A computational work on turbulent flow and heat transfer in a channel fitted with inclined baffles

Numerical studies of momentum and heat transfer characteristics have been investigated of a steady incompressible turbulent flow of air through channel. The channel has inclined baffles which are arranged on the walls in a periodically staggered way. The governing equations, namely, continuity, Navier–Stokes and energy, based on k–ω turbulence model to describe the turbulence phenomenon are solved using the finite volume method and the SIMPLE algorithm. Calculations are performed for a Reynolds number between 12,000 and 38,000. The axial velocity profiles, the velocity fields, the local and average coefficient of friction and the Nusselt number distribution were obtained for all the geometry considered and for different sections selected, upstream, downstream and between the two inclined baffles. Simulation results which were obtained by the use of baffles are validated by an experimental study. Good agreement is observed between numerical and experimental results data in the literature.     

Interacting quantum dot coupled to a kondo spin: a universal Hamiltonian study

We study a Kondo spin coupled to a mesoscopic interacting quantum dot that is described by the "universal Hamiltonian." The problem is solved numerically by diagonalizing the system Hamiltonian in a good-spin basis and analytically in the weak and strong Kondo coupling limits. The ferromagnetic exchange interaction within the dot leads to a stepwise increase of the ground-state spin (Stoner staircase), which is modified nontrivially by the Kondo interaction. We find that the spin-transition steps move to lower values of the exchange coupling for weak Kondo interaction, but shift back up for sufficiently strong Kondo coupling. The interplay between Kondo and ferromagnetic exchange correlations can be probed with experimentally tunable parameters.     

Mixing of miscible liquids in gas-segmented serpentine channels

The chaotic mixing of miscible liquids in gas-segmented serpentine channels is studied computationally in a two-dimensional setting. Passive tracer particles are used to visualize and quantify the mixing. The molecular diffusion is ignored and only the mixing due to chaotic stirring is considered. Mixing is quantified using the entropy and intensity of segregation measures. The effects of various non-dimensional parameters on the quality of mixing are investigated and it is found that the relative bubble size, the capillary number and the non-dimensional channel corrugation length are the most important parameters influencing the mixing. The mixing is found to be weakly dependent on Reynolds number and nearly independent of viscosity ratio.     

Random walks on dynamic configuration models:A trichotomy

We consider a dynamic random graph on $n$ vertices that is obtained by starting from a random graph generated according to the configuration model with a prescribed degree sequence and at each unit of time randomly rewiring a fraction ${\alpha }_n$ of the edges. We are interested in the mixing time of a random walk without backtracking on this dynamic random graph in the limit as $n\to \infty$, when ${\alpha }_n$ is chosen such that ${lim}_{n\to \infty }{\alpha }_n{(logn)}^2=\beta \in [0,\infty ]$. In Avena et al. (2018) we found that, under mild regularity conditions on the degree sequence, the mixing time is of order $1∕\sqrt{{\alpha }_n}$ when $\beta =\infty$. In the present paper we investigate what happens when $\beta \in [0,\infty )$. It turns out that the mixing time is of order $logn$, with the scaled mixing time exhibiting a one-sided cutoff when $\beta \in (0,\infty )$ and a two-sided cutoff when $\beta =0$. The occurrence of a one-sided cutoff is a rare phenomenon. In our setting it comes from a competition between the time scales of mixing on the static graph, as identified by Ben-Hamou and Salez (2017), and the regeneration time of first stepping across a rewired edge.     

Kinetic modeling of Fischer–Tropsch-to-olefins process via advanced optimization

The reaction kinetics of a Fischer–Tropsch (FT) process to produce lower olefins was modeled utilizing the experimental data produced using an in-house synthesized iron-based catalyst. Along with FT chain growth reaction that is assumed to follow alkyl mechanism, water–gas shift reaction was also taken into consideration due to its significance. Not only the rate constants but also apparent activation energies were obtained via an integrated approach utilizing multiobjective and constrained nonlinear minimization methods in order to define a model valid at a temperature range instead of a single point. The adaption of a hybrid optimization method utilizing both population- and individual-based techniques enhanced prediction accuracy compared with the case where only multiobjective genetic algorithm is used. Thanks to the developed model, the effect of process parameters on product distribution was investigated. Finally, the kinetic model was compared with Anderson–Schulz–Flory model and the deviations observed were discussed.     

The effects of using corrugated booster reflectors to improve the performance of a novel solar collector to apply in cooling PV cells-Navigating performance using ANN

Journal of Thermal Analysis and Calorimetry - In this study, turbulent flow and heat transfer of water in a solar collector equipped with corrugated booster reflectors to apply in cooling...     

The role of convective heat transfer coefficient in CuO nanoparticles-PCM cooling ability in heat sinks with insulated side walls: comparison with the air cooled one

Journal of Thermal Analysis and Calorimetry - In this study, the effectiveness of the heat sink with an insulated wall equipped with nano-PCM and air-cooled one was compared. Heat sink...     

Microstructural evolution and intermetallic formation in Zn-Mg hybrids processed by High-Pressure Torsion

High-pressure torsion (HPT) was used to investigate the synthesis of Zn-Mg hybrids by direct bonding of separate disks of Zn and Mg at room temperature under an applied pressure of 6.0?GPa after 1, 5, 15 and 30 turns. Microstructural characterisation of the HPT-processed disks showed the formation of a sub-micron multilayered structure embedded in a Zn-rich matrix with an average grain size of ～ 600?nm at the disk periphery after 30 turns. XRD and TEM analysis revealed the presence of MgZn₂ and Mg₂Zn₁₁ intermetallic compounds, which increased in volume fractions with increasing number of turns. The formation of these intermetallics, together with Hall-Petch strengthening, led to an exceptional increase of the hardness values after 15 turns. Electrochemical testing in simulated body fluid showed that the degree of plastic deformation had an impact on the corrosion resistance of the Zn-Mg hybrids, which would affect their implementation in the biomedical field for absorbable applications. This study confirmed that there is significant potential for using HPT in the joining of dissimilar metals at room temperature to form Zn-Mg hybrids containing ultrafine-grained metal-matrix heterostructures with enhanced hardness.