Effect Of Flow Reversal Research Articles

Examining the Effect of Flow Reversal on Seven-Hole Probe Measurements

Multihole pressure probes are frequently used to gather e ow data, sometimes in highly three-dimensional e ow. If the e ow is reversed, no method currently exists for determining whether the multihole probe is facing the right direction for data acquisition, and that the e ow is as such. A seven-hole probe is rotated in yaw by 360 deg, and rules are formulated to determine if a seven-hole probe is in a reversed e ow. The current study allows seven-hole probes to be used for gathering data in steady reversed e ows and gives an indication whether a pressure probe is insufe cient for the measurement instrument, as in the case of highly recirculating unsteady turbulent e ows. An application of the technique thus developed is also given.

Local mass-transfer distribution in the channels of a serpentine flow baffled parallel plate cell

Mass-transfer measurements were made in a parallel plate cell equipped with baffles which produced a three-channel serpentine flow pattern and three-dimensional mass-transfer distribution effects. The entry and exit configurations were in the form of slots of rectangular cross-section. Local mass-transfer coefficient values obtained in the different channels, using surface-flush microelectrodes, reflected the complex hydrodynamics associated with phenomena such as the cell inlet and exit effects, the flow reversal effects at the baffles and preferential flow phenomena in the channels. Mass-transfer measurements obtained by averaging point measurements over various zones of the cell compared favourably with those of other workers. A hydrodynamic model of flow in the cell corresponded well to the measured mass-transfer distribution.

Impact of E × B drifts on impurity distribution in the scrape-off layer of a tokamak

As shown in recent years, a strong electrostatic field exists in the tokamak Scrape-Off-Layer (SOL) and divertor zone. In the present paper it is demonstrated that the E×B drifts resulting from it, compete with the impurity velocities caused by friction with the main ions, as well as with thermal forces. This effect can redistribute impurity flows significantly. Particularly, it may lead to impurity flow reversal. Fluid equations for the test impurities are derived using the two most representative ionization states model. As shown to first approximation, impurity motion does not depend on the ionization state. For a favorable magnetic-field direction, when the ion ∇B drift is directed towards the X-point, in the private region the impurities flow from the outer to the inner divertor plate. On the contrary, in the SOL the impurity flow is directed from the inner to the outer plate. Significant impurity velocity shear exists near the separatrix, and creates the effect of flow reversal. Diffusion across the flux surfaces transports impurities flowing away from the divertor plates to regions with the opposite flow direction. A reduced visual model is presented.

FLUX ENHANCEMENT USING FLOW REVERSAL IN ULTRAFILTRATION

ABSTRACT The effect of flow reversal on permeate flux in cross-flow ultrafiltration of bovine serum albumin (BSA) has been investigated experimentally. BSA is a well-studied model solute in membrane filtration known for its fouling and concentration polarization capabilities. Ultrafiltration experiments were performed with BSA feed solutions in a hollow-fiber membrane module. The BSA feed concentrations ranged from 0.01 to 5 wt% and were ultrafiltered at a transmembrane pressure of 20 psia. Permeate flux was determined both with and without the use of flow reversal for each concentration. The experimental results indicate that under flow reversal conditions, the permeate flux is enhanced significantly when compared with runs without flow reversal. The effect of flow reversal on flux enhancement is very pronounced for dilute BSA solutions.

The effect of flow reversal on solids suspension in agitated vessels

AbstractFlow patterns in agitated vessels are influenced by geometry, particularly impeller diameter and impeller off‐bottom clearance. Large impellers and/or high off‐bottom clearances lead to reversed flow in which the flow at the base of the vessel is radially‐inward as opposed to radially‐outward as expected with axial‐flow impellers. Reversed flow is detrimental in solids suspension agitation because inordinately high torque and power are required to achieve suspension. This work experimentally characterizes the effect of flow reversal on solids suspension performance, including guidelines for avoiding flow reversal with straight‐blade turbines, pitched‐blade turbines, and high‐efficiency impellers.

Modelling of Contaminated Land Reclamation

A solution for the hydrodynamic clean up of contaminated land with flow reversal has been developed using analytical and numerical methods. This paper presents the results of physical modelling of the clean up process and compares the data with the theoretical predictions. A series of one dimensional laboratory tests are described in which clean water was flushed through a site initially contaminated with sodium chloride. The effects of flow reversal and soil permeability on the clean up process are investigated. A centrifuge test of hydrodynamic clean up using flow reversal is also described. Prototype stress and permeability conditions are modelled enabling the simulation of the clean up of a large scale homogeneous site. The theorectical models produced fairly accurate predictions of the varying contaminant concentrations in the model tests.

The Effect of Flow Reversal on Impurity Behaviour in Tokamaks

AbstractResults are reported for a study of impurity edge transport and core contamination in the presence of flow reversal of the DT plasma, using 2‐D plasma solutions for the ITER CDA configuration produced by the B2 fluid code, coupled to the EIRENE Monte Carlo neutral hydrogenic code and the DIVIMP Monte Carlo impurity neutral/ion code. The effect of different types of impurity source is considered, including (a) target sputtering, (b) wall sputtering, artificial injection (for radiative cooling), and core helium production.

FLOW REVERSAL THROUGH A MARK III HALOTHANE VAPORIZER

A fault in the assembly of a Matrix Large Animal Circle anaesthetic machine resulted in reversal of fresh gas flow through the vaporizer. The fault was discovered only after the sudden development of excessive depth of anaesthesia in two equine patients. Laboratory investigations were conducted to determine the effect of flow reversal on vaporizer output. Results indicated that output concentration was approximately doubled under these conditions.

Analysis of the impurity flow reversal experiment

Experiments performed on the Impurity Study Experiment (ISX-A) tokamak have shown that poloidally asymmetric injection of hydrogen gas can alter the inward transport of injected impurity atoms. The observed transport times and the magnitude of the flow reversal effect have been compared with a model based on the neoclassical theory of impurity transport; the observations are found to be consistent with theory. The diffusion coefficient is between once and twice neoclassical. Uncertainties in the radial profiles do not, however, permit a truly definitive test of the theory.

Pressure Distributions Around Circular Cylinders in Oscillating Flow

Oscillatory motion of a circular cylinder is studied from the viewpoint of the average pressure distribution on the cylinder. Effects of Reynolds number up to 40,000, period, and Keulegan and Carpenter number on the pressure distribution are examined. Results are explained in terms of vortex shedding and its relationship to period and Keulegan-Carpenter number. The effects of flow reversal, sweeping wake vortices back over the cylinder, are discussed.

Experimental and theoretical aspects of the two-roll mill problem

Experiments are described in which two cylinders of the same radii-rotate with identical speeds in a bath of Newtonian or non-Newtonian liquid. The torque on one of the cylinders is measured as a function of rotational speed for various values of the cylinder separation and the flow patterns are observed by a dye-injection technique. The observed experimental results for a Newtonian liquid correlate well with the theoretical predictions but a similar correlation in the case of elastic liquids is made difficult by the strongly three-dimensional nature of the flow in this case and the difficulty in estimating the amount of liquid passing through the rollers. The possibility of flow reversal effects due to the high Trouton ratios in the case of the elastic liquids is investigated both experimentally and theoretically.

“Directional” membrane permeability in polymer–vapor systems

AbstractA theoretical study is presented of the dependence of the vapor permeability of suitable nonhomogeneous polymer membranes on the sense of flow This is based on a simple model of a binary membrane in which the component phases A, B are either intimately mixed, with the composition of the mixture varying continuously across the membrane, or formed into a laminate AB. The influence of various parameters (which represent either properties of the component phases or the experimental conditions) on the magnitude of these flow reversal effects has been investigated. The results have proved useful as an indication of the capability of such membrane valves and of the conditions for optimum performance, as well as for the understanding of the behavior of experimental systems.

Flow reversal effects in a simple laminated membrance diffusion system

AbstractThe dependence of the magnitude of the permeation flux on the sense of flow is studied in the case of a simple membrane laminate AB. The permeability of phase A is assumed to change from a low value at low permeant activity to a higher one at high permeant activity, whereas the permeability of phase B is constant. The results of the analysis of this simple system provide considerable insight into the factors influencing flow reversal effects in binary laminated membranes in general. The conditions under which marked effects of this kind are possible have been established.

Gas mixing during inspiration.

Gas mixing during inspiration.

On Brenner's flow reversal theorem

The effects of flow reversal are studied in a system of interconnected tanks containing sources and sinks for a reacting solute. Under certain conditions the total rate of mass transfer does not change when every flow in the system is reversed in direction without changing its magnitude. Some but not all results are discrete versions of the flow reversal theorem obtained by Brenner [1,2] in the study of infinitely extended distributed systems. New results are discussed pertaining to flow reversal in finitely extended distributed systems and systems containing adsorbing boundaries.