Showing papers on "Pressure drop published in 1980"
TL;DR: In patients less than 50 years of age the aortic jet was easy to find, the measurement was reproducible, and underestimation of the pressure drop obtained at catheterisation was within 25 per cent in 17 of 18 patients, but pressure drop was significantly underestimated in one-third of patients over 50 years.
Abstract: The peak pressure drop across the aortic valve in aortic stenosis has been measured by Doppler ultrasound. Maximum velocity in the Doppler signal from the aortic jet was recorded using a maximum frequency estimator. With an angle close to zero between ultrasound beam and maximal velocity in the jet, peak pressure drop can be calculated from the maximal velocity measured; a larger angle will underestimate maximal velocity and pressure drop. In 57 of 63 patients with aortic stenosis, the aortic jet could be reached by the ultrasound beam and, in 37 of these, peak pressure drop by ultrasound was compared with that obtained at catheterisation. In patients less than 50 years of age the aortic jet was easy to find, the measurement was reproducible, and underestimation of the pressure drop obtained at catheterisation was within 25 per cent in 17 of 18 patients. In patients over 50 years Doppler signals from the aortic jet were more difficult to obtain, and pressure drop was significantly underestimated in one-third, but time of maximum velocity in systole could indicate whether moderate or severe aortic stenosis was present.
488 citations
TL;DR: A cyclone with a 47 mm after-filter has been developed for ambient air size-selective monitoring as discussed by the authors, which has been extensively evaluated with laboratory-generated aerosol and has shown that the cyclone operates in a single flow regime with a vortex in the outlet flow.
Abstract: A cyclone with a 47 mm after-filter has been developed for ambient air size-selective monitoring. It has been extensively evaluated with laboratory-generated aerosol. Variation of the pressure drop and 50% cut point with flow rate show that the cyclone operates in a single flow regime with a vortex in the outlet flow. The particle size cutoff curve is comparable in sharpness to a cascade impactor and is the same for solid or liquid particles. At 21.7 L/min, D 50 is 2.5μm and at 15.4 L/min, D 50 is 3.5 μm. Collection efficiency data for flow rates from 8 to 27 L/min fit a universal curve when plotted vs. the normalized particle diameter, (D-D 50)/D 50 Reentrainment of previously deposited particles is less than 1 % of the loading per day. In field tests the cyclone has proved to be a very satisfactory size-selective sampler.
184 citations
TL;DR: In this article, it was shown experimentally that the dynamics of flow and axial dispersion in such coiled tubes can differ substantially from behaviour in straight tubes, almost quantitatively accounted for by the existence of secondary flow phenomena.
142 citations
TL;DR: Microvascular pressures in the pulmonary circulation were measured under the pleural surface of the isolated perfused dog lung by the servo-null technique, finding negligible pressure drop in venules with diameters larger than 20 micrometers.
Abstract: Microvascular pressures in the pulmonary circulation were measured under the pleural surface of the isolated perfused dog lung by the servo-null technique. Strong glass micropipettes with short beveled tips were used, with a suction ring to stabilize the lung9s surface. Of the total vascular resistance, 45 percent was in the alveolar wall capillaries themselves. Most of the remaining resistance was in the arterioles. There was negligible pressure drop in venules with diameters larger than 20 micrometers.
131 citations
TL;DR: In this article, the effects of peripheral-layer viscosity on the flow characteristics of a bio-fluid due to peristaltic transport has been investigated, and it is shown that, for a given pressure drop, the flow flux increases and the frictional force decreases as the viscosities of the peripheral layer fluid decreases.
Abstract: The effects of peripheral-layer viscosity on the flow characteristics of a bio-fluid due to peristaltic transport has been investigated. It is shown that, for a given pressure drop, the flow flux increases and the frictional force decreases as the viscosity of the peripheral-layer fluid decreases. However, for zero pressure drop, the flux does not depend upon this viscosity while the friction force decreases as it decreases. The analysis has been applied and compared with observed data.
96 citations
TL;DR: In this paper, an equation is developed for use in predicting the two-phase multiplier for pressure drop in bends; the equation simplifies the use of an existing method and is also compared for the first time with data at high density ratios ( ϱl/ϱg = 560 ).
93 citations
TL;DR: In this paper, the authors reviewed correlations for predicting the two-phase flow pressure drop across ideal tube banks and compared with experimental data, and showed that the Martinelli-type method used for tube-side pressure drop correlation appears to be a basically usable approach if correspondingly modified.
Abstract: Published correlations for predicting the two-phase flow pressure drop across ideal tube banks are reviewed and compared with experimental data. No presently available methods can be considered general enough for use under all conditions. The Martinelli-type method used for tube-side pressure drop correlation appears to be a basically usable approach if correspondingly modified. All available data are reasonably well represented in terms of the Martinelli parameters at low liquid loading (Xtt small). At high liquid loading ( Xtt large) there is increasing scatter and additional parameters are needed. Substantial improvement is believed to be possible by adjustment of the Martinelli model through recognition of the different flow regimes.
88 citations
TL;DR: In this article, an experimental investigation was conducted of the tube-side behavior of various internal configurations with turbulent/transitional flow of water in the Reynolds number range 10,000-120,000 and Prandtl number range 2-11.
Abstract: An experimental investigation was conducted of the tube-side behavior of various internal configurations with turbulent/transitional flow of water in the Reynolds number range 10,000-120,000 and Prandtl number range 2-11. By using a heat-momentum transfer analogy, correlations were obtained that enable practical designs with standard products or optimization of tube geometry for specific conditions.
86 citations
TL;DR: In this article, the laminar, transition and turbulent parallel flow pressure drop across wire-wrapped hexagonal rod bundles positioned inside a duct were determined in tests using water, sodium, and air.
Abstract: Laminar, transition, and turbulent parallel flow pressure drop across wire-wrapped hexagonal rod bundles positioned inside a duct were determined in tests using water, sodium, and air A smooth transition region from turbulent to laminar flow that occurred over the Reynolds number range from 5000 to 400 characterized the resulting friction factor behavior The continuous transition region could be explained in terms of the fraction of the flow area in turbulent flowLaminar friction factors calculated from individual subchannel measurements could be correlated by the same expression found for rod-bundle-averaged conditions In the laminar range, the friction factor was correlated by the expression f = 110/Re, in the turbulent range by f = 055/Re025, and in the transition range bywhere is the intermittency factor A general laminar flow friction factor correlation was developed:This correlation agrees satisfactorily with limited laminar flow data from rod bundles having different wire-wrap lead p
74 citations
TL;DR: In this paper, a model for predicting the liquid recirculation rate in gas-lift reactors was developed based on experimentally determined correlations for mean gas holdup and frictional pressure drop in two phase bubble flow.
71 citations
TL;DR: In this paper, the average void fraction in the curved test section was determined, and empirically correlated to the pressure drop, by means of a series of nondimensional numbers, and the combined action of gravity and centrifugal force acting on two-phase flow was expressed in terms of a modified Froude number representing the balance of radial forces between those acting on the liquid and the gaseous phases of the flow passing through the reclined vertical U- bend.
Abstract: Experimental results are presented on the flow behavior, average void fraction and pressure drop in air-water two-phase flow mixture flowing upward through a C-shaped bend curved in vertical plane The curved test section of transparent acrylic resin tubing was varied in four versions of (a) 90 mm, (b) 1325 mm and (c) 180 mm radii of curvature with 16 mm inside diameter tube, and (d) 135 radius with 24 mm diameter tube The combined action of gravity and centrifugal force acting on the two-phase flow is expressed in terms of a modified Froude number representing the balance of radial forces between those acting on the liquid and the gaseous phases of the flow passing through the reclined vertical U- bend The average void fraction in the curved test section was determined, and empirically correlated to the pressure drop, by means of a series of nondimensional numbers
TL;DR: Static mixers as mentioned in this paper are a class of similar, fixed mixing units installed at right angles to each other in series along a tube or a channel, and the mixing effect in static mixers under conditions of laminar flow is accomplished by specially designed feed systems, by cutting and twisting, by displacement and distortion, or by separation and expansion.
Abstract: Static mixers and their applications. Static mixers are generally made up of similar, fixed mixing units installed at right angles to each other in series along a tube or a channel. The energy of mixing is extracted from the flow. Twelve different units are presented. The mixing effect in static mixers under conditions of laminar flow is accomplished either by specially designed feed systems, by cutting and twisting, by displacement and distortion, or by separation and expansion. Depending upon the mixer, very different lengths are required to achieve the same degree of homogeneity. Compared with an empty tube, the pressure drop in static mixers is some 7-to 200-fold greater for laminar flow and 100- to 600-fold greater for turbulent flow. Static mixers are employed in all areas of chemical engineering for homogenization, for reduction of the resisdence-time spectrum, and for heat exchange. Since maintenance and wear are negligible, since incorporation frequently requires no extra space, and since they can be used over wide ranges of viscosity, static mixers are being increasingly employed in continuous processes.
DSM1
TL;DR: In this article, the authors show that the pressure drop over a packed-bed reactor is lower than over a coiled open tubular reactor, and that for a given residence time and equal band-broadening values, the pressure drops over a PBR are lower than those of a COTR.
Patent•
24 Nov 1980
TL;DR: In this article, a particle analyzer for a sample suspension of particles originating in a container in which: a flow director is mounted between the container and a first chamber, a particle sensing aperture is mounted in between the first chamber and a second chamber, and a liquid sheath is introduced into the second chamber for hydrodynamically focusing the particles through the aperture, an electrical current passes through the sensing aperture for generating impedance signals, the pressure drop is regulated across the flow director to assure a constant flow of the suspension through the flow and the aperture.
Abstract: A particle analyzer for a sample suspension of particles originating in a container in which: a flow director is mounted between the container and a first chamber, a particle sensing aperture is mounted between the first chamber and a second chamber, a liquid sheath is introduced into the first chamber for hydrodynamically focusing the particles through the sensing aperture, an electrical current passes through the sensing aperture for generating impedance signals, the pressure drop is regulated across the flow director to assure a constant flow of the suspension through the flow director and the aperture, and the flow director is formed into an optical element for viewing the sensing aperture.
TL;DR: In this article, the authors extend the model to the case of submicron particles, where the main transport mechanism is Brownian diffusion, and present solutions for the cases of nonslip flow around the fiber and nonslip, slip and free molecular flow around particles.
Abstract: When an aerocolloidal suspension flows through a fibrous filter, particles deposit on the fibers and form dendrites. Similar phenomena are observed with collectors other than fibers, provided that the characteristic dimension of the collector does not exceed that of the particles by more than one to two orders of magnitude. This deposition pattern leads to marked increases in capture efficiency and pressure drop, as particles accumulate within the filter. In previous publications, theoretical models of this process were developed for the cases of deposition by interception alone and of deposition by combined inertial impaction and interception. Consequently, those works apply to aerosol particles with diameters of 1 μm or larger. Here we extend the model to the case of submicron particles, where the main transport mechanism is Brownian diffusion. To keep things specific, we consider fine fibers as collectors, but the model can be easily converted to other geometries. We present solutions for the cases of nonslip flow around the fiber and nonslip, slip and free molecular flow around particles. Unlike deposition by inertial impaction and/or interception, convective Brownian diffusion forms dendrites over the entire fiber surface.
TL;DR: In this article, experimental data and analysis of the pressure drop of turbulent flow through rod bundles is presented. But the authors focus on laminar flow and do not consider the effect of spacer grids on the velocity distribution.
Patent•
11 Sep 1980
TL;DR: In this article, the authors describe a system and process for heating and cooling a house, circulated and/or intake air is passed through a system which utilizes low intensity and readily available geothermal heat capacity to heat or cool such air.
Abstract: In a system and process for heating and cooling a house, circulated and/or intake air is passed through a system which utilizes low intensity and readily available geothermal heat capacity to heat or cool such air. The ducts of the system have an internal configuration and size that provides for relatively low velocity and correspondingly low pressure drop through such ducts yet provides air flow patterns that have sufficiently high air velocities adjacent the interior surface of the duct to provide extremely good heat exchange between such air and the interior surfaces of the ducts to utilize the low intensity temperature differentials provided by the earth mantle at only moderate depths adjacent a house in any of a great variety of areas. The exterior surfaces of the ducts are shaped to avoid compaction of porous filling material located between the relatively small diameter ducts and the large diameter hole in which such ducts are located and thereby maintains a porous condition of the material peripheral to the duct and so provides heat exchange by water vapor flow as well as conduction between the external surface of the small diameter ducts and the large surface of the hole in the ground from which desired low intensity heat is absorbed or to which undesired heat is passed.
Patent•
22 Aug 1980
TL;DR: In this paper, the steerable wheels of a hydraulically driven vehicle are provided with fixed displacement type auxiliary motors which are connected in parallel both with each other and with the motor which powers the main drive wheels.
Abstract: AUXILIARY HYDROSTATIC DRIVE SYSTEM Abstract of the Disclosure The steerable wheels of a hydraulically driven vehicle are provided with fixed displacement type auxiliary motors which are connected in parallel both with each other and with the motor which powers the main drive wheels. A selector valve permits the motors for the steerable wheels to be optionally connected and disconnected from the reversible, variable dis-placement main pump. Flow dividers in the hydraulic lines limit the maximum flow of fluid to any one auxiliary drive motor. To prevent large power losses when the steerable wheel assist mode is not being utilized, the selector valves are placed in close proximity to each fixed displacement motor. This al-lows the motors to circulate large quantities of fluid around a closed loop at minimum pressure drop.
TL;DR: In this article, it was shown that at high velocities the loss in permeability is only about 50% of that of an ideal tube and that up to 70 theoretical plates per second can be generated for an inert sample at a pressure drop of only 7 bar.
TL;DR: In this article, a coherent representation of pressure drop in fixed beds and of fluidized bed expansion is derived on the basis of an analysis of the Navier-Stokes equations, which combines an Euler-number, a Reynolds-number and a characteristic dimensional ratio r0/δ.
TL;DR: Theoretical consideration is given to two unsteady pipe flows in this paper, where a combined steady and oscillatory shear flow is generated by a pulsatile pressure gradient in a stationary pipe.
Abstract: Theoretical consideration is given to two unsteady pipe flows. In the first, a combined steady and oscillatory shear flow is generated by a pulsatile pressure gradient in a stationary pipe. In the second, the pressure gradient is constant, but the pipe wall executes axial vibrations.
Patent•
09 May 1980
TL;DR: In this article, a backwashable filtering device is described, which includes a housing, a filter body, and backwash nozzle having a nozzle inlet disposed adjacent to the upstream surface of the filter body.
Abstract: A backwashable filtering device is described of the type including a housing, a filter body, a backwash nozzle having a nozzle inlet disposed adjacent to the upstream surface of the filter body, and pressure sensor means for sensing the pressure drop across the filter body and effective, upon sensing a predetermined pressure drop, to initiate a backwashing operation by connecting the backwash nozzle to the atmosphere and initiating relative rotary movement between the filter body and the backwash nozzle. The filtering device further includes a position sensor for sensing the home angular position of the filter body with respect to the backwash nozzle, and a control effective, only when said home angular position is sensed, for terminating the backwash operation.
Patent•
19 Mar 1980
TL;DR: In this article, a porous web is placed against a surface of a test head 10 of an apparatus for testing the permeability of porous web materials and a pressure transducer 46 is connected to the static port 32 and provides a measurement of the pressure drop across the web.
Abstract: An apparatus for testing the permeability of porous web materials. The porous web 12 is placed against a surface of a test head 10 of the apparatus. The test head 10 contains at least one aperture 28 and a vacuum source 87 connected to the test head 10 causes air to be drawn through the web 12 and then through the aperture 28. The test head 10 also includes at least one static port 32 that communicates with the aperture 28. The static port 32 is located very close to the web 12 and measures the static pressure within the aperture 28 before it leaves the aperture 28. A pressure transducer 46 is connected to the static port 32 and provides a measurement of the pressure drop across the web 12. If the volumetric flow rate of air through the web 12 is kept constant, the pressure transducer 46 output 52 is representative of the permeability of the web 12. If the pressure differential across the web 12 is kept constant, measurement of the volumetric flow rate of air through the web 12 will be representative of the permeability of the web 12.
TL;DR: In this article, the porosity, density, and the average thickness of the corrosion product layer were determined by weight loss determinations over periods up to 210 days, and a general mathematical model was proposed to fit the experimental data with acceptable precision.
Patent•
26 Jun 1980
TL;DR: In this paper, a pilot poppet is unseated when a pressure in a back pressure chamber (39) exceeds a spring (47) preload force to communicate the back pressure chambers with a relief port (33).
Abstract: A pilot poppet (44) is unseated when a pressure in a back pressure chamber (39) exceeds a spring (47) preload force to communicate the back pressure chamber (39) with a relief port (33). The pressure in a pressure port (32) is communicated to the back pressure chamber (39) through a radial clearance between a piston poppet (61) which extends through a relief poppet (31) and the relief poppet (31). A spring (62) maintains the piston poppet (61) engaged with the pilot poppet (44). Alternatively, the piston poppet and pilot poppet may be integral (66). The relief poppet (31) is unseated by a pressure difference between the back pressure chamber (39) and the pressure port (32) to communicate the pressure port (32) with the relief port (33) since communication of the back pressure chamber (39) with the relief port (33) causes the pressure in the back pressure chamber (39) to drop. The relief poppet (31 ) seats when the pressure in the pressure port (32) drops below the pressure in the back pressure chamber (39). The pressure receiving area (AR) of the piston poppet (61) is made as small as possible to reduce the net force on the pilot poppet (44) and thereby the pressure drop in the pressure port (32). The ratio of a pressure receiving area (AP) of the pilot poppet (44) to the pressure receiving area (AR) of the piston poppet (61) is at least 1.1.
TL;DR: In this paper, a theory based on Darcy's law has been derived which relates pressure drop in a pulse-jet cleaned fabric filter to characteristics of the filter and dust, and can be used to identify operating conditions which cause pressure drop to increase without limit.
TL;DR: In this paper, a finite-difference procedure has been developed for predicting flows in dividing and combining flow manifolds, which requires the prescription of total flow rate through the header and the pressure of the surroundings where the fluid is either discharged or sucked.
Patent•
17 Apr 1980
TL;DR: A magnetic/centrifugal-fluid seal comprising a rotating disk-like collar/vane surrounding a rotatable shaft journalled in a housing defined by close-fitting stationary members forming a cavity to accommodate the rotating shaft and disklike collars as mentioned in this paper.
Abstract: A magnetic/centrifugal-fluid seal comprising a rotating disk-like collar/vane surrounding a rotatable shaft journalled in a housing defined by close-fitting stationary members forming a cavity to accommodate the rotatable shaft and disk-like collar/vane. A magnetic fluid is retained in a close clearance magnetic gap region between the rotatable shaft and the stationary members and is magnetized by an external permanent magnet or electromagnet. At standstill or low-speed the magnetic fluid is retained by magnetic force in the close-clearance magnetic gap region formed by several sets of opposing pole-like teeth confronting the inner surfaces of the rotating disk-like collar/vane. By virtue of magnetic attraction the magnetic fluid can withstand a pressure drop between high and low pressure regions and thus effects a magnetic seal at standstill and low speeds. As the shaft rotates faster, the magnetic fluid is forced centrifugally from the magnetic seal region and becomes a rotating mass or pool of fluid at the circumferential rim of the disk-like collar/vane. The fluid then acts as a conventional centrifugal seal. When stopping or slowing down, a speed is reached where the magnetic/gravitational forces again dominate over the centrifugal forces and the magnetic fluid returns to the magnetic seal region.
Dissertation•
01 Jan 1980
TL;DR: In this article, the authors investigated the influence of fluctuating pressure differences on air flow and showed that rapid fluctuations influence the flow rate only a little, while the fluctuations are slow and the problem was a steady state one, using time averaged pressure difference values.
Abstract: This work deals with different aspects of air movements in building components . The investigation shows to what degree the concept of fluid mechanics can be applied to problems concerning air flows in building Components. The applicable parts of fluid mechanics are presented as thoroughly as possible. Based on this concept, routines are outlined to make it possible to handle complex flow and pressure distribution problems. Both manual and computer calculation routines are described and the way they can be used is demonstrated in a number of examples.
Experimental investigations concerning determination of surface roughness of plates - instead of that of pipes which almost always has been investigated earlier were carried out. A test device for this purpose was designed and tested on a number of building materials. Also magnitudes of contraction and bend loss factors were investigated experimentally.
Since, in practice, pressure differences acting across building components are seldom steady the influence of fluctuating pressure differences was investigated theoretically. The analysis shows that rapid fluctuations influence the flow rate only a little. If the fluctuations are slow it is possible to calculate the flow rate as if the problem was a steady state one, using time averaged pressure difference values.
Leakaqe characteristics of different building components are reviewed and the air leakage behaviour of whole building envelopes is discussed. The great effect of entrance, bend, exit and orifice pressure losses is emphasized, and their influences on both leakage rate and flow characteristics are shown. An additional part of the so called pressurization test, taking the form of the leakage rate - pressure difference curve into account, is suggested. Such a procedure could imply a new possibility of detecting larqe, and maybe hidden, flow paths giving rise to substantial contributions to the total leakage rate of a building.
Some tables are also included. They cover surface roughness, permeability and porosity data of different building materials. An extensive list of references is given.