Isothermal liquid networks do not undergo temperature or viscosity changes due to any processes occurring in or around the network, but can support elevated or reduced temperatures.
In R2020a, the Isothermal Liquid library was introduced as a mass flow rate-based alternative to the Hydraulics (Isothermal) volumetric flow rate-based library. The Isothermal Liquid library introduces block usability improvements. For more information on converting models with Hydraulics (Isothermal) blocks to use Isothermal Liquid blocks, see: Upgrading Simscape Fluids Models Containing Hydraulics (Isothermal) Blocks.
If a specific component does not yet exist in a domain library, you can build your own using the Simscape language. For more information, see Creating Custom Components.