Solid Volume Fraction Of Nanoparticles Research Articles

MHD mixed convection of nanofluid in a flexible walled inclined lid-driven L-shaped cavity under the effect of internal heat generation

In this study, mixed convective flow of nanofluid in an inclined L-shaped cavity which has elastic walls is numerically analyzed under the effects of internal heat generation and magnetic field by using the finite element technique with the Arbitrary-Lagrangian–Eulerian method. Simulations are performed for different values Richardson number (between 0.03 and 30), inclination angle of the cavity (between 0°and 180°), Hartmann number (between 0 and 50), orientation angle of the magnetic field (between 0°and 90°), internal Rayleigh number (between 104 and 106), solid nanoparticle volume fraction (between 0 and 0.04), flexible wall elastic modulus (between 104 and 108) and aspect ratio (between 0.2 and 0.7) of the L-shaped cavity. It was observed that the effects of elastic wall on the convective heat transfer features are significant for the lowest value of Richardson number and lowest values of elastic modulus while 11% of discrepancy is obtained in the average Nusselt number when cavity with elastic and rigid walls is compared. The impact of the magnetic inclination angle is significant when compared to magnetic field strength for the variation of the average Nusselt number. Cavity inclination angle has significant impacts on the variation of the average Nusselt number for water and nanofluid. A higher size of the cold wall (aspect ratio) increases the heat transfer rate while the internal Rayleigh number reduces it. Enhancement in the average Nusselt number is about 15%–19% at highest nanoparticle volume fraction of the nanofluid while the trends in the convective heat transfer features with respect to changes in the pertinent parameters are similar for water and nanofluid.

Effect of viscous dissipation on finding dual solutions for mixed convection boundary layer flow for nanofluid

AbstractThe effect of viscous dissipation on mixed convection boundary layer flow for Ag‐water nanofluid under steady‐state condition has been studied numerically for both the buoyancy assisting and opposing flows over a vertical semi‐infinite flat plate. A new co‐ordinate system has been introduced to transform the governing partial differential equations (PDEs) to facilitate the numerical calculations. Then, the local similarity method has been used for approximating the transformed PDEs to ordinary differential equations. Further, the quasi‐linearization method has been introduced to linearize the nonlinear equations and then numerical integration has been carried out using implicit trapezoidal rule along with the principle of superposition. For higher Pr, the coupled differential equations behave like stiff differential equations. To overcome the situation, orthonormalization process has been introduced. The effects of solid volume fraction of nanoparticles , the mixed convection parameter , Prandtl number , and Eckart number have been analyzed on the heat transfer and flow characteristics. It has been observed that the dual solutions are obtained for buoyancy opposing flow only and the range of dual solutions have become wider with the increases in . Further, nanofluids enhance the heat transfer process as compared to conventional heat transfer fluids . Moreover, the addition of viscous dissipation causes less heat transfer in the boundary.

Numerical simulation of water/alumina nanofluid mixed convection in square lid-driven cavity

PurposeThe purpose of this paper is to investigate the mixed convection of a two-phase water–aluminum oxide nanofluid in a cavity under a uniform magnetic field.Design/methodology/approachThe upper wall of the cavity is cold and the lower wall is warm. The effects of different values of Richardson number, Hartmann number, cavitation length and solid nanoparticles concentration on the flow and temperature field and heat transfer rate were evaluated. In this paper, the heat flux was assumed to be constant of 10 (W/m2) and the Reynolds number was assumed to be constant of 300 and the Hartmann number and the volume fraction of solid nanoparticles varied from 0 to 60 and 0 to 0.06, respectively. The Richardson number was considered to be 0.1, 1 and 5. Aspect ratios were 1, 1.5 and 2.FindingsComparison of the results of this paper with the results of the numerical and experimental studies of other researchers showed a good correlation. The results were presented in the form of velocity and temperature profiles, stream and isotherm lines and Nusselt numbers. The results showed that by increasing the Hartmann number, the heat transfer rate decreases. An increase from 0 to 20 in Hartmann number results in a 20 per cent decrease in Nusselt numbers, and by increasing the Hartmann number from 20 to 40, a 16 per cent decrease is observed in Nusselt number. Accordingly, it is inferred that by increasing the Hartmann number, the reduction in the Nusselt number is decreased. As the Richardson number increased, the heat transfer rate and, consequently, the Nusselt number increased. Therefore, an increase in the Richardson number results in an increase of the Nusselt number, that is, an increase in Richardson number from 0.1 to 1 and from 1 to 5 results in 37 and 47 per cent increase in Nusselt number, respectively.Originality/valueEven though there have been numerous investigations conducted on convection in cavities under various configurations and boundary conditions, relatively few studies are conducted for the case of nanofluid mixed convection in square lid-driven cavity under the effect of magnetic field using two-phase model.

Effect of γ-Al2O3/Water Nanofluid on Natural Convection Heat Transfer of Corrugated ┐ Shaped Cavity: Study the Different Aspect Ratio of Grooves

In this paper, the effect of γ-Al2O3/water nanofluid on the flow pattern and natural convection heat transfer of corrugated ⅂ shaped cavity is investigated numerically by the Lattice Boltzmann Method (LBM). The effects of nanoparticles solid volume fraction (ϕ=0-0.006), Rayleigh number (Ra=103-106) and the aspect ratio of grooves cavity (h/H=0.05-0.15) on the streamlines, isotherms and averaged Nusselt number have been examined. In addition, a comparison between γ-Al2O3/water nanofluid and MWCNT-Fe3O4/Water Hybrid Nanofluid on the average Nusselt number are studied. The results showed that the heat transfer rate of γ-Al2O3/water nanofluid is higher than water. For all Rayleigh numbers and solid volume fraction of nanoparticles, increasing the height of grooves leads to an increment in average Nusselt number. Moreover, when the Rayleigh number reaches to 106, the average Nusselt number increases, which the domain mechanism of heat transfer, in this case, becomes convection. As to be expected, the influence of MWCNT-Fe3O4/Water Hybrid Nanofluid on heat transfer rate is higher than the γ-Al2O3/water nanofluid.

Numerical simulation of natural convection heat transfer of copper-water nanofluid in a vertical cylindrical annulus with heat sources

In this work, natural convection of Cu—water nanofluid in a vertical cylindrical annulus enclosure with two discrete heat sources of different lengths is numerically investigated using the finite volume method with SIMPLER algorithm. The adiabatic unheated portions and the discrete heat sources are mounted at the inner wall. The top and bottom walls are thermally isolated, while the outer wall is maintained at a lower temperature. The effects of nanofluid solid volume fraction on hydrodynamic and thermal characteristics such as average and local Nusselt numbers, streamlines, and isotherm patterns for the Rayleigh number ranges from 103 to 106 and solid volume fraction ranges from 0 to 0.1 are presented. The heat transfer and temperature of heaters depend on the Rayleigh number, the solid volume fraction of nanoparticles, and the length of heaters.

Finite Volume Simulation of mixed convection in an inclined lid-driven cavity filled with nanofluids: Effects of a hot elliptical centric cylinder, cavity angle and volume fraction of nanoparticles

In this study, the mixed convection of nanofluid containing water as a base fluid and aluminum oxide as a nanoparticles in a lid-driven cavity including a hot elliptical centric cylinder is studied. The effects of a hot elliptical centric cylinder, cavity angle (α) and solid volume fraction (ϕ) of nanoparticles are investigated. The obtained results show that with increase of solid volume fraction and due to more condensation of nanofluid and more Brownian motion, the claustration phenomena occurred and resulting an increase of thermal conductivity and convection heat transfer coefficients (k, h) and heat transferred more from the higher temperature surface to the lower temperature wall. Also, heat transfer (q) and Nusselt number (Nu) increased due to the increase in the temperature difference (ΔT) between the hot cylinder and lower temperature surfaces at a constant cavity angle, solid volume fraction and Richardson number (Ri). By considering all diagrams, the highest value of nanofluid’s velocity was around the cap and right-side wall and the lowest velocity value was around the thermal cylinder and left side and down walls. The results show that the increase rate of the Nu from 0 to 45∘ in ϕ=0.1% and 0.2% and base fluid is equal to 1.7, 0.8 and 0.3 respectively.

Effect of radiation on laminar natural convection of nanofluid in a vertical channel with single- and two-phase approaches

In the present study, heat transfer and laminar flow of a nanofluid in a vertical channel by considering the effect of radiation with single- and two-phase approaches with prescribed surface temperature conditions and prescribed surface heat flux conditions were simulated. The main goal of this study is to investigate the effect of variations of Grashof number (Gr), radiation parameter (Nr) and volume fraction of nanoparticles (ϕ) on flow and heat transfer characteristics. For this goal, flow with Gr = 5, 10, 15 and 20, volume fractions of 0, 0.1 and 0.2 and radiation parameters of Nr = 0, 0.5 and 1 were simulated. The results show that by increasing Grashof number in both cases of constant heat flux and temperature, nanofluid velocity increases and in both cases of constant temperature and heat flux by increasing volume fraction, the velocity and temperature of the nanofluid drops. The presence of moving wall (plate boundary condition) induces secondary flows in the flow field, and the flow movement in the channel will experience drift because of temperature variations and buoyancy forces due to inducement of secondary forces and the effect of penetration of moving plate velocity into the fluid close by it which will affect the entire fluid flow field in the end. For fixed plate case, the velocity of nanofluid at the walls is zero because of fixed position of the plate and presence of no-slip boundary condition on the solid walls. By increasing the applied temperature, the value of kinetic and internal energy of the velocity field rises which results in higher density gradients and higher buoyancy forces. For both constant heat flux and temperature, increasing solid nanoparticles volume fraction results in lowering of the velocity contour elevations. The quantitative level of axial velocity curves for constant heat flux condition compared with constant temperature case for Gr = 5 and Nr = 0.5 is about 2–3 times less. For constant temperature boundary condition, for Gr = 5 and Nr = 0.5 and volume fraction of 0.1%, the maximum velocity happens at regions 30–50% of channel height from the bottom.

MHD mixed convection of nanofluid in a cubic cavity with a conductive partition for various nanoparticle shapes

PurposeThis paper aims to numerically examine the mixed convection of SiO2-water nanofluid flow in a three-dimensional (3D) cubic cavity with a conductive partition considering various shapes of the particles (spherical, cylindrical, blade, brick). The purpose is to analyze the effects of various pertinent parameters such as Richardson number (between 0.1 and 10), Hartmann number (between 0 and 10), solid nanoparticle volume fraction (between 0 and 0.04), particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition on the fluid flow and heat transfer characteristics.Design/methodology/approachThe numerical simulation was performed by using Galerkin-weighted residual finite element method for various values of Richardson number, Hartmann number, solid nanoparticle volume fraction, particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition. Two models for the average Nusselt number were proposed for nanofluids with spherical and cylindrical particle by using multi-layer feed-forward neural networks.FindingsIt was observed that the average Nusselt number reduces for higher values of Richardson number and Hartmann number, while enhances for higher values of nanoparticle volume fraction. Among various types of particle shapes, blade ones perform the worst and cylindrical ones perform the best in terms of heat transfer enhancement, but this is not significant which is less than 3 per cent. The average Nusselt number deteriorates by about 6.53per cent for nanofluid at the highest volume fraction of spherical particle shapes, but it is 11.75per cent for the base fluid when Hartmann number is increased from 0 to 10. Conductive partition geometrical parameters (length and height) do not contribute to much to heat transfer process for the 3D cavity, except for the case when height of the partition reaches 0.8 times the height of the cubic cavity, the average Nusselt number value reduces by about 25per cent both for base fluid and for nanofluid when compared to case with cavity height which is 0.2 times the height of the cubic cavity.Originality/valueBased on the literature survey, a 3D configuration for MHD mixed convection of nanofluid flow in a cavity with a conductive partition considering the effects of various particle shapes has never been studied in the literature. This study is a first attempt to use a conductive partition with nanofluid of various particle shapes to affect the fluid flow and heat transfer characteristics in a 3D cubic cavity under the influence of magnetic field. Partial or all findings of this study could be used for the design and optimization of realistic 3D thermal configurations that are encountered in practice and some of the applications were already mentioned above. In this study, thermal performance of the system was obtained in terms of average heat transfer coefficient along the hot surface, and it is modeled with multi-layer feed-forward neural networks.

Hydromagnetic Natural Convection Heat Transfer in a Partially Heated Enclosure Filled with Porous Medium Saturated by Nanofluid

In this paper, a computational analysis has been performed for hydromagnetic natural convection in a partially heated porous square enclosure filled with Al2O3-water nanofluid. The bottom wall of the enclosure is partially heated at constant high temperature Th and the vertical walls are kept at constant temperature Tc which is lower than that of hot wall while the remaining walls are thermally insulated. A modified model for effective thermal conductivity of nanofluids is introduced by taking into account the random motion of nanoparticles. Finite element method is implemented to solve the governing partial differential equations which have been formulated based on Navier–Stokes and energy balance equations along with Brinkman equation. The numerical simulation has been carried out for a range of Rayleigh number (103–106), solid volume fraction of nanoparticles (0–5%), Hartmann number (0–100) and Darcy number (0.001–1.0) and detailed discussion has been presented based on results in terms of streamlines, isotherms, average Nusselt number and average velocity, respectively. Comparison of the present results with the previously published results has been performed and excellent agreements were found. The results show that the flow and temperature fields inside the enclosure are sensitive due to the variation of Rayleigh number, concentration of nanoparticles, Hartmann number and Darcy number. It is also found that optimum heat transfer take place in higher Rayleigh number, concentration of nanoparticles and Darcy number. In addition, nanofluid shows a greater heat transfer enhancement as compared to base fluid for all concentrations of nanoparticles considered.

Effects of an inner stationary cylinder having an elastic rod-like extension on the mixed convection of CNT-water nanofluid in a three dimensional vented cavity

Numerical study for the effects of an inner stationary cylinder having an elastic rod like extension on the mixed convection of CNT-water nanofluid in a three dimensional vented cavity was performed by using finite element method. Effects of various pertinent parameters such as Reynolds number (between 100 and 1000), elastic modulus of the flexible rod (between 105 and 108), size of the elastic rod (between 0.05H and 0.3H), size of the circular cylinder (between 0.025H and 0.25H), inclination angle of the left vertical surface of the cavity (between 0° and 30°) and CNT-nanoparticle solid volume fraction (between 0 and 4%) on the convective flow features in a 3D vented cavity were analyzed. It was observed that with the installation of the obstacle (cylinder + elastic rod) and changing its geometrical and other parameters (elasticity of the rod) affect the variations of established multiple re-circulation zones and isotherms with the three dimensional vented cavity. The average heat transfer rate for the left vertical surface deteriorated with higher inclination angle of the side surface of the cavity while the variations in the average heat transfer rate for the upper surface was found to be slight. Inclusion of the CNT nanoparticle results in average heat transfer enhancement which is about 60% at the highest nanoparticle solid volume fraction and the rate of enhancement was found to be independent of obstacle geometrical parameters, elasticity of the flexible wall and side surface inclination angle of the cavity. A correlation for the average Nusselt number is obtained in polynomial form for the configurations in the presence and absence of obstacles.

Cu–Water Nanofluid MHD Mixed Convection in a Lid-Driven Cavity with Two Sinusoidal Heat Sources Considering Joule Heating Effect

The effects of magnetic field and Joule heating on the heat transfer and fluid flow in a Cu–water nanofluid-filled lid-driven cavity are investigated in this paper. The cavity left side wall is heated by two sinusoidal heat sources, while the other walls have constant temperatures. The top wall of the cavity moves with fixed velocity in + x direction, and the other walls are under no-slip boundary conditions. A constant magnetic flux density is applied to the cavity left side wall. Numerical procedures can be applied to solve the dimensionless equations governing the stream function and temperature at various Reynolds number (Re), Hartmann number (Ha), Eckert number (Ec), magnetic field angle(α) and the solid nanoparticles volume fraction(ϕ). The averaged Nusselt number (Nuavg) is used to specify the rate of the heat transfer. It can be observed that increasing ϕ and also increasing Re result in the significant increase of Nuavg, which enhances convective cooling, and furthermore, Nuavg is varied with α. The increase of Ha within the cavity causes decrease in heat transfer, which enhances conduction heat transfer and also reduces Nuavg. The negative influence of Joule heating on the convection within the cavity is observable in this regard, and the convection is decreased by increasing the value of Ec.

Modeling magnetic nanopolymer flow with induction and nanoparticle solid volume fraction effects: Solar magnetic nanopolymer fabrication simulation

A mathematical model is presented for the nonlinear steady, forced convection, hydromagnetic flow of electro-conductive magnetic nanopolymer with magnetic induction effects included. The transformed two-parameter, non-dimensional governing partial differential equations for mass, momentum, magnetic induction and heat conservation are solved with the local non-similarity method subject to appropriate boundary conditions. Keller’s implicit finite difference “box” method is used to validate solutions. Computations for four different nanoparticles and three different base fluids are included. Silver nanoparticles in combination with various base fluids enhance temperatures and induced magnetic field and accelerate the flow. An elevation in magnetic body force number decelerates the flow, whereas an increase in magnetic Prandtl number elevates the magnetic induction. Furthermore, increasing nanoparticle solid volume fraction is found to substantially boost temperatures. Applications of the study arise in advanced magnetic solar nanomaterials (fluids) processing technologies.

Mixed Convection Stagnation-Point Flow of a Nanofluid Past a Permeable Stretching/Shrinking Sheet in the Presence of Thermal Radiation and Heat Source/Sink

In this study we numerically examine the mixed convection stagnation-point flow of a nanofluid over a vertical stretching/shrinking sheet in the presence of suction, thermal radiation and a heat source/sink. Three distinct types of nanoparticles, copper (Cu), alumina (Al2O3) and titania (TiO2), were investigated with water as the base fluid. The governing partial differential equations were converted into ordinary differential equations with the aid of similarity transformations and solved numerically by utilizing the bvp4c programme in MATLAB. Dual (upper and lower branch) solutions were determined within a particular range of the mixed convection parameters in both the opposing and assisting flow regions and a stability analysis was carried out to identify which solutions were stable. Accordingly, solutions were gained for the reduced skin friction coefficients, the reduced local Nusselt number, along with the velocity and temperature profiles for several values of the parameters, which consists of the mixed convection parameter, the solid volume fraction of nanoparticles, the thermal radiation parameter, the heat source/sink parameter, the suction parameter and the stretching/shrinking parameter. Furthermore, the solutions were presented in graphs and discussed in detail.

MHD mixed convection of nanofluid in a three-dimensional vented cavity with surface corrugation and inner rotating cylinder

PurposeThis study aims to numerically examine mixed convection of CuO-water nanofluid in a three-dimensional (3D) vented cavity with inlet and outlet ports under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.Design/methodology/approachThe bottom surface is corrugated with a rectangular wave shape, and the rotating cylinder surface and cavity bottom surface were kept at constant hot temperatures while the cold fluid enters the inlet port with uniform velocity. The complicated interaction between the forced convection and buoyancy-driven convection coupled with corrugated and rotating surfaces in 3D configuration with magnetic field, which covers a wide range of thermal engineering applications, are numerically simulated with finite element method. Effects of various pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 1,000), angular rotational speed of the cylinder (between −30 and 30), solid nanoparticle volume fraction (between 0 and 0.04), corrugation height (between 0 and 0.18H) and number (between 1 and 20) on the convective heat transfer performance are numerically analyzed.FindingsIt was observed that the magnetic field suppresses the recirculation zone obtained in the lower part of the inlet port and enhances the average heat transfer rate, which is 10.77 per cent for water and 6.86 per cent for nanofluid at the highest strength. Due to the thermal and electrical conductivity enhancement of nanofluid, there is 5 per cent discrepancy in the Nusselt number augmentation with the nanoadditive inclusion in the absence and presence of magnetic field. The average heat transfer rate of the corrugated surface enhances by about 9.5 per cent for counter-clockwise rotation at angular rotational speed of 30 rad/s as compared to motionless cylinder case. Convective heat transfer characteristics are influenced by introducing the corrugation waves. As compared to number of waves, the height of the corrugation has a slight effect on the heat transfer variation. When the number of rectangular waves increases from N = 1 to N = 20, approximately 59 per cent of the average heat transfer reduction is achieved.Originality/valueIn this study, mixed convection of CuO-water nanofluid in a 3D vented cavity with inlet and outlet ports is numerically examined under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. To the best of authors knowledge such a study has never been performed. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.

Forced Convection of Fe3O4-Water Nanofluid in a Bifurcating Channel under the Effect of Variable Magnetic Field

In this study, forced convection of Fe 3 O 4 –water nanofluid in a bifurcating channel was numerically studied under the influence of variable magnetic. Galerkin residual finite element method was used for numerical simulations. Effects of various values of Reynolds number (between 100 and 500), Hartmann number (between 0 and 3), and solid nanoparticle volume fraction (between 0% and 4%) on the convective heat transfer characteristics were analyzed. It was observed that location and size of the re-circulation zones established in the walls of the bifurcating channel strongly influenced by the variable magnetic field and Reynolds number. Average Nusselt number versus Hartmann number showed different characteristics for hot walls of the vertical and horizontal branching channels. The average Nusselt number enhancements were in the range of 12–15% and 9–12% for hot walls of the branching channel in the absence and presence of magnetic field (at Hartmann number of 3).

Mixed convection and entropy generation of nanofluid flow in a vented cavity under the influence of inclined magnetic field

In this study, mixed convection and entropy generation in a vented cavity with inlet and outlet ports are examined under the effects of an inclined magnetic field. Galerkin weighted finite element method was used for the solution of the governing equations. The numerical simulations are performed for various values of Reynolds numbers (between 100 and 500), Hartmann number (between 0 and 50) and solid particle volume fractions of CuO nanoparticles (between 0 and $$4\%$$). Different walls and domains of the computational model are considered for the heat transfer and entropy generation analysis. It was observed that at low Reynolds number number, magnetic field has the potential to enhance the heat transfer at the highest strength while the effect of magnetic field is to reduce the convection at higher Reynolds number. The contributions of different hot walls to the overall heat transfer change considerably with the change of Hartmann number while the effect of magnetic inclination angle is marginal. Inclusion of nanoparticle results in heat transfer enhancement in the absence and presence of magnetic field and the amount of enhancement is 25–27% at the highest value of solid nanoparticle volume fraction. Different parts of the cavity contribute differently to the overall entropy generation when Hartmann number varies while the overall entropy generation first decreases and then increases when the value of Hartmann number increases. The addition of nanoparticles increases the overall entropy generation rate.

Effect of hot obstacle position on natural convection heat transfer of MWCNTs-water nanofluid in U-shaped enclosure using lattice Boltzmann method

PurposeThis paper aims to numerically investigate the natural convection heat transfer of multi-wall carbon nanotubes (MWCNTs)-water nanofluid in U-shaped enclosure equipped with a hot obstacle by using the lattice Boltzmann method.Design/methodology/approachThe combination of the three topics (U-shaped enclosure, different positions of the hot obstacle and MWCNTs-water nanofluid) is innovative in the present study. In total, 15 different positions of the hot obstacle have been arranged, and the effects of pertinent parameters such as Rayleigh numbers, the solid volume fraction of the MWCNTs nanoparticles on the flow field, temperature distribution and the rate of heat transfer inside the enclosure are also investigated.FindingsIt is found that the average Nusselt number increased by raising the Rayleigh number, and so did the nanoparticle solid volume fraction regardless the position of the hot obstacle. Moreover, enclosures where the hot obstacle is located at the bottom region proved to provide a better rate of heat transfer at high Rayleigh number (106). It is concluded that at a low Ra number (103-105), the higher heat transfer rate and Nu number will be obtained when the hot obstacle is located in the left or right channel.Originality/valueIn the literature, no trace of studying the natural convection of nanofluids in U-shaped enclosures with heating obstacles was found. Also, MWCNTs were less used as nanoparticles. As the natural convection of nanofluids in thermal engineering applications would expand the existing knowledge, the current researchers conducted a numerical study of the natural convection of Maxwell nanofluid with MWCNTs in U-shaped enclosure equipped with a hot obstacle by using lattice Boltzmann method.

Entropy generation analysis of mixed convection with considering magnetohydrodynamic effects in an open C-shaped cavity

This paper studies the effect of a constant magnetic field on the mixed convection heat transfer and the entropy generation of CuO-water nanofluid in an open C-shaped cavity with a numerical method. The governing equations are presented by control volume method and they are solved simultaneously by the SIMPLE algorithm. This study examines the effect of the Hartman number, aspect ratio, Reynolds number, and Richardson number parameters for different solid volume fraction of nanoparticles. Also Nusselt number, entropy generation, thermal performance criteria and coefficient of performance is studied in this research. The calculated parameters are the Hartman number, aspect ratio, Reynolds number, Richardson number, nanofluid solid volume fraction, Nusselt number, and coefficient of performance. The results show that increasing the Hartmann number reduces the entropy generation. However, the thermal performance increases. Increasing the aspect ratio raises heat transfer and thermal performance. The effects of nanofluid solid volume fraction on mixed convection heat transfer and entropy generation are also investigated and discussed.

Mixed Convection of Hybrid Nanofluids in an Annulus

In this study, mixed convection in an annulus formed by two horizontal isothermal cylinder surfaces and filled with hybrid nanofluids was examined with Galerkin weighted residual finite element method. The outer cylinder is rotating and inner cylinder is stationary. Influence of Rayleigh number, angular rotational speed of the outer cylinder, eccentricity of the inner cylinder, solid volume fractions of different nanoparticles (alumina, copper, hybrid particles between 0 and 0.02) on the fluid flow and heat transfer characteristics were analyzed. It was observed that average heat transfer enhances with Rayleigh number, solid volume fractions of nanoparticles and eccentricity ratio and reduces as the angular rotational speed of the outer cylinder increases. Adding nanoparticles was found to be advantageous for lower values of Rayleigh number and higher values of angular rotational speed. At the highest volume fraction of Cu nanoparticles, average Nusselt number increases by 31.75 % when the inner cylinder center moves in +y direction. Nanofluid with hybrid nanoparticles gives heat transfer rates which are higher than that of with alumina and lower than that of with copper nanoparticles for the same volume fraction.

Effect of tilt angle on the multi-pipe channel with sinusoidal/curved walls – numerical modelling based on finite volume method

PurposeThis paper aims to investigate the two-dimensional numerical modeling of fluid flow and heat transfer in a fluid channel.Design/methodology/approachThe channel is filled with the CuO-water nanofluid. The KKL model is used to estimate the dynamic viscosity and considering Brownian motion. On the other hand, the influence of CuO nanoparticles’ shapes on the heat transfer rate is taken account in the simulations. The channel is included with several active pipes with hot and cold temperatures. Furthermore, the external curved and sinusoidal walls have cold and hot temperatures, respectively.FindingsThree different tilt angles are considered with similar boundary and operating conditions. The Rayleigh numbers, solid volume fraction of CuO nanoparticles in the pure water and the tilt angles are the governing parameters. Different cases studies, such as streamlines, heat transfer rate, local and total entropy generation and heatlines, are analysed under influences of these governing parameters.Originality/valueThe originality of this work is investigation of fluid flow, heat transfer and entropy generation within a nanofluid filled channel using FVM.