Iranian Journal of Chemical Engineering (IJChE)

Abstract This study presents a numerical investigation into the influence of the magnet position and its distance from the channel inlet on heat transfer and flow behavior of ferrofluid (FF), including Fe₃O₄/water flowing through a horizontal channel under a constant wall heat flux. Three magnet positions were considered—at the inlet, middle, and outlet of the channel—to identify the best configuration for heat transfer enhancement. Permanent magnets with a remanent magnetic flux density of 0.4 T were modeled. The nanoparticle concentration was 5 Vol.%, and the Reynolds number was 100. The effects of magnet positions on the local magnetic flux density, Kelvin force, streamlines, velocity and temperature distributions, and Nusselt number (Nu) were investigated. The problem was solved by assuming incompressible, laminar, and steady-state flow. The Galerkin weighted residual finite element method was used to solve the governing equations simultaneously. Results revealed that when magnets were positioned at the inlet or outlet, the magnetic field effects were localized and produced minimal impact on the flow and temperature fields. Conversely, when the magnets were located in the middle of the channel, the most substantial magnetic field gradients and Kelvin forces were generated, which created recirculation zones and increased fluid mixing, resulting in a more uniform temperature distribution and a significant enhancement in the local Nu and an average Nu of 5.31. Finally, this study proposes placing the magnet in the middle of the channel as the most effective configuration for enhancing convection heat transfer.

Abstract In this study, the effect of the presence of a magnetic field (MF) on the thermal conductivity of the nanofluid (NF) ( ) containing spinel ferrite nanoparticles (NPs) (MFe₂O₄, M=Fe, Co) was investigated. CoFe₂O₄ NPs were concentrated by the coprecipitation method. Both NPs were characterized by SEM, EDX, XRD, and VSM. The thermal conductivity was investigated and compared in the presence and absence of an MF. In addition to the intensity of MF (100, 200, 300, and 400 G), the effect of the concentration of NPs (from 0.25 to 2 Vol%) on  at a constant temperature of 25 °C was investigated. According to the results, in the absence of MF, the  of CoFe₂O₄/water ferrofluid (FF) was higher than that of Fe₃O₄/water FF in different concentrations. Furthermore, as the intensity of the MF increased, the  of both Fe₃O₄/water and CoFe₂O₄/water FFs increased. This increase was more observed for the FFs containing Fe₃O₄ NPs. At the highest concentration (2 Vol%), with the increase of MF up to 400 G, the  of Fe₃O₄/water has increased by about 3.2%, while this increase was about 1.8% for CoFe₂O₄/water. Increasing the volume percentage of NPs also had a positive effect on the thermal conductivity coefficient. Finally, according to the obtained results, correlations were presented to predict the  of both FFs according to the intensity of the MF and the concentration of NPs. The proposed correlations had a satisfactory accuracy with R² values of 0.98 for both FFs.

Abstract  This study investigates the two-phase flow simulation in a Y-type  micromixer with a circular pit at the junction with a 1.7 MHz ultrasonic (US) transducer. A CFD simulation is conducted on the micromixer under varying fluid flow rates. Initially, the simulation is performed without US waves, and subsequently, the US waves are applied. The influence of US waves on flow behavior, mass transfer coefficient (KLa), and extraction efficiency (E) is assessed and contrasts with the same in the scenario where no ultrasound is applied. The simulation outcomes exhibit strong agreement with the experimental findings of a reliable reference. The findings indicate that the flow pattern for both aqueous and organic phases is parallel within the micromixer when ultrasound is absent.   However, applying the US waves alters the flow pattern and enhances the mixing. Under the US field, the interface between the two phases is completely disrupted and the contact between them increases. It is concluded that applying US waves into the liquid medium enhances turbulence, mixing, and the mass transfer rate inside the micromixer.  The influence of the flow rate of the aqueous phase at different US powers on KLa and E was investigated. The decreasing trend of KLa is observed. The effect of the power of ultrasound (P=3.5, 5.25, and 7W) on KLa and E is investigated and results show that P= 7 W has the more ability to enhance the mass transfer rate. The maximum error that is obtained for KLa is 5.43 %, which shows the high accuracy of the CFD model.

Abstract The Micromixing plays a key role in the most of industrial processes; enhancing its efficiency is a very important issue. In this study, a typical rotating packed bed (RPB) reactor equipped with the blade packing and high frequency ultrasonic transducers were designed to study the micromixing efficiency using the iodide/iodate reaction. The utilized ultrasonic transducers were ultrasonic atomizer humidifiers with the frequency of 1.7 MHz. Taking advantage of both the controllable high gravitational force and induced effects of the high frequency ultrasound, simultaneously, in a small volume reactor is the novelty of the present work. The effects of different parameters like the rotational speed, volumetric ratio, concentration of acid, ultrasonic power and number of activ transducers were investigated with and without the ultrasonic field. By increasing the rotational speed and volumetric flow, the segregation index decreased and by increasing the concentration of acid and volumetric ratio, the segregation index increased. In all of experiments, the segregation index decreased significantly under the ultrasonic field. Moreover, by increasing the ultrasonic power and number of active transducers the segregation index decreased. The obtained results indicated that the relative segregation index increased up to 41.1 % under the 1.7 MHz ultrasonic field. Therefore, the high frequency ultrasonic waves can intensify micromixing, even in a high efficiency equipment like RPB