Condensation Mass Flux Research Articles

Transient Condensation of Vapor Using a Direct Simulation Monte Carlo Method

Vapor is produced from the ICF event as the x-ray energy is deposited at the first wall of the reactor. This vapor must condense back onto the first wall in a timely fashion (<< 1 s) to establish the necessary conditions for beam propagation and the next ICF event. Transient condensation of vapor is studied on the basis of the Boltzmann equation using a direct simulation Monte Carlo Method. The method describes the molecular behavior of continuum mechanics transition flows in a way consistent with the Boltzmann equation. The thermal resistance of the condensed film is included in the flow representation using a laminar Nusselt analysis to determine the interface temperature of the condensed film. The condensate mass flux in a quasi-steady state is computed and compared with a number of analytical models and experimental data. The results are consistent qualitatively with the experimental data of mercury condensation on a vertical plate.

Laminar film condensation of gravity-controlled convection for ternary vapor mixtures on a vertical flat plate.

Laminar film condensation of gravity-controlled convection for ternary vapor mixtures is theoretically treated. Similarity solutions for methanol-ethanol-water mixtures on an isothermal vertical flat plate are numerically obtained. The effects of mutual intervention of buoyant forces due to temperature and concentration differences on convective heat and mass transfer in the vapor boundary layer are revealed. The dimensionless expressions for heat and mass-transfer coefficients are derived from the numerical results. These expressions approach the characteristics of simultaneous heat and mass transfer in free convection of ternary vapor mixtures with the decrease in condensate mass flux. Heat and mass-transfer characteristics are calculated from the simultaneous algebraic equations which are composed of these expressions, phase equilibrium conditions and the continuity conditions of heat flux and mass transfer at a vapor-liquid interface.

Laminar film condensation in the subcritical region. (Gravity controlled condensation)

This paper treats laminar film condensation of vapours in the subcritical region. The similarity solusions for gravity controlled condensation of pure vapours of water and carbon dioxide on a vertical plate are numerically obtained. The effects of small latent heat, low ρ-μ ratio and high Prandtl number on the boundary values, temperature distribution in the liquid film and velocity distribution in the boundary layer are revealed. The dimensionless expressions for the heat transfer coefficient and the condensate mass flux are derived, which contain the characteristics of Nusselt's theory as a special case. When the reduced temperature of the vapour approaches unity and the temperature difference between vapour and wall is large, the effect of the convection term in the liquid film appears markedly and the heat transfer coefficient becomes independent of H, but depends on GrLx and PrL.

Interphase matter transfer: an experimental study of condensation of mercury

Comparisons between interphase matter-transfer theory and measurements have, in the past, been hindered by uncertainties about the ‘condensation coefficient’. Large experimental errors have often been misinterpreted as indicating low values of the condensation coefficient. Condensation experiments with metals are convenient for the study of interphase matter transfer since, owing to the high thermal conductivity of the liquid, the temperature drop across the condensate film is small and, particularly at low pressures and high condensation rates, the temperature discontinuity at the vapour-liquid interface is of measurable magnitude. Condensation rate, and vapour and condenser surface temperature measurements have been made during film condensation of mercury on a vertical, plane, square (side 40 mm), nickel-plated, copper surface. Thermocouples, accurately located and spaced through the copper condenser block, served to measure, by extrapolation, the temperature of the copper-nickel interface and, from the temperature gradient, the heat flux from which the condensation mass flux was determined. Special care was taken to ensure that the results were not vitiated by the presence in the vapour of noncondensing gases. The observations cover wider ranges of vapour pressure (temperature) and condensation rate (heat flux) than hitherto studied, i.e. 50-4300 Pa (378-493 K) and 0.2- 3.6 kgm ~2 s- 1 (56-1062 kW m -2 ) respectively. The results are considered to have enhanced accuracy. In particular, after the accuracy of calibration and positioning of the thermocouples, and th at of the thermoelectric measurements has been considered, it is estimated that the condenser surface temperature was measured to within around ± 0.1 K. Interface temperature discontinuities up to around 70 K have been observed at low vapour pressure and high condensation rate. The results lend support to recent theoretical studies and indicate that the condensation coefficient exceeds 0.9.