Reprogrammable magnonic band structure of layered Permalloy/Cu/Permalloy nanowires

Reprogrammability of magnonic band structure in layered Permalloy/Cu/Permalloy nanowires is demonstrated to depend on the relative orientation of the two layers magnetization. By using Brillouin light spectroscopy, we show that when the layers are aligned parallel two dispersive modes, with positive and negative group velocity, are observed while when the magnetic layers are aligned anti-parallel, only one dispersive mode, with positive group velocity, is detected. Our findings are successfully compared and interpreted in terms of a microscopic (Hamiltonian-based) method. An explanation for the observed behavior can be attributed to mode-mixing (or hybridization) effect when the two magnetic layers are aligned anti-parallel. This work opens the path to magnetic field-controlled reconfigurable magnonic crystals with multi-modal frequency transmission characteristics

CFD modeling of asphaltene deposition rate from crude oil

In this work, rate of asphaltene deposition from crude oil flowing under forced convection through a vertical pipe have been investigated using computational fluid dynamics (CFD). Effects of operating conditions such as surface temperature, Reynolds number, asphaltene concentration and surface roughness on the heat transfer coefficient, thermal resistance, and asphaltene deposition rate are studied numerically. For smooth pipe, the results showed that deposition rate of asphaltene decreases as crude oil velocity increases while it increases with increasing the surface temparature and flocculated asphaltene concentration. According to the results, by increasing the crude oil velocity from 0.6 to 1.6 m/s, the thermal resistance reduced to 62%. Also by increasing the concentration of flocculated asphaltene from 3.5 to 5.5 kg/m3, reduction in the heat transfer coefficient ratio is 4.5%, while the rate of asphaltene deposition and thermal resistance increases to 18.3%, and 17%, respectively. These are in agreement with previously published experimental results and theoretical models. The simulation then was extended to consider the wall roughness effects on asphaltene deposition rate. It was observed that increasing the wall roughness reduces the deposition. However, the deposition rate plateaus with further increase of the wall roughness beyond 0.2 mm, which is just under 1% of the pipe diameter

Spin-wave Instability Theory for Ferromagnetic Nanostructures

A microscopic, or Hamiltonian-based, theory is outlined for studying the spin-wave instability thresholds of the parametric processes occurring in ferromagnetic nanostructures under conditions of pumping with a microwave field. Most previous work has concentrated on spheres or films with dimensions of order several μm or more, with the theoretical interpretation being made in terms of macroscopic (or continuum) methods. At smaller length scales, as in ultrathin films and nanowires with thickness or lateral dimensions less than about 100 nm, the discreteness of the quantized spin waves and their spatial distributions become modified, making it more appropriate to employ a microscopic approach to the nonlinear dynamics with a lattice of effective spins interacting through the magnetic dipole-dipole and exchange interactions. Effects of microwave pumping (in either the parallel or perpendicular configuration) are incorporated in calculations for the instability thresholds of the quantized spin-wave bands in different nanostructures and materials

Spin-wave Instability Theory for Ferromagnetic Nanostructures

A microscopic, or Hamiltonian-based, theory is outlined for studying the spin-wave instability thresholds of the parametric processes occurring in ferromagnetic nanostructures under conditions of pumping with a microwave field. Most previous work has concentrated on spheres or films with dimensions of order several μm or more, with the theoretical interpretation being made in terms of macroscopic (or continuum) methods. At smaller length scales, as in ultrathin films and nanowires with thickness or lateral dimensions less than about 100 nm, the discreteness of the quantized spin waves and their spatial distributions become modified, making it more appropriate to employ a microscopic approach to the nonlinear dynamics with a lattice of effective spins interacting through the magnetic dipole-dipole and exchange interactions. Effects of microwave pumping (in either the parallel or perpendicular configuration) are incorporated in calculations for the instability thresholds of the quantized spin-wave bands in different nanostructures and materials

Heat transfer of swirling impinging jets ejected from Nozzles with twisted tapes utilizing CFD technique

This research investigated the forced convection heat transfer by using the swirling impinging jets. This study focused on nozzles, which equipped with twisted tapes via a numerical approach. The computational domain created by utilizing the fully structured meshes, which had very high quality from the viewpoint of aspect ratio and skewness. The numerical simulations were performed at four different jet-to-plate distances (L/D) of 2, 4, 6 and 8, four Reynolds numbers of 4000, 8000, 12,000 and 16,000, and also four different twist ratios (y/w) of 3, 4, 5 and 6. The mesh-independent tests were conducted based upon the average Nusselt number. The obtained results revealed good agreement with the available experimental data from the open literature. It was observed that for jet-to-plate distances of L/D=6 and L/D=8, the heat transfer rate of swirling jets was more than regular jets, and heat transfer rate at higher Reynolds numbers increased due to the greater rate of momentum transfer. Besides, the calculation done for a pair of jets, and the results shown that using two jets, instead of one, could increase the rate of heat transfer in the same air flow rate

Interplay between intra- and inter-nanowires dynamic dipolar interactions in the spin wave band structure of Py/Cu/Py nanowires

We have studied both experimentally and theoretically the reprogrammable spin wave band structure in Permalloy(10nm)/Cu(5nm)/Permalloy(30nm) nanowire arrays of width w=280 nm and inter-wire separation in the range from 80 to 280 nm. We found that, depending on the inter-wire separation, the anti-parallel configuration, where the magnetizations of the two Permalloy layers point in opposite directions, is stabilized over specific magnetic field ranges thus enabling us to directly compare the band structure with that of the parallel alignment. We show that collective spin waves of the Bloch type propagate through the arrays with different magnonic bandwidths as a consequence of the interplay between the intra- and inter-nanowire dynamic dipolar interactions. A detailed understanding, e.g. whether they have a stationary or propagating character, is achieved by considering the phase relation (in-phase or out-of-phase) between the dynamic magnetizations in the two ferromagnetic layers and their average value. This work opens the path to magnetic field-controlled reconfigurable layered magnonic crystals that can be used for future nanoscale magnon spintronic devices