Thermal and airflow Thermal and airflow modeling methodology for modeling methodology for

highhighpower-desktop PC chassispower-desktop PC chassis

99thth July 2010 July 2010

Jeehoon ChoiJeehoon Choi

ContentsContents

Introduction - Background & Motivation11

Thermal and airflow design22

Basic test – general desktop PC33

Axial fan – design & analysis44

High power desktop chassis – design & practice55

IntroductionIntroduction- Backgrounds & - Backgrounds &

MotivationMotivation

History on semiconductor development The growth of the electronic industries have been accelerated with the trend of the modularization, the miniaturization and the high integration. In the demands of ever increasing semiconductor performance for the extensive data and graphic processing, the powerful performance of the semiconductors has been developing nowadays.

A TypicalMicroprocessor

Actual size

1971

10 10 μμm Line Width m Line Width

(2,300 Transistors)(2,300 Transistors)

??

130-65nm Line Width 130-65nm Line Width

(Single-Dual(Single-Dual Core)Core)

32nm Line width 32nm Line width

(Octa Core)(Octa Core)

45nm Line Width 45nm Line Width

(Quad Core)(Quad Core)

22nm Line Width22nm Line Width

(This new product line will (This new product line will be established in 2011. )be established in 2011. )

2001 2008

The Needs for Electronic Cooling

RELIABILITY

MECHANICAL

-Wire bond failure- Die fracture- Corrosion

ELECTRICAL

- Electrical overstress- Electromigration- Gate oxide breakdown- Ion diffusion causing parameter shifts

PERFORMANCE

- Output logic swing- Switching speed- Noise margins- Signal degradation

Temperature Temperature 55%55%

Sources of stress in Sources of stress in electronicselectronics

Cooling Technologies

Passive Cooling

Thermal insulation

Standard conduction

Natural convection

Heat pipes

Active Cooling

Thermoelectric cooling (TEC)

Forced air & Liquid convection

Refrigerating & cryogenic cooling

MEMS Cooling

Cooling Technologies : Heat sink

Extruded Al heat sink with a fan

Heat Sink

Users have been feeling inconvenient by a loud noise of the fan or not gratified with low temperature environment of CPUs because the cooling performance of its system depends mainly upon high flow rate of the fan.

Folded fin heat sinkAugmented fin heat sink Bonded fin heat sinkExtruded fin heat sink

Cooling Technologies : HP applicationsHeat pipe application ( 2 phases heat transfer)Heat pipe application ( 2 phases heat transfer)

Heat pipe

Very high thermal conductivity

Power flattening

Efficient transport of concentrated heat

Applications

Thermaltake (Taiwan) Big Typhoon VX CPU Cooler

Aerocool (Taiwan) Silverwind CPU Cooler

Thermacore (USA) Heat sink embedded with HP

Cooling Technologies : Liquid cooling

• Heat rejected outside the computer case• Flexible tubing• Significantly cheaper than refrigeration• Low pressure fluids• Unlimited air heat exchanger• More complex than air-cooling

Reserve tank Coolant

Radiator

Fan

Pump

Liquid Cooling Jacket

Heated Subject

General Desktop PC - Airflow

RearFan

CPU, Heat Sink& Fan Power

Supplier(PSU)

Heat Sink(North Bridge & South Bridge)

GPU Heat Sink& Fan

DRAM

Video Graphic card

(GPU)

MotherBoard

DVD Driver

Hard Disk Driver (HDD)

Thermally Advantaged Chassis(TAC)Design Guide(2008)

Desktop PC components groupingDesktop PCDesktop PC

ChassisChassis

ChipsetChipset

CPUCPU CPU Heat SinkCPU Heat Sink CPU FANCPU FAN

Video Graphic CardVideo Graphic Card(GPU)(GPU) VGA Heat SinkVGA Heat Sink VGA FANVGA FAN

Mother BoardMother Board

Grilles / VentsGrilles / Vents

PSUPSU(POWER SUPPLYER)(POWER SUPPLYER)

Other PCI cardOther PCI card

HDD/DVD DrivesHDD/DVD Drives

Cooling partsCooling parts

Rear FANRear FAN

ChipsetChipset

SDRAM SDRAM

North Bridge Heat SinkNorth Bridge Heat Sink/ South Bridge Heat Sink/ South Bridge Heat Sink

PSU FANPSU FAN

Passive Cooling (Free convection)

Active Cooling (Forced convection)

core

ChipsetChipset

CPUCPU

Graphic Processing UnitGraphic Processing Unit(GPU)(GPU)

Chassis Chassis 내부 공기내부 공기온도 상승온도 상승

Other PCI cardOther PCI card

CPU voltage regulatorCPU voltage regulator

SDRAM SDRAM core

CPU & GPU Coolers

가열된 공기 배출

PSUPSU(POWER SUPPLYER)(POWER SUPPLYER)

HDD/DVD DrivesHDD/DVD Drives

• 고발열 반도체 단일 냉각 기술에 의존한 냉각 - 다양한 냉각기에 의한 주요 소자 냉각 - 추가 발열 요소에 대한 대안 미흡 - 공기 온도 상승에 따른 소음도 향상

• Chassis 내부의 공기 유동 개선의 어려움 - Chassis 중앙부분에서 와류 현상 발생 - 주변기기 장착시 Slot 하단과 밑면 사이 와류 현상 발생 및 유동 정체 현상 미해결 - 공기 흡배기 효율 감소 및 작업 여건의 악화 요소 상승

Why is it necessary to obtain thermaland airflow modeling ?

Tries to improve airflowFor ATX BTX mother board

Center of PSUCenter of PSU

Fresh air ductFresh air duct

Desktop PC mounted with BTX M/BDesktop PC mounted with BTX M/B

BTX mother boardBTX mother board

Ref. Internet Data Center report Ref. Internet Data Center report published on March, 2009published on March, 2009

[Unit : Million]

Year

Even though more laptop PCs are in demand compared to desktop PCs, why is it necessaryto optimize the thermal management for the desktop in future?

For extensive data and graphic processing programs such as 3D games, CAD tools, simulation programs and so on, users have been preferring desktop PCs to laptop PCsso far.

For those programs, the powerful performance of desktops are probably going to go on being required. Simultaneously, thermal problems are necessary to be solved, too.

Is it necessary to cool down desktops ?

Thermal Packaging Constraints

For improving the cooling capacity of desktop chassis,

2nd, to enlarge the volume of chassis

3rd, to add heat exchangers such as heat pipes and etc. to the chassis

1st, to boost high airflow rate

Increasing the volume of the chassis results in the increaseof cost and is discrepant from the recent trends of compact PCs.

Higher flow rate or additional local fans result in significant increasein noise, vibration problems and more power consumptions.

4th, Mechanically robust, Low cost, reliable and efficient

An improved chassis should be satisfied with aspects as mentioned under.

1. Effectively cool ; the total heat dissipation of the desktop PC chassis : ~ 350W - CPU (130W) and GPU(70W) temperature junction should be lower than 80℃.

2. For less noise, vibration and power consumptions ; possible with design goals of below 35dBA

3. To meet the confined space of the desktop PC chassis ; for the recent trends of compact desktop PC (within 55 liter)

4. Simple structure for manufacturing friendly ; not to increase cost

Design target for new improved chassis

Thermal and airflow Thermal and airflow designdesign

Fan

inT

Power dissipation q

eT

inh outh

in g out stE E E E

0in outE E

in outE E

Assumption 1 : Steady State, Steady Flow Process

( ) ( ) 0in outm u pv m u pv q W

stin g out st

d EE E E E

dt

h u pv

1 2 31

......n

i ni

q q q q q q

1 21

( ...... )m

j nj

W F F F F

in( ) ( )in out p em h h mC T T

in( )p eq W mC T T

Assumption 2 : a) Negligible PE & KE change of airflow b) Negligible heat transfer from Chassis to Ambient c) Constant air properties

Assumption 3 : Only “q” taken into consideration

in( ) ( )in out p eq m h h mC T T

Thermal design principle

Thermal design principle

3 3/ ( / )( / )( / )( )J s kg m J kg K m s K

,air p air airQ C T

System ImpedanceAfter the airflow has determined, the amount of resistance to it must be found. This resistance to flow is referred to as system impedance and is expressed in static pressure.

nP K v

K

P

nv

: Static pressure

: Load factor

: air density

: airflow rate: constant (n=1 laminar, n=2 turbulent flow)

Fan Selection

Parallel combination operation Series combination operation

Basic testBasic test- general desktop PC - general desktop PC

Item Manufacture Model/Specification Thermal dissipation (W)

CPU INTEL Core Duo E8400 4GHz 70

GPU NVIDIA GeForce GS 250 / RAM 1024MB 50

Mother Board ASUS P5Q 20

Power Supply ZALMAN ZM1000-HP / 1000W 50

RAM SEC DDR SDRAM / 2GB 15

Hard Disk Drive Western Digital 600GB 10

Test desktop PC specification

Power : 217.15 WattVoltage : 215 VCurrent : 1.01 A

CPU Full loading Program(Prime 95)

VGA Full loading Program(Fur mark)

Full loads condition Full loads condition

MotherboardSouth Bridge

VGA

Power SupplyDVD

HDDRAMNorth

Bridge

CPU

INLETINLET

OUTLETOUTLET

MotherboardSouth Bridge

VGA

Power SupplyDVD

HDDRAMNorth

Bridge

CPU

INLETINLET

OUTLETOUTLET

CASE 1 ; Down-blowing CPU cooler

CASE 2 ; Tower type CPU cooler

Test desktop’s airflow path

CASE 1

Chassis’ each componet TemperatureChassis’ each componet Temperature

Low RPM mode – Chassis fans

High RPM mode - Chassis fans Temperature contour picturetaken by IR – CAMERA

Item FAN Fan RPM range

CPU

80 mm FAN

INTEL Extrude box cooler

1700 (L)~ 3000(H) rpm

GPU

80 mm FAN

GPU cooler

1400(L) to 2700(H) rpm

Chassis

120 mm FAN

(Rear fan only) 1800(L) to 2000(H) rpm

Test desktop’s thermal results (1)

CASE 2

Item FAN Reamarks

CPU

110 mm FAN

ZALMAN CPU cooler

1800(L) to 2800 (H) rpm

GPU

80 mm FAN

GPU cooler

1400(L) to 2700(H) rpm

Chassis

120 mm FAN

(Rear fan only)1800 (L) to 2000 (H) rpm

Chassis’ each componet TemperatureChassis’ each componet Temperature

Low RPM mode – Chassis fans

High RPM mode - Chassis fans Temperature contour picturetaken by IR – CAMERA

Test desktop’s thermal results (2)

Test results

Analysis (Performance curve)

Axial fanAxial fan- design & analysis- design & analysis

FAN velocity contour

FAN pressure contour

FAN mesh generation

Fan airflow simulation

Boundary Conditions– Static pressure : 0 Pa– Steady state

Governing Equations.– Navier-Stokes Equations * Convective term : MUSCL (2nd order) * Pressure correction : SIMPLEC * Turbulence model : MP k-EPS model

anemometer anemometer

Fine pressure gaugeFine pressure gauge

Vena contracta Vena contracta

Fan controller Fan controller

FanFan

Measuring airflow and static pressureGenerally expressed in terms of the relationship between airflow and static pressureRequired to generate such air flow

12V12V

Fan speed controllerFan speed controller

FanFan

MicrophoneMicrophone

Sound level meterSound level meter

Anechoic ChamberAnechoic Chamber

Distance between microphone and sample = 1mDistance between microphone and sample = 1m

-Background Noise : 17.3dBBackground Noise : 17.3dB- RH : 36%RH : 36%- Temperature : 26.7Temperature : 26.7℃℃

Hygrometer : Relative humidityHygrometer : Relative humidity

25 %25 ℃

ThermometerThermometer

Measuring fan acoustic noise At a distance of 1m from the intake at a point above the center line of the intake

4.69

0.92

1.63

26.7

20.217.1

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50

Airflow rate [CFM]

Sta

tic

Pre

ssu

re [

mm

Aq

]

0

6

12

18

24

30

0 0.005 0.01 0.015 0.02

Airflow rate [CMS]

Sou

nd

Lev

el [

dB

A]

Experimental data -Airflow rateExperimental data -Sound Level

P-Q curve with acoustic noise

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60

Airflow rate [CFM]

Fan

Vol

tage

[V

]

0

500

1,000

1,500

2,000

2,500

0.000 0.005 0.010 0.015 0.020 0.025

Airflow rate [CMS]

Fan

Sp

eed

[R

PM

]

CFD analysis data

Experimental data

Fan voltage vs. airflow rate

High power desktop High power desktop chassischassis

- design & practice- design & practice

Thermal and airflow design (1)

Additional fans only add 2 to 3 more dB to the total noise level.

1010logref

WPWL

W

1020log

ref

PSPL

P

Thermal and airflow design (2)

: “q” heat dissipation of each component (W)

: “F” Fans’ work (W)

: Airflow direction

Motherboard

South Bridge

VGA

Power Supply

DVD

HDD

RAM

North Bridge

CPURear Fan

Top Fan 1 Top Fan 2

Bottom Fan

Internal Fan 1

Internal Fan 2

CPU FAN*

VGA FAN

Item Manufacture Model/Specification Thermal dissipation (W)

CPU INTEL Intel Core i7-930 Bloomfield 2.8GHz 130

GPU NVIDIA GIGABYTE GTS UDV 512MB 70

Mother Board ASUS P6X58D-E STCOM 20

Power Supply ZALMAN ZM1000-HP / 1000W 80

RAM SEC DDR SDRAM / 2GB 30

Hard Disk Drive Western Digital 600GB 10

DVD Drive LGE 10

Thermal and airflow design (3)

Thermal and airflow design (4)

Computational simulation

Temperature contour Airflow Contour

Boundary Conditions– Static pressure : 0 Pa– Steady state

Computational Grids– Tetra Mesh / about 30 millions– Prism layer

Governing Equations.– Navier-Stokes Equations * Convective term : MUSCL (2nd order) * Pressure correction : SIMPLEC * Turbulence model : MP k-EPS model

3 3/ ( / )( / )( / )( )J s kg m J kg K m s K

,air p air airQ C T P VI Q-Q-Q+Q+ ( )in outQ m h h

100

Power supply unit Digital Power meter

Data Acquisition

IBM PC

T-type Thermocouple

25 %

Hygrometer : Relative Humidity Acrylic chamber

CPU & VGA Burning S/W

Desktop PC

TiTi

TeTe

Q+Q+Q-Q-

DTDT

Thermal test apparatus

CPUCPU GPUGPUChipsetChipset(NB) (NB)

RAMRAM PSUPSUMean Mean

inside airinside airAmbient airAmbient air DTDT

SimulationResults(℃)

47.2 77.2 51.9 43.5 43.2 33.1 25 7.9

ExperimentalResults(℃)

48.2 59.1 42.6 48.7 36.4 33.4 25.1 8.3

Real Error.(%)

2.07 23.4 17.9 11.1 15.7 6.6 - -

SimulationResults

ExperimentalResults

Unit

Airflow (Exhaust only)

81.32 82.38 CFM

Air density 1.141 1.141 kg/m3

Specific heat 1005 1005 J/kgK

Tm-Ta 7.9 8.3 K

Heat dissipation 347.8 371.3 watt

Sound Level 30.4 32.2 dBA

Results (1)

Full Loading State

Power : 367.65 WattVoltage : 215 VCurrent : 1.71 A

Physchometric calculationInside airMean temperature 33.4 ℃Relative humidity 30 %Dew point temperature 16.03 ℃Web bulb temperature 22.29 ℃Sat. vapor. Pressure 60.62 mbarPartial vapor Pressure 18.19 mbarHumidity ratio 0.0114 kg/kgEthalphy (h1) 65.99 kJ/kgSpecific volume 0.9 m3/kg

Exhaust airAmbient temperature 29.1 ℃Relative humidity 44 %Dew point temperature 20.02 ℃Web bulb temperature 15.64 ℃Sat. vapor Pressure 40.31 mbarPartial vapor Pressure 17.73 mbarHumidity ratio 0.01119 kg/kgEthalphy (h2) 57.83 kJ/kgSpecific volume 0.088 m3/kg

H1-h2 8160 J/kgHeat dissipation 361.9946 Watt

Results (2)

Results (3)

Conclusion

Thermal and airflow modeling methodology was performed to define desktop PC chassis and each semi-conductor cooling requirements for a chassis dissipating 350W, with an 130W CPU, 70W GPU and so on.

With appropriate use of parallel exhaust fans along with intakes fans, the results Show that the desktop chassis having 350W heat dissipation can be satisfactorily cooled at the proper noise level (32dBA).

Using intakes fans mounted inside the chassis, increasing heat dissipation of chipsets, RAMs and the other components on the motherboard is held sufficiently down. Besides the fans can be stimulated to raise both static pressure and airflow rate.

Thank you very much !!!