Free Convection Heat Research Articles

Diffusion Thermo and Chemical Reaction Effects on Magnetohydrodynamic Jeffrey Nanofluid Over an Inclined Vertical Plate in the Presence of Radiation Absorption and Constant Heat Source

This article investigates the Diffusion thermo and chemical reaction effects on the free convection heat and mass transfer flow of Jeffrey nanofluids (Cu and TiO2) over an inclined porous vertical plate embedded in a porous medium in the presence of radiation absorption and constant heat source under fluctuating boundary conditions. The plate is moved with a constant velocity U0, temperature and the concentration are assumed to be fluctuating with time harmonically from a constant mean at the plate. Perturbation technique is applied to solve the governing equations of the flow and pointed out the variations in velocity, temperature and concentration with the use of graphical presentations. The impact of several parameters on local skin friction, Nusselt number and Sherwood number is also noticed and discussed. It is concluded that the resultant velocity reduces with increasing Jeffrey parameter and Suction parameter, velocity and Temperature enhances with increasing Radiation absorption parameter. Also it is noticed that the solutal boundary layer thickness decreases with an increase in chemical reaction parameter. It is because chemical molecular diffusivity reduces for higher values of Kr.

Numerical analysis of combined free convection and radiation heat transfer from an open hemispherical cavity

The present work aims to numerical study the combined effect of free convection and surface radiation from an open hemispherical cavity and the estimation of cooling time using ANSYS-Fluent 15.0. This study warrants a significant novelty. Various parameters, such as Rayleigh numbers (in the range of to ), surface temperatures, and the radius of curvatures varied to elucidate the effect of these parameters on the heat transfer characteristics considering surface radiation. The temperature contours and velocity vectors are obtained pictorially to understand the thermo-fluid characteristics around the hemispherical surface better. For all cases, the radiative heat transfer rate is found to be higher than the convective heat transfer rate for a given condition. The estimation of cooling time is done using lumped system analysis, taking both convection and radiation into account. It is observed that the cooling time estimated with radiation is much lower than that without radiation (only convection). This signifies that the radiation effect should be considered for similar problems. Finally, for the open hemispherical cavity, a correlation for the Nusselt number is developed by incorporating the regression analysis of the available data.

Natural-convection heat transfer from regularly ribbed vertical surfaces: Homogenization-based simulations towards a correlation for the Nusselt number

Free-convection heat transfer from vertical surfaces is widely encountered in engineering applications, yet the role played by surface alterations in the heat transfer process and their practical effectiveness are still points of confusion. In this work, buoyancy-driven flows over periodically ribbed vertical plates of different surface micro-textures are investigated, mainly based on an asymptotic homogenization model through which the expensive resolution of the velocity and thermal fields within the inter-rib regions is bypassed, by imposing equivalent effective boundary conditions at a virtual plane surface. Efficiency of the homogenized simulations in detecting macroscopic behavior of the Nusselt number is first assessed, compared with full feature-resolving simulations in which the effects of complex flow patterns, near and within wall corrugations, on the local Nusselt number are captured. Second, the validated model is used to construct a database of numerical results describing deviations of the average Nusselt number over different ribbed surfaces, relative to a corresponding smooth surface. Under the conditions investigated, it is found that surface roughening generally deteriorates heat transfer from vertical surfaces, with slight enhancement for geometries characterized by low thermal slip, for example, rectangular ribs of narrow inter-rib spaces. Finally, a multiple-regression analysis is conducted to formulate a correlation describing effects of the thermal-slip coefficient, the number of ribs, and the Grashof number on the surface-averaged Nusselt number; accuracy of the proposed correlation is attested via further validation. This paper aims to call attention of the heat transfer society to the ability of the homogenization approach to considerably alleviate the computational requirements for relevant simulations and, thus, to significantly accelerate parametric optimization studies.

Numerical study of mixed and free convection heat transfer under ocean conditions

The mixed and free convection heat transfer of vertical upward flow under ocean conditions is studied numerically. The turbulent heat transfer in a smooth circular tube at low flow rates and the effects of ocean conditions are validated by experimental data. A CFD method based on the v2-f turbulence model and additional inertial force is established. The analysis indicates that the effects of ocean conditions on heat transfer depend on the Buoyancy parameter. In particular, for the mixed convection regime, the overall heat transfer increases, and the local heat transfer deterioration is aggravated. The mixed and free convection heat transfer under ocean conditions is dominated by the Coriolis force and gravity, so the influence of rolling radius is weak. As the rolling period increases, the heat transfer variation increases due to the inclination effects. However, as the rolling amplitude increases, the heat transfer behavior is non-monotonic and difficult to predict due to the combined action of Coriolis effects and buoyancy effects. The introduction of pulsating flow breaks the symmetry of heat transfer, and the hot spot only appears on one side. The overall heat transfer increases, but the local heat transfer deterioration is further aggravated.

Numerical analysis of the effect of porous structure on free convection heat transfer inside an eccentric annular space

Numerical analysis of the effect of porous structure on free convection heat transfer inside an eccentric annular space

Solution of Water and Sodium Alginate-Based Casson Type Hybrid Nanofluid with Slip and Sinusoidal Heat Conditions: A Prabhakar Fractional Derivative Approach

This paper aims to investigate free convection heat transmission in hybrid nanofluids across an inclined pours plate, which characterizes an asymmetrical hybrid nanofluid flow and heat transfer behavior. With an angled magnetic field applied, sliding on the border of walls is also considered with sinusoidal heat transfer boundary conditions. The non-dimensional leading equations are converted into a fractional model using an effective mathematical fractional approach known as the Prabhakar time fractional derivative. Silver (Ag) and titanium dioxide (TiO2) are both considered nanoparticles, with water (H2O) and sodium alginate (C6H9NaO7) serving as the base fluids. The solution of the momentum, concentration, and energy equation is found by utilizing the Laplace scheme, and different numerical algorithms are considered for the inverse of Laplace, i.e., Stehfest and Tzou’s. The graphical analysis investigates the impact and symmetry of significant physical and fractional parameters. Consequently, we surmise that water-based hybrid nanofluid has a somewhat higher velocity than sodium alginate-based hybrid nanofluid. Furthermore, the Casson parameter has a dual effect on the momentum profile. Furthermore, the memory effect reduces as fractional restriction increases for both the velocity and temperature layers. The results demonstrate that increasing the heat transmission in the solid nanoparticle volume fractions enhanced the heat transmission. In addition, the numerical assessment examined the increase in mass and heat transmission, while shear stress was increased with an increase in the Prabhakar fractional parameter α.

Optimization of the distance between the vertical plates in the convective air heat exchanger

This paper examines the influence of the distance between vertical plates on the intensity of free convective heat transfer along with the optimization of this distance. Experimental tests were carried out for one model channel of such an heat exchanger with widths s=0.045, 0.085 and 0.18 m. This channel, open at the top and sides, was formed by two isothermal symmetrically heated parallel vertical plates of dimensions H=0.5 m and B=0.25 m. The influence of the heating surface temperatures tw=30, 40, 50, 55, 60 and 70 °C on the convective temperature fields and velocity generated inside the channels was investigated. Directly measured temperature fields, as well as velocity fields measured indirectly using the NRP, enabled the thermodynamic parameters of the heat exchanger to be determined. Based on the temperature gradient distribution ∂Tw∂x on the wall, its average value was determined for each of the plates and for the entire channel, after which the heat flux Qw transferred from the plates was calculated. The heat flux transferred with the air Q and the efficiency η=Q/Qw of heat transfer in the channel were determined using the balance method based on the average temperatures and air velocities at the inlet t̄bott and ūin and at the outlet t̄top and ūout of the channel obtained from the temperature and velocity fields. A grid placed vertically in the channel, halfway across the panel width and perpendicular to the heating surfaces was used to detect the temperature field in air. The image and matrix of these temperatures were determined using a thermal imaging camera. The numerical reconstruction procedure (NRP) was used to determine the velocity field.For technical reasons and lack of time it was not possible to test more channels. Since three values of the width s were insufficient to determine sopt, it was decided to use numerical research. For this purpose, numerical results were compared with those obtained experimentally for the channels already tested. As the compliance verification was successful, further studies of the channels were continued numerically. As a result of optimizing the heat exchange intensification, optimal widths of a single channel sopt=0.035 m and n channels s0=0.0123 m, included in the heat exchanger, were obtained.

Free convective trickling over a porous medium of fractional nanofluid with MHD and heat source/sink

Nanofluids are considered as smart fluids that can improve heat and mass transfer and have numerous applications in industry and engineering fields such as electronics, manufacturing, and biomedicine. For this reason, blood-based nanofluids with carbon nanotubes (CNTs) as nanoparticles in the presence of a magnetic field are discussed. The nanofluid traverses the porous medium. The nanofluids move on a vertical plate that can be moved. The free convection heat transfer mode is considered when the heat source and heat fluxes are constant. Convective flows are often used in engineering processes, especially in heat removal, such as geothermal and petroleum extraction, building construction, and so on. Heat transfer is used in chemical processing, power generation, automobile manufacturing, air conditioning, refrigeration, and computer technology, among others. Heat transfer fluids such as water, methanol, air and glycerine are used as heat exchange media because these fluids have low thermal conductivity compared to other metals. We have studied the effects of MHD on the heat and velocity of nanofluids keeping efficiency in mind. Laplace transform is used to solve the mathematical model. The velocity and temperature profiles of MHD flow with free convection of nanofluids were described using Nusselt number and skin friction coefficient. An accurate solution is obtained for both the velocity and temperature profiles. The graph shows the effects of the different parameters on the velocity and temperature profiles. The temperature profile improved with increasing estimates of the fraction parameter and the volume friction parameter. The velocity of the nanofluid is also a de-escalating function with the increasing values of the magnetic parameter and the porosity parameter. The thickness of the thermal boundary layer decreases with increasing values of the fractional parameter.

A Free Convection Heat Transfer Enhancement in A Vertical Channel Using Obstructions Inside The Channel

A Free Convection Heat Transfer Enhancement in A Vertical Channel Using Obstructions Inside The Channel

MHD influence on convective heat transfer in a semi-circular cavity using nonhomogeneous nanofluid model

A transient free convective heat transfer in a semicircular vicinity occupied with distinct nanofluids has been examined numerically with a periodic magnetic field. The bottom surface of the cavity is heated non-uniformly as parabolic shape whereas the circular surface is kept at constant cold temperature. In the numerical simulation, ZnO, Fe 3 O 4 , Co, Al 2 O 3 , and Ag have been used as nanoparticles and water and kerosene as the base fluid to investigate the flow regimes and thermal fields developed inside the computed vicinity. Effects of various governing parameters are revealed with depictions of isotherms, streamlines and iso-concentrations. The results show that there is found less computational time to reach a steady-state solution for a higher Rayleigh number and the effects of the periodic magnetic field magnifies the strength of the vortices turning in the cavity. The average heat transfer rate at the bottom surface is uppermost for cobalt-kerosene nanofluid compared to other nine sorts of nanofluids. The results also reveal that the periodic magnetic field as well as the Brownian motion have substantial impacts on the heat transfer rate.

Three-Dimensional Free Convective Heat Transmission Flow of Copper–Water Nanofluid in a Glass Bead Permeable Matrix within a Right Trapezoidal Cavity in Consideration of Thermal Non-Equilibrium Conditions

Three-Dimensional Free Convective Heat Transmission Flow of Copper–Water Nanofluid in a Glass Bead Permeable Matrix within a Right Trapezoidal Cavity in Consideration of Thermal Non-Equilibrium Conditions

Influence of the Aspect Ratio on the Free Convection Heat Transmission Properties of a Container Containing Porous Materials

Nowadays, many industrial and modern applications depend on heat transport in porous zones. An experimental study of the natural convection heat transfer in a corrugated cavity with dimensions of (200, 250, 300) mm in length, a width of 200 mm, a depth of 27 mm, and an amplitude of 30 mm was filled with porous materials: glass balls (3, 6, 10) mm and alumina balls (6) mm, where the water was the working fluid. The top surface was exposed to the environment, while the bottom surface was subjected to constant heat flux (300, 500, 700, 900, 1100 W/m2), The front face, back face, and sides were insulated. In this study, temperature distribution, modified Rayleigh number, and Nusselt number values are foremost criteria, which are presented for three levels of aspect ratio. The influence of various aspect ratios on heat transfer is investigated. The results showed that the heat transfer coefficient decreases with the increase in aspect ratio. The highest value is when aspect ratio = 1. The enhanced Rayleigh number decreases as the aspect ratio increases by 10%.

Hall Current and Soret Effects on Unsteady MHD Rotating Flow of Second-Grade Fluid through Porous Media under the Influences of Thermal Radiation and Chemical Reactions

The unsteady MHD free convection heat and mass transfer flow of a viscous, incompressible, and electrically conducting fluid passing through a vertical plate embedded in a porous medium in the presence of chemical reactions and thermal radiation is investigated. The effects of the Hall current, rotation and Soret are studied. Using the perturbation approach, one can obtain an accurate analytical solution to the governing equations for the fluid velocity, fluid temperature, and species concentration, provided that the initial and boundary conditions are acceptable. It is possible to obtain expressions for the shear stress, rate of heat transfer, and rate of mass transfer for both plates with the ramping temperature and isothermal conditions. On the one hand, the numerical values of the primary and secondary fluid velocities, fluid temperature, and species concentration are presented graphically. On the other hand, the numerical values of the shear stress and rate of mass transfer for the plate are presented in tabular form for various values of the relevant flow parameters. These values are given for a range of pertinent flow parameters. It was determined that an increase in the Hall and Soret parameters over the whole fluid area leads to a corresponding increase in the resulting velocity. The resultant velocity continually climbs to a high level due to the contributions of the thermal and solute buoyancy forces. Lowering the heat source parameter reduces the temperature distribution, resulting in a lower overall temperature. When there is a rise in the chemical reaction parameter over the whole fluid area, there is a corresponding decrease in the concentration. The concentration buoyancy force, Hall current, and Prandtl number reduce the skin friction. On the other hand, the permeability of the porous medium, rotation, chemical reaction, the Soret number, thermal buoyancy force, and mass diffusion all have the opposite effects on the skin friction.

Effect of a rotating cylinder on convective flow, heat and entropy production of a 3D wavy enclosure filled by a phase change material

• Thermal energy storage is studied in a cubic cavity having phase change materials. • A rotating cylinder is added for mixed convection heat transfer. • Mixed convection is better than the natural one for thermal storage units. • High angular speed in the clockwise direction improves the melting process. • A wavy wall with one undulation is sufficient for good performance. In this manuscript, phase change material (PCM), as a thermal energy storage medium, is considered within a 3D wavy cubic enclosure to investigate the effect of free and mixed convection heat transfer on the PCM melting process. Rotating cylinders also are located in the middle of the enclosure to study the effect of their angular velocity in different conditions. Governing equations are solved by Galerkin Finite Element Method (GFEM) and were confirmed by previous studies. As main outcomes, results with enhanced angular velocity, the average temperature, and entropy generation were significantly decreased. Results showed that as the melting process is helpful for thermal energy storage systems, it is recommended by this study to have a rotating cylinder inside the PCM domain and the undulation number of the hot surfaces not to exceed one. It was shown that the cylinder rotation of −5 rad/s enhances the melting process speed by about 88% compared to the stationary cylinder, and about 186% of melting enhancement can be obtained for the undulation number of 1 instead of 4.

The outcome of Newtonian heating on Couette flow of viscoelastic dusty fluid along with the heat transfer in a rotating frame: second law analysis

The outcome of Newtonian heating on the viscoelastic fluid plays a vital role in daily life applications such as conjugate heat transfer around fins, heat exchanger, solar radiation, petroleum industry, etc. Also, rotation of viscoelastic fluid has various importance in product-making industries and engineering. Viscoelastic dusty fluids and Newtonian heating are applicable in nuclear reactors, gas cooling systems, control temperature of the system and centrifugal separators, etc. Therefore, based on this motivation, the present study presents the Newtonian heating effect on the dusty viscoelastic fluid. Additionally, a free convective heat transfer is taken for Couette flow in a rotating frame along with a uniform applied magnetic field. The dust particles possess complex velocities due to rotation and therefore it is the combination of the primary and secondary velocities. For the specified flow, the entropy generation and Bejan number are also computed. Poincare-Light Hill technique has been used for the solution of the system of partial differential equations. The velocity profile for dust particles and fluid are discussed in this article. The influence of different parameters on the Nusselt number, temperature profile, velocity of fluid and dust particle is discussed thoroughly.

MHD Free Convective Heat and Mass Transfer Flow from a Vertical Porous Surface with Variable Thermal Conductivity, Variable Mass Diffusivity and Thermal Diffusion Including Viscous Dissipation and Chemical Reaction

An analysis is carried out to study chemically reactive, viscous dissipative effects of an incompressible and electrically conducting fluid with MHD free convection adjacent to a vertical surface with variable thermal conductivity (VTD) and variable mass diffusivity (VMD). An approximate numerical solution for the steady laminar boundary layer flow over a wall of the surface in the presence of species concentration and thermal mass diffusion has been studied. Using numerical techniques the governing boundary layer equations are solved to get the exact solution. Numerical calculations are carried out for different values of dimensionless parameters. The results are exhibited through various graphs and it is observed from the analysis of the results that the velocity field is appreciably influenced by the magnetic effect, porous effect, chemical reaction and buoyancy ratio between the species and thermal diffusion at the wall of the surface.

Free convective couette flow analysis of viscoelastic dusty fluid along with Newtonian heating in a rotating frame

Applications in daily life heavily rely on the viscoelastic fluid's response to Newtonian heating. The importance of viscoelastic fluid rotation in engineering and the production of goods is also varied. Nuclear reactors, gas cooling systems, system temperature control, centrifugal separators, and other systems can all benefit from viscoelastic dusty fluids and Newtonian heating. In light of this inspiration, the current study describes the Newtonian heating effect on a viscoelastic fluid that contains dust particles. In addition, a uniformly applied magnetic field and a free convective heat transfer are taken into account for Couette flow in a rotating frame. Because the dust particles have complex velocities due to rotation, the primary and secondary velocities are combined. Poincare-Light Hill technique has been used for the solution of the system of partial differential equations. The velocity and temperature profile for dust particles and fluid are discussed in this article. The influence of different parameters on the Nusselt number is also discussed thoroughly.

Numerical Exploration of Soret and Dufour Effect on Unsteady Free Convective Radiating Nanofluid Past a Vertical Moving Porous Plate

The present paper deals with the numerical investigation of Soret and Dufour effect on free convective heat and mass transfer characteristics of radiating water based nanofluid past a vertically moving porous plate in porous medium. The water based nanofluid with copper as a nanoparticle is considered in the present study. The dimensional governing equations relevant to the present model are transformed into non-dimensional form by using the appropriate parameters. The non-dimensional governing equations with the pertinent boundary conditions are solved numerically by using bvp4c function in Matlab software. The influence of suitable parameters on fluid velocity, temperature, concentration, Sherwood number (rate of mass transfer), Nusselt number (rate of heat transfer) and skin friction are exhibited graphically and discussed. Also, the effect of radiation parameter and Prandtl number in the absence of Dufour number has been compared with the help of contours. It is apparent from this study that fluid velocity increases with the increase in K, , & Du and decreases with increase in The fluid temperature increases with the increase in Du & R while it decreases with Pr. The fluid concentration increases with increase in whereas it decreases with . The rate of mass transfer (Sherwood number) increases with increase in Du and decreases with increase in & while the rate of heat transfer (Nusselt number) increases with increase in Du & Pr and decreases with increase in R. Shear stress (skin friction) decreases with the increase in , , K & Du.

Free convection heat transfer with surface radiation from infrared suppression system and estimation of cooling time

• The thermo-fluid characteristics of the full-scale infrared suppression (IRS) system used in the marine gas turbine as an exhaust system are numerically investigated here. • The combined impact of conduction, convection, and radiation on the cooling of the IRS system is intended to be explored. • Various relevant parameters are taken for the analysis, viz., Rayleigh number (Ra), number of funnels, funnel wall temperature, diameter ratio (DR), funnel overlapping (OL), and emissivity of the surface (ε). • A generalized correlation for Nusselt number is developed, considering surface emissivity and the number of funnels as an independent parameter that can be used for academic and industrial applications. • The novelty of the work lies in finding the heat transfer rate and cooling time of the IRS device with varying numbers of funnels (3 to 6 funnels) subjected to the combined effect of free convection and surface radiation. A numerical study is performed on Infrared Suppression (IRS) system having finite wall thickness to observe the combined effect of free convection and surface radiation. The main focus of this work is to obtain thermo-fluid characteristics of natural convection phenomena from the IRS system due to conjugate heat transfer and surface radiation. In addition, the time required to cool down the hot IRS system to atmospheric temperature is also estimated. For the numerical analysis, different governing equations (Navier-Stokes equation, energy equation, and radiation equation) are solved using the finite volume method (FVM) based solver of ANSYS Fluent v 15. Several pertinent parameters, viz., the number of funnels, Rayleigh number, inner surface temperature, geometric ratio, funnel overlapping, and surface emissivity, are varied to elucidate the heat transfer behavior. It is evident from the research that surface radiation has a significant influent on total heat transfer and should not be ignored. In addition, the total heat transfer rate rises with the number of funnels. Both non-dimensional induced mass flow rate and total heat transfer rate have maximum value for zero overlapping cases. At constant temperature contribution of radiative heat transfer varies from 10 to 38% with the rise in emissivity. The inclusion of radiation with convection lowers the cooling time significantly compared to convection alone.

Hall, Soret, and rotational effects on unsteady MHD rotating flow of a second-grade fluid through a porous medium in the presence of chemical reaction and aligned magnetic field

The effects of Hall current, rotation and Soret effects on an unsteady MHD free convection heat and mass transfer flow of a viscous, incompressible and electrically conducting fluid past an inclined plate embedded in a porous medium in the presence of chemical reaction and an aligned magnetic field are investigated. An exact analytical solution of the governing equations for fluid velocity, fluid temperature, and species concentration subject to appropriate initial and boundary conditions is obtained using the perturbation technique. Expressions for shear stress, rate of heat transfer and rate of mass transfer at the plate are derived for both ramped temperature and isothermal plates. The numerical values of primary and secondary fluid velocities, fluid temperature and species concentration are displayed graphically, whereas those of shear stress and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. It is concluded that, the resultant velocity is increased with an increasing in Hall and Soret parameters throughout fluid region. The thermal and solutal buoyancy forces contribute to the resultant velocity ever-increasing to high. The temperature distribution is trim downs through an increasing in heat source parameter. The concentration is reduced with an increase in the chemical reaction parameter in the entire fluid region. Concentration buoyancy force, hall current, and Prandtl number have tendency to reduce in skin friction whereas permeability of the porous medium, Rotation, chemical reaction, Soret number, thermal buoyancy force and mass diffusion have reverse effect on it.