Modelling of heat and thermo-chemical processes in a fluidized bed
Results of this project are highlighted below:
- To understand the effect of immersed parts on fluidization and heat transfer, we simulated the gas-solid flow in a fluidized bed of 0.1 mm alumina (Al2O3) particles. Gas flow was simulated using computational fluid dynamics (CFD), while the motion of particles was described by a Newton equation with additional forces and solved with the discrete element method (DEM) (Figure 1).
- A macroscopic model composed of two particle layers and a porous medium was developed to simulate heat transfer at the surfaces of parts. A calculation algorithm of the model was coded into the above dynamic and heat transfer models to calculate the heat transfer coefficient, which is a function of solid fraction, thermal properties of gas and particles, temperature, velocity of gas-solid mixture and residence time at the part surface.
- Molecule diffusion and chemical reactions in beds were simulated to improve the fundamental understanding of the functions of inert solid particles in fluidised beds. Both the finite rate model (FRM) and the eddy dissipation model (EDM) were employed to model chemical reactions. Figure 2 shows the simulation results for the reaction of methane and air in a fluidized bed.
- The carburizing process of a metallic component using a fluidized bed has been simulated. The carbon transfer at the interface of the heat-treatment atmosphere and the steel surface was expressed as the decomposition of gaseous molecules, the absorption of atoms and chemical reactions. These mass transfer processes were integrated into CFD codes and the carburizing rates at different part surfaces were modelled.
- Mass transfer coefficient in a heat treatment furnace can be extracted from the element concentration at the surface or the element profile in the surface of a sample treated in the furnace. Two methods to extract the mass transfer coefficient were developed through the simulation of the carburizing of a part and the use of theoretical analysis, and this method subsequently used for other heat treatment processes.
Figure 1: Solid particle distribution in a fluidized bed
Figure 2: Distribution of mass fraction for different gases (average particle mass concentration: 420 kg/m3)
Weimin Gao, Lingxue Kong, and Peter Hodgson, Computational Simulation of the Influence of Inert Particles on Incomplete Combustion of Methane at a Low Air Factor, Materials Performance and Characterization, Vol. 9, No. 5, Paper ID MPC104531, 2012
W.M. Gao, L.X. Kong, L.M. Long and P.D. Hodgson, Measurement of Mass Transfer Coefficient at Workpiece Surfaces in Teat Treatment Furnaces, Journal of Materials Processing Technology, 209, 2009, pp497-505.
W. M. Gao, L. X. Kong and P. D. Hodgson, Computational Simulation of Gas Flow and Heat Transfer Near an Immersed Object in Fluidized Beds, Advances in Engineering Software, Vol 38, pp. 826-834, Elsevier SCI, England, 2007.
W.M. Gao, L.X. Kong and P.D. Hodgson, Local total and radiative heat-transfer coefficients during the heat treatment of a workpiece in a fluidised bed, Applied Thermal Engineering, 26(14-15), pp.1463-1470, 2006.
W. M. Gao, P.D. Hodgson and L.X Kong, Experimental Investigation and Numerical Simulation of Heat Transfer in Quenching Fluidised Beds, Int. Journal Material and Product Technology, 24(1-4), pp. 325-344, 2005.
W. M. Gao, J. M. Long, L. X. Kong and P.D. Hodgson, Influence of Geometry of an Immersed Steel Workpiece on Mass Transfer Coefficient in a Chemical Heat Treatment Fluidised bed. ISIJ International, 44(5), pp.869-877, 2004.
W.M. Gao, L.X. Kong and P.D. Hodgson, Numerical Simulation of Heat and Mass Transfers in Fluidized Bed Heat Treatment Furnaces, Journal of Materials Processing Technology, 125-126, 170-178, 2002.