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Research Papers: Micro/Nanoscale Heat Transfer

Transient and Steady-State Experimental Comparison Study of Effective Thermal Conductivity of Al2O3∕Water Nanofluids

[+] Author and Article Information
Calvin H. Li1

Department of Mechanical, Industrial, and Manufacturing Engineering, University of Toledo, Toledo, OH 12180

Wesley Williams, Jacopo Buongiorno

Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Lin-Wen Hu

Nuclear Reactor Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139

G. P. Peterson

Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309-0017bud.peterson@colorado.edu

1

Corresponding author.

J. Heat Transfer 130(4), 042407 (Mar 18, 2008) (7 pages) doi:10.1115/1.2789719 History: Received January 22, 2007; Revised March 05, 2007; Published March 18, 2008

Nanofluids are being studied for their potential to enhance heat transfer, which could have a significant impact on energy generation and storage systems. However, only limited experimental data on metal and metal-oxide based nanofluids, showing enhancement of the thermal conductivity, are currently available. Moreover, the majority of the data currently available have been obtained using transient methods. Some controversy exists as to the validity of the measured enhancement and the possibility that this enhancement may be an artifact of the experimental methodology. In the current investigation, Al2O3∕water nanofluids with normal diameters of 47nm at different volume fractions (0.5%, 2%, 4%, and 6%) have been investigated, using two different methodologies: a transient hot-wire method and a steady-state cut-bar method. The comparison of the measured data obtained using these two different experimental systems at room temperature was conducted and the experimental data at higher temperatures were obtained with steady-state cut-bar method and compared with previously reported data obtained using a transient hot-wire method. The arguments that the methodology is the cause of the observed enhancement of nanofluids effective thermal conductivity are evaluated and resolved. It is clear from the results that at room temperature, both the steady-state cut-bar and transient hot-wire methods result in nearly identical values for the effective thermal conductivity of the nanofluids tested, while at higher temperatures, the onset of natural convection results in larger measured effective thermal conductivities for the hot-wire method than those obtained using the steady-state cut-bar method. The experimental data at room temperature were also compared with previously reported data at room temperature and current available theoretical models, and the deviations of experimental data from the predicted values are presented and discussed.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Steady-state cut-bar facility; (1) stainless steel bell cover; (2) aluminum plain base stage; (3) sustaining rig; (4) rubber o-ring; (5) screw guide; (6) band heater; (7) upper heating copper bar; (8) sample charge tube; (9) cell rubber o-ring; (10) lower cooling copper bar; (11) coolant circulation exchanger; (12) coolant circulation ducts (thermocouples in copper bars and distribution of thermocouples are shown in Fig. 3)

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Figure 2

The distribution of thermocouples in the upper and lower copper bars. Thermocouples 1, 2, 3, 4, and 6 reach the centerline of the upper copper bar (the heating side); Thermocouples 9, 7, 8, 5, and 18 reach the center line of the lower copper bar (the cooling side); Thermocouples 12, 17, 15, and 13, and 10, 16, 15 are located radially halfway between the centerline and the outer surface of the copper bar, respectively (17).

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Figure 3

Diagrams of sample cell and the heat flux (17)

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Figure 4

Results of the tests facility calibration for distilled water and ethylene glycol as a function of temperature (17)

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Figure 5

The steady-state cut-bar method experimental data of DI water (the square represents the first test data set, the diamond the second test data, and the line is the tablular value (20))

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Figure 6

Schematic of transient hot-wire test setup (22)

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Figure 7

Resistance-temperature relationship for the platinum wire (22)

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Figure 8

Measurements of thermal conductivity of water and ethylene glycol (22)

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Figure 9

Measurements of thermal conductivity of water at different temperatures, compared to the tabulated values (NIST) (22)

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Figure 10

The comparison of the absolute values measured by the transient method and steady-state method

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Figure 11

The comparison of the normalized enhancement measured by the transient method and steady-state method

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Figure 12

The comparison of the normalized enhancement measured by the transient method and steady-state method, and other available experimental data and theoretical predictions

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Figure 13

The comparison of thermal conductivity enhancement of current data and previous report on 47nm diameter nanofluids (21)

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Figure 14

Comparison between the measurements and numerical simulations for water at 25°C and 50°C(33)

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