Influence Of Convection Research Articles

Assisting and Opposing Stagnation Point Pseudoplastic Nano Liquid Flow towards a Flexible Riga Sheet: A Computational Approach

Nanofluids are used as coolants in heat transport devices like heat exchangers, radiators, and electronic cooling systems (like a flat plate) because of their improved thermal properties. The preeminent perspective of this study is to highlight the influence of combined convection on heat transfer and pseudoplastic non-Newtonian nanofluid flow towards an extendable Riga surface. Buongiorno model is incorporated in the present study to tackle a diverse range of Reynolds numbers and to analyze the behavior of the pseudoplastic nanofluid flow. Nanofluid features are scrutinized through Brownian motion and thermophoresis diffusion. By the use of the boundary layer principle, the compact form of flow equations is transformed into component forms. The modeled system is numerically simulated. The effects of various physical parameters on skin friction, mass transfer, and thermal energy are numerically computed. Fluctuations of velocity increased when modified Hartmann number and mixed convection parameter are boosted, where it collapses for Weissenberg number and width parameter. It can be revealed that the temperature curve gets down if modified Hartmann number, mixed convection, and buoyancy ratio parameters upgrade. Concentration patterns diminish when there is an incline in width parameter and Lewis number; on the other hand, it went upward for Brownian motion parameter, modified Hartmann, and Prandtl number.

Interferometric Imaging of Solvent Vapor of Evaporating Liquid Films.

The liquid deposition of thin films requires a thorough understanding of the underlying drying process, as it is an essential subprocess, where many defects may arise. To complement experimental studies, the present study uses a laser Michelson interferometer to visualize the vapor cloud of evaporating liquid films. The recorded interferometric patterns are evaluated using windowed Fourier filtering and a novel phase-unwrapping algorithm to allow for a robust analysis. Thin solvent stripes of different lengths are combined to yield a quantitative two-dimensional distribution of the solvent vapor concentration along a thin liquid stripe. The results show a considerable influence of natural convection during evaporation.

Numerical simulation of crystallization on a stationary and rotating cooled disk

The process of crystallization of silicon melt on a monotonically cooled disk located on the free surface of the melt is studied numerically. The influence of thermogravitational, thermal gravitational-capillary and mixed convection on the shape of the crystal-melt interface is investigated. In mixed convection modes, the speed of uniform rotation of the disk is set. The calculations were carried out in an axisymmetric formulation of problems by the finite element method using an adaptive triangular mesh and taking into account the latent heat.

Application of EHD combination and triangular blades to enhance the cooling rate of hot barriers

Cooling of fixed heat sources applying forced convection is one of the most significant issues in increasing heat transfer. In this study, the cooling method of cylindrical ribs was investigated under the influence of forced convection as well as electric field induction. Cylindrical barriers are mounted at the bottom of the channel with an optimal zigzag arrangement. Heat transfer methods are studied with a compound of EHD and turbulence generators in the ranges of Re = 500 to Re = 3500. In the active method, Corona wind is used to disturb mainstream patterns and direct them towards ribbons. In the passive method, by installing turbulence generators on the areas of interest between cylindrical barriers. Also, by crossing the forced mainstream through the channel, a pressure gradient emerged that raises the speed and torsion of the flow followed by an increased heat transfer rate. The results reveal that the secondary flow resulted from corona wind is more effective in lower Reynolds numbers. In the passive method, the rise of Reynolds number improved the effects of this method.

Entropy generation in convective radiative flow of a Casson nanofluid in non-Darcy porous medium with Hall current and activation energy: The multiple regression model

The present article’s primary goal is to analyze entropy generation on unsteady three dimensional thermally radiating magnetohydrodynamic flow of Casson nanofluid past a vertical stretching sheet embedded in a non-Darcy porous medium under the influence of mixed convection, Hall current, viscous dissipation, Ohmic heating, and heat generation. The combined effects of Brownian motion and thermophoretic diffusion are taken into consideration, and the impact of the chemical reaction initiated by activation energy is also incorporated in the flow-field. A mathematical model of the physical problem containing highly nonlinear coupled partial differential equations with convective boundary conditions is developed. Suitable similarity transformation is applied to convert the governing highly nonlinear coupled partial differential equations into nonlinear coupled ordinary differential equations, and then the resulting nonlinear coupled ordinary differential equations are numerically solved with the help of the spectral quasi-linearization method. A detailed investigation is performed to illustrate the impact of several pertinent flow parameters on the velocity, temperature, concentration, entropy generation and Bejan number profiles. In contrast, the numerical values of skin friction coefficients in x and z directions, local Nusselt number, and local Sherwood number are presented in tabular forms for varying values of pertinent flow parameters. Apart from this, linear and quadratic multiple regression analyses for the physical quantities of engineering interest have been executed to upgrade the present model’s efficiency and application in various industrial and engineering processes. With a variation in magnetic parameter, the maximum relative errors in the linear regression estimates for the skin- friction coefficients in x and z directions are found to be 2.28–2.37% and 0.85–1.72%, respectively. Besides, due to the enhancement in magnetic parameter, the maximum relative errors in the quadratic regression estimations for the reduced Nusselt number NuxRex−1/2 and the reduced Sherwood number ShxRex−1/2 are 0.56%−0.58% and 0.30%, respectively. It is observed that the error of each solution of the present physical problem approaches to be less than 10−8 in mere six iterations. Moreover, the findings of the current research work signify that the Brownian motion and thermophoretic diffusion minimize entropy generation adjacent to the sheet; on the contrary, activation energy intensifies entropy generation rate closer to the sheet. Furthermore, the appropriate resemblance is obtained through verifying the present results with previous existing results.

Scanning Thermal Microscopy of Ultrathin Films: Numerical Studies Regarding Cantilever Displacement, Thermal Contact Areas, Heat Fluxes, and Heat Distribution.

New micro- and nanoscale devices require electrically isolating materials with specific thermal properties. One option to characterize these thermal properties is the atomic force microscopy (AFM)-based scanning thermal microscopy (SThM) technique. It enables qualitative mapping of local thermal conductivities of ultrathin films. To fully understand and correctly interpret the results of practical SThM measurements, it is essential to have detailed knowledge about the heat transfer process between the probe and the sample. However, little can be found in the literature so far. Therefore, this work focuses on theoretical SThM studies of ultrathin films with anisotropic thermal properties such as hexagonal boron nitride (h-BN) and compares the results with a bulk silicon (Si) sample. Energy fluxes from the probe to the sample between 0.6 µW and 126.8 µW are found for different cases with a tip radius of approximately 300 nm. A present thermal interface resistance (TIR) between bulk Si and ultrathin h-BN on top can fully suppress a further heat penetration. The time until heat propagation within the sample is stationary is found to be below 1 µs, which may justify higher tip velocities in practical SThM investigations of up to 20 µms−1. It is also demonstrated that there is almost no influence of convection and radiation, whereas a possible TIR between probe and sample must be considered.

Entropy generation and dissipative heat transfer analysis of mixed convective hydromagnetic flow of a Casson nanofluid with thermal radiation and Hall current

The present article provides a detailed analysis of entropy generation on the unsteady three-dimensional incompressible and electrically conducting magnetohydrodynamic flow of a Casson nanofluid under the influence of mixed convection, radiation, viscous dissipation, Brownian motion, Ohmic heating, thermophoresis and heat generation. At first, similarity transformation is used to transform the governing nonlinear coupled partial differential equations into nonlinear coupled ordinary differential equations, and then the resulting highly nonlinear coupled ordinary differential equations are numerically solved by the utilization of spectral quasi-linearization method. Moreover, the effects of pertinent flow parameters on velocity distribution, temperature distribution, concentration distribution, entropy generation and Bejan number are depicted prominently through various graphs and tables. It can be analyzed from the graphs that the Casson parameter acts as an assisting parameter towards the temperature distribution in the absence of viscous and Joule dissipations, while it has an adverse effect on temperature under the impacts of viscous and Joule dissipations. On the contrary, entropy generation increases significantly for larger Brinkman number, diffusive variable and concentration ratio parameter, whereas the reverse effects of these parameters on Bejan number are examined. Apart from this, the numerical values of some physical quantities such as skin friction coefficients in x and z directions, local Nusselt number and Sherwood number for the variation of the values of pertinent parameters are displayed in tabular forms. A quadratic multiple regression analysis for these physical quantities has also been carried out to improve the present model’s effectiveness in various industrial and engineering areas. Furthermore, an appropriate agreement is obtained on comparing the present results with previously published results.

Thermal and concentration convection in nanofluids for peristaltic flow of magneto couple stress fluid in a nonuniform channel

This article addresses the influence of double-diffusivity convection in nanofluids in relation to peristaltic flow of magneto couple stress fluid in a nonuniform channel. Firstly, mathematical formulations of magneto couple stress fluid in the presence of double-diffusivity convection in nanofluids for 2-dimensional and 2-directional flows are described in detail. The highly nonlinear equations are simplified using approximation of long wavelength and low but finite Reynolds number. Exact solutions of stream function, axial induced magnetic field, axial pressure gradient, nanoparticle volume fraction temperature and concentration are computed. Graphical representations of numerous physical parameters of interest are presented to explain the conduct of flow quantities. It is observed from graphical plots that temperature profile and solutal concentration increases by increasing values of thermophoresis, Brownian motion, Soret and Dufour parameters.

The combined effect of natural and thermocapillary convection on the melting of phase change materials in rectangular containers

The results of numerical simulations investigating the influence of natural and thermocapillary convection on the solid/liquid phase transition of n-octadecane in rectangular containers are presented. The melting process is modelled using an enthalpy-porosity formulation of the Navier–Stokes equations. A systematic analysis is performed by varying key dimensionless parameters including the container aspect ratio (Γ), the Rayleigh (Ra) and Marangoni (Ma) numbers, which quantify the strength of natural and thermocapillary convection, and the dynamic Bond number (Bodyn), which measures their relative importance. In large containers with Γ≫1 and Bodyn≪1, thermocapillary convection is shown to significantly accelerate the melting process, enhancing the heat transfer rate of the system by as much as a factor of 20 at large applied Ma. For Γ≲8, this enhancement factor takes reduced values of 1–3 and exhibits relatively weak dependence on Ma. In short containers with Γ≲3 and Bodyn∼O(1), the thermocapillary effect is detrimental on average and increases the total melting time. The presence of normal vertical gravity is seen to stabilise the dynamics of the flow, delaying the appearance of oscillatory convection beyond the range of parameters considered here. By reducing Bodyn, we examine the transition to microgravity and determine the critical value Bodyncr for oscillatory flow at large Ma for the representative aspect ratios 1.5 and 12.

Numerical Study on Heating Process of High Viscosity Crude Oil in Oil Tank of Sunken Ship

This article assumes that the crude oil in the oil tank of the sunken ship is completely solidified, has high viscosity, and loses fluidity before heating. Based on ANSYS software, a three-dimensional numerical model of the sunken oil tank was constructed, and the numerical study of the heating process of high-viscosity crude oil in the sunken oil tank was carried out. According to the theory of heat transfer, the changes in the solid-liquid interface and the flow characteristics of the oil during the heating process of high-viscosity crude oil are analyzed to obtain the heat transfer characteristics during the heating process. Studies have shown that the heat transfer method at the initial stage of heating is mainly heat conduction, as the highly viscous crude oil continues to melt, the influence of natural convection gradually strengthens. This research can provide relevant theoretical basis for the underwater oil pumping work of salvaging sunken ships.

Моделювання динаміки інфекційного захворювання з урахуванням просторово-дифузійних збурень, зосереджених впливів та кривизни середовища

While the study of the interaction patterns of the immune system and the viruses detected in the body wide variety of models is used. Well-known infectious disease model by Marchuk which describes the most common mechanisms of immune defense, was obtained under the assumption that the environment of the "organism" is homogeneous and unlimited, in which all the active factors of the process are instantly mixed. The approach proposed by the authors to take into account the influence of spatially distributed diffusion "redistributions" on the nature of the infectious disease provides an opportunity to detect the reducing effect the model level of maximum antigen concentration at the infection epicenter due to their diffusion "erosion" in the disease development. In particular, in cases where the viral particles concentration at the initial time or the intensity of a concentrated source of viruses in any part of the body of infection exceeds a certain critical level of the immunological barrier such an effect of diffusion "redistribution" in a short time reduces supercritical concentrations of viral particles to values, in particular, already below the critical level and their further neutralization may be ensured by the existing level of own antibodies concentration or requires a more economical procedure of injection with a lower donor antibodies concentration. In this article the infectious disease mathematical model is generalized to take into account the curvature of the bounded environment in the conditions of spatial diffusion perturbations, convection and the presence of various concentrated influences. The corresponding singularly perturbed model problem with delay is reduced to a sequence of "solvable" problems without delay. The influence of "curvature" of a limited environment on the development of an infectious disease in the conditions of diffusion perturbations, convection and concentrated influences is illustrated.

Modelling for Control of Biodiesel Microreactors

Abstract The modelling of biodiesel production through transesterification in chemical reactors has largely been studied, but the control of this process in microreactors is not straightforward without a suitable process model. In this paper, a useful mathematical model for control is proposed. The model suitably represents the dynamics of biodiesel properties in a microreactor. By analysing the physical influences of convection, diffusion and chemical kinetics on biodiesel yield, an explicit relationship between feed flows and mixing ratios with biodiesel output concentration is captured for control. The model responses are analysed and compared against a variety of experimental results in existing literature at similar operating conditions. The proposed model shows appropriate responses and opens the possibilities of more accurate model-based control applications such as Model Predictive Control and Internal Model Control.

Heat transfer and its effect on growth behaviors of crystal layers during static layer melt crystallization

The growth behaviors of crystal layers during static layer melt crystallization was studied from the perspectives of morphology structure, growth rates and temperature evolution. The temperature distributions of the melt and crystal layer were deduced. With these results, the heat transfer during crystallization was analyzed by considering the relative influences of natural convection, heat conduction in the melt and latent heat of crystallization. A model correlating growth rate with physical and experimental parameters was derived based on energy conservation. Effective thermal conductivity of crystal layers was evaluated. It was confirmed that the structure and density of the crystal layer can significantly affect the thermal conductivity. According to the temperature curves of melt, the static layer melt crystallization process in a tubular crystallizer can be divided into four stages as nucleation stage, fast growth stage, slow growth stage and steady state stage.

Thermosolutal Marangoni Impact on Bioconvection in Suspension of Gyrotactic Microorganisms Over an Inclined Stretching Sheet

Abstract Microorganism cells movement in the fluid is universal and affects many ecological and biological processes, including infection, reproduction, and marine life ecosystem. There are many biological and medical applications that require an understanding of the transport process in nanofluids containing a suspension of microorganism. The present problem deals with the bioconvection of Casson nanofluid containing a suspension of motile gyrotactic microorganisms over an inclined stretching sheet in the presence of thermal radiation, viscous dissipation, and chemical reaction and magnetic field. At the surface, the influence of the thermosolutal Marangoni convection and suction/injection impact are considered. The governing equations are solved numerically by using fourth-order Runge–Kutta–Fehlberg method with shooting technique. The impact of the major pertinent parameters on the velocity, temperature, nanoparticles concentration, and density of the motile microorganism is illustrated graphically. Finally, the correlations of various crucial parameters on skin friction, local Nusselt number, Sherwood number, and local motile microorganism density number are displayed through the graphs and tables.

Nonlinear convection flow of dissipative Casson nanofluid through an inclined annular microchannel with a porous medium

AbstractThe nonlinear convection study on the flow of a dissipative Casson nanofluid through a porous medium of an inclined micro‐annular channel is presented. The cylindrical surfaces were conditioned to temperature increase and velocity slip effects. A uniform magnetic field strength was applied perpendicular to the cylinder surface. The heat source and Darcy number influence are explored in the examination of the blood rheological model (Casson) through the annular cylinder. Appropriate dimensionless variables are imposed on the dimensional equations encompassing Casson nanofluid rheology through an annular microchannel. The resulting systems of equations were solved and computed numerically via Chebyshev‐based collocation approach. Thus, the solutions of flow distributions, volumetric flow rate, and other flow characteristics were obtained. The result shows that both nonlinear convection parameters decrease the nanoparticle volume fraction, whereas they increase the energy and momentum distributions. Moreover, the volumetric flow rate is upsurged significantly by a wider porous medium, annular gap, a higher Casson parameter, and nonlinear convection influence.

Heat Transfer From Convecting Magma Reservoirs to Hydrothermal Fluid Flow Systems Constrained by Coupled Numerical Modeling

AbstractMagma flow, heat conduction, and hydrothermal fluid flow control the heat transfer through the upper crust. Magmatic‐hydrothermal activity is essential for the utilization of geothermal energy, formation of ore deposits, and predictions of volcanic hazards, but the interplay between magmatic and hydrothermal processes is not well constrained due to the lack of adequate scientific tools. Simulation results from our novel coupled numerical model resolving both magma (Navier‐Stokes) and hydrothermal (Darcy) flow quantify the influence of magma convection and rock permeability on energy transfer. Convection of a hot‐dry rhyolitic magma has an accelerating effect of up to 15% on the cooling of the reservoir by enhancing the heat transfer toward the magma‐hydrothermal interface. However, at high permeabilities and high brittle‐ductile transition temperatures, magma flow can also have a secondary decelerating effect, because it prevents efficient permeability creation and entrainment of hydrothermal fluids at the edges of the magma reservoir.

The effect of convection on the position of the free liquid surface under zero and terrestrial gravity

Theresults of numerical modelinghas based on the solution of Navier-Stokes equations for convection oftwo-layer system air-water are presented.The influence of thermo-capillary and gravitational convection on the deformation and time averaged position of the interface of air-water system under sudden lateral heating of a square-section cavity are shown.

Non-contact heat transfer models identification: Laser hyperthermia of superficial human tissues

Planning and predicting the processes of biological tissues heating associated with therapeutic effects involves high-precision mathematical modelling. However, the thermophysical properties of tissues can vary greatly from patient to patient. The paper presents a computational and experimental method for identifying mathematical models of heat transfer, not involving the placement of temperature sensors inside of the studied object. The experimental setup consists of a flat sample of the material, a laser setup, and a thermal imaging camera. The surface thermal response to the pulsed heat flux of the laser is an array of input data for the developed software package. The heat transfer coefficient and heat flux density are determined iteratively by minimizing the residual functional between the calculated and experimental values. The method was tested when determining the characteristics of a specimen of low-pressure polyethylene. The result was obtained in 5 iterations and under the influence of external natural convection, and without taking into account the translucency of the material, a discrepancy of calculated and experimental values of 3.5% was shown. The method can be used to plan the therapeutic process in order to ensure its maximum effectiveness.

Modeling of Liquid Magnesium Turbulent Convection in a Titanium Reduction Apparatus Using the RANS and LES Approaches

Abstract—This study focuses on turbulent convection of molten magnesium in a titanium reduction reactor. The reactor retort is a cylindrical vessel with a radius of 0.75 m and a height of 4 m, which contains liquid magnesium at a temperature of 850°C. During a process that lasts for more than 2 days, significant temperature gradients occur in the reduction apparatus due to an exothermic chemical reaction on the metal surface and simultaneous cooling of the side wall of the retort and heating of its bottom. Temperature gradients cause convective flows inside the reactor, which in turn significantly affect the formation of the titanium block. The mathematical model of convective flows in the reactor is based on the equations of thermogravitational convection for a single-phase medium in the Boussinesq approximation. We consider the possibility of modeling turbulent convective flows in a titanium reduction reactor using RANS (Reynolds-averaged Navier–Stokes equations) k–e and k–ω SST (Shear Stress Transport) models. The results of simulations performed with the k–ω SST model on relatively coarse grids (0.825 million finite volumes) are shown to qualitatively and quantitatively agree with the results of LES simulations on fine grids (3.7 million finite volumes). However, the k–e model does not always produce acceptable results. RANS simulations produce average velocity and temperature fields with averaging times much longer than those possible in LES simulations. Several different configurations of heating and cooling of the apparatus were examined, including those that were previously unstudied. It has been found that using the k–ω SST model allows simulation of flow dynamics taking into account changes in the heating and cooling conditions of the apparatus during the entire process and identification of single- and double-vortex large-scale flows in the retort, as well as the transition between them, so the degree of convection influence on the reaction can be assessed.

İZOTROPİK SAÇILMA ORTAMLI KARE GEOMETRİ İÇİNDE TÜRBÜLANSLI DOĞAL TAŞINIM VE IŞINIM ISI TRANSFERİ

The influence of turbulent natural convection and thermal radiation in a differentially heated square enclosure is numerically investigated. The enclosure is heated from the right wall and cooled from the left wall. The other walls are assumed to be adiabatic. The Reynolds Averaged Navier Stokes (RANS) formulation was employed for analyzing turbulent flows together with a Realizable k– model. In addition, the discrete ordinates method (DOM) was used to solve the radiative transfer equation (RTE). Influence of Rayleigh number (Ra), optical thickness (), Planck number (Pl), scattering albedo () and wall emissivity ( ) parameters were studied numerically on square enclosure for the flow and temperature distribution. It is interesting to note that a detailed parametric study focusing on characterizing parameters in turbulent natural convection and radiation was rarely dealt with in details. Solutions were obtained for a range of Rayleigh numbers varying from 109 to 1012. It was found that the radiation heat transfer alters the characteristics of flow fields in the enclosure. Increasing the optical thickness results in a decrease in combined heat transfer for a fixed Rayleigh number and the maximum of heat transfer occurred for low optical thickness with radiation presence. =87.796 and 82.351 is obtained for =0.2 and 5, respectively (Ra=1010, Pl=0.02 and =0). The heat transfer increases with decreasing Planck number, and decreases with the increasing scattering albedo. =445.837 and 68.100 is obtained for Pl=0.001 and 10, respectively (Ra=1010, =1 and =0). When the active walls are black and the insulated walls are reflected, =85.507 is obtained for Ra=1010, Pl=0.02, =1 and =0.