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 In this paper, CFD modeling of ferrofluid convection heat transfer in a micromixer with static magnetic field (SMF) and rotating magnetic field (RMF) is investigated. Applying a magnetic field and the existence of magnetic nanoparticles lead to the creation of transverse vortices in the micromixers by movement of nanoparticles, that improves heat transfer. There is a cylindrical pit in the microcmixer with heat source that is applied to its bottom wall. Top wall of the pit is adjacent to a fixed permanent magnet, which creates the SMF. CFD modeling first is done for heat transfer process in the micromixer in the absence of the magnetic field. Secondly, simultaneous effect of the SMF and magnetic nanoparticles on the flow pattern and heat transfer rate of ferrofluid is evaluated. Results showed that ferrofluid leads to the improvement of the heat transfer rate compared to pure water. The secondary flows induced by nanoparticles’ motion toward SMF decreases the velocity in the area of application of the magnetic field, so the heat transfer coefficient decreases. But, in the case of RMF, applying the magnetic field causes the nanoparticles to rotate inside the pit, which leads to an increase in the heat transfer coefficient. CFD results of heat transfer coefficient are compared with experimental results in a reliable reference and acceptable agreement between them is observed.

Abstract  Magnetorheological fluids contain suspended magnetic particles that arrange in chains in the presence of a magnetic field, causing the conversion of the fluid from a liquid state to a quasi-solid state. These fluids can be used in valves as a tool for pressure drop and flow interruption. This research aims to investigate the feasibility of using magnetorheological fluid (MRF) in industrial valves. The rheological properties of the MRF sample were measured with the MCR300 rheometer in the presence of a magnetic field. In this connection, the Bingham plastic continuous model was used to predict fluid behavior, and model coefficients were obtained using MATLAB software. Then, the model's coefficients were used to simulate the behavior of the magnetorheological fluid in the presence of the magnetic field in the valve. The geometry and dimensions of the valve were designed according to the dimensions of industrial samples. Then the CFD simulation with Fluent software was done by using the Bingham model and fluid characteristics obtained from experimental results. The results showed that the pressure increased by increasing the magnetic field at the center of the sleeve. The magnetic field up to 0.5 Tesla, increases pressure and decreases amplitude. Therefore, as the magnetic field increase, the amplitude of the maximum pressure on the sleeve was significantly reduced.

Abstract Wind energy is used to rotate a magnetic turbine in order to remove heat from the surface of a photovoltaic (PV) panel. A three-bladed turbine, which rotates with wind energy, has rotational motion underneath the studied PV panel in order to move Magnetic Nano-Particles (MNPs). In addition, effects of the magnetic field strength (B=450-830 mT), rotational velocity of the magnetic turbine (ω), and the concentration of MNPs (ϕ) on the heat removal from the PV panel area were investigated. Results showed that heat removal from PV panel was intensified by motion of pinned MNPs in the ferrofluid via the exerted external force of magnetic field. Concurrent application of available magnetic field along with ferrofluid led to 7.6-24 % temperature reduction for a PV panel. Furthermore, the produced electrical energy of the PV panel was augmented between 2.55-3.13 W depending on ϕ, ω, and B. Moreover, the impact of ω on cooling performance was also investigated, and a significant enhancement to generated power was observed. Eventually, the maximum amount of the produced power (3.13 W), maximum power enhancement percentage (32.63 %), and thermal efficiency (24 %) were achieved for B=830 mT, ω=50 cycles/min, and ϕ=0.05 (w/v).