SUMMARYNumerical calculations were carried out at the apex cone and various axial positions of a gas cyclone separator for industrial applications. Two di erent NS-solvers (a commercial one (CFX 4.4 ANSYS GmbH, Munich, Germany, CFX Solver Documentation, 1998), and a research code (Post-doctoral Thesis, Technical University of Chemnitz, Germany, September, 2002)) based on a pressure correction algorithm of the SIMPLE method have been applied to predict the ow behaviour. The ow was assumed as unsteady, incompressible and isothermal. A k-turbulence model has been applied ÿrst using the commercial code to investigate the gas ow. Due to the nature of cyclone ows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as Reynolds stress model (RSM) and large eddy simulation (LES) have been used as well. The RSM simulation was performed using the commercial package activating the Launder et al. 's (J. Fluid. Mech. 1975; 68(3):537-566) approach, while for the LES calculations the research code has been applied utilizing the Smagorinsky model. It was found that the k-model cannot predict ow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. This paper is organized into ÿve sections. The ÿrst section consists of an introduction and a summary of previous work. Section 2 deals with turbulence modelling including the governing equations and the three turbulence models used. In Section 3, computational parameters are discussed such as computational grids, boundary conditions and the solution algorithm with respect to the use of MISTRAL=PartFlow-3D. In Section 4, prediction proÿles of the gas ow at axial and apex cone positions are presented and discussed. Section 5 summarizes and concludes the paper.

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Numerical flow calculations were carried out at various axial positions of a gas cyclone separator for industrial applications. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, we used the advanced turbulence model of Large Eddy Simulation (LES). The application of LES reveals better agreement with the experimental data, however, it requires higher computer capacity and longer running times when compared to standard turbulence models. These calculations of the continuous phase flow were the basis for modeling the behavior of the solid particles in the cyclone. Particle trajectories, pressure drop and the cyclone separation efficiency have been studied in some details. The paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with the LES turbulence calculations of the continuous phase flow. The third section treats modeling of the dispersed phase behavior. In section 4, computational issues are presented and discussed as applied grids, boundary conditions and the solution algorithm. In section 5, prediction profiles of the gas flow at axial positions are presented and discussed in some details. Moreover, pressure drop, particle trajectories and cyclone efficiency are discussed. Section 6 summarizes and concludes the paper.

Thermocapillary convection is studied experimentally using particle-image-velocimetry for flow visualization and analysis. This method offers the advantage of measuring the entire flow field (velocity field, streamlines etc.) in a selected plane within the fluid at a given instant of time in contrast to point by point methods like laser-Doppler-velocimetry (LDV). The paper describes the method and presents quantitative results for different Marangoni numbers.

The surface tension driven flow in the liquid vicinity of gas bubbles on a heated solid wall has been investigated both, in a reduced gravity environment aboard a sounding rocket, and in an earth-bound experiment. Both experiments deal with temperature gradients within the liquid surrounding of a bubble which cause variations of the surface tension. These, in turn, lead to a liquid flow around the bubble periphery termed thermocapillary or thermal Marangoni-convection. On Earth, this phenomenon is widely masked by buoyancy. We therefore carried out an experiment under reduced gravitational acceleration. In order to simultaneously observe and record the flow field and the temperature field liquid crystal tracers have been applied. These particles offer the feature of selectively reflecting certain wavelengths of incident white light depending on the crystals temperature. Although the bubble injection system did not perform nominally during the flight experiment, some interesting flow characteristics could be observed. Comparison of results obtained in microgravity to data measured on Earth reveal that due to the interaction of thermocapillarity and buoyancy a very compact vortex flow results on ground, while in microgravity the influence on the surface tension driven flow penetrates much deeper into the bulk. This result is of special interest regarding the production of materials in space.