Static Pressure Drop Research Articles

Measurements of the nearly isotropic turbulence behind a uniform jet grid

Wind-tunnel turbulence behind a parallel-rod grid with jets evenly distributed along each rod is nearly isotropic. Homogeneity improvement over prior related experiments was attained by the use of controllable nozzles. Compared with the ‘passive’ case, the downwind-jet ‘active’ grid has a smaller static pressure drop across it and gives a smaller turbulence level at a prescribed distance from it, while the upwind-jet grid gives a larger static pressure drop and larger turbulence level. ‘Counterflow injection’ generates larger turbulence energy and larger scales, both events being evidently associated with instability of the jet system. This behaviour is much like that commonly observed behind passive grids of higher solidities.If the turbulent kinetic energy is approximated as an inverse power law in distance, the (positive) exponent decreases with increasing (downwind or upwind) jet strength, corresponding to slower absolute decay rates. No peculiar decay behaviour occurs when the jet grid is ‘self-propelled’ (zero net average force), or when the static pressure drop across it is zero.The injection does not change the general behaviour of the energy spectra, although the absolute spectra change inasmuch as the turbulence kinetic energy changes.

Emulsion flow in porous solids: I. A flow model

Flow of a stable emulsion in a porous solid is explicitly considered. Linear flow relations for both internal and external phases are assumed and gravitation and compression are neglected; however, a capillarity force is defined that may be interpreted in terms of contact angle hysteresis or variations in pore size, with or without three-phase contact. Continuous injection of an emulsion into a solid saturated with the external phase of the emulsion under conditions of constant saturation and pressure drop yields an equation in closed form containing as experimental parameters flow constants for each phase and the capillarity factor. If the saturation is allowed to vary, a wave expression comparable with that of the Buckley—Leverett treatment, but with capillary effects included, is derived. A differential equation describing flow in a radial geometry is derived, but it is amenable only to a numerical solution.

Growth of controlled profile crystals from the melt: Part III — Theory

In this note we outline the theory of the crystal growth technique, “Edge-Defined, Film-Fed Growth: as described in Growth of Controlled Profile Crystals from the Melt: Part II.” Firstly, we examine the static conditions for the stability of the liquid film from which the crystal growth takes place. We next consider the required conditions of pressure drop in the capillary orifice due to viscous drag. The thermal considerations are then discussed, and the way they relate to the stability of the process and its sensitivity to changes in the variables that are imposed on the system with special reference to the heat loss mechanisms. Finally we explain the way in which the micromorphology of the crystals will depend on the topography of the solid-liquid interface, which in turn depends on the thermal conditions in the liquid near the interface.

THROUGH‐CIRCULATION DRYING OF TAPIOCA ROOT

SUMMARY— The drying characteristics of fresh/y harvested tapioca root (Manihot utilissima Pohl) from Posadas, Argentina, have been investigated in a laboratory through‐circulation dryer. Variables studied were bed depth (2‐12 cm), air velocity (2,300‐5,200 kg/(hr)(sq meter), and air temperature (55—100°Cl. Static pressure drops of air passing through beds of dried and wet slices also were investigated. Straight lines are obtained plotting on semilogarithmic paper the nondimensional moisture content (W‐We) (Wo‐We) against time. This allows deduction that a diffusional mechanism is controlling the drying rate. Factors to be considered in the design of a continuous through‐circulation dryer are given.

Dynamic behaviour of a water-cooled boiling channel with twisted tapes

To predict the dynamic behaviour of a Boiling Water Reactor constructed with twisted tapes in the boiling channels, many steady state and dynamic tests have been performed with this new type of boiling channel at the Stability Loop of AEG. The steady state measurements comprised slip correlations and two phase friction factors which must be known for the theoretical calculation of the dynamic void fractions. These local and total void fractions were measured disturbing sinusoidally either the heat power or the mass flow. The frequency responses of the pressure drop were measured for both types of disturbances, also. To simulate the situation of a “hot channel” in the reactor, which is encircled by the greater part of relative “cold channels” with nearly constant pressure drop, the void response was measured disturbing the power, with the condition of constant pressure drop over the whole test section. Constant pressure drop was achieved by a control circuit acting on the flow modulation valve. All experimental results have been compared with calculations done with HYKAMO, a newly developed digital program. The main features of this model are: (1) the introduction of damping factors, a temperature disturbance in the subcooled region or a void disturbance in the boiling region travel with decreasing amplitude through the channel, and (2) the introduction of flow dependent slip ratios. The overall agreement between the experimental and theoretical frequency responses found was very satisfying.

Heat transfer and pressure drop in horizontal annular two-phase, two-component flow

The static pressure drop and both the local and average heat-transfer coefficients were measured for the horizontal annular flow of water and air in a tube with an I.D. of 1 in. The electrically heated stainless steel heat-transfer section 60 in long was located approximately 105 in downstream of liquid injection. Tube wall temperatures were measured by fifty-seven buried and twenty-two surface thermocouples. The water flow rate varied from 0.0714 to 0.3836 lb/s; the air flow rate, from 0.0300 to 0.2573 lb/s; and the heat flux, from 7372 to 12772 Btu/h ft 2. Sizeable circumferential variations in tube wall temperatures were observed at low air flow rates. A correlation for the heat-transfer coefficients was obtained. The pressure drop data agreed well with the Lockhart-Martinelli correlation and the prediction of the Wrobel-McManus wave roughness theory.

Evaporating Fluid Flow in Pipes: A Theory for the Prediction of Phase Velocity, Pressure Drop and Critical Outlet Conditions for Evaporating Annular Flow in Pipes

The theory of evaporating flow given in this paper is believed to be an advance on what has hitherto been available in that it makes due allowance for the effect of vapour condensation which occurs simultaneously with vapour expansion. The basic theory is applicable without modification to any fluid undergoing evaporating flow in the annular mode, given suitable correlations for wall and interphase friction factors as defined in the paper. Preliminary correlations, which can only be very rough, are provided for water. A lot of experimental work on a variety of fluids would be required to achieve a position from which general correlations could be developed. The theory incidentally permits prediction of critical outlet conditions and some interesting comparisons with available experimental data have been made.

並列流路における単相流圧力降下のバーンアウト熱流束に及ぼす影響

As exemplified in the case of boiling water reactors, orificing at the inlet of each channel is considered to be effective in suppressing flow instability in parallel channels. It is also expected that such orificing should affect the burn-out heat flux in parallel channels.In this experiment, the burn-out heat flux in parallel channels was measured by varying the single phase (orifice) pressure drop and other conditions (flow rate and inlet temperature) in atmospheric pressure.It was found as a result that burn-out heat flux generally becomes higher as the single phase pressure drop is increased under fixed conditions of flow rate and inlet temperature. In one certain case however, the burn-out heat flux became higher with decrease of the single phase pressure drop. This was probably due to the large effect of natural circulation caused by the low flow rate of that particular case.

Two-Phase Pressure Drop Across Vertically Mounted Thick Plate Restrictions

The objective of this experimental study was to obtain two-phase (water-steam) flow pressure drop for thick-plate flow restrictions. Two-phase pressure drop data for uniformly heated tubular test sections were also obtained. A statistically designed program encompassing 536 runs was conducted employing 30-in. long test sections of six geometries. Two nozzle type, three thick-plate orifice type, and one straight expansion type flow restrictions were investigated. The ranges of parameters investigated were: Quality: 0–23 percent; Flow Rate: 500–1500 lb/hr; Pressure: 800–1600 psia; Tube Diameters: 0.416, 0.500 in. A complete factorial experimental design was employed which enabled an analysis of variance to be conducted to determine the significance of the flow rate, quality, and pressure on the response of the static pressure drop. Each of these factors was found to be highly significant. Inherent in the statistical methods employed was the establishment of the 95 percent confidence limits on the data for each test section studied. These limits ranged from 0.009 psi to 0.306 psi for the largest and smallest restriction diameters, respectively. The precision of the data was well within the limits for experimental two-phase flow technology. The results of an error analysis indicate that the accuracy with which flow rate, pressure, and geometry were determined gave rise to insignificant errors and the resulting maximum possible error in quality was less than the lower limit of the correlation equation confidence limits. The results of this study were compared with only moderate success to the theoretical models presented in the literature by Tippetts, Hoopes, and Mendler, et al. Several attempts at correlating the data resulted in a design equation to calculate the static pressure drop for the flow restrictions investigated. The form of the equation developed was: ΔPs=Zα′νG+1−α′νFgg0+K′νF2g0GR1−x1−α′2

Experimental Effect of Bluntness and Gas Rarefaction on Drag Coefficients and Stagnation Heat Transfer on Axisymmetric Shapes in Hypersonic Flow

X« = mean free path behind sphere shock A = sphere shock standoff distance FQ = drag force m = mass a = acceleration T,nin = minimum activation temperature of paint = 400°K T = wall temperature n = spectral order number, 3, 5, 7 X = wavelength of light in Angstrom units Inverted hemispheres, circular discs (normal to stream), spheres, 26° total angle 0.368 blunt hemisphere cones, 18° totalangle sharp cones, and other axisymmetric shapes were run in a hyper velocity wind tunnel. Hypersonic drag coefficients at zero angle of attack were measured in the air velocity range, 7,00020,500 ft/sec and Knudsen number range, 0.0001-0.34. Drag coefficient is defined as drag for c<t/qA JL. Knudsen number is defined as 1/3 mean free path behind shock/sphere shock detachment distance. In the case of nonsphere shapes, the Knudsen number is denned as the Knudsen number of a sphere with the same base diameter. These drag coefficients cover the range of gasdynamics to free molecule flow and are given in graphical form. The drag coefficients were measured by means of a ballistic balance in millisecond intervals, and referenced to the drag coefficient of a sphere in the gasdynamics region, for a gamma of 1.4, of 0.92. Tunnel stagnation conditions of pressure, temperature, density, and pressure drop with time were measured directly. In the tunnel test section, velocity, q density, total pressure, and static pressure were measured directly. These experimental curves have been found useful in the analysis of complex shapes if the complex shapes can be easily broken down into simple components with small interactions between components. Heat-transfer distributions have also been obtained on these and other complex shapes in the hypervelocity wind tunnel, by means of a special paint which changes through several visible spectral orders within a heat transfer range of X10 for a single application. Heat transfer rates, so obtained, have been performed in the hypersonic gasdynamic and slip flow regions and are presented for spheres. These data, in the vorticity interaction region, agree with the data of Ferri and Zakkay.*

Air Flow Patterns and Heat Transfer Within the Respiratory Tract: A new method for experimental studies on models

AbstractIngelstedt S. and N. G. Toremalm. Air flow patterns and hat transfer within the respiratory tract.The authors have worked out an experimental method which makes it possible to determine air flow patterns in models of the respiratory tract. The method is based on the close relationship between heat transfer and pressure drop conditions which occur in a tube with a warm inner surface when air is blown or sucked through it. The air temperatures before entering and after leaving a tube of tracheal dimensions are determined and the heat transferred to the passing air is computed. Thus heat is used as a tracer. As a result of friction to flow, an aerodynamic boundary layer is built up. It is stated that the shape of this layer determines the actual degree of heat transfer between the airway mucous membranes and the respired air. The hitherto unknown biological importance of variations in the boundary layer within different parts of the respiratory tract is briefly discussed.

Heat Transfer and Pressure Drop for Viscous-Turbulent Flow of Oil-Air Mixtures in a Horizontal Pipe

Abstract The heat transfer and static pressure drop for two-phase, two-component flow of oil and air were measured for flow in a steam-heated horizontal 15-ft length of ¾-in. extra-heavy copper pipe. This is a second part of a two-phase heat-transfer program for which the first part, on water-air mixtures, was reported in reference (1). Tentative correlations are presented and used in a comparison of the oil-air and water-air results for heat transfer and nonisothermal pressure drop in the same test system.

Through‐circulation drying of seaweed. V. —Ascophyllum nodosum; fucus serratus; fucus vesiculosus

AbstractThe drying characteristics of freshly harvested Ascophyllum nodosum, Fucus vesiculosus and F. serratus have been investigated in a through‐circulation dryer. All tests were carried out with minced seaweed. Variables studied were bed depth (0.5–6 in. approx.), air temperature (100‐220° F), air wet‐bulb depression (30‐115° F), air mass velocity (5‐11 lb./sq. ft. min., and static pressure drops of air through beds of wet and dry weed. Bed‐depth experiments have given equations relating drying times, constant drying rates and outputs to loading. The output versus loading curve shows a well‐defined optimum value for each species of seaweed. Empirical equations have been derived, relating drying times (between definite water content limits) and initial constant drying rates to air mass flow. It has been shown that the drying rates, at average water contents of 3.0 to 0.2, 2.7 to 0.2, and 3.5 to 0.15 lb./lb. of bone‐dry solids (for A. nodosum, F. vesiculosus and F. serratus respectively), are directly proportional and the drying times inversely proportional to the wet‐bulb depression of the air. A study of the water content of various layers in a seaweed bed has been made. A typical drying rate versus water content curve is shown, and a mechanism of drying of deep beds has been postulated. A section is included dealing with the prediction of approximate drying times and rates.

Through‐circulation drying of seaweed I. Laminaria cloustoni stiple

AbstractThe drying characteristics of freshly harvested seaweed stipe of the species Laminaria cloustoni have been investigated in a laboratory through‐circulation drier. The stipes, with a water content of 83‐86%, were cut on a bacon slicer into discs 1/8‐in. thick by I‐I 1/4. in. diameter.Experiments on the effect of interruption of drying, initial water content, and repeatability established the experimental procedure before studying the principal factors. Variables studied were bed depth (0‐5‐7 in), air temperature (120–340° F.), air wet‐bulb depression (44‐228° F.) and air velocity [3‐9.5 lb./(sq. ft.)(min.)], slice thickness (1/165 to 1/16 in.) with an experiment on agitation. Static pressure drops of air passing through beds of dried and wet stipe slices were also investigated.As the initial drying rates of the seaweed beds were virtually constant, the value of this constant rate has been correlated with the drying factors. Drying times between water content limits of 5 to 0‐15 lb, of water/lb. of bone‐dry solids have been related by empirical equations to the drying conditions.It has been demonstrated that the drying rates of seaweed beds at average water contents of 5 to 0‐2 lb./lb. of bone‐dry solids are directly proportional to the wet‐bulb depression of the air, and a unit wet‐bulb depression evaporation coefficient may be used to find approximate drying times and rates.Tests showed that static beds of seaweed stipe were scorched at temperatures of 250° F. or higher.Factors to be considered in the design of a continuous through‐circulation drier for stipe are given.

Heat Transfer and Pressure Drop for Turbulent Flow of Air-Water Mixtures in a Horizontal Pipe

Abstract The static pressure drop and heat transfer for two-phase, two-component flow of air and water were measured for flow in a horizontal 15-ft length of 1-in. 16-gage brass tubing. Flow rates include the range of 1000 to 15,000 lb per hr for the water and 0 to 200 lb per hr for the air. Tentative correlations are presented from which prediction of pressure drop and heat transfer may be made under restricted flow conditions.

Displacement Versus Time Characteristics of Hydraulic Actuators

Abstract This paper develops the relation between the displacement and time of a piston in a hydraulic actuator in terms of the load, mass, pressure drop, viscosity, and special operating conditions. It is based upon the Fanning law of friction in pipes and the value of the friction factor in smooth pipes as given by Hagen-Poiseuille and Blasius. The relation developed will cover most conditions met in the design of hydraulic equipment and will suggest a means to analyze those conditions not covered. This method is valid for pressures up to 100 atm and, with modifications, to higher pressures.

GAS DYNAMIC TREATMENT OF EXOTHERMIC AND ENDOTHERMIC DISCONTINUITIES

Endothermic and exothermic processes in gas dynamic flows taking place in a very narrow zone may be considered as discontinuities. The variation of the static and total head density ratio, pressure ratio, and temperature ratio as well as the angle of deviation, area ratio, and exit normal Mach number have been found as functions of the entry normal Mach number and of heat addition. In addition to these, some other useful quantities such as the area ratio parameter, the difference of the square of velocities, and the normal velocity product have been evaluated. It was found that, in a discontinuity, heat can be added until the exit normal Mach number reaches unity (choking). Depending on the entry normal Mach number, only a limited amount of heat can be added at the discontinuity. An exothermic discontinuity behaves as an expansion when the entry normal Mach number is subsonic, and it is accompanied by a drop in static pressure, density, and total head pressure. An exothermic discontinuity behaves as a compression shock wave when the entry normal Mach number is supersonic, and it is accompanied by an increase in static pressure and density and a decrease in total head pressure. An endothermic discontinuity behaves always as a compression shock wave, and it is accompanied by an increase in static density, pressure, and total head pressure. It is hoped that the results and conclusions found may be useful in a better understanding of many nearly discontinuous phenomena such as flame fronts, condensation and evaporation fronts, and other similar problems.

Isothermal Pressure Drop for Two-Phase Two-Component Flow in a Horizontal Pipe

Abstract The static pressure drop accompanying the isothermal two-phase two-component flow of air and eight various liquids, including benzene, water, and S.A.E. 40 oil, was measured for flow conditions varying from all air to all liquid in a 1-in. glass pipe and a ½-in. galvanized-iron pipe. The flow patterns existing at the various flow rates were studied visually and photographically. A macroscopic analysis of the flow phenomenon is presented, which allows the prediction of two-phase two-component static pressure drop under certain flow conditions. The application of the proposed method to the prediction of pressure drop along a pipe in which a fluid is evaporating is tentatively outlined.