Differences of two-component droplets breakup at the high temperatures

Abstract

Heated liquid droplets may break up in the puffing and micro-explosion regimes. Many gas-vapor-droplet technologies can be improved significantly by using partial or full dispersion and explosive breakup of parent-droplets in a rational and controlled manner. Here we present the findings of experimental research into the fragmentation of boiling two-component droplets of different origin: emulsions, solutions, slurries, and immiscible two-liquid droplets. We consider three ways of energy supply to the droplet – conductive, convective, and radiative – typical of the current thermal liquid treatment technologies. We also identify the conditions that can provide monotonous evaporation, rapid fragmentation, and droplet aerosol. For the most interesting behavior – micro-explosion – the charts are obtained showing droplet heating times before breakup, number and size of child-droplets, and the ratio of the evaporation surface area before and after atomization. We show how much interference is brought by the main factors and processes – temperature, heat fluxes, component concentrations, dimensions or droplets, and their total evaporation surface areas. The scientific novelty of the research findings comes from the comparative dependences of fuel droplet fragmentation characteristics on the magnitude of the heat flux supplied at the heating temperatures ranging from 250 to 450 °C. These functions can be used to predict the optimal schemes of combined heat exchange with several heating mechanisms. This way we can provide the fastest possible micro-explosive breakup and ignition with relatively low energy costs. The practical value of the experimental results is attached to the key characteristics of micro-explosive breakup obtained for a wide range of promising fuels. These characteristics include the minimum heating times, the required threshold values of heat fluxes, and the necessary proportions of flammable and non-flammable components. The functions obtained are important for the testing and development of micro-explosion models, especially in order to update the characteristics of child-droplets. The number of child-droplets ranges from 2 to 3 to several hundreds or even thousands, and their size is several orders of magnitude smaller than that of the parent-droplet. These characteristics traditionally require updating during simulation by arranging more experiments.