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Research Papers: Micro/Nanoscale Heat Transfer

# Convective Heat Transfer for Water-Based Alumina Nanofluids in a Single 1.02-mm Tube

[+] Author and Article Information
W. Y. Lai, S. Vinod

Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85281

P. E. Phelan

Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85281phelan@asu.edu

Ravi Prasher

Intel Corporation, CH5-517, 5000 W. Chandler Blvd., Chandler, AZ 85226ravi.s.prasher@intel.com

J. Heat Transfer 131(11), 112401 (Aug 19, 2009) (9 pages) doi:10.1115/1.3133886 History: Received January 03, 2008; Revised April 16, 2009; Published August 19, 2009

## Abstract

Nanofluids are colloidal solutions, which contain a small volume fraction of suspended submicron particles or fibers in heat transfer liquids such as water or glycol mixtures. Compared with the base fluid, numerous experiments have generally indicated an increase in effective thermal conductivity and a strong temperature dependence of the static effective thermal conductivity. However, in practical applications, a heat conduction mechanism may not be sufficient for cooling high heat dissipation devices such as microelectronics or powerful optical equipment. Thus, thermal performance under convective heat transfer conditions becomes of primary interest. We report here the heat transfer coefficient $h$ in both developing and fully developed regions by using water-based alumina nanofluids. Our experimental test section consists of a single 1.02-mm diameter stainless steel tube, which is electrically heated to provide a constant wall heat flux. Both pressure drop and temperature differences are measured, but mostly here we report our $h$ measurements under laminar flow conditions. An extensive characterization of the nanofluid samples, including $pH$, electrical conductivity, particle sizing, and zeta potential, is also documented. The measured $h$ values for nanofluids are generally higher than those for pure water. In the developing region, this can be at least partially explained by Pr number effects.

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## Figures

Figure 13

Heat transfer coefficient of water-based 20-nm Al2O3 nanofluids in the fully developed region

Figure 12

(a) Local heat transfer coefficients in the thermal developing region for different volume fractions at 1 ml/min volume flow rate, (b) local heat transfer coefficients in the thermal developing region for different volume fractions at 5 ml/min volume flow rate, and (c) local heat transfer coefficients in the thermal developing region for different volume fractions at 9 ml/min volume flow rate

Figure 11

Comparison between measured and calculated (34) heat transfer coefficients for developing flow, for pure DI water (no nanoparticles)

Figure 10

Pressure drop across the test section using pure DI water (no nanoparticles) as the working fluid

Figure 4

Example of a good power spectrum during zeta potential measurements for determining nanofluid concentrations for DLS measurement. The curve having a peak at 0 Hz is the reference spectrum while the other curve is the sample spectrum.

Figure 3

SEM image for 20-nm dry Al2O3 nanopowder

Figure 2

Sketch of heater wire and thermocouple locations

Figure 1

Experimental apparatus sketch

Figure 9

(a) Diluted aggregate mean diameters and vol % versus original nanoparticle volume fraction 60 min after sonication, (b) diluted aggregate mean diameters and vol % versus original nanoparticle volume fraction 70 min after sonication, and (c) diluted aggregate mean diameters and vol % versus original nanoparticle volume fraction 80 min after sonication

Figure 8

An example of a particle size distribution measured with the Nicomp 380/ZLS system. Screen shot is the particle sizing result of diluted 20-nm γ-Al2O3 nanoparticles in DI water taken 70 min after sonication. The distribution is generated by the Nicomp volume-weighted model.

Figure 7

Zeta potential versus time after sonication for diluted Al2O3-DI water nanofluids at different original (undiluted) volume fractions

Figure 6

pH and σ values versus volume fraction of the undiluted Al2O3-DI water nanofluids

Figure 5

Cross-sectional view of test tube (not drawn to scale)

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