A Self-Contained System for Thermal Management of Next Generation High Heat Flux Electronics

A Self-Contained System for Thermal Management of Next Generation High Heat Flux Electronics

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Description: Microgrooved force-fed evaporators and condensers combine high heat transfer rate of microchannels with low pressure drops which make them an attractive alternative for two-phase electronic cooling systems 2nd gen cold plate: cost effective removal of the 1,000 W/Cm2 heat flux.

 
Author: Michael M. Ohadi, Ph.D., Professor of Mechanical Engineering, University of Maryland/Petroleum Insti (Fellow) | Visits: 1651 | Page Views: 1658
Domain:  High Tech Category: Semiconductors Subcategory: Packaging 
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Contents:
A Self-Contained System for Thermal Management of Next Generation High Heat Flux Electronics
Michael M. Ohadi, Ph.D. Professor of Mechanical Engineering University of Maryland/Petroleum Institute
7th Annual Business & Technology Summit , August 22-23, 2007, Natick MA

7th Annual Business & Technology Summit, Aug 22-23, 2007

1

Team Members
Dr. S. Dessiatoun, Research Scientist Thomas Baummer, GRA Edvin Cetegen, GRA Prof. Bar-Cohen, Tech. Advisor

Smart and Small Thermal Systems (S2TS) Lab Department of Mechanical Engineering University of Maryland, College Park

7th Annual Business & Technology Summit, Aug 22-23, 2007

2

Outline
� � � � � � � Background Objectives Micro-structured surfaces Description of force-fed technology Evaporator: experimental setup and results Condenser: experimental setup and results Conclusions

7th Annual Business & Technology Summit, Aug 22-23, 2007

3

Heat Transfer in Channels

Laminar

Turbulent

Developing

Fully-Developed

� Primitive Variables - Fully Developed h = f (Fluid, Diameter, Temp..) � Primitive Variables - Developing h = f (Fluid, Velocity, Distance, Temp. .)
7th Annual Business & Technology Summit, Aug 22-23, 2007

4

"Newton's Law of Cooling"

QL T= AK

V, Tf

h Ts q

Give me low Delta P and Low Delta T
7th Annual Business & Technology Summit, Aug 22-23, 2007

5

Liquid Cooling Capacity
Description Natural air Natural water convection, convection, Heat Transfer Coefficient (W/m2K) 3-25 15-1000 10-200 50-10,000 5000-50,000 3000-100,000 film 10,000-500,000 10,000-1,000,000

Forced convection, air Forced water convection,

Condensing steam Boiling water Ultra thin evaporation

Microchannel Cooling

7th Annual Business & Technology Summit, Aug 22-23, 2007

6

Choice of Fluid as a key parameter
� � � � Natural Convection Cooling Air-Fan Heat Sink Heat Pipe/PCM Chamber Liquid Cooling and Refrigeration Cooling

The selected Cooling Option

FC-72 Heat of Vaporization [KJ/Kg] Thermal Conductivity [W/m.k] Thermal Capacity [J/Kg.K] Surface Tension [dyne/cm] 88.47

HFE-7100

Water 2445.0

125.61

27 times increase in Hfg

0.057

0.061
11 times increase in k

0.661

1052.8

1214.2

4179.0

4 times increase in Cp

12.0

13.6

72.0

7th Annual Business & Technology Summit, Aug 22-23, 2007

7

Example Coolant Figures of Merit
Laminar Flow: Turbulent Flow:
Coolant Water FC-43 FC-75 FC-78 Coolanol-25 Coolanol-45 Glycol/water PAO
7th Annual Business & Technology Summit, Aug 22-23, 2007

FOM =

( )
kC p



FOM =

k 0.67 C p1.33 1.05

0.72


Turbulent (FOM) 27.688 0.633 1.249 1.751 0.980 0.0397 4.482 0.950

Laminar (FOM) 14.207 0.155 0.405 0.666 0.250 0.071 1.382 0.222
8

Current Project Objectives
Investigate the performance of micro-grooved surfaces for improved two-phase heat transfer using force-fed evaporation and condensation Achieve 100,000 W/m2K evaporation heat transfer coefficient at 200 W/cm2 heat flux Achieve 40,000 W/m2K condensation heat transfer coefficient Develop a self-contained, 2 kW line-replaceable cold plate
7th Annual Business & Technology Summit, Aug 22-23, 2007

9

Definitions
� Mehendail et al. (2000) classified channels based on their hydraulic diameter Dh:
� � � � micro heat exchangers: Dh = 1-100 m meso heat exchangers: Dh = 100 m � 1 mm compact heat exchangers: Dh = 1- 6 mm conventional heat exchangers: Dh > 6 mm

� Kandlikar and Grande (2003) proposed another classification based on flow phenomenon and fabrication technology:
� microchannels Dh = 10 -200 m � minichannels Dh = 200 m - 3mm � conventional channels Dh above 3 mm

7th Annual Business & Technology Summit, Aug 22-23, 2007

10

Microchannels
� � � � � � � High heat transfer coefficient (up to 500,000 W/m2) High surface to volume ratio (A/V = 2*104 ...4*105 m2/m3) High pressure drop (10...300 MPa/m) Limited microchannel length (1 to 60 mm) Major use for cooling of high heat flux electronics Mostly single phase cooling In two-phase electronic cooling, high pressure drop in evaporator creates significant saturation temperature change, particularly with low-pressure refrigerants, effecting the performance and reliability of electronics � High pressure drop is not affordable for condensers therefore minichannels or conventional channels are used � Potential condenser volume reduction for two-phase electronic cooling loops is not realized

7th Annual Business & Technology Summit, Aug 22-23, 2007

11

Micro-Grooved Surfaces
� � � Cost effective fabrication using Micro-deformation Technology (Wolverine Tube, Inc.) Can be fabricated from any material with ductility more than 20% Channel width as low as 5 microns and aspect ratio of 20 is possible

Surface Dimensions: Specified (Actual)
Surface Name Material Fins Per Inch (FPI) Channel Width (m) Fin Thickness (m) Channel Height (m) Channel Aspect Ratio A Mo 200 42 84 483 11.5 B Cu 400 (409) 21 (22) 42 (40) 242 (233) 11.5 (10.6) C Cu 400 (409) 21 (22) 42 (40) 483 (415) 23 (18.9) 12 D Cu 800 (645) 10.5 (15.2) 21 (22) 242 (235) 23 (15.4) E Mo 400 21 42 242 11.5 F Mo 400 21 42 483 23

7th Annual Business & Technology Summit, Aug 22-23, 2007

Micro Grooved Surfaces
� Cost effective fabrication using Micro-deformation Technology (Wolverine Tube, Inc.) � Can be fabricated from any material with ductility more than 20% � Has a channel width as low as 5 microns, and has a possible aspect ratio of 20

Dimensions of tested micro-structured surfaces
Surface # FPI Fin Pitch (mm) 0.254 0.254 0.254 0.178 0.127 Fin Height (mm) 0.456 0.660 0.889 0.838 0.483 Channel Width (mm) 0.084 0.084 0.084 0.059 0.042 Channel Aspect Ratio (H/W) 5.5 8.0 10.6 14.0 11.5 Fin Thickness (mm) 0.169 0.169 0.169 0.118 0.085

9 10

100 100 100 143 200

Diagram of micro-grooved surface

11 14 17

7th Annual Business & Technology Summit, Aug 22-23, 2007

13

Comparison Study

� High aspect ratio single minichannel 2800 x 400 m, Dh = 725m 200 mm long � Microgrooved surface with 889 x 84 m grooves, Dh = 175 m � Three refrigerants: HFE 7100, R 245fa, R 134a

7th Annual Business & Technology Summit, Aug 22-23, 2007

14

Forced-Fed Evaporation
Forces incoming liquid under escaping vapor to raise channel `dry-out' heat flux when boiling on finned surfaces Accomplished by an inlet header feeding liquid to the surface
Inlet Header Liquid Flow Feed Channels Vapor Flow

Finned Surface

Heated Surface Convective Boiling Convection Jet Impingement Boiling/ Evaporation

First Generation Header

Second Generation Header

UMD Patented

q"

Microgrooved surface

7th Annual Business & Technology Summit, Aug 22-23, 2007

15

Refrigerants
Two refrigerants were used for testing
HFE 7100 � evaporation, condensation R-245fa � condensation

Low toxicity, low global warming
Property Chemical Formula Boiling Point (1 atm) [�C] Density [kg/m3] Surface Tension [dyne/cm] Kinematic Viscosity [cSt] Latent Heat of Vaporization [kJ/kg] Specific Heat [kJ/kg-K] Thermal Conductivity [W/m-K] Dielectric Strength [kV/mm] Dielectric Constant HFE-7100 C4F9OCH3 61 1402 12.3 0.38 121.22 1.253 0.062 11 7.4 R-134a C2H2F4 -26.09 1377 15.27 2.74 212.07 1.278 0.105 7 9.5 R-245fa CHF2CH2CF3 14.91 1366 3.43 197.3 1.310 0.084 Water H2O 100 1000 58.91 2.94 2257 4.18 0.661 --78.5

7th Annual Business & Technology Summit, Aug 22-23, 2007

16

1st Generation Cold Plate Design
Plate components: Four evaporators: 14mm square, heated by 250+ W heaters One pump: 250 ml/min Two condensers: 10 mm by 70 mm, cooled by a water-cooled slot Plate dimensions are 100 mm x 200 mm; � the final cold plate size Expected capacity is 1 kW; � the final cold plate capacity
Evaporator Power Connections Evaporators with Headers Pressure Measurement Valves Thermocouple Connections

Charging port

Pump

Vapor-side Thermocouple Condensers with Headers

7th Annual Business & Technology Summit, Aug 22-23, 2007

17

1st Generation Cold Plate Testing
Evaporator thermal resistance
3.5E-05 3.0E-05 2.5E-05 R [m2K/W] 2.0E-05 1.5E-05 1.0E-05 5.0E-06 0.0E+00 0 200 400 600 800 Total Power [W] 1000 1200
h [W/m2K]
HFE 7100

Condenser heat transfer coefficient
45000 40000 35000 30000 25000 20000 15000 10000 5000 0 0 200 400 600 800 Total Power [W] 1000 1200
HFE 7100 30% Methanol 70% Water Mixture

Project Goal

Project Goal
30% Methanol 70% Water Mixture

Total plate power dissipation exceeds 1000 W using 30/70 methanol water mixture; equivalent to 4 kW on the full size cold plate Evaporator thermal resistance meets project goals Condenser heat transfer coefficient approaches project goal value Capacity is limited by instability of two-phase loop Condenser should be large to reject heat effectively
7th Annual Business & Technology Summit, Aug 22-23, 2007

18

2nd Generation Plate Design
200 x 400 mm2 plate with 2+ kW expected capacity Consists of discrete, sealed modules of evaporators and condensers
� Up to 8 evaporators 17 mm x 34 mm � 2-3 condensers 34 mm x 135 mm

Hermetic impeller pump provides surplus of flow rate Reservoir included to compensate Condenser fluid expansion Modules Valves in liquid line to manage flow distribution

Reservoir

Evaporator Modules
7th Annual Business & Technology Summit, Aug 22-23, 2007

Pump

19

2nd Generation Plate Construction
Headers constructed from bent copper with "C" cross section Evaporator and condenser designed and constructed by stamping process

7th Annual Business & Technology Summit, Aug 22-23, 2007

20

2nd Generation Cold Plate Pump
Hermetic impeller pump manufactured by Laing, Inc. Designed as a water circulation pump for computer cooling, solar heating, and other applications Up to 6.5 GPM flow rate Up to 3.9 PSI pressure

3 in.

7th Annual Business & Technology Summit, Aug 22-23, 2007

21

2nd Generation Cold Plate
Thermocouple ports Evaporators Condensers

Flow regulator valves Pressure ports

Water cooled cold plate inlets and outlets Reservoir

Pump

7th Annual Business & Technology Summit, Aug 22-23, 2007

22

2nd Generation Cold Plate

In the first stage of tests six evaporators and two condensers will be used

7th Annual Business & Technology Summit, Aug 22-23, 2007

23

2nd Generation Cold Plate
Flexible design allows working in both horizontally and vertically positions Can accommodate up to eight evaporators and three condensers Heat rejection to cold slot Components can be repositioned to accommodate location of heat generation elements Uniform flow distribution can be achieved using flow regulator valves

7th Annual Business & Technology Summit, Aug 22-23, 2007

24

Performance Testing Setup
Designed for more detailed measurements Fluid inlet and outlet temperature Evaporator pressure drop Flow rate Permits sub-cooled boiling tests Designed for higher capacity � 2kW goal

7th Annual Business & Technology Summit, Aug 22-23, 2007

25

Force-Fed Evaporation
Force-Fed Evaporation of HFE-7100 1000
924.07

800 Heat Flux [W/cm2]
1st Generation Header 2nd Generation Header

600

400
Project goal

200

0 0 10 20 30 40 T [�C]=Tsurface -Tsat 50

55.00

60

Sample #17 Data
7th Annual Business & Technology Summit, Aug 22-23, 2007

26

Force-Fed Evaporation
Force-Fed Evaporation of HFE-7100
200,000
168,010

160,000
1st Generation Header 2nd Generatioin Header
Project goal

120,000 h [W/m2-K]

80,000

40,000

0 0 100 200 300 400 500 600 Heat Flux [W/cm2] 700 800

924.07

900

1000

Sample #17 Data
7th Annual Business & Technology Summit, Aug 22-23, 2007

27

Force-Fed Evaporation Data for Sample 17
Heat Flux v s. Temperature
450 400 350

Heat Flux [W/cm 2]

300 250 200 150 100 50 0 0 10 20 30 40

2nd Generation Header, HFE-7100 2nd Generation Header, Ethanol 1st Generation Header, HFE-7100 Pool Boiling Original Projection/Project Goal
50 60

T: T Surface -T Fluid (Saturation) [C]

7th Annual Business & Technology Summit, Aug 22-23, 2007

28

Microgrooved Surface Condenser
Recent UMD development � Uses a combination of micro grooved surface with a developed system of feed channels � Combines high heat transfer of microchannels with low pressure drop � Is suitable for cooling large surfaces � Is based on low production cost of micro groove surfaces
7th Annual Business & Technology Summit, Aug 22-23, 2007

6 7 5 1 2

3 4 1. Refrigerant inlet ; 2. Micro grooved surface; 3. Solder; 4. Chiller water; 5. Refrigerant outlet; 6. Glass; 7. Zigzag header.

29

Condenser Test Setup

7th Annual Business & Technology Summit, Aug 22-23, 2007

30

Minichannel Setup Components
Siliconrubber Sealing Microchannel Condenser

Water Jacket

Condenser Section

a

Vacuum between Dewar Walls Condenser Section Evaporator Section

Sight Glass

Copper Elbow with heater patches

Double-wall Dewar Cylinder

b

Evaporator Section

c
31

Sub-cooler

7th Annual Business & Technology Summit, Aug 22-23, 2007

Condenser Test Section
� Tested micro grooved surface of 70 mm x 10 mm dimensions.
�Header made of soft solder alloy with wall thickness of 0.5 mm �Glass top for visualization �Easy to change and test various surfaces and headers

� Five thermocouples on the micro grooved surface and two for inlet and outlet refrigerant temperatures
Refrigerant Inlet

Glass Frame Glass Header Test Sample
Differential Pressure Transducer Ports

Cooling Structure Plastic Base

Refrigerant Outlet
7th Annual Business & Technology Summit, Aug 22-23, 2007

Zigzag header 32

Properties of Fluids
Property
Chemical Formula Boiling Point (1 atm) [�C] Saturation pressure at 20�C [kPa] Saturation pressure at 80�C [kPa] Density [kg/m3] Surface Tension [dyne/cm] Dynamic Viscosity [mPa s] Latent Heat of Vaporization [kJ/kg] Specific Heat [kJ/kg-K] Thermal Conductivity [W/m-K] Dielectric Strength [kV/mm] Dielectric Constant
7th Annual Business & Technology Summit, Aug 22-23, 2007

HFE-7100
C4F9OCH3 61 22.3 173.2 1402 12.3 0.65 121.22 1.253 0.062 11 7.4
33

R-134a
C2H2F4 -26.09 571.59 2633.1 1377 15.27 0.38 212.07 1.278 0.105 7 9.5

R-245fa
CHF2CH2CF3 14.91 124 788 1366 15.34 0.47 197.3 1.310 0.084 -

Water
H2O 100 2.34 47.37 1000 58.91 0.28 2257 4.216 0.661 ???? 78.5

Force Fed Condensation
45000 40000 35000 30000 h [W/m2K] 25000 20000 15000 10000 5000 0 0 10 20 30 40 Heat Rejection [W/cm2] 50 60 70
HFE 7100 - 1st generation header R-245fa - 1st generation header R-245fa - 2nd generation header

Project goal

�The data points were taken for 100% inlet and 0% outlet vapor quality � 3rd generation header was designed and fabricated
7th Annual Business & Technology Summit, Aug 22-23, 2007

34

Force Fed Condensation
1200

1000

90-210 g/min
800 DP [Pa]

600

30-65 g/min
R-245fa - 1st generation header

400

10-40 g/min
HFE 7100 - 1st generation header R-245fa - 2nd generation header

200

0 0 10 20 30 40 Heat Rejection [W/cm2] 50 60 70

Very low pressure drop for a microscale application
7th Annual Business & Technology Summit, Aug 22-23, 2007

35

Technology Comparison
Condensation in 0.5"ID smooth and microfin tube and in minichannel

5000 4000 h [W/m2K] 3000 2000
Smooth tube

1000 0 0 100 200

Microfin tube Minichannel

300

400

Mass Flux [kg/m2-s]

Area to volume ratio for the tube 360 m2/m3 , for minichannel 5500 m2/m3
7th Annual Business & Technology Summit, Aug 22-23, 2007

36

Technology Comparison
Condensation in 0.5" ID smooth and microfin tube and minicannel
8 6 4 2 0 0 100 200 300 Mass Flux [kg/m2-s] 400
Smooth Tube Microfin Tube Minichannel

Pressure Drop [kPa]

7th Annual Business & Technology Summit, Aug 22-23, 2007

37

Microgrooved Surface Condenser
45000 40000 35000 30000 h [W/m2K] 25000 20000 15000 10000 5000 0 0 10 20 30 40 50 Heat Rejection [W/cm2]
38

HFE 7100 - header #1 R-245fa - header #1 R-245fa - header #2

60

7th Annual Business & Technology Summit, Aug 22-23, 2007

Microgrooved Surface Condenser
45000 40000 35000 h [W/m 2K] 30000 25000 20000 15000 10000 5000 0 0 5 10 15 20 2] Mass flux [kg/ s-m
39

HFE 7100 - header #1 R 245fa - header #1 R 245fa - header #2

25

7th Annual Business & Technology Summit, Aug 22-23, 2007

Microgrooved Surface Condenser
1000 800 600 400 200 0 0 5 10 15 20 M a ss flux [kg/s-m 2] 25 R 245fa - header #1 HFE 7100 - header #1 R 245fa - header #2

Pressure drop in microgrooved surface condenser depends on the header design and is independent from the condenser size
7th Annual Business & Technology Summit, Aug 22-23, 2007

DP [Pa]

40

Reliability Tests
120 100 Temperature ( o C) 12 10 8 6 4 2 0 140 Pump Voltage (V)

Charging Valve

Evaporator

Lytron Heat Exchanger

80 60 40 20 0 0 20 40 60 80 100 120

Laing Pump

Applied Power/Heater (W)

Force fed cold plate components are under testing by ATEC for reliability analysis Single phase tests using EG/Water mixture Tests will be extended for two phase heat transfer

7th Annual Business & Technology Summit, Aug 22-23, 2007

41

Conclusions
� High pressure drops often limit application of microchannel and even minichannel evaporators/condensers with low pressure refrigerants for electronics cooling � Pressure drop in force-fed micro-grooved surface evaporators and condensers is significantly lower than their respective mini or micro channel evaporators/condensers. It also does not significantly effect condenser performance with low pressure refrigerants � Microgrooved force-fed evaporators and condensers combine high heat transfer rate of microchannels with low pressure drops which make them an attractive alternative to conventional evaporators and condensers for two-phase electronic cooling systems
7th Annual Business & Technology Summit, Aug 22-23, 2007

42

Conclusions (Cont.)
� The 2nd generation cold plate results in the current study demonstrate potential of this technology for cost effective removal of the 1,000 W/Cm2 heat flux and appears to be applicable to both commercial and military high flux electronics � Now that the potential of this technology has been demonstrated, it is time to understand the underlying fundamentals, thus a strong need for basic research in this area.

7th Annual Business & Technology Summit, Aug 22-23, 2007

43

Literature
Baummer T., Cetegen E., Ohadi M., Dessiatoun S., "Force-fed evaporation and condensation utilizing advanced micro-structured surfaces and micro-channels,"(in review) Journal of Microelectronics, 2007

Baummer T, Al-Hajri E., Ohadi M., Dessiatoun S., "Forced convection boiling in microchannels for improved heat transfer," The Fourth International Conference on Nanochannels, Microchannels and Minichannels, Ireland, 2006 Baummer T., Cetegen E., Ohadi M., Dessiatoun S., "Force-fed evaporation and condensation utilizing advanced micro-structured surfaces and micro-channels," Thermal Challenges in Next Generation Electronic Systems (THERMES 2007), New Mexico, 2007 Dessiatoun S., Choudhury S., Cetegen E., Al Hajri E., Ohadi M., "Studies on condensation of refrigerants in a high aspect ratio microchannel and in a novel micro-groove surface heat exchanger," 5th ICNMM2007, June 18-20, 2007, Puebla, Mexico Cetegen E., Baummer T., Dessiatoun S., Ohadi M., "Force-fed condensation and evaporation on micro-structured surfaces---application to self-contained thermal management of high flux electronics", (in review) Proceedings of IMECE2007, November 11-15, 2007, Seattle, Washington, USA
7th Annual Business & Technology Summit, Aug 22-23, 2007

44

Thank you

7th Annual Business & Technology Summit, Aug 22-23, 2007

45

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