Waviness Of Walls Research Articles

Natural convection flow in a fluid-saturated non-Darcy porous medium within a complex wavy wall reactor

This study elucidates a numerical simulation of natural convective flow inside a confined 2D reactor containing a fluid-saturated non-Darcy porous medium. The lower wall of the reactor is wavy, while all other walls are plane surfaces. All walls of the reactor are kept at surrounding temperature. A chemically reacting fluid produces flow within the reactor by a heat generating exothermic reaction. A coordinate transform is dispensed to turn the waviness of walls into the plane surface, and then, the flow governing equations in transformed coordinates are solved using the finite difference scheme. Streamlines and isotherms that describe, respectively, the flow patterns and temperature distributions within the reactor are displayed varying the dimensionless numbers, namely the Darcy number (10−4 ≤ Da ≤ 10−2), the Rayleigh number (103 ≤ Ra ≤ 105), the Frank-Kamenetskii number (0.5 ≤ Kf ≤ 3.0) and the Forchheimer drag parameter (0 ≤ F ≤ 1). Also local Nusselt numbers at the upper and lower walls are plotted to observe the heat transfer characteristics. The remarkable results reveal that the strength of vorticity and the highest temperature within the reactor increase with increasing the Frank-Kamenetskii number and the amplitude of waves. Because of increasing the Darcy number and Rayleigh number, the strength of vorticity enhances but the highest temperature diminishes. Opposite characteristics are observed due to an increase in the Forchheimer drag parameter. Heat transfer is relatively stronger in plane wall than in wavy wall in every case of dimensionless number. Moreover, maximum heat transfer is noticed at the points on the upper wall that are exactly above the peaks of the wave.

Local differentiation of cell wall matrix polysaccharides in sinuous pavement cells: its possible involvement in the flexibility of cell shape.

The distribution of homogalacturonans (HGAs) displaying different degrees of esterification as well as of callose was examined in cell walls of mature pavement cells in two angiosperm and two fern species. We investigated whether local cell wall matrix differentiation may enable pavement cells to respond to mechanical tension forces by transiently altering their shape. HGA epitopes, identified with 2F4, JIM5 and JIM7 antibodies, and callose were immunolocalised in hand-made or semithin leaf sections. Callose was also stained with aniline blue. The structure of pavement cells was studied with light and transmission electron microscopy (TEM). In all species examined, pavement cells displayed wavy anticlinal cell walls, but the waviness pattern differed between angiosperms and ferns. The angiosperm pavement cells were tightly interconnected throughout their whole depth, while in ferns they were interconnected only close to the external periclinal cell wall and intercellular spaces were developed between them close to the mesophyll. Although the HGA epitopes examined were located along the whole cell wall surface, the 2F4- and JIM5- epitopes were especially localised at cell lobe tips. In fern pavement cells, the contact sites were impregnated with callose and JIM5-HGA epitopes. When tension forces were applied on leaf regions, the pavement cells elongated along the stretching axis, due to a decrease in waviness of anticlinal cell walls. After removal of tension forces, the original cell shape was resumed. The presented data support that HGA epitopes make the anticlinal pavement cell walls flexible, in order to reversibly alter their shape. Furthermore, callose seems to offer stability to cell contacts between pavement cells, as already suggested in photosynthetic mesophyll cells.

Electroosmotic flow of a Phan-Thien–Tanner fluid in a wavy-wall microchannel

Abstract In this paper the electroosmotic flow (EOF) of a viscoelastic fluid in a wavy-wall microchannel is asymptotically analyzed. The rheological behavior of the fluid corresponds to the simplified Phan-Thien–Tanner model (sPTT). By using the lubrication theory, the governing equations of the flow are considerably simplified, which are written in dimensionless form. For obtaining the solution for the flow and electric fields, and assuming small amplitudes of the waviness of the microchannel walls, the domain perturbation method is used. The EOF is mainly characterized by the following dimensionless parameters: δ modulates the waviness of the walls; n denotes the number of waves along the microchannel and ɛ De κ 2 , which reflects the viscoelastic character of the fluid. The principal results show that the volumetric flow rate is increased when ɛ De κ 2 is increased, due to this parameter influences in an important manner on the velocity gradient at the microchannel wall. Also, for very small values of δ, the volumetric flow rate increases linearly. In contrast, for increasing values of n, the volumetric flow rate diminishes.

Promotion of Self-Assembly Patterning of FePt Nanoparticles by Tuning the Concentration of Oleylamine/Oleic Acid Surfactants in a Coating Solution

To provide a bit-patterned perpendicular magnetic recording medium consisting of an array of FePt magnetic nanoparticles, the effect of the total dispersant concentrations of oleylamine and oleic acid in a FePt-nanoparticle/toluene coating solution on a self-assembled nanoparticle array with a long-range periodicity on a flat SiO2/Si substrate and two patterned substrates, respectively, was examined. At a surfactant concentration greater than 0.8 vol%, FePt nanoparticles with an average size of 4.4 nm were arrayed in a two-dimensional and hexagonal-close-packed ordered array with 8.3-nm pitches on the flat surface. Self-assembled nanoparticles were arrayed on the bottom surface of the patterned trench, the array exhibited a hexagonal-close-packed structure. Furthermore the line defects in the arrays are caused by the waviness of the trench walls, and the surface roughness.

Defects in leaf epidermis of Arabidopsis thaliana plants with CDKA;1 activity reduced in the shoot apical meristem

In Arabidopsis thaliana, like in other dicots, the shoot epidermis originates from protodermis, the outermost cell layer of shoot apical meristem. We examined leaf epidermis in transgenic A. thaliana plants in which CDKA;1.N146, a negative dominant allele of A-type cyclin-dependent kinase, was expressed from the SHOOTMERISTEMLESS promoter, i.e., in the shoot apical meristem. Using cleared whole mount preparations of expanding leaves and sequential in vivo replicas of expanding leaf surface, we show that dominant-negative CDKA;1 expression results in defects in epidermis continuity: loss of individual cells and occurrence of gaps between anticlinal walls of neighboring pavement cells. Another striking feature is ingrowth-like invaginations of anticlinal cell walls of pavement cells. Their formation is related to various processes: expansion of cells surrounding the sites of cell loss, defected cytokinesis, and presumably also, the actual ingrowth of an anticlinal cell wall. The mutant exhibits also increased variation in cell size and locally reduced waviness of anticlinal walls of pavement cells. These unusual features of leaf epidermis phenotype may shed a new light on our knowledge on morphogenesis of jigsaw puzzle-shaped pavement cells and on the CDKA;1 role in regulation of plant development via influence on cytoskeleton and plant cell wall.

Stability characteristics of suspension flow through wavy-walled channels

A numerical study of the linear temporal stability characteristics of particulate suspension flow through a converging-diverging symmetric wavy-walled channel is considered. The basic flow is a superposition of plane channel flow of particulate suspension and periodic flow components arising due to the small amplitude sinusoidal waviness of the channel walls. The disturbance equations are derived within the framework of Floquet theory and solved using the spectral collocation method. The effects of small amplitude sinusoidal waviness of the channel walls and those of the presence of particles on the initial growth of the disturbances are examined. Two-dimensional stability calculations for particulate suspensions indicate the presence of fast growing unstable modes that arise due to the waviness of the walls. Neutral stability calculations are performed in the disturbances wavenumber-Reynolds number (αs−Re) plane, for the wavy channel with representative values of wavenumber (λ) and the wall amplitude to semi-channel height ratio (∈w) for different values of volume fraction density of the particles (C). It is observed that the critical Reynolds number for transition decreases with increase of ∈w and C. However, the flow can be modulated by suitable wall excitation which in turn can stabilize the flow.

Stability characteristics of wavy walled channel flows

The linear temporal stability characteristics of converging–diverging, symmetric wavy walled channel flows are numerically investigated in this paper. The basic flow in the problem is a superposition of plane channel flow and periodic flow components arising due to the small amplitude sinusoidal waviness of the channel walls. The disturbance equations are derived within the frame work of Floquet theory and solved using the spectral collocation method. Two-dimensional stability calculations indicate the presence of fast growing unstable modes that arise due to the waviness of the walls. Neutral stability calculations are performed in the disturbance wavenumber–Reynolds number (αs−R) plane, for the wavy channel with wavenumber λ1=0.2 and the wall amplitude to semi-channel height ratio, εw, up to 0.1. It is also shown that the two-dimensional wavy channel flows can be modulated by a suitable frequency of wall excitation ωg, thereby stabilizing the flow.

Spatially modulated convective motions in a vertical layer with curved boundaries

Mixed convection modes in a vertical layer with periodically curved boundaries are investigated. The amplitude of the waviness of the layer walls and the flow of fluid along the layer are both assumed to be small, and the value of the Grashof number is assumed to be close to critical. It is established that, in addition to the spatially periodic motions where the amplitude of the waviness is small, studied in /1, 2/, stable spatially modulated (quasiperiodic and soliton-type) wave modes of flow are possible, resembling the modulated convective structures in a horizontal layer /3/.

Nonlinear study of convective heat transfer and fluid flows induced by travelling thermal waves

A nonlinear study is made of the convective heat transfer and the fluid flow in an incompressible viscous fluid confined to a vertical wavy channel in four different geometrical configurations. The flow is generated by the periodic thermal waves prescribed at the wavy walls of the channel. The problem is solved by a perturbation technique with the assumption that the solution consists of a mean part and a perturbed part. The mean, perturbed and the total solutions are numerically evaluated for various values of the physical parameters involved in the problem. The mean solution is found to be in good agreement with that obtained by Vajravelu and Sastri [4]. The perturbed part of the solution is made of the contributions from the waviness of the channel walls and the travelling thermal waves. Of all the parameters, the heat source parameter plays an important role in augmenting (diminishing) the skin friction (the heat transfer) at the wally=1. Several interesting properties of the flow field and the heat transfer are discussed. The results of this analysis are also graphically presented.