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Research Papers

An Experimental Study of Heat Pipe Performance Using Binary Mixture Fluids That Exhibit Strong Concentration Marangoni Effects

[+] Author and Article Information
Kenneth M. Armijo, Van P. Carey

 Department of Mechanical Engineering, University of California at Berkeley, Berkeley 6123 Etcheverry Hall, Mailstop 5117, Berkeley, CA 94720-1740

J. Thermal Sci. Eng. Appl 3(3), 031003 (Aug 10, 2011) (7 pages) doi:10.1115/1.4004399 History: Received February 07, 2011; Revised June 09, 2011; Published August 10, 2011; Online August 10, 2011

This paper summarizes the results of an experimental investigation of the performance characteristics of a gravity/capillary driven heat pipe using water/alcohol mixtures as a working fluid. This investigation specifically explored the use of water/alcohol mixtures that exhibit strong concentration-based Marangoni effects. Experiments to determine heat pipe performance were conducted for pure water and water/alcohol solutions with increasing concentrations of alcohol. Initial tests with pure water determined the optimal working fluid charge for the heat pipe; subsequent performance tests over a wide range of heat input levels were then conducted for each working fluid at this optimum value. The results indicate that some mixtures can significantly enhance the heat transfer coefficient and heat flux capability of the heat pipe evaporator. For the best mixture tested, the maximum evaporator heat flux carried by the coolant without dryout was found to be 52% higher than the value for the same heat pipe using pure water as a coolant under comparable conditions. Peak evaporator heat flux values above 100 W/cm2 were achieved with some mixtures. Evaporator and condenser heat transfer coefficient data are presented, and the trends are examined in the context of the expected effect of the Marangoni mechanisms on heat transfer.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Photograph and schematic diagram of experimental apparatus

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Figure 2

Heat pipe multiphase transport schematic, which comprised heat input at the evaporator section and heat extraction at the condenser

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Figure 3

Outer evaporator surface superheat versus evaporator input heat flux for pure water with fill ratios of 35%, 45%, and 70%. The input transport heat flux is based on the heater surface area.

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Figure 4

Finite difference analysis diagram for a three-dimensional half cylindrical channel shape factor

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Figure 5

Experimental data and comprehensive analytical model comparison of evaporator vaporization transport heat flux for pure water with contribution due to the aluminum casing

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Figure 6

Evaporator vaporization transport heat flux experimental data and theoretical model for pure water. The evaporator vaporization heat flux is based on the evaporator passages wetted surface area.

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Figure 7

Heat transfer coefficient comparison between experimental data and theoretical model for evaporator heat transfer coefficient, which comprised contributions due to pool boiling nucleation and liquid water conduction

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Figure 8

Performance experimental results for a liquid charge of 70% and for 2-propanol/water binary mixtures of 0.2 M, 0.05 M, and pure water

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Figure 9

Binary mixture transport heat flux, for a liquid charge of 70% and for 2-propanol/water binary mixtures of 0.2 M and 0.05 M and for pure water. Critical heat flux reached in each case.

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