Free Convection Heat Research Articles

Heat transfer in a non-uniformly heated enclosure filled by NEPCM water nanofluid

Purpose This paper aims to focuses on by investigate the heat transmission and free convective flow of a suspension of nano encapsulated phase change materials (NEPCMs) within an enclosure. Particles of NEPCM have a core-shell structure, with phase change material (PCM) serving as the core. Design/methodology/approach The enclosure consists of a square chamber with an insulated wall on top and bottom and vertical walls that are differently heated. The governing equations are investigated using the finite element technique. A grid inspection and validation test are done to confirm the precision of the results. Findings The effects of fusion temperature (varying from 0.1 to 0.9), Stefan number (changing from 0.2 to 0.7), Rayleigh number (varying from 103 to 106) and volume fraction of NEPCM nanoparticles (changing from 0 to 0.05) on the streamlines, isotherms, heat capacity ratio and average Nusselt number are investigated using graphs and tables. From this investigation, it is found that using a NEPCM nano suspension results in a significant enhancement in heat transfer compared to pure fluid. This augmentation becomes more important for the low Stefan number, which is around 16.57% approximately at 0.2. Secondary recirculation is formed near the upper left corner as a result of non-uniform heating of the left vertical border. This eddy expands notably as the Rayleigh number rises. The study findings indicate that the NEPCM nanosuspension has the potential to act as a smart working fluid, significantly enhancing average Nusselt numbers in enclosed chambers. Research limitations/implications The NEPCM particle consists of a core (n-octadecane, a phase-change material) and a shell (PMMA, an encapsulation material). The host fluid water and the NEPCM particles are considered to form a dilute suspension. Practical implications Using NEPCMs in energy storage thermal systems show potential for improving heat transfer efficiency in several engineering applications. NEPCMs merge the beneficial characteristics of PCMs with the enhanced thermal conductivity of nanoparticles, providing a flexible alternative for effective thermal energy storage and control. Originality/value This paper aims to explore the free convective flow and heat transmission of NEPCM water-type nanofluid in a square chamber with an insulated top boundary, a uniformly heated bottom boundary, a cooled right boundary and a non-uniformly heated left boundary.

Application of fibonacci wavelet frame operational matrix for the analysis of arrhenius-controlled heat transfer flow in a microchannel

The effects of free convective Arrhenius-controlled heat transfer fluid in a microchannel encased by two parallel vertical plates has been examined in the current work. A new functional integration matrix has been developed by implementing Fibonacci Wavelet Frame known as Fibonacci wavelet Frame operational matrix. Primary goal of this study is to provide a unified method via FWF to compute an approximate solution to a non-linear differential equation systems for the fluid flowing in a microchannel. The leading nonlinear coupled differential equations has been tackled by this novel approach. The derived results are discussed visually and displayed with the help of various plots. Additionally, thermophysical parameters of engineering interest, such as the nusselt number and sheer stress are estimated and depicted in the graphs. It is worthwhile to note that fluid velocity and fluid temperature rises as the chemical reaction parameter value enhances. A remarkable agreement comes to light when the numerical data generated through the current method is compared with the findings from the previous work.

Free convective heat transfer flow in a glass bead porous medium varying permeability and sinusoidal wall temperature

Free convective heat transfer flow in a glass bead porous medium varying permeability and sinusoidal wall temperature

Experimental investigation of zinc ferrite/insulation oil nanofluid natural convection heat transfer, AC dielectric breakdown voltage, and thermophysical properties

Improving the thermal and dielectric properties of insulation oil (INO) with nanoadditives is an important challenge, and achieving dispersion stability in these nanofluids is quite challenging, necessitating further investigation. The main goal of this study is the synthesis and use of the hydrophobicity of zinc ferrite (ZnFe2O4) nanoparticles, which can improve both the thermal and dielectric properties of the INO. This oil is made from distillate (petroleum), including severely hydrotreated light naphthenic oil (75–85%) and severely hydrotreated light paraffinic oil (15–25%). A comprehensive investigation was carried out, involving the creation of nanofluids with ZnFe2O4 nanoparticles at various concentrations, and employing various characterization methods such as X-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscopy, energy dispersive X-ray (EDX), zeta potential analysis, and dynamic light scattering (DLS). The KD2 Pro thermal analyzer was used to investigate the thermal characteristics, including the thermal conductivity coefficient (TCC) and volumetric heat capacity (VHC). Under free convection conditions, the free convection heat transfer coefficient (FCHTC) and Nusselt numbers (Nu) were evaluated, revealing enhancements ranging from 14.15 to 11.7%. Furthermore, the most significant improvement observed in the AC Breakdown voltage (BDV) for nanofluids containing 0.1 wt% of ZnFe2O4 amounted to 17.3%. The most significant finding of this study is the improvement in the heat transfer performance, AC BDV, and stability of the nanofluids.

An investigation of the thermal performance of functionally graded annular fins on a horizontal cylinder under natural convection

ABSTRACT In industrial applications, annular fins are commonly made of homogeneous materials such as aluminum, struggling to provide uniform temperature distribution along their length. Recognizing the potential of Functionally Graded Materials (FGMs) to enhance thermal performance by combining two different materials with a gradual variation, this study proposes their use as fin materials to achieve optimum performance. The study consists of three major components: (1) numerical analyses to determine the optimum volume composition of FG fins, (2) the fabrication process of aluminum and FG fins utilizing powder metallurgy and the hot-pressing technique, and (3) experiments to evaluate the thermal performance of FG and aluminum fin arrays attached to a horizontal cylinder of 250 mm length under natural convection. Heat ranging from 25 W to 150 W is applied to the cylinder during these experiments. Based on the experiments, the thermal performances of fins are evaluated in terms of net free convection heat transfer rate, the Nusselt number, and fin effectiveness. Overall, experimental results demonstrate that the net convection heat transfer rate depends on fin spacing, material, and the base-to-ambient temperature difference. Specifically, FG fin arrays enhance the net heat transfer rate by 59%, while aluminum fin arrays increase it by 33% compared to finless cylinders. Moreover, FG fins outperform aluminum fin arrays by 40% in convective heat transfer coefficient h. Due to being the first experimental study, this study sets itself apart.

MHD free convective heat and mass transfer flow passing through semi‐infinite plate for Cu‐water and TiO2‐water nanofluids in presence of radiation embedded in porous medium

AbstractThis research presents an analytical study of magnetohydrodynamics (MHD)‐free convective heat and mass transfer flow of a nanofluid bounded by a semi‐infinite flat plate. A magnetic field of strength is applied throughout the fluid region. The plate is moving with a constant velocity , temperature, and the concentration are assumed to be fluctuating with time harmonically from a constant mean at the plate. The frontier equations are assumed to be of an oscillatory nature and cracked analytically using the perturbation technique. The novelty of the present work is to examine the heat and mass transfer MHD flow for Cu‐water and TiO2‐water nanofluids in the presence of thermal radiation. The influence of physical parameters on the flow domain is described in the discussions by graphically and in tabular form. It was found that the fluid temperature and skin friction were reduced with the increased values of the radiation parameters for Cu‐water and TiO2‐water nanofluids. Also, it is noticed that the concentration boundary layer thickness decreases with an increase in chemical reaction parameters.

Numerical simulation of single-pass selective laser melting of Mg-Y-Sm-Zn-Zr alloy

A three-dimensional finite volume method (FVM) thermal-fluid coupling model was developed to simulate the temperature field distribution and dimensions of the melt pool in selective laser melting (SLM) of Mg-Y-Sm-Zn-Zr alloy powder. This model aims to accurately determine the temperature field and surface morphology of the melt pool by considering the laser's impact on powder particles, free surface dynamics, convection, and multiphase heat transfer. The study explores how laser power and scanning speed influence temperature distribution, melt pool size, and flow dynamics. The findings show that increasing laser power or reducing scanning speed consistently affects the melt pool size, peak temperature, and cooling rate. During the evaporation of the alloy in the melt pool, fluid flow is primarily governed by recoil pressure and Marangoni convection. Notably, increasing the laser power from 40 W to 100 W and the scanning speed at 0.3 m/s enhances the depth of the melt pool indentation from 13.86 µm to 23.35 µm. Furthermore, the indentation depth correlates positively with the laser line energy density.

Electro-Kinetically Free Convective Heat Flow in a Slit Microchannel

Electro-Kinetically Free Convective Heat Flow in a Slit Microchannel

Influence of an inclined thick partition on free convection heat transfer performance under surface radiation in a hollow block

In the present work, a computational analysis of the combined energy transfer by free convection, radiation, and heat conduction in 2D hollow block with an inclined partition was carried out. The inclined partition was made of a heat-conducting material and had a finite thickness. The closed space inside the brick was filled with air (Pr = 0.71) and the airflow is laminar. The external surfaces of the vertical borders are considered to be isothermal, and the remaining horizontal surfaces are supposed to be adiabatic. The finite difference technique is employed to work out numerically the differential equations. The in-house computational code was verified in detail using various problems. The major characteristics that determine the considered phenomena are surface emissivity of internal walls, Ra number, and material of solid walls and partition. As a result of the research, the distributions of streamlines and isotherms combined with the average Nusselt numbers were obtained. Depending on the material of the partition, the flow structure in the cavity changes significantly, which reflects the distribution of streamlines, namely, for the materials with low thermal conductivity the convective cell in the upper part of the cavity is elongated, while in the lower part it is shifted to the lower and left borders. The isotherms reflect the more intensive heating in the left part of the area. With an increase in the thermal conductivity coefficient, the streamlines reflecting the nature of the flow are restructured. It was shown that the presence of an inclined partition significantly reduces the intensity of convective heat transfer.

Viscous dissipation effect on steady free convective hydromagnetic heat transfer flow of a reactive viscous fluid in a bounded domain

Viscous dissipation effect on steady free convective hydromagnetic heat transfer flow of a reactive viscous fluid in a bounded domain

Estimating incident infrared radiation intensity on a horizontal surface

The study aims to characterize external IR heating sources, operating in free convection atmosphere, qualitatively and quantitatively for various applications. It employs non-invasive IR thermography to measure steady-state irradiations from a ceramic IR heater at variable voltages (60–150 V) using the surface energy budget (SEB) method which relies on only two measured parameters (surface and ambient temperature). The free convection heat transfer from the plate is demarcated between the thermal boundary layer (TBL) and buoyant plume-dominated region by temperature histogram tool. Nearly 78 ± 5 % of the plate area is occupied by the hot plume(s) in the studied voltage range. Estimated irradiation agrees fairly well with one another (within ± 10 %). Additionally, the time response of the plate was measured to be ∼ 120 s. This fast response can be made even faster, by reducing the thermal mass, eventually leading to low-cost IR sensors.

Radiative and Lorentz’s effects on MHD free convective mass and heat transfer time-dependent nanofluid flow across vertical perforated plate

The current study investigates the effects of thermal radiation and Lorentz’s force on heat and mass flow in a nanofluid with a magnetic field and free convection, as it passes over a vertical permeable sheet. The dominant PDEs are turned into linked nonlinear ODEs using an appropriate similarity transformation. Using the MATLAB ODE45 tool, dimensionless ODEs are numerically computed using the finite difference procedure. Four different water-based nanofluids are considered, including copper, titanium dioxide, aluminum oxide, and silver. The influence of emerging dimensionless numbers and other parameters, such as the magnetic force parameter, the radiation parameter, the suction parameter, the Prandtl number, the Schmidt number, the Dufour number, as well as for constant values of the modified local Grashof number and local Grashof number on the concentration, velocity, and temperature profiles is emphasized and mentioned. Moreover, the visual representation of the effects of a volume percentage of up to 4% copper nanoparticles on the distributions of concentration, temperature, and velocity is also shown. The temperature profile, concentration profile, and velocity profile all grow with an increase in the volume percent of copper nanoparticles between 0.00 and 0.04. Furthermore, numerous scenarios are investigated for the distributions of the local Sherwood number, the local Nusselt number, and the local skin friction coefficient. The local Nusselt number decreases, and the local skin friction coefficient and Sherwood number increase about by 30 %, 45 %, and 60 % respectively due to increasing the value of volume fraction from 0 % to 4 %. The local skin friction coefficient increases and the local Nusselt number decreases by about 15 % and 39 % respectively for rising values of the thermal radiation number from 0.5 to 3.5. In addition, for magnetic force parameter values between 0.5 and 4.0, the local skin friction coefficient drops by about 13 %.

Computational analysis magnetohydrodynamics natural convection flow round vertical thermally stratified jet: Finite difference method in conjunction with primitive variable formulation

The problem of magnetohydrodynamic free convective heat transfer mechanism across a laminar, round, vertical, and thermally stratified jet is examined. The boundary layer equations are non-dimensionalized, and then, using the primitive variable formulation, the finite difference method is used to find the numerical solution of the problem. The impact of Prandtl number, magnetic parameter, and stratification parameter on velocity distribution, temperature profile, and heat transfer rate is explained graphically and in tabular form. It is found that for increasing values of thermal stratification parameter S, the velocity profile increases while temperature distribution and rate of heat transfer decrease. Similarly, with an increase in the values of Prandtl number, velocity, and temperature distribution decrease, but the rate of heat transfer increases.

Influence of heat flow due to concentration gradient on unsteady MHD heat and mass transform dissipative flow with spanwise fluctuating temperature

This study investigates the influence of heat flow due to a concentration gradient on unsteady Newtonian free convective magnetohydrodynamic heat and mass transform dissipative fluid flow over a heated normal porous plate in the presence of radiation absorption and chemical reaction. The plate temperature is assumed to fluctuate in a spanwise cosinusoidal manner over a time and exhibit heat generation with suction velocity. The analysis employs the multiple regular perturbation method to evaluate the governing equations under stipulated boundary conditions. The outcomes are visually depicted to assess the impact of various parameters on the system dynamics. Graphical representations illustrate the physical significance of various parameters on velocity, temperature, and concentration. Additionally, skin friction, mass transfer rate, and heat transfer coefficients are presented in tabular form. The significant findings indicate that velocity, temperature, and skin friction are directly proportional to parameters such as radiation absorption, heat generation, and heat flux due to a chemical potential gradient, whereas Sherwood and concentration are inversely proportional to the Schmidt number and chemical reaction. The outcomes obtained in this study have been cross-referenced with existing scientific literature, demonstrating strong concordance. This alignment provides confidence in the numerical results.

The Lattice Boltzmann Simulation of Free Convection Heat Transfer of a Carbon-Nanotube Nanofluid in a Triangular Cavity with a Solar Heater

In this paper, the flow and free convection heat transfer of a multi-walled carbon nanotube/water nanofluid in a triangular cavity with a solar heater is studied using the lattice Boltzmann method. The side walls of the cavity are cold and the bottom wall is partially heated by a solar heater, which have a non-uniform temperature distribution. It is assumed that the heating energy is provided by an absorber that is directly exposed to sunlight. Because of the limited variations of density, the Boussinesq approximation is used, which causes the coupling of hydrodynamic and thermal fields. For velocity and temperature distribution functions, a lattice Boltzmann model with two dimensions and nine directions is adopted. The effect of parameters, such as the Rayleigh number, the volume fraction of nanoparticles, and the position of solar heater, on the flow and heat fields is studied. The results show that, for all Rayleigh numbers studied, the Nusselt number increases as nanoparticles volume fraction increases. The addition of 4% nanoparticles causes the average Nusselt number to increase about 11% at low (Ra = 103) and moderate (Ra = 104) Rayleigh numbers and 217% at the high Rayleigh number (Ra = 105). Furthermore, it is shown that for a fixed Rayleigh number, heat transfer can be optimized by adjusting solar heater’s position. This study can provide a useful insight for utilizing solar heaters with non-uniform temperature distribution in triangular cavities.

Thermophysical properties of MWCNT-Alumina/water nanofluid and their influence on the performance of free convection heat transfer

Thermophysical properties of MWCNT-Alumina/water nanofluid and their influence on the performance of free convection heat transfer

Free convective heat transfer induced inside a vented duct having two aligned hot and cold cylinders: An experimental study

AbstractFree convective heat transfer created from two aligned cylinders immersed inside a vented air duct is experimentally investigated. The experiments include the measurements of cylinders temperature and the air temperature inside the enclosure under steady, turbulent, and incompressible flow properties by using steady‐state heat equations. The studied parameters include Rayleigh number (), opening sizes at lower and upper enclosure surfaces (), and space size between cylinders () with the constant ratio of enclosure width to cylinder diameter equal to 6. The findings displayed that the average air temperature inside the enclosure for the low values of S and O is low, and it rises as S is raised. The behaviors of Nu differ with changing Ra values. An interaction between hot cylinder and cold cylinder inside the enclosure is observed that depends on O and S values, and hence, they have a large impact on fluid temperature. The data indicated that rises with the for all and values. The value of for each cylinder depends on the values of and . The maximum value has been obtained when and with maximum enhancement between 30% and 50% depending on Ra values as compared with and , whereas the minimum average has been indicated when and . The profiles of reveal that , , and have a considerable influence on heat transfer.

Influence of porosity properties on natural convection heat transfer in porous square cavity

A numerical investigation was conducted to examine free convection heat transfer within a square cavity containing a fluid-saturated porous layer at the bottom under laminar flow conditions. The enclosure's left and right walls experienced heating and cooling, while the top and bottom walls remained adiabatic. The study explored the influence of the Darcy number, porosity number, and dimensionless thickness of the porous layer on heat transmission. This investigation utilized a FORTRAN computation program alongside the finite volume method, effectively solving the equations governing flow and heat exchange within porous materials through natural convection. The flow pattern is determined by the Navier–Stokes equations in the fluid region and the Darcy–Brinkman–Forchheimer formula in the porous region. The energy equation was employed to compute the thermal field. The increase in the Darcy number results in both an increase in heat transfer rate due to enhanced fluid flow through pores and an intensification of fluid flow patterns. Higher porosity leads to higher heat transfer rates due to greater fluid penetration and an increased surface area for heat exchange. The thicker porous layer reduces heat transfer rate due to increased resistance to fluid flow and decreased contact area.

Free-Convection Heat Transfer on Multirow Bundles of Finned Tubes with Circular Fins

Free-Convection Heat Transfer on Multirow Bundles of Finned Tubes with Circular Fins

Soret Effect on Magneto Hydrodynamic Free Convective Heat and Mass Transfer Effects Flow over an Inclined Plate Embedded in a Porous Medium

Soret Effect on Magneto Hydrodynamic Free Convective Heat and Mass Transfer Effects Flow over an Inclined Plate Embedded in a Porous Medium