Charbel Habchi

Coherent flow structures and heat transfer in a duct with electromagnetic forcing

Coherent vortices are generated electromagnetically in a square duct flow. The vortices are induced by a Lorentz force applied in a small section near the entrance of the duct. The flow structure complexity increases with the electromagnetic forcing since the primary vortices propagating along the duct detach to generate secondary smaller streamwise vortices and hairpin-like structures. The Reynolds number based on the mean flow velocity and hydraulic diameter is 500, and five cases were studied by varying the electromagnetic forcing. Even though this Reynolds number is relatively low, a periodic sequence of hairpin-like structure flow was observed for the high forcing cases. This mechanism enhances the mixing process between the different flow regions resulting in an increase in the thermal performances which reaches 66% relative to the duct flow without forcing. In addition to the flow complexity, lower forcing cases remained steady, unlike high Lorentz forces that induced periodic instabilities with a ...

Inclination Angle Optimization for “Inclined Projected Winglet Pair” Vortex Generator

Vortex generators (VG) are widely used in multifunctional heat exchangers/reactors for augmenting the heat transfer from fin plates to the working fluid. In this study, numerical simulations for longitudinal VGs are performed for both laminar and turbulent flow regimes. The shear-stress transport (SST) κ–ω model is used for modeling turbulence. Inclination angle for a new streamlined VG configuration called inclined projected winglet pair (IPWP) was varied to study the effect of this angle on the heat transfer enhancement and pressure drop. Response surface methodology (RSM) was used to deduce the inclination angle effects on heat transfer, pressure drop, and vorticity from both local and global points of view. Such study highlights the optimization for this VG configuration for better heat transfer intensification, based on thermal enhancement factor (TEF). Finally, it is found that the VG with inclination angle ranging from 30u2009deg to 35u2009deg exhibits the best global performance compared to other inclination angles. This type of studies is important for the enhancement of the thermal performance of heat exchangers and static mixers in various engineering applications.

Effect of the angle of attack of a rectangular vortex generator on the heat transfer in a parallel plate flow

In order to enhance the convective heat transfer, a secondary flow can be generated along with the main flow whose purpose is to increase the mixing of the particles between the cold and the hot regions. One of these passive enhancement methods is to use vortex generators (VG). This study is devoted to the heat transfer enhancement in a laminar parallel plate flow using rectangular wing VG. Three-dimensional numerical simulations are performed to study the effect of the angle of attack of the VG on the heat transfer and pressure drop. For this aim, Nusselt number and friction factor are studied on global perspectives. For all the values of angle of attacks the flow regime is kept laminar. Based on global parameters, it is found that the angle of attack has a direct impact on the heat transfer enhancement. By increasing this value, the global Nusselt number and the global friction factor are increased. This increase leads to a better enhancement until it reaches an optimal value for an angle of attack of 25°, beyond which the thermal performance starts to decrease.