Numerical Simulations of Two-Phase Flow in a Dorr-Oliver Flotation Cell Model
Abstract: Two-phase (water and air) flow in the forced-air mechanically-stirred Dorr-Oliver machine has been investigated using computational fluid dynamics (CFD). A 6 m 3 model is considered. The flow is modeled by the Euler-Euler approach, and transport equations are solved using software ANSYS-CFX5. Unsteady simulations are conducted in a 180-degree sector with periodic boundary conditions. Air is injected into the rotor at the rate of 2.63 m 3 /min, and a uniform bubble diameter is specified. The effects of bubble diameter on velocity field and air volume fraction are determined by conducting simulations for three diameters of 0.5, 1.0, and 2.0 mm. Air volume fraction contours, velocity profiles, and turbulent kinetic energy profiles in different parts of the machine are presented and discussed. Results have been compared to experimental data, and good agreement is obtained for the mean velocity and turbulent kinetic energy profiles in the rotor-stator gap and in the jet region outside stator blades.
Experimental Study of Multi-phase Flow Hydrodynamics in Stirring Tanks
Stirring tanks are very important equipments used for mixing, separating, chemical reaction, etc. A typical stirring tank is a cylindrical vessel with an agitator driving the fluid and generating turbulence to promote mixing. Flotation cells are widely used stirring tanks in phase separation where multiphase flow is involved. Flotation refers to the process in which air bubbles selectively pick up hydrophobic particles and separate them from hydrophilic solids. This technology is used throughout the mining industry as well as the chemical and petroleum industries. In this research, efforts were made to investigate the multi-phase flow hydrodynamic problems of some flotation cells at different geometrical scales. Pitot-static and five-hope probes were employed to labpilotand commercial-scale tanks for velocity measurements. It was found that the tanks with different scales have similar flow patterns over a range of Reynolds numbers. Based on the velocity measurement results, flotation tanks’ performance was evaluated by checking the active volume in the bulk. A fastresponse five-hole probe was designed and fabricated to study the turbulence characteristics in flotation cells under singleand multi-phase flow conditions. The jet stream in the rotor-stator domain has much higher turbulence intensity compared with other locations. The turbulent dissipation rate (TDR) in the rotor-stator domain is around 20 times higher than that near tank’s wall. The TDR could be used to calculate the bubble and particle slip velocities. An isokinetic sampling probe system was developed to obtain true samples in the multi-phase flow and then measure the local void fraction. It was III found that the air bubbles are carried out by the stream and dispersed to the whole bulk. However, some of the bubbles accumulate in the inactive regions, where higher void fractions were detected. The isokinetic sampling probe was then extended to be an isokinetic borescope system, which was used to detect the bubble-particle aggregates in the tank. Aggregates were found in the high-turbulence level zones. The isokinetic sampling probe and the isokinetic borescope provide new methods for flotation tank tests. An experiment was also set up to study the dynamics of bubble particle impact. Four different modes were found for the collision. The criterion is that if the fluid drainage time is less than the residence time, the attachment will occur, otherwise, the particle will bounce back.
Russian Imperialism from Ivan the Great to the Revolution
Chapter 1 Preface to the Paperback Edition Chapter 2 Foreword Chapter 3 Introduction Chapter 4 The Origins of Russian Imperialism Chapter 5 Pan-Slavism or Pan-Russianism Chapter 6 Russia and the Baltic Chapter 7 Russo-Polish Confrontation Chapter 8 The Ukraine and Muscovite Expansion Chapter 9 Russian Domination in the Balkans Chapter 10 Russian Penetration of the Caucasus Chapter 11 Russian Conquest and Colonization of Central Asia Chapter 12 Russian Designs on the Far East Chapter 13 Notes Chapter 14 About the Authors Chapter 15 Index Chapter 16 Maps