Convection to Environment

Use a Convection to Environment constraint to implicitly model natural and forced convection. A Convection to Environment constraint is effective and efficient when:

• The convecting geometry is simple.

• Convection is of secondary interest in the analysis.

For complex or detailed convection problems, use the convection options on the 3D Flow page in the Solution dialog box instead of using the Convection to Environment constraint. For a more detailed explanation of differences between implicit convection modeling using constraints and convection couplings, and explicit convection modeling using 3D flow, see Modeling convection.

A Convection to Environment constraint creates convective couplings to the environment that the software computes using specified coefficients or standard correlations for convection to and from selected surfaces. The software calculates a single global heat transfer coefficient for the entire convecting surface. The shape of the convecting surface corresponds to the selected elements.

Convection to Environment types

Convection to Environment options let you model different types of convection. The type you select determines how you create the constraint and which options are available. See Convection to Environment types for more information.

• Convection to Environment models natural or forced convection when the convection coefficient or related values are previously determined, either experimentally or by reference to other analysis. The solver applies the convection values you specify to the geometry you select.

• Free Convection to Environment models natural convection from the selected geometry. The solver calculates the convection coefficient using the standard correlation you select.

• Forced Convection to Environment models forced convection from selected geometry. The solver calculates the convection coefficient using the standard correlation you select.

Controlling correlation

The Correlation option in the Free Convection to Environment and Forced Convection to Environment lets you specify the correlation the software uses. The software adjusts this correlation according to the gravity. The convecting surface that is created is always assumed to be smooth.

• In Multiphysics, you need to specify the gravity in the Gravity load.

• In Thermal/Flow, Space Systems Thermal, or Electronic Systems Cooling, you can modify the gravity on the Ambient Conditions page in the Solution dialog box. By default, the gravity is set to 9.81 m/s2 in the -Z direction.

See Free convection correlations and Forced convection correlations for more information.

Understanding convection calculations

The software bases all convection calculations on area. The following table shows how the solver calculates that area depending upon the geometry or type of elements you select.

Selection	Area calculation
Surface meshed with 2D elements	Area of the selected polygon face
Surface meshed with 3D elements	Area of the selected polygon face
Curve or polygon edge meshed with 1D elements	Area = perimeter of the beam section × length of the polygon edge or curve
Edge of surface meshed with 2D elements	Area = thickness of 2D elements × length of the polygon edge
Mesh point or point meshed with a 0D concentrated mass element	Area = surface of a sphere of the specified diameter

Excluding thermal coupling elements from the convection to environment

When you define a thermal coupling and a convection to environment boundary condition on the same selection, the solver excludes the thermal coupling elements from the convection to environment.

Supported variables and functions

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

Quantity	Variables	Auto-generated expressions
Convection Coefficient	TimeTemperatureSpatial variablesTime, spatial variablesTemperature, spatial variables	fluid_temperatureheat_flow_ratemass_flow_ratenxnynzpressureradiusrotational_speedtemperaturetemperature_differencethermal_capacitancethicknesstimevolume_flow_ratexyz
Temperature	TimeSpatial variablesTime, spatial variables

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	Convection to Environment
Simulation Navigator	Right-click the Constraint Set node→New Constraint→Convection to Environment

How do I

Create a Convection to Environment constraint

Learn more

Convection to Environment types

Free convection correlations

Forced convection correlations

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

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Convection to Environment, Simcenter 3D 2021.1 Series

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