Explosive disintegration of two-component droplets in a gas flow at its turbulization

The experimental results shown that the mode of droplet disintegration dominates in the laminar flow, and the intensive fragmentation is prevalent in the turbulent flow during almost the entire time of heating. Typical dependences of the time of droplet heatup before disintegration or fragmentation on the temperature, flow rate, structure and regime (laminar and turbulent) are established. The studies are conducted with heated air and flue gases to ensure the application of the research results in the technology of thermal and flame cleaning of liquids from irregular impurities. It is shown that in the flow of combustion products the droplet disintegration occurs 15-20% faster than in the air-flow. In this case, the explosive puffing is more often realized. At high-temperatures (more than 400?C) the characteristics of the explosive droplet disintegration in the studied flows are almost identical (differences in disintegration times do not exceed 5% at different flow turbulization). At lower temperatures, the disintegration times differ 3-4 times for the range Re = 2200-3400. In this case, the more Reynolds number is, the more intense is the fragmentation of two-component droplets throughout the heating time. Due to explosive disintegration of intensely evaporating two-component droplets the growth of the relative area of evaporation was 10-25 times.

The main reasons of rebound, coagulation, and explosive disintegration of the liquid drops in gas-vapor-droplet streams

We have reviewed the known data about mechanisms, conditions, reasons, and characteristics of rebound, coagulation, and explosive disintegration of drops in gas-vapor-droplet streams. The three main factors of altering a direction of motion, a velocity, a size and a concentration of droplets in a gaseous stream have been highlighted. Among of them are the thermal factor (heating and evaporation of drops), the aerodynamic factor (acceleration, reverse motion, and deceleration of drops due to their entrainment by gaseous stream), the dynamic factor (change in size, velocity, and direction of motion of drops after their collision). We have generalized the findings obtained by various authors in experiments with two drops, little group of drops, and aerosol. In addition, we have reviewed the published results about the fields of velocities and motion trajectories of drops in a flow, about the change in size and concentration of drops due to rebound, coagulation, disintegration (i.e. the complete destruction of the parent drops and the detachment of the liquid fragments of different size and volume from the surface).

The features of heterogeneous water droplet evaporation in high-temperature combustion products of typical flammable liquids

This paper presents the experimental results on heating and evaporation features of heterogeneous (with opaque solid particles ? the size of 0.05-0.5 mm, relative mass concentration 0-1%) water droplets (the initial size ? radius 1-3 mm) during their motion through high-temperature (500-1800 K) gases. A significant increase in the integral characteristics of evaporation by introducing opaque inclusions into droplets was observed. The influence of energy accumulation on the conditions of droplet evaporation at the internal solid/liquid interfaces was established. For proportioned inclusions, the conditions of intensive vaporization (leading to the explosive disintegration of droplets) at internal inclusion/liquid interfaces was set. To summarize research results, experiments were conducted with the combustion products of kerosene, gasoline, industrial alcohol, acetone, and oil. The particles of graphite, carbon, and aluminum as solid inclusions were used. The investigation compared integral characteristics of heterogeneous droplet evaporation under the conditions of non-stationary (gas temperature varied from 1800 K to 500 K over the length of channel) and nearly stationary (gas temperature was maintained at about 1100 K) heating.

Vapor Films under Influence of High Heat Fluxes: Nongravity Surface Waves and Film Explosive Disintegration

Linear and non-linear stability analysis of the interface between a thin vapor film and a layer of liquid in the presence of a steady heat flux from a metal surface heated to a high temperature, to the vapor film and then from vapor to the subcooled liquid is investigated. The temperature dependence of saturation pressure is taken into account. Boundary conditions on the vapor–liquid interface that generalizes the known correlations on the free surface of liquid in the gravity field are derived. The thermal processes on the phase boundary lead to the generation of weakly decaying periodic surface waves of low amplitude and may cause small length waves (ripple), which are not capillary ones. Thermal processes on the phase interface are capable to provide the stability of a film of lights vapor under a layer of heavy liquid in the gravity field. The explosive instability may arise in the non-linear stage due to a weak variation of the film thickness or superheating of liquids.