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

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Old   April 21, 2012, 10:00
Default How to deal latent heat during phase change through source term udf
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deepak
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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.
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Old   November 14, 2013, 02:50
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yangbin
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Quote:
Originally Posted by dkb_bg View Post
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?
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Old   November 18, 2013, 02:35
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yangbin
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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.
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