Thermal Conductance of Metallic Contacts

A review of theoretical and experimental studies of thermal effects in solid-state lasers is presented, with a special focus on diode-pumped ytterbium-doped materials. A large part of this review provides however general information applicable to any kind of solid-state laser. Our aim here is not to make a list of the techniques that have been used to minimize thermal effects, but instead to give an overview of the theoretical aspects underneath, and give a state-of-the-art of the tools at the disposal of the laser scientist to measure thermal effects. After a presentation of some general properties of Yb-doped materials, we address the issue of evaluating the temperature map in Yb-doped laser crystals, both theoretically and experimentally. This is the first step before studying the complex problem of thermal lensing (part III). We will focus on some newly discussed aspects, like the definition of the thermo-optic coefficient: we will highlight some misleading interpretations of thermal lensing experiments due to the use of the dn/dT parameter in a context where it is not relevant. Part IV will be devoted to a state-of-the-art of experimental techniques used to measure thermal lensing. Eventually, in part V, we will give some concrete examples in Yb-doped materials, where their peculiarities will be pointed out.

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“…[58]. But even for flat and polished surfaces pressed one against another, this relation is far from reality [59].…”

Section: Ii14 Determining the Absolute Temperature: The Boundary Cmentioning

confidence: 99%

On thermal effects in solid-state lasers: The case of ytterbium-doped materials

Chénais

Druon²,

Forget³

et al. 2006

Progress in Quantum Electronics

332

271

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“…Only Jacobs and Starr (16) have reported tests at low contact pressures in a vacuum. Their results are shown in Fig.…”

Section: Literature Surveymentioning

confidence: 97%

Interface Thermal Contact Resistance Problem in Space Vehicles

Fried

Costello

1962

ARS Journal

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This paper defines and analyzes the thermal contact resistance problem as applied to unpressurized satellites and components. Pertinent experimental results are reviewed, and results of experimental work carried out by the authors are presented. A guarded hot plate thermal conductivity apparatus was operated in a chamber held at a pressure of 10 ~4 to 10 ~6 mm Hg absolute to determine the effects of surface finish, flatness, and contact conductance between aluminum-aluminum and magnesium-magnesium plates. Surface finishes from 6 to 65 Min. (rms) and contact pressures up to 35 psi, as well as heat transfer promoting shim materials, were considered. The test apparatus and procedure also are described.T HE PRESENT trend in the design of space vehicles and long life communication satellites is toward higher and higher power density to conserve vehicle size and weight. A great deal of progress has been made in the development of electronic and other equipment and its associated power system. However, with the higher power output, the inevitable inefficiency products in such equipment, which manifest themselves in the form of heat, have to be accepted. Therefore, in order to keep internal vehicle temperatures within acceptable limits, adequate heat flow paths from the heat sources within the vehicle to the vehicle skin, which is the last link with the ultimate heat sink, must be provided.In attaining the high reliability required of long life satellites, vehicle temperature control is one of the most important design problems. This in turn requires a relatively thorough analysis of all heat flow paths, which depends on a knowledge of the thermal contact resistance at relatively low average contact pressures for structural components between the heatsource and the vehicle skin. Furthermore, just to know the contact resistance for bare joints is not sufficient for a reliable design; how to increase or reduce these contact resistances to control the operating temperatures of critical components must also be known.In spite of this need for knowledge of the thermal contact resistance in such heat flow paths--which can consist of several The modes of heat transfer to be considered are: 1) solid conduction through the true contact area; 2) gaseous, molecular, or other conduction through the interstitial fluid or filler; and 3) thermal radiation. The thermal contact conductance is defined aswhere Ti and T 2 are the temperatures of the bounding surfaces of the contact gap (2). Similarly, the contact resistance, as this effect is sometimes called, is T t -T t £lc = T -where R c 1 1/R. + 1/R f + 1/Rr [lb][2] L Numbers in parentheses indicate References at end of paper. Fig. 1 Representative view of a metal to metal contact FEBRUARY 1962 237 Downloaded by UNIVERSITY OF OKLAHOMA on February 5, 2015 | http://arc.aiaa.org |

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“…This is an important practical point as the actual temperature of the sample may be considerably lower than that of the heating element if conduction alone is relied upon for heat transfer (e.g Jacobs and Starr, 1939) and also because evaporation of entrapped water will absorb sample heat.…”

Section: Nitrogen Porosimetrymentioning

confidence: 99%

“…Similarly prepared and also oven dried samples were placed into their glass containers and further dried and outgassed at 150 "C and 6 x millibar for 4 h. The bulb of the glass container was surrounded by a heating element allowing heat to reach the sample by radiation. This is an important practical point as the actual temperature of the sample may be considerably lower than that of the heating element if conduction alone is relied upon for heat transfer (e.g Jacobs and Starr, 1939) and also because evaporation of entrapped water will absorb sample heat.…”

Section: Nitrogen Porosimetrymentioning

confidence: 99%

Wet and Dry Pore Size Distribution in a Kaolinitic Soil Before and After Removal of Iron and Quartz

Homshaw

Cambier

1980

Journal of Soil Science

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A kaolinitic soil was treated chemically to remove iron and quartz. Before and after treatment the properties of the soil were, respectively: iron content, 7 and 1%; quartz content, 21 and 0%: water content at saturation (water/kaolin content, g/g), 0.40 for both, of which 0.34 was in pores for which the Kelvin radius rj, was S 3 5 nm. Porosity and pore size distribution (PSD) up to this pore size were studied using nitrogen sorption, mercury injection, pressure membrane equilibration and low temperature scanning microcalorimetry (DSC). These analyses justified interpretation in terms of kaolinite content alone. The PSD was unaffected by the removal of iron or quartz or the moisture content of this soil.New DSC techniques show that the pore spaces within the treated samples (rj s 35 nm) are largely unconstricted, and thus, an experimental curve relating temperature depression for melting to pore size is possible using only one sample.Introduction PORE sizes and forms, and their variation upon wetting, are useful data to have about porous materials for further understanding of important physical phenomena related to capillary effects (such as the moisture characteristic and the freezing and melting behaviour of water and ice in soils). As most physico-chemical reactions occur at surfaces and within pores of the soil matrix it is also useful to know of the presence of constrictions within a porous region as these may prevent entry of large molecules into a pore space and thus influence the adsorption and diffusion behaviour of substances (e.g. herbicides) throughout the soil profile. Pore size and form are also intimately related to the phenomena of frost heave and frost damage in cold regions (Taber, 1916; Everett, 1961).The porous region within a soil is generally not stable in time, because weathering, compaction, wetting and drying cycles and many other rate-dependent phenomena play a role in modifying soil structure. In this work, we have studied the effect of some of these parameters on porosity and pore size distribution using mercury injection and nitrogen desorption analyses on dry soils, and pressure membrane equilibration and high resolution low temperature differential scanning microcalorimetry (DSC) on water saturated samples of the same soils. These four techniques have been applied to investigate the influence of iron oxides and hydroxides upon the physical properties of kaolinite in one ferralitic soil. We have limited this investigation to the porous region between crystallites in the dry and water saturated states.

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Thermal Conductance of Metallic Contacts

Cited by 51 publications

References 2 publications

On thermal effects in solid-state lasers: The case of ytterbium-doped materials

On thermal effects in solid-state lasers: The case of ytterbium-doped materials

Interface Thermal Contact Resistance Problem in Space Vehicles

Wet and Dry Pore Size Distribution in a Kaolinitic Soil Before and After Removal of Iron and Quartz

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