HEAT TRANSFER IN NATURAL CONVECTION WITH FINITE-SIZED PARTICLES CONSIDERING THERMAL CONDUCTANCE DUE TO INTER-PARTICLE CONTACTS

The heat transfer problem in solid-dispersed two-phase flow is numerically studied. Temperature gradient within the finite-sized particles and inter-particle heat flux due to collisions are considered, and those effects on the flow structure and heat transfer are discussed. The interaction between fluid and particles is treated by our original immersed solid approach. For the conjugate heat transfer problems, to satisfy the thermal condition at the fluid-solid interface, our interfacial heat flux model is employed. Also, the interfacial flux model is extended to incorporate the heat conduction due to inter-particle contacts, based on 2D and axisymmetric contact heat resistance solutions. The method is applied to 2D and 3D natural convection problems including multiple particles in a confined domain under relatively low Rayleigh numbers (10(4)-10(6)). Heat transfer and particle behaviors are studied for different solid volume fractions (up to about 50%) and heat conductivity ratios (solid to fluid) ranging between 10(-3) and 10(3). Under high solid volume fraction conditions, the particles are observed to form densely concentrated regions, where heat flow tends to channel through the contacting points. In three-dimensional solid-dispersed flows, by decomposing the heat flux into the contributions of the convection and conduction, the change of the major heat transfer mode is studied for different solid volume fractions and conductivity ratios.