using IAPWS to simulate phase change

hao123lcm · September 17, 2016, 11:36

i am trying to use IAPWS material to simulate the phase change of working fluid in micro heat pipe. but there are always errors about absolute pressure happened. does somebody have this kind of problem?

ghorrocks · September 18, 2016, 07:42

Make sure the simulation runs fine using a simple material model before using IAPWS. After the simple model runs successfully start with IAPWS, but use small time steps, an initial condition which is accurate (maybe the simple material model simulation), double precision. Also a very high quality mesh will help.

hao123lcm · September 18, 2016, 21:30

thank u for the suggestion,ghorrocks. i have tried using simple material model, e.g. H2O and H2Ol in interphase mass transfer material, there is no problem happened. i also set time steps below 0.001s for IAPWS and used the ISOthermal model to avoid heat transfer to make sure the right using of IAPWS, but there would still be negative absolute pressure appeared in vertexes.
could u tell me whether CFX can implement the simulation include not only evaporation but also condensation in a closed system, by the way, both phases are continuous.

September 17, 2016, 11:36	using IAPWS to simulate phase change	#1
hao123lcm New Member Join Date: Jan 2016 Posts: 2 Rep Power: 0	i am trying to use IAPWS material to simulate the phase change of working fluid in micro heat pipe. but there are always errors about absolute pressure happened. does somebody have this kind of problem?

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September 18, 2016, 07:42		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Make sure the simulation runs fine using a simple material model before using IAPWS. After the simple model runs successfully start with IAPWS, but use small time steps, an initial condition which is accurate (maybe the simple material model simulation), double precision. Also a very high quality mesh will help.

September 18, 2016, 21:30		#3
hao123lcm New Member Join Date: Jan 2016 Posts: 2 Rep Power: 0	thank u for the suggestion,ghorrocks. i have tried using simple material model, e.g. H2O and H2Ol in interphase mass transfer material, there is no problem happened. i also set time steps below 0.001s for IAPWS and used the ISOthermal model to avoid heat transfer to make sure the right using of IAPWS, but there would still be negative absolute pressure appeared in vertexes. could u tell me whether CFX can implement the simulation include not only evaporation but also condensation in a closed system, by the way, both phases are continuous.