NUMERICAL ANALYSIS FOR HEAT AND MASS TRANSFER OF GRANULAR FLOW IN A DUCT BY THE DISCRETE PARTICLE SIMULATION

摘要

The solid-gas or liquid-gas two phase flow has many industrial applications such as spray drying, pollution control, transport systems, fluidized beds, energy conversion and propulsion, material processing, and so on. Though the solid-gas multiphase flow has been studied experimentally and numerically, the transport phenomena have not been cleared due to its complexity, computational time and economical costs for the hardware. In this study the heat and mass transfer of solid-gas collision dominated flow is analyzed by the Discrete Particle Simulation (DPS), a kind of the Dispersed Element Method (DEM)[1]. This method describes the discrete phase and the continuous phase by Lagrange and Euler methods respectively, and has been used to simulate the multiphase flow of various geometrical systems. In order to analyze the thermal field we took account of the energy equation and heat conduction between colliding particles. The heat transfer rate is summation of conductive heat transfer and convective heat transfer. Furthermore, the fluid flow has a two dimensional velocity profile, because the void fractions are analyzed as two dimensions. But momentum space has not been resolved by the two dimensional simulation. We call this method, the quasi two-dimensional simulation in this paper. To obtain the temperature distribution of the continuous phase the energy equation is solved in addition to the momentum equations. We treated the interaction between continuous and discrete phases as one and two way couplings. The positions, the momentumand the temperature information of particles and the velocity and the temperature distribution of the fluid were obtained as functions of time from results of these numerical simulations.When the hot air that is suspending small glass particles flows in a duct from bottom up, we traced the particles and got the temperature distribution of fluid and compared with the former results of one-dimensional flow. At the beginning, the cooler particles decrease the fluid temperature near the bottom of the vessel. The temperature profile of the particles obtained by the one-dimensional simulation is as same as quasi two-dimensional simulation.After 0.5 second the particles cool the downstream air. At 1.2 second, particles do not decrease the air temperature because the temperatures of particles are close to the inlet temperature of the air.