thyristorRadiator Summary en .pdf



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Flux

www.cedrat.com

Example

Creation
date

Thermal behaviour of a thyristor associated to a radiator

2009

Author : Pascal Ferran - Université Claude Bernard Lyon

Ref. FLU2_TP_THM_01

Program

Dimension

Version

Physics

Application

Work area

Flux

2D

10.3

Thermal

Permanent

Thermal

FRAMEWORK
Presentation
General remarks

Study of the equilibrium temperature of a semi-conductor (thyristor type) associated
to a heat sink when the losses are generated by the electronic component.
This example shows how to define the geometrical and physical properties of the heat
sink associated to the semi-conductor to insure the integrity of the component when
it generates losses.

Objective

Computation of the temperature value in the centre of the thyristor according to the
following parameters :
The parameters the user can change are :
Losses generated by the semi-conductor (P)
Value of the radiator convection coefficient (H)
Value of the radiator radiation coefficient (EPS)

Theoretical
reminders

Analytical computations can be made from thermal equivalent schemes. To do so, the
different heat transfer means have to be considered.

CEDRAT S.A. 15, Chemin de Malacher Inovallée – 38246 MEYLAN Cedex (France) – Tél : +33 (0)4 76 90 50 45 – Email : cedrat@cedrat.com

Erreur ! Style non défini.

Flux

Properties
- Radiator (in aluminium) :
Thermal conductivity:  = 204 W. m-1. °C-1
- Thyristor’s box (in silicon)
Thermal conductivity:  = 78 W. m-1. °C-1
- The thermal transfers between the air (at 20 °C)
and the thyristor are made by radiation and
convection.
Convection coefficient
5 W.m-2. °C-1

Radiation coefficient
0.9

- The thermal transfers between the air (at 20 °C)
and the radiator are made by radiation and
convection.
Convection coefficient
25 W.m-2. °C-1

Radiation coefficient
0.5

- Rated losses generated by the semi-conductor :
P = 75 W.
Illustration

Main characteristics

Some results …

Illustration of the temperature corresponding to the rated values of the parameters

PAGE 2

Thermal behaviour of a thyristor associated to a radiator

Flux

FRAMEWORK

Variation of the temperature in the centre of the thyristor according to the convection coefficient H at the transfer
surface between the radiator and the air (other parameters are rated)

To go further …
-

Same analysis in transient thermal
Radiator geometry optimization…


Thermal behaviour of a thyristor associated to a radiator

PAGE 3

MODEL IN FLUX

Flux

MODEL IN FLUX
Domain
Dimension

2D

Depth

40 mm

Infinite Box

Length unit.

mm

Angle unit.

degrees

Size

Periodicity

In. radius :

Symmetry

Characteristics

Out. Radius :
none

Repetition number :
Offset angle :

Even/odd periodicity
Application

Steady AC thermal

Properties

Geometry / Mesh

Full model in the FLUX environment

Mesh

2nd order type

Mesh

Number of nodes

2912

Input Parameters
Name

Type

H

Physical

EPS

Physical

P

Physical

PAGE 4

Description
Convection coefficient
of region SURFRAD
Radiation coefficient of
region SURFRAD
Losses generated by
the semi-conductor

Rated value
25 W.m-2. °C-1
0.5
75 W

Thermal behaviour of a thyristor associated to a radiator

Flux

MODEL IN FLUX

Material Base
NAME
B(H) model
Magnetic property
J(H) model
Electrical property
D(E) model
Dielectric property
K(T) model
K(T) characteristics

ALU
Isotropic, constant
Thermal conductivity
= 204 W. m-1. °C-1
-

SILICON

THYRISTOR
Surface region
Conducting Thermal region
with heat source
SILICON
-

RADIATOR
Surface region
Conducting Thermal region
with heat source
ALU
-

SURFRAD
Line region
Region with heat
transfer surface
-

-

-

-

Electrical characteristics

P

-

-

Current source

-

-

Thermal characteristics

-

-

Convection : H
Radiation : EPS

Possible thermal source

-

-

NAME
Nature
Type
Material
Mechanical Set
Corresponding circuit
component

SURFTHYR
Line region
Region with heat transfer surface
-

Electrical characteristics

-

Current source

Convection : 5
Radiation : 0.9

RCP(T) model
RCP(T) characteristics

Isotropic, constant
Thermal conductivity
= 78 W. m-1. °C-1
-

Regions
NAME
Nature
Type
Material
Mechanical Set
Corresponding circuit
component

Thermal characteristics
Possible thermal source

-

-

-

Thermal behaviour of a thyristor associated to a radiator

PAGE 5

MODEL IN FLUX

Flux

Mechanical Set
Fixed part :

Compressible part :
Type
Characteristics
Miscellaneous

Mobile part :
Type of kinematics
Internal characteristics:
External characteristics :
Mechanical stops

Electrical circuit
Component

Type

Characteristics

Associated Region

Electric scheme

Solving process options

Type of linear system solver

Type of non-linear system
solver

Automatically
chosen

Parameters
Precision

Newton Raphson

Automatically defined
0.0001

Method for computing the
relaxation factor

Nb iterations

100

Automatically defined

Thermal coupling
Advanced characteristics

Solving

Scenario

Name of
parameter

Controllable
parameter

Variation
method

Interval definition

Step selection

SCENARIO

H

Physical

Step value

5 to 50

Step of 5

Duration of the solving

PAGE 6

5 seconds

Operating System

Windows XP 32 bits

Thermal behaviour of a thyristor associated to a radiator

Flux

ANNEX

ANNEX
Theoretical reminders on heat transfers
Conduction at
permanent state

Conduction is a heat transfer mode coming from the heat difference between 2
mediums.
Fourier’s Law :
At steady state, the Fourier’s Law describes the quantity of heat dQ that goes at x
through a surface S with thickness dx during time dt.

dQ     S 
name
dQ
S
dt
dT/dx
Convection at
permanent state

dT
 dt
dx
description
Elementary energy
Material thermal conductivity
Exchange surface
Elementary time duration
Temperature gradient at a point x

Unit
J
W. m-1. °C-1

s
°C/m

Convection is a heat transfer mode coming from a fluid move (liquid or gaseous).
Newton’s Law :
At steady state, the Newton’s Law describes the heat flow exchanged by convection
between 2 elements.

  h  S  (Tc  Tf )
name
h

S
Tc
Tf

Description
Convection coefficient
Exchanged heat flow
Exchange surface
Hot température
Cold température

Unit
W. m-2. °C-1
W

°C
°C

Values of the convection coefficient according to the type of fluid:

Natural convection
Forced convection

Fluid

h in W. m-2. °C-1

water
air
water
air
oil

100 to 1000
5 to 50
100 to 15000
10 to 500
50 to 150

Thermal behaviour of a thyristor associated to a radiator

PAGE 7

ANNEX

Radiation at
permanent state

Flux

The thermal radiation is a heat transfer mode which happens in vacuum.
When a body radiates, it issues energy and its temperature decreases.
Stephan’s Law :
The Stephan’s Law describes the heat flow exchanged between a surface S at a
temperature Tc and air at a temperature Tf :

      S  (Tc 4  Tf 4 )
name


S
Tc
Tf



PAGE 8

description
Radiation coefficient
Heat flow exchanged
Exchange surface
Hot temperature
Cold temperature
Boltzmann’s constant : 5.67 E-8

Unit
W

°C
°C
W. m-2. °C-4

Thermal behaviour of a thyristor associated to a radiator


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