Thermal Coupling — Convection types

The Type option in the Thermal Coupling — Convection dialog box lets you create the following types of convection couplings:

• Convection Coupling

• Duct Node Convection Coupling

• Forced Convection Coupling

• Free Convection Coupling

• Across Gap Convection Coupling

Convection Coupling

The Convection Coupling type models convective couplings between the fluid ducts and the convecting region. You specify a constant, time-dependent, or temperature-dependent heat transfer coefficient. The heat transfer coefficient can also have a spatial distribution. You can also apply a local correction to the heat transfer coefficient using the Duct Convection Correction modeling object.

Duct Node Convection Coupling

The Duct Node Convection Coupling type models convective couplings between the nodes in the fluid duct and the convecting region.

Forced Convection Coupling

The Forced Convection Coupling type models convective heat transfer between the fluid in a duct network and adjacent surfaces. Convective conductances are established at run time from each convecting surface element to the nearest of the 1D duct elements. You can account for overlap. Fluid properties, temperature, and flow data are extracted from the 1D duct elements to dynamically compute the heat transfer coefficients.

The solver computes forced convective couplings using standard correlations for forced convection in a 1D flow system with a developing boundary layer, or a fully developed boundary layer.

The Forced Convection Coupling type also models convective heat transfer between the fluid in a duct network and a plate in a free stream.

Free Convection Coupling

The Free Convection Coupling types models free convective couplings computed using standard correlations for free convection from regular objects. The softwarre calculates a single global heat transfer coefficient for the entire convecting surface. You can specify different correlation types.

The solver adjusts the correlation according to the Gravitational Acceleration vector that you define on the Ambient Conditions page in the Solution dialog box. The convecting surface that is created is always assumed to be smooth.

The software models free convection in two ways:

• It models free convection in a duct network using the Free Convection Coupling type. The free convection correlations assume a still air condition. When modeling chimney effects, the Forced Convection Coupling type provides a more accurate correlation.

• It models free convection to an ambient fluid environment using the Free Convection to Environment type of the Convection to Environment constraint. When you model free convection to an ambient fluid, the ambient fluid may or may not reflect the geometric shape of the fluid. Elements in selected regions convect to the ambient fluid elements based on the correlation and characteristic shape you select. The correlations are derived experimentally and are applicable to specific geometry. Large differences between the model and the correlation's typical shape will result in a loss of precision.

Free vs forced convection couplings

Whether to model the convection of buoyancy driven flow with a Free Convection Coupling or a Forced Convection Coupling type depends entirely on the physics of the flow.

• The Free Convection Coupling type is used for a still body of gas where some movements occur near the convecting surfaces. This could apply to a duct network with a very large cross-section.

• If a velocity profile develops across the channel cross-section, correlations with the Forced Convection Coupling type is more accurate.

Across Gap Convection Coupling

The Across Gap Convection Coupling type models heat transfer between two parallel surfaces (regions) where a convecting fluid is the medium of heat exchange. The elements on the primary region are called primary elements; those on the secondary region, secondary elements. Each primary element is connected to one or more secondary elements.

You can choose from several different correlation types. The correlation you select calculates convective conductances between the selected primary and secondary elements using the Gravitational Acceleration vector. The convecting surfaces are always assumed to be smooth and parallel, or quasi-parallel, such as concentric cylinders.

How do I

Create a Thermal Coupling — Convection

Define a convection coupling between duct nodes and solid faces

Learn more

Across gap coupling convection correlations

Duct Convection Correction modeling object

Inputs to expressions

Free convection correlations

Forced convection correlations

Specifying a Coupling Resolution

Using the Only Connect Overlapping Elements option

Using the Overlap Projection Direction option

Look up more details

Duct Node Convection Coupling options

Auto-generated expressions

Thermal Coupling — Convection dialog box

Quick links

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Thermal Coupling — Convection types, Simcenter 3D 2021.1 Series

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