ONB and CHF prediction in upward water channel with heated walls

ali_kntu · January 11, 2018, 01:48

hi dears

i have problem in modeling of upward water channel with heated walls. inlet water temperature is 45 C. heat flux is increases until small bubbles appears.

my problem is bubbles make very late, for example when walls temperature reaches to near 180 C initial bubbles are makes, but in text book it is mentioned that by 10C wall supper heating (from saturation ) ONB is occurs.

and second question:
can CFX predict CHF, how could i calculate CHF(DNBR) in CFX.

Thank you

ghorrocks · January 12, 2018, 03:15

I know what the acronym CFX means, but I do not know all the other acronyms you used. Please define all your acronyms.

ali_kntu · January 13, 2018, 05:57

Onb is onset of nucleate boiling ، and it is occurs when wall temperature is about 10C more than saturation temperature

Chf is critical heat flux which film boiling started

Tanx

ghorrocks · January 13, 2018, 17:37

Have you done the CFX tutorial examples on nucleate boiling? They are available in the ANSYS Customer webpage. Note there are many factors you will need to adjust to model your configuration. A critical one is parameters defining the nucleation sites on the heated wall surface, but there are many others.

January 11, 2018, 01:48	ONB and CHF prediction in upward water channel with heated walls	#1
ali_kntu New Member ali Join Date: Dec 2013 Posts: 6 Rep Power: 12	hi dears i have problem in modeling of upward water channel with heated walls. inlet water temperature is 45 C. heat flux is increases until small bubbles appears. my problem is bubbles make very late, for example when walls temperature reaches to near 180 C initial bubbles are makes, but in text book it is mentioned that by 10C wall supper heating (from saturation ) ONB is occurs. and second question: can CFX predict CHF, how could i calculate CHF(DNBR) in CFX. Thank you

January 13, 2018, 05:57	Chf ، dnb	#3
ali_kntu New Member ali Join Date: Dec 2013 Posts: 6 Rep Power: 12	Onb is onset of nucleate boiling ، and it is occurs when wall temperature is about 10C more than saturation temperature Chf is critical heat flux which film boiling started Tanx

January 12, 2018, 03:15		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I know what the acronym CFX means, but I do not know all the other acronyms you used. Please define all your acronyms.

January 13, 2018, 17:37		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Have you done the CFX tutorial examples on nucleate boiling? They are available in the ANSYS Customer webpage. Note there are many factors you will need to adjust to model your configuration. A critical one is parameters defining the nucleation sites on the heated wall surface, but there are many others.