Experimental investigation of interaction processes between droplets and hot walls

A detailed experimental investigation of interaction processes of small liquid droplets with hot walls well above the Leidenfrost temperature has been carried out. The experimental method which uses monodisperse droplet streams in combination with a standard video camera allows very detailed observations and measurements with very high time resolution. The main intent of this paper is to study the mechanical behavior of liquid droplets impacting on hot walls well above the Leidenfrost temperature. A better understanding of this process may lead to a better modeling of two-phase flows, especially for applications in fuel preparation processes, combustion processes, and spray cooling. The loss of momentum of the droplets, the droplet deformation, and the onset of droplet disintegration have been investigated. For all experimental results correlations have been developed, which can be used to improve the numerical modeling of two-phase flows. Using the correlation for the loss of momentum a theoretical approximation for the maximum droplet deformation has been deduced, which yields a very good agreement with our own measurements as well as with results reported in the literature. A minimum impinging angle for droplet disintegration has been discovered for small impinging angles. Below this impinging angle no droplet disintegration is observed. This phenomenon is directly related to the energy dissipation at the wall during the interaction process. With the presented work the understanding of basic interaction processes between droplets and hot walls may be improved. (C) 2000 American Institute of Physics. [S1070-6631(00)00803-5].