modelIsenthalpic

Information

Isenthalpic process (h_in = h_out) suitable for modeling a valve.

The following quantities can be specified either as parameters or as time-varying input signals:

• Pressure loss: dpLoss = p_in - p_out
• Relative pressure loss: prLoss = dpLoss / p_in = 1 - p_out/p_in
• Outlet pressure: p_out

Further assumptions for the isenthalpic process:

• Steady-state conditions: dE_sys/dt = 0, dm_sys/dt = 0
• No heat transfer: Q_flow = 0
• No net external forces on the system: The control volume is not subject to acceleration as a rigid body, i.e. \sum F_external = 0.
• Rigid boundary, no expansion work: w_exp = 0
• Negligible kinetic and potential energy changes: Differences between inlet and outlet are neglected, i.e. g*z_2 + 1/2*c_2^2 ≈ g*z_1 + 1/2*c_1^2.
• Constant composition: No change in species mass fractions across the control volume, i.e. X_in = X_out.

Under these assumptions, an increase in pressure in the direction of the flow violates the second law of thermodynamics; for example, the pressure must not increase within a valve. This condition can be enforced with enforcePressureDrop. Then, a red circle highlights if the prescribed pressure loss would cause a pressure rise in flow direction and is clipped. If enforcePressureDrop = false, violation only triggers an assert, which is also indicated on the icon layer. For inverse calculations, enforcePressureDrop = false is recommended, as this simplifies the equation system.

Parameters

Connectors

Components

Revisions

• 2026-08, by Silvan Keim (silvan.keim@dlr.de):
  Improved icon.
• 2026-06, by Raphael Gebhart (raphael.gebhart@dlr.de):
  The default value of enforcePressureDrop was changed from true to false to improve numerical robustness in inverse calculations. Models that require the previous behavior must now explicitly set enforcePressureDrop=true.
• 2026, by Raphael Gebhart (raphael.gebhart@dlr.de):
  Initial version.