Laminar Flow Pattern Research Articles

Investigations of gas-flow patterns within a cylindrical glass tube having dimensions identical with those of a graphite furnace atomizer under the influence of forced convective flow

Gas-flow patterns within a cylindrical glass tube having the same dimensions as a typical graphite furnace atomizer were investigated by introducing two streams of argon gas seeded with a light-scattering medium of TiO2 particles into the open ends of the tube and viewing the scattering profiles of the particles. By placing a sample of iodine solution near the centre or ends of the cylindrical glass tube, further insight into gas-flow patterns is gained by examining the spatial distributions of the iodine vapour under the influence of convective flow. The TiO2 particle and iodine spatial profiles suggest that at room temperature the argon streams follow a laminar-flow pattern in the bulk-flow region between the ends of the cylindrical tube and the sample introduction hole; however, at the junction region where the two argon streams converge and discharge from the dosing hole, local turbulences or eddies may be generated owing to abrupt changes in gas-flow velocity and direction in the vicinity of an area (boundary layer) directly beneath the dosing hole.

Cellular flow in a rotating heat pipe with stepped wall

A laminar secondary flow pattern (cellular flow or hygrocysts) develops in a co-axial rotating heat pipe with a stepped condenser section. This flow pattern has heat transfer characteristics of its own. The interaction of the cellular flow in the evaporator and the annular flow in the condenser will strongly influence the heat transfer. Visualization experiments are conducted using a glass rotating heat pipe with stepped wall and systematic experiments are performed using a metallic heat pipe.

Strain analysis for extrusion of powder metals

A method is described for determining the strain distribution during axisymmetric extrusion of powder metals. Density variations in these materials are included in the analysis. The method examines these changes together with the laminar flow pattern to determine strain rates and, ultimately, strains.

Use of a Novel Type of Rotating Disc Electrode and a Flow Cell with Laminar Flow Pattern for the Electrochemical Detection of Biogenic Monoamines and Their Metabolites After Sephadex Gel Chromatographic Purification and High Performance Liquid Chromatographic Isolation from Rat Brain

A novel type of rotating disc electrode and a flow cell with laminar flow pattern were developed and applied to the electrochemical detection of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxytyramine (3-MT), noradrenaline, 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid after HPLC of these compounds. The active surface of the rotating disc working electrode was made from solid paraffin (40% wt/wt) and graphite powder (60% wt/wt). The sensitivity of the detector was proportional to the square root of the angular velocity and was practically independent of the flow rate of the mobile phase. The surface of the working electrode was very large (radius = 12 mm), and so the percentage of oxidation was 24-67% (flow rate = 1.0 ml/min), depending on the compound. Electrical noise between 20 and 40 pA and background current of 20-60 nA were observed. In practice, the sensitivity for the detection of the compounds examined here was 8-16 nA/ng, and so a detection limit of 5 pg/injection could be achieved, when the detector was combined with reversed-phase HPLC. Supernatants obtained from the extracts of the tissue samples (nine brain parts of rat brain were studied) were purified by using Sephadex G-10 gel chromatography. Before this procedure, the proteins of the tissue extracts were precipitated by 0.2 M HClO4, and the excess of HClO4 was precipitated by KOH/HCOOH buffer. Simultaneously, the pH of the extracts was set to 2.4 by the above buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficient hydrodynamic modulation voltammetry with a microcylinder electrode

Mlcrocyllnder electrodes afford several useful toatures when combined wlth hydrodymmk modulatkn vottanmetry (HMV). The small diameter of the vlbratlng mlcrocyllnder electrode results In a low Reynolds number even when the electrode Is vlbrated at relatively Mgh velocltles (13 cmls). The result Is a more laminar flow pattern of the solution around the electrode and an Instantaneous current that tracks the electrode velocity. Efflclent modulation may be carrled out at much higher frequencles than those prevlously employed In HMV, allowlng better discrimination against fkker nolse, faster voltammetrlc scan rates, and easler slgnal processing. Secondly, the modulatlon apparatus Is slmple due to the low mass of the electrode. Flnally, the amount of sample consumed is small, permlttlng the analyds of samples of small volume or low concentratbn. A detectlon Umlt of 3.0 X lo-' M was obtained for ferrocene In acetonhrlle, and excellent rejection of background current for a Pt electrode In aqueous solution was demonstrated. Hydrodynamic modulation voltammetry (HMV) has shown significant promise for trace analysis, because it significantly reduces interference from background processes normally encountered in electrochemical analysis. These background interferences include capacitive current, surface faradaic reactions, and redox reactions of the electrolyte and are particularly severe on solid electrodes. HMV exploits the fact that the analytical current for a solution species is mass transport controlled, whereas that for most of the background processes is not. The mass transport rate may be modulated by periodic motion of the electrode relative to the solution (or vice versa) to produce an alternating current that depends on freely diffusing analyte concentration, not on surface or electrolyte reactions. By demodulating the ac current at various applied potentials, a voltammogram that is specific

Temperature Histories in a UHT Indirect Heat Exchanger

An indirect UHT processing system was modeled by a computer program to predict the temperature profile of a mass element of fluid as it progressed through heating, hold and cooling units. The computer program consisted of successive calculations of the temperature at the exit of numerous increments in each unit based on the overall heat transfer coefficient determined for the total length of the unit. The validity of the computer program was determined by correlation of computer results with experimental determinations of sucrose inversion. The percentage of total inversion of sucrose occurring in the heater was 36%, indicating the error associated with the assumption of chemical reactions based exclusively on hold tube temperature, residence time and laminar flow pattern.

Radioactive flow detectors: Liquid or solid scintillator?

technique of fraction collection and consequent aliquot counting in a liquid scintillation counter1. This method, while inherently cumbersome, was acceptable since each chromatographic run was long (2-16 hours); resolution of the chromatogram was good, and the resolution volume allowed the collection of several fractions through each peak. Efforts to use the liquid scintillation counter as an on-line detector for liquid chromatography were never completely successful. The scintillators used in these early attempts were naphthalene or anthracene crystals packed in modified LSC vials with the liquid chromatography effluents fed through the packing, hopefully in a laminar flow pattern.

Pulsed Doppler velocity patterns produced by arterial anastomoses

Centerstream velocity waveforms produced by end-to-end and end-to-side anastomoses constructed in the dog illeofemoral arterial system were studied with a 20 MHz pulsed Doppler velocimeter combined with spectral analysis. Flow disturbance was identified by changes in spectral width during the systolic phase of the cardiac cycle. Measurement of the maximum frequency and the spectral width at peak systole was used to quantify the magnitude of flow disturbance at varying locations proximal and distal to the anastomoses. Disruption of the normal laminar flow pattern observed in the unoperated dog artery was evident distal to both anastomotic configurations. An increase in spectral width reflecting disturbed flow was maximal during the deceleration phase of systole. Flow disturbance was localized to a zone within one diameter distal to the anastomosis and dissipated rapidly downstream. The velocity spectrum changes observed downstream of an anastomosis resemble the flow disturbances produced by low grade, nonpressure reducing arterial stenoses. This study suggests that spectral analysis of pulsed Doppler waveforms is a potentially useful method of anastomosis assessment both to rule out major flow disruption produced by technical error, and to provide insight into the role of turbulence in the development of anastomotic intimal hyperplasia.

Computer simulation: A diagnostic method in comparative studies of valve prostheses

Computer simulation was used to compare flow characteristics through Starr-Edwards and Björk-Shiley valves in the mitral and aortic positions. Pressure and velocity determinations were mathematically computed with the use of a model based on the recognition that blood is a non-Newtonian fluid. The results were displayed in two-dimensional graphic form. In both the mitral and aortic positions the Björk-Shiley prosthesis showed a more favorable laminar flow pattern, producing fewer eddies and smaller pressure and velocity gradients through the occluder. Computer simulation is a valuable adjunct in the comparative testing of the hemodynamic properties of artificial heart valves and offers several advantages over physical simulators.

Thrombosis of the Björk-Shiley Aortic Valve Prosthesis

PROSTHETIC heart valve replacement has become routine surgical procedure in the treatment of advanced cases of valvular heart disease. One of the most popular prostheses in current use is the Björk-Shiley low-profile disk valve. The valve consists of a free-floating pyrolite disk contained in a polytefcovered alloy cage. The popularity of the valve stems from the ability of the disk to tilt in the direction of blood flow permitting a central, nearly laminar flow pattern that decreases turbulence and subsequent trauma to RBCs. Recent five-year follow-up data have demonstrated the durability of this valve and a low level of hemolysis.¹Although initial reports also suggested a low thrombogenic potential,²recent reports have described massive thrombosis of the valve, with fixation of the disk.^2-9 <h3>Report of Cases</h3><h3>Case 1.—</h3> A 79-year-old man underwent valve replacement for aortic stenosis receiving a No. 23 Björk-Shiley prosthetic valve in August 1974. After

The Hygrocyst–a Stability Phenomenon in Continuum Mechanics

CONSIDER a long sealed container partially filled with a liquid or completely filled with two immiscible liquids and oriented horizontally. If the container is rotated about a horizontal axis, a laminar secondary flow pattern develops that is characterized by large regular regions of segregated material. The onset of this new flow pattern appears to be the result of a natural instability in the normal flow, and is found to occur in containers of all geometries. The flow instability and the associated laminar secondary flow pattern discussed here are, to my knowledge, being reported and studied for the first time and do not appear anywhere in the published scientific literature. This might seem surprising at first in view of the apparent simplicity of the phenomenon, but when it is viewed in terms of its mathematics, with its difficult boundary conditions and unusual body force orientation, it becomes understandable why it would be unlikely that anyone could predict its existence from mathematical considerations alone. Further, it is rather difficult to demonstrate the instability by experiment with inelastic fluids.

Laminar flow pressure loss and flow pattern transition of Bingham plastics in pipes and annuli

Analytic and available experimental results have shown that the plastic Reynolds number and the Hedstrom number are two important parameters involved in the flow of Bingham plastics in pipes and annuli. These two parameters can be used to predict the flow pattern, and also serve as important factors in determining the pressure loss of the laminar flow system. In addition to the analytical results, a nomograph has been developed to facilitate the calculation of pressure loss.

Experiments on natural-convection heat transfer from the outer surface of a vertical cylinder to liquids

This paper describes the results of experimental investigations on natural-convection heat transfer from the outer surface of a vertical cylinder one metre high to water, spindle oil and Mobiltherm oil. The characteristics of the experiments are as follows. The experimental apparatus is contrived to enable us to measure local heat transfer coefficients directly; sufficiently long turbulent boundary layers are made to appear under various conditions of temperature and heat flux of the heated cylinder; correspondences of local heat transfer coefficients with flow patterns are clarified from the observations of the boundary layer by means of “mirage method” or other methods, and from the measurements of temperature profiles in it; the influence of Prandtl number upon heat transfer is found in its range from 2 to 2600. The boundary layer develops through laminar, vortex-street, transition-turbulent and turbulent flow pattern, and each flow pattern has respective characteristics of heat transfer. Vortex-street flow provokes abrupt increase of heat transfer coefficients in the transitional region from laminar to transition-turbulent. Especially with respect to water, no distinction was found between transition-turbulent and turbulent flow, and its cause is explained by an indeterminate character of the flow pattern in the transitional region. Local heat transfer coefficients are correlated nondimensionally about each flow region in the cases of uniform wall temperature and uniform heat flux. In each case, two kinds of experimental equations are proposed, respectively, by using the physical properties at a reference temperature and by using the supplementary terms referred to the variation of kinematic viscosity. Non-dimensional equations of average heat transfer coefficients are also proposed for the case of uniform wall temperature. Furthermore, some remarks on the ranges applicable to each equation are presented. The shapes of vortex-pairs, laminar sub-layers and turbulent lumps in the boundary layer as well as their development, are clearly taken in “mirage” photos. The transitions of flow patterns are also concretely described. Temperature fluctuations in the boundary layer are revealed and the time-mean temperature profiles are represented by a non-dimensional parameter. “Quasi-steady state” is defined experimentally as a state equivalent to a steady state with respect to heat transfer coefficients.

Microbiological studies of a laminar air flow unit for patients.

A laminar air flow (LAF) unit consisting of two patient rooms has been installed for patients’ undergoing cancer chemotherapy. Air circulated through the room in a horizontal laminar flow pattern after passing a bank of high efficiency filters. All necessary patient facilities were provided in the room. The rooms were cleaned with an organic tin compound prior to patient occupancy which reduced microbial contamination by 102 organisms. The concentration of organisms in air samples was 103 less in the LAF rooms than in regular hospital rooms. Nearly 80% of samples from floor sites, 86% from wall sites, and 88% from furnishings were sterile during patient occupancy.