High-speed photography applied for the investigation of the dynamics of free falling evaporating droplets

Central Aero—Hydrodynamic Institute140160, Zhukovsky, Moscow region, USSRABSTRACTThree methods to investigate dynamics and heat and mass transfer of nitrogen drop.-let moving in the air are described. Drag coefficient and Nusselt number as functi—ons of Reynolds numder and of temperature values of a droplet and surrounding gasare derived.The investigation of the dynamics and heat mass exchange of a separate droplet inits own vapor is of interest, e.g.,for constracting a physical—mathematical modelof two—phase flows1. Theoretical investigation would require the solution of a self—matched problem with accounting for a simultaneous variation of the shape of a drop—let in vapor, the fluid distribution in it, an unknown a priori distribution of thesubstance evaporation intensity on its surface caused by an exchange of heat withvapor. Therefore, the only promissing way of obtaining the information on the sumof these processes is an experimental investigation. Meanwhile, the empirical data,while being numerous in case of a diffusive evaporation of the droplet substanceinto a "passive" gas of another nature (e.g;2), are very scarce in case of a con—vective evaporation into its own vapor3We have developed three methods (Fig.1) to investigate the dynamics and heat massexchange approved by an example of nitrogen droplets free falling in air. The drop—lets were generated using a simple device 1 consisting of a beaker with liquid ni—trogen and a thin tube with a wick.This choice of the experiment conditions has the following advantages : 1) it iscomparatively easy to obtain "at room conditions" a high value (