Low Axial Flow Research Articles

Numerical Analysis of a Hydrodynamic Herringbone Grooved Journal Bearing

In hydrodynamic lubrication, at very high rotational speed, the phenomenon of axial fluid leakage is often present. This can involve an increase of shear stress in the contact and consequently a considerable increase of the temperature. For that and in order to solve this problem, we took interest in the herringbone grooved journal bearings. The researches made before on these types of groove bearing have shown that they present a good dynamical behavior with a low eccentricity and a low axial flow. In this paper, a numerical study of a herringbone journal bearing operating behavior, under laminar and isothermal regime, is presented. The theoretical model, based on the classical Reynolds equation, is used. In order to include the film rupture and reformation, the Reynolds equation is modified using a mass conservative algorithm. To understand the behavior of these herringbone grooved journal bearings well, numerical modeling, using finite element method, has been developed. Various geometrical shapes of the herringbone grooved journal bearings have been analyzed, allowing us to limit the fluid leakage problem, by working particularly on the contact form.

The influence of the tangential velocity of inner rotating wall on axial velocity profile of flow through vertical annular pipe with rotating inner surface

In the oil and gas industries, understanding the behaviour of a flow through an annulus gap in a vertical position, whose outer wall is stationary whilst the inner wall rotates, is a significantly important issue in drilling wells. The main emphasis is placed on experimental (using an available rig) and computational (employing CFD software) investigations into the effects of the rotation speed of the inner pipe on the axial velocity profiles. The measured axial velocity profiles, in the cases of low axial flow, show that the axial velocity is influenced by the rotation speed of the inner pipe in the region of almost 33% of the annulus near the inner pipe, and influenced inversely in the rest of the annulus. The position of the maximum axial velocity is shifted from the centre to be nearer the inner pipe, by increasing the rotation speed. However, in the case of higher flow, as the rotation speed increases, the axial velocity is reduced and the position of the maximum axial velocity is skewed towards the centre of the annulus. There is a reduction of the swirl velocity corresponding to the rise of the volumetric flow rate.

Osmotically driven flows in microchannels separated by a semipermeable membrane

We have fabricated lab-on-a-chip systems with microchannels separated by integrated membranes allowing for osmotically driven microflows. We have investigated these flows experimentally by studying the dynamics and structure of the front of a sugar solution travelling in 200 microm wide and 50-200 microm deep microchannels. We find that the sugar front travels at a constant speed, and that this speed is proportional to the concentration of the sugar solution and inversely proportional to the depth of the channel. We propose a theoretical model, which, in the limit of low axial flow resistance, predicts that the sugar front should indeed travel with a constant velocity. The model also predicts an inverse relationship between the depth of the channel and the speed, and a linear relation between the sugar concentration and the speed. We thus find good qualitative agreement between the experimental results and the predictions of the model. Our motivation for studying osmotically driven microflows is that they are believed to be responsible for the translocation of sugar in plants through the phloem sieve element cells. Also, we suggest that osmotic elements can act as on-chip integrated pumps with no movable parts in lab-on-a-chip systems.

Types, structure and potential for axial water flow in the deepest roots of field‐grown cereals

Deep root systems that extend into moist soil can significantly increase plant productivity. Here, the components of soil-grown root systems of wheat, barley and triticale are characterized, and types and water conducting potential of deep roots in the field are assessed. Root system components were characterized in plants grown in soil in PVC tubes, based on their origin and number and the arrangement of xylem tracheary elements (XTE) viewed using fluorescence microscopy. A new nomenclature is proposed. Deep roots were harvested in the field, and root types of the current crop and remnant roots from previous crops were identified by fluorescence and cryo-scanning electron microscopy. Four types of axile (framework) and five types of branch root were distinguished in the three cereals. Six per cent of deep roots were axile roots that originated from the base of the embryo; 94% were branch roots, of which 48% had only two XTE (10 microm diameter), and thus potentially low axial flow. Only 30% of roots in the cores were from the current crop, the remainder being remnants. Selection for more deep-penetrating axile roots and increased vascular capacity of deep branches is of potential benefit. Conventional root-length density measurements should be interpreted and applied cautiously.

Dispersion radiale et axiale dans les écoulements tourbillonnaires de Taylor–Couette et Poiseuille: Radial and axial dispersion in Taylor–Couette and Poiseuille vortex flows

Mass transport in Taylor–Couette and Poiseuille vortex flows has been experimentally investigated by dye injection, particle tracking and electrochemical techniques. An annular cavity has been built with an inner/outer radius ratio of 0.5, with a fixed outer cylinder and a rotating inner one. Without any axial flow, the standard Taylor–Couette flow was observed and the Sherwood number for radial dispersion measured. When a low axial flow rate was imposed ( Re a<10), a mechanism for axial dispersion similar to the dispersion of a wave packet was drawn from visualization results.

Perturbation analysis of the helical flow of non-Newtonian fluids with application to a recirculating coaxial cylinder rheometer

This paper analyzes the flow of non-Newtonian fluids between infinitely long coaxial cylinders, when the inner cylinder rotates with given angular velocity Ω, and a given axial flow rate, Q, is superimposed on this rotational motion. Such helical flow is of significance in the modelling of the action of a recirculating coaxial cylinder rheometer, where the axial flow is superimposed on the standard cup-and-bob rheometer to allow accurate rheological measurements involving fluids that are settling in nature. Such fluids are encountered in many mineral, food, and chemical processes of industrial significance. The analysis presented here applies the perturbation approach to analyze the above flows in two situations of physical interest: 1. the case of low axial flow rates; and 2. the case where the radial separation of the cylinders is small. In each case, the appropriate perturbation parameter is identified, and appropriate expressions for the velocity field are obtained for non-Newtonian fluids of interest. More significantly, this analysis allows the construction of approximate forms of the Reiner-Rivlin relation for this flow, which relates the angular velocity Ω to the observed torque, M, at the inner cylinder, through the rheological parameters defining the fluid. Subsequent measurement of Ω and M allows these parameters to be determined for a given fluid model. Where possible, the findings of the perturbation analysis are compared directly with experimental measurements involving a model of such a recirculating rheometer.

FLUID DYNAMICS IN A TUBULAR MEMBRANE: THEORY AND EXPERIMENT

Abstract Measurements of trans-cartridge [axial] pressure drops for pure liquid flowing in a porous tube under all regimes of flow as a function of wall suction and axial flow rate are reported. At very low axial flow rates [ReF 1,000], low values of wall suction [ReW 0.25] have a minimal effect on the non-dimensional axial pressure drop. At very high axial flow rates [ReF20,000], however, all values of wall suction have a minimal effect on the axial pressure drop, Wall suction, on the other hand, has its maximum effect on the axial pressure drop at intermediate axial flow rates [1,000 ReF15,000]. It is in this range that most commercial membrane modules operate. Starting with the equations of continuity and Navier-Stokes we have developed two relatively simple approximate analytical solutions of this problem. The first approach assumes an average constant wall flux and includes the effect of the inertial terms while the second approach accounts for axial pressure-dependent flux but neglects the inert...

Analysis of a rotating annular reactor in the vortex flow regime

A theoretical analysis of a vortex flow reactor is presented. Consecutive (first order) reactions taking place on the inner rotating surface are considered. The concentration profiles of the various species, conversions and yields are obtained along the reactor for low axial flow rates, corresponding to high residence times. The induced vortical flow, obtained due to an imposed rotation imparted on an axial annular flow, is utilized to improve the conversion and yield of diffusion controlled (fast) reactions. Comparison of the performance of the vortex flow reactor with that operated without rotation, utilizing only laminar axial flow, indicates enhanced conversions and yields due to the axially convected vortices through the reaction chamber. The extent of the augmented mass transfer has been explored by the corresponding mass transfer coefficients correlated with rotation.

Intermixing over cell boundary between taylor vortices

AbstractThe rate of exchange of fluid elements between Taylor vortices was experimentally determined for low axial flow rates. A model was formulated defining the exchange coefficient appropriate for this flow system. In the laminar vortex flow region, the measured exchange coefficient increases with Re but is almost independent of Ta.

A Study of Fully-Developed, Laminar, Axial Flow and Taylor Vortex Flow by Means of Shear Stress Measurements

The results of a shear stress investigation for combined axial and rotational flow, under conditions of both laminar flow and laminar flow plus Taylor vortices, are presented. These results show that two distinct régimes of shear stress dependency exist. In the primary régime, the shear stress is constant and depends only on the imposed axial flow, the flow being either laminar (Poiseuille and Couette flows) or laminar with vortices, but with the effect of the vortices being negligible. In the secondary régime, the shear stress is shown to depend only on Ta0.735, irrespective of the imposed axial flow. At low axial flow rates, a tertiary régime was observed, but no satisfactory explanation can be found for this phenomenon. The demarcation between the primary and secondary flow régimes differs markedly from those of other investigators. In the present study, critical conditions are determined by the point at which vortices begin to have an effect on measurements taken at the outer annular wall rather than the conditions under which vortices are initially formed. Evidence is presented for the vortices being formed within a confined layer near to the inner cylinder and thereafter growing with increasing rotational speed until the outer annular wall is approached, resulting in the much higher critical conditions found in the present study.