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In this paper, the free convective flow and heat transfer in a porous rectangular enclosures filled with Cu-water nanofluid is studied and analyzed. The cavity sidewalls are exposed to a constant heat flux and the horizontal walls are assumed to be adiabatic. The governing equations describing the problem are solved using a finite difference method. The main parameters of our problem are: aspect ratio, volume fraction of nanoparticles, types of media, porosity of the medium, and Rayleigh number. The results indicate that an increase in aspect ratio from 0.1 to 0.7 leads to a significant increase of Nusselt number, which then reaches a maximum value. However, the heat transfer rate progressively decreases for aspect ratios greater than 0.7. Moreover, the addition of Cu-nanoparticles weakens the heat transfer. As a result, when the porous medium has low thermal conductivity, the solid matrix porosity becomes particularly more effective in improving heat transfer. Also, a correlation was established between the average Nusselt number and the influencing parameters. Results show that the governing parameters impact the flow regime. [ABSTRACT FROM AUTHOR]

In this paper, a multi-objective permutation flow shop scheduling problem with sequence independent setup time is studied. The bi-objective function that we consider is a linear combination of the makespan and total flow time with a weighted factor for each criterion. We propose a set of exact and approximate methods to minimize the makespan and total flow time in our flow shop optimization problem case. Hence, our main goal is to find the sequence of jobs that minimizes the two criteria of makespan and total flow time. The purpose is to solve this problem, with a mixed integer linear programming model (MILP) and a collection of efficient metaheuristics for different sizes of instances. Moreover, three metaheuristics are used: the Genetic Algorithm (GA), the Iterative Local Search (ILS) algorithm and the Iterated Greedy (IG) algorithm. The three last algorithms GA, ILS and IG are suggested in two ways for exploring the neighborhood. In order to test the efficacy of our resolution approach, different series of instances containing n jobs and m machines are generated randomly ranging from small to relatively large instances. The examination of the suggested simulations allowed us to remark that, for large and medium-scale instances, IG based on the exploration of the neighborhood records the best performances in terms of comparison with the other metaheuristics. [ABSTRACT FROM AUTHOR]

The problem of unsteady laminar, two-dimensional hydromagnetic natural convection heat transfer in a concentric horizontal cylindrical annulus filled with a fluid-saturated porous medium in the presence of a transverse magnetic field and fluid heal generation effects is studied numerically. It is assumed that the inner and outer walls of the cylindrical annulus are maintained at uniform and constant temperatures Ti and To respectively. The model consists of the heat equation and the equations of motion under the Darcy law. The derived problem with the stream function-temperature formulation is solved numerically using the alternating direction implicit method. This investigation concerns the effect of magnetic field inclination angle, Hartmann number and heat generation on the heat transfer and the flow pattern. The obtained numerical results are presented graphically in terms of streamlines and isotherms. It was found that the heat transfer mechanisms and the flow characteristics depend strongly on the magnetic field inclination angle, Hartmann number and heat generation..

The effect of quasi-periodic gravitational modulation on the natural convection in a horizontal porous annulus is studied in this paper. The model we consider includes the heat and the hydrodynamics equations under Darcy law. The derived model with the stream function is solved numerically using the alternate direction implicit method. Results show that the convective instability and the flow regime are influenced by frequencies ratio of the quasi-periodic gravitational modulation.

In this paper, we study the resolution of a permutation flow shop problem with sequence-independent setup time. The objective is to minimize the maximum of job completion time, also called the makespan. In this contribution, we propose three methods of resolution, a mixed-integer linear programming (MILP) model; two heuristics, the first based on Johnson's rule and the second based on the NEH algorithm; and finally two metaheuristics, the iterative local search algorithm and the iterated greedy algorithm. A set of test problems is simulated numerically to validate the effectiveness of our resolution approaches. For relatively small-size problems, it has been revealed that the adapted NEH heuristic has the best performance than that of the Johnson-based heuristic. For the relatively medium and large problems, the comparative study between the two metaheuristics based on the exploration of the neighborhood shows that the iterated greedy algorithm records the best performances. [ABSTRACT FROM AUTHOR]

A numerical simulation of natural convection in a horizontal porous annulus with an internal wavy surface has been carried out. Governing equations include the heat equation and the hydrodynamics equations under Darcy law and Boussinesq approximation. The mathematical model formulated with the temperature-stream function is solved numerically using the finite difference method with the alternating direction implicit scheme. Results show that the heat transfer and the convective instability depend strongly on the waviness of the inner cylinder. Last, streamlines and isotherms are presented for different waviness parameters of the internal wall for better understanding of the influence of amplitude and number of undulations on the thermo-convective instabilities. [ABSTRACT FROM AUTHOR]