# How to deal latent heat during phase change through source term udf

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 April 21, 2012, 10:00 How to deal latent heat during phase change through source term udf #1 New Member   deepak Join Date: Sep 2011 Location: india Posts: 8 Rep Power: 6 Hi all i have written udf for phase change from liquid to vapour in a narrow pipe.i think there is some problem with energy udf, since temperature is not decreasing but it should decrease. DEFINE_SOURCE(enrg_src, cell, mix_th, dS, eqn) { Thread *pri_th; Thread *sec_th; real m_dot; real P_SAT ; real T_SAT; P_SAT=exp(A+(B/(C_T(cell,mix_th)+C))+D*C_T(cell,mix_th)+E*log(C_T (cell,mix_th)))*1e5; T_SAT= -P_SAT*P_SAT*2e-11+P_SAT*7e-5+254.1; pri_th = THREAD_SUB_THREAD(mix_th, 0); sec_th = THREAD_SUB_THREAD(mix_th, 1); if (C_P(cell, mix_th)<=P_SAT) { m_dot = -0.1*C_VOF(cell, pri_th)*C_R(cell, pri_th)*fabs(C_T(cell,pri_th) - T_SAT)/T_SAT; dS[eqn] = -0.1*C_VOF(cell, pri_th)*C_R(cell, pri_th)/T_SAT; } else { m_dot = 0.1*C_VOF(cell, sec_th)*C_R(cell, sec_th)*fabs(T_SAT-C_T(cell,pri_th))/T_SAT; dS[eqn] = 0.1*C_VOF(cell, sec_th)*C_R(cell, sec_th)/T_SAT; } return LAT_HT*m_dot; i am not very much clear with this udf. means due to phase change temp of liquid should drop. plz enlighten me t will be grateful.

November 14, 2013, 02:50
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yangbin
Join Date: Nov 2013
Location: haerbin
Posts: 4
Rep Power: 4
Quote:
 Originally Posted by dkb_bg Hi all i have written udf for phase change from liquid to vapour in a narrow pipe.i think there is some problem with energy udf, since temperature is not decreasing but it should decrease. DEFINE_SOURCE(enrg_src, cell, mix_th, dS, eqn) { Thread *pri_th; Thread *sec_th; real m_dot; real P_SAT ; real T_SAT; P_SAT=exp(A+(B/(C_T(cell,mix_th)+C))+D*C_T(cell,mix_th)+E*log(C_T (cell,mix_th)))*1e5; T_SAT= -P_SAT*P_SAT*2e-11+P_SAT*7e-5+254.1; pri_th = THREAD_SUB_THREAD(mix_th, 0); sec_th = THREAD_SUB_THREAD(mix_th, 1); if (C_P(cell, mix_th)<=P_SAT) { m_dot = -0.1*C_VOF(cell, pri_th)*C_R(cell, pri_th)*fabs(C_T(cell,pri_th) - T_SAT)/T_SAT; dS[eqn] = -0.1*C_VOF(cell, pri_th)*C_R(cell, pri_th)/T_SAT; } else { m_dot = 0.1*C_VOF(cell, sec_th)*C_R(cell, sec_th)*fabs(T_SAT-C_T(cell,pri_th))/T_SAT; dS[eqn] = 0.1*C_VOF(cell, sec_th)*C_R(cell, sec_th)/T_SAT; } return LAT_HT*m_dot; i am not very much clear with this udf. means due to phase change temp of liquid should drop. plz enlighten me t will be grateful.
hi, i am very intrested ijn your problem.
i want to know how the coefficient 0.1 comes from？
is it suitable for every conditions?

 November 18, 2013, 02:35 #3 New Member   yangbin Join Date: Nov 2013 Location: haerbin Posts: 4 Rep Power: 4 Hi,I am working on this udf recently.and I am confused about this sentence"m_dot_v = 0.1*C_VOF(cell, sec_th)*C_R(cell, sec_th)*fabs(C_T(cell, sec_th) - T_SAT)/T_SAT". First,in this sentence,the coefficent is 0.1,but i do not know why. Second,what is the unit of "m_dot_v"? Thank you very much,and any advice will be highly appreciated.

 January 8, 2016, 02:29 phase change problem inside heat pipe #4 New Member   Ram Kumar Pal Join Date: Apr 2015 Posts: 21 Rep Power: 3 Dear friend, I'm doing the simulation of Heat pipe in FLUENT as my project work. I have written udf for mass and energy source for phase change inside the device. But condensation is not happening in condenser zone. If you have completed this problem, please help me. SHUJAN likes this.

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