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The present study aims to investigate the effects of the presence of vortex generators in the cooling fluid flow of a microchannel heat sink and to seek to optimize its performance in terms of heat transfer. In addition, the cooling fluid used is a pure water solution in the presence of aluminum oxide (Al2O3) nanoparticles. The numerical simulation is performed for different cases. Each case is characterized by the rate of the volume fraction of aluminum (Al2O3) in the presence of the base fluid (pure water). Four cases were studied in which the rate of the volume fraction of aluminum (Al2O3) suspended in the base fluid was chosen equal to 1%, 2%, 3%, and 4%, respectively. The heat sink is a microchannel, and the numerical simulations are performed for a Reynolds number in the range (600, 1400). A finite volume scheme resolves the system of differential equations governing the physical problem according to the imposed boundary conditions. The problem of pressure–velocity coupling, imposed by the presence of pressure by its gradient in the equations of the algebraic system to be solved, is solved by using the semi-implicit method for pressure-linked equation (SIMPLE) algorithm. The different thermal factors: the Nusselt number, the friction factor, and the thermal performance enhancement factor, and the two physical fields: the velocity and the temperature field, have been analyzed. The results obtained show that, for Re = 600, the value of Nu increased with increasing concentrations of 5.68, 8.16, 10.08, and 11.66 for a concentration equal to 1%, 2%, 3%, and 4%, respectively. The results also show that playing a vortex generator with a constant concentration equal to 2% could further improve the thermal performance improvement factor from 25 to 67%. Accordingly, the configuration corresponding to Case 2 performs better in heat transfer than the others. Finally, new correlations to predict the friction factor, Colburn j-factor, and Nusselt number as a Reynolds number and design function are located at the end of this study. [ABSTRACT FROM AUTHOR]

This paper performed a three-dimensional numerical analysis of the flow structure and heat transfer enhancement of turbulent airflow through a rectangular channel (without baffles, with baffles). Two partially inclined baffles with different orientations are mounted on the bottom and top walls of the channel. The location of the baffles in the direction of flow through the channel of a heat exchanger is of great importance. It depends mainly on the geometrical parameters and the orientation of the baffles. Hence, our study focused on analyzing the effects of the baffles on the thermal–hydraulic behavior in the exchanger by choosing a flat baffle and four configurations of different orientations. Numerical results are presented in terms of axial velocity U, isotherms (T), turbulent kinetic energy (k), amount of heat dissipated by the channel surfaces (Q), average Nusselt number (Nu), friction factor (f), and thermal performance factor (ƞ). The results show that the insertion of the partially inclined baffles into the channel causes the generation of vortices in the upstream and downstream areas of the baffle location point. Thus the mixing phenomenon occurs, which induces an increase in the heat transfer rate and generates a pressure drop simultaneously. Furthermore, the analysis of the results shows that compared to the smooth case (without baffles), the thermal performance factor (η) is significantly higher in the four configurations with baffles. Thus, for the different cases studied: (2); (3); (4); (5) and (6), the factor (η) is equal to 2.18; 2.16; 2.19; 2.27; and 2.25, respectively, for a Reynolds number equal to 87,300. The results also indicate that the transmitted relative heat quantities are equal to 116.08, 113.93, 118.2, 121.71, and 109.39%, respectively, for the same cases considered. Therefore, the configuration corresponding to case (5) performs better in heat transfer than the others. Finally, new correlations for predicting friction factor and Nusselt number as a function of Reynolds number and configuration are found at the end of this study. [ABSTRACT FROM AUTHOR]

Aluminum honeycomb structures have been frequently used in many industrial applications, especially in aerospace and aeronautics, due to their high strength and stiffness to weight ratio. The machining quality of aluminum honeycomb structures is generally related to plastic deformation of the walls forming the honeycomb structure and burrs. Consequently, the use of this type of structure requires specific machining operations and special tools. In order to carry out in-depth studies on the milling of aluminum honeycombs, a 3D finite element model was developed with the help of Abaqus/Explicit software. The model thus developed is validated with several experimental tests and for different machining conditions. Based on the developed model, the relationship between the cutting forces and the friction coefficient between the cutting tool and the honeycomb during the cutting process is studied. The main objective of this work is to highlight the effect of physical and geometrical parameters during the milling of aluminum honeycomb structures on cutting forces, surface quality generated, chip size, and material accumulation in front of the cutting tool. The comparison between the simulated results and the experimental results indicates that the developed numerical model is in good agreement with the experimental reality. [ABSTRACT FROM AUTHOR]

In this paper, the thermal performance improvements of a heat removal system like an electronic system have been analyzed. The studied case is a horizontal channel in which two partially inclined baffles are attached with variable height and number. The channel is crossed by a forced convective flow of a cooling fluid (air). This numerical work evaluates the influences of the height and number of the baffles on the enhancement of the heat transfer rate. The mathematical model of this system is composed of nonlinear partial equations that the analytical solution for them is very complex, hence the need for numerical analysis is mandatory with the aid of a finite volume method. Accordingly, The numerical results are presented in axial and transverse velocity, temperature, local and average Nusselt number, local friction coefficient, pressure drop, heat transfer rate, and turbulence kinetic energy. The results revealed that it is possible to improve the thermal performance of the considered system by adopting designs that allow the maximum heat transfer rate with the minimum energy loss. In addition, results show that at the lowest Reynolds number (Re = 10,000), as the height of baffles rises from 0.01 to 0.03 m (growth by 200%), the heat transfer rate augments about 59.09%. Moreover, at the highest evaluated Reynolds number (Re = 87,300), by increasing the height of baffles up to 200%, the heat transfer rate increases by approximately 50.53%. Furthermore, employing a higher number of baffles leads to more heat transfer rates and a significant pressure drop. [ABSTRACT FROM AUTHOR]

The present study focused on researching a technique that can make a cooling system more efficient in terms of heat transfer. To achieve this, it is possible to modify the thermal conductivity of its cooling fluid or the structure of its flow. In this study, we have opted for the second technique. To do this, we sought to create singularities in the flow by inserting vertical and rotating baffles around the vertical. The study field is a channel of rectangular section, placed horizontally, and crossed by the incompressible and turbulent flow of a fluid (air) in forced convection. Geometrically, the physical problem describes mathematically. A system of hyperbolic equations governs it; Navier–Stokes equations derive from the laws of conservation of mass and momentum and the state's law that derives from the principle of conservation of energy. A finite volume scheme ensures the discretization of the governing equations and the numerical analysis's boundary conditions. The turbulence is modeled using the standard k-ɛ model, while the pressure–velocity coupling problem solves by applying the SIMPLE algorithm. The proposed numerical computational model validates by comparing the computed results with those of literature correlations. The model was then applied to practical cases where a Reynolds number in the range (12,000, 16,000) has chosen. The orientation angle (θ) of the baffles is chosen equal to (0°, 5°, 7°, 13°, 15°) with a different orientation direction. The calculated results are presented in map form for the different physical fields (of axial velocity, temperature) or in graphical form for the different factors and coefficients (friction factor, amount of heat removal, average Nusselt numbers, and thermal performance factor). The results obtained show that the system is made more efficient with a thermohydrodynamic behavior that varies significantly with the baffles' orientation. The heat transfer rate increased, and the pressure drops reduced. For an orientation angle of (θ = 5°), the thermal performance factor is around 2.323, and 2.45, for Re = 12,000, and 16,000, respectively. [ABSTRACT FROM AUTHOR]

The milling of aluminum honeycomb structures represents today an important scientific and technical research topic for many industrial applications: aerospace, aeronautic, automotive, and naval. The difficulties encountered when milling this type of materials are linked to the small thickness of the walls constituting the honeycomb cells and the ductility of the material structure. The milling of cellular composite structures requires specific and rigorous tools. In the present work, a 3D numerical modeling of the milling process of aluminum honeycombs has been developed using Abaqus Explicit software. The effect of milling parameters, such as the spindle speed, the tilt angle, and the depth of cut, has been particularly investigated in terms of cutting forces, surface integrity, and chip morphology. To properly analyze and optimize the cutting process, experimental validation was done through milling tests with different cutting conditions. The comparison between numerical simulations and experimental tests shows that the three-dimensional model correctly reproduces the milling of this type of structure. [ABSTRACT FROM AUTHOR]

The machining of Nomex honeycomb structures represents a technical and scientific barrier for aeronautical applications. The difficulties encountered during the machining of this type of material are linked to the low density of Nomex paper, and to the low thickness of the walls forming the honeycomb cells of this type of structure. In this work, a finite element calculation code "ABAQUS'- EXPLICIT" was used to optimize and analyze the machining by milling of Nomex honeycomb structures. The main objective of this work is to study the influence of the machining conditions on the cutting forces, and the morphology of the chips. [ABSTRACT FROM AUTHOR]

In the present paper, numerical simulation is carried out to investigate turbulent flow structure and heat transfer analysis in a two-dimensional horizontal plane channel, contains square blocks arranged in tandem or side by side arrangement. The k-e model is used to describe turbulence phenomena, and governing equations are solved by a finite volume method, with SIMPLEC algorithm is applied for the coupling of the velocity-pressure variables. The power-law scheme is used for the discretization of the convective terms in the momentum equations. Presented results illustrates the effect of the transverse (GT) and longitudinal (GL) spacing between the blocks on flow structure and heat transfer for a wide range of Reynolds number (104= Re =5×104). Numerical results show a very good agreement in comparison with available data in the literature. [ABSTRACT FROM AUTHOR]

In the present paper, we report a numerical study of dynamic and thermal behavior of the incompressible turbulent air flow by forced convection in a two-dimensional horizontal channel. This one contains the complicated form of the deflector which has been studied by varying the inclination angle from φ = 40°, φ = 55° to φ = 65°. The baffles are mounted on lower and upper walls of the channel. The walls are maintained at a constant temperature (375 K), the inlet velocity of air is Uint = 7.8 m/s, and the Reynolds number Re = 8.73 × 104. A specifically developed numerical model was based on the finite-volume method to solve the coupled governing equations and the SIMPLE (Semi Implicit Method for Pressure Linked Equation) algorithm for the treatment of velocity-pressure coupling. For Pr = 0.71, the results obtained show that (i) the streamlines and isotherms are strongly affected by the inclinations angles at Re = 8.73 × 104, (ii) the friction coefficient near the baffles increases under the angle exchange effect, and (iii) for a constant Re, the local Nusselt number at the walls of the channel varies with increasing the inclination angle of the deflector. Furthermore, the deflectors are generally used to change the direction of the structure of flow and also to increase the turbulence levels. We can conclude that the contribution of inclined baffles improves the increase of heat and mass transfer in which the Nusselt number at a certain angle increases noticeably. [ABSTRACT FROM AUTHOR]

Nador lagoon is a coastal system connected to the sea through a narrow and shallow inlet; understanding its hydraulic performance is required for its design and operation. This paper investigates the hydrodynamic impacts of the whole lagoon due to tidal waves using a numerical approach. In this study we use a two-dimensional, depth-averaged hydrodynamic model based on so-called shallow water equations solved within triangular mesh by a developed efficient finite volume method. The method was calibrated and validated against observed data and applied to analyze and predict water levels, tidal currents, and wind effects within the lagoon. Two typical idealized scenarios were investigated: tide only and tide with wind forcing. The predicted sea surface elevations and current speeds have been presented during a typical tidal period and show correct physics in different scenarios. [ABSTRACT FROM AUTHOR]

This paper presents details of finite volume and finite element numerical models based on unstructured triangular meshes that are used to solve the two-dimensional nonlinear shallow water equations (SWEs). The finite volume scheme uses Roe's approximate Riemann solver to evaluate the convection terms. Second order accuracy is achieved by means of the MUSCL approach with MinMod and VanAlbada limiters. The finite element model utilizes the Lax–Wendroff two-step scheme, which is second-order in space and time. The models are validated and their relative performance compared for several benchmark problems, including a hydraulic jump, and flows in converging and converging–diverging channels. [ABSTRACT FROM AUTHOR]