Local pressure gradients due to incipience of boiling in subcooled flows

1995 ◽  
Author(s):  
A E Ruggles ◽  
J L McDuffee
Keyword(s):  
Pressure Gradients ◽  
Local Pressure ◽  
Subcooled Flows

An Experiment on Compressible-Flow Perturbations

1959 ◽  
Vol 26 (1) ◽  
pp. 114-119
Author(s):  
T. A. d’Ews Thomson ◽  
R. E. Meyer
Keyword(s):  
Perturbation Theory ◽  
Order Theory ◽  
Linear Perturbation ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Supersonic Wind Tunnel ◽  
First Order ◽  
First Order Theory ◽  
Mach Number Distribution ◽  
Linear Perturbation Theory

Abstract The effect which a slight tilting of the liners of a supersonic wind-tunnel nozzle has on the Mach-number distribution in the test-rhombus is determined on the basis of the linear-perturbation theory of reference [1]. Experiments are reported which (a) confirm that the first-order subsonic and transonic perturbations of the flow may be neglected compared with the supersonic perturbations, and (b) indicate that appreciable effects not accounted for by the first-order theory occur when the flow possesses high local pressure gradients.

Autogenous Suction to Prevent Laminar Boundary-Layer Separation

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Hediye Atik ◽  
Leon van Dommelen
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Laminar Flows ◽  
Computational Techniques ◽  
Pressure Gradients ◽  
Practical Application ◽  
Theoretical Limit ◽  
Local Pressure ◽  
Layer Separation ◽  
Straightforward Application

Boundary-layer separation can be prevented or delayed by sucking part of the boundary layer into the surface, but in a straightforward application the required hydraulics entail significant penalties in terms of weight and cost. By means of computational techniques, this paper explores the possibility of autogenous suction, in which the local pressure differences that lead to separation drive the suction used to prevent it. The chosen examples include steady and unsteady laminar flows around leading edges of thin airfoils. No fundamental theoretical limit to autogenous suction was found in the range of angles of attack that could be studied, but rapidly increasing suction volumes suggest that practical application will become increasingly difficult for more severe adverse pressure gradients.

scholarly journals Sample dispersion in isotachophoresis

2011 ◽  
Vol 679 ◽  
pp. 455-475 ◽  
Author(s):  
G. GARCIA-SCHWARZ ◽  
M. BERCOVICI ◽  
L. A. MARSHALL ◽  
J. G. SANTIAGO
Keyword(s):  
Analytical Model ◽  
Concentration Field ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Sample Distribution ◽  
One Dimensional ◽  
Effective Dispersion ◽  
Detector Placement ◽  
Electro Osmotic Flow ◽  
Sample Dispersion

We present an analytical, numerical and experimental study of advective dispersion in isotachophoresis (ITP). We analyse the dynamics of the concentration field of a focused analyte in peak mode ITP. The analyte distribution is subject to electromigration, diffusion and advective dispersion. Advective dispersion results from strong internal pressure gradients caused by non-uniform electro-osmotic flow (EOF). Analyte dispersion strongly affects the sensitivity and resolution of ITP-based assays. We perform axisymmetric time-dependent numerical simulations of fluid flow, diffusion and electromigration. We find that analyte properties contribute greatly to dispersion in ITP. Analytes with mobility values near those of the trailing (TE) or leading electrolyte (LE) show greater penetration into the TE or LE, respectively. Local pressure gradients in the TE and LE then locally disperse these zones of analyte penetration. Based on these observations, we develop a one-dimensional analytical model of the focused sample zone. We treat the LE, TE and LE–TE interface regions separately and, in each, assume a local Taylor–Aris-type effective dispersion coefficient. We also performed well-controlled experiments in circular capillaries, which we use to validate our simulations and analytical model. Our model allows for fast and accurate prediction of the area-averaged sample distribution based on known parameters including species mobilities, EO mobility, applied current density and channel dimensions. This model elucidates the fundamental mechanisms underlying analyte advective dispersion in ITP and can be used to optimize detector placement in detection-based assays.

Dependence of edge stability on plasma shape and local pressure gradients in the DIII-D and JT-60U tokamaks

2001 ◽  
Vol 41 (3) ◽  
pp. 295-300 ◽  
Author(s):  
L.L Lao ◽  
Y Kamada ◽  
T Oikawa ◽  
L.R Baylor ◽  
K.H Burrell ◽  
...  
Keyword(s):  
Pressure Gradients ◽  
Local Pressure ◽  
Edge Stability

Measurements of the Effects of Pressure-Gradient History on Separation-Bubble Transition

2001 ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Separation Bubble ◽  
Leading Edge ◽  
Transition Process ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Test Plate ◽  
Transition Prediction ◽  
Current Transition

In many boundary-layer situations, particularly in turbomachinery, separation-bubble transition occurs at a local pressure gradient that differs significantly from the values further upstream. Additionally, this upstream history changes substantially from case to case, with the transitioning separation bubble occurring at streamwise positions along the blade chord varying from close vicinity of the leading edge to mid-chord. In the case of low free-stream disturbances, development of instability waves prior to separation would clearly vary as a result of these differences in the history of the boundary layer prior to separation. Measurements are presented to document the effects of pressure gradients that a laminar boundary layer experiences prior to separation on the transition process that follows in the separated region. The boundary layer development was measured on a smooth, flat plate upon which streamwise pressure gradients were imposed by a flexible, contoured wall opposite to the test plate. Only low freestream-turbulence levels were considered to isolate the effects of pressure-gradient history on the transition process. Two Reynolds numbers were considered for each pressure-gradient setting. Measured quantities consisted of velocity and turbulence intensity obtained with a single hot-wire, and of surface pressures. Observed variations in transition onset location with changes in pressure-gradient history provide the basis for further development of current transition prediction schemes.

Direct measurements of skin friction in a turbulent boundary layer with a strong adverse pressure gradient

1980 ◽  
Vol 101 (1) ◽  
pp. 79-95 ◽  
Author(s):  
D. Frei ◽  
H. Thomann
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Skin Friction ◽  
Circular Cross Section ◽  
Adverse Pressure Gradient ◽  
Small Element ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Friction Forces

This paper describes a new balance, suitable for direct measurement of skin friction in turbulent boundary layers with severe pressure gradients. The gaps between the floating element and the surrounding wall are filled with a liquid in order to eliminate disturbing pressure forces on the element. The resulting friction forces are measured with piezo-electric transducers with high sensitivity and extremely small element displacement.Skin friction measurements were taken in the turbulent boundary layer of a wind tunnel with circular cross-section at M [les ] 0·25. Severe adverse pressure gradients were generated by means of a step on the wall or, alternatively, by a conical centre body.The new apparatus was mainly used to investigate the error of Preston tubes in adverse pressure gradients. It was necessary to develop a new measuring technique to improve the repeatability of the Preston tube readings.The Preston tube error was found to depend on both the local pressure gradient P = (dp/dx) ν/ρ3τ and on the Preston tube diameter uτd/ν and to be independent of the upstream pressure distribution for the range of parameters covered by the experiments.

Transport in lymphatic capillaries. II. Microscopic velocity measurement with fluorescence photobleaching

1996 ◽  
Vol 270 (1) ◽  
pp. H330-H337 ◽  
Author(s):  
D. A. Berk ◽  
M. A. Swartz ◽  
A. J. Leu ◽  
R. K. Jain
Keyword(s):  
Flow Velocity ◽  
Fluorescein Isothiocyanate ◽  
Intradermal Injection ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Mean Velocity ◽  
Lymphatic Capillary ◽  
Temporal Decay ◽  
Velocity Magnitude ◽  
Fluorescein Isothiocyanate Dextran

Despite its relevance to the physiology of lymph formation and propulsion, the instantaneous flow velocity in single lymphatic capillaries has not been measured to date. The method of fluorescence recovery after photobleaching (FRAP) was adapted for this purpose and used to characterize flow in the lymphatic capillaries in tail skin of anesthetized mice during a constant-pressure intradermal injection of fluorescein isothiocyanate-dextran (mol wt 2 x 10(6). The median lymph flow velocity was 4.7 microns/s, and the velocity magnitude ranged from 0 to 29 microns/s. The direction of flow was generally proximal, but stasis and backflow toward the site of injection was also detected. Evidence for oscillatory flow was detected in some FRAP experiments, and in separate experiments a periodicity of approximately 120 min-1, directly correlated to respiration frequency, was measured by tracking the motion of fluorescent latex microspheres (1 micron diam) introduced into the lymphatic capillary network. The velocity magnitude showed a correlation with duration of infusion but not with distance from injection site. It is speculated that the temporal decay of mean velocity magnitude could be related to the relaxation of local pressure gradients as partially collapsed vessels expand during the infusion.

Transport in lymphatic capillaries. I. Macroscopic measurements using residence time distribution theory

1996 ◽  
Vol 270 (1) ◽  
pp. H324-H329 ◽  
Author(s):  
M. A. Swartz ◽  
D. A. Berk ◽  
R. K. Jain
Keyword(s):  
Particle Size ◽  
Residence Time ◽  
Uptake Rate ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Injection Pressure ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Lymphatic Uptake ◽  
Lymphatic Network

We present a novel integrative method for characterizing transport in the lymphatic capillaries in the tail of the anesthetized mouse, which is both sensitive and reproducible for quantifying uptake and flow. Interstitially injected, fluorescently labeled macromolecules were used to visualize and quantify these processes. Residence time distribution (RTD) theory was employed to measure net flow velocity in the lymphatic network as well as to provide a relative measure of lymphatic uptake of macromolecules from the interstitium. The effects of particle size and injection pressure were determined. The uptake rate was found to be independent of particle size in the range of a 6- to 18-nm radius; beyond this size, the interstitial matrix seemed to pose a greater barrier. A comparison of 10 vs. 40 cmH2O injection pressure showed a significant influence on the relative uptake rate but not on the net velocity within the network (3.3 +/- 0.8 vs. 3.8 +/- 1.0 micron/s). This suggested the presence of a systemic driving force for baseline lymph propulsion that is independent of the local pressure gradients driving the uptake. This model can be used to examine various aspects of transport physiology of the initial lymphatics.

Pressure gradient induced generation of microbubbles

2015 ◽  
Vol 778 ◽  
pp. 653-668 ◽  
Author(s):  
A. Evangelio ◽  
F. Campo-Cortés ◽  
J. M. Gordillo
Keyword(s):  
Pressure Gradient ◽  
Flow Rate ◽  
Rate Ratio ◽  
Bubble Formation ◽  
Reynolds Numbers ◽  
Flow Rate Ratio ◽  
Physical Situation ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Physical Description

We provide a detailed physical description of the bubble formation processes taking place in a type of flow where the liquid pressure gradient can be straightforwardly controlled. The analysis, which is supported by an exhaustive experimental study in which the liquid viscosity is varied by three orders of magnitude, provides closed expressions for both the bubbling frequencies and the bubble diameters. Different equations are obtained depending on the values of the three dimensionless parameters characterizing this physical situation, namely the Weber and Reynolds numbers and the gas to liquid flow rate ratio. Since both the inertia dominated and viscous dominated bubbling regimes are simply described in terms of the local pressure gradient and the flow rate ratio, the same types of ideas can be applied in the design of bubble makers in which the pressure gradients are controlled in completely different ways.

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