Natural convection heat transfer on surfaces of copper micro-wires

Guan, Ning; Liu, Zhigang; Zhang, Chengwu; Jiang, Guilin

doi:10.1007/s00231-013-1240-x

Cited by 15 publications

(13 citation statements)

References 13 publications

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“…It is because the heat convection behaves more like conduction effect at micro/ ffiffiffi ffi D p Þ 2 for 10 lm < D < 10m, 25 which has been widely adopted to analyze the thermal management problems involving microscale heat convection, 26,27 gives a value of 274 W/m 2 K. Considering that the surface microstructure of the sample can greatly improve the total surface area, our result of $1100 W/m 2 K is comparable with the predicted value. Similar results have been obtained in previous studies: the convection coefficient was measured as 400-500 W/m 2 K for copper microwire (39.9 lm) 28 and $400 W/m 2 K for platinum microwire (32.6 lm). 29 The ultrahigh value of h indicates the nonnegligible energy dissipation through heat convection, which can actually be estimated according to the mapped temperature profile and the fitted h. For example, when the heating power is 97 mW, the heat convection can be calculated as Q air ¼ Ð pDhðT À T 0 Þdx ¼ 59:4 mW, which is about 60% of the total energy.…”

supporting

confidence: 91%

“…The temperature dependence of h comes from two factors: one is the direct temperature effect, reflecting the physical property change of the air and fiber, e.g., thermal diffusivity and viscosity of air; and the other one is the indirect temperature factor, i.e., thermal expansion effect and matrix melting during the heating, which change the inner microstructure. The direct temperature and diameter dependence of convection coefficient for metal microwires have been studied by Guan et al 28 Using their experimental and theoretical data, the relationship between diameter and h can be approximately linearly fitted as h ¼ À3.55 Â 10 À6 D þ 575.32, where D is diameter, and the relationship between temperature and h can be fitted as h ¼ 1.496 T À 12.237, T is the absolute temperature. The direct effects of temperature and diameter change on the heat convection coefficient are listed in Table I.…”

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confidence: 99%

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Parallel measurement of conductive and convective thermal transport of micro/nanowires based on Raman mapping

Wang

et al. 2015

Applied Physics Letters

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Heat conduction and convection are coupled effects in thermal transport of low-dimensional materials especially at micro/nanoscale. However, the parallel measurement is a challenge due to the limitation of characterization pathways. In this work, we report a method to study conductive and convective thermal transport of micro/nanowires simultaneously by using steady-state Joule-heating and Raman mapping. To examine this method, the carbon nanotubes (CNTs) fiber (36 μm in diameter) is characterized and its temperature dependence of thermal properties including thermal conductivity and convection coefficient in ambient air is studied. Preliminary results show that thermal conductivity of the CNTs fiber increases from 26 W/m K to 34 W/m K and convection coefficient decreases from 1143 W/m2 K to 1039 W/m2 K with temperature ranging from 312 to 444 K. The convective heat dissipation to the air could be as high as 60% of the total Joule heating power. Uncertainty analysis is performed to reveal that fitting errors can be further reduced by increasing sampling points along the fiber. This method features a fast/convenient way for parallel measurement of both heat conduction and convection of micro/nanowires which is beneficial to comprehensively understanding the coupled effect of micro/nanoscale heat conduction and convection.

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confidence: 91%

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confidence: 99%

Parallel measurement of conductive and convective thermal transport of micro/nanowires based on Raman mapping

Wang

et al. 2015

Applied Physics Letters

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“…A similar experimental convection coefficient has been obtained for natural convection from copper microwires using both air and water as the ambient fluid [49].…”

Section: Microwire Convection Coefficientsupporting

confidence: 67%

“…Further explanations of the enhanced heat transfer suggest that the increased surface area to volume allow for much larger heat conduction with the ambient fluid [48]. It should also be noted that the thermal boundary layer created by heat transfer from micro-structures is thin, which leads to better heat transfer [49]. This chapter examines the development of a natural convection heat sink, which uses micro-wires as its extended surface.…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric System Modeling and Design

Gamarachchi¹

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allowing me to do research at the Advanced Energy Lab, while providing me great insight in to my research. I would like to thank my lab colleagues Joey Richardson, Nick Kempf and Tony Varghese, without whom this work would have been difficult to complete. I would also like to thank my former lab colleague Luke Schoensee for his help in this work. I would also like to thank the committee members Dr. John Gardner and Dr. Inanc Senocak. Finally, I would like to acknowledge my parents Asoka and Bandula, for all their support throughout my life. vi ABSTRACT Thermoelectric generators (TEGs) convert heat to electricity by way of the Seebeck effect. TEGs have no moving parts and are environmentally friendly and can be implemented with systems to recover waste heat. This work examines complete thermoelectric systems, which include the (TEG) and heat exchangers or heat sinks attached to the hot and cold sides of the TEG to maintain the required temperature difference across the TEG. A 1-D steady state model is developed to predict the performance of a TEG given the required temperatures and device dimensions. The model is first validated using a 3-D model and then is used to examine methods to improve the TEG performance. A numerical model is developed to predict the thermal performance of heat exchangers to be used in combination with the TEG model. The combined thermoelectric generatorheat exchanger model, is compared with a 3-D model and then used to predict the performance of a TEGheat exchanger system used to recover waste heat from a diesel engine. Next natural convection heat sinks are modeled and studied to be implemented with the TEG. A model is developed to predict the performance of a system applied for power harvesting in a nuclear power plant. The model is also used to design a system to recover waste heat from the human body. Finally, a novel natural convection heat sink is suggested, where microwires act as the extended surface for the heat sink. The microwire heat sink is modeled accounting for the relevant thermal physics. The microwire heat sink is used in combination with the TEG model to predict the performance of a system used to recover waste body heat. vii TABLE OF CONTENTS

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“…It can be explored from two inspects. The first is the relative thermal boundary layer thickness to the cylinder diameter [19]. The ratio of the thermal boundary layer thickness t to the cylinder radius d/2 is decreased with rise in cylinder diameter, which is about 19.9 (for diameter of 0.1mm) , 2.08 (for diameter of 1mm) and 0.268 (for diameter of 10mm), respectively.…”

Section: Resultsmentioning

confidence: 99%

Laminar Natural Convection Heat Transfer Characteristics of Molten Salt Around Horizontal Cylinder

et al. 2015

Energy Procedia

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In order to obtain the laminar natural convection heat transfer mechanism of molten salt, the natural convection heat transfer of multi-component molten salts around a cylinder with different diameters was studied by simulation. The result showed that the natural convective heat transfer of molten salt in the Rayleigh number range of 1.57 10 -2 -2.03 10 6 cound be predicted by Fand's correlation that took the viscous dissipation into consideration, in addition to Prandtl and Rayleigh numbers. With the increasing in Rayleigh number, the effect of viscous dissipation decreased, so the other correlations that neglected the effect of viscous dissipation cound also predict the natural convection of molten salt well. Those results cound be a foundation for predicting the natural convection heat transfer of molten salt.

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Natural convection heat transfer on surfaces of copper micro-wires

Cited by 15 publications

References 13 publications

Parallel measurement of conductive and convective thermal transport of micro/nanowires based on Raman mapping

Parallel measurement of conductive and convective thermal transport of micro/nanowires based on Raman mapping

Thermoelectric System Modeling and Design

Laminar Natural Convection Heat Transfer Characteristics of Molten Salt Around Horizontal Cylinder

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