Advances in droplet evaporation

Sammanfattning: Droplet evaporation (and condensation) is one of the most common instances of multiphase flow with phase change, encountered in nature as well as in technical applications. Examples include falling rain drops, fogs and mists, aerosol applications like electronic cigarettes and inhalation drug delivery, and engineering applications like spray combustion, spray wet scrubbing or gas absorption, spray drying, flame spray pyrolysis. Multiphase flow with phase change is a challenging topic due to the intertwined physical phenomena that govern its dynamics. Numerical simulation is a valuable tool that enables us to gain insight in the details of the physics, often in cases where experimental studies would be too expensive, impractical or limited. In the present work, the focus is on the evaporation of small spherical droplets. Simulation of the evaporation of a pure and two−component droplet, in a stagnant flow, with the inclusion of detailed thermodynamics and variable physical and transport properties, shows the importance of enthalpy transport by species diffusion in the thermal budget of the system, and allows the identification and characterization of evaporating regimes for an azeotropic droplet. A new method for the interface resolved numerical simulation of laminar and turbulent flows with a large number of spherical droplets that undergo evaporation or condensationon, based on the immersed boundary concept, is developed. Validation with experimental data of pure and two−component droplets evaporating in homogeneous isotropic turbulence is conducted. The method is employed for the direct numerical simulation of spray evaporation in a turbulent channel flow, whereby mechanisms of spray migration and turbulence modulation are revealed, and a scaling of the evaporation enhancement with the turbulence is found. The sensitivity of the zero-dimensional multicomponent droplet evaporation model, used for general purpose multiphase flow calculations, to its many model parameters is analysed by uncertainty quantification, providing useful guidelines for the design and operation of droplet evaporation experiments and simulations.