Liquid

Description

Model of a hydraulic liquid. The model provides the other components (e.g. pipes) with temperature- and pressure-dependent fluid properties. In order for the fluid properties to reach the other components, the liquid model must be connected to the hydraulic circuit.

The user can choose between the following liquids:

• HLP 32
• HLP 46
• Oil 5W30
• Pentosin CHF 11S
• Skydrol 5
• Water

The model provides the following fluid properties as functions of pressure and temperature:

• Density
• Kinematic viscosity
• Dynamic viscosity
• Isothermal bulk modulus
• Isentropic bulk modulus
• Speed of sound
• Specific heat at constant pressure
• Isobaric thermal expansion coefficient
• Thermal conductivity

As an example, the following diagram shows the variation of density with pressure and temperature for water.

Due to the used mathematical approach, the fluid properties are only valid within a limited range of temperatures and pressures. If the deviations from the actual fluid properties are too large, the custom fluid can be used.

If the effects of undissolved air are to be considered during the simulation, the user can provide the fraction of undissolved air at ambient pressure through the parameter Proportion of undissolved air. The stiffness of the gas bubbles is calculated based on the parameter Polytropic exponent which can assume values between 1.0 (isothermal change of state, slow compression/expansion) and 1.4 (isentropic change of state, fast compression/expansion).