Radiation and convection heat transfer in particle-laden fluid flow

Abstract

Combined radiation, convection, and conduction heat transfer are studied in a dispersed two phase flow of gray, laminar, axisymmetric media, where both phases are radiatively participating. The radiative transfer equation in curvilinear coordinates is coupled with an interpenetrating continua energy and momentum formulation for the two phase flow. The radiative transfer equation is set in a novel coordinate system which allows full variation of the radiation intensity in the plane of symmetry and expression of symmetric boundary conditions, without resort to the frequent assumption of azimuthal symmetry. The radiative transfer equation is solved using the discrete ordinates method, chosen for its relative accuracy and ability to numerically complement a differential energy formulation. An appropriate discrete ordinates quadrature is derived for the novel coordinate system. The heat transfer model is used to study a proposed arrangement in which heated particles are seeded into heat exchange tubes running through a furnace in order to enhance heat transfer to a gas flowing in the tubes. It is found that with particles heated to temperatures approaching the furnace temperature, and mass loading ratios (seeded particle specific mass to carrying gas specific mass) up to the order of 10, significant enhancement in heat transfer to the gas is achieved. Such enhancement has the effect of reducing the required heat exchange tube length, thereby reducing the furnace size. Interphase heat transfer between the dispersed particles and the semi-continuous gas is studied in detail by formally modeling combined radiation, conduction, and convection heat transfer between a particle and a semi-infinite medium. Results of this study demonstrate that in the seeding particle case, simple correlations for combined mode heat transfer are accurate. It is also found that the critical particle spacing at which interphase heat transfer is interfered with by neighboring particles is smaller for radiation dominated cases than for conduction dominated cases