Numerical simulation of heat and mass transfer in fluidised bed heat treatment furnaces

In this paper, a novel combined theoretical and computational model is developed to simulate the heat and mass transfer between a fluidised bed and a workpiece surface, and within the workpiece by considering the fluidised bed as a medium consisting of a double-particle layer and an even porous layer. The heat and mass-transfer flux from the fluidised bed to the workpiece surface is contributed by dense and bubble phases, respectively. The convective heat and mass transfer is simulated by analysing the gas dynamics in the fluidised bed, while radiative heat transfer is modelled by simulating photon emission in a three-dimensional particle array. The simulation shows that convection is approximately constant, while radiation contributes significantly to the heat transfer. The heat-transfer coefficient on an immersed surface near particles is about 6–10 times that on other areas. The transient heat and mass-transfer coefficient, heat and mass-transfer flux on any surface of the workpiece, transient temperature and carbon distributions at any position of the workpiece during the metal carburising process are studied with the simulation.

Experimental investigation and numerical simulation of heat transfer in quenching fluidised beds

Fluidisation characteristics at different surfaces of a work-piece of complex geometry are conducted in a fluidised bed at various conditions including fluidising number, bed temperature and fluidising medium. The quenching of the work-piece is performed experimentally. In particular, the major frequency and energy of the pressure fluctuations are measured as a function of either fluidising velocity or heat transfer position and the results are used to develop a mathematic model. A computational model is developed to simulate gas dynamics and heat transfer between the fluidised bed and the work-piece surface, as well as simulating the temperature within the work-piece. The predicted cooling curves are in good agreement with the experimental results. Based on the simulation results, the flow characteristics of the gas and the temperature of the dense gas-solid phase near the work-piece surface are analysed to understand the heat transfer mechanism in the fluidised bed.

Computational simulation of gas flow and heat transfer near an immersed object in fluidized beds

To improve the understanding of the heat transfer mechanism and to find a reliable and simple heat-transfer model, the gas flow and heat transfer between fluidized beds and the surfaces of an immersed object is numerically simulated based on a double particle-layer and porous medium model. The velocity field and temperature distribution of the gas and particles are analysed during the heat transfer process. The simulation shows that the change of gas velocity with the distance from immersed surface is consistent with the variation of bed voidage, and is used to validate approximately dimensional analysing result that the gas velocity between immersed surface and particles is 4.6Umf/εmf. The effects of particle size and particle residence time on the thermal penetration depth and the heat-transfer coefficients are also discussed.