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DROPLET FLOWS IN MICROCHANNELS USING LATTICE BOLTZMANN METHOD
 Date Issued:
 2009
 Abstract/Description:
 Microelectromechanical systems (MEMS) have widespread applications in medical, electronical and mechanical devices. These devices are characterized by the smallest dimension which is atleast one micrometer and utmost one millimeter. Rapid progress in the manufacture and utilization of these microdevices has been achieved in the last decade. Current manufacturing techniques of such devices and channels include surface silicon micromachining; bulk silicon micromachining; lithography; electrodeposition and plastic molding; and electrodischarge machining (EDM). In recent years, electrostatic, magnetic, electromagnetic and thermal actuators, valves, gears and diaphragms of dimensions of hundred microns or less have been fabricated successfully. Sensors have been manufactured that can detect pressure, temperature, flow rate and chemical composition in such channels. Physical effects such as electrokinetics, pressure gradient and capillarity become prominent for channels where the length scales are of the order of hundreds of micrometers. Also, at such length scales, the application of conventional numerical techniques that use macroscale equations to describe the phenomenon is questionable as the validity of the noslip boundary condition depends on the ratio of the mean free path of the fluid molecules to the characteristic dimension of the problem (called the Knudsen number). Macroscale equations can only be applied if Knudsen number is of the order of 10¬¬3 or less. In recent years, the lattice Boltzmann method (LBM) has emerged as a powerful tool that has replaced conventional macroscopic techniques like Computational Fluid Dynamics (CFD) in many applications involving complex fluid flow. The LBM starts from meso and microscopic Boltzmann's kinetic equation and can be used to determine macroscopic fluid dynamics. The origins of LBM can be drawn back to lattice gas cellular automata (LGCA) which lacked Galilean invariance and created statistical noise in the system. LBM on the other hand possesses none of these drawbacks of LGCA, and is easy to implement in complex geometries and can be used to study detailed microscopic flow behavior in complex fluids/fluid mixtures. Nor does it have any of the drawbacks of the NavierStokes solvers of implementing the slip boundary condition on the surface of a solid. It has also been found to be computationally fast and an alternative to NavierStokes equations. In this study, LBM is used to simulate twofluid flows such as bubbles rising in a liquid, droplet impingement on a dry surface and creation of emulsions in microchannels. Simulation of disperse flows in a continuous medium using simple boundary condition methods lays the foundation of conducting complex simulations for the formation of droplets past a Tjunction microchannel in the framework of this statistical method. Simulations in a Tjunction illustrate the effect of the channel geometry, the viscosity of the liquids and the flow rates on the mechanism, volume and frequency of formation of these micronsized droplets. Based on the interplay of viscous and surface tension forces, different shapes and sizes of droplets were found to form. The range of Capillary numbers simulated lies between 0.001
Title:  DROPLET FLOWS IN MICROCHANNELS USING LATTICE BOLTZMANN METHOD. 
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Name(s): 
Gupta, Amit, Author Kumar, Ranganathan, Committee Chair University of Central Florida, Degree Grantor 

Type of Resource:  text  
Date Issued:  2009  
Publisher:  University of Central Florida  
Language(s):  English  
Abstract/Description: 
Microelectromechanical systems (MEMS) have widespread applications in medical, electronical and mechanical devices. These devices are characterized by the smallest dimension which is atleast one micrometer and utmost one millimeter. Rapid progress in the manufacture and utilization of these microdevices has been achieved in the last decade. Current manufacturing techniques of such devices and channels include surface silicon micromachining; bulk silicon micromachining; lithography; electrodeposition and plastic molding; and electrodischarge machining (EDM). In recent years, electrostatic, magnetic, electromagnetic and thermal actuators, valves, gears and diaphragms of dimensions of hundred microns or less have been fabricated successfully. Sensors have been manufactured that can detect pressure, temperature, flow rate and chemical composition in such channels. Physical effects such as electrokinetics, pressure gradient and capillarity become prominent for channels where the length scales are of the order of hundreds of micrometers. Also, at such length scales, the application of conventional numerical techniques that use macroscale equations to describe the phenomenon is questionable as the validity of the noslip boundary condition depends on the ratio of the mean free path of the fluid molecules to the characteristic dimension of the problem (called the Knudsen number). Macroscale equations can only be applied if Knudsen number is of the order of 10¬¬3 or less. In recent years, the lattice Boltzmann method (LBM) has emerged as a powerful tool that has replaced conventional macroscopic techniques like Computational Fluid Dynamics (CFD) in many applications involving complex fluid flow. The LBM starts from meso and microscopic Boltzmann's kinetic equation and can be used to determine macroscopic fluid dynamics. The origins of LBM can be drawn back to lattice gas cellular automata (LGCA) which lacked Galilean invariance and created statistical noise in the system. LBM on the other hand possesses none of these drawbacks of LGCA, and is easy to implement in complex geometries and can be used to study detailed microscopic flow behavior in complex fluids/fluid mixtures. Nor does it have any of the drawbacks of the NavierStokes solvers of implementing the slip boundary condition on the surface of a solid. It has also been found to be computationally fast and an alternative to NavierStokes equations. In this study, LBM is used to simulate twofluid flows such as bubbles rising in a liquid, droplet impingement on a dry surface and creation of emulsions in microchannels. Simulation of disperse flows in a continuous medium using simple boundary condition methods lays the foundation of conducting complex simulations for the formation of droplets past a Tjunction microchannel in the framework of this statistical method. Simulations in a Tjunction illustrate the effect of the channel geometry, the viscosity of the liquids and the flow rates on the mechanism, volume and frequency of formation of these micronsized droplets. Based on the interplay of viscous and surface tension forces, different shapes and sizes of droplets were found to form. The range of Capillary numbers simulated lies between 0.001  
Identifier:  CFE0002618 (IID), ucf:48279 (fedora)  
Note(s): 
20090501 Ph.D. Engineering and Computer Science, Department of Mechanical Materials and Aerospace Engineering Doctorate This record was generated from author submitted information. 

Subject(s): 
Microfluidics lattice Boltzmann microchannels multiphase flows droplets 

Persistent Link to This Record:  http://purl.flvc.org/ucf/fd/CFE0002618  
Restrictions on Access:  private 20120401  
Host Institution:  UCF 