### 1.6.3. Activating Efficiency Output

Two options are available for efficiency analysis. You can monitor the overall device efficiency within the CFX-Solver Manager as well as post process field efficiencies in CFD-Post.

Efficiency output can be activated on the Monitor tab under Output Control in CFX-Pre, and enables you to monitor the device efficiencies in the CFX-Solver Manager.

#### 1.6.3.1. CFX-Solver Manager Output Variables

To calculate the overall device efficiency requires that you specify both an inlet and outlet boundary condition corresponding to points 1 and 2 on the T-s diagrams shown in Figure 1.2: T-s Diagrams for Compression and Expansion Processes. Only single boundary condition regions of type inlet and outlet are currently supported. The inlet entropy and total enthalpy are based on mass flow average values. The monitored efficiency values are based on mass average field efficiency at the selected outlet boundary condition.

For single phase cases or multiphase cases running the homogeneous model, the following variables are written to the out file:

- `Isentropic Compression Efficiency`

- `Isentropic Expansion Efficiency`

- `Polytropic Compression Efficiency`

- `Polytropic Expansion Efficiency`

For multiphase cases running the homogeneous mass and momentum model, but inhomogeneous energy equations (such as condensing/evaporation disperse droplets, disperse solids):

- <Continuous Phase>.`Isentropic Compression Efficiency`

- <Continuous Phase>.`Isentropic Expansion Efficiency`

- <Continuous Phase>.`Polytropic Compression Efficiency`

- <Continuous Phase>.`Polytropic Expansion Efficiency`

Compression and expansion efficiencies are calculated only for the continuous phase; all other dispersed phases are ignored.

For multiphase cases running the inhomogeneous mass and momentum model and inhomogeneous energy equations:

- <Continuous Phase n>.`Isentropic Compression Efficiency`

- <Continuous Phase n>.`Isentropic Expansion Efficiency`

- <Continuous Phase n>.`Polytropic Compression Efficiency`

- <Continuous Phase n>.`Polytropic Expansion Efficiency`

For each continuous phase, compression and expansion efficiencies are calculated.

All of the output variables are either Total to Total or Total to Static depending on which mode you have selected in CFX-Pre.

#### 1.6.3.2. Results File Output Variables

When efficiency monitoring is activated field efficiencies are also written to the final results file, Standard backup and transient results files, and Selected Variables transient files where required. When efficiency monitoring is activated, the field variables can be used in CEL expressions, monitor points (callback and point monitors), and User Fortran.

In addition to the global efficiency fields, described in the previous section, the following field variables are written to results and backup files during a simulation:

For single phase or multiphase homogeneous mass and momentum with homogeneous energy equation model:

- `Isentropic Enthalpy`

- `Polytropic Enthalpy`

For homogeneous mass and momentum with inhomogeneous energy equation:

- <Continuous Phase>.`Isentropic Enthalpy`

- <Continuous Phase>.`Polytropic Enthalpy`

For inhomogeneous mass and momentum with inhomogeneous energy equation:

- <Continuous Phase n>.`Isentropic Enthalpy`

- <Continuous Phase n>.`Polytropic Enthalpy`.

All of the output variables are either Total to Total or Total to Static depending on which mode you have selected in CFX-Pre.

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