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Gas Properties

Pneumatic domain properties for attached circuit


None (example custom library)

  • Gas Properties block



As of Release R2016b, the Gas block library replaces the Pneumatic library as the recommended way of modeling pneumatic systems. The former Pneumatic library is now included in the product installation as an example custom library. The pneumatic domain definition is still provided with the software, and all the pneumatic blocks in your legacy models continue to work as before. However, these blocks no longer receive full production support and can be removed in a future release. For more information, see the R2016b Release Notes.

The Gas Properties block defines pneumatic domain properties for a circuit, that is, the gas properties that act as global parameters for all the blocks connected to the pneumatic circuit. These gas properties are assumed to be constant during simulation time.

The Gas Properties block lets you specify the gas properties, such as specific heat at constant pressure and constant volume, as well as viscosity, as block parameters. It also lets you specify ambient pressure and ambient temperature.

The Gas Properties block has one port. You can connect it to a pneumatic diagram by branching a connection line off the main line and connecting it to the port. When you connect the Gas Properties block to a pneumatic line, the software automatically identifies the pneumatic blocks connected to the particular circuit and propagates the gas properties to all the pneumatic blocks in the circuit.

Each topologically distinct pneumatic circuit in a diagram requires exactly one Gas Properties block to be connected to it. Therefore, there must be as many Gas Properties blocks as there are pneumatic circuits in the system. If no Gas Properties block is attached to a circuit, the pneumatic blocks in this circuit use the gas properties corresponding to the default Gas Properties block parameter values.


Specific heat at constant pressure

Specify the gas specific heat at constant pressure. The default value is 1.005e3 J/kg/K.

Specific heat at constant volume

Specify the gas specific heat at constant volume. The default value is 717.95 J/kg/K.

Dynamic viscosity

Specify the gas dynamic viscosity. The default value is 1.821e-5 s*Pa.

Ambient pressure

Specify the gas ambient pressure. The default value is 101325 Pa.

Ambient temperature

Specify the gas ambient temperature. The default value is 293.15 K.

Pressure or temperature below absolute zero

Determines how the block handles the out-of-range assertion during simulation:

  • Error — If the pressure or temperature falls below absolute zero, the simulation stops and you get an error message. This is the default.

  • Warning — If the pressure or temperature falls below absolute zero, you get a warning but the simulation continues.


The block has one pneumatic conserving port.

Version History

Introduced in R2009b