Surfactant-Spreading and Surface-Compression Disturbance on a Thin Viscous Film

1999 ◽  
Vol 121 (1) ◽  
pp. 89-98 ◽  
Author(s):  
J. L. Bull ◽  
L. K. Nelson ◽  
J. T. Walsh ◽  
M. R. Glucksberg ◽  
S. Schu¨rch ◽  
...  
Keyword(s):  
Effective Diffusivity ◽  
Leading Edge ◽  
Argon Laser ◽  
Petri Dish ◽  
Fluid Viscosity ◽  
Fluorescent Microspheres ◽  
Quantitative Measurements ◽  
Surface Compression ◽  
Spreading Rates ◽  
Constant Slope

Spreading of a new surfactant in the presence of a pre-existing surfactant distribution is investigated both experimentally and theoretically for a thin viscous substrate. The experiments are designed to provide a better understanding of the fundamental interfacial and fluid dynamics for spreading of surfactants instilled into the lung. Quantitative measurements of spreading rates were conducted using a fluorescent new surfactant that was excited by argon laser light as it spread on an air–glycerin interface in a petri dish. It is found that pre-existing surfactant impedes surfactant spreading. However, fluorescent microspheres used as surface markers show that pre-existing surfactant facilitates the propagation of a surface-compression disturbance, which travels faster than the leading edge of the new surfactant. The experimental results compare well with the theory developed using lubrication approximations. An effective diffusivity of the thin film system is found to be Deff = (E*Γ¯)/(μ/H¯), which indicates that the surface-compression disturbance propagates faster for larger background surfactant concentration, Γ¯, larger constant slope of the σ*−Γ* relation, −E*, and smaller viscous resistance, μ/H¯. Note that σ* and Γ* are the dimensional surface tension and concentration, respectively, μ, is fluid viscosity, and H¯ is the unperturbed film thickness.

scholarly journals Leading Edge Separation Bubbles on Turbomachine Blades

1993 ◽  
Author(s):  
R. E. Walraevens ◽  
N. A. Cumpsty
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbine Blades ◽  
Leading Edge ◽  
Freestream Turbulence ◽  
Compressor Blades ◽  
Pressure Distributions ◽  
Quantitative Measurements ◽  
Small Influence ◽  
Separation Bubbles

Results are presented for separation bubbles of the type which can form near the leading edges of thin compressor or turbine blades. These often occur when the incidence is such that the stagnation point is not on the nose of the aerofoil. Tests were carried out at low speed on a single aerofoil to simulate the range of conditions found on compressor blades. Both circular and elliptic shapes of leading edge were tested. Results are presented for a range of incidence, Reynolds number and turbulence intensity and scale. The principal quantitative measurements presented are the pressure distributions in the leading edge and bubble region, as well as the boundary layer properties at a fixed distance downstream where most of the flows had reattached. Reynolds number was found to have a comparatively small influence, but a raised level of freestream turbulence has a striking effect, shortening or eliminating the bubble and increasing the magnitude of the suction spike. Increased freestream turbulence also reduces the boundary layer thickness and shape parameter after the bubble. Some explanations of the processes are outlined.

The Effect of Spin Upon the Rolling Motion of an Elastic Sphere on a Plane

1958 ◽  
Vol 25 (3) ◽  
pp. 332-338
Author(s):  
K. L. Johnson
Keyword(s):  
Thrust Bearing ◽  
Theoretical Estimate ◽  
Leading Edge ◽  
Small Extent ◽  
Partial Slip ◽  
Elastic Plane ◽  
Rolling Motion ◽  
Elastic Sphere ◽  
Quantitative Measurements ◽  
Wide Range

Abstract The motion and deformation of an elastic sphere rolling on an elastic plane are examined for the case when the sphere, in addition to its straight rolling motion, has an angular velocity of “spin” Ω about an axis normal to the plane. The action of spin is to twist the area of contact. Surface tractions resulting from this rotation are found, which demonstrate the necessity of partial slip in the area of contact. Previous investigations suggest that this slip cannot occur at the leading edge of the contact circle, so that a system of tractions is found which corresponds to zero stress at the leading point. It is shown that such a system of tractions gives rise to a transverse creep of the sphere in the direction of its rotation Ω. The magnitude of this creep is calculated for small values of Ω, when slip occurs to only a small extent. Experiments have been performed using a simple thrust bearing with plane parallel races. As the bearing rotates, the balls creep radially outward in the predicted manner. Quantitative measurements of this creep agree with the theoretical estimate over a wide range.

Nozzle Geometry and Injection Duration Effects on Diesel Sprays Measured by X-Ray Radiography

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
A. L. Kastengren ◽  
C. F. Powell ◽  
T. Riedel ◽  
S.-K. Cheong ◽  
K.-S. Im ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Injection Pressure ◽  
Leading Edge ◽  
Nozzle Geometry ◽  
Diesel Sprays ◽  
X Ray ◽  
Injection Duration ◽  
Quantitative Measurements ◽  
Light Duty ◽  
Trailing Edges

X-ray radiography was used to measure the behavior of four fuel sprays from a light-duty common-rail diesel injector. The sprays were at 250bar injection pressure and 1bar ambient pressure. Injection durations of 400μs and 1000μs were tested, as were axial single-hole nozzles with hydroground and nonhydroground geometries. The X-ray data provide quantitative measurements of the internal mass distribution of the spray, including near the injector orifice. Such measurements are not possible with optical diagnostics. The 400μs sprays from the hydroground and nonhydroground nozzles appear qualitatively similar. The 1000μs spray from the nonhydroground nozzle has a relatively consistent moderate width, while that from the hydroground nozzle is quite wide before transitioning into a narrow jet. The positions of the leading- and trailing-edges of the spray have also been determined, as has the amount of fuel residing in a concentrated structure near the leading edge of the spray.

scholarly journals On the instability of hypersonic flow past a flat plate

1993 ◽  
Vol 247 ◽  
pp. 369-416 ◽  
Author(s):  
Nicholas D. Blackaby ◽  
Stephen J. Cowley ◽  
Philip Hall
Keyword(s):  
Boundary Layer ◽  
Growth Rate ◽  
Flat Plate ◽  
Leading Edge ◽  
Fluid Viscosity ◽  
Hypersonic Boundary Layer ◽  
Interaction Zone ◽  
Viscous Boundary Layer ◽  
Starting Point ◽  
Inviscid Instability

The instability of hypersonic boundary-layer flow over a flat plate is considered. The viscosity of the fluid is taken to be governed by Sutherland's formula, which gives a more accurate representation of the temperature dependence of fluid viscosity at hypersonic speeds than Chapman's approximate linear law. A Prandtl number of unity is assumed. Attention is focused on inviscid instability modes of viscous hypersonic boundary layers. One such mode, the ‘vorticity’ mode, is thought to be the fastest growing disturbance at high Mach numbers, M [Gt ] 1; in particular it is believed to have an asymptotically larger growth rate than any viscous instability. As a starting point we investigate the instability of the hypersonic boundary layer which exists far downstream from the leading edge of the plate. In this regime the shock that is attached to the leading edge of the plate plays no role, so that the basic boundary layer is non-interactive. It is shown that the vorticity mode of instability operates on a different lengthscale from that obtained if a Chapman viscosity law is assumed. In particular, we find that the growth rate predicted by a linear viscosity law overestimates the size of the growth rate by O((log M)½). Next, the development of the vorticity mode as the wavenumber decreases is described. It is shown, inter alia, that when the wavenumber is reduced to O(M-3/2) from the O(1) initial, ‘vorticity-mode’ scaling, ‘acoustic’ modes emerge.Finally, the inviscid instability of the boundary layer near the leading-edge interaction zone is discussed. Particular attention is focused on the strong-interaction zone which occurs sufficiently close to the leading edge. We find that the vorticity mode in this regime is again unstable. The fastest growing mode is centred in the adjustment layer at the edge of the boundary layer where the temperature changes from its large, O(M2). value in the viscous boundary layer, to its O(1) free-stream value. The existence of the shock indirectly, but significantly, influences the instability problem by modifying the basic flow structure in this layer.

Hydrogen Injection Into P-Type Silicon By Chemical Etching

1987 ◽  
Vol 104 ◽  
Author(s):  
A. J. Tavendale ◽  
A. A. Williams ◽  
S. J. Pearton
Keyword(s):  
Secondary Ion Mass Spectrometry ◽  
Schottky Diodes ◽  
Base Material ◽  
Effective Diffusivity ◽  
Near Surface ◽  
Quantitative Measurements ◽  
Chemical Etch ◽  
Injection Mechanism ◽  
P Type ◽  
Secondary Ion

ABSTRACTHydrogen injection with B acceptor neutralization in p-type Si etched in HNOs and HF acid mixtures has been confirmed by isotopic [D] substitution and secondary ion mass spectrometry [SIMS] profiling. Quantitative measurements of the near-surface Injected hydrogen were made following field-aided, in-bulk transport [H+ drift] in reverse-bias annealed Schottky diodes from etched, B-doped Si. Chemical-etch injection is found to be self limiting with neutralization observed over a depth which is characteristic of the base material acceptor concentration and in the range 6–8 extrinsic Debye lengths, indicating that holes are essential in the injection mechanism. An effective diffusivity for hydrogen in etched p-Si of ∼ 2 × 10−9 cm2 s−1 was measured [300 K], considerably higher than previously reported.

Surfactant Transport Over Airway Liquid Lining of Nonuniform Depth

1999 ◽  
Vol 122 (2) ◽  
pp. 159-165 ◽  
Author(s):  
H. A. R. Williams ◽  
O. E. Jensen
Keyword(s):  
Leading Edge ◽  
Airway Wall ◽  
Surfactant Replacement Therapy ◽  
Static Contact ◽  
Dimensional Approximation ◽  
Surfactant Transport ◽  
Wall Buckling ◽  
Thickness Variations ◽  
Spreading Rates ◽  
Lung Airways

Numerous effects (e.g., airway wall buckling, gravity, airway curvature, capillary instabilities) give rise to nonuniformities in the depth of the liquid lining of peripheral lung airways. The effects of such thickness variations on the unsteady spreading of a surfactant monolayer along an airway are explored theoretically here. Flow-induced film deformations are shown to have only a modest influence on spreading rates, motivating the use of a simplified model in which the liquid-lining depth is prescribed and the monolayer concentration satisfies a spatially inhomogeneous nonlinear diffusion equation. Two generic situations are considered: spreading along a continuous annular liquid lining of nonuniform depth, and spreading along a rivulet that wets the airway wall with zero contact angle. In both cases, transverse averaging at large times yields a one-dimensional approximation of axial spreading that is valid for the majority of the monolayer. However, a localized monolayer remains persistently two dimensional in a region at its leading edge having axial length scales comparable to the length scale of transverse depth variation. It is also shown how the transverse spreading of a monolayer may be arrested as it approaches a static contact line at the edge of a rivulet. Implications for Surfactant Replacement Therapy are discussed. [S0148-0731(00)00202-8]

scholarly journals On surfactant-enhanced spreading and superspreading of liquid drops on solid surfaces

2011 ◽  
Vol 670 ◽  
pp. 5-37 ◽  
Author(s):  
GEORGE KARAPETSAS ◽  
RICHARD V. CRASTER ◽  
OMAR K. MATAR
Keyword(s):  
Contact Line ◽  
Surfactant Concentration ◽  
Evolution Equations ◽  
Leading Edge ◽  
Chemical Kinetic ◽  
Droplet Radius ◽  
Liquid Drops ◽  
Air Interface ◽  
Experimental Values ◽  
Spreading Rates

The mechanisms driving the surfactant-enhanced spreading of droplets on the surface of solid substrates, and particularly those underlying the superspreading behaviour sometimes observed, are investigated theoretically. Lubrication theory for the droplet motion, together with advection–diffusion equations and chemical kinetic fluxes for the surfactant transport, leads to coupled evolution equations for the drop thickness, interfacial concentrations of surfactant monomers and bulk concentrations of monomers and micellar, or other, aggregates. The surfactant can be adsorbed on the substrate either directly from the bulk monomer concentrations or from the liquid–air interface through the contact line. An important feature of the spreading model developed here is the surfactant behaviour at the contact line; this is modelled using a constitutive relation, which is dependent on the local surfactant concentration. The evolution equations are solved numerically, using the finite-element method, and we present a thorough parametric analysis for cases of both insoluble and soluble surfactants with concentrations that can, in the latter case, exceed the critical micelle, or aggregate, concentration. The results show that basal adsorption of the surfactant plays a crucial role in the spreading process; the continuous removal of the surfactant that lies upon the liquid–air interface, due to the adsorption at the solid surface, is capable of inducing high Marangoni stresses, close to the droplet edge, driving very fast spreading. The droplet radius grows at a rate proportional to ta with a = 1 or even higher, which is close to the reported experimental values for superspreading. The spreading rates follow a non-monotonic variation with the initial surfactant concentration also in accordance with experimental observations. An accompanying feature is the formation of a rim at the leading edge of the droplet. In some cases, the drop spreads to form a ‘pancake’ or creates a ‘secondary’ front separated from the main droplet.

Evidence for Kupffer cell migration along liver sinusoids, from high-resolution in vivo microscopy

1992 ◽  
Vol 263 (1) ◽  
pp. G17-G23 ◽  
Author(s):  
P. J. MacPhee ◽  
E. E. Schmidt ◽  
A. C. Groom
Keyword(s):  
High Resolution ◽  
Kupffer Cells ◽  
Fluorescent Microspheres ◽  
Fixed Tissue ◽  
Liver Sinusoids ◽  
Quantitative Measurements ◽  
The Mean ◽  
Antigen Presenting

Kupffer cells are generally considered fixed tissue macrophages of the liver. However, we have evidence that this opinion is incorrect. High-resolution in vivo video microscopy shows that Kupffer cells have the ability to migrate along sinusoidal walls. Images recorded from anesthetized mice show active locomotion of cells with or against the direction of blood flow or in the absence of flow. The size, changing morphology, and uptake of carbon or microspheres strongly suggest that these are Kupffer cells. Quantitative measurements were made on 29 migrating Kupffer cells. The mean speed of migration was 4.6 +/- 2.6 (SD) microns/min and was not significantly different whether migration occurred with or against the flow. When fluorescent microspheres were given in vivo as a phagocytic challenge, Kupffer cells containing few microspheres migrated more slowly (0.9 +/- 0.9 microns/min, n = 10), whereas those containing many microspheres were never seen to migrate. Individual Kupffer cells were able to move independently, i.e., in directions different from those of neighboring Kupffer cells. These findings may have major implications for the role of Kupffer cells in scavenging foreign particles and as antigen-presenting cells.

The Fine Structure of Rat Granulosa Cell Cultures Correlated with Progestin Secretion

1973 ◽  
Vol 31 ◽  
pp. 552-553
Author(s):  
T. M. Crisp ◽  
F.R. Denys
Keyword(s):  
Fine Structure ◽  
Granulosa Cell ◽  
Cell Cultures ◽  
Single Injection ◽  
Surrounding Medium ◽  
Petri Dish ◽  
Female Rats ◽  
Vaginal Smear ◽  
Immature Female ◽  
Serum Gonadotropin

The purpose of this paper is to present observations on the fine structure of rat granulosa cell cultures grown in the presence of an adenohypophyseal explant and to correlate the morphology of these cells with progestin secretion. Twenty-six day old immature female rats were given a single injection of 5 IU pregnant mares serum gonadotropin (PMS) in order to obtain ovaries with large vesicular follicles. At 66 hrs. post-PMS administration (estrus indicated by vaginal smear cytology), the ovaries were removed and placed in a petri dish containing medium 199 and 100 U penicillin/streptomycin (P/S)/ml. Under a 20X magnification dissecting microscope, some 5-8 vesicular follicles/ovary were punctured and the granulosa cells were expressed into the surrounding medium. The cells were transferred to centrifuge tubes and spun down at 1000 rpm for 5 mins.

Quantitative Measurements on the Ion Etching of TMV

1973 ◽  
Vol 31 ◽  
pp. 336-337
Author(s):  
Irwin Bendet ◽  
Nabil Rizk
Keyword(s):  
Electron Microscope ◽  
Tobacco Mosaic Virus ◽  
Mosaic Virus ◽  
Ion Current ◽  
Beam Diameter ◽  
Ion Etching ◽  
Preliminary Results ◽  
Quantitative Measurements ◽  
Monitoring Devices

Preliminary results reported last year on the ion etching of tobacco mosaic virus indicated that the diameter of the virus decreased more rapidly at 10KV than at 5KV, perhaps reaching a constant value before disappearing completely.In order to follow the effects of ion etching on TMV more quantitatively we have designed and built a second apparatus (Fig. 1), which incorporates monitoring devices for measuring ion current and vacuum as well as accelerating voltage. In addition, the beam diameter has been increased to approximately 1 cm., so that ten electron microscope grids can be exposed to the beam simultaneously.

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