Computational study of heat transfer in fluid-solid flows.

摘要

Efficient and accurate heat transfer evaluation is essential to the study of thermal flows and energy exchange in fluid-solid systems. For fluid-solid flows with moving solid particles, heat transfer between the colliding particles is investigated computationally using a finite difference method and analytically using various asymptotic methods. An efficient heat transfer evaluation technique for any curved boundary has also been proposed and validated in this dissertation based on the thermal lattice Boltzmann equation (TLBE) method with an improved boundary condition treatment. Two specific topics are further studied with the proposed boundary schemes and heat transfer evaluation technique, including the development of a multiple-relaxation-time (MRT) lattice Boltzmann (LB) model for the axisymmetric convection-diffusion equation (CDE), and a radiation-conduction coupled model for the energy transport in a solar thermochemical reactor.;From the computationally determined heat transfer during the collision, a closed-form formula is developed to predict the heat transfer as a function of the impact Fourier number, the thermal diffusivity ratio and the thermal conductivity ratio of the impacting particles.;To develop a general and efficient technique for evaluating the heat transfer on a curved boundary, the TLBE method is applied for its simple algorithm and capability to deal with complex geometries. An improved thermal boundary condition treatment is proposed based on the "bounce-back" and interpolation of the temperature distribution functions (TDFs) of the TLBE model.;The exact geometry on a boundary is preserved with the proposed boundary condition treatment so that the boundary heat fluxes in the discrete velocity directions of the TLBE model can be directly obtained from the TDFs at the neighboring lattice nodes. The total heat transfer on the boundary is simply a summation of all the discrete heat fluxes with a constant surface area.;As applications of the proposed boundary schemes and heat transfer evaluation technique in the TLBE method, 1) a quasi-two-dimensional (2-D) axisymmetric LB model with an MRT collision operator is proposed to simulate the general axisymmetric CDE in 3-D, and 2) a radiation-conduction coupled model is developed to simulate the energy transport in a solar reactor.