آناليز CFD جريان لخته اي نانو سيال و هوا در ميكرو كانال ها

چكيده انگليسي :

CFD Analysis of Nanofluid Air Slug Flow in Microchannels Changiz Karamian c karamian@ce iut ac ir July 3 2011 Department of Chemical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor M Nasresfahany mnasr@cc iut ac ir E Shirani eshirani@cc iut ac irAbstractThe rapid development of microfabrication techniques creates new opportunities for applications ofmicrochannel reactor technology in chemical reaction engineering The extremely large surface to volumeratio and the short transport path in microchannels enhance heat and mass transfer dramatically and henceprovide many potential opportunities in chemical process development and intensification For gas and liquidtwo phase flow in a microchannel the Taylor slug flow regime is the most commonly encountered flowpattern The performance of microchannels largely depends on the underlying hydrodynamics of the gas andliquid flow Then to study the flow and transport phenomena in microchannels must first hydrodynamicbehavior be determined In this work we study the hydrodynamic behavior of a Taylor slug gas and liquidsystem in flow microchannels using Computational Fluid Dynamics CFD For this a T junction emptymicrochannel with varying cross sectional width 0 25 0 5 0 75 1mm served as the model micro reactor The two phase pressure drop and the lengths of gas and liquid slug with 1 Al2O3 water Nano fluid air asthe working fluid at various operation and fluid conditions were obtained and found to be in good agreementwith the literature data Simulation results show that the volume of fluid in both 2D as well as 3D predictspressure drop in good agreement with theoretical Young Laplace theory Surface tension is the mostdominant parameter in determining the pressure drop and slug properties in microchannels The length averaged friction factor for the liquid slug increased four times from the single phase value f Re 16 Thedimensionless slug length is mainly determined by the phase hold up with a slight effect of Re and Ca Therefore wider channels have longer slug length at the same superficial gas and liquid velocities Gravitational effects can be ignored in microchannels The gas slug length increases with increase insuperficial gas velocity and decrease in superficial liquid velocity The liquid slug length increases withincrease of superficial liquid velocity and decrease of superficial gas velocity The effect of fluid density isnegligible but the fluid viscosity surface tension and wall surface adhesion moderately impact the sluglengths Due to the weak effects of fluid density and moderate impact of fluid viscosity the 1 Al2O3 waterNano fluid air pressure drop and slug length are almost identical to the base fluid It is expected that heattransfer promoted in microchannels by using nanofluids without showing much penalty in pressure drop Correlations for the dimensionless gas slug length and liquid slug length in the model T junctionmicrochannel have been obtained These correlations can be used to predict the slug length based on theoperating condition and subsequently some important transport parameters such as pressure drop Heattransfer and mass transfer coefficients can be estimated Key Words Computational Fluid Dynamics CFD slug flow microchannel nanofluid volumeof fluid

كرميان، چنگيز

آناليز CFD جريان لخته اي نانو سيال و هوا در ميكرو كانال ها

ديناميك سيالات محاسباتي , حجم سيال , جريان دو فازي , جريان تيلور