Pipe with optional heat exchange.
Thermodynamic equations are defined by Partials.TwoPort. Q_flow is defined by heatPort.Q_flow (useHeatPort=true) or zero (useHeatPort=false).
Note: Setting parameter m (mass of medium within pipe) to zero leads to neglect of temperature transient cv*m*der(T).
Note: Injecting heat into a pipe with zero mass flow causes temperature rise defined by storing heat in medium's mass.