Journal of the Korean Physical Society, Vol. 65, No. 3, August 2014, pp. 312∼316

Heat Dissipation for the Intel Core i5 Processor Using MultiwalledCarbon-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 byusing chemical vapor deposition is 600 ± 100 Wm−1K−1 compared with the thermal conductivity419 Wm−1K−1 of Ag. Carbon-nanotube-based liquids – a new class of nanomaterials, have shownmany 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) solutionsby using Tween-80 surfactant and an ultrasonication method. The concentration of MWCNT-OHin EG/DW solutions ranged from 0.1 to 1.2 gram/liter. The dispersion of the MWCNT-OH-basedEG/DW solutions was evaluated by using a Zeta-Sizer analyzer. The MWCNT-OH-based EG/DWsolutions were used as coolants in the liquid cooling system for the Intel Core i5 processor. Thethermal dissipation efficiency and the thermal response of the system were evaluated by directlymeasuring 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 inthermal dissipation systems for computer processors and other high-power electronic devices.

PACS numbers: 81.05.Uw, 81.07.De, 65.80.+n, 73.63.FgKeywords: Carbon nanotubes, Ethylene glycol, Coolant, Nanofluid, Heat dissipation, Intel Core i5 processorDOI: 10.3938/jkps.65.312

I. INTRODUCTION

Thermal management is widely recognized to be animportant aspect of computer design, with device per-formance being significantly affected by temperature. Inaddition, device lifetime can be decreased drastically be-cause of large thermal stresses. The challenge for thermalmanagement is to develop high-conductivity structuresthat can accommodate the fixed temperature drop withthe increasing power densities that characterize new gen-erations of microprocessors [1].

In recent years, many approaches have improved thecooling system performance; the most feasible one isto 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 haverecently shown much interest on the issue of nanofluidthermal properties [2,3]. Nanofluids are considered as anew class of fluids having enormous potential to improvethe efficiency of heat-transfer fluids. Many factors, suchas the particle size, the effect of surfactant, the disper-sion of particles, and the thermal properties of dispersedparticle are expected to the influence thermal propertiesof nanofluids [4].

The nanofluid concept is employed to designate a fluidin which nanometersized particles are suspended in con-ventional heat-transfer base fluids to improve their ther-mal physical properties. The nanoparticles are madefrom various materials, such as metals (Cu, Ag, Au, Al,and Fe), oxide ceramics (Al2O3 and TiO2), nitride ce-ramics (AlN, SiN), carbide ceramics (SiC, TiC), semi-

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Heat Dissipation for the Intel Core i5 Processor· · · – Bui Hung Thang et al. -313-

conductors, carbon nanotubes, and composite materi-als such as alloyed nanoparticles or nanoparticle core-polymer shell composites. Conventional heat transferfluids, 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 haveenhanced thermo- physical properties, such as thermalconductivity, thermal diffusivity, viscosity, and convec-tive heat transfer coefficients compared with those ofbase fluids like oil or water [5].

Carbon nanotubes (CNTs) are some of the most valu-able materials with high thermal conductivity. Thethermal conductivity of individual MWCNTs grown bychemical 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 CNTsin grease or liquid for thermal dissipation systems forcomputer processors and other high-power electronicdevices [9–17]. In this paper, we present the resultsof hydroxyl-functional multiwalled carbon nanotubes(MWCNT-OH)-based ethylene glycol (EG)/distilled wa-ter (DW) solutions applied to thermal dissipation for aIntel Core i5 processor.

II. EXPERIMENTS AND DISCUSSION

MWCNTs were produced at the Vietnam Academy ofScience and Technology by using the thermal chemicalvapor deposition (CVD) technique [18]. The diameterand 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 hydroxylfunctional group (−OH) by using the following steps:

- Step 1: MWCNTs were treated in a mixture of hotacid (HNO3:H2SO4 in a ratio of 1:3) at 60 ◦C for6 h.

- Step 2: The suspension obtained in step 1 wasdried in an argon atmosphere at 80 ◦C for 24 h.

- Step 3: The mixture obtained in step 2 was treatedin the SOCl2 to obtain MWCNTs-COCl.

- Step 4: The MWCNTs-COCl were filtered in H2O2

and dried in an argon atmosphere at 80 ◦C for 24h to obtain MWCNTs-OH.

In order to disperse the MWCNT-OH in the EG/DWsolutions, we used the Tween-80 surfactant and theHielscher Ultrasonics Vibration instrument. The volumepercent of ethylene glycol in the EG/DW solution was50%. The MWCNT-OH were dispersed in the EG/DWsolution 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-basedEG/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 usingMWCNT-based EG/DW solutions for the CPU.

the tracks inside the copper substrate were fabricated toallow liquid to flows through the substrate and absorbheat from the processor. The pump power consumptionof the cooling system was 1.8 W. The dimensions andthe power consumptions of the two fans were 120 × 120× 38 mm3 and 3.6 W, respectively. The heat radiatorwas made of aluminum material, and the dimensions ofheat radiator were 150 × 120 × 25 mm3, respectively.The environmental temperature was kept at 20 ◦C for allmeasurements by using an air conditioner. The thermaldissipation efficiency and the thermal response of the sys-tem were evaluated by using dedicated software and fourbuilt-in temperature sensors inside the micro-processorto 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-VS3Main-board, and Window 7 Ultimate Service Pack 1 Op-erating System for all experiments. The temperatureof the micro-processor was measured by using the CoreTemp 1.0 RC5-32bit software. The micro-processor waspushed 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 sidewallswas 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

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Fig. 2. (Color online) Raman spectra of MWCNTs: pris-tine MWCNTs (black line), MWCNT-COOH (red line) andMWCNT-OH (blue line).

the structures of MWCNTs. Figure 2 clearly shownthat the two bands around 1583.10 cm−1 and 1333.69cm−1 in 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 functinalizedMWCNTs compared to the pristine MWCNTs. Thepeak intensity ratios (ID/IG) of the D-band to the G-band of 0.99 and 1.87 corresponding to MWCNT-COOHand MWCNT-OH exceeded those of pristine MWCNTs(ID/IG = 0.79). The intensity ratio of D lines to G lineswere different, suggesting some changes in the surfacesand the structures of the MWCNTs. This result indi-cates that some of the sp2 carbon atoms (C=C) wereconverted to sp3 carbon atoms (C−C) at the surfaces ofthe MWCNTs after the acid treatment in HNO3/H2SO4.The intensity ratio of MWCNT-OH was higher thanthat of MWCNT-COOH indicating that the two chem-ical treatment processes had formed new defects on thesurfaces of the MWNCTs.

Figure 3 presents typical FTIR spectra of the pristineMWCNTs, MWCNT-COOH and MWCNT-OH. Someimportant peaks are seen after the MWCNTs have beentreated with a mixture of H2SO4 and HNO3. The vibra-tion of O-H bonding in the carboxyl group is shown as apeak at 3431.81 cm−1. It was expanded more than thatof the O-H bonding of H2O. The peak at 1707.31 cm−1

showed the existence of vibrations of the C=O bond inthe carboxyl group. This shows the importane of provingthe existence of carboxyl (COOH) functional groups dueto the oxidation resulting from the nitric and the sulfuricacids. This clearly shows that the acids functionalizedthe surfaces of the MWCNTs. The FTIR transmittancespectra of MWCNT-OH show that the peak of the conju-gated O-H stretching vibration mode appears at 3431.81cm−1 and that the central position of the O-H peak isshifted 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 inthe EG/DW solutions by number with 10 minutes of ultra-sonication: (a) immediately after the sonication and (b) 72hours after the sonication.

the vibration peak and the disappearance of the vibra-tion peak of the C=O bond at 1707.31 cm−1 indicatethe generation of hydroxyl groups on the surfaces of theMWCNTs.

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 spectraof 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 largebundles, with peaks at 437 nm and 93.5 nm. The 437-nmpeak corresponds to the large bundles of MWCNT-OHwhereas the 93.5-nm peak corresponds to the individ-ual MWCNT-OH in the EG/DW solutions. In order

Heat Dissipation for the Intel Core i5 Processor· · · – Bui Hung Thang et al. -315-

Fig. 5. (Color online) MWCNT-OH size distribution inthe EG/DW solutions by number at 72 hours after from thesonication: (a) 20 minutes of sonication, (b) 30 minutes ofsonication, and (c) 40 minutes of sonication.

to remove large bundles from the EG/DW solutions, wesettled the solutions for 72 hours. Figure 4(b) showedthat after 72 hours from ultrasonication, the 437-nmpeak didn’t exist, which means there were no longer largebundles 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 bynumber was from 18 nm to 95 nm. This result showedthat MWCNT-OH were better dispersed in the EG/DWsolutions with a 20-minute ultrasonic vibration time.However, the range didn’t match with the 15- to 80-nmdiameter of the MWCNT-OH. In the case of 30-minute ora 40-minute ultrasonic vibration time, the MWCNT-OHwere well dispersed in the EG/DW solutions are shown asFigs. 5(b) and (c). The spectra of the MWCNT-OH sizedistribution by number in Figs. 5(b) and (c) matchedwith 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 ofthe 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 ofusing the cooling fan method.

Fig. 7. (Color online) Measured temperature of the micro-processor as a function of the operation time in the case ofusing a MWCNT-OH-based EG/DW solution.

minutes of ultrasonic vibration time for all subsequentexperiments.

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 themicro-processor’s temperature as a function of workingtime when using a cooling fan. As seen in Fig. 6, at theinitial time, the temperature of the micro-processor was35 ◦C, and then the temperature of the micro-processorbecame saturated at approximately 71 ◦C after 200 sec-onds of working time.

In order to reduce the saturation temperature and slowdown the temperature increase of the processor, we usedMWCNT-OH-based EG/DW solutions as coolants in a

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liquid cooling system for the micro-processor. Figure7 shows the micro-processor’s experimental temperatureas a function of working time when using MWCNT-OH-based EG/DW solutions for thermal dissipation. At theinitial time, the temperature of the micro-processor wasabout 30 − 32 ◦C. The saturation temperature of themicroprocessor reached 57, 54 and 51 ◦C when using anEG/DW solution without CNTs, an EG/DW solutionwith 0.5 g of MWCNT-OH/liter of concentration, andan EG/DW solution with 1g of MWCNT-OH/liter ofconcentration after 350 seconds of working time, respec-tively. These results indicated that, in comparison to thecooling fan, the saturation temperature of the processordecreased about 14 − 20 ◦C, and the time for the tem-perature to increase was prolonged from 200 seconds to350 seconds. By mixing MWCNT-OH (1 g/l of concen-tration) in the EG/DW solution, we could decrease thesaturation temperature of CPU 6 ◦C compared to usingEG/DW solutions without MWCNT-OH.

III. CONCLUSION

The successful hydroxyl functionalization of nanotubeswith a mixture of acid solution was proven by Ramanand FTIR spectral measurements to have opened newapplications for thermal-dissipation-based liquids in elec-tronic devices. We have successfully dispersed MWCNT-OH into EG/DW solutions by using Tween-80 surfactantand an ultrasonication method. The thermal dissipationefficiency of the PC’s micro-processor using the cool-ing fan and liquid cooling was examined and evaluated.Compared to the cooling fan, the saturation temperatureof the processor using the EG/DW solutions decreasedabout 14 ◦C. By mixing MWCNT-OH (1 g/l of con-centration) into the EG/DW solutions, the saturationtemperature of the CPU decreased 6 ◦C compare to us-ing the EG/DW solution without MWWCNTs-OH. Theexperimental results confirmed the advantage of using aMWCNT-based liquid in thermal dissipation for micro-processors and other high-power electronic devices.

ACKNOWLEDGMENTS

The authors acknowledge the financial support fromthe Vietnam National Foundation for Science and Tech-

nology Development (Project No. NAFOSTED 103.99-2012.35). The authors declare that there is no conflictof interests regarding the publication of this article.

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