using IAPWS to simulate phase change
 

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?

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.

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.