DISPERSED MULTIPHASE HEAT AND MASS TRANSFER

This review provides a snapshot of the current status of our understanding of heat transfer in multiphase flows. The presence of particles, droplets, and bubbles alters both the mean flow and turbulence substantially and as a result makes the multiphase flow different from the corresponding single-phase flow. This difference in fluid velocity greatly influences the convective heat transfer behavior of the mixture. There are three other mechanisms that differentiate the thermal behavior of a multiphase flow: thermal-inertia, thermal-transport, and thermal-slip effects. Much of the review's focus is on the third mechanism, where the particle and the surrounding fluid temperature are different, allowing heat transfer between the two. First, we review the state-of-the-art models of heat transfer between an isolated particle and the surrounding fluid and consider several extensions of critical importance to environmental and industrial applications, including consideration of drops and bubbles; mixed conditions of forced and natural convection; and effects of evaporation, particle rotation, velocity, temperature slip, and radiation. The review also defines the regime under which heat transfer cannot be considered quasi-steady and presents appropriate models of unsteady heat transfer. The results of an isolated particle are then extended to heat transfer from a random array of particles. Our current understanding of the effects of free-stream turbulence on heat transfer is also reviewed. In each section, unanswered questions and outstanding challenges that must be tackled by future research are also presented.