Showing papers on "Convection published in 2020"

Hall and ion slip effects on unsteady MHD free convective rotating flow through a saturated porous medium over an exponential accelerated plate

Abstract: In this paper, we have investigated the Hall and ion slip effects on the unsteady magnetohydrodynamic (MHD) free convective rotating flow over an exponentially accelerated inclined plate entrenched in a saturated porous medium with the effect of angle of inclination, variable temperature and concentration. The flow induced by the presence of heat source/sink and destructive reaction. The Laplace transform technique has been used to solve the governing equations. The effects of the non-dimensional parameters on the governing flow velocity, temperature and concentration are examined with graphical profiles. Also for engineering interest the shear stress, Nusselt number and Sherwood number are obtained analytically and discussed computationally with reference to foremost flow parameters. It is reported that the presence of magnetic field prevents the flow reversal. Angle of inclination sustains a retarding effect on velocity distribution. The present study has an immediate application in understanding the drag experienced at the heated and inclined surfaces in a seepage flow.

Boosting solar steam generation by structure enhanced energy management

Abstract: Interfacial solar-steam generation is a promising and cost-effective technology for both desalination and wastewater treatment. This process uses a photothermal evaporator to absorb sunlight and convert it into heat for water evaporation. However solar-steam generation can be somewhat inefficient due to energy losses via conduction, convection and radiation. Thus, efficient energy management is crucial for optimizing the performance of solar-steam generation. Here, via elaborate design of the configuration of photothermal materials, as well as warm and cold evaporation surfaces, performance in solar evaporation was significantly enhanced. This was achieved via a simultaneous reduction in energy loss with a net increase in energy gain from the environment, and recycling of the latent heat released from vapor condensation, diffusive reflectance, thermal radiation and convection from the evaporation surface. Overall, by using the new strategy, an evaporation rate of 2.94 kg m−2 h−1, with a corresponding energy efficiency of solar-steam generation beyond theoretical limit was achieved.

Effect of thermal radiation on MHD Casson fluid flow over an exponentially stretching curved sheet

Abstract: This paper presents the flow and heat transfer characteristics of an electrically conducting Casson fluid past an exponentially stretching curved surface with convective boundary condition. The fluid motion is assumed to be laminar and time dependent. The effects of temperature-dependent thermal conductivity, Joule heating, thermal radiation, and variable heat source/sink are deemed. Suitable transformations are considered to transform the governing partial differential equations as ordinary ones and then solved by the numerical procedures like shooting and Runge–Kutta method. Graphs are outlined to describe the influence of various dimensionless parameters on the fields of velocity and temperature and observe that there is an enhancement in the field of temperature with the radiation, temperature-dependent thermal conductivity, and irregular heat parameters. Also, the Casson parameter has a tendency to suppress the distribution of momentum but an inverse development is noticed for the curvature parameter. Attained outcomes are also compared with the existing literature in the limiting case, and good agreement is perceived.

Radiative MHD Casson Nanofluid Flow with Activation energy and chemical reaction over past nonlinearly stretching surface through Entropy generation

Abstract: In the present research analysis we have addressed comparative investigation of radiative electrically conducting Casson nanofluid. Nanofluid Flow is assumed over a nonlinearly stretching sheet. Heat transport analysis is carried via joule dissipation, thermal behavior and convective boundary condition. To employ the radiative effect radiation was involved to show the diverse states of nanoparticles. Furthermore entropy optimization with activation energy and chemical reaction are considered. Thermodynamics 2nd law is applied to explore entropy generation rate. Nonlinear expression is simplified through similarity variables. The reduced ordinary system is tackled through optimal approach. Flow pattern was reported for wide range of scrutinized parameters. Computational consequences of velocity drag force, heat flux and concentration gradient are analyzed numerically in tables. Results verify that conduction mode augments with enhance of magnetic parameter.Increasing radiation boosts the temperature and entropy. Activation energy corresponds to augmented concentration. Heat transmission rate augments with the consideration of radiation source term.

Changes in the convective population and thermodynamic environments in convection-permitting regional climate simulations over the United States

Abstract: Novel high-resolution convection-permitting regional climate simulations over the US employing the pseudo-global warming approach are used to investigate changes in the convective population and thermodynamic environments in a future climate. Two continuous 13-year simulations were conducted using (1) ERA-Interim reanalysis and (2) ERA-Interim reanalysis plus a climate perturbation for the RCP8.5 scenario. The simulations adequately reproduce the observed precipitation diurnal cycle, indicating that they capture organized and propagating convection that most climate models cannot adequately represent. This study shows that weak to moderate convection will decrease and strong convection will increase in frequency in a future climate. Analysis of the thermodynamic environments supporting convection shows that both convective available potential energy (CAPE) and convective inhibition (CIN) increase downstream of the Rockies in a future climate. Previous studies suggest that CAPE will increase in a warming climate, however a corresponding increase in CIN acts as a balancing force to shift the convective population by suppressing weak to moderate convection and provides an environment where CAPE can build to extreme levels that may result in more frequent severe convection. An idealized investigation of fundamental changes in the thermodynamic environment was conducted by shifting a standard atmospheric profile by ± 5 °C. When temperature is increased, both CAPE and CIN increase in magnitude, while the opposite is true for decreased temperatures. Thus, even in the absence of synoptic and mesoscale variations, a warmer climate will provide more CAPE and CIN that will shift the convective population, likely impacting water and energy budgets on Earth.

Mixed Convective Magneto Flow of SiO2–MoS2/C2H6O2 Hybrid Nanoliquids Through a Vertical Stretching/Shrinking Wedge: Stability Analysis

Abstract: Hybrid nanoliquid as an expansion of nanoliquid is acquired by scattering combination of nano-powder or numerous distinct nanomaterials in the regular liquid. Hybrid nanofluids are impeding fluids which furnish better performance of heat transport and thermo-physical properties than convectional heat transport fluids (ethylene glycol, water and oil) and nanofluids with single material. At this juncture, a sort of hybrid nanofluid comprising nano-size materials through an ethylene glycol as a regular liquid is modeled to expand the magnetic impact on the mixed convection flow through a shrinking/stretched wedge. The impacts of Joule heating and viscous dissipation are also revealed. The PDEs which governed the flow problem with heat transport are changed into a dimensionless ODEs system through a similarity technique. Then these equations are numerically exercised by utilizing bvp4c solver. The impact of emerging constraints on the flow field with heat transport is discussed with the aid of plots. Also, the stability analysis is implemented to classify which result is physically reliable and stable.

Transportation of radiative energy in viscoelastic nanofluid considering buoyancy forces and convective conditions

Abstract: These days, the most important requirement of contemporary technological activities is extraordinary performance chilling for standard construction. Weaker thermal transference is meaningful issue to keep the extraordinary performance chilling throughout manufacturing systems. This difficulty can be determined by the nanoparticles submersion. Thus, a rheological model featuring thermophoretic and Brownian diffusions is introduced to formulate the two-dimensional viscoelastic (second-grade) nanoliquid flow considering mixed convection and magnetohydrodynamics. Modeling subject to viscous dissipation, convective conditions, Joule heating, heat absorption/generation, stratifications and radiation aspects is presented. Non-dimensionalization process is performed introducing apposite variables. Homotopy algorithm is opted for nonlinear analysis. Graphs are exhibited for interpretation of distinct variables influence against dimensionless quantities. We found opposing behavior for radiation and thermal stratification variables against thermal field.

Magnetohydrodynamic Natural Convection Heat Transfer of Hybrid Nanofluid in a Square Enclosure in the Presence of a Wavy Circular Conductive Cylinder

Abstract: In this paper, steady natural convective heat transfer and flow characteristics of Al2O3-Cu/water hybrid nanofluid filled square enclosure in the presence of magnetic field has been investigated numerically. The enclosure is equipped with a wavy circular conductive cylinder. The natural convection in the cavity is induced by a temperature difference between the vertical left hot wall and the other right cold wall. The steady 2-D equations of laminar natural convection problem for Newtonian and incompressible mixture are discretized using the finite volume method. The effective thermal conductivity and viscosity of the hybrid nanofluid are calculated using Corcione correlations taking into consideration the Brownian motion of the nanoparticles. A numerical parametric investigation is carried out for different values of the nanoparticles volumic concentration, Hartmann number, Rayleigh number, and the ratio of fluid to solid thermal conductivities. According to the results, the corrugated conductive block plays an important role in controlling the convective flow characteristic and the heat transfer rate within the system.

Influence of Arrhenius activation energy in MHD flow of third grade nanofluid over a nonlinear stretching surface with convective heat and mass conditions

Abstract: This topic addresses the influence of binary chemical reaction and activation energy in hydromagnetic flow of third grade nanofluid associated with convective conditions. Flow is developed through nonlinearly stretched surface. Nanoparticles concentration and temperature profiles are considered in the presence of Brownian dispersion and thermophoresis effects. Third grade liquid is electrically conducted via uniform applied magnetic field. Assumption of boundary layer has been used in the problem development. Governing differential systems have been computed in frame of NDsolve. The graphical illustrations explore influences of various sundry variables. Further surface drag force, heat and mass transfer rate are sketched and analyzed. Temperature and concentration distributions are declared increasing functions of Hartman number while reverse trend is seen for velocity distribution. Furthermore an enhancement is observed in temperature and concentration distributions for the higher values of thermal and concentration Biot numbers respectively.

Adverse effects of a hybrid nanofluid in a wavy non-uniform annulus with convective boundary conditions

Abstract: The presented investigation theoretically studies the physical characteristics of a two-dimensional incompressible hybrid nanofluid in a non-uniform annulus where the boundaries are flexible. A mixed convective peristaltic mechanism is implemented to model blood-based nanofluids using two different nanoparticles (Ag + Al2O3). Convective boundary conditions are employed and different forms of nanoparticles are discussed (bricks, cylinders and platelets). The problem is shortened by engaging a lubrication method. Exact expressions for the temperature of cumulative heat source/sink standards, hemodynamic velocity, pressure gradient and streamlines of different shapes of nanoparticles are obtained. Special cases of pure blood and the Al2O3 nanofluid of our model are derived. A comparison is set between nanofluids and hybrid nanofluids from which we observed variations in heat transfer rate in different regions due to the oscillatory nature of the waves. The current model has the potential to be useful for applications related to the metabolic structures that play a vital role in heat sources inside the human body.

Second Grade Bioconvective Nanofluid Flow with Buoyancy Effect and Chemical Reaction

Abstract: This study mainly concerns with the examination of heat transfer rate, mass and motile micro-organisms for convective second grade nanofluid flow. The considered model comprises of both nanoparticles as well as gyrotactic micro-organisms. Microorganisms stabilize the suspension of nanoparticles by bio-convective flow which is generated by the combined effects of nanoparticles and buoyancy forces. The Brownian motion and thermophoretic mechanisms along with Newtonian heating are also considered. Appropriately modified transformations are invoked to get a non-linear system of differential equations. The resulting problems are solved using a numerical scheme. Velocity field, thermal and solute distributions and motile micro-organism density are discussed graphically. Wall-drag (skin-friction) coefficient, Nusselt, Sherwood and motile micro-organisms are numerically examined for various parameters. The outcomes indicate that for a larger Rayleigh number, the bio-convection restricts the upward movement of nanoparticles that are involved in nanofluid for the given buoyancy effect. Furthermore, larger buoyancy is instigated which certainly opposes the fluid flow and affects the concentration. For a larger values of fluid parameter, the fluid viscosity faces a decline and certainly less restriction is faced by the fluid. In both assisting and opposing cases, we notice a certain rise in fluid motion. Thermal layer receives enhancement for larger values of Brownian diffusion parameter. The random motion for stronger Brownian impact suddenly raises which improves the heat convection and consequently thermal distribution receives enhancement. Thermal distribution receives enhancement for a larger Lewis number whereas the decline is noticed in concentration distribution. The larger Rayleigh number results in a strong buoyancy force that effectively increases the fluid temperature. This also increases the concentration difference, thus more nanoparticles transport between surface and micro-organisms. Furthermore, for larger (Nb), the thermal state of fluid receives enhancement while a decline in motile density is observed. Numerical results show that mass flux is an enhancing function of both the (Le) and (Nb).

Enhancement of heat transfer in peristaltic flow in a permeable channel under induced magnetic field using different CNTs

Abstract: The flow of salt water as a base fluid containing nanoparticles of different shapes, viz. zigzag, chiral, and armchair, in an asymmetric permeable channel has been investigated. Such particles in peristaltic flow with a magnetic field have noteworthy medical applications. Two illustrative models, namely those of Hamilton and Crosser, are utilized. The set of governing partial differential equations is solved analytically to find exact solutions, and numerical results are obtained using computer software. A rich summary of the latest findings for pertinent parameters and trapping phenomena is presented using graphs, tables, and streamline diagrams.

Magnetohydrodynamic natural convection of hybrid nanofluid in a porous enclosure: numerical analysis of the entropy generation

Abstract: The effect on the entropy production and MHD convection of the hybrid nanofluid Al2O3–Cu/water (water with Cu and Al2O3 nanoparticles) in a porous square enclosure is studied numerically via Galerkin finite element method. The enclosure used for flow and natural convection analysis is subjected to sinusoidal varying temperatures at the boundaries. Calculations were performed for specific parameters of the Rayleigh number (Ra = 103–106), porosity ratio (e = 0.1–0.9), Darcy number (Da = 10−5–10−2), Hartmann number (Ha = 0–100) and nanoparticles concentration (φ = 0–0.08). The numerical results are presented by velocity profiles, isotherms, streamlines, and Nusselt number. They indicate that the isotherms subject to estimation variations under Ha boost from 0 to 100 as Ra enhances. At high Ha, the conduction transfer mechanism is more obvious. Also, it is seen that the convective heat transfer becomes stronger with the enhancement of the Ra while it detracts with the rise in Ha. Due to the Ra increase, the flow cell becomes stronger. For Ra = 106 and higher Hartmann numbers, the isotherms remain constant which is an indication of convection predominance.

Classical 1/3 scaling of convection holds up to Ra = 1015.

Abstract: The global transport of heat and momentum in turbulent convection is constrained by thin thermal and viscous boundary layers at the heated and cooled boundaries of the system. This bottleneck is thought to be lifted once the boundary layers themselves become fully turbulent at very high values of the Rayleigh number R a —the dimensionless parameter that describes the vigor of convective turbulence. Laboratory experiments in cylindrical cells for R a ≳ 1 0 12 have reported different outcomes on the putative heat transport law. Here we show, by direct numerical simulations of three-dimensional turbulent Rayleigh–Benard convection flows in a slender cylindrical cell of aspect ratio 1 / 10 , that the Nusselt number—the dimensionless measure of heat transport—follows the classical power law of N u = ( 0.0525 ± 0.006 ) × R a 0.331 ± 0.002 up to R a = 1 0 15 . Intermittent fluctuations in the wall stress, a blueprint of turbulence in the vicinity of the boundaries, manifest at all R a considered here, increasing with increasing R a , and suggest that an abrupt transition of the boundary layer to turbulence does not take place.