modelAdiabatic

Information

Adiabatic process suitable for modeling both hydraulic pumps and turbines (incompressible media) as well as compressors, blowers, fans, and turbines (compressible media) with a fixed isentropic efficiency eta_is.

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

• Pressure difference: dp = p_out - p_in
• Pressure ratio: pRatio = p_out / p_in
• Outlet pressure: p_out

Different assumptions can be used to calculate the adiabatic reversible reference process, see UsersGuide.AdiabaticThermodynamicModels.

The power can optionally be an EnergyFlowInput or an EnergyFlowOutput; see UsersGuide.EnergyFlow for details. During simulation, the physical positive direction of power is visualized on the icon layer by an orange arrow.

The model supports four possible operating modes:

1. If the outlet state is set and the power is not an input, the model is balanced.
   In this case, the power P is computed from the given specific enthalpy difference dh and mass flow rate m_flow: P = m_flow*dh.
2. If the outlet state is set and the power is an input, the model is locally overdetermined.
   This condition is indicated by a plus symbol on the icon layer. The mass flow rate is then computed from the given power P and specific enthalpy difference dh: m_flow = P/dh. In this case zero specific enthalpy difference dh = 0 can cause the simulation to fail. To obtain an overall balanced system, a locally underdetermined component, such as Sink_free , must be connected.
3. If the outlet state is not set and the power is an input, the model is balanced.
   In this case, the specific enthalpy difference dh is calculated from the given mass flow rate m_flow and power P: dh = P/m_flow. In this case, zero mass flow rate m_flow = 0 can cause the simulation to fail. Determining the outlet pressure p_out from dh introduces one implicit nonlinear equation. This implicit equation can be avoided by enabling enableFilter. The filter behavior can be tuned using the time constant TC, the nominal pressure difference dp_nom, and the nominal power P_nom. Note that all three parameters are signed quantities.
4. If the outlet state is not set and the power is not an input, the model is not permissible.
   In this case, both the power P and the specific enthalpy difference dh are unknown, and the equation P = m_flow*dh cannot be balanced. This condition is indicated by a prominent red lightning symbol.

Further assumptions for the adiabatic process:

• Steady-state conditions: dE_sys/dt = 0, dm_sys/dt = 0
• No heat transfer: Q_flow = 0
• Losses accounted for via isentropic efficiency: eta_is
• 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.

Parameters

Connectors

Components

Contents

Name	Description
ThermodynamicModel

Revisions

• 2026-08, by Silvan Keim (silvan.keim@dlr.de):
  Improved icon.
• 2026, by Raphael Gebhart (raphael.gebhart@dlr.de):
  Initial version.