Entropyk/docs/modelica-boundary-proof.md

Modelica Fixed/Free — sources consulted (Entropyk alignment)

Official MSL (fetched)

1. Package Modelica.Fluid.Sources
   https://doc.modelica.org/om/Modelica.Fluid.Sources.html

2. MassFlowSource_T — prescribed mass flow + temperature (not pressure)
   https://doc.modelica.org/om/Modelica.Fluid.Sources.MassFlowSource_T.html

   Quote from OpenModelica HTML (fetched 2026-07-17):

   Models an ideal flow source, with prescribed values of flow rate, temperature…

   • Prescribed mass flow rate.
   • Prescribed temperature.

   No “prescribed pressure” in the component description.

3. Boundary_pT — prescribed pressure + temperature (not ṁ)
   https://doc.modelica.org/om/Modelica.Fluid.Sources.Boundary_pT.html

   Quote (fetched 2026-07-17):

   • Prescribed boundary pressure.
   • Prescribed boundary temperature.

4. Context7 /modelica/modelicastandardlibrary — SimplePipeline example:

   Boundary_pT → StaticPipe (wall friction / ΔP) → Boundary_pT

   Double Fixed P is legal only with hydraulic resistance between the ends. An isobaric secondary path must not Fixed-P both ends.

Community

Rene Just Nielsen — legal pipe-end combinations:
https://stackoverflow.com/questions/79349553/how-pressure-and-flow-ports-are-different-in-modelica

Inlet	Outlet	OK?
Boundary_pT	Boundary_pT	Yes → ṁ from ΔP
Boundary_pT	MassFlowSource_T	Yes
MassFlowSource_T	Boundary_pT	Yes
MassFlowSource_T	MassFlowSource_T	No

Quote: “There is no boundary component specifying both mass flow rate and pressure.”

Entropyk mapping

Mode	Source	Sink	HX secondary
MassFlowSource_T (default)	Fixed T, Fixed ṁ, Free P	Fixed P (anchor), Free T_out	P_out−P_in+ΔP_sec(ṁ)=0
Boundary_pT + friction	Fixed P, Fixed T, Free ṁ	Fixed P	Needs frictional ΔP (pipe / HX)
T_out rating	Free ṁ, Free P	Fixed P + Fixed T_out	Same secondary momentum

Secondary water ΔP (quadratic, Modelica dp_nominal style): secondary_rated_pressure_drop_pa + secondary_rated_m_flow_kg_s — not refrigerant dp_model=msh (tube two-phase only).

Why HX secondary isobaric P was missing (bug)

Entropyk stores two edges on a water loop (source→HX, HX→sink), each with its own P.
Without P_out − P_in = 0 on the HX, Free P on the source left P_in unconstrained → DoF under by 1 per loop.

Modelica closes that via the connection/pipe graph; Entropyk now closes it on Condenser / Evaporator / FloodedEvaporator secondary residuals.

Implementation:

• UI: apps/web/src/lib/boundaryFix.ts
• Components: condenser.rs, evaporator.rs, flooded_evaporator.rs (n_secondary + residuals)
• Ledger: apps/web/src/lib/dofLedger.ts