The process of absorbing CO2 gas in a liquid is one of the most important ways to prevent emission of this important greenhouse gas in the atmosphere. It helps to reduce global warming and prevent climate change and maintain the natural balance of our planet. The stable suspension of magnetic nanoparticles in an aqueous or organic carrier liquid is called magnetic nanofluid, which has received much attention in recent years in various processes related to many scientific fields. The special magnetic properties of these nanoparticles and their reactivity in the presence of a magnetic field cause their effect on improving heat and mass transfer. Applying the magnetic field and exciting the magnetic nanoparticles in the magnetic nanofluid act like mixers in nano dimensions and cause the fluid flow to be stimulated and create nano/micro turbulence in it. On the other hand, recently microchannels have been recognized as a new tool in improving and controlling mass transfer characteristics. In this research, the use of Fe3O4 magnetic nanoparticles with a particle size of 8 nm in the presence of an alternating magnetic field (AC) has been investigated to improve the efficiency of CO2 mass transfer in a Y-shaped microchannel. In order to eva‎luate the size and stability of nanoparticles, DLS, TEM and zeta potential analyzes were performed and in order to eva‎luate the magnetic properties of these nanoparticles, VSM analysis was utilized. CO2 absorption has been investigated under different operating conditions, different concentrations of magnetic nanoparticles, and variable intensity of the magnetic field. Mass transfer coefficient of the entire liquid side (KLa), CO2 absorption efficiency (E), nanoparticle enhancement factor (α), magnetic field enhancement factor (γ), as well as the effect of pressure drop (Δp) as indicators to determine the improvement of mass transfer in were considered. By applying an alternating magnetic field, electromagnetic energy is transferred to the fluid in the form of kinetic energy. Therefore, this energy is expected to affect phenomena that are rooted in mixing, i.e., mass transfer in the gas-liquid boundary layer flow. In order to study the effect of magnetic nanoparticles and magnetic field on the gas-liquid mass transfer process, magnetic field intensity of 7, 12.6, and 21 mT and magnetic nanofluid concentrations of 0.001-0.004 (v/v) were used. The speed of the two phases were chosen so that the alternating Taylor flow pattern prevails in all the experiments, and the quantitative analysis of CO2 absorption in two states, absence and presence of magnetic nanoparticles, was investigated and compared with each other. In addition, the effect of the position of the microchannel in the alternating magnetic field was investigated as an effective factor in increasing CO2 absorption, and the position where the microchannel was above the magnetic field showed more absorption. By inserting a magnetic field intensity of 21 mT, the maximum increase in KLa by 72.2% was observed compared to the case where the magnetic field was not applied. In order to better understanding of the effect of an alternating magnetic field on the absorption of CO2 in magnetic nanofluid, two-dimensional modeling of microchannel (2D computational fluid dynamics) was conducted, after validating the model, two-dimensional simulation of CO2 concentration profile changes in magnetic nanofluid with and without magnetic field. The simulation results showed a good agreement with the experimental results. The input of mass transfer coefficient and pressure drop in the range of gas phase flow rate corresponds well with the experimental results with a maximum relative error of 11.67% and 20.28%, respectively. The deviation of the simulation results from the two-dimensional model can be due to simplifying assumptions such as considering a constant diffusion coefficient, the fully developed flow hypothesis, and also human errors.

مسعود حق شناس فرد , محسن نصراصفهاني

محمدرضا احساني

ابراهيم افشاري , احمد محب , مهدي ستاري نجف آبادي