Experimental investigation of interaction processes between droplets and hot walls

A detailed experimental investigation of interaction processes of small liq uid droplets with hot walls well above the Leidenfrost temperature has been carried out. The experimental method which uses monodisperse droplet strea ms in combination with a standard video camera allows very detailed observa tions and measurements with very high time resolution. The main intent of t his 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, especial ly for applications in fuel preparation processes, combustion processes, an d spray cooling. The loss of momentum of the droplets, the droplet deformat ion, and the onset of droplet disintegration have been investigated. For al l 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 dropl et deformation has been deduced, which yields a very good agreement with ou r own measurements as well as with results reported in the literature. A mi nimum impinging angle for droplet disintegration has been discovered for sm all 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 und erstanding of basic interaction processes between droplets and hot walls ma y be improved. (C) 2000 American Institute of Physics. [S1070-6631(00)00803 -5].