The aerodynamic performance of an aircraft mainly depends on the lift force, drag force, and the lift to drag ratio. The geometric shapes of aircraft wings are considered crucial for this aerodynamic performance. The purpose of this study is to determine the most efficient wing shape that improves the aerodynamic performance of the airfoil. For that purpose, a numerical comparative study was carried out between the rectangular and tapered wing shapes of the NACA 4412 airfoil for a wide range of angles of attack in the subsonic regime. ANSYS Fluent software, based on the finite volume method, was used for the numerical resolution of the governing equations. The Realizable k-ε model was chosen for the turbulence modeling. The numerical procedure was validated based on experimental results obtained from the literature. The results show an improvement in the lift coefficient and a reduction in the drag coefficient of the Tapered shape compared to the rectangular shape at all angles of attack. However, a gain was achieved in the lift-to-drag coefficient ratio of the Tapered shape.

In this study, a passive solar house prototype was built using Trombe wall and was tested in the semi-arid region of Batna, in eastern Algeria. Traditional local materials (stone and adobe) were used for the construction of the thermal storage wall. A new local bio-based material made from date palm trunks was used for the insulation of the passive house prototype. For a better understanding of passive house heating and for a comparative study, a numerical simulation, using Fluent, was carried out. The aim of this study was to supply recommendations for improving the passive systems and to participate to the energy consumption control in the building sector. The results show that the experimental and numerical simulation results are in good agreement. The optimal orientation of the solar passive house has been determined, which is at 160° southeast. The use of local and bio-based materials has proven its effectiveness in the construction of the passive house. The thermal behavior of date palm wood has been found to be close to those of insulation materials commonly used in buildings. That means it has the same thermal insulation ability (thermal conductivity). On the other hand, the results show that the thermal efficiency of the passive solar heating system, with an adobe wall is significantly higher (50%) than that with a stone wall (30.7%).

Heat transfer in a finned absorber of a parabolic trough collector was studied numerically. The main aim of this work was to study the effect of attached fins on the enhancement of the thermal performance of a parabolic trough collector. The values of the fin’s length varied from 0 to 20 mm; their thicknesses varied from 0 to 8 mm and their number was 5. The parameters used in the current study are: the thermal and dynamic field, friction coefficient, Nusselt number, the thermal efficiency and thermal enhancement index. Obtained results show that inclusion of fins to the lower half of the absorber tube can enhance the heat transfer between the absorber tube and working fluid. The increase of the fin’s length increases the friction factor, Nusselt number and thermal efficiency, and the increase of fin’s thickness also increases the previous parameters. Starting the value 6 mm of thickness, its effect remains the same, but thickness is less effective than length. The values 15 mm of length and 6 mm of thickness are selected as optimal values. Results show that the inclusion of the fins enhances the thermal performance of the parabolic collector by 8.45%.

The aim of this study is to numerically examine the improvement techniques of the heat transfer in inclined tubes. The passive enhancement techniques are some of the most important means to improve heat transfer rates in engineering devices. In this research a passive enhancement technique (vortex generation) is combined with the tube inclination in order to improve heat transfer rates in solar concentrator absorber. Fins, acting as vortex generators, were attached to the internal wall of the tubes at different positions. A numerical simulation was performed using fluent software in which the finite volume method was used to solve the governing equations. The heat transfer rates obtained numerically were compared to those calculated using well known correlation (i.e. correlation of Shah and London) or others obtained experimentally. Through this study, it was found that the influence of fins on heat transfer rates is more important for the laminar regime than for the turbulent one for all considered inclinations. The optimal inclinations, which allow increasing the heat transfer, have also been determined for both laminar and turbulent flows. The findings of this research can be used to improve the heat transfer rates and therefore the efficiency of the solar concentrator absorber.

Improvement of the airfoil NACA 4415 aerodynamic performances by flow control using a passive technique was achieved in this study. Gothic-shaped vortex generators were added at the profile upper surface. Vortex Generators (VG) were used to avoid boundary layer separation at the profile trailing edge, thus reducing the drag force and improving aerodynamic performances. A numerical simulation with fluent code was performed. A parametric study was carried out to determine optimal disposition and dimensions of the VG. Six VG parameters were tested; thickness (E), height (H), length (L), aspect ratio (r), incidence angle (α) and the VG position relative to the chord of the profile (XVG). The results show an increase in the lift coefficient for the profile with vortex generators in the range of high attack angles. Optimal dimensions and positions of the VG were obtained.

The objective of the present study is the active flow control of blood in the aorta with atherosclerosis using an External Magnetic Field (EMF) in order to facilitate the blood flow. For that purpose, a numerical investigation has been developed with a Magneto-hydrodynamics flow modelisation. The blood is considered homogeneous, incompressible and Newtonian and the fluid flow is assumed to be unsteady, two-dimensional and laminar. The aorta tissue is electrically conductive. Fluent software has been used to solve the governing equations. The results relating to velocity, pressure and the wall shear stress indicate that the presence of the EMF considerably influences the blood flow. The flow control deals with the effects of the EMF direction of application and its intensity. The results show that by applying an EMF, the blood velocity and pressure in the aorta are entirely affected. The direction and the intensity of the EMF allow minimization of the flow instabilities due to the geometrical singularities. Therefore, applying an EMF can be considered an appropriate method for flow control in order to obtain a uniform blood circulation around the atherosclerosis.

This chapter covers a numerical method for the resolution of the problem of subcooled convective boiling flows in microchannels heat sink. The focus is on the numerical procedure for tracking or capturing interface/surface shape. Fundamentals of the boiling phenomena and the thermophysical properties with dimensionless numbers usually used in the resolution of the two-phase flow problems are presented in Chapter 18. In particular, an analysis of the transition of phase change pattern between conventional macrochannels and mini/microchannels is given in that chapter. Since the focus of this chapter is the numerical modeling rather than the fundamentals of the boiling process, analysis and interpretation are limited to the concerned subject. Analysis of some experimental research works in the literature is also given in Chapter 18. For an in-depth understanding of fundamentals and analysis of convective boiling heat transfer in microscale, readers are referred to different excellent sources available in the literature. One can quote Refs. [1–13] among a long list of interesting studies.
Mini- and microchannel heat sinks have become known as one of the effective cooling techniques. The advantage of such devices is their ability to dissipate large heat flux in relatively small volumes, which makes them very efficient cooling systems. Mini- and microchannel heat sinks combine the attributes of very high surface-area-to-volume ratio, large convective heat transfer coefficient (even in single-phase flows), and small coolant fluid quantity. These attributes make mini/microchannels heat sinks very suitable for cooling devices with high dissipating energy like integrated circuits, microprocessors, and high-energy laser mirrors.

Passive heat transfer techniques are considered to be one of the most important means to enhance heat transfer in heat exchangers that allow also reducing their size and manufacturing cost. Moreover, this passive technique can also be used to control the thermal instabilities caused by the two-phase flow in the evaporators. The thermal instabilities are undesirable because they can lead to a tube failure. For this purpose, a numerical study of the two-phase flow with evaporation in a vertical tube has been performed in this work. The volume of fluid (VOF) multiphase flow method has been used to model the water vapor–liquid two-phase flow in the tube. A phase-change model, for which source terms have been added in the continuity and energy equation, has been used to model the vaporization. The numerical simulation procedure was validated by comparing the obtained results with those given in the literature. The passive control technique used here is a ring element with square cross section, acting as a vortex generator, which is attached to the tube wall at various positions along the tube. Instabilities of temperature and void fraction at the tube wall have been analyzed using fast Fourier transforms (FFTs). The results show that the attachment of the control element has a significant influence on the value and distribution of the void fraction. Higher positions of the control element along the tube allow reducing the magnitude of void fraction oscillations.

The aim of this paper is to predict the location of azeotropes for binary mixtures using two methods: firstly from the experimental data and secondly with a thermodynamic model. The model is composed of the Peng–Robinson equation of state, the Mathias–Copeman alpha function and the Wong–Sandler mixing rules involving the NRTL model. The binary systems of refrigerants considered in this paper are: Pentafluoroethane (R125) + Propane (R290) [1], 1,1,1-Trifluoroéthane (R143a) + Propane (R290) [2] and Carbon Dioxide (R744) + Propane (R290) [3]. The mixtures mentioned above have been chosen because they are environment friendly with a null ODP and a low GWP. The results proved that there is a good agreement between the predicted values and the experimental data. The presented methods are able of predicting the azeotropic positions.

In this paper, a numerical study is carried out to characterize the transient local heat transfer coefficient at the fluid-solid wall interface of a solar collector. For that purpose, the considered collector wall geometry is a flat plate with nonnegligible thickness which is subjected to a variable solar heat flux. The transient conjugated conduction-convection heat transfer has been taken into account. The heat transfer coefficient is calculated as a function of the plate thickness as well as the position along the plate. A good agreement has been found between the calculated temperatures and other experimental results. The heat transfer coefficient evolutions, as a function of time, have been obtained for various positions along the plate. The results showed that at first, high values of the heat coefficient are reached, and then it decreases and tends to constant values. It has been also noticed that at a fixed value of time, the heat transfer decreases when the position is increased from the beginning of the plate towards its end. The parametric study allowed obtaining a correlation of the transient convective heat transfer coefficient as a function of the steady state coefficient (which depends on the flow velocity and the coordinate of the considered point on the plate), multiplied by a function of time and the plate properties. The results have been used to optimize the heat transfer coefficient measurement technique using the pulse method. The pulse method consists in imposing a heat flux on a wall, and then to calculate, by an inverse method, the heat transfer coefficient from the time evolution of surface temperature (thermo-gram). Measurement of the heat transfer coefficient is based on the introduction into the inverse model of a function that represents the theoretical evolution of this coefficient due to the energy excitation. This function is deduced from the numerical study conducted in this work.

Dans ce travail, nous présentons une étude numérique de la convection naturelle dans une enceinte rectangulaire verticale simulant un thermosiphon. Les équations qui régissent ce phénomène ont été résolues par une approche numérique, basée sur la méthode des volumes finis en utilisant le code Fluent et le mailleur Gambit. Un premier travail de validation a été mené en comparant notre travail avec ceux d’autres auteurs. Par la suite, on a fait varier le fluide de travail, la longueur et la position de l’ailette. L’influence de ces paramètres sur les champs de température, la densité de flux de chaleur et le nombre de Nusselt moyen a été ainsi considérée et les conditions optimales qui maximalisent les transferts de chaleur déterminées.

In this paper, three dimensional two phase flow with vaporization has been numerically studied in a mini-channel heat sink. The modeling of the two phase flow was achieved using the Volume of fluid method. The geometric reconstruction scheme, that is based on the piecewise linear interface calculation method was applied to reconstruct the liquid-vapor interface. For an accurate modeling, the effect of axial conduction has been also taken into account, using a conjugate heat transfer model. The vaporization was modeled by developing a numerical code for which appropriate source terms have been added in the momentum and energy equations to take into account heat absorption during vaporization or heat release during condensation. The developed numerical procedure has been validated by the comparison of the obtained results for vaporization inside a cylindrical tube with the correlation given in the literature. A good agreement has been reached between the heat transfer coefficient calculated and that obtained by the used correlation, especially for higher positions along the tube for which the flow regime is well established and disturbances due to the entrance effects disappear. Some typical results are also displayed and discussed. The obtained results show the evolution of the vapor fraction from the inlet of the heat sink to its outlet where all the liquid becomes a vapor. The obtained results of both vapor fraction and velocity contours showed the benefit of such numerical procedure in representing the phase change in heat sinks.

Laminar fluid flows and heat transfers, by forced convection, in a rectangular horizontal channel, have been numerically investigated. Three blocks, simulating electronic components, have been attached to the channel bottom wall. In order to control the flow and enhance the heat transfer rate, a rectangular cross section bar, acting as a vortex generator, has been attached to the channel top wall. The Navier-Stokes and energy equations are solved using FLUENT. Velocity and temperature fields as well as local Nusselt numbers have been obtained for various imposed conditions. Our numerical simulation procedure has been validated by comparison with results of other authors. The obtained results indicate that thanks to the control element, heat transfer in the channel is enhanced. For each block, the best position of the vortex generator, which allows maximal heat dissipation, is when the control element is located above the considered block.

A better understanding of two-phase flows with evaporation allows leading to an optimal design of evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study has been carried out in order to model and simulate the combination of a two-phase flow with evaporation in a vertical tube. The VOF (volume-of-fluid) multiphase flow method and a phase-change model for the mass transfer have been used. For an accurate modeling, the effect of axial conduction has been also taken into account using a conjugate heat transfer model. Since thermal oscillations are undesirable as they can lead to the failure of the tube, flow instabilities have also been analyzed, using FFT (fast Fourier transforms), in order to comprehend their behavior and influence. A control study of the flow instabilities in the tube is also presented. For that purpose tube inlet temperature has been varied using a gain control parameter.

A better understanding of two-phase flows with evaporation allows leading to an optimal design of heat exchangers particularly evaporators. For that purpose, numerical simulations are very useful. In this paper, a numerical study using Fluent has been carried out in order to model and simulate the combination of a two-phase flow with evaporation in a vertical tube. For that purpose, the VOF multiphase flow model and a phase-change model for the mass transfer have been used. For an accurate modelling, the effect of axial conduction has been also taken into account using a conjugate heat transfer model. Our numerical simulation procedure has been validated by comparing our results with those obtained by other authors. Temperature and void fraction fields as well as the heat transfer rate have been calculated for various conditions. Indeed a parametric study has been carried out for various conditions (Reynolds number, imposed lateral heat flux, position along the tube, etc…). Since thermal oscillations are undesirable as they can lead to the failure of the tube, flow instabilities have also been analyzed, using FFT (Fast Fourier transforms), in order to comprehend their behaviour and influence. A control study of the flow instabilities in the tube is also presented. For that purpose tube inlet temperature has been varied using a gain control parameter.

In this paper, a numerical study has been carried to simulate a two-phase flow with evaporation in a vertical tube. The VOF multiphase flow method and a phase-change model have been used. For an accurate modeling, the effect of axial conduction has been also taken into account, using a conjugate heat transfer model. Our numerical simulation procedure has been validated by comparing our results with those obtained by other authors. Temperature and void fraction fields have been calculated for various conditions. Since thermal oscillations are undesirable, as they can lead to a tube failure, flow instabilities have also been analyzed, using FFT (Fast Fourier transforms), in order to comprehend their behavior. A control study of the flow instabilities in the tube has also been carried out. For that purpose, an annular control element with a rectangular cross section, acting as a vortex generator, has been attached to the tube wall.

Nous présentons dans ce papier une étude numérique d’un dissipateur de chaleur à mini-canaux destiné au refroidissement de l’absorbeur de lumière sur la ligne PSICHE du Synchrotron-Soleil. Un refroidissement efficace de l’absorbeur permet d’une part d’améliorer la qualité du faisceau à la sortie des lignes de lumière et d’autre part de réduire les contraintes thermiques et mécaniques dans les composants du Synchrotron. L’absorbeur est soumis à un flux de photons sur l’une de ses faces internes, les minicanaux sont gravés sur une partie de sa face externe. La simulation numérique nous a permis d’appréhender les champs hydrodynamique et thermique dans l’absorbeur fabriqué. Nous nous limitons ici à la présentation des résultats du champ hydrodynamique en régime turbulent. La géométrie des répartiteur et collecteur du fluide a été optimisée pour assurer une répartition uniforme du débit sur les différents canaux. On montre qu’il y a une bonne concordance des pertes de pressions dans tout le dissipateur avec l’expérience et la corrélation de Phillips.

The present study concerns the measurement of the convective heat transfer coefficient on the solid-fluid interface by the pulsed photothermal method. This non-intrusive technique is applied for the measurement of the local heat transfer coefficients in cooling of a rectangular slab that simulates an electronic component. The heat transfer coefficient is deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab. In order to draw up the heat transfer cartography by a non-destructive tool, the infrared thermography has been used. Two inverse techniques for the identification of the heat transfer coefficient are presented here. The first one is based on the assumption that heat transfer coefficient remains constant during the pulsed experiment, and the second one considered it variable in space and time. The temporal and spatial evolutions are expressed as a constant heat transfer coefficient (h0) multiplied by a function of time and space f(x,t). The function f is deduced from the resolution of the conjugated convection-conduction problem, by a control volume technique for the case of thermally thick sample. The results are given for different air velocities and deflection angles of the flow.

The present study concerns the measurement of the convective heat transfer coefficient on the solid-fluid interface by the pulsed photothermal method. This non-intrusive technique is applied for the measurement of the local heat transfer coefficients in cooling of a rectangular slab that simulates an electronic component. The heat transfer coefficient is deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab. In order to draw up the heat transfer cartography by a non-destructive tool, the infrared thermography has been used. Two inverse techniques for the identification of the heat transfer coefficient are presented here. The first one is based on the assumption that heat transfer coefficient remains constant during the pulsed experiment, and the second one considered it variable in space and time. The temporal and spatial evolutions are expressed as a constant heat transfer coefficient (h0) multiplied by a function of time and space f(x,t). The function f is deduced from the resolution of the conjugated convection-conduction problem, by a control volume technique for the case of thermally thick sample. The results are given for different air velocities and deflection angles of the flow.

In this work, a numerical study is carried out to characterize transient conjugated heat transfer coefficient at the fluid-solid wall interface of a flat plate having a non-negligible thickness. The plate is subjected to variable wall heat flux. The heat transfer coefficient is calculated as a function of the plate material, the plate thickness and the density of heat flux applied at its back face. Air flows with various inlet velocities have also been considered. The heat transfer coefficient evolutions, as a function of time, have been obtained for various positions along the plate. At first, high values of the heat coefficient are reached, and then it decreases and tends to constant values. It has been also noticed that at a fixed value of time, the heat transfer decreases when the position is increased from the beginning of the plate to its end.