Radial acceleration


In ultracentrifugation a solution is placed in the cavity of a rotor which is spun at very high speeds in an instrument which allows vibration-free, constant-temperature operation. Two sidewalls of the sample compartment follow the radial lines of the rotor to prevent gradients of concentration from developing perpendicular to the radial direction of the acceleration. The sides of the sample space which are perpendicular to the axis of rotation are transparent, and an important part of the instrument is the optical system which allows a beam of light to pass through the rotating sample. The light which passes through the system can be analyzed by spectrophotometry or, most commonly, by Schlieren optics to monitor the progress of the molecules as they migrate in response to the radial acceleration.  [c.635]

Since the radial acceleration functions simply as an amplified gravitational acceleration, the particles settle toward the bottom -that is, toward the circumference of the rotor-if the particle density is greater than that of the supporting medium. A distance r from the axis of rotation, the radial acceleration is given by co r, where co is the angular velocity in radians per second. The midpoint of an ultracentrifuge cell is typically about 6.5 cm from the axis of rotation, so at 10,000, 20,000, and 40,000 rpm, respectively, the accelerations are 7.13 X 10, 2.85 X 10 , and 1.14 X 10 m sec" or 7.27 X 10, 2.91 X 10, and 1.16 X 10 times the acceleration of gravity (g s).  [c.635]

The force of a molecule subject to radial acceleration is given by Newton s second law  [c.635]

A buoyant force is given by the product of the volume V of the particle, the density p of the solution, and the radial acceleration  [c.636]

A process receiving considerable attention as a way of burning coal and rejecting ash as slag is that used in the cyclone furnace (71). Vortex flow in the chamber promotes efficient combustion, by maintaining continuous ignition. Strong radial accelerations promote separation of particles and slag droplets and tend to bring the unreacted oxidant (cool air) into contact with coal particles on the chamber wall. The wall is protected primarily by a layer of molten slag, which also reduces the heat flux. There would normally be considerable ash vaporization in a high temperature vortex coal combustor but this can be minimized by use of a two-stage configuration. The idea of the two-stage cyclone coal combustor for MHD systems was first introduced in 1963-1965 (72).  [c.427]

A centrifugal fluidized bed (CFB) has a number of operating advantages over conventional fluidized beds, which make it attractive for a wide range of applications. A rotating bed is mechanically more complex than a conventional one, however. A CFB is cylindrical in shape and rotates about its axis of symmetry, as shown in Figure 38. Asa consequence of the circular motion, the bed material is forced into the annular region at the circumference of the container and "fluid flows radially inward through the porous surface of the cylindrical distributor, fluidizing the bed material against the centrifugal forces generated by the rotation. Radial accelerations many times in excess of gravity can be generated with modest speeds of rotation, permitting much larger gas flowrates at minimum fluidization than are possible with the conventional fluidized bed operating against the vertical force of gravity. The advantages of a CFB over a conventional fluidized bed are as follows  [c.485]

Radial acceleration Rate of velocity change with respect to time in a radial direction.  [c.1470]

One of the more notable advantages of using a full eoverage scanning technique is the identification of tube eccentricity and of wastage superimposed upon the eccentricity. The radial location of wastage on tubes that conform to nominal specifications is of interest mainly to identify the source (i.e. soot blower) causing any accelerated wastage. In the case of eccentric tubes, it is important to note the location of the wastage and relate it to the eccentricity of the tube.  [c.1039]

If 1 /b is neglected in comparison to 1 /a, then k-aV and the field at the tip F a) - V/a or 10 V/cm in the present example. This very high value, equivalent to 100 V/nm, is sufficient to pull electrons from the metal, and these now accelerate along radial lines to hit the fluorescent screen. Individual atoms serve as emitting centers, and different crystal faces emit with different intensities, depending on the packing density and work function. Since the magnification factor b/a is enormous (about 10 ), it might be imagined that individual atoms could be seen, but the resolution is limited by the kinetic energy of the electrons in the metal at right angles to the emission line and obtainable resolutions are about 3-5 nm. Nevertheless, the technique produces miraculous pictures showing the various crystal planes that form the tip in patterns of light and dark. Adsorbates, such as Ni, may increase the emission intensity providing a means to follow the surface migration of adsorbed species.  [c.299]

Accelerating voltage (high voltage) scan. An alternative method of producing a momentum (mass) spectrum in magnetic-deflection instruments. This scan can also be used, in conjunction with a fixed radial electrical field, to produce an ion kinetic energy spectrum.  [c.433]

Forced-draft fans generally operate on clean air and at pressures from a few hundred Pa to as high as 20 kPa (80 in. of water) for pressurized furnaces. Backward-inclined blading is used almost exclusively for high efficiency. Blades with airfoil contours give improved stmctural strength, higher efficiency, and lower sound levels in large fans. Conveying systems in which the soHds pass through the fan almost always use low speed wheels of the radial-blade paddle-wheel-type of constmction. In the area of hot and corrosive process gas handling, fan designs are adapted to the specific need of the process. Frequendy stainless steel or other alloy constmction is required. Where dilution of the gas with atmospheric air is objectionable, the fan shaft is equipped with a stuffing box, a mbber labyrinth seal, or even a purged rotary seal depending on the degree of contamination control required. Occasionally, fans must handle gases having sticky or tarry particulates where soHds buildup can occur. Continuous or intermittent flushing of the fan with a Hquid spray in the fan inlet is helphil. In addition to deHberate flushing, fans may be called on to handle gases containing mist or entrained Hquid droplets. A large percentage of such mist may be coUected and agglomerated in the fan, particulady if operated at a high tip speed. Liquid-handling fans must be equipped with oversize motors as the acceleration of the Hquid within the fan can utilize considerable power. Particular attention must be paid to the corrosiveness of the wet—dry environment within the fan. The presence of chloride ions and high wheel stress can lead to stress corrosion cracking in stainless-steel wheels. Although elimination of the chlorides is the best solution, the use of much lower wheel-tip speeds and wheels that can be stress-reHeved to remove residual fabrication stresses is often helpful. Fans with mbber and polymeric coatings are often useful in moist environments, but special considerations in fan design are necessary to assure thorough bonding of such coatings to the wheel. Buildup of Hquid within the fan casing can also be a problem with liquid-handling fans. The use of bottom—horizontal discharge designs with a large discharge duct drain is generally more satisfactory than a small fan-housing drain.  [c.114]

Jigs, generally very effective for relatively coarse (typically 0.5—200 mm) material, have relatively high unit capacities. The sharpness of separation is a function of size distribution. Fine specific gravity separation is possible for a closely sized material. The principal usage of jigs is in coal beneficiation. Other apphcations include concentration of cassiterite, tungsten, gold, barites, and iron ores. The basic jig (Fig. 10) has a large tank or hutch divided in the upper portion into two main sections. One section contains the stationary screen with the mineral bed on it, the bed depth being many times the thickness of the largest particle, and the other section contains the pulsating device, most commonly using air pressure rather than mechanical means. Mineral separation is achieved by applying a vertical oscillatory (pulsating) motion to the soHds—fluid bed. This pulsating motion produces dilation of the bed and subsequent stratification. The denser and larger particles form a lower layer whereas the finer lighter particles ate on top. The processes occurring in a fliU cycle of operation may be considered differential initial acceleration, hindered settling, and consoHdation trickling. Several other theories have been developed, however, notably the center-of-gravity theory (6,10). The pulsing action is supplemented by using additional water in the hutch during the settling period. This extends the open state of the bed for a longer time. The dense minerals are collected either on the screen or under the screen depending on the screen aperture size. In the latter case, a layer of dense (ragging) particles larger than the aperture size are placed on the screen to regulate the collection of dense fraction. Examples ate feldspar in coal cleaning, and hematite in cassiterite and scheelite separation. Several stages of jigging are used to achieve efficient separation. The commercial jigs have a variety of designs for the pulsating device and the removal of products. Some examples are shown in Figure 11. The Batac jig, which uses multiple air chambers under the screen, is the industry standard in coal cleaning. A more recent development is the Kelsey centrifugal jig (33,34). The circular or radial jig is a variation of the conventional rectangular design of hutches in series. The pulp is fed at the center and flows radially over the jig bed and exits at the circumference. A raking mechanism ensures an even bed depth throughout. It is mechanically simple and has very high capacity, up to 300 m /h for a maximum particle size of 25 mm. It achieves a fast compression/slow suction stroke with virtually no hutch water. The slow suction stroke allows more time for the fines to settle to the bed.  [c.404]

Equation 26 is accurate only when the Hquids rotate at the same angular velocity as the bowl. As the Hquids move radially inward or outward these must be accelerated or decelerated as needed to maintain soHd-body rotation. The radius of the interface, r, is also affected by the radial height of the Hquid crest as it passes over the discharge dams, and these crests must be considered at higher flow rates.  [c.403]

In most existing styrene processes, the catalyst is loaded into large, radial flow reactors, which are operated adiabaticaHy at low pressure and temperatures near 600°C. Heat is suppHed by superheated steam. During start-up, dehydrogenation begins slowly and accelerates as the Fe (HI) is reduced to Fe (II,III). The catalyst, which was red in color when fresh, turns to the characteristic black color of Fe O.  [c.198]

The inward-flow radial turbine has many components similar to a centrifugal compressor. The mixed-flow turbine is almost identical to a centrifugal compressor—except its components have different functions. The scroll is used to distribute the gas uniformly around the periphery of the turbine. The nozzles, used to accelerate the flow toward the impeller tip, are usually straight vanes with no airfoil design. The vortex is a vaneless space and allows an equahzation of the pressures. The flow enters the rotor radially at the tip with no appreciable axial velocity and exits the rotor through the exducer axially with little radial velocity. These turbines are used because of lower production costs, in part because the nozzle blading does not require any camber or airfoil design. They are also more robust, but due to cooling restrictions are used for much lower turbine inlet temperatures.  [c.2510]

The acceleration or deceleration of the process fluid imparts a net tangential force on the blading. If the clearance between the wheel and housing varies circumferentially, a variation of the tangential forces on the blading may also be expected, resulting in a net destabilizing force as shown in Figure 5-23b. The resultant force from the cross-coupling of angular motion and radial forces may destabilize the rotor and cause a whirl motion.  [c.209]

The radial-inflow turbine can be the cantilever type as shown in Figure 8-3, or the mixed-flow type as shown in Figure 8-4. The mixed-flow radial-inflow turbine is a widely used design. Figure 8-5 shows the components. The scroll or collector receives the flow from a single duct. The scroll usually has a decreasing cross-sectional area around the circumference. In some designs the scrolls are used as vaneless nozzles. The nozzle vanes are omitted for economy to avoid erosion in turbines where fluid or solid particles are trapped in the air flow. Frictional flow losses in vaneless designs are greater than in vaned nozzle designs because of the nonuniformity of the flow and the greater distance the accelerating air flow must travel. Vaneless nozzle configurations are used extensively in turbochargers where efficiency is not important, since in most engines the amount of energy in the exhaust gases far exceeds the energy needs of the turbocharger.  [c.321]

Secondary ions are accelerated from the surface to an energy E. After passing an entrance slit different masses are forced to different radial paths in the homogeneous magnetic field. Only mass m ( Am) defined by  [c.110]

Transportation accounts for about one-fourth of the primary energy consumption in the United States. And unlike other sectors of the economy that can easily switch to cleaner natural gas or electricity, automobiles, trucks, nonroad vehicles, and buses are powered by internal-combustion engines burning petroleum products that produce carbon dioxide, carbon monoxide, nitrogen oxides, and hydrocarbons. Efforts are under way to accelerate the introduction of electric, fuel-cell, and hybrid (electric and fuel) vehicles to replace sonic of these vehicles in both the retail marketplace and in commercial, government, public transit, and private fleets. These vehicles dramatically reduce harmful pollutants and reduce carbon dioxide emissions by as much as 50 percent or more compared to gasoline-powered vehicles.  [c.479]

Organic chemicals which are used primarily in the mbber industry contributed 415 million to the United States economy in 1994 (1). The historical sales of the primary classes of organic mbber-processing chemicals are summarized in Table 1. Accelerators and antidegradants are the two main types of mbber chemicals. The U.S. production of accelerators has been declining, due to longer-lasting radial tires and to fewer domestic producers. The production of antidegradants shows the effect of the adoption of radial tires in the 1970s but has been increa sing more recently because of the desire for articles with longer service life. Antidegradants are discussed elsewhere (see Antioxidants Antiozonants). A significant component of the "other" category in Table 1 is alkyl mercaptans, used as polymerization regulators. Total organic rubber chemical use has remained stable at about 6% of synthetic mbber production.  [c.219]

There are three types of rotors swinging bucket, fixed-angle head, or smaU perforate or imperforate baskets for larger quantities of material. In the swinging bucket type, the bottles are vertical at rest but swiag to a horizontal radial position duriag acceleration so that soHds are deposited ia a peUet at the bottom of the tube. Although sedimenting particles must travel up to the fliU depth of the Hquid layer, which requires appreciable time, the long path of travel and the perpendicularity of the sedimenting boundary to the axis of the tube are distinct advantages ia effecting fractional sedimentation. Heads carrying fixed tubes at a 35—50° angle reduce centrifugiag time because the maximum distance traveled by a particle is the secant of the tube angle times the diameter of the tube. Particles strike the wall and sHde down the tube to coUect near the bottom, but the angle makes it difficult to measure relative volumes of supernatant Hquid and sedimented soHds. Rotors carry 2 to 16 metal containers having tubes and bottles of various sizes and shapes. Containers range ia capacity from capiUaries for microanalysis to a 1-L maximum, limiting the batch capacity of this type of centrifuge to 4 L. Although glass bottles and tubes are generaUy used, plastic and metal containers are available for high speed operation or corrosive Hquids. Tubes are usuaUy cylindrical, tapered, and graduated special shapes for analytical work are avaUable, including pear-shaped tubes having capiUary tips for measuriag smaU quantities of soHds.  [c.406]

Density and Pressure Gradients. Consider a centrifuge of length Z and of radius r the internal dimensions of the centrifuge bowl, that rotates at a constant angular velocity of CO radians per second. If the centrifuge contains a single pure gas rotating at the same angular velocity as the centrifuge bowl, each element of the gas has a force impressed on it by virtue of its angular acceleration. This force is directed outward in a cylindrical coordinate system, and can be expressed as p(Spr) rdrd d. At steady state this force must be balanced by a force resulting from the radial pressure gradient estabHshed in the centrifuge bowl. The inward force on an element of the gas owing to this pressure gradient is given by dp dr)(rdrd dp). Equating these two forces gives  [c.91]

A device which combines the use of centrifugal force with mechanical impiilse to produce an increase in pressure is the axial-flow compressor or pump. In this device the fluid travels roughly parallel to the shaft through a series of alternately rotating and stationaiy radial blades having airfoil cross sections. The fluid is accelerated in the axial direction by mechanical impulses from the rotating blades concurrently, a positive-pressure gradient in the radial direction is established in each stage by centrifugal force. The net pressure rise per stage results from both effects.  [c.900]

Direct-Heat Rotaiy Dryers The direct-heat rotary diyer is usually equipped with flignts on the interior for hfting and showering the solids through the gas stream during passage through the cylinder. These flights are usually offset eveiy 0.6 to 2 m to ensure more continuous and uniform curtains of sohds in the gas. The shape of the flights depends upon the handhng characteristics of the solids. For free-flowing materials, a radial flight with a 90° hp is employed. For sticky materials, a flat radial flight without any hp is used. When materials change characteristics during drying, the flight design is changed along the diyer length. Many standard drver designs employ flat flights with no hps in the first one-third of tlie diyer measured from the feed end, flights with 45° hps in the middle one-third, and flights with 90° lips in the final one-third of the cylinder. Spiral flights are usually provided in the first meter or so at the feed end to accelerate forward flow from under the feed chute or conveyor and to prevent leakage over the feed-end retainer ring into the gas seals.  [c.1201]

Disk Centrifuges One of the commonest clarifier centrifuges is the vertically mounted disk machine, as illustrated in Fig. 18-142, b. Feed is introduced proximate to the axis of the bowl, accelerated to speed typically by a radial vane assembly, and flows through a stack of closely spaced conical disks in the form of truncated cones. Generally 50 to 150 disks are used. They are spaced 0.4 to 3 mm (0.015 to 0.125 in) apart to reduce the distance for solid/liqmd separation. The angle made by conical disks with the horizontal is typically between 40 to 55° to facilitate solids conveyance. Under centrifugal force the solids settle against the underside of the disk surface ana move down to the large end of the conical disk and subsequently to the bowl wall. Concurrently, the clarified hquid phase moves up the conical channel. Each disk carries several holes spaced uniformly around the circumference. When the disk stack is assembled, the holes provide a continuous upward passage for the lighter clarified liquid released from each conical channel. The liqmd coUec ts at the top of the disk stack and discharges through overflow ports. To recover the kinetic energy and avoid foaming due to discharging of a high-velocity jet against a stationary casing, the rotating liquid is diverted to a stationary impeller from which the kinetic energy of the stream is converted to hydrostatic pressure. Unlike most centrifuges operating with a slurry pool in contac t with a free surface, disk centrifuges with a rotary seal arrangement can operate under high pressure. The settled sohds at the bowl wall are discharged in different forms, depending on the type of disk centrifuges.  [c.1731]

Shiny is introduced into the feed accelerator through a stationaiy pipe located proximate to the axis of the machine. The feed shiny is accelerated tnroiigh contact with the rotating surfaces to angular speed before discharging to the separation pool through a series of ports in the conveyor hiib. In the separation pool, under centrifugal gravity the solids which are heavier compared to the liquid settle toward the bowl wall, while the clarified hqiiid moves radially toward the pool surface. Subsequently, the liquid flows along the hehcal channel (or channels, if the screw conveyor has multiple leads) formed by adjacent blades of the conveyor to the liquid bowl head, from which it discharges over the weirs. The annular pool can be changed by adjusting the radial position of the weir openings, which take the form of circular holes or crescent-shaped slots.  [c.1732]

Standard modern LEED optics are of the "rear view type, and are shown schematically in Eig. 2.45. The incident electron beam, accelerated by the potential Vo, is emitted from the electron gun behind the hemispherical fluorescent glass screen and hits the sample through a hole in the screen. The surface is at the center of the hemisphere so that all back-diffracted electrons travel towards the LEED screen on radial trajectories. Before the electrons hit the screen they must pass a retarding field energy analyzer. It typically consists of four (or three) hemispherical grids concentric with the screen, each containing a central hole through which the electron gun is inserted. The first grid (nearest to the sample) is connected to earth ground, as is the sample, to provide an essentially field-free region between the sample and the first grid. This minimizes undesirable electrostatic deflection of diffracted electrons. A suitable negative potential - (Vo - AV) is applied to the second and third (only second) grids, the so-called suppressor grids, to enable a narrow energy range eAVof elastically scattered electrons to be transmitted to the fluorescent screen. The fourth  [c.72]

Pulsed operation of the APFIM leads to analysis of all atoms within a volume consisting of a cylinder of ca. 2 nm diameter along the axis of the tip and aperture, with single atomic layer depth resolution but no indication of just where within that volume any particular atom originated. The advent of position-sensitive detectors has enabled APFIM to be extended so that three-dimensional compositional variations within the analyzed volume can be determined. The development is called position-sensitive atom probe (POSAP). The aperture and single-ion detector of APFIM are replaced by a wide-angle double channel plate, with a position-sensitive anode just behind the plate. Field- or laser-evaporated ions strike the channel plate, releasing an electron cascade which is accelerated toward the anode. The impact position is located by the division of electric charge between three wedge-and-strip electrodes. From this position the point of origin of the ion on the tip surface can be determined, because the ion trajectories are radial. Thus after many evaporation pulses, leading to removal of a volume of material from the tip, both the identities and the positions of all atoms within that volume can be mapped in three dimensions. Because an evaporated volume can contain many thousands of atoms, the data collection and handling capabilities must be particularly sophisticated.  [c.180]

Tubular-bowl centrifuges are used extensively for the purification of oils by separating suspended solids and free moisture from them for removal of oversize particles from dye pastes, pigmented lacquers and enamels for "polishing" citrus and other aromatic oils and other small-scale separating applications. The tubular-bowl clarifiers and separators are comprised of small-diameter cylinders (about 100 mm) which allows operation at very high velocities. Commercial machines typically work at 15,000-19,000 rpm, which corresponds to = 13,000 to 18,000. For special applications (e.g., treatment of vaccines, etc.), the diameter of the tubular-bowl centrifuge is only several centimeters, with values of N, as high as 50,000. The tubular centrifuge rotor is suspended from its drive assembly on a spindle that has a built-in degree of flexibility. It essentially hangs freely with a sleeve bushing in a dampening assembly at the bottom. In some designs a similar dampening assembly is included at the upper end of the rotor. This permits the rotor to determine its own mass axis after it exceeds its critical speed. The feed liquid is introduced to the rotor at the bottom through a stationary feed nozzle. The inlet feed is under sufficient pressure to create a standing jet, which ensures a clean entrance into the rotor. Often, an acceleration device is provided at the bottom of the rotor to bring the feed sUeam to the rotational speed of the bowl. The feed moves upward through the bowl as an aimulus and discharges at the top. To effect this, the radius of the discharge at the top must be larger than the opening at the bottom through which the feed enters. Solids move upward with the velocity of the annulus and simultaneously receive a radial velocity that is a function of their equivalent spherical diameter, their relative density, and the applied centrifugal force. If the trajectory of a particle intersects the cylindrical bowl wall, it is removed from the liquid if it does not, the particle flows out with the effluent overflow. Multichamber (multipass) centrifuges combine the process principles of a tubular clarifier with mechanical drive and the bowl contour of a disk centrifuge. The suspension flows through a series of nested cylinders of progressively increasing diameter. The direction of the flow from the smallest to the largest cylinders is in parallel to the axis of rotation, as in the tubular bowl. The rotor usually contains six annuluses, so that the effective length of suspension travel is approximately six times the interior height of the bowl. The multipass bowl can be considered as a  [c.431]

A radial force on the pipe wall ahead of the deflagration wave. There is a varying pressnre between the aconstic wave and the flame front where the pressnre bnilds from near atmospheric pressnre, Pi (step change at the wave front) to eight times Pi (or higher) at the flame front. The pressnre ratios depend on the flame acceleration. There is no snch effect with a detonation.  [c.144]

This surprising equality arises because an efficient appliance saves expensive electricity at the meter, at an average retail price of 8 cents/kWli whereas one kWh of new wholesale supply is worth only 2-3 cents at the power plant. Thus, even if electricity from some future new remote power plant is too cheap to meter, it still must be transmitted, distributed, and managed for 5—6 centsAWh. It is impossible to disentangle the contribution of standards and of accelerated improvement in technology, but clearly the combination has served society well.  [c.372]


See pages that mention the term Radial acceleration : [c.23]    [c.1082]    [c.426]   
Industrial ventilation design guidebook (2001) -- [ c.1471 ]