Control of Thermal Contact Conductance Using Interstitial Materials and Coatings
01 Jan 2014-pp 139-179
TL;DR: In this article, the authors introduce foils, powders, wire screens and epoxies to control the TCC of a solid-to-solid contact area, which is only a small fraction of the apparent area.
Abstract: As noted in Chapter 1, the actual solid-to-solid contact area, in most mechanical joints, is only a small fraction of the apparent area. The voids between the actual contact spots are usually occupied by some conducting substance such as air. Other interstitial materials may be deliberately introduced to control, that is, either to enhance or to lessen, the TCC: examples include foils, powders, wire screens and epoxies. To enhance the conductance the bare metal surfaces may also be coated with metals of higher thermal conductivity by electroplating or vacuum deposition. Greases and other lubricants also provide alternative means of enhancing the TCC.
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TL;DR: In this paper, an experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coatings.
Abstract: An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhances through the use of vapor-deposited metallic coatings
34 citations
TL;DR: In this article, the effect of reducing the amount of thermoelectric (TE) material used (namely by reducing the module thickness) on the electrical output of conventional bismuth telluride TEGs was assessed.
Abstract: Conventional thermoelectric generators (TEGs) used in applications such as exhaust heat recovery are typically limited in terms of power density due to their low efficiency. Additionally, they are generally costly due to the bulk use of rare-earth elements such as tellurium. If less material could be used for the same output, then the power density and the overall cost per kilowatt (kW) of electricity produced could drop significantly, making TEGs a more attractive solution for energy harvesting of waste heat. The present work assesses the effect of reducing the amount of thermoelectric (TE) material used (namely by reducing the module thickness) on the electrical output of conventional bismuth telluride TEGs. Commercial simulation packages (ANSYS CFX and thermal–electric) and bespoke models were used to simulate the TEGs at various degrees of detail. Effects such as variation of the thermal and electrical contact resistance and the component thickness and the effect of using an element supporting matrix (e.g., eggcrate) instead of having air conduction in void areas have been assessed. It was found that indeed it is possible to reduce the use of bulk TE material while retaining power output levels equivalent to thicker modules. However, effects such as thermal contact resistance were found to become increasingly important as the active TE material thickness was decreased.
25 citations
TL;DR: In this article , a new modular gas target suitable for high-order harmonic generation using high average power lasers is presented, which can be used in multiple-cell configurations, allowing to control the cell length and aperture size.
Abstract: We present the design and implementation of a new, modular gas target suitable for high-order harmonic generation using high average power lasers. To ensure thermal stability in this high heat load environment, we implement an appropriate liquid cooling system. The system can be used in multiple-cell configurations, allowing us to control the cell length and aperture size. The cell design was optimized with heat and flow simulations for thermal characteristics, vacuum compatibility, and generation medium properties. Finally, the cell system was experimentally validated by conducting high-order harmonic generation measurements using the 100 kHz high average power HR-1 laser system at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS) facility. Such a robust, versatile, and stackable gas cell arrangement can easily be adapted to different experimental geometries in both table-top laboratory systems and user-oriented facilities, such as ELI ALPS.
1 citations
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TL;DR: In this paper, single-wall carbon nanotubes (SWNTs) were used to augment the thermal transport properties of industrial epoxy composites and showed a 70% increase in thermal conductivity at 40 K, rising to 125% at room temperature; the enhancement due to 1 wt'% loading of vapor grown carbon fibers was three times smaller.
Abstract: Single-wall carbon nanotubes (SWNTs) were used to augment the thermal transport properties of industrial epoxy. Samples loaded with 1 wt % unpurified SWNT material showed a 70% increase in thermal conductivity at 40 K, rising to 125% at room temperature; the enhancement due to 1 wt % loading of vapor grown carbon fibers was three times smaller. Electrical conductivity data showed a percolation threshold between 0.1 and 0.2 wt % SWNT loading. The Vickers hardness rose monotonically with SWNT loading up to a factor of 3.5 at 2 wt %. These results suggest that the thermal and mechanical properties of SWNT-epoxy composites are improved, without the need to chemically functionalize the nanotubes.
1,683 citations
TL;DR: This work discusses sources of uncertainty and proposes a simple analytical model for the SWNT thermal conductivity including length and temperature dependence, which is attributed to second-order three-phonon scattering between two acoustic modes and one optical mode.
Abstract: The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I−V) electrical characteristics over the 300−800 K temperature range, achieved by Joule self-heating. The thermal conductance is approximately 2.4 nW/K, and the thermal conductivity is nearly 3500 Wm-1K-1 at room temperature for a SWNT of length 2.6 μm and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. We discuss sources of uncertainty and propose a simple analytical model for the SWNT thermal conductivity including length and temperature dependence.
1,660 citations
TL;DR: In this paper, single-wall carbon nanotubes (SWNTs) were used to augment the thermal transport properties of industrial epoxy, and the results suggest that the thermal and mechanical properties of SWNT-epoxy composites are improved.
Abstract: Single-wall carbon nanotubes (SWNTs) were used to augment the thermal transport properties of industrial epoxy. Samples loaded with 1 wt% unpurified SWNT material show a 70% increase in thermal conductivity at 40K, rising to 125% at room temperature; the enhancement due to 1 wt% loading of vapor grown carbon fibers is three times smaller. Electrical conductivity data show a percolation threshold between 0.1 and 0.2 wt% SWNT loading. The Vickers hardness rises monotonically with SWNT loading up to a factor of 3.5 at 2 wt%. These results suggest that the thermal and mechanical properties of SWNT-epoxy composites are improved, without the need to chemically functionalize the nanotubes.
1,330 citations
TL;DR: In this paper, the authors consider the resistance to the flow of heat between two thick solid bodies in contact in a vacuum and compare the performance of single idealized contacts with results of recent electrolytic analog tests to predict the conductance of multiple contacts.
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TL;DR: In this article, the authors describe an experimental study of thermal contact conductance enhancement enabled by carbon nanotube (CNT) arrays synthesized directly on silicon wafers using plasma-enhanced chemical vapor deposition.
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