# The UDF of Heat Transfer Coefficient In TFM

 Register Blogs Members List Search Today's Posts Mark Forums Read August 14, 2023, 22:51 The UDF of Heat Transfer Coefficient In TFM #1 New Member   Haocheng_Ding Join Date: Aug 2023 Posts: 5 Rep Power: 2 Hello everyone, may I ask in the ANSYS FLUENT two-fluid model (Eulerian Model), when using a User Defined Function (UDF) to define the interphase heat transfer coefficient for the gas-liquid two-phase flow, is the return value the heat transfer coefficient "h" (in units of W/m²K) or the product of the heat transfer coefficient "h" multiplied by the interface area "Ai" (in units of 1/m)? Additionally, I have a few questions to inquire about: 1. I have written the heat transfer coefficient between the liquid phase and the interface based on the Ranz-Marshall correlation. However, the computed results differ from the results calculated using Fluent's built-in Ranz-Marshall correlation. I'm unsure about the reason for this discrepancy. 2. Is the "Pr" in the correlation equation the Prandtl number of the gas phase? I read this in Fluent's theory guide, but I'm not certain if it's accurate? Here is the UDF code that I have written: #include "udf.h" DEFINE_EXCHANGE_PROPERTY(htc_1, c, mixthread, pi1, pi2) { Thread* liqthread, * vapthread; real Nu, h, h_eff, Re, Pr, vel,d,k,cp,mu,Ai; real NV_VEC(v); liqthread = THREAD_SUB_THREAD(mixthread, pi1); vapthread = THREAD_SUB_THREAD(mixthread, pi2); d = C_PHASE_DIAMETER(c, vapthread); k = C_K_L(c, vapthread); cp = C_CP(c, vapthread); mu = C_MU_L(c, vapthread); Pr = (cp * mu) / k; NV_DD(v, =, C_U(c, liqthread), C_V(c, liqthread), C_W(c, liqthread), -, C_U(c, vapthread), C_V(c, vapthread), C_W(c, vapthread)); vel = NV_MAG(v); Re = (C_R(c, liqthread) * vel * d) / (C_MU_L(c, liqthread)); Nu = 2.0 + 0.6 * pow(Re, 0.5) * pow(Pr, 1. / 3.); h = C_K_L(c, liqthread) * Nu / d; Ai = 6.0 * C_VOF(c, vapthread) / d; h_eff = h * Ai; return h_eff; } Thanks！  Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post emmkell Fluent UDF and Scheme Programming 18 August 7, 2018 04:44 gartz89 FLUENT 0 May 26, 2018 02:23 rajendra1 Fluent UDF and Scheme Programming 35 October 13, 2017 05:04 Mike_Tom CFX 6 September 29, 2016 02:27 Shankar Fluent UDF and Scheme Programming 9 February 18, 2013 10:13