Contents lists available at ScienceDirect International Journal of Greenhouse Gas Control journal homepage: www.elsevier.com/locate/ijggc CFD modeling of CO 2 capture by water-based nanofluids using hollow fiber membrane contactor Nasibeh Hajilary a, ⁎ , Mashallah Rezakazemi b a Department of Chemical Engineering, Faculty of Engineering, Golestan University, Gorgan, Iran b Faculty of Chemical and Materials Engineering, Shahrood University of Technology, Shahrood, Iran ARTICLE INFO Keywords: CFD CO 2 capture Hollow fiber Membrane contactor Nanofluid ABSTRACT A two-dimensional (2D) model was developed for CO 2 removal from a gas mixture using a hollow fiber mem- brane contactor. Nanofluids of silica and carbon nanotube (CNT) nanoparticles were used as absorbents. The governing equations were solved using computational fluid dynamics technique (CFD). The results of the model were compared with the experimental data and good agreements confirmed the validity of the developed mass transfer model. The results showed that increasing absorbent flowrate enhances the CO 2 absorption rate, especially at a low flowrate. The performance of CNT nanofluids is much better than nanosilica. At high liquid flowrate (40 L/h) CNT captures CO 2 up to 53.53% while nanosilica captures 37.38%. Also, an increase in the concentration of CNT nanofluid from 0.2 to 0.5 wt.% at a constant flowrate of 20 L/h leads to 20% increase in the CO 2 separation while its enhance for nanosilica is 16%. 1. Introduction Global warming is one of a main challenge in the world to achieving sustainable development (Soroush et al., 2018; Mesbah et al., 2018). Greenhouse gas (GHG) emissions especially CO 2 emissions (about 80%), is the main reason for global warming and estimated to increase by 170% until 2030 (Hajilary et al., 2018; Rezakazemi et al., 2014, 2018a). There are various technologies for CO 2 separation like ab- sorption by solid sorbents or solvents, pressure and temperature swing adsorption using different solid sorbents, membranes (Sodeifian et al., 2018), electrical desorption, cryogenic distillation, chemical-looping combustion, hydrate-based separation, and some novel technologies (Rezakazemi et al., 2017). One of the effective methods for CO 2 capture is using of membrane contactors (Zhang et al., 2017). The prominent features of membrane contactor are simplicity, flexibility in operation, economic, easy to scale up or down, less energy demand, the depen- dence of liquid and gas flowrate to each other, and applying in a remote area. The conventional absorbents used for CO 2 capture are often from a family of amines. Although these absorbents have better performance, they have some problems such as corrosion, membrane degradation, and etc. Hence, researchers have been seeking for a green absorbent to substitute with an amine such as microalgae and/or water-based na- nofluid. Peyravi et al. (2015) investigated the effects of suspensions of Fe 3 O 4 , CNT (carbon nanotube), SiO 2 , and Al 2 O 3 nanoparticles in dis- tilled water in a gas-liquid HFMC on the rate of mass transfer during CO 2 absorption. The results indicated that the liquid flowrate and concentration of nanoparticles have the most significant effects on the CO 2 absorption. Also, they found that the nanofluid stability and hy- drodynamic diameter of nanoparticles in the base fluid play a key role in the selection of nanoparticle for CO 2 separation in membrane con- tactor. Darabi et al. (2017) presented a 2D mathematical model to simu- lated CO 2 absorption in the presence of nanoparticles in HFMCs with considering Brownian motion and Grazing effect. The governing equations for membrane, liquid and gas phase developed and solved with respect to boundary conditions using CFD technique and appro- priate algorithm. The results of the simulation were in good agreement with the experimental. The results showed that CO 2 absorption could be encouraged 16 and 32% by adding 0.05 wt.% silica and CNT nano- particles, respectively. Totally, using nanoparticles with optimum concentration can improve the efficiency of CO 2 absorption through the HFMCs. Mohammaddoost et al. (2018) experimentally studied the mass diffusion in a water-based nanofluid containing Al 2 O 3 , TiO 2 and SiO 2 nanoparticles in an HFMC. The results clearly showed that the CO 2 flux increased in optimum concentration of Al 2 O 3 . https://doi.org/10.1016/j.ijggc.2018.08.002 Received 17 June 2018; Received in revised form 25 July 2018; Accepted 3 August 2018 ⁎ Corresponding author. E-mail address: n.hajilari@gu.ac.ir (N. Hajilary). International Journal of Greenhouse Gas Control 77 (2018) 88–95 1750-5836/ © 2018 Elsevier Ltd. All rights reserved. T