Conjugate Free Convection Research Articles

Corrigendum to “Transient conjugate free convection within flexible enclosure having discrete heat source”

Corrigendum to “Transient conjugate free convection within flexible enclosure having discrete heat source”

Combined conjugate free convection and thermal radiation in a porous inclined enclosure occupied with Cu-Al2O3 hybrid nanofluid

This study deals numerically with a steady laminar combined conjugate natural convection and thermal radiation heat transfer within an inclined porous enclosure occupied with Cu-Al2O3 /water hybrid nanofluid; the thermal conductivity and nanofluid viscosity are correlated experimentally. The centered heat sink and source are attached respectively to the upper and lower enclosure walls at a set distance of 0.5 from the sidewall and were parameterized with length values of 0.2, 0.4, 0.6, 0.8, and 1. This analysis is performed in wide ranges of enclosure inclination angles (0≤ α ≤ 180°), thermal radiation parameters (0≤ Rd ≤ 200), hybrid nanofluid volume fractions (0.1, 0.33, 0.75, 1, 2, 3, 4, and 5%), Rayleigh numbers (103≤ Ra ≤ 106), Darcy numbers (10−5≤ Da ≤ 10−2), medium porosities (0.1≤ ε ≤ 0.9), and thermal conductivity ratios (1≤ γ ≤ 10). The Nusselt number increases as the heat sink/source length decreases. This trend is even more pronounced when the length of the sink/source is reduced. Furthermore, the average Nusselt numbers for the fluid and solid matrix gradually increase as the inclination angle of the enclosure varies from 0° to 45°. However, beyond 45°, both Nusselt numbers exhibit a noticeable decrease with increasing inclination angle of the enclosure. The average Nusselt number of the fluid significantly increases with varying thermal radiation parameters. When the thermal radiation parameter ranges from 0 to 2 and 0 to 200, the average Nusselt number of the fluid increases by 192% and 7343%, respectively. The Nusselt numbers significantly improve when the porosity decreases and the thermal conductivity ratio increases. For a porosity of 0.1 and a porous thermal conductivity ratio ranging from 1 to 10, the average Nusselt number of the fluid increases by approximately 129% and 141% when the Darcy number increases from 10−5 to 10−2.

Conjugate free convection in a non-uniform heating walled enclosure filled by ternary hybrid nanofluid under magnetic field

A study was conducted using numerical simulations to analyse the behaviour of heat transfer in a square enclosure filled with a ternary hybrid nanofluid in the occurrence of a magnetic field. The flow in the enclosure is characterised by steady and laminar conjugate-free convection. The enclosure has a vertical border with a finite thickness, while the other three borders are assumed to be very thin. The investigation aims to analyse the impact of several key factors on the average Nusselt number using the finite element method. These parameters include the volume fraction of ternary hybrid type nanoparticles (ranging from 0 to 0.03), Rayleigh number (varying from 103 to 106), solid wall thickness (changing from 0.1 to 0.3), Hartmann number (varying from 0 to 100), and the ratio of thermal conductivities (ranging from 0.1 to 10). A notable enhancement in heat transfer is found by employing a ternary hybrid nanofluid. This enhancement becomes more significant for small Rayleigh numbers, where heat conduction governs the primary means of heat transfer. Also, at low levels of Ra, the development of energy transfer strength becomes insignificant in the existence of a magnetic field. This magnetic field effect is primarily controlled by high values of Ra, which consequently leads to an enhancement in the strength of energy transmission.

Transient conjugate free convection within flexible enclosure having discrete heat source

Transient conjugate free convection in flexible enclosure is examined numerically. Isoflux heat sources are mounted in a left wall of finite thermal conductivity while a right wall is assumed to be hyper-flexible. The finite element method (FEM) is adopted to solve the governing partial differential equations, an arbitrary Lagrangian–Eulerian (ALE) approach inherent in the unstructured mesh. The governing parameters under consideration are: the number of the heat source, [Formula: see text], the thickness of the heat source, [Formula: see text], and the Rayleigh number, [Formula: see text]. It is determined that the development of conjugate convection heat transfer experiences through an initial phase, a transition phase, and a steady state phase. Each phase interval is shifted by adjusting the thickness of the heat source. Higher number and thicker of heat source cases had an ignorant effect on the shape of the flexible wall, but they tend to suppress the heat transfer rate. Increasing the block amplitude by 25% for [Formula: see text] results in reductions of the values of [Formula: see text] to 24%, 20%, and 28% respectively.

Entropy generation on magnetohydrodynamic conjugate free convection with Joule heating of heat-generating liquid and solid element inside a chamber

This study presents the entropy production of MHD conjugate free convective flow within a square chamber infused with water encasing a heat-generating and conducting square solid element. The chamber’s vertical side is exposed to an external magnetism effect. The flowing fluid circulating inside the hollow space of the chamber produces a volumetric heat generation rate. The finite element approach is used to solve the model equations for mass, momentum, and heat energy conservations, which are affected by a number of variables, including the Rayleigh number (Ra), Hartmann number (Ha), Joule heating parameter, and internal heat generation parameter (Δ), and the area ratio of the solid element (Ab). By systematically varying those parameters (e.g., 103 ≤ Ra ≤ 106, 0 ≤ Ha ≤ 20, 0 ≤ Δ ≤ 10, 0.1 ≤ Ab ≤ 0.3), variations of hydro-thermal properties are observed and analyzed through streamline, isotherm, Nusselt number, entropy generation, thermal performance criterion, and mean fluid temperature of the system. It can be declared that convective heat transport increases as the area ratio of the solid element and the internal heat generation decrease. However, the minimum thermodynamic irreversibility is obtained for the highest area ratio and lowest heat generation parameter. The study shows a 48.37% increase in convective heat transfer as Ab decreases from 0.3 to 0.1. Similarly, reducing Ha and Δ to zero leads to an 8.76% and 526% reduction in TPC, respectively.

Cooling of different IRS systems: A three-dimensional comparative study

Different types of infrared suppression (IRS) systems are numerically investigated to characterize heat transfer and fluid flow behavior three-dimensionally. In this context, the conical funnel, Cylindricallouv funnel, Conicallouv funnel and cylindrical funnel type of IRS systems subjected to integrate effect of radiation from the surface and conjugate free convection heat transfer are elucidated here. Besides this, cooling time is obtained for the conjugate problem with surface radiation. Different governing equations are resolved three-dimensionally for the flow caused by the buoyancy to obtain the distribution of temperature and flow around the funnel. The operational parameters, namely Rayleigh number, emissivity and temperature of the surface, and the number of louvers (holes) are changed for the parametric study. The total Nusselt number and ratio of mass suction are vital functions of the louver numbers. The louvered funnel gives the highest Nusselt number and mass suction rate. It is found that the contribution of radiation from the surface in estimating the rate of total heat transfer is noteworthy, even for the low emissivity cases. The cooling time is much lower for the convection united with radiation than for convection only.

Conjugate free convection from an array of discrete heat sources with water and nano-encapsulated phase change particle in a cold enclosure

The present works investigates the conjugate free convection in a cold enclosure containing a hot circular cylinder. An array of discrete heat sources are attached to the cylinder surface. The free space between the enclosure and the cylinder was filled with a heterogeneous mixture of water and nano-encapsulated phase change particle (NEPCP). This nanoparticles have an outer shell and a core inside. Specifically, the NEPCP core can absorb thermal energy on charging state or releases energy on discharging state. The governing parameters considered are the number of heated segment, 1≤n≤4, the heat source thickness, 0≤A≤0.1, the fusion temperature, 0.1≤Θf≤0.5, the heating intensity, 104≤Ra≤106, and the NEPCP concentration, 0≤ϕ≤0.05. The results shows that the Θf, n, A, and Ra modify the position and size of the area of phase change zone. The maximum Nusselt number was found at different angular positions depending on the heat source arrangement. The maximum value increases by increasing the NEPCP concentration, but its position almost unchanged by adjusting the concentration. There is critical A=Ac and max(ϕ) for the optimum arrangement of discrete heat source.

Conjugate free convection with surface radiation from real-scale IRS system with multiple conical funnels: A numerical analysis

In the present investigation, a numerical computation is carried out on the infrared suppression (IRS) device to study the combined effect of free convection and surface radiation. The main aim is to obtain the fluid flow and heat transfer features of the conjugate free convection with surface radiation from an IRS device consisting of multiple diathermic conical funnels. In addition, the time required to cool down the hot IRS to ambient temperature is also determined. A comparison between cooling time considering only convection and the combined effect of convection and radiation is made. The real-scale IRS device is numerically simulated using ANSYS-Fluent 15.0. Different appropriate parameters (like funnel overlapping, geometric ratio, Rayleigh number, funnel numbers, surface temperature, and surface emissivity) are changed in the workable operating range for understanding the thermo-fluid behavior and impact of cooling time on some parameters. Results indicate that the surface radiation should not be ignored because it significantly influences convection characteristics. The maximum heat transfer rate and fastest cooling time are obtained for IRS with the highest funnels. The cooling time is 39% lesser for the combined effect of convection and radiation than convection alone.

Conjugate Free Convection Heat Transfer and Thermodynamic Analysis of Infrared Suppression Device With Cylindrical Funnels

AbstractA convection system can be designed as an energy-efficient one by making a considerable reduction in exergy losses. In this context, entropy generation analysis is performed on the infrared suppression system numerically. In addition, results due to heat transfer are also shown. The numerical solution of the Navier–stokes equation, energy equation, and turbulence equation is executed using ansysfluent 15.0. To perform the numerical analysis, different parameters such as the number of funnels, Rayleigh number (Ra), inner surface temperature, and geometric ratio are varied in the practical range. Results are shown in terms of heat transfer, entropy generation, irreversibility (due to heat transfer and fluid friction), and Bejan number with some relevant parameters. Streamlines and temperature contours are also provided for better visualization of temperature and flow field around the device. Results show that heat transfer and mass flow rate increase with the increase in the number of funnels. Entropy generation and the irreversibility rise with an increase in the number of funnels and geometric ratio. Also, the Bejan number decreases with an increase in Ra and the number of funnels. A cooling time is also obtained using the lumped capacitance method.

Effect of Al2O3/water nanofluid on Conjugate Free Convection in a Baffle Attached Square Enclosure

A numerical study of conjugate free convection heat transfer of Al2O3/water nanofluid inside a differentially heated square enclosure with a baffle attached to its hot wall has been carried out. A detailed parametric study has been carried out to analyze the effect of Rayleigh number (104 < Ra < 106), length, thickness and position of baffle, conductivity ratio and volume fraction of the nanoparticle (0<<0.2) on heat transfer. The thermal conductivity ratio of the baffle plays a major role on the conjugate heat transfer inside the enclosure. Higher the baffle length better is the effectiveness of the baffle. The average Nusselt number is found to be an increasing function of both thermal conductivity ratio and volume fraction of the nanofluid. The minimum enhancement of conjugate heat transfer is 30% when Al2O3/water nanofluid of 0.1 volume fraction is used for the entire range of Rayleigh number considered.

MHD conjugate natural convection in a porous cavity involving a curved conductive partition and estimations by using Long Short-Term Memory Networks

In this study, MHD conjugate free convection of a porous cavity having a curved shape conductive partition is numerically analyzed by using the Galerkin weighted residual finite element method. The numerical simulation is performed for different values of pertinent parameters: Rayleigh number (between $$10^4$$ and $$10^6$$), Hartmann number (between 0 and 60), Darcy number (between $$5 \times 10^{-4}$$ and 0.05), porosity of the medium (between 0.25 and 0.75), curvature of the partition (minor axis radius of the horizontal ellipse, between 0.01H and 0.3H) and conductivity ratio (between 0.05 and 50). It was observed that the heat transfer rate enhances locally and in average for higher values of Rayleigh number, Darcy number, porosity of the medium and conductivity ratio, whereas the impact is opposite for higher values of Hartmann number. The amount of average Nusselt number reduction is obtained as $$22\%$$ when Hartmann number is changed from 0 to 60 at Rayleigh number of $$10^5$$. Curvature and conductivity of the curved partition affect the variation in fluid flow and heat transfer characteristics. Maximum of $$7\%$$ variation in the average Nusselt number is achieved when the curvature of the conductive partition is varied but the effects of thermal conductivity ratio on heat transfer rate are higher. Long Short-Term Memory Networks are used for estimation of the velocity and temperatures in the computational domain for various values of pertinent input parameters variation in the system which includes conjugate heat transfer mechanism in a porous enclosure with complex-shaped conductive partition under the effects of magnetic field.

Local thermal non-equilibrium analysis of conjugate free convection within a porous enclosure occupied with Ag–MgO hybrid nanofluid

Current investigation aims to analyze the conjugate free convection inside a porous square cavity occupied with Ag–MgO hybrid nanofluid using the local thermal non-equilibrium (LTNE) model. Hybrid nanofluids are a novel kind of enhanced working fluids, engineered with enhanced thermo-physical and chemical properties. Two solid walls located between the horizontal bounds in two sides of cavity play the role of a conductive interface between the hot and cold walls, and moreover, the top and bottom bounds have been insulated. The governing differential equations are obtained by Darcy model and then for better representation of the results, converted into a dimensionless form. The finite element method is utilized to solve the governing equations. To evaluate the correctness and accuracy of the results, comparisons have been performed between the outcomes of this work and the previously published results. The results indicate that using the hybrid nanoparticles decreases the flow strength and the heat transfer rate. The heat transfer rate augments when Rk rises and the flow strength augments when Ra grows. Enhancing the porosity increases strongly the size and strength of the vortex composed inside the porous medium. When Kr is low, the heat transfer rate is low and by increasing Kr, thermal fields become closer to each other. The effect of hybrid nanoparticles on thermal fields with the thinner solid walls is more than that the thicker ones. An increment in H eventuates the enhancement of heat transfer and hence, the thermal boundary layer thickness. By increasing the volume fraction of the hybrid nanoparticles, Nuhnf and Nus decrease in constant Ra. Besides, increase in Ra enhances the Nuhnf and Nus. For a certain d, the reduction of Nus due to using the hybrid nanoparticles is more than that for Nuhnf. The increment of d lessens Nuhnf for all values of Kr and has not specific trends for Nus. Utilizing hybrid nanoparticles decreases Nus (except d = 0.4), rises Nus when Kr 42. In constant d, increment of H, respectively, decreases and boosts Nuhnf and Nus. For all values of d, increment of e declines Nuhnf. In low value of d, the increase in e reduces Nus, whereas at higher values, Nus has continuously enhancing trend. For different values of d, the increase in e scrimps Nuhnf. The increment of d and also e, and H are, respectively, decreases and increases the heat transfer rate.

Numerical Solution of Conjugate Free Convection From a Vertical Fin Embedded in a Non-Darcy Porous Medium

Abstract The problem of conjugate free convection from a vertical fin embedded in a fluid-saturated porous medium is investigated. The governing nonlinear equations are solved iteratively by a highly implicit finite difference scheme. In this paper, the results based on four models, viz the Darcy model, the Brinkman model, the non-Darcian model with nonlinear inertia and viscous terms, and also the non-Darcian model with viscous, nonlinear inertia and velocity square terms, are compared. It is seen that fin cooling is more effective at higher Grashof or Darcy numbers due to stronger convection effects. The local Nusselt number is observed to increase with the Grashof or Darcy numbers and decrease slightly with the conduction–convection parameter. The limitation of the Darcy’s law is observed at higher values of permeability when the non-Darcian models are more relevant.

Numerical Simulation of Conjugate Free Convection in a Vertical Cylinder Having Porous Layer

Numerical Simulation of Conjugate Free Convection in a Vertical Cylinder Having Porous Layer

Conjugate Free Convection in a Square Cavity Filled with Nanofluid and Heated from Below by Spatial Wall Temperature

Conjugate Free Convection in a Square Cavity Filled with Nanofluid and Heated from Below by Spatial Wall Temperature

Conjugate free convection with surface radiation in open top cavity

This paper reports the numerical study of two-dimensional, steady, incompressible, conjugate, laminar, natural convection with surface radiation in open top cavity having air as the intervening medium for different locations of uniform volumetric heat generating source at the left wall. For surface radiation calculations, radiosity–irradiation formulation has been used, while the view factors required therein, are calculated using the Hottel’s Crossed-string method. The analysis has been done for a constant property of fluid, with the Boussinesq approximation assumed to be valid. The effects of the magnitude of heat source, location, the material and surface properties of the heat source on both heat transfer and fluid flow have been studied and discussed. An important contribution from the present work is to find the location of heat source for efficient cooling and it is found at the top of the left wall. Based on a large set of numerical data, correlations have been developed for maximum non-dimensional temperature of heat source for three different locations at the left wall.

Effects of Viscous Dissipation and Heat Generation on MHD Conjugate Free Convection Flow from an Isothermal Horizontal Circular Cylinder

Magnetohydrodynamic (MHD) conjugate free convection boundary layer solution for the heat transfer of an electrically conducting fluid from a horizontal circular cylinder has been studied. The heat due to viscous dissipation and internal heat generation are also included into the energy equation. The developed governing equations and the associated boundary conditions are transferred to dimensionless forms and then solved numerically using the implicit finite difference method. Numerical results for the magnetic parameter, conjugate conduction parameter, Prandtl number, viscous dissipation parameter and heat generation parameter are given for the velocity profiles, temperature distributions, coefficient of skin friction and heat transfer rate.

Natural convection from a horizontal annulus partially filled with porous medium

A steady laminar flow conjugate free convection from a horizontal annulus is investigated. Two cases concerning the location of the porous layer were considered. In the first case the porous layer is located adjacent to the inner cylinder. In the second case the porous layer is located adjacent to the outer cylinder. Solution is obtained using a finite volume method. The effect of the p hysical parameters, Grashof number, Darcy number, and porous layer thickness, on the local and average Nusselt number were calculated and presented. Comparison with completely filled with porous media annulus, and with clear fluid case is also presented

Conjugate free convection from a vertical plate fin with a rounded tip embedded in a porous medium

In this paper the two-dimensional conjugate free convection in a porous medium is investigated from a vertical plate fin. Both physically and mathematically it is important to consider a smooth profile for the tip of the fin, such as a rounded tip of an arbitrary shape. Such fin shapes approximate well the rectangular fin, and their study allows a more accurate prediction of the heat transfer quantities, since no restrictive conditions have to be imposed, such as an insulated tip, and there are no singularities appearing in the mathematical formulation. The governing equations of the convective flow in the porous medium are coupled to the governing equation for the heat flow in the fin by the conditions of continuity of the temperature and the heat flux at the solid/porous media interface. The governing non-dimensional parameters are the convection–conduction parameter, N cc, and the aspect ratio of the fin, λ.

CONJUGATE FREE CONVECTION FROM VERTICAL FINS EMBEDDED IN A POROUS MEDIUM

The problem of conjugate free convection in a porous medium from a vertical plate and a vertical cylindrical fin is considered. The governing equations for the convective flow in the porous medium are coupled to the governing equation for the heat flow in the fin by the conditions of continuity of the temperature and the heat flux at the interface. The heat flow in the fin is taken to be either two-dimensional or one-dimensional, in order to compare the results provided by both approaches. The nondimensional parameters that appear are the convection-conduction parameter, N cc , and the aspect ratio of the fin, u p for the plate fin and u c for the cylindrical fin. The surface curvature parameter u C appears as a parameter which is directly dependent on u c in the case of the cylindrical fin. Considering two-dimensional conduction in the solid fin is a more realistic approach from a practical standpoint, but the shortcoming of specifying zero heat flux at the tip of the fin is discussed.