Showing papers on "Vaporization published in 1982"

Vaporization of refractory oxides during pulverized coal combustion

Abstract: A laboratory coal combustor was used to study the vaporization behavior of ash duringpulverized coal combustion. The variation in the amount and composition of the ash vaporized with coal type was investigated. The effect of coal size and combustion temperature on the vaporization rate of Si, Mg and Ca was also investigated. At a moderate combustion temperature of 2000° K, the amount of ash vaporized was onthe order of a few percent of the total ash content of the coals tested. The ash vaporized from combustion of subbituminous coals and lignites is composed primarily of MgO or of Na2O if the coal contains high concentrations of sodium. The ash vaporized from combustion or bituminous coals is composed primarily of SiO2 and iron oxide. This effect of rank is a result of the appreciable vaporization of the organically bound magnesium present in the low rank coals. The vaporization rates of Si and Mg are dependent on the coal size and vary by over four orders of magnitude in the combustion temperature range of 1600–3000° K. A model presented to interpret the experimental results considers the degree of dispersion of mineral matter in coal, chemical reduction of refractory oxides (SiO2, MgO, CaO) to the corresponding volatile suboxide or metal vapor, and the internal and boundary layer transport processes. The model adequately describes the vaporization rate of both metals associated with mineral inclusions and those organically bound in the parent coal, and the changes in vaporization rates with changes in temperature and in coal particle size.

Mass Spectrometry of Large, Fragile, and Involatile Molecules

Abstract: Desorption ionization makes it possible to obtain mass spectra of molecules whose vaporization by heating may lead to thermal degradation. Several methods are in use, but in general desorption is achieved by particle or photon bombardment of the sample and the mass spectra obtained by different methods are fundamentally similar. Desorption ionization techniques have been used to obtain mass spectra of biomolecules, including peptides, antibiotics, and oligosaccharides, for which normal mass spectral methods have been of limited power. Several examples are given of recent applications of these new techniques, and prospects for their further evolution are discussed.

Temperature Dependence of InP and GaAs Etching in a Chlorine Plasma

Abstract: and etching in chlorine plasmas at 0.3 Torr follows an Arrhenius dependence on substrate temperature. Apparent activation energies, , of and , respectively, were determined from both optical emission of product species, and step height or weight change measurements. For , equals the heat of vaporization of , and the absolute etch rate (7 μm/min at 250°C) is in reasonable agreement with the predicted vaporization rate of . Hence, volatilization of is most likely the rate‐controlling step for etching . Sputter Auger analysis shows that etching in a chlorine plasma leaves multiple layer coverage of on (removable by washing with deionized water), and submonolayer levels of chlorine on . Both surfaces are rich in the group III element. The etched surface morphologies of and are strongly dependent on temperature, exhibiting a rough‐to‐smooth texture transition above ~250° and ~120°C, respectively.

Heat transfer to a single particle exposed to a thermal plasma

Abstract: This paper is concerned with an analytical study of the heat and mass transfer process of a single particle exposed to a thermal plasma, with emphasis on the effects which evaporation imposes on heat transfer from the plasma to the particle. The results refer mainly to an atmospheric-pressure argon plasma and, for comparison purposes, an argon-hydrogen mixture and a nitrogen plasma are also considered in a temperature range from 3000 to 16,000 K. Interactions with water droplets, alumina, tungsten, and graphite particles are considered in a range of small Reynolds numbers typical for plasma processing of fine powders. Comparisons between exact solutions of the governing equations and approximate solutions indicate the parameter range for which approximate solutions are valid. The time required for complete evaporation of a given particle can be determined from calculated values of the vaporization constant. This constant is mainly determined by the boiling (or sublimation) temperature of the particles and the density of the condensed phase. Evaporation severely reduces heat transfer to a particle and, in general, this effect is more pronounced for materials with low latent heat of evaporation.

Coupling of pulsed 0.35‐μm laser radiation to aluminum alloys

Abstract: An experimental and theoretical study has been performed on the response of a titanium alloy surface in vacuum to a XeF laser pulse (λ = 0.35 μm, pulse time = 1 μs). Thermal coupling measurements indicate an optical absorptance of 0.4–0.5. The onset of a measurable impulse is shown to result from bulk target vaporization for fluences ?5 J/cm2. The plasma formation threshold is obtained both theoretically and from experimental data, and good agreement is found. The theoretical model includes laser absorption in the target vapor through inverse bremsstrahlung and photoionization absorption, and collisional energy transfer between free electrons and bound electronic states of Ti.

Laser excitation spectra and lifetimes of Pb2 and Sn2 produced by YAG laser vaporization

Abstract: A new and very general technique, combining pulsed laser vaporization with laser induced fluorescence is described. The gas phase electronic spectra of Pb2 cooled to near 77 °K by liquid N2 are very simple and yield the vibrational constants for the ground state and two low lying electronic states. Some lifetime information is also obtained and preliminary observations of Sn2 spectra are reported.

A first-order estimate of shock heating and vaporization in oceanic impacts

Abstract: The vaporization of water in oceanic impacts of asteroids or comets of multikilometer dimensions is estimated by a semianalytical modeling of impact heating and shock isobar geometry that is based on computer code calculations. The mass of water vaporized in an infinitely deep ocean by the impact of a 10 km diameter asteroid at 25 km/sec (these values have been proposed for the Cretaceous/Tertiary extinction bolide) is approximately equal to the total mass of water vapor present in the earth's atmosphere, and 3-4 orders of magnitude larger than the mass of water vapor in the stratosphere. For projectiles of this size, however, the finite depth of the ocean becomes significant and may considerably reduce the amount of water vapor initially generated by the impact. Climatological models and extinction scenarios invoking the effects of impact-generated water vapor may critically depend on the a priori ambiguous details of the hypothesized impact.

Ash Vaporization and Condensation During Combustion of a Suspended Coal Particle

Abstract: The results of a theoretical study of the formation and growth of the submicron flyash aerosol around a single burning coal particle are presented. The vaporization of ash and subsequent aerosol formation near the coal particle are studied because the local combustion environment influences these processes strongly. A mathematical model is developed that describes the transport of ash vapor and and the growth of the aerosol. The ash aerosol calculation is superimposed on an existing solution to the combustion problem. Included in the model are the effects of convective transport and of both homogeneous and heterogeneous condensation of the ash vapor. The results of the calculations show that refractory compounds with low surface tension, like silica, nucleate very near the coal particle's surface and produce a substantial mass loading of aerosol. The presence of the aerosol does not greatly affect the ash vaporization rate, which is primarily a function of combustion conditions. The size and amount of the submicron ash aerosol are determined by both the local combustion conditions and the ash's physical properties.

The group combustion of a spherical cloud of monodisperse fuel droplets

Abstract: The vaporization and combustion of a spherical, uniform monodisperse cloud of fuel drops in equilibrium with a quiescent atmosphere is considered. For typical fuel sprays in which the drops are separated by five to ten drop diameters only the droplets within a thin inwardly propagating vaporization wave at the edge of the cloud will vaporize. In analogy with single drop theory the cloud radius is found to decrease acording to a “d2 law,” although with a modified vaporization constant for both purely vaporizing and burning clouds. The cloud interior in all cases remains in saturated, non vaporizing equilibrium at a temperature determined by ambient conditions. Burning occurs at a spherical diffusion flame front outside the cloud. The flame radius to cloud radius ratio is found to be constant and independent of the cloud radius and the droplet radius and number density within the cloud. An external ignition temperature is determined by considering the bifurcation of steady state solutions for single step, irreversible Arrhenius kinetics. At ignition the cloud interior reaches a new equilibrium which is still too cool and rich for single drop ignition. Under conditions of the present analysis a fuel cloud, if it burns at all, will do so with an external diffusion flame.

Radiant energy device

Abstract: Radiant energy such as solar energy is utilized to form a vapor from a liquid state of a material. Concentrated radiant energy is directed through a liquid lens to a target for absorption of the radiation. The target in this way is heated to a high temperature and produces steam or other vapor at high pressure. High efficiency at low over-all cost is achieved by (1) the direct vaporization of a liquid within a collector enclosing the target structure; (2) the recovery of energy absorbed by the liquid lens; (3) the reduction in conductive and convective heat losses in the solar collector by special enclosure of the target within the collector; (4) recovery of heat as blackbody radiation from the target by using reflective walls within the enclosure and/or permitting absorption of the blackbody radiation by the liquid lens; and (5) an optional use of a heat pump effect for increasing the output of the collector.

Transient Vaporization from a Surface into Vacuum

Abstract: This paper is motivated by a general interest in pulsed energy addition to a surface in vacuum at high power fluxes (> 1 MW/cm absorbed). The theoretical treatment assumes a perfect gas without plasma formation, and examples are for aluminum. Transient heat conduction into the surface, vapor flux through a Knudsen layer at the surface, and transient one-dimensional flow of vapor into the surrounding vacuum are included as part of the modeling. Results show that the Knudsen layer remains choked so long as the absorbed power is constant or increasing, and it is unchoked when the absorbed power is decreasing. The problem is fully coupled in the latter case. Quasisteady vapor efflux from the surface is established within a fraction of the pulse time at sufficiently high power fluxes. Impulse coupling coefficients due to vapor recoil are noted.

Thermophysical properties of normal butane from 135 to 700 K at pressures to 70 MPa

Abstract: Using a modified version of the nonanalytic equation of state, thermophysical properties of normal butane are derived from physical properties data and are tabulated at integral temperatures from 135 to 700 K along isobars at pressures to 70 MPa. These isobar tables, along with a table for the saturated liquid, give values for densities, compressibility factors, internal energies, enthalpies, entropies, heat capacities, fugacities, sound velocities, dielectric constants, and isochore and isotherm derivatives. Equations, whose coefficients are determined from a least squares fit to selected experimental data, are also presented for vapor pressures, orthobaric liquid and vapor densities, ideal gas properties, second virial coefficients, dielectric constants, heats of vaporization, melting pressures, and orthobaric liquid specific heats, enthalpies, and entropies. Comparisons between experimental and calculated values for all properties considered here are reported in detail.

Vapor-liquid equilibrium calculations for polymer solutions

Abstract: Bonner's theory for the prediction of vapor-liquid equilibria of polymer solutions has been modified. A new equation of state and corresponding vapor-liquid equilibrium equation are proposed. Good results have been obtained for mixtures of nonpolar and moderately polar compounds, containing polymers and subcritical or supercritical solvents. Predictions can be based on a single measurement of the infinite dilution activity coefficient or Henry's Law constant to determine a single interaction parameter for the mixture. Reliable calculations also can be made for the complete concentration range up to the highest vapor pressures. Vaporization of polymer also can be included in the calculations. 32 references.

Diagnostic Measurements of Fuel Spray Dispersion

Abstract: Plume shape, vaporization, droplet-size distribution, and number density of a solid-cone fuel spray were studied with both conventional and novel measurement techniques. Minor differences in spray plume shape were observed by measurements with photography, pulsed laser shadowgraphy, and in-line infrared spectroscopy. Laser Mie scattering showed the dispersion of small numbers of droplets beyond spray boundaries as determined by other measurements. A new optical method for nonintrusive, local, time-averaged measurement of vapor concentration, droplet-size distribution and number density within an axisymmetric spray is introduced. For the spray studied this method showed that vapor is confined to the spray plume and that vapor concentration and the concentration of small-diameter droplets exhibit analogous behavior.

Polymeric film coating apparatus

Abstract: Method and apparatus are disclosed for coating substrates with a film polymer based on p-xylylene by vapor-shaped polymerization. The apparatus monitors the monomer vapor pressure after pyrolization of the cyclic di-p-xylylene dimer, compares the measured pressure to a predetermined pressure needed to effect a completed vapor-phase polymerization reaction, and adjusts the temperature of vaporization in response to variations between measured pressure and the predetermined pressure.