Y. Guo, R. Bennacer, S. Shen, D.E. Ameziani and M. Bouzidi
The purpose of this paper is to apply the lattice Boltzmann method (LBM) to simulate mixed flow, which combines natural convection for temperature difference and forced convection…
Abstract
Purpose
The purpose of this paper is to apply the lattice Boltzmann method (LBM) to simulate mixed flow, which combines natural convection for temperature difference and forced convection for lid driven, in a two‐dimensional rectangular cavity over a wide range of aspect ratios (A), Rayleigh numbers (Ra) and Reynolds numbers (Re).
Design/methodology/approach
The LBM is applied to simulate the mixed flow. A multi‐relaxation technique was used successfully. A scale order analysis helped the understanding and predicting the overall heat transfer.
Findings
In the considered lid driven cavity, the Richardson number emerges as a measure of relative importance of natural and forced convection modes on the heat transfer. An expression of the overall heat transfer depending on the cavity slender (A) is deduced. The validity of the obtained expression was checked in mixed convection under the condition of low Richardson number (Ri) and the limitation condition was deduced.
Practical implications
This paper has implications for cooling system optimization and LBM technique development.
Originality/value
This paper presents a new cooling configuration, avoiding critical situation where the opposing effect induce weak heat transfer; and a stable and fast LBM approach allowing complex geometry treatment.
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Damodara Priyanka, Pratibha Biswal and Tanmay Basak
This study aims to elucidate the role of curved walls in the presence of identical mass of porous bed with identical heating at a wall for two heating objectives: enhancement of…
Abstract
Purpose
This study aims to elucidate the role of curved walls in the presence of identical mass of porous bed with identical heating at a wall for two heating objectives: enhancement of heat transfer to fluid saturated porous beds and reduction of entropy production for thermal and flow irreversibilities.
Design/methodology/approach
Two heating configurations have been proposed: Case 1: isothermal heating at bottom straight wall with cold side curved walls and Case 2: isothermal heating at left straight wall with cold horizontal curved walls. Galerkin finite element method is used to obtain the streamfunctions and heatfunctions associated with local entropy generation terms.
Findings
The flow and thermal maps show significant variation from Case 1 to Case 2 arrangements. Case 1 configuration may be the optimal strategy as it offers larger heat transfer rates at larger values of Darcy number, Dam. However, Case 2 may be the optimal strategy as it provides moderate heat transfer rates involving savings on entropy production at larger values of Dam. On the other hand, at lower values of Dam (Dam ≤ 10−3), Case 1 or 2 exhibits almost similar heat transfer rates, while Case 1 is preferred for savings of entropy production.
Originality/value
The concave wall is found to be effective to enhance heat transfer rates to promote convection, while convex wall exhibits reduction of entropy production rate. Comparison between Case 1 and Case 2 heating strategies enlightens efficient heating strategies involving concave or convex walls for various values of Dam.
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Souad Morsli, Mustapha Boussoufi, Amina Sabeur, Mohammed El Ganaoui and Rachid Bennacer
The use of natural ventilation by large openings to maintain thermal comfort conditions in the premises is a concept that is perfectly integrated into the traditional architecture…
Abstract
Purpose
The use of natural ventilation by large openings to maintain thermal comfort conditions in the premises is a concept that is perfectly integrated into the traditional architecture of countries in the Mediterranean region or in tropical climates. In a temperate climate where the architecture is not usually designed to respond to the use of natural ventilation is seasonal and is done at the initiative of the occupants by making changes in the design of their doors. The European interest in natural ventilation, as a passive building air-conditioning technology, is increasing and has been the subject of a research program commissioned by the European Community. In this work, the authors consider a part of a housing compound as a refreshing floor. This floor is maintained at a constant cold temperature, the one vertical wall at hot temperature and other surfaces are adiabatic. Various scenarios are considered for this work. Mixed convection for different boundary conditions and different configurations is carried out. In addition, an airflow is injected through a window and extracted on the opposite window. Classical conclusion and transitional value on Richardson number have been completed by the new thermal configuration with nonsymmetric thermal conditions. The complex 3D flow structure is more obvious when one of the two flows (ventilation or natural convection) dominates. However, the induced heat transfer is less sensitive to the added ventilation. In this study, the authors consider a part of a housing compound as a refreshing floor. This floor is maintained at a constant cold temperature, the one vertical wall at hot temperature and other surfaces are adiabatic.
Design/methodology/approach
This is a qualitative preliminary study of a 2D–3D flow. The authors examine the competition between the natural convective flow and the added airflow on the flow structure and indoor air quality. The numerical model shows a good agreement with that obtained by researchers analytically and experimentally. To deal with turbulence, the RNG k-ε model has been adopted in this study.
Findings
The transfer is more sensitive between the 2D and 3D cases for the present analyzed case.
Originality/value
The study of ventilation efficiency has shown the competition between the big and small structures and the induced discomfort.
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Mubbashar Nazeer, N. Ali and T. Javed
The main purpose of this study is to examine the effects of moving wall on the mixed convection flow and heat transfer in a right-angle triangular cavity filled with a micropolar…
Abstract
Purpose
The main purpose of this study is to examine the effects of moving wall on the mixed convection flow and heat transfer in a right-angle triangular cavity filled with a micropolar fluid.
Design/methodology/approach
It is assumed that the bottom wall is uniformly heated and the right inclined wall is cold, whereas the vertical wall is adiabatic and moving with upward/downward velocity v0/−v0, respectively. The micropolar fluid is considered to satisfy the Boussinesq approximation. The governing equations and boundary conditions are solved using the Galerkin finite element method. The Penalty method is used to eliminate the pressure term from the momentum equations. To accomplish the consistent solution, the value of the penalty parameter is taken 107. The simulations are performed for a wide range of Richardson number, micropolar parameter, Prandtl number and Reynolds number.
Findings
The results are presented in the form of streamlines, isotherms and variations of average Nusselt number and fluid flow rate depending on the Richardson number, Prandtl number, micropolar parameter and direction of the moving wall. The flow field and temperature distribution in the cavity are affected by these parameters. An average Nusselt number into the cavity in both cases increase with increasing Prandtl and Richardson numbers and decreases with increasing micropolar parameter, and it has a maximum value when the lid is moving in the downward direction for all the physical parameters.
Research limitations/implications
The present investigation is conducted for the steady, two-dimensional mixed convective flow in a right-angle triangular cavity filled with micropolar fluid. An extension of the present study with the effects of cavity inclination, square cavity, rectangular, trapezoidal and wavy cavity will be the interest of future work.
Originality/value
This work studies the effects of moving wall, micropolar parameter, Richardson number, Prandtl number and Reynolds number parameter in a right-angle triangular cavity filled with a micropolar fluid on the fluid flow and heat transfer. This study might be useful to flows of biological fluids in thin vessels, polymeric suspensions, liquid crystals, slurries, colloidal suspensions, exotic lubricants, solar engineering for construction of triangular solar collector, construction of thermal insulation structure and geophysical fluid mechanics, etc.
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This paper aims to investigate spontaneous movement of single droplet on chemically heterogeneous surfaces induced by the net surface tension, using the improved three-dimensional…
Abstract
Purpose
This paper aims to investigate spontaneous movement of single droplet on chemically heterogeneous surfaces induced by the net surface tension, using the improved three-dimensional (3D) lattice Boltzmann (LB) method.
Design/methodology/approach
D3Q19 Shan-Chen LB model is improved in this paper. Segmented particle distribution functions coupled with the P-R equation of state are introduced to maintain the higher accuracy and greater stability. In addition, exact difference method (EDM) is adopted to implement force term to predict the droplet deformation and dynamics.
Findings
The numerical results demonstrate that spontaneous movement of single droplet (=1.8 µm) along wedge-shaped tracks is driven by net surface tension. Advancing angle decreases instantaneously with time, while receding angle changes slightly first and then decreases rapidly. Wetting length is affected by vertex angle and wetting difference, whereas the final value is only dependent on the stronger wettability. Although the velocity of single droplet on wedge-shaped tracks can be increased by the larger vertex angle, it has a negative influence on the displacement. For the same wetting difference, vertex angle equal to 30º is an optimization strategy in this model. If the simulation length is extended enough, then the smaller vertex angle is beneficial for the droplet movement. In addition, a larger wetting difference is beneficial to spontaneous movement, which can speed up the droplet movement.
Originality/value
The proposed numerical model of droplet dynamics on chemically heterogeneous surfaces provides fundamental insights for the enhancement of drop-wise condensation heat transfer.
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Alireza Rahimi, Abbas Kasaeipoor, Emad Hasani Malekshah and Lioua Kolsi
This paper aims to perform the lattice Boltzmann simulation of natural convection heat transfer in cavities included with active hot and cold walls at the side walls and internal…
Abstract
Purpose
This paper aims to perform the lattice Boltzmann simulation of natural convection heat transfer in cavities included with active hot and cold walls at the side walls and internal hot and cold obstacles.
Design/methodology/approach
The cavity is filled with double wall carbon nanotubes (DWCNTs)-water nanofluid. Different approaches such as local and total entropy generation, local and average Nusselt number and heatline visualization are used to analyze the natural convection heat transfer. The cavity is filled with DWCNTs-water nanofluid and the thermal conductivity and dynamic viscosity are measured experimentally at different solid volume fractions of 0.01 per cent, 0.02 per cent, 0.05 per cent, 0.1 per cent, 0.2 per cent and 0.5 per cent and at a temperature range of 300 to 340 (K).
Findings
Two sets of correlations for these parameters based on temperature and solid volume fraction are developed and used in the numerical simulations. The influences of different governing parameters such as Rayleigh number, solid volume fraction and different arrangements of active walls on the fluid flow, heat transfer and entropy generation are presented, comprehensively. It is found that the different arrangements of active walls have pronounced influence on the flow structure and heat transfer performance. Furthermore, the Nusselt number has direct relationship with Rayleigh number and solid volume fraction. On the other hand, the total entropy generation has direct and reverse relationship with Rayleigh number and solid volume fraction, respectively.
Originality/value
The originality of this work is to analyze the two-dimensional natural convection using lattice Boltzmann method and different approaches such as entropy generation and heatline visualization.
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Ahad Zarghami, Stefano Ubertini and Sauro Succi
The main purpose of this paper is to develop a novel thermal lattice Boltzmann method (LBM) based on finite volume (FV) formulation. Validation of the suggested formulation is…
Abstract
Purpose
The main purpose of this paper is to develop a novel thermal lattice Boltzmann method (LBM) based on finite volume (FV) formulation. Validation of the suggested formulation is performed by simulating plane Poiseuille, backward-facing step and flow over circular cylinder.
Design/methodology/approach
For this purpose, a cell-centered scheme is used to discretize the convection operator and the double distribution function model is applied to describe the temperature field. To enhance stability, weighting factors are defined as flux correctors on a D2Q9 lattice.
Findings
The introduction of pressure-temperature-dependent flux-control coefficients in the streaming operator, in conjunction with suitable boundary conditions, is shown to result in enhanced numerical stability of the scheme. In all cases, excellent agreement with the existing literature is found and shows that the presented method is a promising scheme in simulating thermo-hydrodynamic phenomena.
Originality/value
A stable and accurate FV formulation of the thermal DDF-LBM is presented.
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Nan Xie, Yihai He, Ming Yao and Changwei Jiang
The purpose of this paper is to apply the lattice Boltzmann method (LBM) with multiple distribution functions model, to simulate transient natural convection of air in a…
Abstract
Purpose
The purpose of this paper is to apply the lattice Boltzmann method (LBM) with multiple distribution functions model, to simulate transient natural convection of air in a two-dimensional square cavity in the presence of a magnetic quadrupole field, under non-gravitational as well as gravitational conditions.
Design/methodology/approach
The density-temperature double distribution functions and D2Q9 model of LBM for the momentum and temperature equations are currently employed. Detailed transient structures of the flow and isotherms at unsteady state are obtained and compared for a range of magnetic force numbers from 1 to 100. Characteristics of the natural convection at initial moment, quasi-steady state and steady state are presented in present work.
Findings
At initial time, effects of the magnetic field and gravity are both relatively limited, but the effects become efficient as time evolves. Bi-cellular flow structures are obtained under non-gravitational condition, while the flow presents a single vortex structure at first under gravitational condition, and then emerges a bi-cellular structure with the increase of magnetic field force number. The average Nusselt number generally increases with the augment of magnetic field intensity.
Practical implications
This paper will be useful in the researches on crystal material and protein growth, oxygen concentration sensor, enhancement or suppression of the heat transfer in micro-electronics and micro-processing technology, etc.
Originality/value
The current study extended the application of LBM on the transient natural convective problem of paramagnetic fluids in the presence of an inhomogeneous magnetic field.
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The purpose of this paper is to determine the overall free convective heat transfer coefficient for an assembly constituted by a Quad Flat Non-lead QFN16 welded on a Printed…
Abstract
Purpose
The purpose of this paper is to determine the overall free convective heat transfer coefficient for an assembly constituted by a Quad Flat Non-lead QFN16 welded on a Printed Circuit Board (PCB) which may be inclined with respect to the horizontal plane by an angle varying between 0° and 90° corresponding to the horizontal and vertical position, respectively. This electronic device widely used in electronics generates during its effective operation a power ranging from 0.1 to 0.8 W. The assembly is installed in an air-filled cavity.
Design/methodology/approach
Calculations are done by means of the finite volume method for many configurations obtained by varying the generated power, the inclination angle and the position of the QFN16 on the PCB. The dynamic and thermal aspects are presented and commented.
Findings
The study shows that the thermal state of the electronic device is influenced by the previous three physical parameters. A correlation between the global convective exchange coefficient, the generated power and the PCB inclination angle is proposed in this survey.
Practical implications
The results of this survey allow a better thermal control of this conventional arrangement widely used in electronic applications.
Originality/value
The correlations proposed in this work are original and unpublished. The considered power varies between 0.1 and 0.8W corresponding to the effective operation of the device, associated to a PCB inclination angle ranging between 0° and 90°.
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The purpose of this paper is to analyze the thermal and fluid dynamic behaviors of mixed convection in air because of the interaction between a buoyancy flow and a moving plate…
Abstract
Purpose
The purpose of this paper is to analyze the thermal and fluid dynamic behaviors of mixed convection in air because of the interaction between a buoyancy flow and a moving plate induced flow in a horizontal no parallel-plates channel to investigate the effects of the minimum channel spacing, wall heat flux, moving plate velocity and converging angle.
Design/methodology/approach
The horizontal channel is made up of an upper inclined plate heated at uniform wall heat flux and a lower adiabatic moving surface (belt). The belt moves from the minimum channel spacing section to the maximum channel spacing section at a constant velocity so that its effect interferes with the buoyancy effect. The numerical analysis is accomplished by means of the finite volume method, using the commercial code Fluent.
Findings
Results in terms of heated upper plate and moving lower plate temperatures and stream function fields are presented. The paper underlines the thermal and fluid dynamic differences when natural convection or mixed convection takes place, varying minimum channel spacing, wall heat flux, moving plate velocity and converging angle.
Research limitations/implications
The hypotheses on which the present analysis is based are two-dimensional, laminar and steady state flow and constant thermo physical properties with the Boussinesq approximation. The minimum distance between the upper heated plate of the channel and its lower adiabatic moving plate is 10 and 20 mm. The moving plate velocity varies in the range 0-1 m/s; the belt moves from the right reservoir to the left one. Three values of the uniform wall heat flux are considered, 30, 60 and 120 W/m2, whereas the inclination angle of the upper plate θ is 2° and 10°.
Practical implications
Mixed convection because of moving surfaces in channels is present in many industrial applications; examples of processes include continuous casting, extrusion of plastics and other polymeric materials, bonding, annealing and tempering, cooling and/or drying of paper and textiles, chemical catalytic reactors, nuclear waste repositories, petroleum reservoirs, composite materials manufacturing and many others. The investigated configuration is used in applications such as re-heating of billets in furnaces for hot rolling process, continuous extrusion of materials and chemical vapor deposition, and it could also be used in thermal control of electronic systems.
Originality/value
This paper evaluates the thermal and velocity fields to detect the maximum temperature location and the presence of fluid recirculation. The paper is useful to thermal designers.