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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.

Artificial roughness in the form of repeated ribs on a surface is an effective technique to improve the heat transfer rate. A numerical study on the heat transfer characteristics and flow structure of a fully developed turbulent flowing fluid in a rectangular duct having repeated transverse rib roughness. The thermo-hydrodynamic performance was obtained by varying important parameters, such as rib configurations: Six different configurations were analyzed. In this analysis, the Reynolds number of the flow is chosen in the range (40,000, 100,000). The system of equations governing the physical phenomenon is composed of nonlinear partial equations whose analytical solution is complex, and approximation methods are therefore essential. In this work, we have adopted numerical modeling based on a finite volume scheme allowing us to pass from the problem defined on a continuous study domain and governed by a system of equations with an infinite number of unknowns to the equivalent problem defined on a discrete study domain and governed by a system of equations with a finite number of unknowns. The turbulence phenomenon is modeled using the classical turbulence model (k–ɛ). The results show the relative evolution of the Nusselt number for the different cases studied. The different cases: case (1), case (2), case (3), and case (4) show better performance, respectively, by 54.12; 54.08; 69.27, and 74.89% compared to the case of a smooth channel. The results also indicate that the thermal performance improvement factor is more significant in cases (3) and (4).

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.

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.

•Proposition of a heat exchanger configuration using small helical baffle turbulators.The numerical simulations were performed by using a three dimensional CFD computer code.•The average deviation between the numerical and experimental data is between 4 and 8%.•The improvements in heat transfer (ηTPF) can reach 2.71 for a pitch distance of 48 mm.For high Renumbers a tube with a configuration A3 is the optimal choice with an air inlet-outlet temperature difference of 39.91 °K in comparison to the smooth tube.•The variation of Nu/Nusmoothshows that the case (D3) is the best choice for high Renumbers with 4.41.