Thermal Loads

Use Thermal Loads to define known heat sources in your model. You can create the following types of Thermal Loads:

• Heat Load defines the heat flow or power into the selected geometry or elements.

• Heat Flux defines the heat flux or heat load per unit area for the selected surface.

• Heat Generation defines the heat generation or heat load per unit volume for the selected body.

You can define a thermal load magnitude:

• As a constant value.

• As a function of independent variables listed in Supported variables and functions.

• That is controlled by a heat sensing device, which turns the thermal load on or off as temperatures change with time. You can define that heat sensing device with either a Thermostat or an Active Heater Controller type modeling object. For more information, see Thermostat and Active Heater Controller.

Understanding the application of Thermal Loads

You can create and apply thermal loads directly to elements, to geometry, or to non-geometric elements. The thermal solver uses the heat load per element. How the solver computes the heat load per element depends on the Thermal Load type, the geometry you select, and how the geometry is meshed.

Load Type	Heat load per element	Applied to	Select one of the following	Solver computes heat load based on
Heat Load NOTE	Heat load per element = q x S / ST**q is the heat load that you specify.S is either the area or the volume of the element.ST is the total area or total volume of the selection.	Volume	A body meshed with 3D elements, or the 3D elements	Total volume = Volume of the selected body or 3D elements
Area	A face meshed with 2D elements, or the 2D elements	Total area = Area of the selected face or 2D elements
A face of a body meshed with 3D elements
Implied Area	An edge or curve meshed with 1D elements, or the 1D elements	Total area = Perimeter of the beam section × length of the selected edge or 1D elements
An edge of a face meshed with 2D elements	Total area = Thickness of 2D elements × length of the selected edge
Mesh point meshed with a 0D element	Total area = Surface of a sphere of the specified diameter
Non-geometric element	Non-Geometric Element modeling object	S / ST = 1
Heat Flux	Heat load per element = q’’ x A**q’’ is the heat flux that you specify.A is the area.	Area	A face meshed with 2D elements, or the 2D elements	Actual surface area
A face of a body meshed with 3D elements
Implied Area	An edge or curve meshed with 1D elements, or the 1D elements	Area = Perimeter of the beam section × length of the edge
An edge of a face meshed with 2D elements	Area = Thickness of 2D elements × length of the edge
Mesh point meshed with a 0D element	Area = Surface of a sphere of the specified diameter
Heat Generation	Heat load per element = q’’’ x V**q’’’ is the heat generation that you specify.V is the volume.	Volume	A body meshed with 3D elements, or the 3D elements	Actual volume
Implied Volume	A face meshed with 2D elements, or the 2D elements	Volume = Surface area of the face × thickness of 2D elements
An edge or curve meshed with 1D elements, or the 1D elements	Volume = Area of the beam section × length of the edge
Mesh point meshed with a 0D element	Volume = Volume of a sphere of the specified diameter

Controlling thermal loads through heat sensing device

The Heater Control options in the Thermal Loads dialog box let you control whether the load is activated by a temperature sensor or whether it remains active at all times. The software lets you create two different types of sensor:

• A Thermostat modeling object. For more information, see Thermostat.

• An Active Heater Controller modeling object. For more information, see Active Heater Controller.

During a transient analysis, the sensor's temperature activates or deactivates the thermal load, depending on parameters you specify.

For a steady state analysis, you can define the effect of a selected Active Heater Controller or Thermostat. For more information, see Understanding thermostat options for steady state analyses.

Internal thermal boundary conditions

You can define a thermal boundary condition directly on a surface embedded in the fluid without having to create a 2D mesh or an embedded flow surface. The heat load is applied on the fluid faces. No flow surface is created and the selected surface will therefore not block the fluid. The thermal boundary condition automatically transfers heat to the fluid using global convection properties. This makes it possible to apply thermal boundary conditions to model geometry embedded in the flow domain without blocking the flow. A typical application is a coarse screen or other device that convects heat to the fluid but does not impede flow.

Supported variables and functions

The following table lists the independent variables and auto-generated expressions for the Thermal Loads quantities that you can define using fields and expressions.

Type	Quantity	Variables	Auto-generated expressions
Heat Load	Heat Load	TimeTemperatureThermal capacitance	contact_pressurefluid_temperaturegap_distanceheat_flow_ratemass_flow_ratenxnynzpressureradiusrotational_speedtemperaturetemperature_differencethermal_capacitancethicknesstimevolume_flow_ratexyz
Heat Flux	Heat Flux	TimeTemperatureThermal capacitanceSpatial variablesTime, spatial variablesTemperature, spatial variablesThermal capacitance, spatial variables
Heat Generation	Heat Generation	TimeTemperatureThermal capacitanceSpatial variablesTime, spatial variablesTemperature, spatial variablesThermal capacitance, spatial variables

Note:

1. The temperature is taken either from the elements that you selected in:The Thermal Loads dialog box when Specify Reference Temperature Set is cleared.The Reference Temperature Set modeling object when Specify Reference Temperature Set is selected in the Thermal Loads dialog box and you specified the modeling object. The temperature is the average temperature of the elements in the modeling object selection.

2. The auto-generated expressions are not supported when you override the heat load region with a non-geometric element.

In expressions, you can also use all built-in functions that are listed in Mathematical functions in expressions and most built-in functions that are listed in Thermal-flow functions in expressions.

Where do I find it?

Application	Pre/Post
Command Finder	Thermal Loads
Simulation Navigator	Right-click the Loads node→New Load→Thermal Loads

Learn more

Understanding thermostat options for steady state analyses

Inputs to expressions

Look up more details

Auto-generated expressions

Quick links

Simcenter 3D Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal boundary conditions

Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Thermal Loads, Simcenter 3D 2021.1 Series

© 2020 Siemens

If you select a polygon body to define a

Heat Load

, you may not include any other order of geometry in the selection.

If you select the

Per Element

check box from the

Distribution

group, the solver applies the specified load value to each element of the selected geometry. Use this option only when the selected elements or the elements on the selected geometry are all of identical size.

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