بررسي تجربي ضريب انتقال جرمِ جريان لخته اي حين استخراج مايع-مايع در ميكروكانال ها

چكيده انگليسي :

AbstractTwo phase microchannels can provide precise control of specific interfacial area narrow residencetime distribution and two to three orders of magnitude higher heat and mass transfer coefficients ascompared to those of the conventional two phase contactors Thus liquid liquid extraction inmicrochannels has taken into account during the recent decades Different flow regimes are observedin two phase microchannels however slug flow can be considered as the most popular one due to itshigh stability In this work the influence of the hydraulic diameter of the square microchannels onhydrodynamics and mass transfer of slug flow was studied using 200 400 and 600 m channels Atconstant flow velocity the specific interfacial area was enhanced by 51 3 and 90 5 as themicrochannel size was reduced from 600 to 400 m and from 400 to 200 m respectively due tosignificant plug length enlargements The overall mass transfer coefficient was augmented by 41 6 and 16 1 respectively as the result of deterioration of the mass transfer resistances due toimprovement of the internal recirculations The influence of size on the interfacial area wassignificantly greater than that on the mass transfer resistances Hydrodynamics and mass transfer inmicrochannels with the same hydraulic diameter but different aspect ratios were compared Thedispersed and continuous phase slug lengths in the rectangular microchannel were 41 0 and 50 0 respectively larger than those in the square microchannel However there were no considerablevariations in the interfacial area comparing the results of the two investigated aspect ratios Theoverall mass transfer coefficient in the rectangular microchannel was reduced on average by 13 7 as compared to that in the square microchannel This could be attributed to development of thestagnant zones inside the dispersed phase slugs as well as deterioration of the wall film renewal due todispersed phase slug enlargement Three different junction structures were investigated using the 400 m microchannel The overall volumetric mass transfer coefficient in the microchannel with cross shaped junction was enhanced on average by 21 5 compared to that using T junction and cross shaped T junction This could be due to higher shear forces exerted by the continuous phase on theemerging dispersed phase slug in the microchannel with cross shaped junction structure resulting ingreater internal recirculation in dispersed phase slugs Further mass transfer inside 0 7 mm capillarywas compared when n hexane and toluene were used as the organic solvents The two phase sluglengths and interfacial area were almost the same for the two chemical systems However lowerinterfacial tension as well as higher viscosity of toluene water system as compared to those of n hexane water system led to greater internal circulations resulting in enhancement of the overall masstransfer coefficient on average by 82 7 In the following the influence of the presence of sodiumdodecyl sulfate SDS on hydrodynamics and mass transfer was examined using n hexane watersystem and a 0 6 mm capillary The surfactant led to reduction of the slug lengths of both phases atconstant total flow velocitiy due to deterioration of the interfacial tension The specific interfacial areahad an insignificant improvement when the system was contaminated with SDS However the overallvolumetric mass transfer coefficient was augmented by 20 1 and 35 1 in the presence of 0 02 and0 10 wt of SDS respectively as the result of interfacial tension reduction and non uniformdistribution of the surfactant molecules on the interface Marangoni effects Keywords liquid liquid extraction microchannel mass transfer hydrodynamics hydraulic diameter aspect ratio mixing junction configuration surfactant

ستاري نجف آبادي، مهدي

بررسي تجربي ضريب انتقال جرمِ جريان لخته اي حين استخراج مايع-مايع در ميكروكانال ها

استخراج مايع - مايع , ميكروكانال , انتقال جرم , هيدروديناميك , قطر هيدروليكي , نسبت ابعاد سطح مقطع , هندسه نقطه اختلاط , ماده فعال سطحي