Showing papers on "Pressure drop published in 1985"

hydrodynamic parameters for gas-liquid cocurrent flow in packed beds

Abstract: The hydrodynamics of cocurrent gas-liquid flow in packed beds is analyzed by extending the concept of relative permeability to the inertial regime. The relative permeabilities of the gas and liquid phases are functions of the saturation of the liquid phase. These functions are found from an analysis of experimental data. The relations obtained are used to develop empirical correlations for predicting liquid holdup and pressure drop in gas-liquid cocurrent downflow in packed beds over a wide range of operating conditions. The correlations proposed give very good results when compared to experimental data yielding, in general, mean relative deviations lower than existing correlations. In addition, a new equation is proposed for predicting static holdup in packed beds which is based on a more physically realistic characteristic length than that used in previous studies.

Interfacial drag and film height for vertical annular flow

Abstract: New measurements are presented for film height and pressure drop for vertical gas-liquid annular flows. Improved methods for predicting the film height and interfacial friction factor are developed for situations in which the liquid film flow rate is known.

Cyclone Collection Efficiency: Comparison of Experimental Results with Theoretical Predictions

Abstract: This paper describes the results of tests conducted on a Stairmand high-efficiency cyclone. The cyclone was pilot-plant scale with a design air flow of 0.139 m3/s (300 cfm). Collection efficiency and pressure drop were measured over a range of air flows at ambient temperature and pressure. An oil mist was used as a test aerosol because it consisted of spherical drops of uniform density unlikely to bounce or reentrain after striking the cyclone wall. At each air flow, a fractional efficiency curve (collection efficiency versus particle diameter) was determined. Experimental curves were compared with fractional efficiency curves generated by several cyclone efficiency theories. Over the range of particle sizes measured (1 to 7 μm), the predictions of a modified version of Barth's theory and the Leith-Licht theory were closest to experimental results.

Pressure Drop Correlations for Inclined Two-Phase Flow

Abstract: Presentation de correlations pour la perte de charge de differents types d'ecoulements diphasiques dans une conduite inclinee

Pulsating flow in a pipe

Abstract: Turbulent and laminar pulsating flows in a straight smooth pipe are compared at identical frequencies and Reynolds numbers. Most measurements were made at a mean Reynolds number of 4000, but the influence of Re was checked for 2900 < Re < 7500. The period of forcing ranged from 0.5 to 5 s, with corresponding change in the non-dimensional frequency parameter α = R √(ω/ν) from 4.5 to 15. The amplitude of the imposed oscillations did not exceed 35% of the mean in order to avoid flow reversal or relaminarization. Velocities at the exit plane of the pipe and pressure drop along the pipe were measured simultaneously; velocity measurements were made with arrays of normal hot wires. The introduction of the periodic surging had no significant effect on the time-averaged quantities, regardless of the flow regime (i.e. in both laminar and turbulent flows). The time-dependent components at the forcing frequency, represented by a radial distribution of amplitudes and phases, are qualitatively different in laminar and turbulent flows. The ensemble-averaged turbulent quantities may also be represented by an amplitude and a phase; however, the non-harmonic content of these intensities increases with increasing amplitude of the imposed oscillations. A normalization procedure is proposed which relates phase-locked turbulent flow parameters in unsteady flow to similar time-averaged quantities. An integral momentum equation in a time-dependent flow requires that a triad of forces (pressure, inertia and shear) will be in equilibrium at any instant of time. All the terms in the force-balance equation were measured independently, providing a good check of data. The analysis of the experimental results suggests that turbulence adjusts rather slowly to the local mean-flow conditions. A simple eddy-viscosity model described by a complex function can account for ‘memory’ of turbulence and explain the different phase distribution in laminar and turbulent flows.

The resistance of the trabecular meshwork to aqueous humor outflow

Abstract: A theoretical model is presented that is able to explain for the first time the pressure drop across the trabecular meshwork. The ramified flow paths in the subendothelial region of the trabecular meshwork can be interpretated as a filter bed. Data from transmission electron microscope (TEM) photographs are the starting point of the theoretical consideration. Taking shrinkage of the sections into account, the pressure gradient across the subendothelial region amounts to 0.05 mm Hg. As these canaliculi are coated by a film of glycosaminoglycans (GAGs), the pressure drop is presumably a function of the film thickness. Only film thicknesses of 0.35 μm lead to pressure gradients in the experimentally verified magnitude. As the whole filter bed probably does not contribute to the filtration but only about 10%, the pressure drop specified is reached when the GAG coating is 0.25 μm. As these values seem to be fairly realistic, it can be concluded that the subendothelial region of the juxtacanalicular meshwork (about 2 μm thickness) can be regarded as the “locus generis” of aqueous humor outflow resistance.

Measurements of rotating bubble shapes in a low-gravity environment

Abstract: Measurements of rotating equilibrium bubble shapes in the low-gravity environment of a free-falling aircraft are presented. Emphasis is placed on bubbles which intersect the container boundaries. These data are compared with theoretical profiles derived from Laplace's formula and are in good agreement with the measurements. The interface shape depends on the contact angle, the radius of intersection with the container, and the parameter F, which is a measure of the relative importance of centrifugal force to surface tension. For isolated bubbles F has a maximum value of 1/2. A further increase in F causes the bubble to break contact with the axis of rotation. For large values of F the bubble becomes more cylindrical and the capillary rise occurs over a thinner layer in order that the small radius of curvature can generate a sufficient pressure drop to account for the increased hydrostatic contribution.

Measurement of Width and Pressure in a Propagating Hydraulic Fracture

Abstract: Measurements of width and pressure in a propagating hydraulic fracture have been made in tests conducted at the U.S. DOE's Nevada test site. This was accomplished by creating an ''instrumented fracture'' at a tunnel complex (at a depth of 1,400 ft (425 m)) where realistic insitu conditions prevail, particularly with respect to stress and geologic features such as natural fractures and material anisotropy. Analyses of these data show that the pressure drop along the fracture length is much larger than predicted by viscous theory, which currently is used in models. This apparently is caused by the tortuosity of the fracture path, multiple fracture strands, roughness, and sharp turns (corners) in the flow path resulting from natural fractures and rock property variations. It suggests that fracture design models need to be updated to include a more realistic friction factor so that fracture lengths are not overestimated.

Dynamics of an expanding fluid-filled crack

Abstract: The dike intrusion mechanism proposed recently by B. R. Julian and his colleagues for several large earthquakes at Long Valley caldera has stimulated new interest in the mechanics of fluid injection. This study is an attempt to resolve some of the questions raised by this interpretation by numerically simulating the dynamics of a propagating fluid-filled crack. The computations are based on the two-dimensional finite difference method applied by Aki and coworkers to a similar problem of a fluid-driven crack. We extend this earlier study by improving the boundary conditions applied in the plane of the crack and by analyzing a crack containing a viscous fluid that supports acoustic wave propagation. The problem has two time scales: the duration of the rupture, which is proportional to the distance the crack propagates, and the period of the acoustic resonance of the fluid, which is a function of the length of the crack and the acoustic velocity in the fluid. For a small extension of a long crack containing a fluid of low bulk modulus, these time scales are markedly different. The initial motion of the walls near the propagating crack tip is directed outward, so the radiated first motion is compressive everywhere. The increase of the crack tip volume, however, induces a pressure drop in the fluid which propagates over the length of the crack with the velocity of the acoustic wave, causing a partial collapse of the wall radiated as a long-period dilatation. The dilatation following the short compressional first arrival is well marked in the vicinity of the crack plane, and for a buried vertical crack it is a conspicuous feature of the near-field vertical ground motion close to the crack trace. These properties of the signal suggest that first motion studies of this frequency-dependent source may be delicate without broadband instruments. Inhomogeneous waves propagating at the liquid-solid interface produce high-frequency vibrations which are observed only in the immediate vicinity of the crack. The source duration depends strongly on the fluid viscosity and associated viscous damping at the crack wall; damping of the motion by the radiation of elastic waves is a comparatively small effect.

Drop sizes in annular two-phase flow

Abstract: Drop sizes in annular flow have been measured using a diffraction technique. Several series of experiments were carried out to determine the effect of gas velocity, drop concentration, film flow rate and tube diameter on drop size. Film flow rate and tube diameter have been found to have very little influence on the sizes of drops produced. An empirical equation which describes the drop sizes is presented.

Performance of a TSI aerodynamic particle sizer

Abstract: Calibration curves of the aerodynamic particle sizer (APS) under different sets of operating conditions (i.e., pressure drop across the nozzle, flow rate, and ambient pressure) were obtained. Materials used included oleic acid (OA), dioctyl phthalate (DOP), polystyrene latex (PSL), and fused aluminosilicate particles (FAP). The effect of particle density on the calibration was not found to be significant among test aerosols (in the density range from 0.89 to 2.3 g/cm3). Calibration curves obtained at reduced ambient pressure were different from the manufacturer's curve, indicating that recalibration of the APS is required if other than standard operating conditions are used. However, all the curves can be consolidated into a unique curve that relates the Stokes number at the nozzle exit to the normalized particle velocity (particle velocity divided by gas velocity). Methods for calculating gas velocity, particle velocity, and other pertinent parameters for the APS were developed and the results are presen...

Turbulent boundary layer perturbed by a screen

Abstract: A detailed experimental investigation has been carried out on the effects of different types of screens on turbulent flow, in particular turbulent boundary layers. The boundary-layer turbulence is reorganized and the thickness reduced, thus making it less susceptible to separation. The aerodynamic properties of plastic screens are found to differ significantly from those of the conventional metal screens. The "overshoot" in mean velocity profile near the boundary-layer edge is shown to be a result of the effect of screen inclination on pressure drop coefficient. A more accurate formulation for the deflection coefficient of a screen is also proposed.

Total pressure loss in vortical solutions of the conical Euler equations

Abstract: A technique for the solution of the conically self-similar form of the Euler equations is described. Solutions for the flow past a flat-plate delta wing at angle of attack are presented. These solutions show strong leading edge vortices with large total pressure losses in the cores. A study of the effects of various computational parameters on the total pressure loss is made. An explanation for the cause of the total pressure loss is presented. It is shown to be consistent with the results for both a quasi-one-dimensional model problem and the conically self-similar flow past the flat-plate delta wing.

Fluid and heat flow in gas-rich geothermal reservoirs

Abstract: Numerical simulation techniques are used to study the effects of noncondensable gases (CO/sub 2/) on geothermal reservoir behavior in the natural state and during exploitation. It is shown that the presence of CO/sub 2/ has a large effect on the thermodynamic conditions of a reservoir in the natural state, especially on temperature distributions and phase compositions. The gas will expand two-phase zones and increase gas saturations to enable flow of CO/sub 2/ through the system. During exploitation, the early pressure drop primarily results from ''degassing'' of the system. This process can cause a very rapid initial pressure drop, on the order of megapascals, depending on the initial partial pressure of CO/sub 2/. The flowing gas content from wells can provide information on in-place gas saturations and relative permeability curves that apply at a given geothermal resource. Site-specific studies are made for the gas-rich, two-phase reservoir at the Ohaaki geothermal field in New Zealand. A simple lumped-parameter model and a vertical column model are applied to the field data. The results obtained agree well with the natural thermodynamic state of the Ohaaki field (pressure and temperature profiles) and a partial pressure of 1.5 to 2.5 MPa (217 to 363 psi) ismore » calculated in the primary reservoirs. The models also agree reasonably well with field data obtained during exploitation of the field. The treatment of thermophysical properties of H/sub 2/O/CO/sub 2/ mixtures for different phase compositions is summarized.« less

Glass fiber‐filled thermoplastics. II. Cavity filling and fiber orientation in injection molding

Abstract: Mold filling of a rectangular cavity of three different thick nesses fed from a reservoir is studied for unfilled and glass fiber-filled polypropylene and polystyrene. The shapes of flow fronts studied by short-shots are affected predominantly by the thickness of the cavity with other parameters playing a less important role. Pressure drop versus volumetric flow rate inside the thinnest cavity is studied experimentally and predictions are made from a computer simulation of mold filling. The orientation of fibers in the cavity is examined using a reflect-type microscope and the orientation is found to depend on cavity thickness, melt temperature, fiber content, and to a lesser extent, on volumetric flow rate. In the thinnest cavity, where the flow is quasi-unidirectional, the fibers remain in the plane of flow oriented either along the flow direction or perpendicular to it, except in the region near the flow front, where they follow a “fountain” flow behavior.

Two-phase flow in heat exchangers and pipelines

Abstract: This paper discusses procedures for the prediction of pressure gradients, flow patterns, entrainment, and void fraction on the shell side of heat exchangers and in pipes during horizontal flow.

Pressure drop in cross flow across tube bundles

Abstract: The commonest methods of calculating the pressure drop in cross flow across tube bundles are discussed, and a new method, which is valid over a wide range of Reynolds numbers, is described. A comparison of the calculated coefficients of the pressure drop with experimental values from the literature shows that these new equations have the smallest deviations.

Flow through porous media: comparison of consolidated and unconsolidated materials

Abstract: Etude experimentale et modele mathematique portant sur les forces de trainee exercees par le milieu poreux et sur l'influence qu'exerce la structure des pores

Resistance to Air Flow of Oranges in Bulk and in Cartons

Abstract: PRESSURE drop, as a function of air flow, was measured for four different sizes of oranges in bulk with four different stacking arrangements for each fruit size At a given air flow, bed porosity had a much greater influence on pressure drop than did fruit size Pressure drop was also measured on carton vent holes and on simulated cartons of packed fruit Equations were developed for prediction of pressure drop of bulk fruit and of fruit packed in cartons as related to air flow rate and packing porosity

Incipient fluidization condition for a centrifugal fluidized bed

Abstract: A model has been proposed for the condition of incipient fluidization in a centrifugal fluidized bed. The model is based on the balance between the overall forces, including the centrifugal and fluid frictional forces, exerted on the fluidized particles and the overall effective weight of the particles. Equations have been derived from the model for predicting the critical fluidizing velocity and the maximum pressure differential (or pressure drop) through the centrifugal bed. A series of experiments was carried out with different solid particles, bed rotational speeds, and bed heights. The resultant data for the critical fluidizing velocity and the maximum pressure drop of the bed indicate that the proposed model is valid and the derived equations are of practical use.