MULTIPHASE HYDRODYNAMICS OF GAS-SOLIDS FLOW (MULTIPHASE, TWO PHASE, HYDRODYNAMICS).

摘要

General flow equations for the flow of gas and solid particles of different sizes and densities were developed. The empirical information used in the model are as follows. The gas-particle momentum transfer term used is a generalization of the correlation used by Gidaspow and Ettehadieh (1983) in their single particle size fluidized bed model. A generalization of the solids stress term used by them is also used to prevent the solids volume fraction from becoming unrealistically large. To describe the momentum transfer between purpose computer program to solve the multiphase flow equations based on the K-FIX program (Rivard and Torrey, 1977) was developed.;Energy equations were added to a single particle version of the computer model and heat transfer from bed to wall was studied. The large heat transfer coefficients characteristic of fluidized beds were computed without an enhancement of heat transfer by turbulence. They agreed with measurements reported by Ozkaynak and Chen (1980) within the accuracy of estimated thermal conductivity of solids.;A viscosity term was added to model radial velocity profiles in a pneumatic conveyor. The velocity profiles were similar to one of two contradicting sets of published experimental data. One-dimensional simulation to study segregation in a pneumatic conveyor for a binary mixture was carried out.;Three multiphase flow models were studied to determine critical flow conditions. It was found that the dense phase transport may be limited by a critical velocity equal to SQRT.(G/(rho)(,s)) where G is an "elastic" modulus of the power and (rho)(,s) is its density.;The model was applied to the study of mixing in a fluidized bed by a bubble. The initial condition was that of two segregated layers of particles. At time zero a central jet was turned on and the grid flow was increased to keep the large particles at minimum fluidization. The computations, carried out up to 0.56 s, showed a bubble in the bottom layer and the mixing induced by the drift behind the bubble. The upper layer expanded considerably as seen in an experiment.