Hi sgopal1,

I don't think the problems are related to phase change (to begin with). However, I notice a couple of other things:

1) In both models you haven't assigned a usable medium model for "tJunctionIdeal1"
2) In the dynamic model you attempt to initialize "m_flows" for all the pipe models. You should remove this since "m_flows" is a vector to which you attempt to assign a scalar value.
3) You initialize all your components with no pressure drops (all pressures are 42 bar). You should change this.
4) The T-Junction components connect the pipes which all end with "volume model" (modelStructure = av_vb). This means that you constrain all the pressure states in the pipes to be equal. I my opinion, you should use the dynamic junction model instead and make sure that the pipes connected to that junction end with a "flow model". For example, the model structure of "Pipe" should be "a_v_b" and "pipe1" should be "av_b".
5) You could reduce the discretization of the pipe models until the simulation works well.
6) You should consider starting with simpler pressure drop models in the pipes. For example "NominalLaminarFlow" or "NominalTurbulentPipeFlow". The parameters needed for the models are nominal mass flow rates and pressure drops.
7) Since Dymola (in my case) chooses p and h as states, you should consider using initial enthalpies instead of temperatures.

Best regards,
Rene Just Nielsen

Rene,
I made some changes based on your suggestion. The model run now but is very slow. I am not sure if any other changes can be made to speed up the analysis. Also, can we get phase as an output instead of 1 phase, 2 phase or unknown.

Gopal
1510316965_SteamHammer-DynPipe.mo