Defect and Diffusion Forum Vol. 409

Abstract: The impact of space dependent heat source in the transport of micropolar fluid in the existence of magnetic dipole, Joule heating, viscous heating, thermal radiation, hydrodynamic slips and convective condition effects has been numerically investigated. The dimensioned governing equations are non-dimensionlzed by using dimensionless variables then non-dimensional forms of the corresponding equations are than tackled by the versatile Finite Element Method (FEM). The effects of pertinent physical parameters characterize the flow phenomena are presented through graphs and discussed. It is found that, the impact of thermal based heat source advances the heat transfer characteristics significantly than exponential to space dependent. The thermal performance can be improved through the effects of magnetic dipole, viscous heating, Joule heating and convective condition. Further, the present numerical results are compared with previously published results in the literature as a limiting case of the considered problem and found to be in good agreement with the existing results.

Abstract: This study aimed to investigate numerically the heat transfer improvement and pressure drop inside annular channel of a rotor-stator provided with fins mounted on the stator without and with Taylor number. The impact of mounting various types of fins (triangular, rectangular, trapezoidal shapes with small and large base) is studied by varying the fin width b from 0 to 14 mm. In the presence of axial air flow, numerical simulations are carried out by solving the governing continuity, momentum and energy equations of turbulent flow in cylindrical coordinates using the Finite Volume Method. The results obtained by Reynolds Stress Model RSM model have indicated that the heat transfer enhances as the surface area of the fins and the effective Reynolds number increase, while there is an increase in pressure drop. Furthermore, we have shown that the presence of Taylor number has a slight increase in Nusselt number and pressure drop compared to the case without Taylor number. Among the four geometries, it is found that the rectangular cavity is the best geometry which gives maximum heat transfer and minimum pressure loss.

Abstract: This paper deals with studying numerically two circular turbulent jets impinging on a flat surface with a low velocity cross flow by using ANSYS CFX 16.2, with the aim of proving the effect ofReynolds number on the flow demeanor in a vertical circular free turbulent jet with cross flow. Five turbulence models of the RANS (Reynolds Averaged Navier–Stokes) approach were tested and the k -ω SST model was chosen to validate CFD results with the experimental data. Average velocity profiles, velocity and turbulent kinetic energy contours and streamlines are presented for four case configurations. In the first three cases, the following parameters have been varied: Reynolds number at the level of the two jets ( ), wind velocity at the level of the cross-flow ( ), and the distance between the two jets (S = 45mm, 90mm and 135mm). In the last case, a new configuration of the phenomenon not yet studied so far was treated, where horizontal cross-flows were introduced from both sides in order to simulate gusts of wind disrupting a VSTOL aircraft which tries to operate close to the ground. This case was carried out for Reynolds number based on the crossflow of 4 10⁴, 10 10⁴ and 20 10⁴ .The numerical results obtained show that the deflection of the jets is minimal when the Reynolds number at the level of the jets is greater than that of the cross-flow. The increase of Reynolds number at the level of the cross-flow reveals a significant deviation of the two jets with an intensity which always remains less for the second jet. As for the space parameter between the two jets, it turns out that the fact of further spacing the two jets makes the first jet even more vulnerable and leads to a greater deflection. Finally, the simulation of the wind gusts from the front and the back caused a zone of turbulence which resulted from a form of "interlacing" of the two jets under the effect of the transverse current imposed by the two sides.

Abstract: In this paper, the flow of a shear thinning nanofluid in a mechanically stirred tank has been numerically analyzed. This tank is cylindrical with a flat bottom. It is filled with Al₂O₃ nanoparticles suspended in the base fluid and equipped with an anchor-type stirrer whose shape is tilted upwards at an angle α. The purpose of this research is to study the impact of the tilt angle (0≤α≤π/6) and the effect of the alumina nanoparticles concentration (0≤φ≤0.1) on the hydrodynamic behavior and energy consumption. In the new anchor design (α>0), the fluid volume that is swept during the rotation of the anchor is the same as that in the case of a standard anchor (α=0). The laminar flow of the nanofluid is governed by the continuity and momentum equations taking into account the physical properties of the nanofluid introduced through correlations cited in the literature. The results obtained have shown that the tilt angle significantly contributes to the reduction of the power number, and leads to a decrease in the intensity of the tangential flow at the level of the extreme transverse planes of the tank. However, this reduction in intensity is compensated by increasing the axial flow. The use of nanoparticles in this work aims to show the role of the new design of anchor in creating a vortex at the bottom of the tank and to avoid of particles sedimentation.

Abstract: The two-dimensional steady-state natural convection of shear-thinning fluids is studied numerically between two concentric horizontal cylinders with different constant temperatures. The inner cylinder was put eccentrically into the outer one. The inner cylinder are held at constant temperatures with the inner one heated isothermally at temperature (T_h) and the outer cylinder have one fin cooled isothermally at temperature T_c (T_h > T_c). The simulations have been taken for the parameters 10² ≤ Ra ≤ 10⁴, = 0.71 ≤ Pr ≤ 10 and 0.6 ≤ n ≤1.The effects of Rayleigh number and Prandtl number on the dimensionless velocity and temperature are investigated for both shear-thinning and Newtonian fluids. Also the mean Nusselt number for various values of governing parameters is obtained and discussed. Although huge researches were conducted for natural convection in non-circular enclosures, researches for annular enclosures are very limited, especially finned enclosures. The length of the fin is also studied. The results show that increase in the length of fin increases the effectiveness of heat transfer. Also, the increase in Ra number increases the heat transfer effectiveness.