Dmitry Kirichenko

Interaction of Levitating Microdroplets with Moist Air Flow in the Contact Line Region

ABSTRACT Self-organization of levitating microdroplets of condensate over a liquid–gas interface has been observed in several recent experiments involving evaporation at high heat fluxes, although the nature of this phenomenon is still not completely understood. We conduct an experimental investigation of the behavior of such an ordered array of microdroplets as it approaches a region of intense evaporation near the contact line. Interaction of the array with the local highly nonuniform gas flow results in breakup of the pattern. Some droplets fly over the contact line region and end up above the dry part of the solid substrate, whereas others are trapped before they approach the contact line. Our experimental setup provides a unique tool for investigation of the moist air flow near the contact line by using microdroplets as tracers. Local gas flow velocities near the contact line are obtained based on trajectories of the droplets.

Levitation and Self-Organization of Liquid Microdroplets over Dry Heated Substrates

Levitating droplets of liquid condensate are known to organize themselves into ordered arrays over hot liquid-gas interfaces. We report experimental observation of similar behavior over a dry heated solid surface. Even though the lifetime of the array is shorter in this case, its geometric characteristics are remarkably similar to the case of droplets levitating over liquid-gas interfaces. A simple model is developed that predicts the mechanisms of both droplet levitation and interdroplet interaction leading to pattern formation over a dry surface; the model is shown to be in good agreement with the experimental data. Using the insights from the new experiments, we are able to resolve some long-standing controversies pertaining to the mechanism of levitation of droplets over liquid-gas interfaces.