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Thermal Liquid Library

Why Use Thermal Liquid Blocks?

The thermal behavior of liquid systems is of interest in many engineering applications. Liquids can store energy and release it back to their surroundings, often doing work in the process. Oil flow through an underground pipeline and hydraulic fluid flow in an aircraft actuator are two examples.

When temperature fluctuations are negligible, liquids behave as isothermal fluids, which simplifies the modeling process. However, when detailed thermal analysis is a goal, or when temperature fluctuations are significant, this assumption is no longer suitable.

The Thermal Liquid library provides a modeling tool that you can use to analyze the thermal behavior of thermal liquid systems. Three featured examples show some applications well-suited for Thermal Liquid modeling:

  • ssc_tl_oil_pipeline — Model oil temperature along an insulated underground pipeline.

  • ssc_tl_hydraulic_fluid_warming — Model hydraulic fluid warming due to viscous dissipation inside a hydraulic actuator.

  • ssc_tl_water_hammer — Model the water hammer effect due to a fast-turning hydraulic valve.

Representing Thermal Liquid Components

Thermal liquid systems can range in complexity from basic to highly specialized. To model a basic system, simple components often suffice. These are components such as chambers, pipes, pumps, and the liquid medium itself. Simple components are often industry independent and can be modeled using a single Thermal Liquid block. For example, you can model a pipeline segment using a single Pipe (TL) block.

To model a specialized system, generally you use custom components. These are components that you cannot represent by a single Thermal Liquid block. The five-way directional control valve in the ssc_tl_hydraulic_fluid_warming example is one such component. Custom components are often industry specific and must be modeled by grouping Thermal Liquid blocks into more complex subsystems.

The Thermal Liquid library shares the structure of other Simscape™ Foundation libraries. Four sublibraries supply the Thermal Liquid blocks: Elements, Sources, Sensors, and Utilities. With these sublibraries you can represent the most common components of a thermal liquid system. The table summarizes these components.

Component TypeDescriptionThermal Liquid Blocks
Liquid storageStore liquid in chambers or reservoirs.Constant Volume Chamber (TL), Reservoir (TL), Controlled Reservoir (TL)
Liquid transport Transport thermal liquid through closed conduits such as pipes.Pipe (TL)
Flow restriction Restrict thermal liquid flow, e.g., due to valves or fittings.Local Restriction (TL)
Mechanical interfacesInterface thermal liquid and mechanical systems, e.g., to convert liquid mechanical energy into useful work.Translational Mechanical Converter (TL), Rotational Mechanical Converter (TL)
Power sourcesProvide a power source to the thermal liquid system, e.g. , pressure difference or mass flow rate.Mass Flow Rate Source (TL), Pressure Source (TL), Controlled Mass Flow Rate Source (TL), Controlled Pressure Source (TL)
SensorsOutput measurement data for dynamic variables such as mass flow rate, energy flow rate, pressure, and temperature.Flow Rate Sensor (TL), Pressure & Temperature Sensor (TL), Thermodynamic Properties Sensor (TL),
Thermal liquidSpecify thermodynamic properties and pressure-temperature validity region of thermal liquid medium.Thermal Liquid Settings (TL)

Specifying Thermal Liquid Medium

The Thermal Liquid Settings (TL) block specifies the thermodynamic properties of the liquid medium. These properties are assumed functions of both pressure and temperature. This assumption boosts model fidelity, especially in models in which pressure, temperature, or both, vary widely.

The block accepts two-way lookup tables as input. These tables provide the different thermodynamic property values at discrete pressures and temperatures. You can populate these tables using empirical data from product data sheets or values calculated from analytical expressions.

Modeling Multidomain Systems

Thermal Liquid blocks can contain different types of conserving ports. These ports include not only Thermal Liquid conserving ports but also thermal and mechanical conserving ports. By using these ports, you can interface a Thermal Liquid subsystem with thermal and mechanical subsystems.

For instance, you can use the thermal conserving port of a Pipe (TL) block to model conductive heat transfer through a pipe wall. Oil pipeline modeling is one application. The example ssc_tl_oil_pipeline shows this approach.

Similarly, you can use the translational mechanical conserving ports of a Translational Mechanical Converter (TL) block to convert hydraulic pressure in a thermal liquid system into a mechanical actuation force. Hydraulic actuator modeling is one application. The example ssc_tl_hydraulic_fluid_warming shows this approach.

The table lists the Thermal Liquid blocks that have thermal or mechanical conserving ports. You can use these blocks to create a multidomain model containing thermal liquid, thermal, and mechanical subsystems.

Thermal Liquid BlockThermal Conserving PortMechanical Conserving Port
Constant Volume Chamber (TL)
Pipe (TL)
Rotational Mechanical Converter (TL)
Translational Mechanical Converter (TL)

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