Showing papers on "Pressure drop published in 1987"

Influence of interfacial waves in stratified gas‐liquid flows

Abstract: Interfacial stresses are calculated from new measurements of liquid height and pressure drop for fully developed horizontal stratified flow. These are related to wave properties. An improved design method is suggested.

Effect of valve closure time on the determination of respiratory resistance by flow interruption.

Abstract: The resistance of the respiratory system to flow may be conveniently assessed by the flow-interruption technique, in which the flow of gas at the mouth of a subject is suddenly interrupted, while the pressure just distal to the point of interruption, is recorded There is a rapid change in pressure immediately upon interruption, presumably giving the resistive pressure drop across the pulmonary airways This is followed by a further slow change in pressure reflecting stress relaxation in the respiratory system and possibly gas redistribution between different regions of the lung The diagnostic potential of the post-occlusion pressure signal is dependent on the airway opening being occluded effectively instantaneously We present a description of an occlusion valve we have designed and built for performing rapid airway occlusions We are able to measure the closing characteristics of our valve precisely, and show that its finite closure time of 12 ms causes the initial rapid drop in pressure to be underestimated by about 7 per cent A simple numerical correction scheme allows us to estimate this pressure drop correctly to within one or two per cent

The nature of flows through porous media

Abstract: The present paper points out that the pressure drop of a porous media flow is only due to a small extent to the shear force term usually employed to derive the Kozeny—Darcy law. For a more correct derivation, additional shear terms have to be taken into account since the fluid is also exposed to elongational forces when it passes through the porous media matrix. These are usually not taken into account in the conventional theoretical treatment of flow through porous media as is explained in the literature. This explains why the available theoretical derivations of the Kozeny—Darcy relationship, which are based on one part of the shear-caused pressure drop only, require an adjustment of the constant in the theoretically derived equation to be applicable to experimental results. Details of this derivation are given in this paper and existing derivations are extended to yield better agreement with experiments. To verify experimentally some of the results of the theoretical derivation provided, porous media flows of dilute polymer solutions are studied experimentally. It is shown that the addition of small amounts of high molecular weight polymers to a solvent with Newtonian flow properties causes drastic pressure drop increases if the flow rate exceeds an onset flow rate corresponding to a critical Deborah number of the porous matrix-polymer solution system. This can only be explained if the flow field in the porous medium is exposed to shear and elongational strain. The extent of this interaction is deduced from experimental findings.

Drop volume measurement system

Abstract: Apparatus and method for measuring the volume of a drop, and with a series of drops the volumetric flow rate of a fluid utilizing a vertically oriented, transparent drop chamber through which the fluid is directed in drop form. A plurality of drop sensors positioned adjacent to the drop chamber in vertically spaced relation to each other emit signals in response to the detection of the entrance and exit of each drop to and from separate sensor fields preferably established by light emitting sources. The drop sensors are connected to control circuitry incorporating an electronic processor programmed to determine volumetric flow rate in response to drop dimension and drop rate signals received from the drop sensors. The drop size in terms of the vertical dimension of each drop in the direction of gravity flow through the drop chamber is determined by measuring the time it takes a drop to pass through each and both of the two sensor fields. Timers used for this purpose are triggered by the aforesaid sensor signals. The volume of each drop is electronically calculated as a function of the drop vertical dimension, and drop volume and drop rate are multiplied to determine volumetric flow rate.

A Mechanistic Model for Two-Phase Vertical Slug Flow in Pipes

Abstract: This paper presents the formulation of a mechanistic model for slug flow in vertical pipes. The equations required to determine holdup, the relevant velocities and pressure loss are presented. The model is fully deterministic and the pressure drop predictions of the model are compared to experimental field data for oil and gas and gas and water wells. For the 143 data points, the model shows an average percent difference of 4.83 percent, which is felt to be excellent.

Fundamentals of a centrifugal fluidized bed

Abstract: A fundamental theory based on the local momentum balances is proposed to explore the fluidizing phenomena of a centrifugal particle bed. Unlike the conventional vertical bed, a centrifugal bed is predicted to be fluidized layer by layer from the inner free surface outward, in a range of aeration rates. The span of this range increases with the depth of the particle bed. The pressure drop is predicted to exhibit a plateau, which agrees very well with the observations of many investigators, but disagrees with the investigations of Takahashi et al. and Fan et al., in which the pressure drop exhibited a maximum. Predictions of the critical fluidizing velocity and the corresponding pressure drop agree well with the data of Fan et al.

Performance of Dust Respirators with Facial Seal Leaks: I. Experimental

Abstract: The ability of representative half-mask and single-use respirators with facial seal leaks to provide protection against aerosols was evaluated by experimental measurement. Respirators were mounted on a manikin in a test chamber and operated at seven steady flow rates over the range of 2 to 150 L/min. Samples of polydisperse and monodisperse aerosols were taken from inside and outside the respirator and analyzed by a calibrated optical particle counter over the particle-size range 0.1 to 11.3 µm. Measurements were made separately for filter performance as a function of particle size and flow rate, and simulated leak performance (penetration) as a function of particle size, pressure drop, and leak size. Flow rate vs. pressure drop measurements were made for all filters and leaks tested. For a given leak condition the percentage of the total flow traversing the leak varied several fold over the usual range of airflow rates through a respirator. Aerosol penetration was found to depend strongly on particle siz...

Pressure drop in gas‐liquid downflow through packed beds

Abstract: Pressure-drop in cocurrent gas-liquid downflow through packed beds was experimentally measured for nonfoaming, foaming Newtonian, and non-Newtonian liquids. The variables include the column diameter, packing size and shape, flow rates of the phases, and their physical properties. Unified correlations are presented for the data of the present study as well as data available in literature in terms of Lockhart-Martinelli parameters and flow variables and packing characteristics. The data were modeled using a dynamic interaction model.

Method and system for determining fluid pressures in wellbores and tubular conduits

Abstract: Friction pressure losses are obtained for non-Newtonian or generalized Newtonian fluids being pumped through conduits at high flow rates, such as in hydraulic fracturing of subterranean formations, by measuring friction pressure losses in a pipe viscometer under laminar flow conditions. The pipe viscometer includes a pump which supplies fluid to a continuous loop having three pipe sections of different diameter for measuring pressure drop at different flow velocities. Sets of data points of generalized shear stress and shear rate are measured for determining the consistency index (K") and the Power Law or flow behavior index (n'). The generalized Reynolds number of the fluid being pumped is determined using the values of consistency index and flow behavior index and this Reynolds number is maintained in a second pipe viscometer section arranged in parallel with the laminar flow loop by pumping the same fluid wherein the second pipe viscometer section has the same roughness as the conduit through which friction pressure loss is to be determined. The Fanning friction factor (f) is determined for the pipe viscometer section from known values of friction pressure drop over a predetermined length of the pipe viscometer section at a known flow velocity, known fluid density and known hydraulic radius of the pipe viscometer section. The actual pressure drop over a predetermined length of conduit is determined using the calculated value of friction factor (f) and measured values of fluid density, flow velocity and conduit dimensions.

Dehumidification: on the correlation of wet and dry transport processes in plate finned-tube heat exchangers

Abstract: The transverse velocity of the condensing phase during dehumidification is analogous to the transverse velocity at the wall when exercising boundary layer control by fluid extraction through a permeable wall. Wet and dry pressure drop and heat transfer rates are analyzed for correlation using boundary layer suction theory. Data are presented for flat-plate finned-tube heat exchangers during air heating and dehumidification operations and the data show a significant effect of transverse velocity correlated by the boundary layer suction formulation. The condensate film is considered isothermal in this analysis and the results indicate that an improved modeling of the condensate film is required. The authors find that the transverse velocity of the condensing phase has an important effect on transport phenomena during dehumidification and that the validity of the Chilton-Colburn heat and mass transfer analogy in describing dehumidification is supported by these results. It should be noted that the dry data form the beginning of a plate fin heat exchanger data base. The present data show the effect of tube diameter and, independently, fin density variation on the Colburn and friction factors with all other geometric parameters held invariant.

Reynolds Stresses and Dissipation Mechanisms Downstream of a Turbine Cascade

Abstract: An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10 percent of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The measured Reynolds stresses are combined with measured distributions of velocity to show how and where losses are being produced. The mechanisms for the dissipation of mean kinetic energy in this swirling three-dimensional flow are revealed.

Apparatus for flow distribution in packed towers

Abstract: Process tower vapor/liquid flow distributor and packing bed comprising a plurality of relatively thin corrugated layers stacked one atop the other. The corrugated sheets are disposed in face to face contact with respective corrugations inclined to the horizontal and facing one another for the countercurrent passage of vapor and liquid therethrough. At least two layers are utilized and rotationally offset for diverting the vapor liquid in two separate directions to effect maximum vapor liquid distribution for countercurrent fluid flow passing therethrough. An improved homogenous mixture of vapor/liquid within the process tower packing sections may thus be provided. The assembly affords optimal pressure drop characteristic while maximizing even vapor/liquid distribution into the packing regions. In this manner the distribution sections may be disposed throughout the process tower above and below each packing section, or in place of the packing section for distributing the descending liquid flow as well as the ascending vapor flow therethrough. This configuration maximizes the efficiency of the distribution thereacross and the homogenous mixture interaction therein.

Compressibility of Paniculate Structures in Relation to Thickening, Filtration, and Expression—A Review

Abstract: Compressibility of cakes is basic to separation of solids from slurries. Cake compression is caused by collapsing, particulate structures in which particles are forced into existing voids. Stresses causing the collapse arise from unbuoyed weight of solids in thickeners, radial acceleration in centrifuges, frictional pressure drop in filters, and mechanical forces in press belts and membrane actuated filters. Compressibility is a function of particle size and shape and the degree of aggregation. Flow through very compressible cakes produces a highly non-uniform structure with a tight skin of low porosity next to the supporting medium. This skin leads to adverse effects in which increasing filter pressure has little effect on flow rate or average porosity. Similarly increasing the squeezing pressure indefinitely in expression has little effect upon the rate of removal of liquid.

Split vaned nuclear fuel assembly grid

Abstract: Integral vanes 4 with optimized size, shape and bend angles maximize coolant mixing and fuel rod 12 heat transfer downstream. Recessed weld nuggets 5 with no vane cutout are optimized for size, strength and corrosion resistance. Staggered arches 20',22' and springs 20,22 minimize turbulence and reduce grid pressure drop and promote coolant mixing. Crowned arches 20',22' and springs 20,22 decrease scoring of fuel rods 12 and are sized to minimize turbulence and pressure drop. Minimum cutouts in unslotted section of grid strip 46,46' give 15-20% strength increase. Intermediate weld and tapered end slots 48 give 15% strength increase. Ribbed and round dimple stiffeners 38,39 on outer strips increase buckling resistance, reduce handling damage and spreads accidental loading. Outer strips 32 are optimized for strength, handling, turbulence generation and pressure drop. They also divert enough flow to interior of fuel assembly to match thermal power distribution and eliminate fuel rod corrosion concerns.

Fluid flow speed measuring apparatus

Abstract: A fluid flow speed measuring apparatus comprising a first pipe having an opening exposed into a fluid to be measured, a direction of the opening having an angle larger than a critical negative pressure angle, a second pipe having an opening exposed into the fluid to be measured, a direction of the opening of the second pipe having an angle larger than the critical negative pressure angle and at least one of conditions such as a diameter, a direction, and the number of the openings for determining a magnitude of the negative pressure being different from that of the opening of the first pipe, negative pressure difference detector for detecting a difference between negative pressures acting on the openings of the first and second pipes, and device for calculating a flow speed of the fluid to be measured on the basis of an output from the negative pressure difference detector.

Wide-range, adjustable flowmeter

Abstract: A fluid bypass type flowmeter has a main passage which is configurable to various effective diameters by selectably adding pre-defined additional cross-sections comprised of an adjustable laminar flow element located within a bore for fine adjustm=ent of the full-scale range of the flowmeter, and an adjustable restriction secondary passage for crude adjustments of the range of the meter. With adjustment of the flowmeter, all or a selected portion of the flow to be measured can be diverted through the secondary passage, where a flow measuring device is located, thereby allowing the flowmeter to operate at or near its full scale and thereby improving the accuracy of the flowmeter over various ranges of flow rate. A laminar flow element is employed in the main passage so that the pressure drop across the element varies linearly with flow rate and, accordingly, the ratio of diverted to un-diverted flow is a constant ratio even though the flow rate varies. The secondary passage adjustable restriction is also designed to give laminar flow to obtain linearity over flow rate variations.

Critical Heat Flux and Flow Characteristics of Subcooled Flow Boiling in Narrow Tubes

Abstract: The critical heat flux (CHF) of subcooled flow boiling in narrow tubes and its flow characteristics were investigated, and the bubble boundary layer concept was discussed. For subcooled flow boiling in narrow tubes of 1 mm inside diameter, the void fraction was estimated to be several ten percent smaller than the predicted by the subcooled void fraction correlations for large-inside-diameter tubes. This caused the CHF in the narrow tubes to increase and the friction pressure drop multiplier to decrease. The Tong CHF correlation based on the bubble boundary layer separation model was examined. Considering the dependence of pressure on the empirical parameter C in the Tong correlation, a modified correlation was proposed.

Isothermal extrusion of non-dilute fiber suspensions

Abstract: The extrusion of a rod-like fiber suspension is a Newtonian solvent, as a first step to the fast and inexpensive production of composite materials, is investigated. The analysis is carried out by means of an integral constitutive equation for a non-dilute suspension, streamlined finite element for liquid with memory, and Newton iteration of nonlinear integro-differential equations. The predictions show substantial differences between dilute and nondilute fiber suspension regarding the processing conditions (pressure drop, velocity distribution, die-swell) and the resulting fiber orientation. Nondilute fiber suspensions exhibit substantial shear-thinning and negligible elasticity as evidenced by the small die-swell, and fiber concentration viscosity-thickening as evidenced by the large pressure drop. The fiber orientation is computed by solving the orientation distribution function along selected streamlines of the complex velocity field. It is shown that the fiber orientation far downstream can be made independent of the random fiber orientation at the inlet.

Water/wastewater treatment apparatus

Abstract: A method and apparatus for removing volatile organic contaminants from water. Water to be treated is mixed with a small proportion of higher pressure gas (air, ozone, etc.)-saturated water in a static mixer causing the release of a very large number of very fine gas (air, ozone, etc.) bubbles in the mixture. The mixture is directed into a chamber which has a device, such as a transverse perforated plate, to reduce water pressure. The pressure drop, which need only be about 10 psi, causes the volatile organic contaminants to enter the vapor phase and, through mass transfer absorption, mix with the gar bubbles. The bubbles rise to a free headspace at the top of the chamber from which the now-contaminated gas can be withdrawn. The substantially decontaminated water then exits the chamber, still nearly at line pressure.

Acoustic Resonance in Heat Exchanger Tube Bundles—Part I: Physical Nature of the Phenomenon

Abstract: The intense acoustic resonance resulting from gas flow across a bank of heat exchanger tubes in a duct has been investigated experimentally and theoretically. At low gas velocities, the acoustic tone emanating from tube bundles increases in proportion to the flow velocity. When the frequency approaches a bound acoustic transverse mode of the tube bundle, intense sound can result. Sound levels as high as 173 db were measured within the bundle. During resonance, the sound correlates vortex shedding from the tubes and the pressure drop increases in some bundles.