Showing papers on "Natural convection published in 2022"

Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer

Abstract: Recent advances in thermally localized solar evaporation hold significant promise for vapor generation, seawater desalination, wastewater treatment, and medical sterilization. However, salt accumulation is one of the key bottlenecks for reliable adoption. Here, we demonstrate highly efficient (>80% solar-to-vapor conversion efficiency) and salt rejecting (20 weight % salinity) solar evaporation by engineering the fluidic flow in a wick-free confined water layer. With mechanistic modeling and experimental characterization of salt transport, we show that natural convection can be triggered in the confined water. More notably, there exists a regime enabling simultaneous thermal localization and salt rejection, i.e., natural convection significantly accelerates salt rejection while inducing negligible additional heat loss. Furthermore, we show the broad applicability by integrating this confined water layer with a recently developed contactless solar evaporator and report an improved efficiency. This work elucidates the fundamentals of salt transport and offers a low-cost strategy for high-performance solar evaporation.

Effect of magnetic field and thermal radiation on natural convection in a square cavity filled with TiO2 nanoparticles using Tiwari-Das nanofluid model

Abstract: Numerical investigation on natural convection heat transfer of Tiwari - Das model nanofluid inside a square cavity with thermal radiation and magnetic field is carried out in this analysis. Ethylene Glycol E G is considered as base fluid and T i O 2 (Titanium Oxide) considered as nanoparticles for the present investigation. The side horizontal walls of cavity are assumed to be adiabatic and isothermal conditions on both sides walls are considered in this analysis. The finite difference method is implemented to solve the governing non-linear partial differential equations representing momentum and temperature equations. The sway of volume fraction parameter ( 0.01 ≤ ϕ ≤ 0.09 ) , magnetic field parameter ( 1.0 ≤ M ≤ 3.0 ) , Rayleigh number ( 100 ≤ R a ≤ 1000 ) , radiation parameter ( 0.1 ≤ R ≤ 0.9 ) , Reynolds number ( 0 . 1 ≤ R e ≤ 0 . 5 ) and Prandtl number ( 5.2 ≤ P r ≤ 7.2 ) on T i O 2 - E G nanofluid flow and heat transfer is illustrated through graphs. Furthermore, the codes of average Nusselt number with dissimilar values of pertinent parameters are also calculated and results are depicted through graphs. The result shows that, temperature of T i O 2 - E G nanofluid escalates inside the cavity with higher values of (M). Higher heat can be transferred from hot wall to cold wall when radiation parameter (R) intensifies.

Effect of magnetic field and thermal radiation on natural convection in a square cavity filled with TiO2 nanoparticles using Tiwari-Das nanofluid model

Abstract: Numerical investigation on natural convection heat transfer of Tiwari - Das model nanofluid inside a square cavity with thermal radiation and magnetic field is carried out in this analysis. Ethylene GlycolEGis considered as base fluid and TiO2 (Titanium Oxide) considered as nanoparticles for the present investigation. The side horizontal walls of cavity are assumed to be adiabatic and isothermal conditions on both sides walls are considered in this analysis. The finite difference method is implemented to solve the governing non-linear partial differential equations representing momentum and temperature equations. The sway of volume fraction parameter(0.01≤ϕ≤0.09), magnetic field parameter(1.0≤M≤3.0), Rayleigh number (100≤Ra≤1000), radiation parameter (0.1≤R≤0.9), Reynolds number (0.1≤Re≤0.5) and Prandtl number (5.2≤Pr≤7.2) on TiO2-EG nanofluid flow and heat transfer is illustrated through graphs. Furthermore, the codes of average Nusselt number with dissimilar values of pertinent parameters are also calculated and results are depicted through graphs. The result shows that, temperature of TiO2-EG nanofluid escalates inside the cavity with higher values of (M). Higher heat can be transferred from hot wall to cold wall when radiation parameter (R) intensifies.

Numerical analysis of MHD nanofluid flow and heat transfer in a circular porous medium containing a Cassini oval under the influence of the Lorentz and buoyancy forces

Abstract: This paper reports our study on the flow characteristics and heat transfer performance of magnetohydrodynamics (MHD) nanofluid in an innovative porous, circle‐shaped enclosure incorporating a Cassini oval cavity using the Darcy law. The MHD nanofluid considered in this study is Al2O3–H2O. A two‐dimensional (2D) mathematical model is developed based on a homogeneous model. The formulation of the vorticity stream function is then used to obtain coupled equations. Finally, the coupled partial differential equations are solved numerically using the finite element method. Model predictions are then compared against results from the previously published study to verify the accuracy and validity of the developed model, and a good agreement is achieved. Figures demonstrate the effects of nanoparticle volume fraction, inclined angle, Lorentz, and buoyancy forces on the MHD nanofluid flow. The results indicate that the convection mechanism becomes weaker with an increase in solid nanoparticle volume fraction. A significant increase in the Rayleigh number will lead to a stronger and more cohesive core vortex. In addition, when magnetic force is applied horizontally, favorable Nuave occurs. Based on the numerical results, a correlation to predict the average Nusselt number within the enclosure is developed as a function of Hartmann number (Ha), Rayleigh number (Ra), and inclined angle (γ).

Heat flow saturate of Ag/MgO-water hybrid nanofluid in heated trigonal enclosure with rotate cylindrical cavity by using Galerkin finite element

Abstract: MHD Natural convection, which is one of the principal types of convective heat transfer in numerous research of heat exchangers and geothermal energy systems, as well as nanofluids and hybrid nanofluids. This work focuses on the investigation of Natural convective heat transfer evaluation inside a porous triangular cavity filled with silver-magnesium oxide/water hybrid nanofluid [H2O/Ag-MgO]hnf under a consistent magnetic field. The laminar and incompressible nanofluid flow is taken to account while Darcy-Forchheimer model takes account of the advection inertia effect in the porous sheet. Controlled equations of the work have been approached nondimensional and resolved by Galerkin finite element technique. The numerical analyses were carried out by varying the Darcy, Hartmann, and Rayleigh numbers, porosity, and characteristics of solid volume fraction and flow fields. Further, the findings are reported in streamlines, isotherms and Nusselt numbers. For this work, the parametric impact may be categorized into two groups. One of them has an effect on the structural factors such as triangular form and scale on the physical characteristics of the important outputs such as fluidity and thermal transfer rates. The significant findings are the parameters like Rayleigh and slightly supported by Hartmann along with Darcy number, minimally assists by solid-particle size and rotating factor as clockwise assists the cooler flow at the center and anticlockwise direction assists the warmer flow. Clear raise in heat transporting rate can be obtained for increasing solid-particle size.

Thermal management and natural convection flow of nano encapsulated phase change material (NEPCM)-water suspension in a reverse T-shaped porous cavity enshrining two hot corrugated baffles: A boost to renewable energy storage

Abstract: Renewable energy systems may be turning to be more effectual and inexpensive and contributing lion's share of whole energy utilization in today's power hungry planet. The efficacious usage of solar energy needs a storage appliance which could simplify the storage of surplus energy, and finally provide such energy when it desires. One of the efficacious approach of storing thermic energy of higher density from renewable source is executed in a varying range of temperature positions by phase change materials (PCMs) or nano encapsulated phase change material (NEPCM) as their significant role in air-conditioning systems, thermal energy storage, computer chipsets, and thermal management of buildings. In view of this, the present investigations aims at natural convection flow, heat transfer, and entropy of NEPCM-water suspension in a reverse T-shaped porous cavity enshrining two hot corrugated baffles. The thermal control within the cavity is maintained by hot corrugated baffles, cooling of bottom and upper walls and managing the side walls as adiabatic. The governing equations are well established and converted into dimensionless structure and then solved subsequently by Finite Element method (FEM). Simulated outcomes might well be validated accurately and the influence of Rayleigh number (104≤Ra≤106), porosity (0.4≤ε≤0.8), Darcy number (10−4≤Da≤10−2), NEPCM particle volume fraction (0≤φ≤5%), length of the corrugated walls (0.10L≤b≤0.20L), and fusion temperature (0.2≤θf≤0.8) on the heat transfer features, isotherms, heat capacity ratio and streamlines is explored efficaciously. The outcomes of this study are that amplifying Raleigh number leads to the intensification of streamlines, velocity fields and structural change of phase change zone while decaying of Darcy number exhibits the opposite effect. Strengthening porosity of porous medium intensifies the streamlines, horizontal and vertical velocity. Growth of the length of baffles yields emaciation of streamlines, flow fields, and enormous rate of heat transfer. Heat capacity ratio attains a constant value 0.97 outside melting-solidification zones within the cavity. Rise in the fusion temperature results in the expansion and shifting of melting-solidification zone. When φ rises from 1% to 2%, Nuave uplifts and yields its minimum enhancement while with rise of φ from 1% to 5%, Nuave upgrades and yields its maximum enhancement at fixed Darcy and Raleigh numbers.

Heat flow saturate of Ag/MgO-water hybrid nanofluid in heated trigonal enclosure with rotate cylindrical cavity by using Galerkin finite element

Abstract: MHD Natural convection, which is one of the principal types of convective heat transfer in numerous research of heat exchangers and geothermal energy systems, as well as nanofluids and hybrid nanofluids. This work focuses on the investigation of Natural convective heat transfer evaluation inside a porous triangular cavity filled with silver-magnesium oxide/water hybrid nanofluid [H2O/Ag-MgO]hnf under a consistent magnetic field. The laminar and incompressible nanofluid flow is taken to account while Darcy-Forchheimer model takes account of the advection inertia effect in the porous sheet. Controlled equations of the work have been approached nondimensional and resolved by Galerkin finite element technique. The numerical analyses were carried out by varying the Darcy, Hartmann, and Rayleigh numbers, porosity, and characteristics of solid volume fraction and flow fields. Further, the findings are reported in streamlines, isotherms and Nusselt numbers. For this work, the parametric impact may be categorized into two groups. One of them has an effect on the structural factors such as triangular form and scale on the physical characteristics of the important outputs such as fluidity and thermal transfer rates. The significant findings are the parameters like Rayleigh and slightly supported by Hartmann along with Darcy number, minimally assists by solid-particle size and rotating factor as clockwise assists the cooler flow at the center and anticlockwise direction assists the warmer flow. Clear raise in heat transporting rate can be obtained for increasing solid-particle size.

Unsteady natural convection flow due to fractional thermal transport and symmetric heat source/sink

Abstract: Unsteady natural convection flow of viscous fluids in a circular cylinder, due to a generalized fractional thermal transport is analytically studied. The considered mathematical model is based on a new fractional differential constitutive equation of the thermal flux suitable to describe the thermal memory effects. To develop the mathematical model, the time-fractional Caputo-Fabrizio derivative is used. The generalized constitutive equation becomes equivalent to the classical Fourier's law for the zero value of the fractional order of derivative. Analytical solutions for the fluid temperature and velocity are determined using the Laplace and finite Hankel transforms. The influence of the memory parameter on heat transfer and fluid motion is discussed by numerical simulations and graphical illustrations.

MHD natural convection of a hybrid nanofluid in an enclosure with multiple heat sources

Abstract: Natural convective flow and heat transfer of a hybrid nanofluid contained in an enclosure with multiple heat sources at the bottom wall are investigated in the presence of magnetic field applied to an angle with the horizontal axis. The system of equations is formulated systematically using dimensionless variables and parameters as well as defining stream function in terms velocity components. Solutions obtained by the finite difference method are then validated with experimental and numerical results which provides a good agreement. A grid independent test is also performed. Results reveal that flow pattern is substantially changed with the change of the magnetic field parameter, angle of magnetic field, number and breadth of heat sources and Rayleigh number. The intensity of the stream function is stronger for higher Rayleigh number and smaller magnetic field parameter. When the volume fraction of Cu nanoparticles is more than 6% the streamlines and isotherms demonstrate distinct pattern from those for its lower value. Moreover, symmetric pattern of streamlines is observed for angle of magnetic field equal to 0 and π/2. Due to the increase of the number of heat sources, angle of magnetic field and Rayleigh number, average Nusselt number is found to increase.

Simulation of mixed-convection of water and nano-encapsulated phase change material inside a square cavity with a rotating hot cylinder

Abstract: Nano-encapsulated PCM consists of a solid shell and a phase change material (PCM) in the core that improves the thermal properties of base fluids. The heat capacity of the nanofluid increases due to the latent heat of the NEPCM core and the heat transfer rate increases dramatically. Also, a phase change occurs in a certain range of temperature. In the present study, the core and shell of NEPCM are n-nonadecane and polyurethane, respectively. Mixed convection of water-NEPCM is simulated inside a square chamber with cold walls and a hot rotating cylinder in the center. Coupled PDE equations are solved by the SIMPLE algorithm and developing C++ code. The parameters of Grashof number, Reynolds number, intensity of stored energy in the core of NEPCM (χ), and fusion temperature (θf) have been studied on the flow pattern, temperature contour, heat capacity ratio (Cr) contour, and Nusselt number. Based on this study it can be concluded that in general the optimal state of θf is in moderate values or especially numbers close to 0.5 and at this range of θf, χ reduction can enhance Nusselt number more. Also, at high Gr number by increasing Re number, heat transfer rate reduces. The results also show that adding NEPCM can increase the Nusselt number by more than 13%.

Non-Newtonian nanofluid natural convective heat transfer in an inclined Half-annulus porous enclosure using FEM

Abstract: In this paper, by means of the finite element method, the MHD free convection flow of non-Newtonian nanoliquid inside a halved annulus enclosure considering a constant heat flux is being applied to the straight walls has been analyzed. The enclosure is loaded with water and nanoparticles of alumina (Al2O3) the combination of these tows produces a liquid that shows shear-thinning behavior. The governing parameters of this study are the Rayleigh number (103 ≤ Ra ≤ 106), inclination angle (0 ≤ α ≤ 90), power-law index (0.6 ≤ n ≤ 1) and Hartmann number (0 ≤ Ha ≤ 100). The outcomes indicate that the inclination angle of the cavity and the Hartmann number can be considered as effective control parameters at different Rayleigh numbers. While the magnetic field is applied the velocity field retarded and hence convection heat transfer and the Nusselt number diminished, and the increment of power-law index prompts the heat transfer to drop. It is shown that the power-law index and Hartmann reduces the local Nusselt number. Also, the average Bejan numbers corresponding of active parameters are discussed in this study.

Numerical treatment of time dependent magnetohydrodynamic nanofluid flow of mass and heat transport subject to chemical reaction and heat source

Abstract: The thermophysical properties of the nanofluids override the physical properties of conventional fluids due to the high thermal conductivity of the nanoparticles. The applications of nanofluids have varied use in the era of bio-engineering and thermal sciences. Moreover, the nanoparticles attributed the significances in human blood arteries. Therefore, the present analysis manifests with the free convection of electrically conducting nanofluid embedding with resistive forces such that the magnetic field and permeability of the medium. The augmentation in the heat transfer properties is obtained because of the inclusion of radiative heat energy and absorption diffusion. Moreover, the nanoparticles volume fraction is focused with implementation of chemical reaction. Numerical treatment using the code in-build MATLAB code pdepeis employed for the transformed unsteady flow problem. The graphical computations against flow parameters are worked with justified physical importance. A declining change in nanoparticles is examined due to Prandtl number which is more progressive for steady case. The decreasing change in velocity is more dominant for nanoparticles as compared to pure fluid. The nanoparticles concentration reduces for effective variation of chemical reaction constant and Lewis number.

MHD effects on natural convection in a U-shaped enclosure filled with nanofluid-saturated porous media with two baffles

Abstract: The present work examines numerically the heat transfer and the buoyancy-driven flow within a U–shaped baffled enclosure filled with a nanofluid-saturated porous medium in the presence of an inclined magnetic field using a finite element scheme. The enclosure bottom wall is heated sinusoidally while the two baffles and the inner walls are maintained at a constant cold temperature. The rest walls of the enclosure are kept adiabatic. The parameters under investigation are Hartmann number ( Ha ), volume fraction (φ), Darcy number (Da), Rayleigh number (Ra), nanoparticles aspect ratio (AR), and the angle of applied magnetic field (γ). The results are crucial and illustrate that increasing the values of Ra, Da and the nanoparticles volume fraction enhances the heat transfer while the Hartmann number inversely affects the heat transfer augmentation. Moreover, the average Nusselt number (Nu ave ) increases by increasing the enclosure aspect ratio. For the geometry under consideration and for a better heat transfer rate , it is recommended to choose an AR = 0.6 at Ha = 0 with a 0.1 vol fraction.

MHD natural convection of a hybrid nanofluid in an enclosure with multiple heat sources

Abstract: Natural convective flow and heat transfer of a hybrid nanofluid contained in an enclosure with multiple heat sources at the bottom wall are investigated in the presence of magnetic field applied to an angle with the horizontal axis. The system of equations is formulated systematically using dimensionless variables and parameters as well as defining stream function in terms velocity components. Solutions obtained by the finite difference method are then validated with experimental and numerical results which provides a good agreement. A grid independent test is also performed. Results reveal that flow pattern is substantially changed with the change of the magnetic field parameter, angle of magnetic field, number and breadth of heat sources and Rayleigh number. The intensity of the stream function is stronger for higher Rayleigh number and smaller magnetic field parameter. When the volume fraction of Cu nanoparticles is more than 6% the streamlines and isotherms demonstrate distinct pattern from those for its lower value. Moreover, symmetric pattern of streamlines is observed for angle of magnetic field equal to 0 and π/2. Due to the increase of the number of heat sources, angle of magnetic field and Rayleigh number, average Nusselt number is found to increase.

Numerical investigation and optimization of natural convection and entropy generation of alumina/H2O nanofluid in a rectangular cavity in the presence of a magnetic field with artificial neural networks

Abstract: The SIMPLE algorithm and the volume control technique are used to investigate the natural convection of alumina/H2O nanofluids (NFs) flow in a cavity. The cavity consists of two hot triangular blades on the bottom wall. The two sidewalls are insulated and the upper wall is at a low-temperature. The cavity can have different angles. Brownian nanoparticle motion is also considered to model their thermal conductivity and viscosity. Finally, the values ​​of Nusselt number (Nu), Bejan number (Be) entropy generation rate (Sgen) are estimated by changing the cavity angle (γ), the Hartmann number (Ha), and the Rayleigh number (Ra). It is found that an increment in the Ra enhances the amount of Nu and Sgen, but the amount of Be is reduced. An enhancement in the Ha does not effect on Sgen and Nu at low values of Ra, while for high amounts of Ra, Sgen and Nu are reduced. The maximum value of Sgen and Nu and the minimum amount of Be, which are 10.36, 5.21, and 0.34, respectively, occur when γ = 30°. Also, the minim values of Nu and Sgen occur for strong free convection in the horizontal and vertical cavity, respectively.