The MWCNT-OH-based EG/DW solutions were used as coolants in the liquid cooling system for the Intel Core i5 processor.. In this paper, we present the results of hydroxyl-functional multi
Trang 1Heat Dissipation for the Intel Core i5 Processor Using Multiwalled
Carbon-nanotube-based Ethylene Glycol
Bui Hung Thang,∗ Pham Van Trinh and Le Dinh Quang
Institute of Materials Science (IMS), Vietnam Academy of Science and Technology (VAST), Vietnam
Nguyen Thi Huong
Hanoi University of Science (HUS), Vietnam National University (VNU), Vietnam
Phan Hong Khoi and Phan Ngoc Minh†
Center for High Technology Development (HTD), Vietnam Academy of Science and Technology (VAST), Vietnam
(Received 14 January 2014)
Carbon nanotubes (CNTs) are some of the most valuable materials with high thermal
conduc-tivity The thermal conductivity of individual multiwalled carbon nanotubes (MWCNTs) grown by
using chemical vapor deposition is 600± 100 Wm −1K−1compared with the thermal conductivity
419 Wm−1K−1 of Ag Carbon-nanotube-based liquids – a new class of nanomaterials, have shown
many interesting properties and distinctive features offering potential in heat dissipation
applica-tions for electronic devices, such as computer microprocessor, high power LED, etc In this work,
a multiwalled carbon-nanotube-based liquid was made of well-dispersed hydroxyl-functional
mul-tiwalled carbon nanotubes (MWCNT-OH) in ethylene glycol (EG)/distilled water (DW) solutions
by using Tween-80 surfactant and an ultrasonication method The concentration of MWCNT-OH
in EG/DW solutions ranged from 0.1 to 1.2 gram/liter The dispersion of the MWCNT-OH-based
EG/DW solutions was evaluated by using a Zeta-Sizer analyzer The MWCNT-OH-based EG/DW
solutions were used as coolants in the liquid cooling system for the Intel Core i5 processor The
thermal dissipation efficiency and the thermal response of the system were evaluated by directly
measuring the temperature of the micro-processor using the Core Temp software and the
temper-ature sensors built inside the micro-processor The results confirmed the advantages of CNTs in
thermal dissipation systems for computer processors and other high-power electronic devices
PACS numbers: 81.05.Uw, 81.07.De, 65.80.+n, 73.63.Fg
Keywords: Carbon nanotubes, Ethylene glycol, Coolant, Nanofluid, Heat dissipation, Intel Core i5 processor
DOI: 10.3938/jkps.65.312
I INTRODUCTION
Thermal management is widely recognized to be an
important aspect of computer design, with device
per-formance being significantly affected by temperature In
addition, device lifetime can be decreased drastically
be-cause of large thermal stresses The challenge for thermal
management is to develop high-conductivity structures
that can accommodate the fixed temperature drop with
the increasing power densities that characterize new
gen-erations of microprocessors [1]
In recent years, many approaches have improved the
cooling system performance; the most feasible one is
to enhance the heat transfer (dissipation) performance
∗E-mail: thangbh@ims.vast.ac.vn
†E-mail: pnminh@vast.ac.vn
through the working fluid without modifying the me-chanical design or the key components Researchers have recently shown much interest on the issue of nanofluid thermal properties [2,3] Nanofluids are considered as a new class of fluids having enormous potential to improve the efficiency of heat-transfer fluids Many factors, such
as the particle size, the effect of surfactant, the disper-sion of particles, and the thermal properties of dispersed particle are expected to the influence thermal properties
of nanofluids [4]
The nanofluid concept is employed to designate a fluid
in which nanometersized particles are suspended in con-ventional heat-transfer base fluids to improve their ther-mal physical properties The nanoparticles are made from various materials, such as metals (Cu, Ag, Au, Al, and Fe), oxide ceramics (Al2O3 and TiO2), nitride ce-ramics (AlN, SiN), carbide cece-ramics (SiC, TiC), semi-
Trang 2-312-conductors, carbon nanotubes, and composite
materi-als such as alloyed nanoparticles or nanoparticle
core-polymer shell composites Conventional heat transfer
fluids, such as oil, water, and ethylene glycol, in
gen-eral, are well known to have poor heat transfer
proper-ties compared to those of most solids Nanofluids have
enhanced thermo- physical properties, such as thermal
conductivity, thermal diffusivity, viscosity, and
convec-tive heat transfer coefficients compared with those of
base fluids like oil or water [5]
Carbon nanotubes (CNTs) are some of the most
valu-able materials with high thermal conductivity The
thermal conductivity of individual MWCNTs grown by
chemical vapor deposition is 600± 100 Wm −1K−1
com-pared with thermal conductivity 419 Wm−1K−1 of Ag
[6–8] This suggests an approach in applying CNTs
in grease or liquid for thermal dissipation systems for
computer processors and other high-power electronic
devices [9–17] In this paper, we present the results
of hydroxyl-functional multiwalled carbon nanotubes
(MWCNT-OH)-based ethylene glycol (EG)/distilled
wa-ter (DW) solutions applied to thermal dissipation for a
Intel Core i5 processor
II EXPERIMENTS AND DISCUSSION
MWCNTs were produced at the Vietnam Academy of
Science and Technology by using the thermal chemical
vapor deposition (CVD) technique [18] The diameter
and the length of the grown MWCNTs used in this
ex-periment were 15− 80 nm and several tens of μm,
respec-tively The MWCNTs were functionalized with hydroxyl
functional group (−OH) by using the following steps:
- Step 1: MWCNTs were treated in a mixture of hot
acid (HNO3:H2SO4 in a ratio of 1:3) at 60◦C for
6 h
- Step 2: The suspension obtained in step 1 was
dried in an argon atmosphere at 80◦C for 24 h
- Step 3: The mixture obtained in step 2 was treated
in the SOCl2to obtain MWCNTs-COCl
- Step 4: The MWCNTs-COCl were filtered in H2O2
and dried in an argon atmosphere at 80◦C for 24
h to obtain MWCNTs-OH
In order to disperse the MWCNT-OH in the EG/DW
solutions, we used the Tween-80 surfactant and the
Hielscher Ultrasonics Vibration instrument The volume
percent of ethylene glycol in the EG/DW solution was
50% The MWCNT-OH were dispersed in the EG/DW
solution in concentrations from 0.1 to 1.2 g/l
Figure 1 is a schematic view of the thermal
dissipa-tion system for computer processor using CNTs-based
EG/DW solutions In this system, the copper
heat-sink was set in direct contact with the processor, and
Fig 1 (Color online) Scheme of the cooling system using MWCNT-based EG/DW solutions for the CPU
the tracks inside the copper substrate were fabricated to allow liquid to flows through the substrate and absorb heat from the processor The pump power consumption
of the cooling system was 1.8 W The dimensions and the power consumptions of the two fans were 120× 120
× 38 mm3 and 3.6 W, respectively The heat radiator
was made of aluminum material, and the dimensions of heat radiator were 150 × 120 × 25 mm3, respectively.
The environmental temperature was kept at 20◦C for all measurements by using an air conditioner The thermal dissipation efficiency and the thermal response of the sys-tem were evaluated by using dedicated software and four built-in temperature sensors inside the micro-processor
to measure the temperature of the micro-processor di-rectly
We chose a personal computer with the following con-figuration: Intel Core i5 – 3570 K Processor (6M Cache, 3.4 GHz), Corsair’s 4 GB DDR3 SODIMM Memory, Toshiba’s 1 TB Hard Disk Drive, Asrock H61M-VS3 Main-board, and Window 7 Ultimate Service Pack 1 Op-erating System for all experiments The temperature
of the micro-processor was measured by using the Core Temp 1.0 RC5-32bit software The micro-processor was pushed to operate at full load (100% usage of the pro-cessor) by using Prime 95 v27.9 build 1 software The existence of carboxyl (COOH) and hydroxyl (OH) functional groups bonded to the ends and the sidewalls was demonstrated by Raman and Fourier transform in-frared (FTIR) spectra Raman scattering is a power-ful technique to probe the changes in the surfaces and
Trang 3Fig 2 (Color online) Raman spectra of MWCNTs:
pris-tine MWCNTs (black line), MWCNT-COOH (red line) and
MWCNT-OH (blue line)
the structures of MWCNTs Figure 2 clearly shown
that the two bands around 1583.10 cm−1 and 1333.69
cm−1in the spectra were assigned to the tangential mode
(G-band) and the disorder mode (D-band), respectively
The D-band intensity was increased in the functinalized
MWCNTs compared to the pristine MWCNTs The
peak intensity ratios (ID/IG) of the D-band to the
G-band of 0.99 and 1.87 corresponding to MWCNT-COOH
and MWCNT-OH exceeded those of pristine MWCNTs
(ID/IG = 0.79) The intensity ratio of D lines to G lines
were different, suggesting some changes in the surfaces
and the structures of the MWCNTs This result
indi-cates that some of the sp2 carbon atoms (C=C) were
converted to sp3 carbon atoms (C−C) at the surfaces of
the MWCNTs after the acid treatment in HNO3/H2SO4
The intensity ratio of MWCNT-OH was higher than
that of MWCNT-COOH indicating that the two
chem-ical treatment processes had formed new defects on the
surfaces of the MWNCTs
Figure 3 presents typical FTIR spectra of the pristine
important peaks are seen after the MWCNTs have been
treated with a mixture of H2SO4and HNO3 The
vibra-tion of O-H bonding in the carboxyl group is shown as a
peak at 3431.81 cm−1 It was expanded more than that
of the O-H bonding of H2O The peak at 1707.31 cm−1
showed the existence of vibrations of the C=O bond in
the carboxyl group This shows the importane of proving
the existence of carboxyl (COOH) functional groups due
to the oxidation resulting from the nitric and the sulfuric
acids This clearly shows that the acids functionalized
the surfaces of the MWCNTs The FTIR transmittance
spectra of MWCNT-OH show that the peak of the
conju-gated O-H stretching vibration mode appears at 3431.81
cm−1 and that the central position of the O-H peak is
shifted to a lower frequency as well; the expansion of
Fig 3 FTIR transmission spectra of pristine MWCNTs, MWCNT-COOH, and MWCNT-OH
Fig 4 (Color online) MWCNT-OH size distribution in the EG/DW solutions by number with 10 minutes of ultra-sonication: (a) immediately after the sonication and (b) 72 hours after the sonication
the vibration peak and the disappearance of the vibra-tion peak of the C=O bond at 1707.31 cm−1 indicate the generation of hydroxyl groups on the surfaces of the MWCNTs
In order to evaluate the dispersion of the
MWCNT-OH in the EG/DW solutions, we used the Malvern Ze-tasizer Nano ZS Instrument Figure 4 presents spectra
of the MWCNT-OH size distribution in EG/DW solu-tions by number for 10 minutes of ultrasonication Fig-ure 4(a) shows that immediately after the ultrasonica-tion, the MWCNT-OH were still gathering into large bundles, with peaks at 437 nm and 93.5 nm The 437-nm peak corresponds to the large bundles of MWCNT-OH whereas the 93.5-nm peak corresponds to the individ-ual MWCNT-OH in the EG/DW solutions In order
Trang 4Fig 5 (Color online) MWCNT-OH size distribution in
the EG/DW solutions by number at 72 hours after from the
sonication: (a) 20 minutes of sonication, (b) 30 minutes of
sonication, and (c) 40 minutes of sonication
to remove large bundles from the EG/DW solutions, we
settled the solutions for 72 hours Figure 4(b) showed
that after 72 hours from ultrasonication, the 437-nm
peak didn’t exist, which means there were no longer large
bundles of MWCNT-OH in the EG/DW solutions
How-ever, the MWCNTs were still gathering into small
bun-dles with a size distribution from 70 to 270 nm
Figure 5 presents spectra of the MWCNT-OH size
dis-tributions in the EG/ DW solution by number for
son-ication times from 20 to 40 minutes In the case of
20-minute ultrasonic vibration time (shown as Fig 5(a)),
the spectrum of the MWCNT-OH size distribution by
number was from 18 nm to 95 nm This result showed
that MWCNT-OH were better dispersed in the EG/DW
solutions with a 20-minute ultrasonic vibration time
However, the range didn’t match with the 15- to 80-nm
diameter of the MWCNT-OH In the case of 30-minute or
a 40-minute ultrasonic vibration time, the MWCNT-OH
were well dispersed in the EG/DW solutions are shown as
Figs 5(b) and (c) The spectra of the MWCNT-OH size
distribution by number in Figs 5(b) and (c) matched
with the 15- to 80-nm diameter of the MWCNT-OH
The results show that the ultrasonic vibration time
re-quired is more than 30 minutes for good dispersion of
the MWCNT-OH in EG/DW solutions, so we chose 30
Fig 6 (Color online) Measured temperature of the micro-processor as a function of the operation time in the case of using the cooling fan method
Fig 7 (Color online) Measured temperature of the micro-processor as a function of the operation time in the case of using a MWCNT-OH-based EG/DW solution
minutes of ultrasonic vibration time for all subsequent experiments
We measured directly the temperature of the micro-processor during the operation of the computer at full-load mode (100% usage micro-processor mode) To es-timate the role of the MWCNT-OH-based EG/DW so-lutions, we investigated the temperature of the micro-processor when using a cooling fan Figure 6 shows the micro-processor’s temperature as a function of working time when using a cooling fan As seen in Fig 6, at the initial time, the temperature of the micro-processor was
35◦C, and then the temperature of the micro-processor became saturated at approximately 71◦C after 200 sec-onds of working time
In order to reduce the saturation temperature and slow down the temperature increase of the processor, we used MWCNT-OH-based EG/DW solutions as coolants in a
Trang 5liquid cooling system for the micro-processor Figure
7 shows the micro-processor’s experimental temperature
as a function of working time when using
MWCNT-OH-based EG/DW solutions for thermal dissipation At the
initial time, the temperature of the micro-processor was
about 30 − 32 ◦C The saturation temperature of the
microprocessor reached 57, 54 and 51 ◦C when using an
EG/DW solution without CNTs, an EG/DW solution
with 0.5 g of MWCNT-OH/liter of concentration, and
an EG/DW solution with 1g of MWCNT-OH/liter of
concentration after 350 seconds of working time,
respec-tively These results indicated that, in comparison to the
cooling fan, the saturation temperature of the processor
decreased about 14 − 20 ◦C, and the time for the
tem-perature to increase was prolonged from 200 seconds to
350 seconds By mixing MWCNT-OH (1 g/l of
concen-tration) in the EG/DW solution, we could decrease the
saturation temperature of CPU 6◦C compared to using
EG/DW solutions without MWCNT-OH
III CONCLUSION
The successful hydroxyl functionalization of nanotubes
with a mixture of acid solution was proven by Raman
and FTIR spectral measurements to have opened new
applications for thermal-dissipation-based liquids in
elec-tronic devices We have successfully dispersed
MWCNT-OH into EG/DW solutions by using Tween-80 surfactant
and an ultrasonication method The thermal dissipation
efficiency of the PC’s micro-processor using the
cool-ing fan and liquid coolcool-ing was examined and evaluated
Compared to the cooling fan, the saturation temperature
of the processor using the EG/DW solutions decreased
about 14 ◦C By mixing MWCNT-OH (1 g/l of
con-centration) into the EG/DW solutions, the saturation
temperature of the CPU decreased 6 ◦C compare to
us-ing the EG/DW solution without MWWCNTs-OH The
experimental results confirmed the advantage of using a
MWCNT-based liquid in thermal dissipation for
micro-processors and other high-power electronic devices
ACKNOWLEDGMENTS
The authors acknowledge the financial support from
the Vietnam National Foundation for Science and
Tech-nology Development (Project No NAFOSTED 103.99-2012.35) The authors declare that there is no conflict
of interests regarding the publication of this article
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