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help,why the negative energy source does'nt make the temperature decrease, thank you! 

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November 6, 2009, 04:04 
help,why the negative energy source does'nt make the temperature decrease, thank you!

#1 
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patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
I am simulating the overheated liquid evaporation. but the temperature did not decrease. Actually it should because some liquid evaporate into gas and the latent heat is from the liquid. I have done this for over months, but little progress is obtained. who can help me? I would appreciate your help. the model is as below:
liquid saturation temperature:3.7K liquid initialstate temperature:4.2K the liquid is in the state of overheated. It should be evaporate by absorbing the energy of partion of liquid. the model is vof. udf is as below: DEFINE_ADJUST(m_dot_adjust, domain) {cell_t cell; Thread *mix_th,*pri_th ,*sec_th; Domain *d; d=Get_Domain(1); thread_loop_c(mix_th,d) {pri_th= THREAD_SUB_THREAD(mix_th, 0); sec_th= THREAD_SUB_THREAD(mix_th, 1); begin_c_loop(cell,mix_th) { if(C_T(cell, mix_th)>=T_SAT) { m_dot_l=0.1*C_VOF(cell,pri_th)*C_R(cell,pri_th)*(( C_T(cell,mix_th)/T_SAT)1); C_UDMI(cell,pri_th,3)=m_dot_l; m_dot_l_m=0.1*C_R(cell,pri_th)*fabs(C_T(cell,mix_t h)T_SAT)/T_SAT; C_UDMI(cell,pri_th,4)=m_dot_l_m; m_dot_l_eng=0.1*C_VOF(cell,pri_th)*C_R(cell,mix_th )/T_SAT; C_UDMI(cell,pri_th,5)=m_dot_l_eng; } else { m_dot_v=0.1*C_VOF(cell,sec_th)*C_R(cell,sec_th)*(( C_T(cell,mix_th)/T_SAT)1); C_UDMI(cell,sec_th,9)=m_dot_v; m_dot_v_m=0.1*C_R(cell,sec_th)*((C_T(cell,mix_th)/T_SAT)+1); C_UDMI(cell,sec_th,10)=m_dot_v_m; m_dot_v_eng=0.1*C_VOF(cell,sec_th)*C_R(cell,sec_th)/T_SAT; C_UDMI(cell,sec_th,11)=m_dot_v_eng; } }end_c_loop(cell,pri_th) } } DEFINE_SOURCE(liq_src, cell, pri_th, dS, eqn) { Thread *mix_th,*sec_th; mix_th = THREAD_SUPER_THREAD(pri_th); sec_th = THREAD_SUB_THREAD(mix_th, 1); if(C_T(cell, mix_th)>=T_SAT) {source0=C_UDMI(cell,pri_th,3); dS[eqn]= C_UDMI(cell,pri_th,4);} else {source0=C_UDMI(cell,sec_th,9); dS[eqn]=0;} C_UDMI(cell,pri_th,12)=source0; return (source0); } DEFINE_SOURCE(gas_src, cell, sec_th, dS, eqn) { Thread *mix_th,*pri_th; mix_th = THREAD_SUPER_THREAD(sec_th); pri_th = THREAD_SUB_THREAD(mix_th, 0); if(C_T(cell, mix_th)>=T_SAT) {source1=C_UDMI(cell,pri_th,3); dS[eqn]= 0;} else {source1=C_UDMI(cell,sec_th,9); dS[eqn]=C_UDMI(cell,sec_th,10);} C_UDMI(cell,sec_th,13)=source1; return (source1); } DEFINE_SOURCE(mixture_eng_src, cell, mix_th, dS, eqn) { Thread * sec_th,*pri_th; pri_th= THREAD_SUB_THREAD(mix_th, 0); sec_th= THREAD_SUB_THREAD(mix_th, 1); if(C_T(cell, mix_th)>=T_SAT) {source3=20800*C_UDMI(cell,pri_th,3); dS[eqn]= 20800*C_UDMI(cell,pri_th,5);} else {source3=20800*C_UDMI(cell,sec_th,9); dS[eqn]=20800*C_UDMI(cell,sec_th,11);} C_UDMI(cell,mix_th,14)=source3; return (source3);} the evaprated liquid is monitored. the source0 is negative and the source1 is positive. the source3 is negative. therefore, the source3 is added into the energy equation, the temperature should decrease, why it increase? who can help me, it drives me crazy. 

November 6, 2009, 04:07 

#2 
New Member
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
my email address is bjluo@hotmail.com, welcome everyone to communicate with me, thank you very much!


November 6, 2009, 05:04 
help,why the negative energy source does'nt make the temperature decrease, thank you!

#3 
Member
Shane
Join Date: Oct 2009
Posts: 52
Rep Power: 9 
Try to check the value of C_UDMI(cell,sec_th,(3,4,5,9,11) and source1(2,3).
Try to check these two steps. 1) Are they are geeting properly assigned. 2)Also I believe real value are getting truncated. sircorp 

November 6, 2009, 11:08 

#4 
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patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
hello sircorp,
thank you for your help. the C_UDMI(cell,sec_th,(3,4,5,9,11) and source1(2,3) are correct. source0=1.79，sour1=1.79，source3=1.79*20800; I have spent lots of time on it. it is very strange. the energy source is negative, but the temperature is increasing. begging for help!!! 

November 8, 2009, 08:25 

#5 
New Member
patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
maybe the problem is from the enthalpy. I assigned both the gas' and the liquid's standard state enthalpy is 0 with a 4.2K reference. but now I found the enthalpy is 1058514j/kg for liquid and 2147306j/kg for gas at 4.2K. I feel confused "is not it 0"? why? who can give me some words, thank you


November 8, 2009, 11:54 

#6 
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patrick
Join Date: Apr 2009
Posts: 14
Rep Power: 9 
is there someone who give me some words about redefined the enthalpy? h=cp*t? is it possible?


May 12, 2010, 17:39 

#7 
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Wei Shao
Join Date: Apr 2009
Posts: 3
Rep Power: 9 
Have you solved your problem? I have the same problem


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