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Effect of near-wall blockage on the magnetohydrodynamics-based double-diffusive convection in rectangular cavities

NUMERICAL HEAT TRANSFER PART A-APPLICATIONS 2025年第2期86卷 336-367页

作者： Kumar, Sudhanshu Gangawane, Krunal M. Oztop, Hakan F. Panda, Sibasish Natl Inst Technol Dept Chem Engn Rourkela India Indian Inst Technol Jodhpur Dept Chem Engn Jodhpur India Univ Sharjah Coll Engn Dept Mech & Nucl Engn Sharjah U Arab Emirates Firat Univ Technol Fac Dept Mech Engn Elazig Turkiye

This research work reports the numerical investigation of magnetohydrodynamics (MHD) characteristics around the near-wall blockage (NWB) for various separation distances owing to double-diffusive convection (DDC) in a rectangular cavity. The distance between the bottom wall of the cavity and the lower wall of blockage is called separation distance Sd, and it has varied from (H/4 <= Sd <= H/8), where H is the height of the cavity. The working fluid is considered as liquid metal - Sodium-Potassium alloy (Pr=0.054). The numerical computations are conducted by using an in-house developed lattice Boltzmann method (LBM) solver. The simulations are conducted for the steady-state, laminar, incompressible, and Newtonian fluid flow. The effect of NWB has been explored for a range of parameters, such as Rayleigh number (Ra=104 and 105), Lewis number (0.5 <= Le <= 1.5), buoyancy ratio (-1.5 <= N <= 1) and Hartmann number (0 <= Ha <= 300). The variation and contour plots show the higher heat and mass transfer (HMT) rates for Sd=H/4 at constant Ra. As Sd increases, HMT rates enhance. The increase in Ra, N, and Le induces multiple-cell formation inside the cavity for a given Sd. As Ha augments HMT rates get decreased monotonically. For Ha >= 150, negligible or slight variation was observed in the rate of HMT. As the obstruction between the bottom wall of the blockage and the adiabatic bottom wall of the cavity increases, shear force occurs, and the buoyancy-driven flow decreases. The outcomes of the numerical investigation are summarized in the form of empirical correlation of NuTotal for Ra = 104 and 105 at various separation distances, which might be utilized for probable design purposes.

关键词： double-diffusive convection lattice Boltzmann method magnetohydrodynamics near-wall blockage separation distance

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Three-dimensional simulations of double-diffusive convection of nanofluids and conjugate heat transfer in an n-shaped cavity with non-uniform boundary conditions using the multigrid method

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INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER 2025年 162卷

作者： Chou, Yen-De Hwang, Wei-Shien Solovchuk, Maxim Natl Taiwan Univ Dept Engn Sci & Ocean Engn 1Sec 4Roosevelt Rd Taipei 10617 Taiwan Natl Hlth Res Inst Inst Biomed Engn & Nanomed 35 Keyan Rd Miaoli Cty 35053 Taiwan

Nanofluids are a new type of fluid designed to enhance heat transfer. Brownian motion is one of the key mechanisms by which nanofluids enhance heat transfer. In engineering applications involving double-diffusive convection, the temperature and concentration distributions on the surfaces of objects are often non-uniform. The aim of this study is to develop a fast solver to investigate: (1) the effects of non-uniform heating, non-uniform concentration, and Brownian motion on the heat and mass transfer in nanofluids within a threedimensional n-shaped cavity, and (2) the effects of the composition and arrangement of multi-layer solids on the conjugate heat transfer. The results show that the multigrid method can accelerate the computations by a factor of 1000. Compared to uniform heating and uniform concentration, non-uniform heating and non-uniform concentration can enhance the heat transfer rate by 23.73% and the mass transfer rate by 28.04%. The heat transfer rate of the 5-layer solid is 6.91% higher than that of the 3-layer solid. This study provides important guidance for improving heat and mass transfer efficiency, with potential applications in cooling of electronic devices, solar collectors, and chemical reactors.

关键词： double-diffusive convection Conjugate heat transfer Nanofluid Brownian motion Non-uniform heating Multigrid method

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Modulation of the local mass and heat transfer of turbulent double-diffusive convection under stable thermal stratifications

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INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW 2025年 111卷

作者： Kenjeres, S. Roovers, R. Delft Univ Technol Fac Appl Sci Dept Chem Engn Transport Phenomena Sect Maasweg 9 NL-2629 HZ Delft Netherlands J M Burgerscentrum Res Sch Fluid Mech Mekelweg 2 NL-2628 CD Delft Netherlands

We report on numerical studies of bounded double-diffusive turbulent convection, which involves the combined effects of concentration/solutal and thermal buoyancy forces. Our study focuses on an intermediate range of the characteristic non-dimensional numbers, specifically 10(7) <= Ra-c <= 10(9), and 0 <= Ra-theta <= 10(6). We use fixed values for the concentration and temperature Prandtl numbers (i.e. Pr-c = 700, Pr-theta = 7), which approximately correspond to seawater properties. We apply wall-resolved Large Eddy Simulations (LES) and compare the obtained results with available Direct Numerical Simulations (DNS) in the literature. Our findings show an overall good agreement in predicting the global wall mass and heat transfer coefficients, achieved with significantly reduced computational costs. Furthermore, the local mass and heat transfer distributions reveal a high sensitivity to the strength of the vertically imposed stable thermal stratification. Finally, we present the vertical profiles of the long-term time-averaged first and second moments.

关键词： double-diffusive convection Turbulence Scalar transport LES Local mass and heat transfer Second-order moments

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Strengthened double-diffusive convection induced by the combined effect of tropical cyclones and a mesoscale eddy

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PROGRESS IN OCEANOGRAPHY 2025年 232卷

作者： Zhang, Yanwei Ruan, Weihan Lyu, Danni Yu, Jiancheng Tongji Univ State Key Lab Marine Geol Shanghai 200092 Peoples R China Chinese Acad Sci Shenyang Inst Automat Shenyang Peoples R China

double-diffusive convection (DDC) is a critical driving mechanism for diapycnal mixing in the ocean. However, there is limited quantitative investigation on the impacts of dynamic ocean-atmospheric processes, such as the interaction between tropical cyclones and mesoscale eddies, on DDC generation. In this study, we analyzed the cyclone-eddy induced DDC based on measurements obtained by an underwater glider in the northern South China Sea, where is frequently impacted by tropical cyclones and eddies. We observed abnormally increased salinity and a notable upwelling resulting from cyclone-eddy interaction. Our observations further reveal the coexistence of detached salt fingers (SF) and shear-driven turbulence. Strengthened salt finger dominates DDC with SF-driven salinity diapycnal diffusivity (10- 4 m2 s- 1) in the deepened halocline, which is an order of magnitude higher than background values. Shear-driven turbulence, characterized by large density overturns below 600 m, is generated due to enhanced geostrophic shear around the eddy. Further investigation indicates that SF thermohaline staircases evolve from lateral saline fronts driven by Ekman-pumping-induced upwelling and Kuroshio intrusion. The convective structure generates strong diapycnal mixing and vertical/lateral salinity fluxes that are urgently needed to be incorporated into estimations of ocean energy/material balance and ocean modeling.

关键词： double-diffusive convection Shear-driven turbulence Glider observations Cyclone-eddy interaction The South China Sea

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Regularity estimations of the 2D/3D unsteady incompressible Darcy-Brinkman equations with double-diffusive convection and their finite element analysis based on incremental pressure correction method

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COMMUNICATIONS IN NONLINEAR SCIENCE AND NUMERICAL SIMULATION 2025年 143卷

作者： Jiang, Linlin Liu, Demin Xinjiang Univ Coll Math & Syst Sci Urumqi 830046 Peoples R China

In this paper, the 2D/3D unsteady incompressible Darcy-Brinkman equations with double- diffusive convection are considered. Firstly, several a priori regularity estimates of the weak solutions are derived, and then two fully decoupled incremental pressure correction finite element methods (IPC FEMs) are proposed, i.e., the first-order and second-order standard IPC (SIPC) methods. Based on the above regularity results, the unconditional stability and optimal error estimates for the first-order SIPC method are proved, and then the unconditional stability for the second-order SIPC method is established. Some numerical experiments are carried out to illustrate the effectiveness of the proposed methods.

关键词： Darcy-Brinkman equations double-diffusive convection Regularity estimations Incremental pressure correction method Stability and convergence

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Exploration of Arrhenius activation energy and thermal radiation on MHD double-diffusive convection of ternary hybrid nanofluid flow over a vertical annulus with discrete heating

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CASE STUDIES IN THERMAL ENGINEERING 2025年 65卷

作者： Shilpa, B. Leela, V. Badruddin, Irfan Anjum Kamangar, Sarfaraz Ganesan, P. Khan, Abdul Azeem Dayananda Sagar Coll Engn Dept Math Bangalore 560078 Karnataka India PES Univ Dept Sci & Humanities Bangalore 560085 Karnataka India King Khalid Univ Coll Engn Mech Engn Dept Abha 61421 Saudi Arabia Univ Malaya Fac Engn Dept Mech Engn Kuala Lumpur 50603 Malaysia Univ Islam Sultan Sharif Ali Fac Islamic Technol Bandar Seri Begawan Brunei

The primary objective of this article is to examine the effect of discrete heating on MHD doublediffusive convection and thermal radiation of ternary hybrid nanofluid flow heat and mass transfer in a vertical cylindrical annulus along with Arrhenius activation energy and chemical reaction. In this study, the cavity inner wall has two distinct flush-mounted heat sources, while the outer wall is isothermally cooled at a lower temperature. The top and bottom walls are thermally insulated. The ensuing equations that govern the physical framework are solved using the implicit Crank-Nicholson finite difference technique. As the heater advances upward, the flow intensity decreases, leaving a part of the fluid static at the bottom of the cylinder. Because more heat induces high buoyant flow in the annulus, the absolute value of axial velocity and wall temperature rises as the length of the heat source rises. Enhancing the values of activation energy parameter drops the Arrhenius energy function, elevating the pace of the generative chemical process and hence the concentration. Increasing the thermal radiation parameter lowers the surface heat flux while enhancing the nanofluid temperature. The Brownian motion parameter corresponds to the random motion of nanoparticles in a fluid, and this irregular movement augments the collision of nanoparticles with fluid particles, causing the particle's kinetic energy which leads to thermal energy and hence increases temperature. Also, the heat and mass transfer characteristics are forecasted and analyzed by considering the Levenberg-Marquardt backpropagating artificial neural network technique.

关键词： double-diffusive convection Ternary hybrid nanofluid Thermal radiation Activation energy Vertical annulus Crank Nicholson finite difference method Artificial neural network model

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double-diffusive convection induced by selective absorption of radiation in a fluid overlying a porous layer

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MECCANICA 2013年第1期48卷 201-210页

作者： Olali, Princewill Baysa Univ Nottingham Sch Math Sci Nottingham NG7 2RD England

A linear instability analysis for the inception of double-diffusive convection with a concentration based internal heat source is presented. The system encompasses a layer of fluid which lies above a porous layer saturated with the same fluid. Detailed stability characteristics results are presented for key physical parameters including the solute Rayleigh number, depth ratio of the fluid to porous layer and strength of radiative heating.

关键词： double-diffusive convection Superposed porous-fluid convection Internal heat source

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double-diffusive convection from a Discrete Heat and Solute Source in a Vertical Porous Annulus

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TRANSPORT IN POROUS MEDIA 2012年第3期91卷 753-775页

作者： Sankar, M. Park, Youngyong Lopez, J. M. Do, Younghae Kyungpook Natl Univ Dept Math Taegu 702701 South Korea Arizona State Univ Sch Math & Stat Sci Tempe AZ 85287 USA

This article reports a numerical study of double-diffusive convection in a fluid-saturated vertical porous annulus subjected to discrete heat and mass fluxes from a portion of the inner wall. The outer wall is maintained at uniform temperature and concentration, while the top and bottom walls are adiabatic and impermeable to mass transfer. The physical model for the momentum equation is formulated using the Darcy law, and the resulting governing equations are solved using an implicit finite difference technique. The influence of physical and geometrical parameters on the streamlines, isotherms, isoconcentrations, average Nusselt and Sherwood numbers has been numerically investigated in detail. The location of heat and solute source has a profound influence on the flow pattern, heat and mass transfer rates in the porous annulus. For the segment located at the bottom portion of inner wall, the flow rate is found to be higher, whereas the heat and mass transfer rates are higher when the source is placed near the middle of the inner wall. Further, the average Sherwood number increases with Lewis number, while for the average Nusselt number the effect is opposite. The average Nusselt number increases with radius ratio (lambda);however, the average Sherwood number increases with radius ratio only up to lambda = 5, and for lambda > 5 , the average Sherwood number does not increase significantly.

关键词： double-diffusive convection Porous annulus Discrete heating and salting Radius ratio Darcy model

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double-diffusive convection with gravitationally unstable temperature and concentration gradients in homogeneous and heterogeneous porous media

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JOURNAL OF FLUID MECHANICS 2024年 999卷 A62-A62页

作者： Hu, Chenglong Yang, Yantao Peking Univ Coll Engn State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China Peking Univ Coll Engn Dept Mech & Engn Sci Beijing 100871 Peoples R China Laoshan Lab Qingdao 266299 Shandong Peoples R China

Geothermal gradients and heterogeneous permeability are commonly observed in natural geological formations for underground CO2 sequestration. In this study, we conduct three-dimensional direct numerical simulations on the double-diffusive convection with both unstable temperature and concentration gradients in homogeneous and heterogeneous porous media. For homogeneous porous media, the root-mean-squared velocity increases linearly with density ratio defined as the buoyancy ratio by temperature and concentration differences. The flow structures show no remarkable changes when temperature Rayleigh number R(aT )is less than its critical value, but alter from sheet-like to cellular structures as R-aT surpasses this threshold. The concentration wavenumber scales approximately as k(r)S similar to Ra(e)(0.47 )with a defined effective Rayleigh number Ra-e. By using a scale analysis, the concentration flux exhibits a consistent linear relation with the total driving forces for all simulations. For heterogeneous porous media, where the Dykstra-Parsons coefficient VDPVDP and correlation length l(r )determine the spatial distribution of the permeability field, the flow is strengthened in places with higher permeability. The velocity and concentration flux are less affected by l(r )than that by V-DP. For small correlation length, the flow structures coarsen and their characteristic width generally increases with increasing heterogeneity. For large correlation length, small structures emerge in the regions with large permeability, which can be attributed to the intensified local Rayleigh number triggering more vigorous convection there. The variations of concentration flux with lrlr and V-DP can be explained by the portion of area covered by high concentration with large vertical velocity near the boundaries.

关键词： convection in porous media double-diffusive convection turbulent convection

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double-diffusive convection in a micropolar ferromagnetic fluid

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APPLIED MATHEMATICS AND COMPUTATION 2007年第2期189卷 1648-1661页

作者： Sunil Chand, Prakash Kumar Bharti, Pavan Deemed Univ Natl Inst Technol Dept Appl Sci Hamirpur 177005 Himachal Prades India Jawahar Lal Nehru Govt Engn Coll Dept Appl Sci Sunder Nagar 174401 Himachal Prades India

This paper deals with the theoretical investigation of the double-diffusive convection in a micropolar ferromagnetic fluid layer heated and soluted from below subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained. A linear stability analysis theory and normal mode analysis method have been carried out to study the onset of convection. The influence of various parameters like solute gradient, non-buoyancy magnetization and micropolar parameters (i.e. coupling parameter, spin diffusion parameter and micropolar heat conduction parameter) has been analyzed on the onset of stationary convection. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of buoyancy magnetization parameter M, and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the micropolar ferromagnetic fluid heated from below in the absence of micropolar viscous effect, microinertia and solute gradient. The oscillatory modes are introduced due to the presence of the micropolar viscous effect, microinertia and solute gradient, which were non-existent in their absence. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability. (c) 2007 Elsevier Inc. All rights reserved.

关键词： double-diffusive convection micropolar ferromagnetic fluid solute gradient vertical magnetic field magnetization

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