The effect of Weber number, droplet sizes and wall roughness on crisis of droplet boiling

Abstract

Various boiling modes in a wide range of droplet sizes and wall temperature under droplet Tw were studied experimentally. Dynamics of droplets boiling is determined not only by Tw, Weber number We, wall roughness but also by the droplet shape. Application of two different methods of forming a suspended spheroid (ellipsoid) for We=0 and We>1 allowed separate investigation of the influence of the key factors on evaporation. To form the spheroids with We=0 (no droplet fall, V0=0m/s), the limiting rings were used. For We=0, an increase in pressure inside a droplet and its disintegration were excluded because there was no fall. An increase in roughness at We=0 promotes an increase in Leidenfrost temperature TL, and conversely, at We>1, high roughness leads to a decrease in TL due to the pressure drop in liquid and decay of a spheroid. With the growth in the initial diameter of a suspended drop at We=0, temperature TL increases significantly and approaches the value of TL at pool boiling in water. The lower value of this temperature is also consistent with theoretical predictions. Experimental data demonstrate the importance of taking into account the size maldistribution of droplets for the correct prediction of the uneven temperature field on the heated wall surface.