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Constant Volume Chamber (IL)

Chamber with one port and fixed volume of isothermal liquid

  • Library:
  • Simscape / Foundation Library / Isothermal Liquid / Elements

  • Constant Volume Chamber (IL) block


The Constant Volume Chamber (IL) block models accumulation of mass in a chamber containing a fixed volume of isothermal liquid. The chamber has one inlet, labeled A.

The chamber can exchange mass with the connected isothermal liquid network. The pressure inside the chamber evolves based on the compressibility of the fluid volume.

Mass conservation relates the mass flow rate to the pressure of the internal node representing the fluid volume:



  • m˙A is the mass flow rate at port A. The flow rate associated with a port is positive when it flows into the block.

  • pI is the pressure inside the chamber. There is no flow resistance between port A and the chamber interior, therefore, pressure at port A is assumed to be equal to this pressure, pA = pI.

  • V is the volume of fluid inside the chamber.

  • ρmix is fluid mixture density.

The fluid can be a mixture of pure liquid and a small amount of entrained air, as specified by the Isothermal Liquid Properties (IL) block connected to the circuit. Equations used to compute ρmix depend on the selected isothermal liquid model. For detailed information, see Isothermal Liquid Modeling Options.


To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Assumptions and Limitations

  • The chamber walls are perfectly rigid.

  • There is no flow resistance between port A and the chamber interior.



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Isothermal liquid conserving port associated with the chamber inlet.


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Volume of fluid in the chamber. This volume is constant during simulation.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020a