Presenter: Pier Angelo Favarolo 18th March...

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The hot side of the light Presenter: Pier Angelo Favarolo

18th March 2014

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The zumtobel group Our companies

Annual revenues: 1,243.6 million €

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The zumtobel group Production plants

7162 employees in 18 production plants in four continents with one common denominator:

The passion for light!

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Modern luminaires contain electronic devices (e.g. drivers) and semiconductors

(LEDs, OLED). Their performances and reliability strongly depend on their

temperatures: the lower, the better.

CFD is a powerful tool to investigate the underlying physics of the problem and

hence make suitable design changes.

Thermal management Why?

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Anode

Junction

Cathode

PCB

Light Emitting Diodes Light generation

The recombination of electrons

and holes generate photons

Electrodes

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Light Emitting Diodes Dice

In a typical COB (Chip-On-Board) module the dice have a surface of

almost 0.5 mm² and the generated heat and radiant fluxes are of the

order of some Megawatts per square meters.

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Light Emitting Diodes Phosphor conversion

InGaN emission

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Light Emitting Diodes Heat sources

Die

Phosphor

Board

Heat ~ 70%

Light ~ 30% of the electrical power

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Light Emitting Diodes Heat sources

The Silicon-Phosphor compound

has a poor thermal conductivity.

What happens if some accidentally trapped foreign particle is absorbing the

light on the glob-top?

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- Analysis of the thermal behavior of the

glob-top due to the presence of an

accidental light absorption.

- Control of the glob-top temperatures in

order to avoid alterations of the physical

and optical properties of the Silicon-

Phosphor compound.

- Impact of several parameters like the

position and the dimension of the

absorbing particles.

Light absorption on the glob-top Purpose of the investigation

Foreign particle

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The simulation model Physical phenomena

Physical phenomena to be simulated

Light generated by the dice

Conversion losses in the phosphor

Light absorption on the glob-top

Heat conduction

Buoyancy-driven convection

Heat radiation

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Glob-top model

The glob-top is a compound of Silicon and Phosphor

The whole glob-top volume is involved in the Stokes‘

shift

The simulation model Phosphor conversion (Stokes‘ shift) losses

The discrete ordinates radiation model (DORM) is adopted

in order to take into account the volumetric absorption of

the radiation

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The simulation model Modelling the light

The multi-band model is used in order to separate

the luminous radiation from the thermal one.

The spectrum is divided into two bands: one for the

visible and the other one for the IR part of the

spectrum

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The simulation model Modelling the light source

The dice are modelled as gray bodies

The radiant temperature and the emissivity are

chosen in order to radiate the desired amount of

energy in the visible part of the spectrum.

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The simulation model Modelling the light source

The light source has a high temperature used to generate the radiant flux.

As this temperature is not realistic, it is necessary to isolate thermally, the light source from

the rest of the model → Non-conductive baffles

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The simulation model Temperature distribution of the glob-top

Simulation IR-Camera image

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The simulation model Temperature distribution

Ø 250 µm Ø 250 µm

Ø 1000 µm Ø 500 µm

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Thank you for your attention