Phase-Change Heat Transfer at Micro-/Nano-Scale:
from Fundamentals to Manufacturable Devices
Ronggui Yang, Associate Professor
S.P. Chip and Lori Johnson Faculty Fellow
Department of Mechanical Engineering
Materials Science and Engineering Program
University of Colorado, Boulder, CO 80309
Tel: (303) 735-1003, Fax: (303) 492-3498
Email: Ronggui.Yang@Colorado.Edu
http://spot.colorado.edu/~yangr
Outline
1. Introduction and Motivation
2. Micro/Nanotechnology-enabled Thermal Management
Hybrid Wicking Structures for Phase-Change Heat Transfer
3. Micromesh-enhanced Microchannels
Capillary Evaporation
Flexible Thermal Ground Planes
4. Hybrid Micro/Nano-Structured Surfaces
Porous Anodized Alumina-Templated Fabrication of 3-D Nanowire Structures
(Copper – metals and alloys, Silicon)
Pool Boiling and Capillary Evaporation
Research Themes
Nano-enabled Energy Conversion, Storage, and Thermal Management Systems (NEXT)
• Energy Conversion: Thermoelectrics, Liquid-Vapor Thermodynamic Cycles
• Thermal Management: Phase-Change Heat Transfer, Thermal Interface Materials, & Thermoelectrics
• Energy Storage: Lithium Ion Batteries, & Thermal Energy Storage
Advanced Characterization
• Solid-Solid and Solid-Liquid
Thermal Interfaces
• Ultrafast and Nanoscale
Thermal Imaging
Nanostructured Materials and
Devices
• Physics-Based Design
• Cost-Effective Manufacturing
Multi-scale and Multi-physics Modeling and Simulations:
Quantum Mechanics, Molecular Dynamics, Nonequilibrium Green’s
Function Theory, Boltzmann Transport Equation (Monte Carlo, Finite
Element/Difference Methods), Simplified Physical Models.
Electronic Thermal Management
“Hot” Electrons are in the News
Phase-Change Heat Transfer
•
•
•
•
Phased-array radar (100-1000 W/cm2);
High-energy lasers (500-1000 W/cm2);
Electrical propulsion (>1000W/cm2);
Light-emitting-diode (LED) 1000 W/cm2.
Evaporation
Boiling
Condensation
Multiscale Problems in Electronic Thermal Management
Courtesy of Professor Kenneth Goodson’s interpretation of DARPA’s Thermal Management
Technologies and ICECool program led by Dr. Avi Bar-Cohen and Dr. Tom Kenny
Characterization and Fabrication Facilities at CU
Femtosecond Laser-based Pump-and-Probe System for
Nanoscale Heat Conduction
Some NanoManufacturing Facilities
Low-temperature CVD growth
Phase-Change Heat Transfer Characterization Facilities
Pool Boiling with High Speed
Visualization
Spray Loop (Boiling,
Evaporation and Jet), at NREL
Scalable manufacturing of
porous alumina templates
CHI electrochemical workstation
Flow Boiling Loop
Condensation Loop
7
Outline
1. Introduction and Motivation
2. Nanotechnology-enabled Thermal Management
Hybrid Wicking Structures for Phase-Change Heat Transfer
3. Micromesh-enhanced Microchannels
Capillary Evaporation
Flexible Thermal Ground Planes
4. Hybrid Micro/Nano-Structured Surfaces
Porous Anodized Alumina-Templated Fabrication of 3-D Nanowire Structures
(Copper – metals and alloys, Silicon)
Pool Boiling and Capillary Evaporation
Nanotechnology-enabled Thermal Management
Kinetic limits for phase-change heat transfer (Ideal Limit)
qmax = 0.741ρ v chlv
Evaporation enthalpy
Sound velocity
R. W. Schrage, A Theoretical Study of Interphase Mass Transfer; Columbia
University Press: New York, 1953.
Critical Heat Flux [W/cm 2 ]
1000000
Upper bound for the CHF (water)
The reported highest CHF of
evaporation (water)
10000
100
250
300
350
Saturation Temperature [K]
400
Nanowires could directly provide heat to
molecules for evaporation!
Evaporation Heat Transfer on Capillary Wicks
1 .10
8
Evaporation heat transfer coefficient [W/m2K]
Size Effect due to Area Change
373.15
Kwick=100 W/mK
dpore=2 µm
1 .10
Non-evaporation equilibrium
thin film region (Tw=Tδ)
δ0
7
dpore=20 µm
dpore=40 µm
1 .10
δ
Microfilm region
(Tsat< Tδ <Tw)
θ
Meniscus region (Tδ
=Tsat )
6
Test data [Li and Peterson, 2006]
245000
dpore=109 µm, Kwick =82.7 W/mK
1 .10
5
Thin liquid film on a solid surface
290
300
310
320
330
340
350
360
Saturation temperature [K]
370
380
Wettability Control with Nanowires
Wenzel’s Model
d
Cassie-Baxter Model
Nanowire
coverage: Φ
Micro/Nano-Structured Surfaces and Coatings (our practice): Manufacturing Technologies
Silicon nanowires
More Realistically: Effective Contact Angle Change
The effect of nanostructures on phase-change heat transfer are more like an assembling effect
than any individual nanowires, since droplets and bubbles are much larger than nanowires
Hybrid Wicking Structures
Hybrid Wicking Structures
Fluid Mechanics Limitation
GaN
Si-on-Si
Rwall
GaN on GaN
Re
1mm
re
40cm
To Next Cooling Level
∆Pflow
θe
10000
C apillary Pressure an d Pressu re D ro p
[K Pa]
Evaporating
Vapor core
rc
θc
Pressure drop from Dcube=10 µm
1000
Re-c
Condensing
Rc
100
Rwall
Capillary pressure from the dpore=400 nm
10
Pressure drop from Dcube=50 µm
1
0.1
250
270
290
310
330
350
Working Temperature [K]
370
390
Hybrid Wicking Structures
Biporous/Modulated Wicking
Superhydrophobic Lotus Leaf
Liter and Kaviany, 2000
Hybrid Wicking Structures developed at CU-Boulder
a). Micromesh-enhanced Microchannel Wicking Structure b). Patterned Nanowires
NW bundle (p)
space(s)
With Chen Li at Univ. South Carolina
Height:
60µm
Outline
1. Introduction and Motivation
2. Nanotechnology-enabled Thermal Management
Hybrid Wicking Structures for Phase-Change Heat Transfer
3. Micromesh-enhanced Microchannels
Capillary Evaporation
Flexible Thermal Ground Planes
4. Hybrid Micro/Nano-Structured Surfaces
Porous Anodized Alumina-Templated Fabrication of 3-D Nanowire Structures
(Copper – metals and alloys, Silicon)
Pool Boiling and Capillary Evaporation
Capillary Evaporation Testing Apparatus
Heaters
1
q
Valve
Thermocouples
2 3 4
Pressure
gauge
5
"
h
Water level
Guard Heaters to maintain
saturation temperature
X.M. Dai, et al, Int. J. Heat Mass Transfer, Vol. 64, pp. 1101-1108, 2013
X.M. Dai, et al, Applied Physics Letter, Vol. 103, Art #151602, 2013
X.M. Dai, et al, Applied Physics Letter, , Vol. 105, Art #191611, 2014
Capillary Evaporation on Hybrid Wicking Structure
X.M. Dai, et al, Int. J. Heat Mass Transfer, Vol. 64, pp. 1101-1108, 2013
Enhanced Capillary Evaporation with Coatings
X.M. Dai, et al, Applied Physics Letter, Vol. 103, Art #151602, 2013
X.M. Dai, et al, Applied Physics Letter, , Vol. 105, Art #191611, 2014
Thermal Ground Planes with Hybrid Wicking
Si-on-Si
GaN on GaN
1mm
40cm
To Next Cooling Level
Flexible Thermal Ground Planes with a size of 20cm * 40cm
* 1mm, with a thermal conductivity > 20000 W/m2K
X.M. Dai, et al, AJTEC2011-44088, 2011
Print Circuit Board-Based Thermal Ground Plane
Area=
3cmX3cm
Thickness = 1.7 mm
Weight = 15.5 grams
Effective Thermal Conductivity:
> 1,500 W/mK at 0g and > 500 W/mK at 10g
200 micron diameter thermal vias; ~10,000
vias per pad
1.7 mm
3 cm
Micro copper mesh
bonded on pillars
LCP: Liquid Crystal Polymer
C. Oshman, et al, Journal of Micro-Electro-Mechanical
Systems, Vol. 20, n2, pp. 410-417, 2011
Effective Thermal Conductivity under Acceleration
C. Oshman, et al, Journal of Micro-Electro-Mechanical Systems, Vol. 20, n2, pp. 410-417, 2011
C. Oshman, et al, Journal of Micromechanics and Microengineering, Vol. 22, Art #045018, 2012
Flexible Thermal Ground Planes (Gen-3)
Thermally Welded Seams
Nylon/Al/PET (metallized boPET foil)
Flexible Casing
Evaporator
2.5”X5”
Sintered Copper Mesh
Encapsulated by ALD
Coating (liquid wicking)
Coarse Polymer Vapor Mesh
90°
° flex
(2.5 cm radius)
Nylon/Al/PET (metallized boPET foil)
Flexible Casing
Condenser
FTGP Thermal Resistance w.r.t. Different Flex Angles
Copper Reference
5W
10W
15W
20W
25W
45°
°
0°
°
0°
°
45°
°
0°
°
45°
°
90°
°
90°
°
90°
°
0°
°
Flex Angles
C. Oshman, et al, Journal of Micromechanics and Microengineering, Vol. 23, Art # 015001, 2013
Outline
1. Introduction and Motivation
2. Nanotechnology-enabled Thermal Management
Hybrid Wicking Structures for Phase-Change Heat Transfer
3. Micromesh-enhanced Microchannels
Capillary Evaporation
Flexible Thermal Ground Planes
4. Hybrid Micro/Nano-Structured Surfaces
Porous Anodized Alumina-Templated Fabrication of 3-D Nanowire Structures
(Copper – metals and alloys, Silicon)
Pool Boiling and Capillary Evaporation
Functionalized Hybrid Micro/Nano-Structured Surfaces
for Phase-Change Heat Transfer
1. Pool Boiling
2. Dropwise Condensation
Pm2
θA
Hybrid Micro/NanoStructured Surfaces
θR
Pm1
g
g+adrop
microfin
θR
Nanofin
A. Uniform micro
fin pattern
3. Microchannels
θA
B. The micro fin density
increase in the flow direction
4. Thermal Ground Planes
GaN
Si-on-Si
GaN on GaN
1mm
40cm
To Next Cooling Level
Porous Anodic Alumina (PAA) Templates
PAA templates
5×5 cm2
Anodization
Commercial
Aluminum
Diameter (20 - 300 nm) ∝ Voltage (20 – 190 V)
H2SO4
Oxalic acid
M. Tian, et al, Journal of Power Sources, Vol. 196, pp. 10207-10212, 2011
H3PO4
Two-Step Growth of Nanowire Arrays
Screw: Maintaining the force
1: Bonding on substrate
Copper plate: Counter electrode
Cellulose paper separator:
absorbing the electrolyte solution
DC
power
PAA template: template for
fabricating copper nanowire arrays
Force
Copper plate: Substrate
Hard PMMA plate:
Providing uniform force
2: Growth of Cu nanowires
M. Tian, et al, Journal of Power Sources, Vol. 196, pp. 10207-10212, 2011
Cu Nanowire Arrays with Different Lengths
10 mins
1 hr
20 mins
2 hrs
30 mins
4 hrs
Gap size between clusters changes with the length increase of Cu nanowires
Patterned Cu Nanowire Arrays
Force
Cr Evaporation & Lithography
RIE and soap with H3PO4
Growth of Cu nanowire
Facile Synthesis of Si Nanowire Arrays
Wafer Size
High Aspect Ratio
Tunable Size
> 1000:1
28
Advantages: Facile approach, Large-scale synthesis, High degree of control, Compatible
with complex structure
W. Wang, et al. Applied Surface Science, Vol. 258, pp. 8649–8655, 2012.
Dimension Control
Tunable diameter
40V
Tunable filling ratio
Low ratio
80V
Big gap
High ratio
Small gap
29
Diameter ~ 20-80 nm
Tunable porosity
Hybrid structure
0.1M H2O2
Porosity=47%
0.2M H2O2
Porosity=66%
W. Wang, et al. Applied Surface Science, Vol. 258, pp. 8649–8655, 2012.
Outline
1. Introduction to Phase-Change Heat Transfer
2. Nanotechnology-enabled Thermal Management
Hybrid Wicking Structures for Phase-Change Heat Transfer
3. Micromesh-enhanced Microchannels
Capillary Evaporation
Flexible Thermal Ground Planes
4. Hybrid Micro/Nano-Structured Surfaces
Porous Anodized Alumina-Templated Fabrication of 3-D Nanowire Structures
(Copper – metals and alloys, Silicon)
Pool Boiling and Capillary Evaporation
Fundamentals in Boiling Heat Transfer Process
2σ Tsat
Rc =
h fg ρv ∆T
CHF: Critical Heat Flux
q′′
h=
∆T
Functionalized Hybrid
Micro/Nano-Structured Surfaces
V.P. Carey, Liquid-vapor Phase-Change Phenomena, 2008.
Q. Li, et al, IMECE2011-64921, 2011
Pool Boiling Testing Apparatus
Testing Articles:
1). Micro-Pillared Surface
2). Nanowired Surface
3). Hybrid Micro/Nano-structured Surface
Q. Li, et al, IMECE2011-64921, 2011
CHF Enhancement on Micro-Pillared Surfaces
20µm×20µm micropillars
decreased contact angle -> increased CHF
45µm×45µm micropillars
Q. Li, et al, IMECE2011-64921, 2011
Boiling Heat Transfer on Hybrid Structured Surfaces
Significant enhancement in CHF due to improved liquid
supply and separated liquid-vapor flow. An increasing
trend of HTC due to a wide range size of cavities.
Q. Li, et al, IMECE2011-64921, 2011
Thermal Ground Planes with Pattened Nanowire Arrays
10-6 torr
vacuum
Glass plate
1mm
condensation area
evaporation area
Tevp
TC1 TC2 TC3
solder
TC4
TC7 TC8 TC9
Ceramic
heater
NW bundle (p)
3cm
5mm for sealing
space(s)
=
TC6
∆x
∆x
_
7−
2∆
9
Cold plate
wicking
structure
3cm
TC5
Tcond
Height:
60µm
Q. Li, et al, Summer Heat Transfer Conf. HT2013-17674, 2013
Heat Transfer Performance of Patterned NW TGPs
80
NW bundle (p)
70
space(s)
∆T=Tevp-Tcond (⁰C)
sample #1 p70-s45
60
sample #2 p50-s65
1mm thick copper reference
50
Simulated copper reference
dry out
40
Wickability Experiment:
Wicking Front
0s
30
Evaporation
Liquid flow
20
0.3s
0s
10
Wicking front
0
0
50
100
150
heat flux (W/cm2)
200
250
0.5s
Q. Li, et al, IMECE2011-64921, 2011
Q. Li, et al, Summer Heat Transfer Conference HT2013-17674, 2013
Sample #2
Thermal Management for Futuristic Electronics
There are great opportunities in enhancing phase-change heat transfer using
hybrid wicking structures to avoid liquid supply bottleneck (increase
wickability) while taking advantage of enhanced wettability and surface
area increase.
Further research work needs to be performed to systematically study surfaceliquid interaction: coolants, substrate material, selective coatings, size
optimization, long term reliability, …
High Power & 3-D Electronics
Wearable and Flexible Electronics