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in Wiley InterScience (www.interscience.wiley.com).The approach of combined discrete particle simulation (DPS) and computational fluid dynamics (CFD), which has been increasingly applied to the modeling of particle-fluid flow, is extended to study particle-particle and particle-fluid heat transfer in packed and bubbling fluidized beds at an individual particle scale. The development of this model is described first, involving three heat transfer mechanisms: fluid-particle convection, particle-particle conduction and particle radiation. The model is then validated by comparing the predicted results with those measured in the literature in terms of bed effective thermal conductivity and individual particle heat transfer characteristics. The contribution of each of the three heat transfer mechanisms is quantified and analyzed. The results confirm that under certain conditions, individual particle heat transfer coefficient (HTC) can be constant in a fluidized bed, independent of gas superficial velocities. However, the relationship between HTC and gas superficial velocity varies with flow conditions and material properties such as thermal conductivities. The effectiveness and possible limitation of the hot sphere approach recently used in the experimental studies of heat transfer in fluidized beds are discussed. The results show that the proposed model offers an effective method to elucidate the mechanisms governing the heat transfer in packed and bubbling fluidized beds at a particle scale. The need for further development in this area is also discussed.

This report presents a numerical study of segregation and mixing of binary mixtures of particles in a gas-fluidized bed by means of discrete particle simulation, where the motion of individual particles is 3-D and the flow of continuous gas is

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This paper presents a numerical study of the angle of repose, a most important macroscopic parameter in characterizing granular materials, by means of a modified distinct element method. Emphasis is given to the effect of variables related to factors such as particle characteristics, material properties, and geometrical constraints. The results show that sliding and rolling frictions are the primary reasons for the formation of a sandpile; particle size and container thickness significantly influence the angle of repose; and the angle of repose is not so sensitive to density, Poisson's ratio, damping coefficient, and Young's modulus. Increasing rolling friction coefficient or sliding friction coefficient increases the angle of repose. Conversely, increasing particle size or container thickness decreases the angle of repose. The underlying mechanisms for these effects are discussed in terms of particle-particle and particle-wall interactions.

b thermal coeYcient of volumetric expansion, K -1 c porosity The erosion of hearth refractories is widely e rate of dissipation of turbulent energy, m 2 s -3 recognised as the main limitation for a long l thermal conductivity, W m -1 K -1 campaign blast furnace life. Distributions of liquid m e f f eVective viscosity, kg m -1 s -1 iron flow and refractory temperatures have a m L laminar viscosity, kg m -1 s -1 significant influence on hearth wear. In this m T turbulent viscosity, kg m -1 s -1 investigation, a comprehensive computational fluid r density of liquid iron, kg m -3 dynamics model is described which predicts the fluid flow and heat transfer in the hearth; specifically, the flow and temperature distributions in the liquid INTRODUCTION iron melt, and temperature distributions in theThe erosion of hearth refractories is widely recognised as refractories. The accuracy and representativeness the main limitation for a long campaign blast furnace life, of the model was evaluated using plant data from i.e. greater than 15 years. While it is possible to maintain BHP Steel's Port Kembla no. 5 blast furnace and the bosh and shaft areas by gunning practices, cooling OneSteel's Whyalla no. 2 blast furnace. Generally, element replacements, etc., the repair of hearth refractories there is good agreement between measured and requires prolonged shutdowns, and hence major losses in calculated refractory temperature profiles. A series production and cash ow. The timing of such shutdowns of sensitivity tests provided cause-effect is made more problematic because precise measurement of relationships between operational and fluid flow hearth refractory wear is extremely diYcult. Furthermore, parameters (floating deadman, different extent of strategies to retard the rate of refractory wear are comrefractory erosion, presence of embrittled layer).promised by the lack of sound causal relationships between I&S/1673 wear and the condition of the coke bed in the hearth, refractory cooling levels, ow distribution, etc.

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