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

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.