1. 0 10 20 30 40 50 60
37
47
57
67
77
87
97
107
117
Temperature,T(K)
Time, t (s)
Theory and Modeling
Composite Thin Films with Microencapsulated Phase Change Materials for
Passive Thermal ControlChristopher Perez, Alexander M. Thiele, Laurent Pilon
Mechanical and Aerospace Engineering Department - University of California, Los Angeles
Abstract
Motivation
Thermal management of microprocessors and
electronic packaging remains a major concern
as devices shrink in size and their computing
power increases.
The thermal energy generated at hot spots
could be readily accommodated by phase
change materials (PCMs) until the thermal
energy dissipates or conventional thermal
management removes it.
Through multi-physics modeling and simulation software, a simplified thermal analysis of composite thin films embedded with micro-encapsulated phase change materials(PCMs) was performed. Such films may accommodate the
heat generated by transient surges in the power output of electronic devices. Parameters were varied to gain insight into the thermal mechanisms involved in reducing maximum temperatures below 100℃ and minimizing cooling time
for PCM re-solidification. For the film thicknesses considered and a matrix thermal conductivity of 5W/(m∙K), three effective configurations were identified: film thickness of 450μm with PCM volume fractions of (i) 40% and (ii) 60%,
and (iii) film thickness of 400μm with a PCM volume fraction of 60%. The first two configurations yielded temperature reductions of 9% and 13% and cool time reductions of 11% and 13%, respectively, compared with a plain film
without PCM. The third configuration yielded a temperature reduction of 11% and a cool time reduction of 19%.
What are phase change materials (PCMs)?
 Substances that store and release thermal energy in the form of latent
heat at a relatively constant temperature during the process of melting
and freezing.
Stored heat
Latent
Temperature
Sensible
Sensible
Phase
change
temperature
Why microencapsulated PCMs?
 Prevents reaction between PCM and composite matrix
 Inorganic shells can protect against flammability of organic PCMs
 Encourages 100% change of phase in all PCM regions
Acknowledgements
This work was supported by Intel and the Semiconductor Research Corporation Education Alliance through the SRC Education Alliance
Grant 2009-UR-2035G, Amendment No. 4. • The researchers also wish to acknowledge the UCLA Center for Excellence in Engineering
and Diversity (CEED)—Enrique (Rick) Ainsworth, Director • Audrey Pool O’Neal• Nadia Alvarez •Melissa Moz •Michael Gervasoni
Introduction
Demonstrate that composite thin films with embedded phase change
materials applied to planar surfaces can accommodate heat generation and
hot spots within the substrate.
 Maintain surface temperature below 100oC for at least 10 min. with
realistic surface heat fluxes.
 Reduce amplitude of surface temperature oscillations in response to
variation in substrate heat flux.
Successful Configurations
Objective
p,c,s pc pc
sf
p,c p,c,s pc pc pc pc
pc
p,c,l pc pc
sf
p
pc
c T < T T / 2
h
c = +c T T / 2 T T T / 2
ΔT
c T > T T / 2
h : Latent heat of fusion [kJ/kg]
c : Specificheat of PCMinsolid(s)andliquid(l) [kJ/kg K]
T : Onset of melting tempera
  


     

  

pc
ture [ C]
ΔT : Melting temperature range [ C]
o
o
Numerically confirmed model where specific heat is a function of
temperature:
   
   
s s c s s
m c s c s c s
c c s c c
eff
s s c s c s s
c s c s
c c s c m c m
k
k 1- - 6+4 +2 + 1+2 +2 3+ k +2 k
k
k =
k k k
2+ + 3+2 + + 1- - 3+ +2
k k k
   
   
   
   
   
   
    
   
    
    
   
    
        p c p s p c s peff c s m
ρc (T) = ρc (T) + ρc + 1 - - ρc   
Effective thermal conductivity:
Volumetric heat capacity (weighted volume average):
h air , T∞PCM/matrix layer
qyꞌꞌ(x, y, z, t) = 0
W
m2
qxꞌꞌ(x, y, z, t) = 0
W
m2
Laa
keff, (ρcp)eff (T)
xy
z
Model Parameters
L
Model Assumptions:
• PCM/matrix is homogeneous
medium with effective thermal
properties
• All material properties isotropic
• Specific heat of PCM a function
of temperature; all other
properties constant
• Heat transfer was one
dimensional in z-direction,
(a >> L)
• Thermal contact resistance
between thin film and heat
source negligible
Energy equation under given assumptions:
𝜕T
𝜕t
= αeff
𝜕2
T
𝜕z2
where: αeff =
keff
ρcp eff
T
Boundary conditions:
• Insulated x & y boundaries
q′′x 0, y, z, t = q′′x a, y, z, t = 0
W
m2
q′′y x, 0, z, t = q′′y x, a, z, t = 0
W
m2
• Top surface boundary
−keff
𝜕T
𝜕z
= hair T L, t − T∞
• Bottom surface boundary
−keff
𝜕T
𝜕z
x, y, 0, t = q′′pulse
Initial conditions:
T z, t = Ti
Simulating Phase Change
General Results
Idle heat flux: 𝐪ꞌꞌ idle = 𝟗𝟎
𝐤𝐖
𝐦 𝟐
Constant
Convection coefficient : hair = 80
W
m2∙K
Idle temperature: Ti = 40℃
Air temperature: T∞ = 25℃
Varying
Film thickness: L = 75 − 1000 μm
PCM volume
fraction: ϕPCM= 0.20 − 0.60
k (W/m∙K) ρ (kg/m3) cp (kJ/kg∙K) hsf (kJ/kg) Tpc ℃
Matrix material 5 - 100 1,200 3.062 N/A N/A
PCM 0.21 870 1.6095 245 Optimize
Pulse heat flux: 𝐪ꞌꞌ 𝐩𝐮𝐥𝐬𝐞
= 𝟏𝟑. 𝟓
𝐤𝐖
𝐦 𝟐 15% of qꞌꞌ idle
Adding PCM
Temperature,T(℃)
75
150
225
325
400
450
575
750
1000
0 20 40 60 80 100
47
67
87
107
127
147
167
187
207
Time, t (s)
L(mm):
kmatrix = 5 W/m∙K
Tpc = 52o
C
0 20 40 60 80 100
47
67
87
107
127
147
167
187
207
Temperature,T(℃)
Time, t (s)
Phase
change
region
Design Rules
Future Work
14
Intel
IBM Prescott
Bipolar ES9000 Intel
12 Jayhawk
2 CMOS
10 IBM
Intel z990
McKinley
Fujitsu IBM
VP2000 POWER 5
8 IBM
m
IBM IBM GP
c 3090S RY5
/
W 6 NTT Fujitsu IBM Pentium IV
ux, M780 RY7
l F
Heat Cyber IBM RY6 RS64 III
4 CDC IBM IBM
e
odul
205 3090
IBM IBM
M 2 3081 IBM IBM RY4
vacuum IBM IBM IBM 4381 RS64 Intel tubes 360
370 3035 Fujitsu Merced
M380 Pentium II
0
1950 1960 1970 1980 1990 2000 2010
Year of Product Launch
0
20
40
60
80
100
120
140
Time, t (s)
10
Powerinput,P(W)
20 30 40 …
Thermal conductivity 𝐤 𝐦𝐚𝐭𝐫𝐢𝐱
 Effect of thermal resistance is negligible for the film thicknesses considered
PCM volume fraction 𝛟 𝐏𝐂𝐌
 For smaller thickness, large volume fractions have negligible effect on maximum
temperature
 For larger thicknesses, increase in volume fraction decreased maximum temperature and
cool time once phase change temperature was optimized
o Diminished sensible heat storage
ρcp eff
as PCM has smaller density
Phase change temperature (𝐓𝐩𝐜)
 For all thicknesses, the phase change temperature
should be closer to desired peak temperature (100℃ in
this case)
o Lowers maximum temperature without
prolonging cool time
16 18 20 22 24
0
10000
20000
30000
40000
50000
60000
70000
Tpc
liquidmelting
PCMspecificheatcapacity,cp,c(J/kg.K)
Temperature, T
 Tpc
hsf
Tpc
solid
 Refine model to include thermal interaction between chip material and PCM/matrix film
 Further explore range of film thicknesses and categorize them by their ability to
accommodate power inputs of different magnitude and frequency
 Create composite(s) and measure the film temperature to validate numerical results
q
1
hairA
L
keffA
T1
T2
q =
∆T
Rtot
Rtot =
1
h A
+
L
keff A
20 40 60 80
47
67
87
107
Temperature,T(℃)
Time, t (s)
52
70
90
Tpc ℃ :
ϕPCM = 0 ϕPCM = 0.60
www.wallpaperup.com
www.microteklabs.com
[2]
[3]
0
2
4
6
8
10
12
14
1950 1960 1970 1980 1990 2000 2010
Year of Product Launch
Bipolar CMOS
vacuum tubes
IBM 360
IBM 370 IBM 3035
Fujitsu M380
IBM 3081
IBM 4381
CDC Cyber 205
IBM 3090
Fujitsu
M780
IBM 3090S
Fujitsu
VP2000
IBM ES9000
IBM RY4
IBM
RY7 Pentium IV
IBM RY5 IBM GP
IBM POWER 5
Intel McKinley IBM z990
Intel Jayhawk
Intel Prescott
ModuleHeatFlux,W/cm2
NTT
Intel Merced
IBM RS64
Pentium II
IBM RY6
IBM RS64 III
[4]
[5]
[7]
[6]
References
 Larger thicknesses result in lower temperatures
o More material volume with which to make use of PCM latent and sensible heat storage
+
Processor
Film/chip interface
temperature is of
interest
Phase change temperature [℃]
Phase change temperature window [℃]
ϕPCM = 0
ϕPCM = 0.60
L = 400 μm
Temperature,T(℃)
0 10 20 30 40 50 60
37
47
57
67
77
87
97
107
117
Time, t (s)
ϕPCM = 0
ϕPCM = 0.40
ϕPCM = 0.60
L = 450 μm
 Configurations that would have exceeded 100℃ without PCM
 𝐭 𝐜𝐨𝐨𝐥 = Time required to cool back to within 1% of idle temperature, (Ti)
100℃100℃
100℃100℃
𝐋 = 𝟒𝟓𝟎 𝛍𝐦 Tpc ℃ 𝐓 𝐦𝐚𝐱 ℃ 𝐭 𝐜𝐨𝐨𝐥 𝐬 𝐓𝐫𝐞𝐝 𝐭 𝐜𝐨𝐨𝐥 𝐫𝐞𝐝
𝛟 𝐏𝐂𝐌
0 105.2 63.4
0.40 91 96.2 56.6 9 % 11 %
0.60 86 91.5 55.1 13 % 13 %
𝐋 = 𝟒𝟎𝟎 𝛍𝐦
𝛟 𝐏𝐂𝐌 0 111.4 58
0.60 93 98.8 48.9 11 % 19 %
qzꞌꞌ(t) = Pulse Heat Flux
[1]
[1] www.pugetsystems.com [5] T. Atarashi, Journal of Electronics Cooling and Thermal Control, vol.4, 2014
[2] P. Lamberg et al., International Journal of Thermal Sciences, vol. 43, 2004 [6] O. Raghu, J. Philip, Measure. Sci. Technol., vol. 17, 2006
[3] J.D. Felske, International Journal of Heat and Mass Transfer, vol. 47, 2004 [7] www.puretemp.com
[4] M.J. Ellsworth, Proc. 2008 Therm Conf., 2008
℃
*