IncompressibleFluidNetworkMultiway connections of pipes and incompressible medium model 
This information is part of the Modelica Standard Library maintained by the Modelica Association.
This example demonstrates two aspects: the treatment of multiway connections and the usage of an incompressible medium model.
Eleven pipe models with nNodes=2 each introduce 22 temperature states and 22 pressure states. When configuring pipeModelStructure=a_v_b, the flow models at the pipe ports constitute algebraic loops for the pressures. A common workaround is to introduce "mixing volumes" in critical connections.
Here the problem is treated alternatively with the default pipeModelStructure=av_vb of the DynamicPipe model. Each pipe exposes the states of the outer fluid segments to the respective fluid ports. Consequently the pressures of all connected pipe segments get lumped together into one mass balance spanning the whole connection set. Overall this treatment as highindex DAE results in the reduction to 9 pressure states, preventing algebraic loops in connections. This can be studied with a rigorous medium model like StandardWaterOnePhase.
The pressure dynamics completely disappears with an incompressible medium model, like the used Glycol47. It appears reasonable to assume steadystate mass balances in this case (see parameter systemMassDynamics used in system.massDynamics, tab Assumptions).
Note that with the stream concept in the fluid ports, the energy and substance balances of the connected pipe segments remain independent from each other, despite of pressures being lumped together. The following simulation results can be observed:
The fluid temperatures in the pipes of interest are exposed through heatPorts.
pipeModelStructure 
Value: Modelica.Fluid.Types.ModelStructure.av_vb Type: ModelStructure 

systemMassDynamics 
Value: if Medium.singleState then Dynamics.SteadyState else Dynamics.SteadyStateInitial Type: Dynamics 
filteredValveOpening 
Value: not Medium.singleState Type: Boolean 
source 
Type: Boundary_pT 


pipe1 
Type: DynamicPipe 

pipe2 
Type: DynamicPipe 

pipe3 
Type: DynamicPipe 

pipe4 
Type: DynamicPipe 

pipe6 
Type: DynamicPipe 

valve1 
Type: ValveIncompressible 

valve2 
Type: ValveIncompressible 

pipe7 
Type: DynamicPipe 

valve3 
Type: ValveIncompressible 

sink 
Type: Boundary_pT 

system 
Type: System 

valveOpening1 
Type: Step 

valveOpening2 
Type: Step 

valveOpening3 
Type: Step 

pipe8 
Type: DynamicPipe 

pipe9 
Type: DynamicPipe 

pipe10 
Type: DynamicPipe 

pipe5 
Type: DynamicPipe 

heat8  
pipe11 
Type: DynamicPipe 