Fred W. Staub

Stability of dry patches forming in liquid films flowing over heated surfaces

Abstract Criteria are derived which predict the stability of dry patches forming in thin liquid films flowing over a heated surface. The analysis of Hartley and Murgatroyd [1, 2], applicable to isothermal films, is extended to include the effects of vapor thrust and of thermocapillarity. Numerical evaluations are carried out that indicate the relative importance of the various effects in conjunction with typical heated water and liquid metal films. The results show that for liquids of high wettability (for example for liquid metals) the thermal effects become dominant in determining the stability of dry patches.

THE PROPAGATION AND THE WAVE FORM OF THE VAPOR VOLUMETRIC CONCENTRATION IN BOILING, FORCED CONVECTION SYSTEM UNDER OSCILLATORY CONDITIONS

Abstract Various aspects and characteristics of the void propagation equation are discussed. This equation predicts the transient response of the volumetric concentration to perturbations of (1) power input, (2) inlet flow, (3) system pressure, (4) thermodynamic nonequilibrium, (5) compressibilities of the vapor and of the liquid and (6) body forces acting on the two-phase mixture. This transient response is predicted both as function of space and function of time. Solutions of the void propagation equation are derived for the following operating conditions: (1) constant power and inlet flow, (2) oscillatory power input, (3) oscillatory inlet flow and (4) oscillatory power and oscillatory flow. It is shown that perturbations of the mixture density are propagated through the two-phase mixture by the velocity of kinematic waves . Expressions which predict the rate of propagation of these waves and which are appropriate to the operating conditions listed above are presented. The finite rate of propagation of kinematic waves introduces a “delay time” which characterizes the response of the volumetric concentration to various perturbations. The “delay times”, appropriate to the operating conditions enumerated above, are also presented. The predicted results are compared to available experimental data, satisfactory agreement is shown.

Steady-state and transient gas—solids flow characteristics in vertical transport lines

Abstract The generalized application of the drift velocity approach to gas—solids flow is given, together with supporting data and suggested parameter evaluation techniques, to allow the prediction of the phase densities, phase flow rates and allowable operating conditions related to gas—solids flow in vertical pipe systems. Both steady-state and transient flow conditions are considered in co-current and countercurrent flow. Continuity wave velocities are employed to determine the stability of the flow and the presence of flooding. The method of analysis outlined here, previously used successfully in gas—liquid systems, is shown to also hold for gas—solid systems.