Flow andmasstransferpropertiesunderair–waterTaylorflowhavebeeninvestigatedintwosquare microchannels withhydraulicdiametersof400and200m. ExperimentaldataonTaylorbubblevelocity, pressure dropandliquidsidevolumetricmasstransfercoefficient(kLa) havebeenpresented.Itwasshown that themeasuredTaylorbubblevelocityinsquaremicrochannelscouldbewellinterpretedbasedupon an approximatemeasurementoftheliquidfilmprofiletherein.Then,theobtainedtwo-phasefrictional pressure dropvaluesinbothmicrochannelswerefoundtobesignificantlyhigherthanthepredictions of thecorrelationproposedbyKreutzeretal.[2005b.Inertialandinterfacialeffectsonpressuredropof Taylor flowincapillaries.A.I.Ch.E.Journal51,2428–2440]whentheliquidslugwasveryshort,which can beexplainedbytheinadequacyoftheircorrelationtodescribetheexcesspressuredropcausedby the stronginnercirculationinsuchshortliquidslugs.Anappropriatemodificationhasbeenmadetothis correlation inordertoimproveitsapplicabilityinmicrochannels.Finally,theexperimental(kLa) values in themicrochannelwithhydraulicdiameterof400m werefoundtobeinpooragreementwiththose predicted bytheexistingcorrelationsproposedforcapillarieswithdiametersofseveralmillimeters. The observeddeviationwasmainlyduetothefactthatmasstransferexperimentsinthismicrochannel actually correspondedtothecaseofshortfilmcontacttimeandratherpoormixingbetweentheliquid film andtheliquidslug,whichwasnotinaccordancewithmasstransferassumptionsassociatedwith these correlations.Anewempiricalcorrelationhasbeenproposedtodescribemasstransferdatainthis microchannel.