Conjugate Heat Transfer Simulations

Nicolas Huc

Product Manager Heat Transfer

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Vice President of Sales

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EXAMPLES

Heat losses in a Vacuum flask

Temperature Velocity

Turbulent heat exchanger

water

air

Temperature and flow field

Electronics cooling

P = 1.0 W

Temperature

Conjugate heat transfer and thermal expansion

Temperature and displacement

PHYSICAL EFFECTS

Heat transfer in solids

• Conduction: transfer of heat through materials

• Materials are characterized by their thermal conductivity, noted k

Hot temperature (white)

Cold temperature (red)

Heat transfer in solids

• Heat source/sink: power source due other phenomena (chemical reactions, electric current, …)

• Heat flux: heat transfer at the boundaries due to environment (fluid, radiation, …)

Convective cooling

Heat source

Velocity

Convection

Temperature

Fluid Properties

Heat transfer in fluids

In non-isothermal flows the velocity and the temperature fields influence each other

Temperature Velocity

Conjugate heat transfer – laminar case

Conjugate heat transfer : heat transfer between solids and fluids

Hot temperature in the chip package

Low temperature in air stream

Temperature gradient in the fluid domain

Conjugate heat transfer – turbulent case

Sharp temperature change close to the fluid/solid interface

Turbulence increases apparent thermal conductivity of the fluid

Specialized interfaces are needed to capture temperature and velocity fields

Hot temperature

Low temperature in air stream

Sharp temperature gradient at the fluid/solid interface

Heat sources

• Conversion of energy into heat

• Example of multiphysics sources – Viscous heating

– Pressure work

– Electromagnetic losses (Joule, induction and microwave heating)

– Chemical reactions

Effect of heat on other physics

• Effect on material properties

• Density change – Compressible flow

– Thermal expansion

• Phase change, damage

Q & A at the end of the webinar

Questions are welcome !

COMSOL INTERFACES

Conjugate Heat Transfer Capabilities

• Conjugate Heat Transfer – Predefined coupling between solid

and fluid domains

• Heat Transfer in Porous Media – Porous media flow coupled to heat

transfer in the solid matrix and pore fluid

The Physics Interfaces with flow and heat transfer

Heat transfer in solid capabilities

• Conduction

• Convective cooling

• Highly conductive layer

• Thin thermal resistive

• Radiation (Surface to surface and participating media)

Light bulb

Composite thin thermal resistive layer

Heat transfer in fluid capabilities

• Heat transfer in fluids – Compressible fluid

– Viscous heating

– Pressure work

• Laminar and turbulent flows

• Coupling to temperature in solids with and without boundary layer approximations

• Numerical stabilization

Temperature and velocity for a turbulent compressible flow in a transonic diffuser

High-Performance Computing Support

Multi-Core Parallel Computing

Cluster Parallel Computing – Parametric Sweep

– Distributed Single Large Problem

Solvers: – Direct / Iterative / Multigrid

– Fully Coupled / Segregated

DEMO

Heat sink model

• A 1W chip generates heat which is dissipated by the heat sink

• Conductive heat in the solid part (aluminum)

• Convective cooling due to the air flow

Air flow

Demo – improved default mesh

Default mesh now automatically defines boundary mesh layers !

Automatically enhanced resolution of the sharp gradients close to the wall

Demo – going further

• Improvement of the heat source description

Enables to model the interface between the chip package and heat sink

Surface temperature Volumic heat source

Demo – going further

• Using thermal grease at the interface decrease the maximum temperature by more than 10% !

COMSOL Multiphysics enable to modify a model easily and the test hypothesis rapidly

Interface between 2 solids

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