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TECHNICAL PAPERS: Micro/Nanoscale Heat Transfer

# Experimental Model of Temperature-Driven Nanofluid

[+] Author and Article Information
A. G. Nnanna

Department of Mechanical Engineering, Micro- and Nano-scale Heat Transfer Laboratory, Purdue University Calumet, Hammond, IN 46323-2094nnanna@calumet.purdue.edu

J. Heat Transfer 129(6), 697-704 (Sep 12, 2006) (8 pages) doi:10.1115/1.2717239 History: Received September 06, 2005; Revised September 12, 2006

## Abstract

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm $Al2O3$$H2O$ nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, $0.2⩽ϕ⩽2%$ the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction $ϕ>2%$, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for $Nuϕ$ as a function of $ϕ$ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

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## Figures

Figure 7

Effect of volume fraction on thermophysical properties, Q=9.16W

Figure 8

Effect of volume fraction on Rayleigh number

Figure 9

Nusselt number as a function of Rayleigh number using de-ionized water. A comparison of the Nu obtained in this study with correlations for conventional fluid.

Figure 10

Nusselt number as a function of modified Rayleigh number

Figure 3

Temperature as a function of time at Q=20.91W for volume fraction, ϕ=0 and 0.0021

Figure 4

Temperature as a function of time at Q=20.91W for volume fraction, ϕ=0 and 0.027

Figure 5

Variation of dimensionless temperature with dimensionless distance across the cavity for Q=9.16W

Figure 6

Variation of dimensionless temperature with dimensionless distance across the cavity for Q=20.91W

Figure 11

Variation of Nusselt number with volume fraction

Figure 1

Experimental setup. The numbers refer to: (1) insulation, (2) resistive electrical heater, (3) heated wall, (4) nanofluid medium, (5) thermocouple wire, (6) the black dots indicate the thermocouple locations, (7) unheated wall, and (8) spout; L=35mm, H=215mm.

Figure 2

Temperature as a function of time at Q=14.3W for volume fraction, ϕ=0 and 0.0021

Figure 12

Nuϕ as a function of parameter ϕRae−mϕ

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