Atomization and Deposition in Two-Phase Annular Flow: Measurement and Modeling (Pressure Drop, Thin Films, Turbulent Dispersion)
Leman, Gregory W.
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https://hdl.handle.net/2142/69761
Description
Title
Atomization and Deposition in Two-Phase Annular Flow: Measurement and Modeling (Pressure Drop, Thin Films, Turbulent Dispersion)
Author(s)
Leman, Gregory W.
Issue Date
1985
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
Models have been developed for the rate processes of atomization from the wall layer in vertical annular two-phase flow and of deposition of this liquid back to the liquid film. These models have been incorporated into a design scheme for the prediction of two-phase pressure drop and fully developed entrained liquid fraction for the annular regime.
Experimental measurements of these rates were taken via the salt tracer method introduced by Quandt (1965). The rates of atomization are found to depend upon gas velocity, gas and liquid densities, and upon the liquid film flow rate. The existence of a critical film flow rate, which is required for atomization, is confirmed. A Kelvin-Helmholz instability analysis of the small waves which are growing on top of the roll waves agrees with the observed dependence of atomization rate, R(,A), on gas velocity and gas and liquid densities. The effect of liquid film flow rate is shown to enter because the roll wave intermittency depends linearly upon the liquid film flow rate.
Experimental results for deposition rate, R(,D), are compared with published correlations. The deposition rates are well correlated by the turbulent dispersion model for low droplet concentrations but are shown to dampen with increased concentrations, eventually attaining a constant maximum value. The mechanism of this inhibition of deposition is undetermined, because the phenomena appear to be explained equally well as an effect of the droplets on the turbulence which deposits them or as an effect of droplet size. Good correlation is obtained by using a turbulent dispersion model in which the rate "constant", k(,D), is allowed to be a function of the ratio of the droplet flux to the gas flux.
Droplets atomizing from the slow moving film are accelerated by the gas phase. Correlation of R(,A) allows the overall two phase pressure drop data of previous researchers to be reexamined, accounting for this momentum loss term distinct from interfacial friction. This results in better predictions for two-phase pressure drops in the annular regime. Hence improved design algorithms have been developed.
At fully developed conditions R(,A) (TURNEQ) R(,D) and so the correlations which have been developed for these two rates are equated to derive a prediction for the fully developed entrained liquid fraction, E. This design prediction has the advantage of greater accuracy than previous correlations, but does require a two-step iterative calculation sequence because the pressure drop and entrainment are each affected by the other.
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