Optimization of a heat sink for a LED device using SC/Tetra and HyperStudy

Multi-Objective Optimization Study of LED

Light using SC/Tetra and HyperStudy

2014 European ATC

©2014 Cradle North America Inc.

Overview

• The goal is to minimize the LED temperature and the heat sink volume

for the typical LED downlight.

• 2 objective functions (responses) are defined.

• Optimization will be performed using HyperStudy.

• For the CFD simulation, SC/Tetra will be used.

• Heatsink dimensions can be changed.

• 5 design parameters are defined.

Design

Parameters

The number of fins

Fin height

Bore thickness

Inner radius

Outer radius

Objective

Function

LED temperature

Heatsink volume


• The following computational domain is set since heatsink, housing, and

LED is installed in the closed double ceiling.

• The following assumption is made to run the simulation.

• Upper side is exposed to outside air with 30[C].

• Lower side is exposed to inside air with air conditioned(24[C]).

• Quarter (1/4) model is used to reduce the CFD computation time.

Analysis Model

0.245[m]

1.0[m] 1.0[m]


• Detail geometry of LED downlight is shown below.

Analysis Model

Heatsink

Housing

LED

Lateral View from upper side Lateral View from lower side

View for Separated Parts


• Design Parameters

Analysis Model

Design Parameter Min Max Type

Number of fins 24 48 Integer(Discrete)

Fin height 80 120 Real(Continuous)

Bore thickness 2 5 Real(Continuous)

Inner radius 25 35 Real(Continuous)

Outer radius 65 75 Real(Continuous)

Fin height

Inner radius

Outer radius

Bore thickness

Close View in Red Square


• Diagram to show the relationship of HyperStudy and SC/Tetra

Analysis Procedure

HyperStudy

Setup

HyperStudy

DOE

HyperStudy

Optimization

Suitable Design

HyperStudy

Fit (Approximation)

Response Curve

Updated

Response Curve

Pareto Graph

SCT/Tetra

Base Run

SCT/Tetra

Sampling Run

SCT/Tetra

Check Run

VBScript

VBScript

VBScript


• Brief Procedure

1. Build VBScript to run CFD simulation in SC/Tetra

2. Prepare template to set design variables using VBScript from 1

3. Setup “New Study” with parameterized file in HyperStudy

4. Execute the base run using the initial value to test the VBScript

5. Set up Objective Functions (responses)

6. Execute Design of experiment (DOE) to obtain response surface

7. Execute Fit to obtain meta model and update the response surface

8. Execute Optimization to obtain pareto graph.

Analysis Procedure


• Analysis Type

• Steady State

• Flow(laminar flow), temperature and radiation are considered

• Boundary Condition

• Xmin, Xmax, Ymin and Ymax: Symmetry

• Zmax: Heat transfer coefficient (22.4 [W/(m2.K)]*), outside temperature (30 [C])

• Zmin: Heat transfer coefficient (6.13 [W/(m2.K)]*), inside temperature (24 [C])

• Other Conditions

• Gravity: 9.80665 [m/s2] to the negative Z direction

• Heat Generation: 12.5 [W] for LED

Analysis Condition for CFD Simulation

*Ashrae Handbook 2013 p26.20


• Material Property

Analysis Condition for CFD Simulation

Material Density

[kg/m3]

Viscosity

[Pa.s]

Specific Heat

[J/(kg.K)]

Thermal

Conductivity

[W/(m.K)]

Emissivity

[-]

Thermal

Expansion rate

[1/K]

Air (1) 1.1763 1.862-e5 1007 0.02614 n/a 0.00333

Heat Sink (2) 2690 n/a 900 209 0.8 n/a

LED (3) 8880 n/a 386 398 0.8 n/a

Housing (5) 1200 n/a 1050 0.2 0.8 n/a

TopCeil (4) 2400 n/a 900 0.2 0.8 n/a


• DOE

• Full factorial with 48 samplings

• Fit

• Least Squares Regression method

• Optimization

• MOGA

Analysis Condition for HyperStudy


• Response Surface

• Kriging-based interpolation method

DOE Result

Number of Fins [-]

Fin Height [mm] Bore Thickness [mm] Inner Radius [mm]

Heats

ink V

olu

me [m

^3]

Outer Radius [mm] H

eats

ink V

olu

me [m

^3]

Heats

ink V

olu

me [m

^3]

Heats

ink V

olu

me [m

^3]

Heats

ink V

olu

me [m

^3]


• Contributing Percentage

• Based on the contributing percentage, almost 50% of contribution

to rising LED temperature is outer radius. This makes sense

because the outer radius directly affects the surface area of the

heatsink.

• The contribution of Fin Height, Bore thickness and Inner radius to

the thermal effect is very small, so these design parameters can

be changed freely without affecting the LED temperature.

Fit Result

0

10

20

30

40

50

%

Contributing Percentage

Rising LED Temperature

Heatsink Volume

Ou

ter

radiu

s incre

ase

65[mm]

70[mm]

75[mm]


• Variable Distribution (Part 1)

Optimization Result

Bo

re T

hic

kn

es

s [

mm

]

Ou

ter

Ra

diu

s [

mm

]


• Optimal Pareto Graph

Optimization Result R

isin

g L

ED

Te

mp

era

ture

[C

]

Heatsink Volume [m^3]


• Priority on light weight

Optimum Design Result

case1 case2 case3

Heatsink Volume [m^3] 0.00015 0.00028 0.00041

Rising LED Temperature [C] 48.09 38.26 32.73

Number of Fins 24 36 48

Heatsink Height [mm] 82.76 92.48 119.09

Bore Thickness [mm] 2.01 2.06 3.76

Outer Radius [mm] 28.97 25.00 25.00

Inner Radius [mm] 65.02 75.00 74.94

Simulation result [C] 48.92 36.71 33.86

Case1 Case2 Case3

Case1

Case2

Case3

Ris

ing

LE

D T

em

pera

ture

[C

]

Heatsink Volume [m^3]


• Preparation time is shown below.

• Note that once the VBS is created, this can be reused for similar project.

Total Time to Obtain Result

Software Process Machine Time

[hr]

Human Time

[hr]

SC/Tetra Build VBS to create geometry, create mesh, run

simulation and extract values in SC/Tetra

0 10

HyperStudy

(SC/Tetra)

Setup DOE Study and execute VBS automatically 73 0.5

HyperStudy Setup Fit and execute 0.1 0.1

HyperStudy Setup Optimization 0.5 0.1


• Min, max and average value are shown blow.

• Computation time and memory consumption is for solver only.

Mesh and Computation Time

Case No. of Node No. of Elements Computation time

[hr:min]

Memory Consumption

[GB]

Min 2,359,133 8,434,121 0:30 13.5

Max 7,267,109 24,351,288 2:02 37.2

Average 4,300,727 14,857,177 1:16 23.0

Total (48 cases) - - 60:44 -


• Machine used for this simulation is below.

• Cluster1 is used to generate the meshes.

• Cluster2 is used to run the simulation.

• Software used for this simulation is below.

• SC/Tetra V11

• HyperStudy v12.0.0

Environmental Information

Cluter1 Cluster2

OS Windows 7 Professional Windows Server 2012

CPU Intel Core i7 3.20GHz (6 cores) * 2 / node Intel Xeon E5-2687W 3.10GHz (8 cores) * 2

RAM 24GB 64GB

Date post:	06-May-2015
Category:	Engineering
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Optimization of a heat sink for a LED device using SC/Tetra and HyperStudy

Engineering