# The UDF of Heat Transfer Coefficient In TFM

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 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/mēK) 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！

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