On the impingement of free, thin sheets of liquids—A photographic study of the impingement zone

Robert J Demyanovich

doi:10.1063/5.0040336

Abstract

The impingement zone created by the impingement of two free, thin sheets of liquids was studied using photographic techniques. The experimental parameters studied were the impingement angle, single-sheet velocity, single-sheet thickness at impingement, liquid surface tension, and liquid viscosity. Momentum balances of the impingement are in good agreement with observations that a critical mixed sheet velocity must be achieved in order for the liquid to flow in the backward direction of the mixed sheet. The critical mixed sheet velocity for backflow was found to correlate well with the Taylor–Culick velocity. However, if all of the kinetic energy associated with the single-sheet component velocity that is destroyed upon impingement is dissipated into the mixed sheet, then that critical velocity cannot be achieved, and there will be no backflow from the backward part of the mixed sheet. An unusual result of the study is that the projection of the single sheets onto the mixed sheet at impingement presents as a “skin” that can be clearly seen in photographs or a video. This “skin” feature potentially allows for the use of macro photography to measure the thickness of the single sheet at impingement.

Highlights

Micromixing of liquid reactants undergoing fast reactions is important since it is often the rate-limiting step, especially in applications where high yield is important
It was initially not clear what the photographs would reveal, Fig. 4 clearly shows that there is liquid above the projection of the front single sheet onto the mixed sheet, which would be in the direction of mixed sheet backflow
The term “inelastic collision” as used here is defined as a collision that results in the dissipation of kinetic energy from the single-sheet component velocities that are destroyed upon impact

Summary

Introduction

Micromixing of liquid reactants undergoing fast reactions is important since it is often the rate-limiting step, especially in applications where high yield is important. The impingement of free, thin liquid sheets as proposed by Demyanovich[3] was shown by Demyanovich and Bourne[4] to yield rapid micromixing of relatively large flow rates of liquids. Two equal, single sheets produced at 1.0 bar, with a flow rate of 2.3 l/min each, were impinged at a 30○ angle and at a distance of 2 cm from the origin of each sheet. A. Prior research on the impingement of free, thin sheets of liquid. To the best of the author’s knowledge, there is no prior published research on the nature of the collision in the impingement zone of impinging thin sheets of liquids. The prior work of Demyanovich and Bourne[5] was limited in scope to estimating the energy released in the impingement zone under inelastic collisions at two impingement angles. The ratio of these characteristic lengths is approximately a factor of 28

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