Showing papers on "Thermal published in 1983"

Thin film thickness measurement with thermal waves

Abstract: A method and apparatus for thin film thickness measurements with thermal waves in which heating and detection laser beams are focused onto the film, normal to the surface of the film, with the two beams parallel and non-coaxial.

Thermal structure of the atmosphere of Venus

Abstract: The available data sets determining the thermal structure are critically discussed and combined into a mean model. The implications of the oberved contrasts for atmospheric motions, on small and large scales, are discussed. Greenhouse models which allow a convective atmosphere below 35 to 50 km give a reasonable explanation of the high surface temperature. Surprisingly, however, the deep atmosphere is generally stable. The radiative imbalance thus drives the general circulation rather than local convection. A distinct tropopause occurs at the cloud tops. Above this, the atmosphere is very stably stratified and not far from radiative equilibrium. Gravity waves are present. The upper atmosphere, with its very large day-night temperature contrast, must be in motion away from the sun, but velocities are strongly limited to a sizable viscous dissipation.

Optical bistability observed in amorphous semiconductor films

Abstract: The optical properties of amorphous self-supporting GeSe1 films show strong non-linear behaviour under the influence of relatively low-intensity c.w. laser irradiation. Discontinuities, bistability and, in special circumstances, oscillation in the optical properties have been found. The importance of thermal effects is experimentally proved. A theoretical model is constructed which explains some of the experimental findings. Evidence is presented, however, that, as well as thermal effects, photostructural changes also play an important role in the bistability and oscillatory phenomena.

Nonlinear convection in a porous layer with finite conducting boundaries

Abstract: The problem of finite-amplitude thermal convection in a porous layer with finite conducting boundaries is investigated. The nonlinear problem of three-dimensional convection is solved by expanding the dependent variables in terms of powers of the amplitude of convection. The preferred mode of convection is determined by a stability analysis in which arbitrary infinitesimal disturbances are superimposed on the steady solutions. Square-flow-pattern convection is found to be preferred in a bounded region [Gcy ] in the (γ b , γ t )-space, where γ b and γ t are the ratios of the thermal conductivities of the lower and upper boundaries to that of the fluid. Two-dimensional rolls are found to be the preferred pattern outside [Gcy ]. The qualitative features of the convection problem appear to be essentially symmetric with respect to γ b and γ t . The dependence of the heat transported by convection on γ b and γ t is computed for the various solutions analysed in the paper.

Fiber optic scanning system for laser/thermal inspection

Abstract: An apparatus for inspecting a device made up of a plurality of different infrared radiating elements includes an optical head which is moveable along X-Y coordinates above the fixed device to sequentially scan the infrared radiating elements. A laser beam source is operatively connected to the moveable head for injecting thermal energy into the infrared radiating elements and an infrared detector is provided for sensing the infrared radiation emanating from the elements. The infrared detector may be mounted directly on the moveable head or in a remote location wherein the detector would be connected to the moveable head by a flexible optical fiber. A second moveable head may be located on the opposite side of the device so that thermal energy from the laser source may be injected into opposite sides of the infrared radiating element.

A thermal model of sunspot influence on solar luminosity

Abstract: Recent measurements of the solar irradiance have confirmed that sunspots block energy flow to the photosphere in rough proportion to their area and photometric contrast. We have constructed a time-dependent two-dimensional model of heat flow blocking in a turbulent convective layer, to investigate the physical interpretation of the observed irradiance dips. Our numerical model shows how formation of a spot at or below the photosphere leads to heating of surrounding convective layers over a diffusive time scale tau/sub D/ >10/sup 4/ s. This heating rapidly propagates outward, storing the blocked heat throughout the convection zone. The stored thermal (and potential) energy is only released very slowly by radiation through a gradually increasing photospheric temperature. The very long radiative time scale tau/sub R/ >10/sup 10/ s for this release is quite insensitive to reasonable uncertainties in the model parameters or the diffusion approximation we have used. We point out that this very efficient storage implies a sunspot contribution to the modulation of L/sub sun/ over the 11 year cycle, at a level somewhat below 0.1%. Our study indicates that the amplitude, duration, shape, and phase of the observed spot-correlated irrdiance dips can be easily explained by extending a conventional thermal blockingmore » model of spots to include time dependence. We find no reason to expect that the contribution of faculae to S and L/sub sun/ cancels that of spots, on any time scale« less

Electrically conductive sintered ceramics and ceramic heaters

Abstract: An electrically conductive sintered ceramics of the present invention comprises, as the main ingredients thereof, (a) silicon carbide, (b) an inorganic compound which exhibits a positive resistance-temperature coefficient, and preferably (c) a sintering assistant. The electrically conductive sintered ceramics obtained exhibits a positive resistance-temperature coefficient as a whole. A ceramic heater of the invention makes use of the electrically conductive sintered ceramics in an electrically conductive portion thereof. A sintered product which exhibits a positive resistance-temperature coefficient helps to prevent the occurrence of thermal runaway or thermal destruction.

Laser-induced optical recording in thin films. Modelling of the hole opening and experiments with organic sublayers

Abstract: A model is presented to describe the hole opening in ablative optical recording. The model accounts for changes in geometry of the sensitive film, for adhesion of the film to the substrate, for surface tension gradients in the sensitive film and for evaporation or sublimation at the film-substrate interface. The changes in geometry during hole opening are shown to be responsible for an energy barrierFact=10−16 to 10−15 J, corresponding to 1.5–6J/cm3 which is much too large to make thermal activation of hole opening possible.Fact is reduced by surface tension gradients in the liquid film and/or evaporation at the filmsubstrate interface.

Development of mixed time partition procedures for thermal analysis of structures

Abstract: The computational methods used to predict and optimize the thermal-structural behaviour of aerospace vehicle structures are reviewed. In general, two classes of algorithms, implicit and explicit, are used in transient thermal analysis of structures. Each of these two methods has its own merits. Due to the different time scales of the mechanical and thermal responses, the selection of a time integration method can be a difficult yet critical factor in the efficient solution of such problems. Therefore mixed time integration methods for transient thermal analysis of structures are being developed. This proposed methodology would be readily adaptable to existing computer programs for structural thermal analysis.

Natural convection experiments in a liquid-saturated porous medium bounded by vertical coaxial cylinders

Abstract: An experimental effort is presently underway to investigate natural convection in liquid-saturated porous media utilizing a geometry and hydrodynamic/thermal boundary conditions relevant to the problem of nuclear-waste isolation in geologic repositories. During the first phase of this research program, detailed measurements were made of the steady state thermal field throughout an annular test region bounded by a vertical, constant-heat-flux inner cylinder and a concentrically placed, constant-temperature outer cylinder. An overlying, constant-pressure fluid layer was utilized to supply a permeable upper surface boundary condition. Results showed the heater surfae temperature to increase with increasing vertical distance due to the buoyantly driven upflow. The measured temperature difference (..delta..T) between the average heater surface temperature and the constant outer-surface temperature was found to be progressively below the straight-line/conduction-only solution for ..delta..T versus power input, as the latter was systematically increased. Comparisons between measured results and numerical predictions obtained using the finite element code MARIAH showed very good agreement, thereby contributing to the qualification of this code for repository-design applications.

Condensing atmospheric engine and method

Abstract: A thermodynamic method and engine is provided for extracting natural thermal energy from ambient atmospheric air and converting it into mechanical work. The extraction process is accomplished by isentropically expanding ordinary air at atmospheric pressure into a thermally insulated vacuum chamber maintained at low pressure. By employing sufficiently high expansion ratios, a large portion of the air can be made to undergo a spontaneous phase transformation into the solid state at cryogenic temperature. This results in a substantial reduction of the specific volume of the condensed air which enables the vacuum environment of the chamber to be maintained by expending less mechanical work than that gained from the initial expansion. Thus, the net amount of mechanical work generated therefrom is positive. Substantial additional mechanical work is generated by harnessing the thermal potential difference between the low temperature condensed air and the ambient environment via additional cryogenic engine stages.

Aquifer thermal energy storage: An attempt to counter free thermal convection

Abstract: In previous Aquifer Thermal Energy Storage (ATES) experiments, appreciable free thermal convection was observed. In an attempt to counter the detrimental effects of convection, a dual recovery well system was constructed at the Mobile site and a third injection-storage-recovery cycle performed. Using a partially penetrating well, cycle 3-3 injection began on April 7, 1982. A total of 56,680 m3 of 79°C water were injected. After 57 days of storage, production began with a dual recovery well system. Due to the dominating effect of nonhomogeneities, the dual well system did not work particularly well, and a recovery factor of 0.42 was achieved. The degree of aquifer heterogeneity at the location of the present experiments was not apparent during previous experiments at a location only 109 m away, although pumping tests indicated similar values of transmissivity. Therefore aquifers with the same transmissivity can behave quite differently in a thermal sense. Heat conduction to the upper aquitard was a major energy loss mechanism. Water sample analyses indicated that there were no important changes in the chemical constituents during the third set of experiments. There was a 19% increase in total dissolved solids. At the end of injection, the land surface near the injection well had risen 1.39 cm with respect to bench marks located 70 m away.

Role of thermal conduction in the acceleration of the solar wind

Abstract: The thermal and suprathermal processes involving solar wind electrons are discussed from a theoretical point of view A model for the electron distribution function, f(e), based on the solutions of the Boltzmann equation in Krook's approximation is outlined: the angular and energy dependences of for various distances from the Sun between the coronal base and the Earth are presented with the express purpose of obtaining the radial profile of the heat flux generated by the suprathermals The basic fluid-dynamical equations for the solar wind plasma as a whole along any given magnetic field line are solved Results are in good agreement with observations The predicted density and temperature profiles for positive ions exhibit the characteristics of recent measurements, both in the corona (above the coronal holes) and between 03 and 1 AU (the Helios region) It is concluded that the suprathermal electrons play an important role in the formation and the dynamics of the solar wind

Thermal Properties of Beef Loaf Produced in Foodservice Systems

Abstract: There is a lack of information on thermal and other properties of foods, especially food mixtures. Physical properties of beef loaf prepared following formula and procedures used in alternate foodservice systems were determined: heat capacity (0.88 cal/g°C uncooked, 0.91 heated to 60°C) moisture content (72.1% uncooked, 66.2% heated), thermal conductivity (0.40 w/cm°C uncooked, 0.47 heated), fat (17.6% uncooked, 13.0% heated) and density (1.00 g/cm3 uncooked and 0.70 heated). The surface heat transfer coefficient for a forced convection oven was also determined (62 w/ m2°C.) Times to heat beef loaves to specified ending temperatures in a forced convection oven at 163°C and 176°C were calculated. There was less than 1 min difference in calculated heating time required to reach the desired end temperature. The actual times to reach ending temperature show very good agreement with the calculated times.

Laser‐Enhanced Electroplating on Good Heat‐Conducting Bulk Materials

Abstract: Laser-enhanced electroplating on good heat-conducting bulk materials is not very effective, as laser-beam irradiation results in a limited temperature rise only. It is shown, both experimentally and theoretically, that the application of a thin layer of a relatively poor heat-conducting material may lead to a considerable local temperature increase. The dimensionless parameter determining this effect is given by the product of the ratio of the thermal conductivities of bulk and layer material and that of layer thickness to laser-spot diameter.

A modified finite difference scheme for the Stefan problem

Abstract: In this paper we describe an algorithm which can be used to approximate the solution to the enthalpy formulation of the Stefan problem. We allow the thermal properties to have a space and temperature dependence. The algorithm is not explicit in the time variable and, hence, the stability condition on t t is not too severe. A proof of convergence is given and two numerical examples are presented. 1. Introduction. In this paper we describe an algorithm that may be used to approximate the solution of

Transient convection due to the sudden change of the temperature gradient

Abstract: Changing the imposed angular temperature distribution suddenly into another angular temperature yields a transient convection due to the thermal Marangoni effect inside the liquid column until the final velocity distribution is reached. This transient has been determined analytically for a liquid bridge, for which no axial dependency exists,i.e. for the two-dimensional case. The method may also be applied to time-periodic temperature fields.

Laser resonant photo-ionization spectroscopy for trace analysis

Abstract: A new analytical method based on laser resonant photo-ionization of atoms combined with thermal atomization of analysed substances in vacuum has been developed The results of highly sensitive direct analysis of high-purity crystals, seawater and human blood with detection limits up to 10−9% are presented

Reactions of oxasilacyclopropane. Generation of silanediyl by photo and thermal induced cycloelimination

Abstract: Dimesitylsilanediyl was generated from photolysis and pyrolysis of the oxasilacyclopropane (1)via a [3 → 2 +1] cycloelimination reaction.

Rapid Thermal Annealing of III–V Compound Materials

Abstract: Rapid thermal process utilizing radiation from halogen lamps has been used to post-anneal ion-implanted GaAs. Annealing conditions for Si implants in GaAs are discussed from the view point of applying this technique to GaAs MESFET fabrication. Also, the properties of S and Mg implants in GaAs followed by rapid thermal annealing are comparatively studied with the results after conventional furnace annealing. High electrical activation and minimized implant diffusion for both low and high dose implants are the principal features of this technique. The fabricated MESFET showed much higher transconductance without any anomalous characteristics, indicating this technique to be a promising alternative to conventional furnace annealing.

Performance of plastic solar air heating collectors with a porous absorber

Abstract: The thermal performance of solar air heaters consisting of a porous textile absorber between two PVC foils has been investigated. The efficiency of the heaters depends strongly on the characteristics of the textile forming the absorber and on the back insulation. For an incident solar radiation of 687 W/m2 at the collector's surface, a temperature rise of 16-6°C in the air flowing through the solar collector at a rate of 800 m3/h, was achieved, thus yielding an efficiency of nearly 71 percent. Further it was found that the linear approximation for the Hottel-Bliss equation leads to erroneous estimations for the collector's parameters when the absorber is porous; for the same type of collector with a denser textile as absorber, however, such an approximation yields, as usual, correct numerical values for the characteristic parameters of the collector.