Eulerian modeling of reactive gas-liquid flow in a bubble column

Despite the widespread application of bubble columns and intensive research efforts devoted to understand their complex behavior, detailed knowledge on the fluid flow, mass transfer and chemical reactions as well as their interactions is currently very limited. Gas-liquid flow in bubble column reactors is characterized by a combination of inherently unsteady complex processes with widely\ud varying spatial and temporal scales. The complicated interactions between the gas and the liquid phases comprising hydrodynamics, mass transfer and chemical reaction cause many challenging modeling problems to be solved.\ud The Euler–Euler model is adopted throughout this thesis to investigate gas-liquid flow in bubble columns. In this study, efforts have been focused on the assessment of suitable closure laws for interfacial forces and for turbulence in the continuous phase. Furthermore, gas-liquid heterogeneous flow and reactive gas-liquid flows have been studied. All the numerical simulations were carried out with the commercial CFD package CFX-4.4 and all simulation results were compared with the available experimental PIV data of Deen (2001)

A review of dynamics design methods for high-speed and high-precision CNC machine tool feed systems

With the development of CNC machine tools toward high speed and high precision, the traditional static design methods can hardly meet the demand. Hence, in this paper, the dynamics matching design methods of existing CNC machine tool feed systems were investigated and analyzed. Further, sub-system coupling mechanisms and optimization design studies were carried out for each sub-system. First, the required kinematic indexes must be achieved when designing the feed system dynamics of high-speed, high-precision CNC machine tools. Second, the CNC machine tool feed systems generally have four sub-systems: motion process, control system, motor, and mechanical structure. The coupling effect between the sub-systems should also be considered in the design. Based on the dynamics design, each sub-system should be optimized to maximize the system dynamic performance with minimum resource allocation. Finally, based on the review, future research directions within the field were detected

Is I-Voting I-Llegal?

The Voting Rights Act was passed to prevent racial discrimination in all voting booths. Does the existence of a racial digital divide make Internet elections for public office merely a computer geek\u27s pipe dream? Or can i-voting withstand scrutiny under the current state of the law? This i-Brief will consider the current state of the law, and whether disproportionate benefits will be enough to stop this extension of technology dead in its tracks