高温氦气物性补全；三通四通能量计算bug修正

app/simulation/components/amesim/junctions/nodes.py

@@ -11,9 +11,11 @@ class _AmesimPneumaticNode(AlgebraicComponent):
     """Shared implementation for AMESim pneumatic junction submodels.
 
     PN3NODE2/P4NODE2 use port 2 as their pressure and temperature reference.
-    Non-reference outlet ports use that reference temperature. When port 2 is
-    an outlet, its enthalpy is the residual that closes the junction energy
-    balance, matching the AMESim dh2 causality.
+    Non-reference outlet ports use that reference temperature. Signed branch
+    enthalpy flows are summed and delivered to port 2 independently of its net
+    mass flow, matching AMESim dh2 causality even at zero net mass flow.
+    The finite h_outflow diagnostic cannot encode that zero-flow energy.
+    Branch volumes and volume rates are also summed towards port 2.
     """
     REFERENCE_PORT = 'port_2'