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• The arrangement of heaters and coolers affects the temperature distribution. • The highest value of Nu loc occurs at the junction of the heater and the cooler. • The existent magnetic field suppresses the nanofluid convection. • By increasing the block side length, the Nu ave increases. • The heat transfer rate in Case 1 is most effective, followed by Case 3 and Case 2. A two-dimensional (2D) numerical simulation is presented to study the effect of magnetic field on Ag-MgO nanofluid forced convection and heat transfer in a channel with active heaters and coolers. A Fortran code according to Lattice Boltzmann method (LBM) is developed for this purpose. The effects of thermal arrangement (Case1, 2 and 3), block side length (0.3 ≤ h ≤ 0.5), Reynolds number (50 ≤ Re ≤ 100), Hartmann number (0 ≤ Ha ≤ 60) and volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.02) on flow pattern and heat transfer characteristics are analyzed systematically. The obtained results showed that the highest value of local Nusselt number occurs at the junction of the heater and the cooler due to the high temperature gradient, followed by the sharp corner of heaters and coolers. Moreover, the heat transfer at the heater sharp corner is higher than that of the cooler sharp corner. The average Nusselt numbers indicated that the rate of heat transfer increases with increasing ϕ or decreasing Ha. Finally, the heat transfer rate in Case 1 is more than Case 3 and Case 2. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MHD natural convection in a baffled U-shaped enclosure is studied. • KKL correlations are used to obtain nanofluid thermal conductivity and viscosity. • Governing equations have been solved by the lattice Boltzmann method. • Effects of Ra , Ha , ϕ and AR on the flow and heat transfer have been examined. Abstract In this study, nanofluid natural convection in a baffled U-shaped enclosure in the presence of a magnetic field is investigated. Lattice Boltzmann method (LBM) is used to study present problems. KKL (Koo-Kleinstreuer-Li) correlation is applied to calculate the effective thermal conductivity and viscosity of nanofluid. The effect of the Brownian motion on the effective thermal conductivity is considered in this correlation. The combination of the four topics (nanofluid, U-shaped enclosure, baffle, magnetic field) is the main novelty of the present study. Effect of Rayleigh number, Hartmann number, nanoparticle volume fraction and cavity aspect ratio on the flow field and heat transfer characteristics have been investigated. The results demonstrate that the average Nusselt number increases by increments of the Rayleigh number, nanoparticle solid volume fraction and aspect ratio. However, the rate of heat transfer is suppressed by the magnetic field. The effect of magnetic field on heat transfer is more significant at higher Rayleigh number and the effect of Ra on the average Nusselt number is more noteworthy at lower Ha. Besides, the effect of Rayleigh number on heat transfer enhancement becomes more significant at higher aspect ratio. [ABSTRACT FROM AUTHOR]

In this study, we present a numerical simulation of MWCNT-Fe 3 O 4 /water hybrid nanofluid forced convection heat transfer over the forward- and backward-facing steps channel having a baffle fixed on its top wall. A FORTRAN's homemade code based the lattice Boltzmann method (LBM) is used here. The effects of the Reynolds number (25 ≤ Re ≤ 100), the volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.003), the position of baffle (3 ≤ X 2 ≤ 7), the length of baffle (0 ≤ h ≤ 1.5) and the geometry parameter (2 ≤ X 1 ≤ 4) on flow pattern and heat transfer characteristics are provided a deep insight. The results indicate that the average Nusselt number is an increasing function of Re and ϕ. The baffle has a significant effect on the flow pattern and heat transfer characteristics. When the length of the baffle increases, the recirculation region behind the backward-facing step shrinks. The average Nusselt number increases by increasing the length of the baffle or moving the baffle towards the backward-facing step. • Nanofluid forced convection over steps with a baffle was investigated. • Simulations have been performed via Lattice Boltzmann Method (LBM). • Effects of magnetic field on heat transfer are evaluated and examined. • When baffle length increases, the recirculation region downstream shrinks. • To increase Nu, the baffle should be moved towards the backward-facing step. • Increasing the baffle length leads to the rise of Nu. [ABSTRACT FROM AUTHOR]

The present work is investigated the heat management of thermogravitational convection inside a shell and tube heat exchanger filled with Fe 3 O 4 /water nanoliquid by lattice Boltzmann method (LBM). The seven internal pipes with hot or cold temperature insert in the I-shaped heat exchanger. The impacts of Rayleigh number (104-106), nanoparticles concentration (0–0.06), Hartmann number (0–60), magnetic field inclination angle (0- π /2) and the thermal arrangement of active pipes (Case 1–4) on the flow structure and energy transport characteristics are examined. The computational data are shown by streamlines, isothermal lines and the variations of the mean Nusselt number. It has been ascertained that the thermal arrangement of active pipes affects the velocity patterns and thermal transmission performance significantly. However, an increasing in the volume fraction of nano-size particles and Rayleigh number, the average Nusselt number raises regardless of the thermal arrangement. The rate of energy transport showed an opposite dependence with Hartmann number, but a direct relationship with the magnetic field inclination angle. The most suitable thermal arrangements for heat transfer rate of heated and cooled pipes are same at low magnitudes of the Rayleigh number, but different at high Rayleigh number. • Natural convection in a heat exchanger filled with nanofluid is studied. • There are seven active internal pipes with hot or cold temperature. • The governing equations are solved by the lattice Boltzmann method. • Thermal arrangement of active pipes affects the flow pattern and heat transfer. [ABSTRACT FROM AUTHOR]

In the present study, the Buongiorno's two-phase method was implemented to investigate the nanofluid heat transfer in a triangle solar collector with corrugated bottom wall. A novel hybrid Lattice Boltzmann method (LBM) with using Total Variation Diminishing (TVD) method was developed. The effects of important physical parameters such as Rayleigh number, volume fraction of nanoparticle and different types of corrugated walls on the fluid flow pattern, nanoparticles distribution and temperature fields are studied in details. Three cases were considered for the numerical simulation. It was found that the Case 2 has the largest heat transfer rate. Based on the obtained results, the center region (inside the enclosure) has nearly uniform particle distribution. However, the region near cold and hot wall have higher and lower nanoparticle concentration, respectively. With increasing nanofluid concentration (φ) while it is smaller than a critical value, the heat transfer enhancement's ratio increases. In addition, when solid volume fraction of nanofluid is larger than the critical value, the heat transfer efficiency will be decreased by increasing the φ. • A novel hybrid LBM-TVD method is used to simulate fluid flow and heat transfer. • The Buongiorno's two-phase method is implemented to study nanofluid. • Effect of corrugated walls on the heat transfer is significant. • Nanoparticles gather near the cold walls. [ABSTRACT FROM AUTHOR]