12. Multiphase Flows with Heat and Mass Transfer

Developing new engineering technologies relies on the understanding of complex multiphase flows with heat and mass transfer. Such flows involve two- and four-way interactions between particles/droplets and the continuous career phase in both laminar and turbulent spectrums. This paper provides an overview of these flows in a number of engineering applications including (i) spray flows in diesel and gas turbines, (ii) biomass pyrolysis, and (iii) nanofluid microchannels. The methods addressing such multiphase flows are classified into two main groups including Eulerian–Eulerian and Lagrangian–Eulerian methods. Eulerian–Eulerian methods treat the particle/droplet phase as a continuous phase along with the carrier phase. Lagrangian–Eulerian techniques track individual particles and droplets while treating the fluid phase surrounding the particles/droplet as a continuum. Eulerian–Eulerian models are more common when the particle/droplet mass loading is high such as biomass pyrolysis that can be modelled in the concept of the Granular flows while Eulerian–Lagrangian methods are more suitable for the secondary breakup and dilute spray regions. For nanofluid applications with low mass loading (<5%), it is also common to use mixture models that solve one set of equations for the mixture, while the properties such as density and viscosity are computed for the mixture. If the flow is turbulent, as presented in spray flows, models are required to address the effect of turbulence. Both large eddy simulation (LES) and Reynold averaged Navier–Stokes (RANS) frameworks have been widely adopted for modelling spray flows in internal combustion engines. The next requirement for such flows involves sub-models for different physical phenomena such as particle/droplet dispersion, breakup, phase change, heat transfer, and particle/particle interactions such as collision and agglomeration.