Junction¶

Description¶

The Junction asset represents a connection point where two or more thermal-network assets meet. In simulation, it acts as a mixing and continuity node: incoming and outgoing flows are balanced, and the node state provides a common pressure and thermal state that connected assets use at their connection points. The junction is created from ESDL connectivity (for example Joint connections) during network mapping and is represented internally by a solver node.

Parameters¶

Parameter	Description	Unit	ESDL Asset Property
`pn_bar`	Junction pressure set value used as nominal/initial node pressure	Pa	derived from mapped network settings
`tfluid_k`	Junction fluid temperature set value used as nominal/initial node temperature	K	derived from mapped network settings

Physics and Assumptions¶

The junction enforces local conservation and state consistency between connected assets. It does not model component behavior on its own; instead, it provides the coupling equations that connect asset ports.

Mass flow¶

The junction enforces continuity of mass flow. The algebraic sum of node discharge and all connected port mass flows is zero:

\[\dot{m}_{node} + \sum_i \dot{m}_i = 0\]

where \(\dot{m}_{node}\) is the node discharge variable and \(\dot{m}_i\) are mass flows at all connected asset ports.

Energy and mixing¶

When connected flows indicate mixing at the node, the junction enforces a flow-weighted energy balance:

\[\dot{m}_{node} u_{node} + \sum_i \dot{m}_i u_i = 0\]

where \(u\) is specific internal energy. This relation determines the node thermal state and, through fluid properties, the effective mixed temperature seen by connected assets.

For special flow situations (all connected flows with the same sign or near-zero flow), the node temperature is prescribed to its configured initial value to keep the system well posed.

Pressure¶

The junction acts as a common hydraulic state for connected ports. Connected assets use this shared node pressure in their coupling equations. The node can also be operated with a fixed pressure value:

\[p_{node} = p_{set}\]

This is used when pressure must be prescribed at the junction.

Assumptions¶

The junction has no thermal capacity and no dynamic storage of mass or energy.
Mixing at the junction is ideal and instantaneous within a timestep.
Pressure losses and heat losses inside the junction are neglected.
Node discharge is represented as an algebraic balancing variable.

Limitations¶

The model does not represent detailed geometry-driven mixing effects.
No local pressure-drop model is included for fittings or manifolds at the junction.
No transient stratification or delay effects are represented at the node.

References¶

References

(No references listed.)