Select the Working Fluid

The Simscape™ Fluids™ software enables you to model a variety of isothermal, thermal, and multi-phase systems. Key application areas include fluid transport, power generation, as well as heating and cooling. Simscape Fluids blocks are organized by domain:

  • Isothermal Liquid: Use this domain to model adiabatic liquid systems. This library is based on mass flow rates and uniformly accounts for density as a function of pressure. This domain is best suited for models with little or no variation in temperature, or where changes in fluid viscosity do not significantly influence network dynamics, even if the network is at an elevated or reduced temperature.

  • Hydraulic (Isothermal Liquid): Use this domain to model adiabatic liquid systems. This domain is best suited for models with little or no variation in temperature, or where changes in fluid viscosity do not significantly influence network dynamics, even if the network is at an elevated or reduced temperature.

  • Thermal Liquid: Use this domain to model liquid systems with varying temperatures and viscosities, including systems with convective or conductive heat transfer. The fluid properties are functions of pressure and temperature.

  • Gas: Use this domain to model a perfect, semiperfect, or real gas system. This domain is best suited for applications with one predominant network gas.

  • Two-Phase Fluids: Use this domain to model systems where the working fluid may be both a liquid and a vapor. This domain does not support more than one fluid in the network. The model is based on the average fluid density in each phase; as a result, opalescence and the effect of gravity are not taken into account.

  • Moist Air: Use this domain to model air-based systems with water vapor present. This domain is best suited for models where condensation or CO2 fluctuations contribute to the dynamics of the system.

The connecting lines in each network are colored according to its domain:

Simscape Fluids Color Coding

You can also model heat exchange and mass transfer within and between domains using blocks from the Fluid Network Interfaces library.

Specify Fluid Properties

A fluid properties block is a block that defines the fluid properties of a network. The Simscape Fluids software uses lookup tables to set these fluid properties. If you do not attach a fluid properties block, the domain defaults apply. For the default properties of the different domains, see:

To set the fluid properties in an isothermal liquid network using a fluid properties block, you can either:

  • Specify your own properties by connecting an Isothermal Liquid Properties (IL) block from the Simscape Foundation library. This block lets you specify whether the liquid bulk modulus is constant or pressure-dependent. You can also specify whether the fluid contains entrained air, and, if present, whether its amount is constant or pressure-dependent. The default working fluid is water, with constant bulk modulus and zero entrained air.

  • Connect an Isothermal Liquid Predefined Properties (IL) block from the Simscape Fluids Isothermal Liquid library and select one of the predefined liquids. You can also visualize fluid properties as a function of pressure with this block.

To set the fluid properties in a Hydraulic (Isothermal Liquid) network, you can either:

  • Specify your own properties by connecting a Custom Hydraulic Fluid block from the Simscape Foundation library.

  • Connect a Hydraulic Fluid block from the Simscape Fluids Hydraulic (Isothermal Liquid) library and select one of the predefined liquids.

To set the fluid properties in a Thermal Liquid network, you can either:

  • Specify your own properties by connecting a Thermal Liquid Settings (TL) block at any point in the network. This block is in the Simscape Foundation library.

  • Connect a Thermal Liquid Properties (TL) block from the Simscape Fluids Thermal Liquid library and select one of the predefined liquids.

To set the properties in a Two-Phase Fluid network, you can either:

  • Specify your own properties by connecting a Two-Phase Fluid Properties (2P) block from the Simscape Foundation library. This block lets you define the properties of liquid and vapor separately, each as a tabulated function of pressure and temperature.

  • Connect a Two-Phase Fluid Predefined Properties (2P) block from the Simscape Fluids Two-Phase Liquid library and select one of the predefined liquids. You can also visualize fluid properties as a function of specific internal energy or specific enthalpy and pressure with this block.

To set the properties in a moist air network, you can specify your own properties by connecting a Moist Air Properties (MA) block from the Simscape Foundation library. You can provide tabulated data for dry air and water vapor and specify the fluid temperature and pressure ranges.

To set the fluid properties in a gas network, you can specify your own properties by connecting a Gas Properties (G) block from the Simscape Foundation library. You can use this block to model a perfect, semi-perfect or real gas.

See Also

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