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Numerical simulation and experimental validation of heat sinks fabricated using selective laser melting for use in a compact LED recessed downlight

  • Yi-Cheng Huang
  • Huan-Chu Hsu
Technical Paper
  • 39 Downloads

Abstract

The aim of this study was to design and fabricate heat sinks with high heat dissipation capacity by using selective laser melting (SLM). A low junction temperature was maintained and the lifetime and reliability of the resultant compact LED recessed downlight (CLDL) was increased. A trapezoidal-finned heat sink with horizontal holes (HFSLM) and three-dimensional metal-foam-like heat sink (3DSLM), which both have large surface-area-to-volume ratios, were designed in this study. Each heat sink was mounted to a 10 W CLDL and installed in a test box with the dimensions 105 mm × 105 mm × 100 mm (L × W × H) for evaluating the lifespan of the CLDL in a high-temperature environment with natural convection. The downlights withstood the test, and according to the Arrhenius equation, they had a long lifetime at normal usage temperatures. The results of the stationary simulations agreed with the experimental results. The temperatures at the solder point of the CLDL with the HFSLM and 3DSLM were 88.6 and 91.4 °C, respectively, corresponding to LED junction temperatures of 118.6 and 121.4 °C. These junction temperatures were lower than the specified LED limit temperature of 135 °C. The results of an accelerated life test prediction and in situ temperature measurement testing based on TM-21 extrapolations using LM-80 data indicated that the lumen maintenance of the CLDLs complied with Energy Star® requirements.

List of symbols

A.F.

Acceleration Factor is the test time multiplier derived from the Arrhenius equation

Β

The volumetric thermal expansion coefficient of the fluid

Cp

The specific heat capacity

e

Natural logarithms (2.71828)

Ea

Acceleration energy in electron-volts (eV), thermal activation energy 0.5–0.7 eV for assembly defects

εp

The porosity of the porous material

F

The volume force (body force) in any point of the fluid

I

The identity matrix

K

Temperature Kelvin

k

The thermal conductivity

κ

The permeability tensor of the porous media

kb

Boltzmann’s constant (Kb = 8.617 × 10−5 eV/k)

MCPCB

Metal core printed circuit board

μ

Dynamic viscosity of air

p

The pressure

Ptotal

Total power (W) input to LED (If × Vf, If is LED forward current, Vf is forward Voltage)

ρ

Density of air

Qbr

A mass source or mass sink, accounts for mass deposit and mass creation within the domains

Rth

Thermal resistance

Rth, b-h

Thermal resistance between MCPCB and aluminum housing

Rth, h-ref

Thermal resistance between aluminum housing and reference point

Rth, hs-box

Thermal resistance between heat sink and test box

Rth, h-hs

Thermal resistance between aluminum housing and heat sink

Rth, j-sp

Thermal resistance between junction and solder point

Rth, sp-b

Thermal resistance between solder point and MCPCB

Rth, sp-ref

Thermal resistance between solder point and reference point

T

Temperature

T0

The room atmosphere temperature at 25 °C

Tb

MCPCB temperature

Tbox

Test box temperature

Th

Aluminum housing temperature

Ths

Heat sink temperature

Tj

Junction temperature

Tref

Reference point temperature

Troom

Room atmosphere temperature (25 °C)

Tsp

Solder point temperature

Tuse

Temperature in normal use, in degrees Kelvin (K =  °C + 273)

Ttest

Temperature in testing, in degrees Kelvin

u

The velocity vector

Superscript

T

The transpose matrix

Notes

Acknowledgements

The authors would like to acknowledge the support from Laser and Additive Manufacturing Technology Center (LAMC), Industrial Technology Research Institute (ITRI). The authors express their gratitude to Pitotech Co., Ltd., for their technical support. Special thanks is offered to Dr. Forcea Cheng.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Mechatronics EngineeringNational Changhua University of EducationChanghuaTaiwan, ROC

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