Showing papers on "Pressure drop published in 1988"

Breakup of fluid droplets in electric and magnetic fields

Abstract: A drop of fluid, initially held spherical by surface tension, will deform when an electric or magnetic field is applied. The deformation will depend on the electric/ magnetic properties (permittivity/permeability and conductivity) of the drop and of the surrounding fluid. The full time-dependent low-Reynolds-number problem for the drop deformation is studied by means of a numerical boundary-integral technique. Fluids with arbitrary electrical properties are considered, but the viscosities of the drop and of the surrounding fluid are assumed to be equal. Two modes of breakup have been observed experimentally : (i) tip-streaming from drops with pointed ends, and (ii) division of the drop into two blobs connected by a thin thread. Pointed ends are predicted by the numerical scheme when the permittivity of the drop is high compared with that of the surrounding fluid. Division into blobs is predicted when the conductivity of the drop is higher than that of the surrounding fluid. Some experiments have been reported in which the drop deformation exhibits hysteresis. This behaviour has not in general been reproduced in the numerical simulations, suggesting that the viscosity ratio of the two fluids can play an important role.

An approximate analysis for contraction and converging flows

Abstract: An approximate analysis is presented for the flow of fluids through planar and axisymmetric contractions. Energy principles are employed to relate the entry pressure drop to flow rate and fundamental rheometric properties. One of the aims of the analysis is to investigate the influence of extensional viscosity on such flows, particularly with regard to the occurrence and enhancement of vortex motion in the entry corners. For the sake of mathematical simplicity, independent power-law models are used to represent the shear and extensional viscosity functions. The analysis indicates that, once significant vortex motion is present, enhancement occurs whenever the Trouton ratio is an increasing function of shearrate (or stretch-rate). It is readily seen how the occurrence of vortices serves as a stress relief mechanism. Indeed, for highly stretch-thickening materials, the entry pressure drop is seen to be dominated by shear properties. The power-law parameters of the extensional viscosity function may be obtained in a straight-forward way from entry pressure drop versus flow rate data. Finally, the extension and application of the analysis to other similar flows, such as through converging nozzles, is briefly discussed.

On the use of flow through a contraction in estimating the extensional viscosity of mobile polymer solutions

Abstract: We consider the use of pressure measurements in contraction flows in the determination of the extensional viscosity behaviour of polymer solutions. The experimental data are interpreted on the basis of the recent theory of Binding. The resulting extensional viscosities are compared with those obtained from a commercial Spin Line Rheometer. We conclude that contraction flows provide a convenient means of determining the extensional viscosity of shear-thinning polymer solutions. The case is not so clear for constant viscosity Boger fluids. In the course of the experiments, it is shown that excess pressure losses in the contractions can be brought about by two distinct flow mechanisms in the case of Boger fluids. In the axisymmetric case, both vortex enhancement and excess pressure loss are observed, although there is not a strict one-to-one correlation between these phenomena. In the planar case, vortex enhancement is not conspicuously present, although there is still a substantial excess pressure loss at high flow rates. This excess must be associated with the ‘bulb’ flow field which essentially replaces the vortex-enhancement regime of the axisymmetric case.

Non-Darcian Convection in Cylindrical Packed Beds

Abstract: Non-Darcian transport describes the nonuniform flow and thermal anomaliesoften found in flow through packed beds These effects include the high-flow-rate inertial pressure loss, near-wall porosity variation, solid-boundary shear, and thermal dispersion Inclusion of these effects significantly alters the velocity and temperature profiles from those predicted by models using uniform or Darcian flow In this paper, the non-Darcian formulation is used to predict the heat transfer rates for cylindrical packed beds such as chemical reactors Traditional analyses of chemical reactors assume slug flow and must include a temperature-slip boundary condition to predict the measured temperature profiles The present analysis predicts similar temperature variations by allowing the velocity and diffusivity to vary across the bed The results agree with experimental relations needed in conventional reactor models

Electronic blood pressure meter

Abstract: Disclosed is an electronic blood pressure meter which is adapted to measure blood pressure from a finger A cuff for applying pressure to the finger comprises a plurality of chambers which are communicated to each other and, thereby, provides a sufficient flexibility to closely conform to the contour of the finger A sensor for detecting pulse wave data may be conveniently place on the inner surface of the cuff and is adapted to detect the reflection of light by an artery Further, an air buffer can increase the effective air volume of the cuff and can reduce the rate of the pressure drop of the air cuff for a given rate of air vent from the cuff By deriving the pulse wave data and computing the systolic and diastolic blood pressure therefrom in the course of increasing the air pressure of the cuff, the discomfort to the patient whose blood pressure is to measured can be substantially reduced

Two‐phase pressure drop in vertical crossflow across a horizontal tube bundle

Abstract: An experimental investigation has been made to evaluate the friction, acceleration, and hydrostatic pressure drops in two-phase vertical crossflow across a horizontal tube bundle through the measurement of the void fraction and determination of the two-phase friction multiplier. The void fractions were found to increase with increasing mass velocity for a fixed quality level. The two-phase friction multiplier increased with increasing mass velocity for a fixed value of the Martinelli parameter in both slug and spray flow and decreased with increasing mass velocity in bubbly flows. The void fraction and two-phase friction multiplier data were correlated and used to predict with very good results the total pressure drop occurring in simulated diabatic flow tests and in actual diabatic tests using R-113.

Numerical modelling of nonlinear effects in laminar flow through a porous medium

Abstract: This paper deals with the introduction of a nonlinear term into Darcy's equation to describe inertial effects in a porous medium The method chosen is the numerical resolution of flow equations at a pore scale The medium is modelled by cylinders of either equal or unequal diameters arranged in a regular pattern with a square or triangular base For a given flow through this medium the pressure drop is evaluated numericallyThe Navier-Stokes equations are discretized by the mixed finite-element method The numerical solution is based on operator-splitting methods whose purpose is to separate the difficulties due to the nonlinear operator in the equation of motion and the necessity of taking into account the continuity equation The associated Stokes problems are solved by a mixed formulation proposed by Glowinski & PironneauFor Reynolds numbers lower than 1, the relationship between the global pressure gradient and the filtration velocity is linear as predicted by Darcy's law For higher values of the Reynolds number the pressure drop is influenced by inertial effects which can be interpreted by the addition of a quadratic term in Darcy's lawOn the one hand this study confirms the presence of a nonlinear term in the motion equation as experimentally predicted by several authors, and on the other hand analyses the fluid behaviour in simple media In addition to the detailed numerical solutions, an estimation of the hydrodynamical constants in the Forchheimer equation is given in terms of porosity and the geometrical characteristics of the models studied

Computer Modeling of Aerosol Filtration by Fibrous Filters

Abstract: An inline array of parallel circular cylinders, placed transverse to the flow, is used as a model for fibrous filters. The flow field within the array is obtained by solving the full Navier—Stokes equations with the assumption of periodic, fully developed flow. A control volume differencing scheme is used for this purpose. The flow field can be computed for both the viscous and laminar flow regimes. Predictions of pressure drop and particle collection due to interception and diffusion have been obtained using the inline array model, for packing densities varying from 0.029 to 0.136. The collection efficiency for deposition due to interception is directly calculated from the computed flow field. The deposition or particles due to diffusion is studied by numerically solving a separate transport equation for particle concentration, without making any boundary layer approximations. The results have been compared with the data from previous studies, both theoretical and experimental. It is shown that the resul...

Apparatus for dispensing fluid materials

Abstract: Apparatus and method for dispensing fluid material whereby the fluid is discharged from a nozzle onto a workpiece. Delivery of fluid to the nozzle is controlled by a metering valve located in close proximity to the nozzle. The flow of dispensed fluid is sensed by a pressure transducer disposed to sense the pressure drop across the nozzle. The pressure transducer generates a feedback signal which can be applied by way of a closed loop control system to an electropneumatic servovalve which operates a double-acting air cylinder the pressure drop across the nozzle thereby controlling the flow of dispensed fluid in accordance with a driving signal. Where the dispenser is carried by a robot, the driving signal can be correlated to the relative speed between the workpiece and the nozzle to accurately control the amount of fluid per unit length contained in a bead deposited on the surface of the workpiece. Due to the rapid response of the system such precise control is possible even during relatively rapid changes in the relative speed between the nozzle and the workpiece. Also disclosed are means for insuring that the volume of fluid dispensed over a predetermined interval corresponds to a desired setpoint thereby correcting for changes in the intrinsic viscosity of the dispensed fluid as may be caused by changes in its temperature.

Bubble shapes in a liquid-filled rotating container under low gravity

Abstract: The effect of surface tension on steady-state rotating fluids in a low-gravity environment is studied. AH values of the physical parameters used in the present calculations, except in the low-gravity environments, are based on the measurements carried out by Leslie in the low-gravity environment of a free-falling aircraft. The profile of the interface of two fluids is derived from Laplace's equation relating pressure drop across an interface to the radii of curvature that has been applied to a low-gravity rotating bubble that contacts the container boundary. The interface shape depends on the ratio of gravity to surface-tension forces, the ratio of centrifugal to surface tension forces, the contact radius of the interface to the boundary, and the contact angle. The shape of the bubble is symmetric about its equator in a zero-gravity environment. This symmetry disappears and gradually shifts to parabolic profiles as the gravity environment becomes nonzero. The location of the maximum radius of the bubble moves upward from the center of the depth toward the top boundary of the cylinder as gravity increases. The contact radius of interface to the boundary r0 at the top side of cylinder increases, and r0 at the bottom side of the cylinder decreases as the gravity environment increases from zero to 1 g.

Subcooled Water Flow Boiling Experiments Under Uniform High Heat Flux Conditions

Abstract: This work involves steady-state high heat flux removal in fusion reactor beam dumps, first walls in compact fusion reactors, and other applications with smooth surfaces and/or irregular coolant channel cross sections. In such applications, the coolant pressure is required to be low (/approx/ 1.0 MPa), and the coolant channels are moderately long (length-to-diameter ratio (L/D) /approx/ 100). The present experiments have resulted in high heat flux data in a region where only sparse data existed. Subcooled flow boiling measurements were performed for the critical heat flux (CHF), local (axial) variations of the coolant channel's heat transfer coefficients, and pressure drop for horizontal, uniformly heated tubes. The tubes had inside diameters of 0.3 cm, a heated L/D ratio of 96.6, and were made of amzirc (zirconium-copper). The coolant was degassed, deionized water. The exit pressure and the inlet water temperature were held approximately constant at 0.77 MPa and 20/sup 0/C, respectively. From experiment to experiment, the inlet temperature varied slightly (+- 1.5/sup 0/C) from 20/sup 0/C. The actual measured inlet temperature was used in reducing the experimental data. Measurements of the above quantities were performed for the mass velocity and exit subcooling, varying from 4.6 to 40.6 Mg/m/sup 2/ . smore » and 30 to 74/sup 0/C, respectively. For these ranges, (a) the subcooled flow boiling CHF varied from 625 to 4158 W/cm/sup 2/, (b) the heat transfer coefficients during fully developed nucleate boiling varied from 30 to 400 kW/m/sup 2/ . K (Nusselt number = 150 to 1700), and (c) the overall pressure drop varied from -- 1.75 to 0.9 times the adiabatic pressure drop. For the flow conditions and geometry parameters given above, least-squares equations for the CHF were developed in terms of both the liquid Reynolds number and the exit subcooling. The average percent deviation of the developed equations from the data was <12.5%.« less

Method and apparatus for foaming high viscosity polymer materials

Abstract: Polymer materials having viscosities ranging from about 50,000 up to above 1,000,000 centipoises are mixed with a gaseous foaming agent to provide a polymer/gas solution under pressure such that when the polymer/gas solution is subsequently dispensed at atmospheric pressure the gas is released from the solution and becomes entrapped in the polymeric material to form a homogeneous polymer foam. Mixing is accomplished by force feeding the gas and polymeric material into and through a low energy input disk mixer with a low pressure drop across the mixer such that premature foaming or reaction of the polymeric material is avoided. The disk mixer includes a tubular housing, one or more driven shafts extending along the length of the housing, and a series of disks spaced along the shafts. The foaming gas enters into solution in the polymer in the compartments between the rotating disks. The process is characterized in that relatively high viscosity polymeric materials are mixed with gas and foamed with relatively low horsepower requirements, high throughput and low temperature rise of the polymer from conversion of the work of mixing to heat.

Measurements of Pressure Drop and Heat Transfer in Turbulent Pipe Flows of Particulate Slurries

Abstract: Report on the results of a study to develop phase-change slurries as advanced energy transmission fluids.

Forced Convection in the Entrance Region of a Packed Channel With Asymmetric Heating

Abstract: The problem of a thermally developing forced convective flow in a packed channel heated asymmetrically is analyzed in this paper. The flow in the packed channel is assumed to be hydrodynamically fully developed and is governed by the Brinkman-Darcy-Ergun equation with variable porosity taken into consideration. A closed-form solution based on the method of matched asymptotic expansions is obtained for the axial velocity distribution, and the wall effect on pressure drop is illustrated. The energy equation for the thermally developing flow, with transverse thermal dispersion and variable stagnant thermal conductivity taken into consideration, was solved numerically. To match the predicted temperature distribution with existing experimental data, it is found that a wall function must be introduced to model the transverse thermal dispersion process in order to account for the wall effect on the lateral mixing of fluid. The variations of the local Nusselt number along the streamwise direction in terms of the appropriate parameters are illustrated. The thermal entrance length effect on forced convection in a packed channel is discussed.

Powder flow control valves

Abstract: The disclosure relates to a powder flow control valve comprising a nozzle formed from a material such as high density polythene having an upper frusto-conical section which converges towards the lower end of the nozzle and terminates in a cylindrical section. The nozzle is encircled by a plenum chamber to which sources of vacuum and air pressure are selectively connectable through a pneumatic control system. When vacuum is connected to the plenum chamber, the resulting pressure drop across the wall of the porous nozzle causes powder flowing through the nozzle to consolidate in the nozzle and terminate the flow. When air pressure is applied to the plenum chamber, the resulting pressure rise across the boundary surface accelerates powder flow through the nozzle. The control means is arranged to establish air pressure in the plenum chamber to initiate opening of the valve and flow through the valve and, after a pre-determined time, to terminate the air pressure supply and allow powder to flow under gravity through the nozzle before flow is terminated when a pre-determined quantity of powder has been delivered by the nozzle by applying vacuum to the plenum chamber.

A survey of oscillating flow in Stirling engine heat exchangers

Abstract: Similarity parameters for characterizing the effect of flow oscillation on wall shear stress, viscous dissipation, pressure drop and heat transfer rates are proposed. They are based on physical agruments and are derived by normalizing the governing equations. The literature on oscillating duct flows, regenerator and porous media flows is surveyed. The operating characteristics of the heat exchanger of eleven Stirling engines are discribed in terms of the similarity parameters. Previous experimental and analytical results are discussed in terms of these parameters and used to estimate the nature of the oscillating flow under engine operating conditions. The operating points for many of the modern Stirling engines are in or near the laminar to turbulent transition region. In several engines, working fluid does not pass entirely through heat exchangers during a cycle. Questions that need to be addressed by further research are identified.

Multiple lubricating oil filter for internal combustion engines, with a member for monitoring the degree of clogging of the filtration surface

Abstract: The filter according to the invention comprises an outer casing (1) which is provided with an end cover (5) having means (4) for connection to the engine lubrication circuit, and which houses a first filter pack or element (2) positioned to be traversed by the engine lubricating oil, there being provided a pressure relief valve (6) which prevents the oil passing through the first filter pack or element (2) in the case of excessive pressure drop, the pressure relief valve (6) cooperating with a piston element (13) associated with an electrically conducting spring (11) to establish electrical connection between a point of contact (12) and a part of the filter casing (1), a second filter pack or element (3) being positioned to filter part of the oil which the pressure relief valve (6) allows to pass in the case of high pressure drop in the oil flow through the first filter pack or element (2).

Liquid transfer manifold system for maintaining plug flow

Abstract: A manifold system is constructed for evenly distributing a liquid to, and/or evenly collecting a liquid from, a cell of a separator system. The flow paths between the manifold inlet(s) and manifold outlet(s) are all approximately hydraulically identical in numbers, types, and dimensions of flow components, such that: (a) the flow rates to/from each of multiple inlets/outlets is equivalent, even with changes in overall pressure drop or flow rate, and (b) the time required for liquid to traverse each of the manifold flow paths is approximately identical, enabling plug flow through the cell.

Application of modern packings in thermal separation processes

Abstract: A report is presented on the performance of modern dumped and structured packings for application in the field of thermal separation processes. The evaluation of the results is based on extensive experimental investigations of rectification, absorption, and desorption systems. The following are indicated: the efficiency in terms of the number of theoretical stages per unit height or in terms of the height of transfer unit or volumetric mass transfer coefficient, the pressure drop per unit height as well as per theoretical stage or per gas phase transfer unit, and the liquid hold-up, whereby either the gas capacity factor or the liquid load was adopted as influencing parameter, and finally the maximum gas capacity factor as a function of the flow parameter. The results are presented in diagrams and tables.

Apparatus for pneumatically conveying bulk material

Abstract: An apparatus for pneumatically conveying bulk material includes a conveyor line for transporting the bulk material and a secondary line which carries clean gas and is sectionized by spaced three-way/two-way directional control valves. Each control valve is actuated by a pressure transmitter which compares the actual pressure in the conveyor line with the desired pressure in a third line carrying a fluid at a desired pressure decreasing in downstream direction in accordance with the pressure drop in the conveyor line during normal operation. A communication between the conveyor line and the second line is provided by respective branch lines which define the third connection of the control valves and are multiply connected to the conveyor line. Thus, upon encountering a pressure drop in an area of the conveyor line, the respective pressure transmitter actuates the pertaining control valve which shuts off downstream section of the second line and connects the second line with the conveyor line for introducing clean gas into the conveyor line at the desired area thereof.

Low pressure drop condenser/evaporator pump heat exchanger

Abstract: A heat exchanger includes a porous cylindrical sleeve with a bore into which liquid coolant is admitted. The liquid permeates the sleeve but cannot leave the outer surface. A pipe surrounds the sleeve. The pipe has a cylindrical outer surface and an inner surface defining protrusions and vapor channels about the protrusions. The inner ends of the protrusions bear against the outer surface of the sleeve. A plurality of helical channels are helically arranged about and in thermal contact with the outer surface of the pipe. The ends of the helical channels are coupled to plenums. Each plenum is coupled by a pipe and a fluid disconnect to one end of a thermal loop including a heat source. Heat-laden vapor passes through the helical channels and is cooled to liquid. The heat is withdrawn into the pipe and passes through the protuberances to vaporize the liquid near the surface of the porous sleeve. The resulting vapor is collected and coupled to a condenser.