Heat transfer in ternary droplets: an application to the modelling of puffing/micro-explosions

A novel approach to the modelling of heat transfer in ternary droplets before the start of puffing/micro-explosion is described. It is assumed that a spherical droplet of a low-boiling fuel component is located in the centre of the ternary droplet. A spherical shell of a high-boiling fuel component is assumed to form a droplet outer layer, while water is assumed to fill the space between the outer shell and the inner droplet. Heating of the ternary droplet is described using the heat transfer equation with the Robin boundary condition at the droplet surface and the continuity conditions at the interfaces between liquids. The analytical solution to this equation at each time step is incorporated into the numerical code. The results of calculations using the new numerical code allowed us to obtain the time evolution of the temperature and its derivative with respect to time at the water/fuel interfaces. This allowed us to estimate times to puffing/micro-explosion in ternary droplets assuming that these processes take place when water reaches the water nucleation temperature, or the low-boiling component reaches the boiling temperature, whichever happens first. Using the original and published experimental data and COMSOL Multiphysics software, the new model is validated and verified. Times to puffing/micro-explosion in ternary droplets, depending on various input parameters, and temperature distributions in large (diameters equal to 1 mm) and small (diameters equal to 10 μm) droplets are obtained.