Heat transfer coefficient of porous copper with homogeneous and hybrid structures in active cooling
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Yuyuan Zhaoa) School of Engineering, University of Liverpool, Liverpool L69 3GH, United Kingdom (Received 7 February 2013; accepted 14 June 2013)
Heat transfer coefficients of porous copper samples with single- and double-layer structures, fabricated by the lost carbonate sintering process, were measured under forced convection conditions using water as the coolant. Compared with the empty channel, introducing a porous copper sample enhanced the heat transfer coefficient 5–8 times. The porous copper samples with double layers of porosities of 60% and 80% often had lower heat transfer coefficients than their single layer counterparts with the same overall porosities because the coolant flowed predominantly through the high-porosity layer. For the same double-layer structure, the order of the double layer had a large effect on the heat transfer coefficient. Placing the high-porosity layer next to the heat source was more efficient than the other way around. The predictions of a segment model developed for the heat transfer coefficient of multilayer structures agreed well with the experimental results.
I. INTRODUCTION
Thermal management is a significant issue for many devices or systems because of the increasing volumetric power density they experience. The conventional passive cooling techniques are often inadequate for high rates of heat dissipation, and hence, active cooling techniques need to be used. Open-cell porous metals have excellent thermal conductivity, large specific surface area, and good permeability,1–3 making them good candidates for use in active cooling devices, such as heat exchangers and heat sinks. The heat transfer performance of a number of commercial porous metals has been studied. Jiang et al.4 reported that particle-sintered bronze samples with porosities from 40 to 46% enhanced the heat transfer performance up to 15 times for water and up to 30 times for air in comparison with an empty channel. Porous copper samples with high porosities from 88 to 94% enhanced the heat transfer performance by about 17 times in comparison with an empty channel.5,6 Boomsma et al.7 conducted an experimental study on 6101-T6 aluminum foams with porosities from 60.8 to 88.2% and found that the thermal resistance of the foams was up to three times lower than that of commercially available heat exchangers under the same pumping power. These studies were conducted either on sintered metals with porosities lower than 50% or on metal foams manufactured by the investment casting method, which a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.190 J. Mater. Res., Vol. 28, No. 17, Sep 14, 2013
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have high porosities between 87% and 97%. The highporosity foams were sometimes compressed to reduce porosity.7 However, very little research has been conducted on the porous metals manufactured by the space-holder methods, which typically have porosities in the range of 50–85%. In addition, all these studies were conducted on porous meta
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