Showing papers on "Pressure drop published in 1971"

Low Reynolds number flow in slowly varying axisymmetric tubes

Abstract: An asymptotic series solution is obtained for the low Reynolds number flow through an axisymmetric tube whose radius varies slowly in the axial direction. Expressions for the pressure drop along the tube and the shear stress at the wall are derived. The analysis is applicable to such problems as the flow through viscometric capillary tubes and the flow through blood vessels.

Flow and pressure drop in systems of repeatedly branching tubes

Abstract: The airways of the lung form a rapidly diverging system of branched tubes, and any discussion of their mechanics requires an understanding of the effects of the bifurcations on the flow downstream of them. Experiments have been carried out in models containing up to two generations of symmetrical junctions with fixed branching angle and diameter ratio, typical of the human lung. Flow visualization studies and velocity measurements in the daughter tubes of the first junction verified that secondary motions are set up, with peak axial velocities just outside the boundary layer on the inner wall of the junction, and that they decay slowly downstream. Axial velocity profiles were measured downstream of all junctions at a range of Reynolds numbers for which the flow was laminar.In each case these velocity profiles were used to estimate the viscous dissipation in the daughter tubes, so that the mean pressure drop associated with each junction and its daughter tubes could be inferred. The dependence of the dissipation on the dimensional variables is expected to be the same as in the early part of a simple entrance region, because most of the dissipation will occur in the boundary layers. This is supported by the experimental results, and the ratio Z of the dissipation in a tube downstream of a bifurcation to the dissipation which would exist in the same tube if Poiseuille flow were present is given by \[ Z = (C/4\surd{2})(Re\,d/L)^{\frac{1}{2}}, \] where L and d are the length and diameter of the tube, Re is the Reynolds number in it, and the constant C (equal to one for simple entry flow) is equal to 1·85 (the average value from our experiments). In general, C is expected to depend on the branching angles and diameter ratios of the junctions used. No experiments were performed in which the flow was turbulent, but it is argued that turbulence will not greatly affect the above results at Reynolds numbers less than and of the order of 10000. Many more experiments are required to consolidate this approach, but predictions based upon it agree well with the limited number of physiological experiments available.

Polymer Melt Flow Instabilities in Extrusion: Investigation of the Mechanism and Material and Geometric Variables

Abstract: A comprehensive study of the effect of material, geometric, and operating variables on the onset of melt flow instabilities in extrusion was made. Primary objectives were to compare such melt instabilities for a variety of materials and to correlate instability criteria with independent rheological parameters. Seven polymer melts were studied: two polyethylenes, polypropylene, polystyrene, two polybutadienes, and an SBR copolymer. Two distinct extrusion apparatuses were used: a die fed by a screw extruder system and a die fed by an Instron rheometer. The variables studied were temperature, entry cone angle, length/diameter ratio of the die, and flow rate. Independent rheological measurements were performed. These consisted of the evaluation of normal stresses on the Weissenberg rheogoniometer, entrance pressure drop measurements on the Instron rheometer, and viscosity measurements on both instruments and the screw extruder. In a companion study, flow visualization studies were made in the die entry region of the Instron rheometer, for most of the above materials and also a solution of polyisobutylene and glycerine. Distinctively different patterns were observed for the various materials, ranging from severe channeling with corner eddies to nonchanneling flow. Interrelationships between the onset of instabilities with other measurements were noted. In comparing a variety of materials, a decrease in the critical shear rate is generally associated with an increased tendency of the material to channel, an increased normal stress/shear stress ratio and an increased entrance pressure drop/shear stress ratio. It is argued that the instability phenomena are strongly associated with the elastic properties of the materials.

The development of the velocity field in polymer melts in a reservoir approaching a capillary die

Abstract: Color motion pictures have been made of the flow of low-density polyethylene, polystyrene, and isotactic polypropylene at 180°C in the reservoir approach to a capillary extrusion rheometer Detailed observations of the variation of flow patterns with extrusion rate were made At low flow rates, essentially radial flow into the capillary entrance was observed in all polymers With increasing flow rate, the included entrance angle α for the polyethylene and polystyrene decreased from 180°C and a “wine glass” structured velocity field was observed with stagnant circulating regions in the corners and the melt channeling in through the wine glass to the capillary entrance The angle α was related to entrance pressure drop Δpe and capillary wall shear stress σw data through the semilogarithmic equation where α is in degrees; Δpe/σw is interpreted as a Weissenberg number The breakdown of stable laminar flow of the melts in the reservoir and the distortion of extrudates was observed These phenomena seemed to be initiated by the formation of a spiralling motion in the reservoir

Study on Distribution of Flow Rates and Flow Stabilities in Parallel Long Evaporators

Abstract: Distributions of flow rates and flow stabilities in parallel evaporator tube systems have been experimentally investigated. The evaporator is composed of three parallel copper tubes of 4mm inside diameter and 40 m long. Experiments were carried out by using refrigerant R-113 as the fluid in pressure range from atmospheric pressure to supercritical pressure, in order to simulate phenomena in steam generators. It has been shown that distributions of flow rates, their hysterisis and onset of excursion phenomena can be estimated from pressure drop versus flow rate curves for single tubes. Moreover, description is made of behaviors of thermal oscillative instability which are observed at relatively low flow rate. In addition to the experimental results, by a theoretical analysis of a simple model, stability criteria in parallel tube system have been described.

Study On a Gas-Liquid Two-Phase Flow in Helically Coiled Tubes

Abstract: In this paper the frictional pressure drop, void fraction and flow pattern of an air-water two-phase flow in helically coiled tubes are presented. The coils are constructed of 9.92 mm I.D. copper tube and the ratios of inside diameter to coil diameter are 1/11 and 1/22.7, and the lengths are 4 m and 4.5 m respectively. The experiments were conducted in the range of superficial water velocity wlo: 0.35∼1.16 m/sec and superficial air velocity wgo: 0∼5 m/sec. The frictional pressure drop of the two-phase flow in these coils is 1.1 to 1.5 times as much as that in a straight tube in the range of the experiment. Three types of empirical equations for the frictional pressure drop are proposed, and also the experimental data are correlated by a modified Lockhart-Martinelli method. The values of void fraction in the coils are approximately equal to those in a straight tube for the same water and air flow rates.

Pressure characteristics of fibrous aerosol filters

Abstract: Theoretical equations for the pressure drop of high-porosity fibrous aerosol filters for low-speed Newtonian flow are summarized, and the relations between them are discussed. Using these equations the general character of the dependence of the pressure drop on the gas pressure (pressure characteristics) is analyzed over the whole range of Knudsen numbers. The dimensionless equations describing the reduction of the pressure drop with decreasing gas pressure are derived. Analyzing these equations, it is concluded that the pressure-drop reduction is dependent on three factors: the character of flow through a filter at normal pressure (continuum, slip, transient and free molecule flow), the dilution (reduction of the gas pressure), and porosity of the filter. The theory is checked against available experimental data.

Reverse flow cooling system for a dynamoelectric machine

Abstract: A dynamoelectric machine with internal gas cooling system has a reverse flow pattern with gas flowing from the fan through the coolers and then to the parts to be cooled. The gas is separated into two flow portions at the cooler, one portion undergoing a low pressure drop and then serving to cool the rotor end turns and transition section, the other undergoing a relatively high pressure drop and then serving to cool the stator core and to supply the gas gap for ''''gap pickup'''' cooling of the rotor body.

Improved parametric characterization of flow geometries

Abstract: An improved parametric method is presented for characterization of the flow geometry in the rectilinear flow of non-Newtonian fluids in open and closed conduits of arbitrary crosssection and in purely viscous, inelastic flow of non-Newtonian fluids through packed beds and porous media. In the new formulation, an infinite number of geometric parameters characterize the flow geometry. The actual number required in a particular application is shown to be determined by the fluid model equation representing the rheological behavior of the fluid. For Ostwald-de-Waele and Ellis fluids with flow behavior indices s = 1/n and α integers, the number of geometric parameters required to represent the relationship between flow rate and pressure drop is given by s + 1 and α + 1, respectively. The efficacy of the present method is demonstrated by comparisons with available results for various fluid models and flow geometries.

Control unit and method

Abstract: A control unit which is particularly useful in controlling the output pressure of a turbocharger in response to the manifold pressure with compensation for pressure drop at the throttle characterized by a reference unit disposed in the housing for the manifold pressure to act on and at least one diaphragm extending across said housing to apply the pressure differential between the manifold pressure and the output pressure of the turbocharger. In one embodiment, the reference unit includes a bellows of a predetermined volume of gas which schedules the displacement of the reference unit in response to the temperatures of the gases of the manifold. Another embodiment includes an additional diaphragm and valve means for applying additional pressures to the reference means to compensate for the altitude for the system to prevent overspeeding of the turbocharger.

Pressure drop and holdup in horizontal slug flow

Abstract: The Dukler-Hubbard slug-flow model is used along with independent correlations for in situ holdup and slug frequency to predict pressure drops for two-phase slug flow. The holdup and frequency correlations are for the most part based on data for air-water flowing in a 1.50-in. pipe. Predictions of pressure drop using this approach are compared with experimental data taken from studies utilizing various systems and pipes from 1.50 to 6.065 in. in diameter. Alternative correlations by Dukler and Hughmark for predicting two-phase pressure drops and holdup, respectively, are included for comparison. In general, the present approach is at least equivalent to the Dukler-Hughmark method, and for values of ΔP/L > 0.06 lb./sq. in./ft. appears to be slightly better.

The influence of return bends on the downstream pressure drop and condensation heat transfer in tubes

Abstract: Sponsored by Technical Committee 1.3, American Society of Heating, Refrigeration, and Air Conditioning Engineers DSR Project

Flow divider control valve assembly

Abstract: In a preferred form, this disclosure relates to a flow divider control valve assembly for controlling the flow of a fluid from a variable fluid pressure and supply source and which has a flow divider valve means with a first flow control orifice permanently operatively connecting an inlet port with a first or priority outlet port and a second flow control orifice operatively connected with the inlet port. The flow divider valve means is shiftable in response to a predetermined pressure drop across the first flow control orifice to limit the flow out the first outlet port to a predetermined rate by diverting the excess fluid to a second outlet port via the second flow control orifice. An operating valve means which is operatively connected with the inlet port and with the second flow control orifice at its downstream side is shiftable in response to a predetermined pressure drop across the second flow control orifice to limit the flow out the second outlet port to a second predetermined rate by allowing the excess fluid supply to pass out an exhaust port.

Upward Liquid Flow in Small Tube into which Air Streams : 1st Report, Experimental Apparatus and Flow Patterns

Abstract: In the main fuel pipe (main nozzle) of the carburetor of gasoline engine, a little air is let into the fuel stream, in general. This two-phase flow streams into the venturi-tube. The author's experiments are made with simple models to elucidate the basic phenomena of the confluence of air and fuel in a small tube, that is, the flow pattern of a two-phase flow, the pressure drop caused by the confluence, the two-phase flow friction, and the relaxation oscillation. In 1st Report, experimental apparatus and flow pattern are described. Vertical tubes are 6, 3, 2 mm of diameter. Liquid is tap water in the most part of experiments, and in some part of them, is distilled water, gasoline, solvent, or surface active agents solution, Unless the air holes are large, stable fish-scale type slug flow appears in some range of air and liquid. This is attributed not to the effect of so-called entrance length but to that of the small diameter of tube.

Effect of pressure in capillary flow of polystyrene

Abstract: Several corrections possibly required for capillary flow are based on the existence of a linear relationship between the pressure drop along the capillary and the length-to-diameter ratio at a given temperature and shear rate. Recently, the appearance of nonlinearities in this relationship has created some concern as to the cause of this behavior. The occurrence and an explanation of the nonlinearities for polystyrene form the basis of this study. A narrow-distribution, low molecular weight (20,400) polystyrene was tested in eight capillaries at temperatures of 140 and 160°C to initiate the discussion of the nonlinearity in a ΔP (pressure) versus L/D (length/diameter of capillary) plot. The sample exhibits negligible extrudate swelling at all pressures which reinforces the idea that pressure is influencing the flow. The pressure dependence of viscosity is determined using the equivalent expression of the WLF equation derived from free volume theory. Justification for its use is presented. A pressure correction, representing the increased shear stress necessary for flow of the higher viscosity material, is found to linearize the ΔP versus L/D data. A narrow-distribution, high molecular weight polystyrene (670,000) is subjected to a similar analysis at 165°C by using nine capillaries. The situation is quite different, as the high molecular weight sample is not nearly as ideal as the low molecular weight polystyrene.

Effect of gas slip on the pressure drop in a system of parallel cylinders at small reynolds numbers

Abstract: The dependence of pressure drop across a model filter on the Knudsen number has been studied experimentally and theoretically for a simplest fiber filter model—a system of parallel cylinders arranged perpendicular to the flow. It has been shown that the reciprocal value of the drag on the fibers increased linearly with the Knudsen number.

Automatic alignment bearings for guiding in translational or rotational motion

Abstract: A bearing which ensures automatic alignment of a part to be guided and comprises a stationary supporting frame, a core which is placed within the frame and provided with elements for securing the part, pistons fitted within cylinders which are formed in the frame and each open on the core. Each piston is applied against an oil chamber of small width by means of the piston face which is remote from the core. Each chamber is connected through a high pressure drop inlet to a reservoir which contains oil under pressure and is fitted with a compensation system for maintaining the pressure at a practically constant value.

Pressure Losses for Laminar Flow in the Entrance Region of Ducts of Rectangular and Equilateral Triangular Cross Section

Abstract: The velocity profiles upon which the pressure-loss calculations are based, are recomputed using the previously described method of reference (1960). The pressure drop is then computed using the energy integral equation; both rectangular and equilateral triangular ducts are considered. It is demonstrated that, using this equation, the pressure-drop parameter can be improved.

Pressure sensitive control apparatus with magnet actuated switch and valve

Abstract: A fuel ignition system and a flow switch therefor which can be used for leak detection and otherwise. Upon detection of the flow, ignitor elements in the system are heated to cause combustion of the fuel at the point of release of the fuel in the system. The flow switch includes a diaphragm which separates a pressure chamber from the outlet side of the system. The inlet side is connected to the pressure chamber to cause the chamber pressure to be the same as that on the inlet side. A permanent magnet is connected to the diaphragm and is responsive to a pressure differential between the inlet side and the outlet side to actuate the switch when there is a very small inlet-to-outlet flow of fuel. Also connected to the diaphragm is a stem for actuating the main valve connecting the inlet side of the system to the outlet. The main valve permits fuel to flow through the switch with a very small pressure drop across the switch. The stem and main valve have a lost motion connection therebetween to insure positive closing of the valve and positive engagement of the permanent magnet with the switch casing.

Composite pipeline sampler

Abstract: Apparatus for obtaing a composite and proportional sample of liquid flowing through a pipeline in which an obstruction is installed to produce a pressure drop sufficient to cause appreciable flow through a sampling line connected to the pipeline upstream and downstream of the obstruction A sampler pump connected into the sampling line periodically displaces a predetermined portion of the liquid flowing through the pipeline into a sample container maintained full of liquid and at a pressure enough higher than the vapor pressure of the most volatile component present in the product to be sampled to prevent vaporization of the volatile components of the liquid sampled An accumulator in the line from the sample container to a displacement liquid reservoir protects the sample container from drops in pressure that might cause vaporization of the sample, and a bypass and rupture plug assembly protects the sample container from excessive pressure

Flow of viscous fluid through a circular aperture

Abstract: The creeping flow of a highly viscous incompressible fluid through a circular aperture located in an infinitely wide horizontal plate is analyzed by solving Navier-Stokes equations without inertia terms. Solutions for vertical and radial velocities as well as pressure have been obtained in terms of integral equations with an undetermined Kernal function. This function has been evaluated by assuming several different velocity distributions at the aperture, and the corresponding pressure drop for each case has been calculated. The results show that the pressure loss for a given flow rate goes through a minimum as the assumed velocity profile changes from flat to parabolic. Based on the minimum energy dissipation theorem of Helmholtz, the most appropriate velocity distribution is discussed. Experimental data obtained using sharp-edged orifices are compared with theoretical predictions.

Methods and compositions for reducing frictional pressure loss in theflow of hydrocarbon liquids

Abstract: THE PRESENT INVENTION RELATES TO THE METHODS AND COMPOSITIONS FOR REDUCING THE FRICTIONAL PRESSURE LOSS ENCOUNTERED IN THE TURBULENT FLOW OF HYDROCARBON LIQUIDS THROUGH A CONDUIT. BY THE PRESENT INVENTION A FRICTIONAL PRESSURE LOSS ADDITIVE IS INTERMIXED WITH THE HYDROCARBON LIQUID, THE ADDITIVE BEING A HOMOPOLYMER OR A COPOLYMER OF THE MONOMER R1-C(=CH2)-C6H4-R2 OR COPOLYMERS OF SUCH MONOMER AND CERTAIN STYRENE, ACRYLATE OR METHACRYLATE TYPE MONOMERS.

Entrance region flow of polymer melts

Abstract: An experimental study has been made to investigate polymer melt flow in the entrance region of a circular tube. For the study, a capillary rheometer was used to measure wall normal stresses in polymer melts in the reservoir and along the axis of the capillary. In order to investigate the influence of reservoir diameter on the entrance pressure drops, reservoir-to-capillary diameter (DR/D) ratios of 3, 6, 9, and 12 were used, with the capillary length-to-diameter (L/D) ratio being 20 and the capillary diameter being 0.125 in. Analysis of the experimental data shows that the entrance pressure drop increases and then levels off as DR/D ratio is increased. A correlation between the dimensionless entrance pressure drop and Reynolds number has been obtained, which follows the creeping flow analysis by Weissberg over the range of the area contraction ratio studied, 0.00694 <β< 0.111.