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MAKING LIGHTWEIGHT DEVICES Scientists from the National University of Science and Technology MISIS, Russia, in collaboration with LG Electronics, South Korea, created new high heat conductivity magnesium alloys that differ [...]

The work deals with evaluation and simulation of the thermal discrete element method (TDEM) for particle-particle collision and thermal conduction in a packed bed. The effects of different granular properties, such as particle size, stiffness factor or compression degree, thermal diffusivity, void fraction or concentrations, and packing states, on the thermal conduction and insulation characteristics of granular assembly are discussed. The thermal conductivity and diffusion still play dominant roles in the overall thermal conduction and insulation of the granular bed. However, it is also indicated that increasing compression degree, reducing particle size and void concentration will increase the thermal conduction throughout the granular materials, and vice versa. Key words: thermal discrete element method, heat conduction, thermal insulation, granular material, packed bed, model evaluation. Nous presentons une evaluation et une simulation par la methode des elements discrets thermiques (TDEM) pour les collisions particule-particule et la conduction thermique dans un garnissage dense. Nous analysons les effets de differentes proprietes granulaires, comme la grosseur des particules, le facteur de rigidite ou degre de compression, la diffusivite thermique, la fraction de vide ou concentration et les etats de tassement, sur la conduction thermique et les caracteristiques isolantes des assemblages granulaires. La conductivite thermique et la diffusion continuent de jouer les roles dominants dans la conduction thermique et l'isolation du garnissage granulaire. Cependant, il apparait aussi qu'une augmentation de la compression, qui reduit la grosseur des particules et diminue la fraction de vide, augmentera la conduction thermique a travers tout le milieu granulaire et vice-versa. [Traduit par la Redaction] Mots-cles : methode des elements discrets thermiques, conduction de chaleur, isolation thermique, materiau granulaire, garnissage dense, evaluation de modele., 1. Introduction Granular materials are widely utilized in chemical reactors, pharmaceutical manufacturing devices, food production technologies, nuclear reactors, and powder metallurgy industries [1-4], which are always accompanied by the processes [...]

In 1756, Leidenfrost (1) observed that water drops skittered on a sufficiently hot skillet, owing to levitation by an evaporative vapour film. Such films are stable only when the hot [...]

The wave nature of the heating model is considered, incorporating the Cattaneo equation with the presence of a volumetric heat source. The volumetric heat generation resembles the step input laser short-pulse intensity. The governing of the heat equation is solved analytically using the Laplace transformation method. The stress field generated due to thermal contraction and expansion of the substrate material is formulated and the closed-form solution is presented. It is found that the wave nature of the heating is dominant during the period of the irradiated short-pulse; however, in the late cooling period, the wave nature of heating is replaced by diffusional heat conduction, governed by Fourier's law. The stress field during the heating cycle is compressive and becomes tensile in the cooling cycle. PACS No: 44.10.+i Nous etudions la nature ondulatoire du modele de chauffage incorporant l'equation de Cattaneo, avec la presence de la source volumique de chaleur. La generation volumique de chaleur ressemble a intensite d'un laser a impulsion courte avec signal d'entree en echelon. Nous solutionnons analytiquement l'equation gouvernante de la chaleur en utilisant la methode de la transformation de Laplace. Le champ de contrainte genere par la contraction et l'expansion thermique du materiel du substrat est mis en formule et nous en presentons une solution analytique. Nous trouvons que le caractere ondulatoire du chauffage est dominant pendant la periode d' irradiation en impulsion courte, mais la conduction de chaleur de Fourier par diffusion domine la periode du refroidissement. Le champ de contrainte est en compression pendant le chauffage, mais en etirement pendant le refroidissement. [Traduit par la Redaction], 1. Introduction In short-pulse laser heating of metal surfaces, the absorption depth is small and the heating time is short. This results in a heat wave propagatiing at finite speed [...]

This paper presents an experimental study on thermal radiation and the thermal conductivity of rock-fill materials using a 1 m x 1 m x 1 m heat transfer cell. Testing temperatures are applied by temperature-controlled fluid circulation at the top and bottom of the sample. Heat flux and temperature profiles are measured to establish the effective thermal conductivity [λ.sub.e], which includes contributions from both conduction and radiation heat transfer mechanisms. The materials studied had an equivalent particle size ([d.sub.10]) ranging from 90 to 100 mm and porosity (n) ranging from 0.37 to 0.41. The experimental results showed that thermal radiation greatly affects the effective thermal conductivity of materials with [λ.sub.e] values ranging from 0.71 to 1.02 W x [m.sup.-1] x [K.sup.-1], compared with a typical value of 0.36 W x [m.sup.-1] x [K.sup.-1] for conduction alone. As expected, the effective thermal conductivity increased with particle size. An effective thermal conductivity model has been proposed, and predictions have been successfully compared with the experimental results. Radiation heat transfer becomes significant for [d.sub.10] higher than 10 mm and predominant at values higher than 90 mm. The results of the study also suggest that the cooling potential of convection embankments used to preserve permafrost conditions may not be as efficient as expected because of ignored radiation effects. Key words: radiation, effective thermal conductivity, particle size, porosity, rock-fill materials. Cet article presente une etude experimentale sur la radiation et la conductivite thermique de materiaux de remblai rocheux realisee a l'aide d'une cellule de transfert de chaleur de 1 m x 1 m x 1 m. Les temperatures sont appliquees sur les echantillons par la circulation d'un fluide a temperature controlee au haut et au bas de l'echantillon. Les flux de chaleur et les profils de temperature sont mesures afin d'etablir la conductivite thermique effective [λ.sub.e], qui comprend les deux mecanismes de transfert de chaleur : la conduction et la radiation. Le diametre equivalent des particules ([d.sub.10]) des materiaux etudies varie entre 90 mm et 100 mm, et ils ont une porosite (n) variant de 0,37 a 0,41. Les resultats montrent que la radiation affecte de facon importante la conductivite thermique effective, avec des valeurs de [λ.sub.e] variant de 0,71 a 1,02 W x [m.sup.-1] x [K.sup.-1], comparativement a une valeur typique de 0,36 W x [m.sup.-1] x [K.sup.-1] lorsque seulement la conduction est consideree. La conductivite thermique effective augmente avec la taille des particules. Un modele de conductivite thermique effective est propose, et les predictions correspondent bien aux resultats experimentaux. Le transfert de chaleur par radiation devient significatif lorsque [d.sub.10] est superieur a 10 mm et devient predominant lorsque [d.sub.10] est superieur a 90 mm. Les resultats de cette etude suggerent aussi que [λ.sub.e] potentiel de refroidissement des digues de convection utilisees pour preserver les conditions du pergelisol n'est possiblement pas aussi efficace que prevu puisque les effets de la radiation sont ignores. Mots-cles : radiation, conductivite thermale effective, granulometrie, porosite, enrochement. [Traduit par la Redaction], Introduction The ground thermal regime is generally governed by conduction heat transfer (Johansen 1975). However, in rock-fill embankments made of gravel, cobbles, and boulders, other heat transfer processes may be [...]

The polyoxymethylene (POM) composites with different copper contents were prepared by extrusion. The thermal conductivity and tribological behavior of POM-Cu composites with various contents of copper particles were investigated by a hot disk thermal analyzer and an M-2000 friction and abrasion testing machine, respectively. The effect of copper particles on the thermal conductivity of POM composites was negligible when copper content was below 10 wt %. As the copper content increased, the thermal conductivity of composites increased and reached 0.477 W [m.sup.-1] [K.sup.-1] for POM-25 wt % Cu composite, which increased by 35.9% compared with that of unfilled POM. The incorporation of copper particles into POM reduced the friction coefficient of POM composites. The wear mechanisms of POM-Cu composites were adhesive and abrasive wear. POLYM. ENG. SCI., 50:2153-2159, 2010. [C] 2010 Society of Plastics Engineers, INTRODUCTION Polyoxymethylene (POM) as a good wear resistant material with excellent friction and wear properties, high strength, and good chemical stability is widely employed to replace the traditional metals and [...]

The thermal conductivity of a metallic test piece is one of the principal parameters that influence the temperature buildup at tribocontacts and this normally plays an important role in the unlubricated dry sliding wear of metallic materials. It is, however, not clear whether thermal conductivity is an equally important parameter in the case of wear of metals at cryogenic temperatures, in particular, at liquid nitrogen temperature ([LN.sub.2]) of -196[degrees]C. In order to assess the influence of such a physical property of selected nonferrous metals on their tribological behavior in the [LN.sub.2] environment, we have studied the friction and wear properties of high purity copper (Cu) and titanium (Ti) against the bearing grade steel. These two materials have been processed to produce samples of comparable hardness that have widely different thermal conductivities at room temperature and at test temperature. Wear tests were conducted at three different sliding speeds (0.89 m/s, 1.11 m/s, and 1.34 m/s) under 10 N load, and the friction and wear data were compared. Ti exhibited an order of magnitude higher wear rate (~[10.sup.-3] [mm.sup.3]/N m) as compared with Cu in identical test conditions. While evidences of abrasive wear and adhesive wear, without any oxidative wear, were found in worn Cu surfaces, worn Ti surfaces showed evidences of significant oxidative wear and mechanical damage of tribolayers. Higher wear rate in Ti appeared to be a result of oxidative wear of Ti, which seemed to be driven by the depletion of [LN.sub.2] blanket at the tribocontacts under the influence of high flash temperature (14-76 [degrees]C) as compared with the boiling temperature of [LN.sub.2] (-196[degrees]C). These results demonstrate that the materials with similar hardness subjected to identical [LN.sub.2] wear test conditions can have significantly different wear rates because of the difference in the flash temperatures, which depend on the thermal conductivity of the test pieces. [DOI: 10.1115/1.4002503] Keywords: cryogenic wear, titanium, copper, flash temperature

The dual-probe heat-pulse (DPHP) method is useful for measuring soil thermal properties; however, the probes of a DPHP sensor can deflect when inserted into the soil. Theoretical analysis has shown that measurements of thermal conductivity (h) should be unaffected by deflection-induced changes in probe spacing. To verify this result, the conductivities of water, dry sand, and saturated sand were measured using DPHP sensors with probes subject to inward deflection, no deflection, and outward deflection. No error in X was detected when probes were deflected inward by an amount that caused a 14% reduction in probe spacing. Outward deflection (15% increase in spacing) caused error in X estimates, but the errors were small ([less than or equal to] 0.04 W [m.sup.-1][ K.sup.-1]) and likely to be of little consequence in most applications. We conclude that estimates of X obtained with the DPHP method are largely unaffected by changes in probe spacing caused by deflection. doi: 10.2136/sssaj2010.0016N

We examine the effect of photodarkening-induced pump light absorption on Yb-doped fiber thermal loading. In these experiments, the fiber is cladding pumped at 915 nm, air cooled by natural convection, and monitored with a midinfrared thermal camera. The fiber temperature is found to correlate with progressive photodarkening. The maximum observed fiber temperature was 120 [degrees]C, recorded at a pump power of 10.5 W. The observed increase in fiber temperature can be explained by a model that takes into account the combined effects of the Yb-silica quantum defect, the temperature dependence of the Yb-absorption cross section, and photodarkening-induced loss at 915 nm. We hypothesize that the latter effect results in the progressive activation of temperature-dependent photochemical processes (e.g., bleaching) and is ah important consideration with regard to the accurate modeling of Yb-doped fiber photodarkening kinetics. OCIS codes: 140.3510, 160.5690, 140.6810, 140.3615.

Problem statement: Jet impingement quenching has a very effective and large cooling potential and is a very effective means of cooling for many applications. It gives rise to heterogeneous and/or homogeneous nucleation of bubbles, which is yet to be explored. Approach: Analytically investigate the phenomenon that happened during a brief contact of a water jet impinging on a hot surface. In particular, explore the possibility of homogeneous bubble formation during jet impingement quenching. A simple semi-infinite conduction heat transfer model was considered in this case and the heat transfer analysis had been carried out for two heating cases of the impinging liquid, namely with (i) Prescribed Surface Temperature (PST-case) and (ii) Time-dependent Surface Temperature (TST-case). For each of above cases, explicit equations for temperature distribution within liquid, average liquid temperature, average internal energy and surface heat flux had been derived as a function of liquid depth and contact time. These equations were solved numerically and their outcomes were discussed. Furthermore, a critical contact time, t * at which the temperature on the opposite side of the liquid depth reached saturation temperature, [T.sub.sat] was determined. The heat flux ([q.sub.s]) at time t * was also determined and compared with the thermodynamic limit of the maximum heat flux ([q.sub.max]) which decided the validity of this analytical investigation. Results: During jet impingement quenching of hot surfaces near/above the thermodynamic limiting temperature, water stored enough energy for a contact period of 5-10 [micro]s depending on the type of boundary conditions considered for triggering homogeneous bubble nucleation. A contact time of 4[micro]s was required to trigger homogeneous bubble nucleation for the conditions where the impinging surface had a fixed temperature throughout the cooling process. A contact time of 6.5 [micro]s was required to initiate homogeneous bubble nucleation for the conditions where the impinging surface temperature dropped at a rate depending on time. For both cases, the average internal energy of the liquid exceeded the minimum energy necessary for bubble formation. Moreover, the average heat flux, q never exceeded the thermodynamic limit of the maximum heat flux, [q.sub.max]. Conclusion: When water was heated above the thermodynamic limit of superheat during jet impingement, there is always a chance of homogeneous bubble nucleation. Key words: Homogeneous nucleation of bubbles, heat conduction, jet impingement quenching, semiinfinite solid, thermodynamic limit of liquid superheat, INTRODUCTION Jet impingement quenching has a very effective and large cooling potential and is a very effective means of cooling for many applications. It is very important in Loss Of [...]

Thermal conductivity measurement is a quick and easy test for compacted soils. This study presents the results of thermal conductivity testing on silt compacted under standard and modified Proctor efforts. A comparison of moisture content measurements from both lab oven and field oven is also presented and discussed. Measured thermal conductivity was correlated to the bulk density and water content. It is further correlated to Young's modulus and Shear modulus of the compacted silt, which were determined through ultrasonic pulse velocity measurements. Several trends were observed which may be used to correlate soil thermal conductivity of the compacted silt to compaction and elastic moduli for quality control/quality assurance of compacted soil. DOI: 10.1061/(ASCE)MT.1943-5533.0000035 CE Database subject headings: Fiber reinforced polymer; Composite materials; Sustainable development; Silts; Elasticity; Compacted soils. Author keywords: Thermal conductivity; Compacted silts; Elastic modulus.

Thermal conductivity of the Earth's lower mantle greatly impacts the mantle convection style and affects the heat conduction from the core to the mantle. Direct laboratory measurement of thermal conductivity of mantle minerals remains a technical challenge at the pressure-temperature (P-T) conditions relevant to the lower mantle, and previously estimated values are extrapolated from low P-T data based on simple empirical thermal transport models. By using a numerical technique that combines first-principles electronic structure theory and Peierls--Boltzmann transport theory, we predict the lattice thermal conductivity of MgO, previously used to estimate the thermal conductivity in the Earth, at conditions from ambient to the core-mantle boundary (CMB). We show that our first-principles technique provides a realistic model for the P-T dependence of lattice thermal conductivity of MgO at conditions from ambient to the CMB, and we propose thermal conductivity profiles of MgO in the lower mantle based on geotherm models. The calculated conductivity increases from 15-20 W/K-m at the 670 km seismic discontinuity to 40-50 W/K-m at the CMB. This large depth variation in calculated thermal conductivity should be included in models of mantle convection, which has been traditionally studied based on the assumption of constant conductivity. first-principles | phonon transport theory | phonon lifetime | high pressure | Lower Mantle www.pnas.org/cgi/doi/10.1073/pnas.0907194107

A three-dimensional inverse heat conduction problem is solved in the present study by using the conjugate gradient method (CGM) and the general-purpose commercial code CFD - ACE+ to estimate the strength of the unknown heat generation for an encapsulated chip in a three-dimensional irregular domain. The advantage of calling CFD - ACE+ code as a subroutine in the present inverse calculation lies in that many difficult but practical 3D inverse problem can be solved under this construction since the general-purpose commercial code has the ability to solve the direct problem easily. The results obtained by using the CGM to solve this 3D inverse problem are justified based on the numerical experiments using the simulated exact and inexact measurements. It is concluded that reliable heat generation can be estimated by the present inverse algorithm. [DOI: 10.1115/1.4000720]

We present a simple and inexpensive experimental setup that can determine the thermal fluctuations near a superconducting transition. By using equipment common in undergraduate laboratories, the in-plane dc electrical resistivity of a cuprate superconductor as a function of temperature is measured with resolution sufficient to analyze the fluctuation conductivity above the superconducting critical temperature, including the values of the critical exponents. We also present a simple calculation of the fluctuation conductivity, including its dependence on the layered structure of the material, within the Gaussian--Ginzburg--Landau formalism. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3276713]

As global warming entails new conditions for the built environment, the thermal and energy performance of existing buildings, which are designed based on current weather data, may become unclear and remain a great concern. Through building computer simulation and qualitative analysis of the weighted factor for the outdoor temperature impact on building energy and thermal performance, this paper investigates the sensitivity of different office building zoning to the potential global warming. A standard office building type is examined for all eight capital cities in Australia. Results show that comparing the middle and top floors, except for cool climate (i.e. Hobart), the ground floor appears to be the most sensitive to the effect of global warming and has the highest tendency for a overheating problem. From the analysis of the responses of different zone orientations to the outdoor air temperature increase, it is also found that there are widely varied responses between zone orientations, with South zone (in the southern hemisphere) being the most sensitive. With an increased external air temperature, the variation between different floors or zone orientations will become more significant, up to 53 percent increase of overheating hours in Darwin and 47 percent increase of cooling load in Hobart. Keywords: Building form, Building performance, Global warming, Office building, Zone type, Introduction Greenhouse gas emissions and associated global warming is a significant concern for the world community. This problem is now widely recognised as having significant potential to seriously affect the [...]

A finite element method was developed to predict the effective thermal conductivity of particle filled epoxy composites. Three-dimensional models, which considered the effect of filler geometry, filler aspect ratio, conductivity ratio of filler to matrix, and interfacial layer were used to simulate the microstructure of epoxy composites for various filler volume fractions up to 30%. The calculated thermal conductivities were compared with results from existing theoretical models and experiments. Numerical estimation of ellipsoids-in-cube model accurately predicted thermal conductivity of epoxy composites with alumina filler particles. The number of length division during mesh process and particle numbers used in the finite element analysis affect the accuracy of calculated results. At a given value of filler content, the numerical results indicated a ratio of conductivity of filler to matrix for achieving the maximum thermal conductivity. [DOI: 10.1115/1.4000210] Keywords: composite materials, thermal analysis, encapsulant, underfill, finite element method

Effect of formalin fixation on thermal conductivity of the biological tissues is presented. A self-heated thermistor probe was used to measure the tissue thermal conductivity. The thermal conductivity of porcine aorta, fat, heart, and liver was measured before the formalin fixation and then 1 day, 4 days, and 11 days after formalin fixation. The results indicate that the formalin fixation does not cause a significant change in the tissue thermal conductivity of the tissues studied. In the clinical setting, tissues removed surgically are often fixed in formalin for subsequent pathological analysis. These results suggest that, in terms of thermal properties, it is equally appropriate to perform in vitro studies in either fresh tissue or formalin-fixed tissue. [DOI: 10.1115/1.3147745] Keywords: tissue thermal conductivity, self-heated thermistor, bioheat transfer, formalin fixation, tissue fixation, formaldehyde

This note presents a sampled-data strategy for a boundary control problem of a heat conduction system modeled by a parabolic partial differential equation (PDE). Using the zero-order-hold, the control law becomes a piecewise constant signal, in which a step change of value occurs at each sampling instant. Through the 'lifting' technique, the PDE is converted into a sequence of constant input problems, to be solved individually for a sampled-data formulation. The eigenspectrum of the parabolic system can be partitioned into two groups: a finite number of slow modes and an infinite number of fast modes, which is studied via the theory of singular perturbations. Controllability and observability of the sampleddata system are preserved, irrelevant to the sampling period. A noncollocated output-feedback design based upon the state observer is employed for set-point regulation. The state observer serves as an output-feedback compensator with no static feedback directly from the output, satisfying the so-called 'low-pass property'. The feedback controller is thus robust against the observation error due to the neglected fast modes. Index Terms--Boundary control, distributed parameter system (DPS), sampled-data systems, singular perturbation.

The article presents a new pseudospectral time-domain method for the analysis and characterization of the thermally induced photoacoustic wave propagation. The approach is shown to be much more accurate and efficient, as compared to the other conventional methods.

To acquire polymer composites with high thermal conductivity and mechanical properties, the aluminum nitride (AIN) microparticles modified with titanate coupling reagent of isopropyltrioleictitanate (NDZ-105) were employed to blend linear low-density polyethylene (LLDPE) via powder mixing method. Thermal conductive coefficient of the AlN/LLDPE composites was measured using hot disk thermal analyzer, and the thermal stability characteristics of AlN/LLDPE composites were mainly investigated via thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The results indicated that the use of AlN particles modified by NDZ-105 significantly enhanced thermal conductivity and mechanical properties of AlN/LLDPE composites. The thermal conductivity coefficient λ was 1.0842 W/mk with 30% volume fraction of AlN, about three times higher than that of native LLDPE. The tensile strength of composites was maximum (17.42 MPa) with 20% mass fraction of AlN. DSC analyses results indicated that AlN had an influence on the melting temperature and the crystallinity of LLDPE. Additionally, TGA analyses showed that the thermal stability of LLDPE was significantly increased with addition of AlN. POLYM. ENG. SCI., 49:1030-1034, 2009. [C] 2009 Society of Plastics Engineers, INTRODUCTION Polymers materials have gained wide applications in different branches of industry because of their low cost, low density, case of forming, chemical inertia, and low thermal conductivity (1). In [...]

Thermal forming is a method to form a curved plate by inducing local shrinkage and angular distortion through heating and cooling. In this approach, two different methods are available: line heating and triangle heating. Among them, this paper discusses triangle heating and presents algorithms for determining heating shapes and locations. The heating shape is determined by using the in-plane strain distributions, which are calculated by nonlinear kinematics analysis between the designed and initial shapes, field survey results, and mechanics based on the neutral axis. To predict the angular distortion and shrinkage in various heating conditions, a functional relation of residual deformations is formulated. For the formulation, multivariate analysis and multiple regression techniques are used with data obtained from experiments of unit triangle heating and numerical analysis. Using the determined heating shapes and the functional relation for the residual deformations, a correct triangle heating position is determined by an algorithm, which can predict qualitatively correct angular distortion and shrinkage in the interior and quantitatively correct distortion values on the edge. Finally, analytic verification of the proposed method has been done by applying the method to a convex type plate used in the field. The proposed work can be used for automation of curved plate fabrication in the shipyards. [DOI: 10.1115/1.3090886] Keywords: thermal forming, triangle heating, heating shape, heating location, residual deformation, angular distortion

A breadboard GC detector based on Penning ionization electron spectroscopy in plasma (PIES) was investigated. The PIES detector was set up in series with a gas chromatograph and a thermal conductivity detector. Two-dimensional PIES chromatograms were recorded for carbon monoxide, carbon dioxide, and methane. The analytes were identified independently of the GC retention time, and their concentrations were measured in a range between I and 100 ppm. PIES spectra for methane were observed for the first time and displayed two characteristic peaks with electron energies of 7.1 and 5.4 eV. Rate coefficients for Penning ionization due to collisions between [2.sup.3]S helium metastable atoms and analyte molecules under study were found to be [k.sup.*.sub.co] = (0.7 [+ or -] 0.2) x [10.sup.-10], [k.sup.*.sub.co2] = (1.8 [+ or -] 0.7) x [10.sup.-10], [k.sup.*.sub.7.1 CH4] = (4.7 [+ or -] 0.6) x [10.sup.-10], and [k.sup.*.sub.5.4 CH4] = (8 [+ or -] 2) x [10.sup.-10] [cm.sup.3]/s. The work provides the basis for the development of a portable and robust analytical platform capable of in situ real-time monitoring of greenhouse gases, with a perspective toward laboratory-on-chip realization.

A photothermal experiment with mirage detection was used to determine the thermal conductivity of various thin films deposited on semiconductor substrates. The first type consisted of conducting oxide films: ZnO and CdO deposited on GaSb:Te, while the other contained high dielectric constant Hf[O.sub.2] layers on Si. All films were fabricated using a magnetron sputtering technique. Experimental results showed that the value of the thermal conductivity of ZnO and CdO films is lower than the value obtained for Hf[O.sub.2]. Thermal conductivities of investigated thin films are about 2 orders of magnitude lower than those corresponding to bulk materials. OCIS codes: 310.0310, 310.6870, 310.7005, 310.1210.

This paper reports the design study performed on a heat conduction panel having several heat sources at separate locations and a heat sink on one of the panel corners. The panel is given a thickness distribution so as to provide spatially varying heat conduction paths from the heat sources to the heat sink. The objective of thickness distribution design is to reduce the variation among heat source temperatures and the maximum heat source temperature simultaneously. The genetic algorithm is used to search for an optimum thickness distribution. The problem is a generic representation of the situations that are becoming common in a compact electronic equipment. [DOI: 10.1115/1.2993137] Keywords: heat conduction path design, multiple heat sources, displaced heat sink, genetic algorithm application

An analytical model is developed to estimate the heat transfer performance of printed circuit board (PCBs). The PCB under study is the substrate for a ball-grid-array (BGA) package. Under the BGA, the PCB has a belt of densely populated through-vias that penetrate the laminate of horizontal copper and resin; outside the BGA-covered area the board is a copper/resin laminate and its surfaces are exposed to cooling air. Calculations are performed on a sample board having the dimensions 11 x 11 [cm.sup.2] (footprint) x 1.26 mm (thickness). The model of the board has two internal layers of continuous copper (0.03 mm thick) and through-vias under a 4.4 x 4.4 [cm.sup.2] BGA package. The impacts of board design parameters on the temperature and the heat flow are presented; the parameters are the width of the insulation gap around the via, the area of copper coverage at the via bottom, and the population of vias. [DOI: 10.1115l/1.2993126] Keywords: printed circuit board, heat conduction, analytical modeling, through-vias, copper/rein laminate

An internal mixer was used to prepare polycarbonate (PC)-based nanocomposites containing carbon fibers, carbon nanofibers (CNF), and mixtures of the two fillers. The influence of the filler volume fraction, the relative amounts of the two fillers, and the filler orientation relative to the direction of heat flow on the thermal conductivity was examined. Filler orientation was obtained by the extrusion of strands of the nanocomposite. The thermal conductivity was measured using a steady-state heat conduction technique. The CNF were fragile, and their aspect ratio could be decreased during processing. In general, the composite thermal conductivity increased with increasing filler content. Fiber alignment in the heat flux direction resulted in a significant increase in thermal conductivity. Mixing of nanofibers with microfibers resulted contacts between the microfibers. This, together with fiber alignment provided large increases in the thermal conductivity. POLTM. ENG. SCI., 48:2474-2481, 2008. [C] 2008 Society of Plastics Engineers, INTRODUCTION Nanomaterials are increasingly being used as additives to polymers to simultaneously enhance a variety of properties without sacrificing any qualities of the base polymer. Carbon nanotubes (CNT) and carbon [...]

The problem of thermoelasticity, based on the theory of Lord and Shulman with one relaxation time, is used to solve a boundary value problem of one dimensional semi-infinite medium heated [...]