John A. Tallmadge

Theory of drag out of liquids on flat plates

A theoretical relationship is given for estimating the film thickness and flow rate at which a liquid is dragged out of a bath by a moving flat plate. This is derived by the integration of the Navier-Stokes equation for flow in films on solid supports given by Levich and by consideration of the linearized form of this equation and a similar simpler one derived by Landau and Levich. The numerical integration of the Landau and Levich equation was carried out and a more accurate value of a required constant is presented. The approximation used by the authors in obtaining a more general solution follows from considerations of the course of the numerical integration of both differential equations, the Landau and Levich and the general one. The resulting equation embodies elements of previous theory and gives good agreement with all experimental data over the entire range of dimensionless withdrawal velocity, (u0μ/σ), studied: which no previously derived theoretical relationship has done.

A variable-coefficient plate withdrawal theory for power law fluids

Abstract A new theory for withdrawal of flat plates from power law fluids has been developed and tested with film thickness data. The theory was found to be superior to previous theories. Agreement between theory and data was found to be sensitive to the relevant curvature coefficient. Properties of the variable coefficient were described.

The additional parameter in withdrawal

Abstract Dimensional analysis indicates one more non-dimensional parameter in withdrawal than the number predicted by previous theories. For the case of continuous plate withdrawal from Newtonian fluids, the suitable independent parameter is foudn to be fluid property number ( F p ) which is a function of viscosity, surface tension, density, and gravitational field. The Reynolds number is defined for withdrawal and is shown to be a function of F p and capillary number for laminar flow. The onset of wavy flow in withdrawal is shown to occur near Re of one, based on tests with eight liquids having an 80-fold range of F p . It appears that the Froude number may also be used as a wave point criterion, but use of the Weber number does not appear to be useful for the conditions studied. Comparisons are made with wetted wall flow.

Properties of static menisci on cylinders: Analytical expressions for curvature and height at contact

Abstract Analytical expressions are derived for properties of static menisci based on recently published tabular values. The first case considered is the profile on the outside of a vertical cylinder at zero wetting angle. An expression is derived for the curvature at the top of the meniscus and is shown to be precise for a wide range of radii. Expressions are developed to describe the effect of radii on the height of the meniscus. The height expressions for large radii and small radii are compared with asymptotic expressions in the literature. Also discussed are the cases for nonzero wetting angle.

Quench Atomization of Iron-Base Alloys into Metal Powders

Quench atomization is discussed as a powder formation step used in the production of structural shapes by powder metallurgy. Emphasis is placed on the continuing study of atomization of liquid metals by the two-fluid nozzle method. The influence of atomization control variables on powder properties is considered, where the important characteristics include particle size, chemistry, grain size, and particle shape. Results from a 3–20 kg pilot unit are reported for the case of nitrogen atomization with an annular nozzle. Size, shape, and other powder properties are compared for the case of low and high carbon iron alloys. Some of the interrelationships between atomization and concurrent parts of the powder metallurgy study include fundamental mechanisms and process optimization as well as powder production and experimental studies.