Direct numerical simulations of heat and momentum transfer in dispersed multiphase flows

Paper in proceeding, 2013

In a number of industrial applications, more than two types of dispersed phases co-exist and interact. Important examples include flotation (solid particles and bubbles in a liquid), and in-cylinder diesel spray combustion and spray drying with particle nucleation (droplets and solid particles in a gas). The transport of momentum and heat can be strongly coupled in these systems, so that the motion of the dispersed phases is significantly affected by the heat transfer and vice versa. In the derivation of closure laws for use in numerical simulations of industrial units, direct numerical simulations of the events on the microscale are important. In the present work, we propose a comprehensive framework for direct numerical simulations of the motion of solid particles in non-isothermal systems. The computational method is based on solving a shared set of momentum and energy balance equations for the carrier phase and the dispersed phases. Measures are taken to ensure that all non-deformable entities (solid particles) behave like rigid bodies. Moreover, deformable entities (e.g. bubbles) as well as rarefaction effects can be accommodated within this framework. The predictions of the numerical method are in very good agreement with the available data for a number of important validation cases: isothermal solid particles motion in the presence of walls and other particles, natural convection around a stationary particle, solid particles motion accompanied with heat transfer effects and isothermal solid particles motion under rarefied conditions. Finally, it is shown how the method can be applied to investigate in detail the simultaneous effects of heat transfer and rarefaction on the motion of a solid catalyst particle in an enclosure and the outcome of the interaction of a solid particle and a microbubble in a flotation cell.