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This study investigates the heat index by combining factors affecting the enhancement of heat transfer, including the modeling of three turbulators with 3D innovative geometries, hybrid nanofluid, including Cu and Al2O3, and high Reynolds numbers. Using the Eulerian method and the phase-coupled simple algorithm, a 3D tube in which turbulators with different sizes were embedded along with a hybrid nanofluid with a two-phase view were investigated. The geometry of rectangular turbulator is a = 1 cm, b = 3, 5, and 7 cm, and L = 40 cm, and geometry of twisted rectangular turbulator is like rectangular turbulator, and each part has a 5-cm length; also, the geometry of triangular turbulator is considered with b = 3, 5, and 7 cm, and L = 40 cm. In the two-phase view, because each phase can have a different velocity gradient and a different temperature gradient, the results were close to the experimental results. The results indicated that turbulators, hybrid nanofluid, and Reynolds number influenced heat transfer rate enhancement; for the rectangular turbulator, changing the turbulator size, volume fraction, and Reynolds number from the minimum values to the maximum values increased heat transfer by 49.17%. The same conditions increased heat transfer for the twisted rectangular and triangular turbulators by 44.28% and 45.19%, respectively. The proposed factors are practical and can be beneficial in heat transfer and fluid mechanics. Overall, at minimum conditions Re = 15,000 and φ = 0% up to maximum conditions Re = 25,000 and φ = 4% for rectangular, twisted rectangular, and triangular turbulators increasing heat transfer rates of 79.49%, 97.5%, and 82.45% have been observed, respectively.

In the current study, the turbulent forced convection heat transfer of Fe3O4/-CNT/water hybrid nanofluid (HNF) in a heat exchanger (HE) equipped with blade-shape turbulators is studied. The 3D governing equations have been solved numerically with SIMPLEC algorithm and solution domain by employing the control volume method (CVM). The impact of Reynolds number (Re), volume concentration of Fe3O4 nanoparticles (φM) and CNTs (φCNT) and blade-rod diameter (dr) on the performance features of HE are evaluated. The results showed that the PEC of HNF augments with the augmentation of Re and φM, while with intensifying dr, the PEC first rises and then declines. The outcomes showed that the highest PEC occurs at Re = 9000, φM = 0.9%, φCNT = 1.35% and dr = 15mm.

In the current study, fluid flow and heat transfer characteristics of forced convection ferromagnetic hybrid nanofluid (Fe3O4/CNT/water) flow in a sweep-shape collector are studied numerically. The three-dimensional governing equations have been solved numerically in the solution domain using control volume approach employing SIMPLE algorithm. Studied Reynolds numbers are determined in turbulent range between 6000 and 8000. The optimization was carried out by comparison of different parameters to reach the optimal case with the maximum performance evaluation criteria index. Based on obtained results, it is concluded that the model with Reynolds number of 8000 has the maximum values of performance evaluation criteria indexes during all studied volume fractions which followed by Reynolds numbers 7500, 7000 and 6000, respectively. Also, the model with tube diameter of 8 mm has the maximum values of performance evaluation criteria index during all studied Reynolds numbers and is followed by cases with 4 mm and 12 mm tube diameters, respectively. Since based on all obtained results in this work using nanofluid at φCNT = 1.35% leads to more thermal–hydraulic performances than using nanofluid with φCNT = 0.10%, the sweep-shape collector with tube diameter of 8 mm filled with Fe3O4/CNT/water hybrid nanofluid with φCNT = 1.35% and φM (%) = 0.9% volume fraction and 30 nm nanoparticle diameter at Reynolds number of 8000 is presented as the best model in the current study.

In the present numerical study, the free convective flow between several differentially hot and cold tubes enclosed in a space between two horizontal adiabatic coaxial cylinders which filled with three different kinds of nano-fluids is investigated. The effects of influential aspects including; location of heat source/sink, number of tubes, Rayleigh number (Ra), volume concentration (ϕ) and type of the nanoadditives on the isotherms, streamline, stream function and average Nusselt number ( N u ¯ i ) are explored. The governing equations are solved numerically employing control-volume based finite volume technique. For pressure-velocity coupling, the Semi-Implicit Method is utilized. According to the obtained results, usage of nano-fluid leads to the considerable enhancement of heat transfer in the studied cavity. For all the examined configurations with two cylinders, the configuration 30° has the most N u ¯ i values which is followed by configurations 60° or 0°, 90°, 120°, 150° and 180°, respectively. It is clearly seen that for all the assessed configurations with three cylinders, the highest to lowest N u ¯ i respectively belongs to the Case 2C, Case 2A and Case 2B. Moreover, for all the investigated configurations with four cylinders, the highest and lowest N u ¯ i respectively occurs at Case 3B and Case 3A.