Copyright (c) 2008 All rights reserved. http://works.bepress.com/abid_akhtar Recent documents in Abid Akhtar Mr en-us Wed, 02 Apr 2008 17:29:42 PDT 3600 http://works.bepress.com/abid_akhtar/4 http://works.bepress.com/abid_akhtar/4 Tue, 22 Jan 2008 20:30:01 PST Two- and three-dimensional numerical simulations have been performed on a laboratory scale bubble column reactor using a volume-of-fluid approach. The effect of hole-size and superficial gas velocity on the bubble size distribution and their trajectories has been investigated on a 20 cm diameter and 1 m high cylindrical reactor. All simulations were performed in a transient manner using a FLUENT solver. Surface tension between two phases has been modelled as a body force with a constant value. Turbulence was modelled using the k-(epsilon) turbulence approach. A comparison between simulation predictions and the reported experimental studies has shown a good agreement. Abid Akhtar http://works.bepress.com/abid_akhtar/3 http://works.bepress.com/abid_akhtar/3 Thu, 08 Mar 2007 17:33:32 PST Hydrodynamics study of a continuous bubble chain rising through liquid column has been performed for laboratory scale bubble column using the volume-of-fluid (VOF) approach. The effect of operating and design parameters on the bubble size distribution and rise trajectory has been investigated for air-water system. For the same distributor, simulation results have indicated the formation of small bubbles at low superficial gas velocity and relatively large bubbles at higher velocities. The increase in the hole-size of distributor has shown similar behaviour. Analysis of bubble trajectories for different superficial gas velocities and distributors has demonstrated an oscillatory behaviour exhibited by small bubbles formed at low superficial gas velocity. A reasonable agreement between the predicted values of gas hold-up with the experimental work has validated the present model. Abid Akhtar http://works.bepress.com/abid_akhtar/2 http://works.bepress.com/abid_akhtar/2 Fri, 12 Jan 2007 00:14:14 PST A two-fluid Eulerian model has been used to study the effect of various sieve plate gas distributors and gas superficial velocities on the hydrodynamics of three-dimensional flow in bubble columns. Turbulence has been modelled using the k-Õ turbulence model. Inclusion of gas distributors showed asymmetric flow patterns which are otherwise smoothened when modelled using a uniform gas source. The asymmetric behaviour increased with increase in the number of holes giving better mixing. The gas hold-up increased with superficial gas velocity, and was independent of the distributor design at high superficial gas velocities. Comparison of simulation results with the experimental work from literature has provided a successful validation of the model. This study demonstrates the significance of real distributor in hydrodynamic studies that has been largely neglected in past. Abid Akhtar http://works.bepress.com/abid_akhtar/1 http://works.bepress.com/abid_akhtar/1 Fri, 15 Dec 2006 02:16:35 PST Multiphase flow processes are frequently observed in several important reactor technologies. These technologies are found in diverse applications such as in manufacture of petroleum-based fuels and products, conversion of synthesis gas into liquid hydrocarbons (Gas-to-liquid technology), production of commodity chemicals, pharmaceuticals, herbicides, pesticides, polymers etc. Due to the inherent complexity of these processes, the knowledge of fluid dynamic and transport parameters is necessary for development of appropriate reactor models and scale-up rules. It is, therefore, of paramount importance to develop understanding and predictive tools to simulate multiphase flow processes for better and economically viable reactor technologies. In the past, knowledge of hydrodynamics and transport characteristics of multiphase reactors has been interpreted in the form of empirical correlations, which have numerous restrictions in terms of their validity for different operating conditions. Computational fluid dynamics (CFD) simulation, on the other hand, deals with the solution of fluid dynamic equations on digital computers, requiring relatively few restrictive assumptions and thus giving a complete description of the hydrodynamics of these reactors. This detailed predicted flow field gives an accurate insight to the fluid behaviour and can sometimes give information, which cannot be obtained from experiments. These days, due to cheaper computational resources, CFD simulations are becoming economically reliable for modeling of multiphase processes including GTL (Gas-to-liquid) processes. In this paper, a comprehensive review of different multiphase flow simulation approaches has been presented. The recent progress made in hydrodynamic modeling of multiphase reactors, their capabilities and limitations (with special focus on GTL processes) are discussed in detail. Finally, case studies with different simulation approaches (Eulerian-Eulerian and VOF (Volume of fluid) simulations of bubble column reactors operating in different flow regimes) are discussed to demonstrate the power of this emerging research tool. Abid Akhtar Computational Fluid Modeling