Compressor/Fan

The Compressor/Fan junction modeling of the pressure added to a system by a compressor, and modeling many transient events involving compressors/fans. Because all compressors/fans are different, AFT xStream does not provide preset configurations for centrifugal compressors/fans. For these junctions, pressure and flow data that describes the device must be obtained from the manufacturer or from test data. To reduce repeated data entry, frequently-used compressors/fans can be added to the Junction Library.

Common Input Information

Like all junctions, Compressor/Fan junctions require a junction number, junction name, and inlet and outlet elevations. Similar to other junctions, compressors can have Design Alerts and Notes applied to them. They require two connecting pipes. Note that the direction of the connected pipes define which side of the compressor/fan is suction and which is discharge.

Compressor Model

This tab requires the selection and definition of what type of compressor/fan the junction represents. There are several compressor models available:

  • Centrifugal (Rotodynamic) - Represents a typical centrifugal compressor or fan where the head added to the fluid is related to the flow through the compressor via a compressor curve.

  • Positive Displacement (Fixed Flow Rate) - Represents a steady state approximation of a positive displacement compressor. The flow is fixed to a constant value, and whatever head is necessary to obtain that flow will be supplied.

  • Positive Displacement (Reciprocating) - Represents a compressor in which pistons connected to one or more crankshafts are used to pressurize a volume of gas. Cylinders can be arranged by single cylinder, opposed cylinders, inline, and vee cylinder options. Single and double-acting configurations are available.

Figure 1: Compressor/Fan Models

Variable Speed

This allows the speed of the centrifugal compressor to vary.

Transient

Centrifugal compressors/fans and fixed flow rate positive displacement compressors allow for transients. This allows the user to directly specify how the speed of the centrifugal compressor/fan or the flow rate of the fixed flow rate positive displacement compressor changes over time. This can be used to model startups, trips, or control transients.

For more information on transient data, including event transients, see Junction Transient Data.

All of the transient options need to know when to start with Initiation of Transient and allow the definition of a Transient Special Condition.

Reciprocating compressors operate at constant speed and do not allow Speed vs Time transients.

Optional

There are several optional parameters that can be defined for a compressor/fan. The Workspace Icon can be adjusted, as is the case for most junctions.

Also present are several compressor junction specific options:

  • Special Condition

    • None - The compressor/fan operates normally.

    • Compressor Off No Flow - The compressor/fan is shut off and blocked. This is identical to a closed valve.

    • Compressor Off With Flow Through - The compressor/fan is shut off but allows flow to continue through. This is identical to a lossless connection.

Related Topics

Common Junction Input Parameters

Junction Transient Data

Initiation of Transients