Showing papers on "Pressure drop published in 1974"

Apparatus for obtaining uniform gas flow through an in situ oil shale retort

Abstract: An in situ oil shale retort in which a cavity filled with broken particles of oil shale is formed within the subsurface oil shale formation and air is forced down through the cavity to sustain combustion of the top layer of oil shale particles. The products of combustion are withdrawn through a plurality of transverse exhaust pipes at the bottom of the cavity, the exhaust pipes each being provided with a series of holes along the length of the pipes within the cavity, the holes being graded in size to compensate for the pressure drop along the length of the pipe so as to provide substantially equal volume of gas flow through each of the openings.

Quantitative Studies of Microcirculatory Structure and Function: I.Analysis of Pressure Distribution in the Terminal Vascular Bed in Cat Mesentery

Abstract: A modified version of the Wiederhielm electronic servo system for micropressure recordings was used to establish the details of the pressure drop across successive segments of the microcirculation from arterioles (150µ) to venules (200µ) in the mesentery of the cat; most of the readings were made in vessels less than 25jz in diameter. Micropressures correlated with central pressure only in arterial vessels larger than 50µ. Frequencydistribution plots of micropressures showed a wider spread in the vessels that were 50-1Oµ in diameter than they did in capillary vessels that were less than 20µ in diameter.Therefore, it appears that classification of vessels on the basis of diameter, which is at present the only practical way of comparing pressure measurements in presumably identical segments of a continuously branching system, is not adequate and makes statistical analysis difficult. In the present study, micropressures remained pulsatile throughout the bed, although the pulse pressure could be narrowed to 2-4 mm Hg in the capillaries. Simultaneous measurement of pressure in two vessels showed that the greatest pressure drop occurred in the region where arterioles (40-50)u) distributed numerous precapillary branches (10-15/x); in this region arteriolar pressures were reduced from a level of 45-65 mm Hg to about 30-35 mm Hg. These data suggest that application of the resistance term for Poiseuille flow in the microcirculation should take into account the relative sizes of the parent vessel and the branch, the entry dimensions into the branch and the length of the neck or junctional segment. Evidence found in this investigation indicated that precapillary branching configurations were self-regulatory. A small number of low-resistance, shunt pathways between arterioles and venules were regularly present, as shown by the extremely small pressure drop in 15-18% of the vessels. The data indicate that much more caution is needed in interpretation of pressure-related phenomena in the microcirculation because of their strong dependence on the anatomical and physical features characteristic of individual tissues.

The ignition of a thin layer of explosive by impact

Abstract: The behaviour of thin layers of solid materials under drop-weight impact is studied with the aid of high-speed photographic and pressure-measuring techniques. Photographic sequences taken with a high-speed framing camera show that explosive materials suffer large-scale deformation before initiation of explosion. The sample may undergo plastic flow in bulk, show evidence of partial fusion, and even (with PETN) melt completely. There is also evidence of Munroe jetting and instability of flow of material at the anvil/layer interfaces. The flow speed of the sample during these processes is considerable and may reach 300 m/s. When ignition of the layer occurs it does so at a small number of local hot spots, following which rapid combustion develops at speeds of 200-700 m/s. Strain-gauge measurements show that the pressures attained during drop-weight impact are typically 0.5-1 GPa (5–10 kbar) and the duration of impact 300–500 μs. In the course of impact of a thin layer of granular material a sharp pressure drop may occur, frequently from several hundred MPa down to zero. With an explosive layer, ignition occurs immediately following the instant of the pressure drop. The sudden fall in pressure is due to mechanical failure of the sample, and correlation of the two experiments shows that this is the cause of the very high flow speeds attained during impact. On the basis of these results a possible mechanism of ignition is suggested.

Air cleaning adsorption process

Abstract: A process for air cleaning by the removal of water and one or more undesirable gases such as NO x , SO x and CO 2 by a continuous atmospheric pressure and low pressure drop system wherein the adsorbent body is a wheel of thin sheets or layers of fibrous material containing about 10 to 90% by weight of a finely divided crystalline molecular sieve material. The process is especially useful for the removal of NO 2 from confined areas.

Desiccant apparatus and method

Abstract: A process and apparatus for drying air by a continuous atmospheric pressure and low pressure drop system wherein the adsorbent body is a wheel of thin sheets or layers of fibrous material containing about 10 to 90% by weight of a finely divided crystalline molecular sieve material. The process and apparatus is especially useful for drying air for confined areas down to and less than 0.001 lbs. of moisture per pound of air.

Viscous dissipation in die flows

Abstract: The flow of polymer melts in cylindrical, annular, and slit dies has been examined. Large temperature rises at the outer surface of the extrudate were measured with an infrared pyrometer. Calculations show that severe radial temperature gradients exist in these flow geometries under conditions similar to those encontered in polymer processing and in viscometry measurements. A common method of estimating the average temperature rise from the total mechanical energy input seriously underestimates the maximum temperature rise. A numerical solution of the flow and energy equations models the flow in all three geometries. A very simple Nusselt number correlation allowed an estimate of the temperature rises possible if heat transfer with the die wall occurrs. Good agreement was obtained between predicted and infrared measured melt surface temperature rises. The pressure drop gives only an indication that nonisothermal flow is occuring and is not sensitive enough to distinguish the type of heat transfer boundary condition present. The mathematical model presented could be helpful in die design and in process modeling, allowing the designer to obtain some knowledge of the kind of flow situations which might be encountered.

Shunt system for the transport of cerebrospinal fluid

Abstract: A shunt system is disclosed for treating hydrocephalus by transporting cerebrospinal fluid from a source of such fluid to a selected site in the body of the patient, wherein the fluid is conducted through tubing in which a pressure-operated check valve is included, and connected in series with that valve is a second valve including gravity-operated means effective to urge the second valve to closed position until a higher pressure is reached when the patient is in substantially vertical position and to permit the valve to open freely when the patient is in substantially horizontal position, thus compensating for the pressure drop and consequent siphoning of fluid which would otherwise occur when the patient moves from horizontal to vertical position.

Drag reduction in the turbulent flow of fiber suspensions

Abstract: An analysis of the velocity profile and pressure drop relationships for turbulent flow of fiber suspensions through smooth tubes was evaluated experimentally over a range of flow rates, tube sizes, fiber concentrations, and fiber geometries (aspect ratios). This work shows that drag reduction in these systems, in marked contrast to that in viscoelastic polymeric fluids, involves processes in the turbulent core of the velocity field. As a result the drag reduction achieved is independent of the scale of the system. The implications of these results with respect to rates of heat and mass transport are considered in a preliminary way. The measurement of such transport rates, and of the turbulent velocity profiles in dilute suspensions, is seen to be of mechanistic interest.

Turbulent flow in smooth concentric annuli with small radius ratios

Abstract: Fully developed turbulent flow through three concentric annuli was investigated experimentally for a Reynolds-number range Re = 2 × 104−2 × 105. Measurements were made of the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distribution in annuli of radius ratios α = 0.02, 0.04 and 0.1, respectively. The results for the key problem in the flow through annuli, the position of zero shear stress, showed that this position is not coincident with the position of maximum velocity. Furthermore, the investigation showed the strong influence of spacers on the velocity and shear-stress distributions. The numerous theoretical and experimental results in the literature which are based on the coincidence of the positions of zero shear stress and maximum velocity are not in agreement with reality.

Studies of Liquid Film Flow in Two-Phase Annular and Annular-Mist Flow Regions : (Part 1, Downflow in a Vertical Tube)

Abstract: Experimental data are presented on the pressure drop, mean liquid film thickness, state of gas-liquid interface and droplet entrainment for upward annular-mist two phase flow in a vertical tube. Using these data, the relations between the shear stress at gas-liquid interface, the liquid film flow rate and the mean film thickness are investigated, and the characteristics of the mean film thickness with respect to the film Reynolds number are revealed by comparing with the analytical predictions for laminar and turbulent films. A heat transfer experiment is also performed and the results are compared with the analytical values of heat transfer coefficient for laminar and turbulent film flow. On the basis of the experimental data of heat transfer coefficient, the nondimensional thickness of the laminar sublayer of liquid film is calculated for both upflow and downflow, and correlated with the nondimensional film thickness. The result represents the difference in flow state between the upflow film and the downflow film.

Non-newtonian fluid flow in an eccentric annulus

Abstract: Non-Newtonian fluid flow in an eccentric annulus was studied for high polymer aqueous solutions of CMC, HEC and MC. The macroscopic relations between the pressure drop and the flow rate were found to be in fairly good agreement with the results obtained by application of the conventional variational principle. Velocity profiles were measured by a hydrogen bubble method in which photographs were taken of the hydrogen bubbles. The authors observed very interesting secondary flows in the eccentric non-Newtonian fluid flow which may be due to the viscoelastic effect of the high polymer aqueous solution. The authors could not observe such secondary flows for non-Newtonian fluids in a concentric annulus or Newtonian fluids in an eccentric annulus. The authors present an equation giving the relation between the flow rate and the pressure drop for the flow of a non-Newtonian fluid in an eccentric annulus in terms of the experimental data for flow in a circular tube.

Augmentation of Heat Transfer in Tubes by Use of Mesh and Brush Inserts

Abstract: This paper summarizes the results of a study to determine the heat transfer and pressure drop characteristics of two types of tube inserts developed specifically for augmenting heat transfer and accommodating high heat fluxes. The best performing mesh-insert tubes exhibited heat transfer coefficients nine times the coefficients with empty tubes while brush-insert tubes had coefficients averaging five times the empty tube values, both comparisons being made at equal mass velocity. Both inserts produced very large pressure drops. Subcooled boiling curves and burnout points are presented; burnout heat fluxes are two to three times the empty tube values at equal mass velocity. For single-phase conditions and for burnout, the mesh and brush tubes have favorable performance characteristics, based on pumping power, which suggest use of these inserts in certain special cooling systems.

Pressure drop for flow of polymer solution in a model porous medium

Abstract: The flow of polymer solutions in porous media is of considerable practical importance in such applications as secondary oil recovery. At sufficiently large deformation rates, the viscoelasticity of the polymers has been observed to cause gross increases from pressure drop predictions based on purely viscous behavior. Of similar importance in oil recovery operations is the fact that addition of polymer may effect significant changes in flow distribution in a porous bed. Apparently no attempt has been made to relate visual studies to observed changes in pressure drop behavior. It was felt there is a need to provide data on elasticity effect on pressure drop in well-defined systems which are amenable to simple but detailed analyses. These may be useful in studying related phenomena such as changes in flow distribution. (12 refs.)

Turbine vane cooling

Abstract: A method and apparatus for providing high pressure cooling air to the turbine vanes of a gas turbine engine is disclosed. A centrifugal compressor stage is interposed in the flow path of cooling air to the turbine vanes. The centrifugal compressor stage raises the pressure of the cooling air to a value substantially greater than the pressure of the combustion gases entering the turbine. The availability of high pressure cooling air allows the incorporation of improved cooling systems in the turbine vanes. Increasingly effective cooling systems are necessary to the continued development of low pressure drop combustion chambers which discharge high temperature gases to the inlet of the turbine.

Apparatus for spraying liquid product

Abstract: A liquid distributor apparatus for use on a vehicle including a liquid product supply tank and a pump for pumping liquid from the tank to a spray bar system for spraying liquid product in a preselected width of the spread along a path traversed by the vehicle. The rate of flow of liquid product through the nozzles on the spray bar system varies as a function of the square root of the pressure drop across the nozzle and a control system is provided to sense the pressure in the spray bar system and the vehicle speed and to control flow of product to the spray bar system to vary the pressure on the product in the spray bar system as a function of the square of the speed of the vehicle to thereby maintain a preset spread density independent of variations in the speed of the vehicle.

Pressure drop and holdup in stratified gas‐liquid flow

Abstract: A mathematical model and an iterative procedure to calculate holdup and pressure drop in horizontal gas-liquid flow is developed. The predictions of the model agree with well over a hundred data points collected with air-water and air-glycerine solutions in 0.0254-, 0.0381-, and 0.0508-m. diameter pilot pipelines. A design procedure using the verified model is presented.

Waterhammer and Surge Control

Abstract: When the velocity of flow in a steady-state system is altered at any cross section, an hydraulic transient is initiated. The alteration of velocity requires that an un­ balanced pressure impulse be applied, which is· transmitted through the system at the acoustic speed a of the liquid in the system. The magnitude of the pressure pulse may be attenuated due to the action of fluid friction, or it may be changed due to changes in cross-sectional area of the conduit. For a frictionless liquid in a horizontal, prismatic, elastic tube, the application of a pressure differential Ap would result in a change in liquid velocity Av given by Ap = pa Av. in which p is the density. This Av and Ap would be transmitted unchanged throughout the length of the tube at speed a. This relation is a consequence of the impulse-momentum principle. The acoustic speed is determined by the bulk modulus of the liquid, Young's modulus for the pipe wall material, pipe wall thickness, pipe diameter, and method of supporting the pipe. An additional complication is that the bulk modulus of the liquid changes greatly with very small amounts of entrained gases or air. In the simple case of a reservoir, a pipe of length L. and a downstream valve, we can see how pressure waves are transmitted and reflected through the system. If the frictional effects are neglected and the valve is suddenly closed during a steady uniform flow of velocity Vo. the pressure suddenly jumps by Ap = paVo' This wave travels upstream, bringing the velocity to zero and raising the pressure by Ap. At instant L/a. the liquid in the pipe is at rest, the pipe diameter is enlarged, and the liquid is compressed. An unbalanced force exists on the segment of liquid at the upstream end of the pipe, causing it to be set in motion with speed Vo upstream and causing the pressure to drop to reservoir pressure. This wave arrives at the valve at 2L/a sec, at which time all the liquid is moving upstream at speed Vo. with pressure throughout at reservoir pressure. An un­ balanced condition exists at the closed valve, however, as the liquid cannot move away from the valve without causing a drop in pressure. In fact (if the transient isn't too strong and vapor pressure is not attained), the layer of liquid at the gate is held at zero velocity by a drop in pressure at the gate. This pressure drop

Fluid cooled mirror

Abstract: A system for cooling reflective surfaces of optical mirrors such as laser mirrors is provided, featuring use of multiple smallsized cavities or cells in the mirror body directly behind the reflective surface, through which coolant is caused to flow in short-length paths against the mirror surface between inlet/outlet openings serviced by a single or multiple manifold system, independently servicing each cavity. High coolant flow velocities at regulated rates against various surfaces of the mirror may thus be achieved according to the design requirements without incurring a large pressure drop penalty.

Research Note: Pressure Drop during Steam/Water Flow through Orifices

Abstract: A method of predicting the pressure drop during steam/water flow through orifices is presented, which extends an existing procedure to give improved agreement with experiment at conditions of low dryness fraction.

Air conditioner servicing unit

Abstract: Apparatus for servicing automobile air conditioning systems, as for charging them with refrigerant and compressor lubricant. Hoses connect to the high and low pressure charging fittings on the system and lead to pressure gauges for checking the system. The high pressure hose also leads to a dumping valve for emptying the system. The low pressure hose is connected through control valves (a) to a vacuum pump for purging the system, and also through a constant flow valve both (b) to a pressurized source of refrigerant liquid and (c) to a pressurized source of oil. Charging is done to the suction side of the compressor while it is operating. The flow valve passes liquid through a small orifice at a controlled pressure drop. This limits oil flow to a rate, such as one ounce in 45 seconds, slow enough to avoid damaging the compressor, and meters refrigerant in liquid state at a constant rate, e.g. one pound per 90 seconds. As refrigerant leaves the metering valve it is atomized and vaporized before entering the system. Preset timers control the periods of constant flow of oil and refrigerant and thereby meter the quantities charged to the system. A third hose and pressure gauge are provided for servicing those systems having a pressure ratio valve between the evaporator and the compressor.

Quieting means for a fluid flow control device using vortical flow patterns

Abstract: Quieting means for a fluid flow control device is shown in connection with a typical pressure relief type valve. The quieting means consists of a stack of washer-like members or disks which cooperate to define a large number of finely-divided flow paths across the stack of disks. To provide a configuration which is very economical of space, the disks are arranged such that the flow path turns back and forth through different planes. Groups of flow paths are defined by a number of groups of two or three perforated disks confined between two imperforate disks. In one embodiment, two perforated disks having patterns of small vortical flow directors are positioned on opposite sides of a similar disk having a pattern of small orifices. By proper juxtaposition of the three disks, a circuitous flow pattern is established through a radial passage tangentially into a first vortical chamber defined by a first cylindrically shaped opening in one disk, axially through a small orifice in the orifice disk to a third cylindrically shaped opening and another radial passage arranged to produce an oppositely directed flow pattern substantially radially through said opening and axially in the opposite direction through another small orifice to another such cylindrically shaped vortical chamber and continuing in this manner across the stack of disks. The dimensions of the passageways and orifices are chosen such that the velocity of flow across any orifice never exceeds a desired limit. The pressure drop is shared between the vortical effects and the series orifices whereby the fluid velocity is reduced and controlled. The vortex effect minimizes the approach velocity from one orifice to another. A second embodiment does not use the intermediate orifice plate, but places two similar disks having the vortical flow-directing pattern adjacent to each other but nonaligned such that axial flow occurs through a section where the essentially cylindrical portions of the pattern on the plates are in registry and radial flow occurs along paths leading to and from the cylindrical sections. The radial flow paths are oriented such that a reversal in the vortical flow pattern occurs at the end of each cylindrical pattern.