Add Surface Boundary Condition

Introduction

Conduction Surface Boundary Conditions are used to apply thermal boundary conditions directly to the surfaces of a static body conduction. Unlike volume boundary conditions, which apply thermal constraints throughout a three-dimensional region of the solid, surface boundary conditions act only along the surfaces of the conduction geometry. These boundary conditions can be used to prescribe surface temperature or heat flux conditions that drive thermal transport within the solid conduction field. Surface boundary conditions are commonly used to model heated or cooled vessel walls, external jackets or heating mantles, or prescribed wall temperatures The applied boundary conditions act directly on the conduction field and influence the resulting conductive heat transfer throughout the solid body.

These boundary condition surfaces can be defined either by (i) selecting surfaces directly from the associated conduction geometry or (ii) importing a child geometry that overlaps a surface region of the conducting solid. In both cases, the geometry associated with the boundary condition appears as a child of the Surface Boundary Condition component (and as a grandchild of the Static Body Conduction component). Multiple surface boundary conditions can be applied across different regions of the static body geometry.

Access

When you select Add Conduction Surface BC on the Static Body Conduction context-specific toolbar, a new child geometry is formed and the property grid below will launch.

Property Grid

General

Boundary Condition

This defines the type of thermal boundary condition applied to the surface conduction region. Options include a user-defined boundary condition temperature or a user-defined heat flux.

Temperature

This efines the system-level temperature UDF used for the boundary condition.

Temperature UDF

K | This defines a custom temperature boundary condition through a user-defined function. This is a System UDF.

Download Sample File: Temperature

Uniform Heating

This defines the system-level heat flux UDF used for the surface boundary condition. This can be specified as either a total applied heat rate or an applied heat flux. In both cases, the boundary condition is applied uniformly across the surface. Regardless of the input form, the heating is converted into a flux. If a total heat rate is provided, it is automatically converted to a surface flux using the surface area computed at runtime.

Heating Specification

This defines how the uniform heating rate is specified.

Total

This specifies the total heat flow rate applied to the static body. At runtime, this value is divided by the computed static-body surface area to determine the equivalent uniform heat flux.

Per Unit Area

This specifies the heat flux directly. This value is applied uniformly over the static-body surface.

Heat Flux UDF

W or W/ \(m^2\) | This UDF defines the heat flux along the surface of the conduction surface body. One output must be defined within the UDF: a floating point variable named value. This output variable defines the heat flux at the along the surface boundary condition. This value can be specified as either a total flux (flow) or aerial flux (per unit surface area).

If the Custom Flux Specification is set to Areal, this value will be used directly in the code to define a local flux field boundary condition along the solid surface. If the Flux Specification is set to Total, this value will be divided by the local solid surface area to define a local flux field boundary condition along the solid surface. This is a System UDF.

Local Heating

Defines a spatially varying heat flux along the static body surface. Unlike Uniform Heating, this option allows the local heat flux to vary as a function of local fluid conditions and position along the wall.

This capability is useful for implementing custom convective heat transfer models where the local heating or cooling rate depends on nearby fluid properties such as temperature, velocity, turbulence, species concentration, or other user-defined quantities.

Heat Flux UDF

W/ \(m^2\) | This UDF defines the heat flux along the surface of a static body. One output must be defined within the UDF: a floating point variable named qDot. This output variable defines the heat flux at the solid/liquid interface. This is a Local UDF, calculated on a voxel-by-voxel basis using the local fluid properties. The UDF is only applied to cells adjacent to the solid surface.

Download Sample File: Heat Flux

Location

Static Body Conduction

Surface Boundary Conditions Toolbar

Context-Specific Toolbar Forms	Description
Select Faces	The Select Faces tool selects the faces where the surface boundary condition will be applied.
Add Geometry	The Add Geometry form adds child geometry by importing from external CAD files, extracting from external CAD assemblies, or defining internally using built-in parametric geometry.
Help	The Help command launches the M-Star reference documentation in your web browser.

See also Child Geometry Context Specific Toolbar.

For a full description of each selection on the Context-Specific Toolbar, see Toolbar Selections.