Coupled Temperature (Legacy) - Boundary Condition

Coupled Temperature (Legacy) - Boundary Condition   Description

Coupled Temperature (Legacy) is a boundary condition designed for conjugate heat transfer (CHT) simulations involving multiple regions, such as fluid-solid interfaces. It couples the temperature and heat flux across patches, accounting for conductive heat transfer. The condition ensures continuity of temperature and balances the heat fluxes, including optional thermal resistance layers.

Note

This is a legacy boundary condition. For Conjugate Heat Transfer (CHT) simulations, it is recommended to use the Coupled Temperature boundary condition, which supports both conduction and radiation.

The heat flux balance at the interface is given by:

\[Q_s = -Q_f\]
where:
  • \(Q_s\) - conductive heat flux from solid region
  • \(Q_f\) - conductive heat flux from fluid region

This boundary condition is particularly useful in multi-region solvers like CHT Multi Region SIMPLE or CHT Multi Region.

Coupled Temperature (Legacy) - Boundary Condition   Understanding Coupled Temperature (Legacy)

The Coupled Temperature (Legacy) enforces thermal equilibrium at the interface between two regions. It calculates a mixed boundary condition based on the thermal conductivities and distances to the neighboring cells. The value fraction is determined by:

\[f = \frac{\kappa_{nbr}}{\kappa + \kappa_{nbr}}\]
where:
  • \(\kappa\) - thermal conductivity of the local region
  • \(\kappa_{nbr}\) - thermal conductivity of the neighbor region

The reference value for temperature is the weighted average:

\[T_{ref} = \frac{\kappa \cdot T + \kappa_{nbr} \cdot T_{nbr}}{\kappa + \kappa_{nbr}}\]
where:
  • \(T\) – internal temperature of the local region
  • \(T_{nbr}\) – temperature of the neighbor region

Optional thermal resistance layers (e.g., thin walls) are included by adjusting the effective thermal conductivity.

Coupled Temperature (Legacy) - Boundary Condition   Application & Physical Interpretation

The Coupled Temperature (Legacy) is used in conjugate heat transfer simulations where heat transfer occurs between different materials or phases, without radiation effects.

Coupled Temperature (Legacy) in Heat Exchangers applications

Example applications: heat exchangers, boilers, furnaces

This problem can be solved using chtMultiRegionFoam (solver). The Coupled Temperature (Legacy) is applied at solid-fluid interfaces to couple temperature and heat flux.

Example Boundary Conditions set for Heat Exchangers applications
BoundaryPressureVelocityTemperature

Solid Region Interface

Fixed Flux Pressure

No Slip

Coupled Temperature (Legacy)

Fluid Region Interface

Fixed Flux Pressure

No Slip

Coupled Temperature (Legacy)

Example usage of Coupled Temperature (Legacy) for Heat Exchangers applications in SimFlow
TutorialDescription

Heat Exchanger

Simulates heat transfer between hot and cold regions in a heat exchanger with separate flows, using thermal resistance to model conduction through a single boundary.

Coupled Temperature (Legacy) in Electronics Cooling applications

Example applications: electronic devices, CPUs, circuit boards

Using chtMultiRegionSimpleFoam (solver) for steady-state simulations. The Coupled Temperature (Legacy) models heat dissipation from hot components to coolant.

Example Boundary Conditions set for Electronics Cooling applications
BoundaryPressureVelocityTemperature

Solid-Fluid Interface

Fixed Flux Pressure

No Slip

Coupled Temperature (Legacy)

Example usage of Coupled Temperature (Legacy) for Electronics Cooling applications in SimFlow
TutorialDescription

Cylinder Cooling

Demonstrates cooling a steel cylinder with water flow, creating a multi-region mesh to solve conjugate heat transfer between solid and fluid.

Electronics Cooling

Models electronic cooling with Joule heating in a CPU and conjugate heat transfer at the interface with flowing air.

Coupled Temperature (Legacy) - Boundary Condition   Coupled Temperature (Legacy) in SimFlow

The definition of boundary conditions in SimFlow is both simple and intuitive. To specify the Coupled Temperature (Legacy) boundary condition, the user must navigate to the Boundary Conditions panel, select the appropriate boundary, and choose the correct option from the drop-down menu.

For temperature fields in multi-region setups, select Coupled Temperature (Legacy).

Coupled Temperature (Legacy) definition in SimFlow
Figure 1. Coupled Temperature (Legacy) definition in SimFlow

Parameters include:

Resistance - Enable/disable thermal resistance layer
\(\delta\) - Thickness of resistance layer
\(\kappa\) - Thermal conductivity of resistance layer

Coupled Temperature (Legacy) - Boundary Condition   Coupled Temperature (Legacy) - Alternatives

In this section, we propose boundary conditions that are alternative to Coupled Temperature (Legacy). While they may fulfill similar purposes, they might be better suited for a specific application and provide a better approximation of physical world conditions.

Boundary ConditionDescription

Coupled Temperature and Radiation

Similar to Coupled Temperature (Legacy) but includes radiation effects, suitable for cases with radiative heat transfer.

Zero Gradient

Sets zero temperature gradient, used when no heat transfer occurs.

Fixed Value

Sets a fixed temperature value at the boundary.