Free Convection Heat Research Articles

Morphological Effects on Natural Convection Heat Transfer of Magnesium Ferrite Ferrofluid

This investigation intends to analyze the influence of nanoparticles morphology on the magnetic flux dependent thermo-physical properties and magnetohydrodynamic free convection heat transfer performance of water-based magnesium ferrite ferrofluid under various volume fractions. The thermo-physical parameters of the ferrofluid suspended with cube shaped particles are examined at 25 °C using KD2 pro thermal analyzer, Ostwald viscometer and specific gravity bottle under magnetic flux. The free convection heat transfer is obtained using heat pipes assisted cubical enclosure. Without the influence of magnetic flux, the thermal conductivity of the ferrofluid was improved by a maximum of 12.75% at a volume fraction of 0.15%. At the same time, the maximum viscosity and density were raised by 32.92% and 6.11% at a volume fraction of 0.20% in comparison with water. Under the influence of 350 Gauss, thermal conductivity, and viscosity of ferrofluid enhanced by 21.81% and 37.41% while the density decreased by 4.91%. It was revealed that the addition of cube-shaped magnesium ferrite particles in ferrofluid improved the thermo-physical properties. The optimum concentration for maximum heat transfer is reduced to 0.025% with the use of cube shaped particles compared to other types of nanoparticles reported in previous studies.

Numerical analysis of Magnetohydrodynamic convection heat flow in an enclosure

This article investigates the modeling and numerical simulation of Magnetohydrodynamic (MHD) buoyancy-driven convection flow in a differentially heated, square enclosure. Left vertical side is given a high temperature and the right vertical side is sustained at a low temperature. Horizontal sides of the enclosure are insulated. A constant magnetic field is presumed horizontally. Findings of the governing differential equations are explored numerically considering the impact of Magneto-hydrodynamic (MHD). Problem is deciphered by Galerkin finite element approach in COMSOL Multiphysics. Numerical solutions are computed for different values of Rayleigh number ranging 103≤Ra≤107 and Hartmann number ranging 0≤Ha≤40. Rate of heat that passes from the heated side is affected by increasing Rayleigh and Hartmann numbers. Comportment of MHD free convection heat flow from transient to steady state is numerically examined for a period of 0 to 1 s. The numerical solutions are discussed in respect of streamlines, iso-contours, and isotherms. In addition, physical quantities such as velocity and Nusselt number are studied. It is seen that with increasing values of Rayleigh number there is increase in local Nusselt number distribution on heated side of the cavity. Velocity distribution in the flow domain decreases in variations with increasing Hartmann number.

Free convective heat for nano-fluids stagnation-point flow a past a shrinking sheet in a saturated porous medium

Free convective heat for nano-fluids stagnation-point flow a past a shrinking sheet in a saturated porous medium

Performance improvement of a heat sink with triangular slotted and interrupted fins: A computational study

The present study reports a three-dimensional computational analysis of free convection heat transfer from heat sinks with vertical fins mounted on a vertical base. The difference in the base and ambient temperature varies from 10 °C to 60 °C. This work proposes four novel geometrical modifications on the continuous rectangular fins intending to augment the heat transfer rate. These modifications include (a) providing triangular slots, (b) changing the value of minimum thickness at the neck of the slotted fin, (c) offsetting the position of the neck, and (d) interrupting the slotted fins. Thus, the work investigates the thermal performances of six different heat sink configurations concerning heat dissipation rate (Q), specific heat transfer rate (Q/m), average Nusselt number (Nu), the weight of the heat sink, and effectiveness. In all these cases, the heat sink volume remains the same. The current analysis shows that the heat sink with a single slot, with the neck at the base (ε=0) and having interruptions, dissipates the maximum heat (14.89% higher than the conventional continuous fin heat sink) with a weight reduction of 24.1%. The present study also proposes a correlation for the average Nusselt number in terms of relevant parameters, which has an accuracy of 6 %.

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.

Combination effect of [formula omitted] and [formula omitted] nanoparticles on natural convection inside an inclined enclosure: CFD numerical approach

In the present paper, the free convection heat transfer was simulated through an inclined circular enclosure with a square inside. The effects of Al2O3-Fe3O4 hybrid nanoparticles on heat transfer and fluid flow were evaluated using Buongiorno’s mathematical model. The modeling was performed using the SIMPLE algorithm. The equation of each type of nanoparticle was solved separately in a water-based fluid. In this study, adding 2% volume fraction of each nanoparticle (Al2O3andFe3O4) to water, Rayleigh number (Ra=103and105), inclined angle (θ=0to60), the ratio of Brownian to thermophoresis diffusion for each nanoparticle (NBT=0.1to0.3) were studied on flow and heat transfer parameters. The study showed that increasing Rayleigh number, NBT,Al2O3, and NBT,Fe3O4 decreases the maximum value of Al2O3andFe3O4 concentration. Also, at high Rayleigh numbers, the inclined angle did not change the heat transfer rate.

DOUBLE DIFFUSIVE FREE CONVECTION IN A PACKED BED SQUARE ENCLOSURE BY USING LOCAL THERMAL NON-EQUILIBRIUM (LTNE) MODEL

In the present study, free convection heat and mass transfer of fluid in a square packed bed enclosure is numerically investigated. For the considered geometrical shape, the left vertical wall of enclosure was assumed to be kept at high temperature and concentration while the opposite wall was kept at low temperature and concentration with insulating both the top and bottom walls of enclosure. The Brinkman– Forchheimer extended Darcy model was used to solve the momentum equations, while the energy equations for fluid and solid phases were solved by using the local thermal non-equilibrium (LTNE) model.Computations are performed for a range of the Darcy number from 10-5 to 10-1, the porosity from 0.5 to 0.9, and buoyancy ratio from -15 to 15. The results showed that both the buoyancy ratio and the packed bed characteristics have significant effect on each one of the flow field, heat transfer and mass transfer.

Analysis of a Two-Phase MHD Free Convection Generalized Water–Ethylene Glycol (50 : 50) Dusty Brinkman-Type Nanofluid Pass through Microchannel

The water–ethylene glycol (50 : 50) nanofluid has applications in the manufacture of polyester as a raw agent, air conditioning systems, antifreeze formulation, dehydrating agents in the gas industry, a precursor in the plastic industry, and convective heat transfer. These developments in nanotechnology and nanoscience have caught the interest of several researchers. Because it keeps machines and engines cool by reducing friction between their different parts, grease is a vital part of many machinery and engines. Also, due to the extensive use of fractional derivatives, this work seeks to evaluate the combined impacts of free convection flow and heat transfer, magnetic field, and Brinkman-type water–ethylene glycol (50 : 50) dusty nanofluid among microchannel. The flow that the buoyant force provides helps to carry heat naturally via convection. While the left plate moves at a consistent velocity and the right plate stays stationary, the fluid is also evenly dispersed with all dust particles that have a spherical form. Partial differential equations (PDE) are used to present the mathematical modeling. The resultant PDEs are generalized by utilizing the Caputo–Fabrizio fractional derivative. The problem’s closed-form solution is produced by combining a Laplace transformation with a finite sine Fourier transformation. It has also been studied that temperature, Brinkman nanofluid, and dust particle velocity relate to a variety of other factors, such as the magnetic parameter, Grashof number, dusty fluid parameter, and volume friction parameter. The graphical outcomes for the dusty fluid, Brinkman nanofluid, and temperature profiles are plotted using Mathcad-15. The Brinkman nanofluid and dusty fluid behave similarly for a variety of embedded factors. It is found that compared to the traditional one, the fractional dusty nanofluid model displays more realistic characteristics. The addition of nanoparticles in water–ethylene glycol (50 : 50) dusty nanofluid enhances the rate of heat transfer up to 41.04478% by increasing their volume fractional.

The Effect of Elliptical Form of Cylinder on Free Convection in Annular Space

We try through this research to present a detailed study on free convection heat transfer inside a closed space. The work is carried out in numerical way, using the method called finite volume. The governing equations are solved for numerical simulations of steady state and laminar regime. The studied domain is an annular space consisting mainly of two cylinders positioned horizontally, the inner cylinder has an elliptical shape with different aspect ratio (E) while the outer one has a single shape which is circular. The primary conditions adopted in this research are as follow: the outer cylinder has a cold surface, while the inner cylinder has a cold surface. The space between cylinders is considered to be filled with fluid of different values of thermo-physical proprieties (Pr). The fluid in the space moves under the influence of thermal buoyancy which is controlled by Ri number. The pertinent parameters for this research are: the aspect ratio of elliptical cylinder which is E = 0.1 to 1, the Prandtl number Pr = 1 to 100 and finally the Richardson number Ri = 103, 104 and 105. The results of this work show that the elliptical form allows an increase in thermal transfer activity. Also, values of the number Pr have a limited effect on heat transfer.

Three Dimensional Free Convection Heat and Mass Transfer between Two Vertical Walls filled with Porous Materials having Periodic Temperature and Concentration on a Wall

Three Dimensional Free Convection Heat and Mass Transfer between Two Vertical Walls filled with Porous Materials having Periodic Temperature and Concentration on a Wall

Convective flow analysis for moderate Rayleigh numbers of nano encapsulated phase change materials-water filled enclosure with various thermal conditions

The numerical study of free convection heat transfer inside a square enclosure having exponential and sinusoidal thermal profiles filled with hybrid nanofluid is reported. The hybrid nanofluid is nano-encapsulated phase change materials (NEPCMs) and water (H2O). The NEPCMs are constructed by a polyurethane as a shell and an n-nonadecane as a core. The n-nonadecane undergoes a phase transition and capable of storing or releasing a large quantity of latent heat. The study focuses on the effect of heating exponent and heating frequency to the convective flow and melting distribution. A Galerkin finite element method is applied to solve the governing equations. The result from the present model is compared with the previously published articles. The controlling parameters under consideration are the heating exponent, 0≤λ≤2, the heating frequency, 1≤N≤4, the Rayleigh number, 104≤Ra≤106. It is found that the lowest exponent and frequency of heating gives the best thermal performance.

CONVECTIVE HEAT AND CASSON NANOFLUID FLOW OVER A VERTICAL PLATE WITH HEAT SOURCE

This paper considers the Casson nanofluid flow of a free convective heat transfer with heat source over a vertical plate and its thermophysical properties. The governing partial differential equations were reduced to couple nonlinear ordinary differential equations using similarity variables. The couple nonlinear ordinary differential equations were solved numerically using Runge-Kutta fourth order method with shooting technique and implemented using MatLab. The effects of various non-dimensional governing parameter namely, Prandtl number, Biot number, Grashof number, heat source parameter, skin-friction coefficient, Nusselt number and Sherwood number is analysed for Casson nanofluid flow, discussed and presented graphically. The result showed that heat source parameter increases in skin-friction coefficient, velocity and temperature profiles but, decreases in concentration profiles and Nusselt number.

Transient MHD Free Convection Flow, Heat and Mass Transfer in Darcy–Forchheimer Porous Medium in the Presence of Chemical Reaction and Heat Absorption with Soret and Dufour Effects: Element-Free Galerkin Modelling

Transient MHD Free Convection Flow, Heat and Mass Transfer in Darcy–Forchheimer Porous Medium in the Presence of Chemical Reaction and Heat Absorption with Soret and Dufour Effects: Element-Free Galerkin Modelling

Experimental investigation of heat transfer in a cavity filled with (50% CuO-50% Al2O3)/Water with hybrid nanofluid attached to a vertically heated wall partially integrated with PCM

An empirical evaluation of free convective heat transmission was conducted in a rectangular enclosure containing a hybrid nanofluid of (50% CuO-50% Al2O3)/water linked to a PCM-containing wall. The enclosure's left and right surfaces were kept at constant warm and cold temperatures, whereas the remaining surfaces were assumed to be isolated. The left side was filled partially with PCM. Several variables were examined, such as the hot-side temperature differential (∆T =10, 15,20 ◦C) and the hybrid nanofluid concentration (Φ=0.03,0.05,0.07)%. The findings show that the rate of heat transmission through natural convection rises as the concentration of nanomaterials rises. Due to its great absorbability and heat storage capacity, PCM was also shown to have the potential to lower the hot side temperature by up to 15.5%. The Nusselt number rises over time as the left cavity is filled partially with PCM. When added hybrid nanofluid is, PCM’s heat-storage efficiency and, by extension, its ability to cool the hot side is greatly improved.

Thermal Management for Natural Convection within Porous Enclosures

Various simulations and numerical studies have been carried out for free convection heat transfer of a square enclosure filled with porous matrix for sinusoidal and uniform heating conditions also varying Rayleigh values from 1 to 500 by using a mathematical finite element simulation. The porous media chosen for this research is saturated water medium (H2O).The enclosure properties have been predefined as follows: The top and base walls of the enclosure are made adiabatic, whereas the right wall is kept at a steady cold temperature. The hot left wall is treated at varying temperatures. The Nusselt values as well as mean Nusselt values have been quantified for the aforementioned values. It has been observed that the mean Nusselt values rise with the surge in Rayleigh values. For the Rayleigh value of 500, we found that uniform heating condition showed larger values of streamline function when compared to Sinusoidal heating conditions. These simulations were performed by considering a Solar Fresnel as a real-world example. We hope that scholars and engineers collectively working on enhancing or aspiring to numerically model the thermal exchange through a square enclosure filled porous matrix will benefit from the information provided in this research article.

Numerical study of thermal performance of yield stress rheological liquid under suspension of hybrid nanostructures: The finite element approach

Enhancement of heat transfer employing nanofluids, studied numerically, observed profound effects in thermophysical and theological properties used in various applications such as avionics, laser diode, rocket nozzels and microelectronics. In this paper, the influence of thermal radiations and hybrid nanoparticles on free convection flow and heat transfer of Casson hybrid nanofluid over vertical plate is investigated. A mixture of pure water and ethylene glycol has been considered as a base Casson fluid while Copper oxide ([Formula: see text]) as nanofluid (single kind) and, Copper oxide ([Formula: see text]) and Silicon dioxide ([Formula: see text]) (double kind known as hybrid nanofluid) are disseminated in base Casson fluid mixture to be formed as hybrid nanofluid. The governing system of partial differential equations of the flow and heat transfer processes is converted to a system of well-posed coupled nonlinear ordinary differential equations by using the similarity transformations. The resulting system is solved using the Galerkin finite element (GFE) technique. The quadratic Lagrange polynomials are used as basis functions over the mesh of about 1000 to 2000 finite elements and the nonlinear system of order 6003 and upto 12003 is solved. The accuracy of developed numerical methods is confirmed by comparing their results with convection flow and heat transfer with nanoparticles. Thereafter, the said solutions are used to investigate the effects of thermal radiation, hybrid nanoparticle volume friction, Prandtl number, type of flow and heat transfer behavior. The innovative results of the present study reported higher velocities in suspensions with low sphericity particles and the radiation parameter is directly proportional to the temperature with the use of nano and hybrid nanoparticles. It has also been noted that the GFE method is a more stable numerical technique as compared with other existing analytic and semi-analytical methods.

Experimental Study of Free-Convective Heat Transfer of Single-Row Bundles of Tubes with Spiral Aluminum Fins of Different Heights in an Air Flow Intensified by an Exhaust Shaft

Experimental Study of Free-Convective Heat Transfer of Single-Row Bundles of Tubes with Spiral Aluminum Fins of Different Heights in an Air Flow Intensified by an Exhaust Shaft

Experimental Study to Improve Solar Photovoltaic Performance by Utilizing PCM and Finned Wall

The temperature of a photovoltaic (PV) module has a significant impact on the module's ability to produce electricity. PV cells module’s passive cooling is critical for increasing electrical efficiency and power output. In this work, two scenarios of the passive cooling technique were presented for use in the cooling of the monocrystalline silicon PV modules. An aluminium finned wall and a combination of aluminium finned wall with phase change material were connected to the backside of the PV in order to bring the working temperature down and maintain it under the hot climate conditions in southern Iraq. Paraffin wax was employed as a PCM placed into an aluminium container with internal and exterior longitudinal aluminium fins in order to enhance the PCM's poor thermal conductivity, speed up the rates at which it melts and solidifies, and increase the amount of heat that is dissipated through free convection heat transfer. The PV modules were simultaneously tested and compared with a PV reference module under different solar radiation. According to the findings, the average temperature of the PV-Aluminium Finned wall-PCM module is reduced by 19.9 degrees Celsius when compared with the temperature of the reference PV module. This results in an increase in the average maximum output power of up to 23.1% compared to an identical reference PV module. Furthermore, the average electrical efficiency of the PV-Aluminium Finned wall-PCM is enhanced by 23.2% during the testing time from 9:00 AM to 12:00 PM in July 2022 at maximum solar radiation of 1130.7 W/m2 when compared with the PV reference module under the same conditions. This indicates a significant increase in both electrical and thermal performance. The testing took place in July 2022.

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.