Combined Effect Of Forced Convection Research Articles

Microstructure and property optimization of Al–8Ce alloys: Electromagnetic stirring and Sc–Zr microalloying

To further improve the strength of an Al–Ce alloy, the effects of electromagnetic stirring treatment, Sc–Zr microalloying, and their compound action on the microstructure and properties of the Al–8Ce alloy were investigated for the first time in this study. The results show that the primary α-Al becomes coarse, the eutectic Al11Ce3 phase is refined and the lamellar spacing increases significantly due to the combined effect of forced convection of electromagnetic field and dendrite fragmentation and nucleation in Al–8Ce alloy after electromagnetic stirring treatment. After the Sc–Zr microalloying treatment of the Al–8Ce alloy, the α-Al changes from a dendritic to fine round morphology, and the eutectic Al11Ce3 phase changes from lamellar to fibrous, which is due to the heterogeneous nucleation of Al3(Sc, Zr) phase and the adsorption refinement caused by the enrichment of Sc and Zr. The optimization effect of Sc–Zr microalloying on the mechanical properties of the Al–8Ce alloy was better than that of electromagnetic stirring and their synergistic treatment. The tensile strength and yield strength of Al–8Ce alloy with Sc–Zr additions were increased from 157 MPa to 85 MPa–192 MPa and 115 MPa, respectively, by 22.3 % and 35.3 %. After aging treatment, the tensile strength (from 192 to 272 MPa) and yield strength (from 115 to 221 MPa) significantly improved owing to the secondary precipitation of Al3(Sc, Zr) particles. The precipitation strengthening of the Al3(Sc, Zr) phase was the main contributor to the high yield strength of the alloy.

Flow and heat transfer simulation in a wall-driven porous cavity with internal heat source by multiple-relaxation time lattice Boltzmann method (MRT-LBM)

Laminar mixed convection characteristics in a wall driven porous cavity with an isothermally heated square blockage inside have been investigated numerically by the Non-orthogonal multiple-relaxation time lattice Boltzmann method (MRT-LBM). Various directions of wall driven and placement of the blockage have been considered. In the current study, the geometrical and flow parameters being investigated are the directions of wall driven, blockage position (ex, ey), the Richardson number (Ri). From the analysis of the mixed convection process with different directions of wall driven, the results show that under the configuration of central placement of the blockage, the most preferable heat transfer is obtained in the right wall driven at any values of the Richardson number. Because the movement of the wall can lead to an assisting effect on the buoyancy flow in the right wall driven. Since the right wall driven has the best heat transfer effects, the influences of blockage location and Richardson number is investigated in this condition. When the value of the Richardson number is 0.1, the most preferable heat transfer is obtained when the blockage is placed at the top right and bottom right. When the value of the Richardson number is 1.0 or 10.0, both the middle left and middle right blockage placement have the best heat transfer rate. That is mainly due to the influence of the size, strength and position of the vortex, the combined effect of forced convection and natural convection is stronger when the blockage is placed at those locations.

Mass Transfer under Combined Gas Evolution and Forced Convection

The combined effect of forced convection and bubble‐induced convection on mass transfer in an electrochemical cell with vertical planar electrodes is investigated experimentally. The results indicate that a minimum is established in the mass‐transfer coefficient due to the opposing effects of the two convections. A linear correlation exists between the rate of gas evolution and the rate of liquid flow at the minimum points. The effect of the cell gap is nonlinear, and it appears that a power dependence exists. Beyond the point of minimum, the mass‐transfer coefficient is dominated by the bubble‐induced convection and a universal correlation exists between the rate of gas evolution and the increase in mass‐transfer coefficient beyond the minimum value.