COMPUTATIONAL INVESTIGATION OF LAMINAR FLOW AND CONVECTIVE HEAT TRANSFER IN AN OBSTRUCTED CHANNEL USING LATTICE BOLTZMANN METHOD

International audienc

Lattice Boltzmann Simulation of Convective Heat Transfer from Heated Blocks in a Horizontal Channel

International audienc

Study of Two Layered Immiscible Fluids Flow in a Channel with Obstacle by Using Lattice Boltzmann RK Color Gradient Model

Lattice Boltzmann method (LBM) is employed in the current work to simulate two-phase flows of immiscible fluids over a square obstacle in a 2D computational domain using the Rothman-Keller color gradient model. This model is based on the multiphase Rothman-Keller description, it is used to separate two fluids in flow and to assess its efficacy when treating two fluids in flow over a square obstacle with the objective of reducing turbulence by adjusting the viscosities of the two fluids. This turbulence can cause major problems such as interface tracking techniques in gas-liquid flow and upward or downward co-current flows in pipes. So, the purpose of the study is to replace a single fluid with two fluids of different viscosities by varying these viscosities in order to reduce or completely eliminate the turbulence. The results show that to have stable, parallel and non-overlapping flows behind the obstacle, it is necessary that the difference between the viscosities of the fluids be significant. Also, showing that the increase in the viscosity ratio decreases the time corresponding to the disappearance of the vortices behind the obstacle. The results presented in this work have some general conclusions: For M≥2, the increase in the viscosity difference leads to an increasing of friction between fluids, reducing of average velocity of flow and decreasing the time corresponding to the disappearance of the vortices behind the obstacle. However, for M≤1/2, the opposite occurs

Double MRT thermal lattice Boltzmann method for simulating convective flows

International audienc

Estimation of absorptivity of Earth-atmosphere system over the MENA areas

The developed Annual Columnar Radiative Absorptivity (ACRA19) model that describes, in annual mean, the terrestrial radiation balance of an atmospheric column, allows the determination of the various regional, absorption and reflection of solar and infrared radiation using 2018’s annual data of eight sites in MENA region ( between 22N-38N) of latitude obtained from AERONET and NASA POWER. The atmospheric thermal absorptivity (ATA) is very significant at high temperatures with an average of 0.85±0.1 for 1020 nm and the atmospheric visible absorptivity (AVA) registers 0.36 ± 0.06 when the total optical depth observes its maximum linked to dust aerosol advection

Study of coupled double diffusive convection–radiation in a tilted cavity via a hybrid multi-relaxation time-lattice Boltzmann-finite difference and discrete ordinate methods

International audienc

Heat transfer enhancement of a microchannel cooler with V-shaped partitions

The ongoing evolution of electronic systems that operate under extreme conditions has led to persistent concern about potential failures caused by escalating temperature levels which provokes the decline the operating quality. In response to this challenge, cooling solutions based on microchannels have emerged as promising prospects for improving thermal management in such scenarios. This paper explores the importance of these innovative cooling techniques and their potential for mitigating the risks of overheating in electronic systems. Furthermore, the introduction of microfluidic techniques and microchannels, specifically constricted microchannels, offers promising approaches to improve cooling efficiency. These cooling systems enable efficient heat dissipation and thermal regulation, mitigating the risk of overheating and enhancing system performance. Constricted microchannels facilitate compact and efficient heat transfer by leveraging increased surface area-to-volume ratios and improved convective cooling. Nowadays, microchannel-based heat sinks, heat exchangers, and cooling systems have been developed, showcasing improved heat dissipation, reduced temperature gradients, and enhanced energy efficiency. This research focuses on a parametrical study that examines the fluid nature, Reynolds number analysis, and system design. Numerical results demonstrate successful thermal management of high-temperature electronic systems using constricted microchannel cooling. These results mitigate temperature-related failures and support the development of robust systems for harsh operating conditions

3D Numerical Investigation of Free Convection using Lattice Boltzmann and Finite Difference Methods

Numerical study of various physical phenomena in three dimensions has become a necessity to better understand the physical process than in two dimensions. Thus, in this paper, the code is elaborated to be adapted to the simulation of heat transfer in three dimensions. The numerical simulations are performed using a hybrid method. This method is based on the lattice Boltzmann approach for the computation of velocities, and on the finite difference technique for the calculation of temperature. The used numerical code is validated by examining the free convection in a cubic enclosure filled with air. Then, the analysis of the heat exchange between two cold vertical walls and a heated block located at the center of a cubic cavity is considered.  The performed simulations showed that for a small value of the Rayleigh number (Ra=103 for example), the fluid exchanges its heat almost equally with all hot surfaces of the obstacle. However, for large values of Ra (Ra≥104), the numerical results found showed that the heat exchange rate is greater on the bottom face compared to the other faces of the obstacle

Study of heat transfer in an enclosure with a square cylinder using Lattice Boltzmann method

The purpose of this paper is to numerically examine the conjugate surface radiation-natural convection heat transfer in a 2D differentially heated enclosure with an inner square body, which generates heat. The numerical model is based on the coupling of the MRT-lattice Boltzmann model with finite difference method (FDM). The first one is used to compute the velocity field, while the second is adopted to obtain the temperature field. Various key parameters are studied, such as Rayleigh number (103 ≤ Ra ≤ 106), temperature-difference ratio ΔT*(0 ≤ ΔT* ≤ 50), body’s thermal conductivity (0 < Ks < ∞) and locations. In this study, the air is considered as perfectly transparent to radiation. Among the salient findings, we can state that (i) the inner body location has a meaningful effect on isotherms, streamlines and total heat transfer through the enclosure, (ii) the heat transfer is affected considerably by increasing the body size and radiation exchange, specially at high Ra

Effect of a Detached Bi-Partition on the Drag Reduction for Flow Past a Square Cylinder

The objective of this research is to study the fluid flow control allowing the reduction of aerodynamic drag around a square cylinder using two parallel partitions placed downstream of the cylinder using the lattice Boltzmann method with multiple relaxation times (MRT-LBM). In contrast to several existing investigations in the literature that study either the effect of position or the effect of length of a single horizontal or vertical plate, this work presents a numerical study on the effect of Reynolds number (Re), horizontal position (g), vertical position (a), and length (Lp) of the two control partitions. Therefore, this work will be considered as an assembly of several results presented in a single work. Indeed, the Reynolds numbers are selected from 20 to 300, the gap spacing (0 ≤ g ≤ 13), the vertical positions (0 ≤ a ≤ 0.8d), and the lengths of partitions (1d ≤  Lp ≤  5d). To identify the different changes appearing in the flow and forces, we have conducted in this study a detailed analysis of velocity contours, lift and drag coefficients, and the root-mean-square value of the lift coefficient. The obtained results revealed three different flow regimes as the gap spacing was varied. Namely, the extended body regime for 0 ≤ g ≤ 3.9, the attachment flow regime for 4 ≤ g ≤ 5.5, and the completely developed flow regime for 6 ≤ g ≤ 13. A maximal percentage reduction in drag coefficient equal to 12.5%, is given at the critical gap spacing (gcr = 3.9). Also, at the length of the critical partition (Lpcr = 3d), a Cd reduction percentage of 12.95% was found in comparison with the case without control. Moreover, the position of the optimal partition was found to be equal to 0.8d i.e. one is placed on the top edge of the square cylinder and the second one is placed on the bottom edge. The maximum value of the lift coefficient is reached for a plate length Lp = 2d when the plates are placed at a distance g = 4. On the other hand, this coefficient has almost the same mean value for all spacings between the two plates. Similarly, the root means the square value of the lift coefficient (Clrms) admits zero values for low Reynolds numbers and then increases slightly until it reaches its maximum for Re = 300