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In this research, the average Nusselt number in tall and narrow enclosures in the presence of mixed convection of a water-based nanofluid (H2O–Cu–TiO2) is determined and compared. The effect of quantities such as Richardson number of 0.01–100, the volume fractions of 0–2% and geometric shape of the enclosure on average Nusselt number and maximum value of flow function is numerically investigated. The FVM and SIMPLER algorithm are used for resolving the nonlinear equations. According to numerical results, for all the Richardson number and two tall and narrow enclosures, the average Nusselt number rises with growing the nanoparticles volume fractions. Comparison of the tall and narrow enclosures shows that for obtaining the highest heat transfer, by growing the nanoparticles volume fractions under similar conditions, it is better to use tall enclosures for large Richardson number and narrow enclosures for small Richardson number. The highest enhancement of the average Nusselt number with increasing the nanoparticles volume fractions for narrow enclosures was 10.44% at the Ri = 0.01. Whereas in the tall enclosures, the highest increase in the average Nusselt number was 14.51% at Ri = 100. For all the Richardson number and two tall and narrow enclosures, the maximum flow function value of the nanoparticles increases with increasing volume fractions. This increase in small Richardson number is greater than in large Richardson number. [ABSTRACT FROM AUTHOR]

• Effects of magnetic field on heat transfer and entropy generation. • Inclined cavity with Straight, Inclined and Curved Blades containing nanofluid. • Solving nonlinear governing equations by finite volume method and SIMPLE algorithm. • Four different nano powders shapes, namely platelets, cylinders, Fins, and bricks. • The average Nusselt number and entropy generation are decreased by adding different nano powders. Nanopowder shapes are highly effective in nanofluids properties. This study was a numerical analysis of the effect of nanopowder morphology on the natural convection and irreversibilities of water/alumina nanofluids. To this end, a square enclosure was used with constant cold (T c) and hot (T h) temperatures at its right and left walls, respectively. The horizontal surfaces were isolated and the enclosure was exposed to a magnetic field. Two Fins were located on the left wall sharing the same temperature as the wall. The control volume method was used to derive the algebraic form of the equations, and a SIMPLE algorithm written in Fortran was used for the simulations. To investigate the effect of nanopowder shapes, four different shapes, namely platelets, cylinders, blades, and bricks, were used. For a better comparison, nanofluids with different morphologies were compared with a Brownian motion-incorporated model. The results showed that this model predicts the highest heat transfer rate and entropy generation. As its most important result, this paper concluded that free heat convection in nanofluids is not necessarily increased by addition of nanopowder, and in some cases, the Nu number and irreversibilities can be decreased because of the significant increase in nanofluid viscosity. It was also observed that the Nu rises with Ra and falls with the magnetic field intensity. Generally speaking, the greatest and lowest heat transfer coefficients were obtained using the Angled and straight Fins, respectively. [ABSTRACT FROM AUTHOR]

Present numerical investigation studies the influence of inserting rods with helical fins in a shell and tube heat exchanger (ShT-HEX) under magnetic field (MF) and filled with two-phase nanofluid (NF) on the thermal–hydraulic performance (THP). The goal of the present article is to study the influence of different geometrical factors of fins, different Re, various MFs and also different nanoparticles concentrations on the THP of Newtonian NF flow under MF in a novel HEX using the finite volume method. Also, an economic analysis is done with the interesting parameter heat flux to reduce the weight of the HEX. It was found that the novel configuration with b = 100 mm and a = 23 mm filled with MgO-SAE10 NF at φ = 1.500% under the MF of B = 0.5 T has the optimum characteristics with the q" = 98.08 W/m2 and 143.60 W/m2 at Re = 8,000 and 20,000, respectively. Based on obtained results, the costs of manufacturing of novel model can be 88% of the basic model. Therefore, the economic enhancement is done in this investigation using ANSYS-Fluent and SolidWorks software. [ABSTRACT FROM AUTHOR]

• Optimal geometry for parabolic solar collectors based on energy efficiency. • Nanofluid effect on parabolic solar collectors using two-phase simulation. • Eulerian-Eulerian method is employed to simulate two-phase nanofluid flow. • Energy efficiency for the dual-pass pipe is higher than that of single-pass one. In the present paper, the effect of U-shaped absorber tube on the performance of parabolic solar collector containing two-phase non-Newtonian nanofluids is studied numerically. The present study aims to obtain an optimal geometry for parabolic solar collectors based on energy efficiency. In this study, the effect of using nanofluid on parabolic solar collectors is investigated using two-phase simulation. The effect of Re number (2500

In this study, the effect of the presence of MWCNTs on the surface tension of paraffin-based fluid was examined. Surface tension measurements of samples containing MWCNTs (0.005–5 wt%) were performed at temperatures of 25–70°C by SITA dynotester. Surface tension corresponds to the adhesive and cohesive forces resultant. Adding nanoparticles diminishes the cohesive force and simultaneously strengthens the adhesive force. Owing to the presence of MWCNTs, the effect of adhesion on the surface tension was superior to the effect of cohesion which consequently diminishes the surface tension. The loading nanoparticles efficacy on surface tension is weekend as the temperature increases. On the other hand, the presence of particles diminishes the sensitivity of surface tension to the temperature growth. In other words, temperature and mass fraction weaken each other's effects. The highest decrease in surface tension is reported to be 18.6%, which occurs at the lowest temperature as well as the maximum mass fraction. The prediction of MWCNTs/liquid paraffin surface tension behavior was performed by applying nonlinear regression and artificial neural network techniques, and statistical calculations revealed that the R-squared for the first and second techniques was calculated to be 0.99 and 0.998, respectively. Both techniques accurately predict nanofluid surface tension. • Suspending MWCNTs in liquid paraffin • Inspection of nanofluid stability using DLS and zeta potential tests • Surface tension measurements of samples by SITA dynotester Measuring surface tension • Presence of MWCNTs diminishes sensitivity of surface tension to temperature growth. • Maximum decrease in surface tension occurred at lowest temperature and highest mass fraction. [ABSTRACT FROM AUTHOR]