Motion Of Vapor Research Articles

TREATMENT OF THE NONEQUILIBRIUM VAPOR MOTION NEAR AN EVAPORATING INTERPHASE BOUNDARY

Strong evaporation problems are characterized by the nonequilibrium vapor motion near the interphase boundary. The solution of this nonequilibrium region, known as Knudsen layer, requires the use of kinetic theory. Kinetic equations have been solved numerically for a plane evaporation problem. Numerical solutions have led to the establishment or the validity of a simple kinetic theory approach to calculate the jump conditions across the Knudsen layer and the net mass, momentum, and heat fluxes. This approach can be used together with the conventional continuum method to calculate How parameters at the outer edge of the Knudsen layer for heat transfer problems in which evaporation occurs at the interphase boundary.

Effects of Recent Modeling Developments in Prompt Burst Hypothetical Core Disruptive Accident Calculations

The main objective of the development of multifield, multicomponent thermohydrodynamic computer codes is the detailed study of hypothetical core disruptive accidents (HCDAs) in liquid-metal fast breeder reactors. The main contributions such codes are expected to make are the inclusion of detailed modeling of the relative motion of liquid and vapor (slip), the inclusion of modeling of nonequilibrium/nonsaturation thermodynamics, and the use of more detailed neutronics methods. Scoping studies of the importance of including these phenomena performed with the parametric two-field, two-component coupled neutronic/thermodynamic/hydrodynamic code FX2-TWOPOOL indicate for the prompt burst portion of an HCDA that: (1) Vapor-liquid slip plays a relatively insignificant role in establishing energetics, implying that analyses that do not model vapor-liquid slip may be adequate. Furthermore, if conditions of saturation are assumed to be maintained, calculations that do not permit vapor-liquid slip appear to be conservative. (2) The modeling of conduction-limited fuel vaporization and condensation causes the energetics to be highly sensitive to variations in the droplet size (i.e., in the parametric values) for the sizes of interest in HCDA analysis. Care must therefore be exercised in the inclusion of this phenomenon in energetics calculations. (3) Insignificant differences are observed between the use of space-time kinetics (quasi-staticmore » diffusion theory) and point kinetics, indicating again that point kinetics is normally adequate for analysis of the prompt burst portion of an HCDA. (4) No significant differences were found to result from assuming that delayed neutron precursors remain stationary where they are created rather than assuming that they move together with fuel. (5) There is no need for implicit coupling between the neutronics and the hydrodynamics/thermodynamics routines, even outside the prompt burst portion.« less

Evaporation of a solid into a vacuum

In this article the boundary conditions relating the values of the hydrodynamic variables in a rarefaction wave to the surface temperature are derived. The gas-kinetic problem of the motion of vapor in a thin layer directly adjacent to a phase boundary is solved approximately for this case. If the temperature of the surface is held constant by external radiation, the resulting solution makes it possible to compute the surface temperature, the velocity of the evaporation front, and the recoil momentum.

Metal evaporation under powerful optical radiation

The experimental results of our studies of metal evaporation under powerful optical radiation are presented. The theory of this phenomenon based on a liquid-vapor phase transition is developed. An approximate solution of the Clapeyron-Clausius equation is applied to the present problem. The method permits calculations of metal surface temperature versus incident light intensity I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> . When a certain critical intensity is exceeded ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_{md} \sim 10^{7}-10^{8}</tex> W .cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) a new effect is shown to arise due to disappearance of the metallic properties of the target. The new effect is a "transparency wave" in whose front a liquid metal turns into a liquid dielectric. For <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_{0} &gt; I_{md}</tex> it is the surface "transparent" (dielectric) layer that is evaporated. Its temperature is no longer raised and it remains below a critical value. This layer is separated from the metal by the transparency wave front, which propagates towards the interior of the metal. The transparency wave causes some other effects to arise, such as a sharp drop of the reflectivity from the metal surface, an essential change in the dependence of the observed evaporation front speed on I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> , and, finally, occurrence of a maximum on the curve of specific recoil impulse versus I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> . These other effects may be used to identify the transparency wave. The experimental results support some corollaries of our theoretical model. The vapor dynamics of metal evaporation under powerful millisecond optical radiation are investigated. Vapor heating near the target under laser light has been observed. The initial conditions of vapor motion are studied. From the gas-dynamic measurements the mass flow of the gas phase j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> is calculated. The dependence of j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> upon the incident light intensity is indicative of the fact that the metal surface has attained the temperature <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T = T_{md} &lt; T_{cr}</tex> , which corresponds to the liquid metal-liquid dielectric transition.

On Some Aspects of Steam Bubble Collapse

Further consideration is given to the problem of the collapse of a vapor bubble, with the bubble initially in equilibrium with an isothermal liquid of infinite extent and with the collapse produced by a sudden increase in the pressure at infinity. In the numerical analysis, made for a steam bubble surrounded by water, the energy equation is solved in finite increments rather than by use of the Plesset-Zwick method, and comparisons are made to the results of the latter method as used by Florschuetz and Chao. The assumption of zero vapor velocity is also replaced by an alternative hypothesis which allows vapor motion, and this alternative approach yields a prediction of an oscillatory collapse rather than the relatively monotonic collapse indicated by the former assumption.

A Photographic Study of Boiling in the Absence of Gravity

A photographic study was made to determine the qualitative effect of zero gravity on the mechanism of boiling heat transfer. The experimental equipment included a container for boiling water and a high-speed motion-picture camera. To eliminate the influence of gravity, these were mounted on a platform which was allowed to fall freely approximately 8 ft. During the free fall, photographs were taken of boiling from various surface configurations such as electrically heated horizontal and vertical ribbons. The heat flux was varied to produce conditions from moderate nucleate boiling to burnout. The results indicate that gravity plays a considerable role in the boiling process, especially in connection with the motion of vapor within the liquid.

Structure and Internal Motion of C2F6 and Si2Cl6 Vapors

The molecular structure and internal motion of C2F6 vapor and of Si2Cl6 vapor have been investigated by means of the sector-microphotometer method of electron diffraction. Both molecules exhibit hindered internal rotation, with equilibrium in the trans position. The interdependence of the potential barrier and the modes of vibration other than the torsional is presented graphically. The values for the bonded distances are: C – F = 1.32±0.01 A, C – C = 1.56±0.03 A with ∠ CCF = 109½°±1½° and Si – Cl = 2.01±0.01 A, Si – Si = 2.24±0.06 A with ∠ SiSiCl = 109½°±1°.

Motion and Condition of Calcium Vapor Over Sun-Spots and Other Special Regions. II.

Motion and Condition of Calcium Vapor Over Sun-Spots and Other Special Regions. II.

Motion and Condition of Calcium Vapor Over Sun-Spots and Other Special Regions. I.

Motion and Condition of Calcium Vapor Over Sun-Spots and Other Special Regions. I.

Some Notes on the H and K Lines and the Motion of the Calcium Vapor in the Sun

Some Notes on the H and K Lines and the Motion of the Calcium Vapor in the Sun