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Research Papers: Electronic Cooling

# On the Cooling of Electronics With Nanofluids

[+] Author and Article Information
W. Escher

IBM Research GmbH, Zurich Research Laboratory, 8803 Rüschlikon, Switzerland; Department of Mechanical and Process Engineering, Laboratory of Thermodynamics in Emerging Technologies, ETH Zurich, 8092 Zurich, Switzerland

T. Brunschwiler, B. Michel

IBM Research GmbH, Zurich Research Laboratory, 8803 Rüschlikon, Switzerland

N. Shalkevich

Laboratoire de chimie physique des surfaces, Institut de Physique, Universite de Neuchâtel, Rue Emile-Argand 11, 2009-Neuchatel, Switzerland

A. Shalkevich

Adolphe Merkle Institute, Université de Fribourg, P.O. Box 209 11, CH-1723 Marly 1, Switzerland

T. Burgi

Laboratoire de chimie physique des surfaces, Institut de Physique, Universite de Neuchâtel, Rue Emile-Argand 11, 2009-Neuchatel, Switzerland; Physikalisch-Chemisches Institut, Ruprecht-Karls-Universitat Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany

D. Poulikakos1

Department of Mechanical and Process Engineering, Laboratory of Thermodynamics in Emerging Technologies, ETH Zurich, 8092 Zurich, Switzerlanddimos.poulikakos@ethz.ch

1

Corresponding author.

J. Heat Transfer 133(5), 051401 (Feb 04, 2011) (11 pages) doi:10.1115/1.4003283 History: Received August 31, 2009; Revised December 02, 2010; Published February 04, 2011; Online February 04, 2011

## Abstract

Nanofluids have been proposed to improve the performance of microchannel heat sinks. In this paper, we present a systematic characterization of aqueous silica nanoparticle suspensions with concentrations up to $31 vol %$. We determined the particle morphology by transmission electron microscope imaging and its dispersion status by dynamic light scattering measurements. The thermophysical properties of the fluids, namely, their specific heat, density, thermal conductivity, and dynamic viscosity were experimentally measured. We fabricated microchannel heat sinks with three different channel widths and characterized their thermal performance as a function of volumetric flow rate for silica nanofluids at concentrations by volume of 0%, 5%, 16%, and 31%. The Nusselt number was extracted from the experimental results and compared with the theoretical predictions considering the change of fluids bulk properties. We demonstrated a deviation of less than 10% between the experiments and the predictions. Hence, standard correlations can be used to estimate the convective heat transfer of nanofluids. In addition, we applied a one-dimensional model of the heat sink, validated by the experiments. We predicted the potential of nanofluids to increase the performance of microchannel heat sinks. To this end, we varied the individual thermophysical properties of the coolant and studied their impact on the heat sink performance. We demonstrated that the relative thermal conductivity enhancement must be larger than the relative viscosity increase in order to gain a sizeable performance benefit. Furthermore, we showed that it would be preferable to increase the volumetric heat capacity of the fluid instead of increasing its thermal conductivity.

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Copyright © 2011 by American Society of Mechanical Engineers
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## Figures

Figure 5

(a) Experimentally determined pressure drop (marker) across the three different test-vehicles operated with water. Lines indicate the theoretical expected pressure drop (cf. Eq. 1), (b) comparison of average effective viscosity, fitted to the pressure drop volumetric flow rate data, to measured viscosity by rheology at a shear rate of 5740 s−1 and T=20°C and T=40°C as a function of particle fraction.

Figure 6

(a) Total thermal resistance and (b) Nusselt number as a function of volumetric flow rate for the three different test-vehicles and different particle concentrations (markers indicate experimental results and lines the theoretical predictions)

Figure 7

Comparison of measured and predicted Nusselt number of all experimentally obtained data points (also shown in Fig. 6)

Figure 8

Impact of relative change of (a) thermal conductivity, (b) dynamic viscosity, (c) specific heat, and (d) density on the total thermal resistance of the heat sink, the optimum channel width and the volumetric flow rate for a constant pumping power of 1 W

Figure 9

Contour plot of COP at the respective design optimum for different combinations of relative changes in thermal conductivity and dynamic viscosity for a constant pumping power of 1 W

Figure 1

Schematic of experimental setup, (a) side view of a test-vehicle, (b) isometric view of a section of a parallel microchannel array, and (c) closed fluid loop

Figure 2

(a) Measured intensity correlation functions for silica suspensions at different particle concentrations as a function of decay time with incorporated TEM image of silica nanoparticles and (b) particle size distributions of silica suspensions at different particle concentrations

Figure 3

Relative change of thermal properties, namely, thermal conductivity, density, and specific heat as a function of particle concentration; dots indicate experimental data, and lines indicate theoretical predictions

Figure 4

Dynamic viscosity as a function of shear rate for different particle concentrations at 20°C and 40°C

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