Nano?uids has been attracting considerable attention worldwide recently because nano?uids can be used to enhance the heat and mass transfer and can solve the problems of sedimentation, corrosion and clogging that are associated by millimeter or micrometer-sized particles. Many studies have conducted to study the thermal conductivity and heat transfer enhancement in nano?uids, but little studies for the mass transfer characteristics of nano?uids have found in the literature. Therefore effects of nanoparticles have been overlooked in mass transfer in the existing literature and more research must be done to determine the effects of nanoparticles on the mass transfer. Gas absorption is a mass transfer operation in which a gas mixture is contacted with a liquid for the purpose of preferentially dissolving one or more components of the gas mixture and to provide a solution of them in the liquid. Unfortunately the absorption rate of gases into a liquid is limited. The absorption rate of soluble gases into a liquid in the presence of a third, dispersed phase, e.g. droplets, solid particles, can signi?cantly be improved when the solubility gases in the particles is higher than that in the continuous liquid phase. In the present study the effects of Fe 3 O 4 /water nanofluids with concentrations of 0.001%, 0.005 %, 0.01%, 0.025% and 0.05% by volume on the CO 2 absorption have been investigated experimentally. These nanofluids have been obtained by diluting initial nanofluid with 7% of nanoparticles. Measurements of viscosity in nanofluids besides mass transfer coefficients have also been carried out by capillary viscometer. A glass tube with inner diameter of 1 millimeter has been connected to a liquid container. For meassuring mass transfer coefficient, vertical plastic tubes of 6, 8, 10 and 14 mm inner diameter were used in the experiments as falling film columns. All these tubes have been connected to a perfectly vertical base. In these tubes the rising bubble contacted with falling liquid and the amount of CO 2 absorption has been measured. The Simple design of the apparatus leaded to easy measurement and the cost reduction. Reynolds number was being changed in the range of 450-2100 by changing tube diameter from 6-14 mm. In order to verify accuracy of experimental set up and procedure, experimental Sherwood number were compared with theoretical values which were calculated by existing correlations. Experimental results were in reasonable agreement with theoretical values. According to the experimental mesurment of mass transfer coefficient, for nanofluids 0.001% and 0.005% mass transfer coefficient decreased into the base fluid in all Reynolds numbers. It can be seen that mass transfer coefficient was enhanced at Reynolds numbers higher than 1250 in the nanofluid of 0.01%. Nanofluid with 0.025% of nanoparticles enhanced mass transfer coefficient for Reynolds number higher than 750 But mass transfer coefficient was enhanced in all Reynolds numbers studied here in the nanofluid of 0.05%. Experimental results of nanofluid viscosity showed an increase trend with increasing nanofluid concentration. Considerable differences are observed between measured values and calculated values by existing equations. Keywords : Gas absorption process, mass transfer coefficient, Sherwood number, falling film column, nanofluid, viscosity
