500 axial divisions. <\/p>\n

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For the FLUENT conditions, I am using: <\/p>\n

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Gravity On in the -x direction<\/p>\n

<\/p>\n

Multiphase -> Eulerian -> Boiling Model -> Critical Heat Flux<\/p>\n

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Energy On<\/p>\n

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Realizable k-epsilon model with standard wall functions and Mixture turbulence multiphase model<\/p>\n

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Phase Interactions: <\/p>\n

<\/p>\n

   Virtual mass -> constant -> 0.5<\/p>\n

<\/p>\n

   Drag model -> Ishii<\/p>\n

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   Lift model -> Moraga<\/p>\n

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   Wall lubrication model -> Antal et al. <\/p>\n

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   Turbulent dispersion force -> lopez-de-bertodano<\/p>\n

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   Turbulence interaction -> Troshko-Hassan<\/p>\n

<\/p>\n

   Heat transfer -> Ranz-Marshall <\/p>\n

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   Mass transfer -> Boiling from Liquid to Vapor at 497.1 K saturated temperature<\/p>\n

<\/p>\n

      Bubble departure diameter -> Tolubinski-Kostanchuk<\/p>\n

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      Frequency of bubble departure -> Cole<\/p>\n

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      Nucleation site density -> Lemmert-Chawla<\/p>\n

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      Area influence coefficient -> Delvalle-Kenning<\/p>\n

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      Surface tension -> Constant -> 0.032148 N\/m<\/p>\n

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      Interfacial area -> particle <\/p>\n

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To get inlet velocity, k, and epsilon profiles, I first ran the model with no heating and vapor generation and exported the outlet profiles to be read for the inlet profiles. The outlet profile was specified using 1% turbulent intensity and 0.0025 hydraulic diameter. In addition, the backflow temperatures of the liquid and vapor were set to the saturation temperature. <\/p>\n

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For a solver, a Coupled -> Pseudo-transient set up was used. The explicit relaxation factors were not adjusted while the timescale factor was adjusted to 0.1. <\/p>\n

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As a model for departure from nucleate boiling, I increased the heated wall heat flux from a heat flux where convergence was achieved up to the critical heat flux, which is about 27 MW\/m^2 in this case. I think that to see if CHF has occurred, a large jump in maximum wall temperature (which I recorded in the model as the vertex maximum liquid static temperature at the wall) should be seen after applying a higher heat flux value. However, I’ve seen in previous work that the model achieves convergence after this jump in wall temperature and I am not getting the same type of convergence at higher temperatures when a very high heat flux has been applied. <\/p>\n

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Does anybody know how to achieve convergence for this CHF modeling? <\/p>\n

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Any help that can be provided is very much appreciated! <\/p>\n","protected":false},"template":"","class_list":["post-46342","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["18525"],"_bbp_old_topic_author_name_id":["Anonymous"],"_bbp_old_is_topic_anonymous_id":["false"],"_bbp_old_closed_status_id":["publish"],"_bbp_author_ip":[null],"_bbp_old_sticky_status_id":["normal"],"_bbp_likes_count":["0"],"_btv_view_count":["1030"],"_bbp_subscription":["253817"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["46342"],"_bbp_forum_id":["27792"],"_bbp_engagement":["22555","179699"],"_bbp_voice_count":["2"],"_bbp_reply_count":["1"],"_bbp_last_reply_id":["121996"],"_bbp_last_active_id":["121996"],"_bbp_last_active_time":["2020-07-21 11:25:26"]},"test":"dannyouk"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/46342","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\/46342\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=46342"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}