Airflow


Tunnel dryers are shown in Fig. 3.15a. Wet material on trays or a conveyor belt is passed through a tunnel, and drying takes place by hot air. The airflow can be countercurrent, cocurrent, or a mixture of both. This method is usually used when the product is not free flowing.  [c.89]

With this technology even boreholes, up to 2mm underneath the surface, can be identified, A remarkable borehole is represented in illustration 10, For the elucidation of the temperature contrast, a three-dimensional temperature distribution of the entire blade is shown beside the infrared picture (the similarity of the temperature distribution with the actual blade airfoil is purely coincidental).  [c.406]

Although a leaf blower is probably way too strong it may still be adequate at its lowest setting. To insure that a correct airflow is being pulled the chemist holds a lit cigarette about a foot in front of the hood s opening and looks to see If the smoke trail is being pulled into the hood. If so, then the hood works just fine.  [c.23]

From the point of view of reactivity, there is little difference betvv een 2-amino-selenazoles and aryl- Or alkyl-2-aminoselenazoles, except that the A"-arvl derivatives are generallv less basic and that their salts are more easily hydrolyzed.  [c.232]

Airfoil Design. The airfoil design is similar to the backward-curved blade (Fig. 3d), except that it is designed for maximum mechanical efficiency. Each blade is composed of two pieces, with the upper surface contoured to reduce air friction and provide for most efficient compression of the air. For a given performance, this fan has the highest rotational speed of any of the wheel designs. The scroU is usually designed for the most efficient conversion of velocity head to static pressure. Performance characteristics are generally similar to a backward-curved blade but power requirements are somewhat less. Such fans are generally more expensive to constmct and are used only in larger sizes with higher pressures or large flow volumes where reduced operating cost justifies the increased initial expense.  [c.106]

When fan speed is changed (/) the capacity or flow rate varies directly with the speed ratio (2) discharge pressure varies directly with the square of the speed (J) power varies directly with the cube of the speed (at constant inlet density with no change in temperature, absolute pressure, or composition) and (4) discharge pressure and power requirements at a constant capacity and fan speed vary directly with gas density,. These laws apply to varying the operating conditions of the same fan, and can be used to predict the performance of a given fan if sped up or slowed down. Other laws (4) describe the effects of varying the diameter of a fan or the soHdity ratio. For example, when considering performance of different diameter fans, airflow capabiUty is a function of diameter squared, although not necessarily at the same power requirement.  [c.106]

Noise level has to be considered in fan selection. Most manufacturers provide tables of operating ranges of quietest operation. There is no set fan discharge velocity that is appHcable to all fans to ensure quiet operation. Fans do not operate as quietly when throttled back as when allowed to handle substantial quantities of air. Figure 5 illustrates the range of quiet operation of a specific airfoil fan as a function of outlet velocity and discharge pressure. Outlet velocity and hence fan capacity must be allowed to increase with static pressure to stay in the quiet region. Table 1 fists typical fan outlet velocities for quiet operation. Industrial process fans having backward-inclined blades should usually be selected with discharge velocities somewhat higher than  [c.106]

Fig. 5. Static pressure vs oudet velocity for a specific airfoil fan, where the dashed lines define the quiet operating range of an airfoil fan. Fig. 5. Static pressure vs oudet velocity for a specific airfoil fan, where the dashed lines define the quiet operating range of an airfoil fan.
Static pressure Forward-curved fan Flow-nozzle airfoil fans  [c.107]

Design Elements. Ideal conditions are obtained ia the design of an axial-flow fan when energy transfer from the blade to the gas is uniform along the length of the blade, resulting ia uniform pressure generation, minimum losses, and maximum efficiency and stabiHty. Because the blade linear velocity varies with position from tip to hub, attainment of a uniform pressure rise along the blade at different radii requites variation of the blade angle from hub to tip. The choice of blade section is dictated by the requited aerodynamic characteristics and varies ia practice from cast or molded precise airfoil profiles to formed materials to single-thickness plate materials. Hub size is iacreased for higher pressure designs where it is impractical to generate equal pressures nearer the center of the wheel. Low pressure designs have hubs ranging from 1/3 to 1/2 wheel diameter whereas hubs ia higher pressure designs may occupy 75—85% of the tip diameter. The number of blades must also be iacreased as pressure rise is iacreased 3 to 5 may be used with lower pressure desigas, as many as 24 with higher pressures. Close clearance between blade tips and fan housiag is a stringent requirement to prevent backflow losses at the housiag wall. High pressure desigas requite clearances of less than 0.79 mm. The cylindrical housiag of a vane-axial fan may be cast or roUed. To attain the close clearance at the blade tips, either very careful forming or machining is requited. Inlet and outlet connections ate carefully designed to minimize turbulence and connecting inlet and outlet ducts should be straight for at least 2—3 diameters to avoid undue effect on fan performance. Performance curves ate shown ia Figure 10.  [c.110]

Propeller Fa.ns, Propeller fans may have from 2 to 6 blades mounted on a central shaft and revolving within a narrow mounting ting, either driven by belt drive or directiy coimected. The form of the blade ia commercial units varies from a basic airfoil to simple flat or curved plates of many shapes. The wheel hub is small ia diameter compared to the wheel. The blades may even be mounted to a spider frame or tube without any hub. The housiag surrounding the blades can range from a simple plate or flat ring to a streamlined or curved beU—mouth orifice.  [c.111]

The vane-axial fan wheel has short, stubby airfoil blades mounted on a hub which may be as large as 75% of the wheel diameter. The air leaving the axial-flow wheel has an appreciable rotational component which can be converted to static pressure ia a suitably designed set of stationary straightening vanes. The straightening vanes are shaped to pick up the air leaving the wheel blades without shock. Although straightening vanes of airfoil cross section are theoretically desirable, vanes formed of pressed heavy sheet metal are less expensive. The motor is enclosed ia a housiag having the same diameter as the hub and has either a rounded cap or a bullet-shaped tail to reduce eddy losses. The straightening vanes surround the motor housiag and can serve as stmctural supports for the housiag. GeaeraHy, the number of guide vanes exceeds the number of propeller vanes by one, with the numbers selected so that there is no common divisor for the number of hub vanes and guide vanes. This minimises flow pulsation and noise. Siagle-stage fans can develop pressures to 1.5 kPa (6 ia. of water) with some desigas going as high as 2.25 kPa (9 ia. of water). Standard designs are available either belt-driven or directly connected to motors with speeds as high as 3450 rpm. In addition, two-stage units have been developed that produce considerably higher pressures but have received Httle iadusttial use. Performance curves show a dip to the left of the pressure peak (Fig. 10). Whereas vane-axial-flow fans can be designed that do not have such dips, those that do have dips should be operated to the right of the pressure peak. The principal advantage of the vane-axial fan is compactness and convenience of use ia inline ducts, plus its better efficieacy whea carefully desigaed. The higher manufacturiag precisioa required geaeraHy eliminates any cost savings that might result from its smaller size.  [c.111]

Variable Air Flow Fans. Variable air flow fans are needed ia the process iadustry for steam or vapor condensing or other temperature critical duties. These also produce significant power saviags. Variable air flow is accompHshed by (/) variable speed motors (most commonly variable frequency drives (VFDs) (2) variable pitch fan hubs (J) two-speed motors (4) selectively turning off fans ia multiple fan iastaHations or (5) variable exit louvers or dampers. Of these methods, VFDs and variable pitch fans are the most efficient. Variable louvers, which throttle the airflow, are the least efficient. The various means of controlling air flow are summarized ia Table 3.  [c.111]

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]

The basic fluid-bed unit consists of a refractory-lined vessel, a perforated plate that supports a bed of granular material and distributes air, a section above the fluid bed referred to as freeboard, an air blower to move air through the unit, a cyclone to remove all but the smallest particulates and return them to the fluid bed, an air preheater for thermal economy, an auxiUary heater for start-up, and a system to move and distribute the feed in the bed. Air is distributed across the cross section of the bed by a distributor to fluidize the granular soflds. Over a proper range of airflow velocities, usually 0.8-3.0 m/s, the sohds become suspended in the air and move freely through the bed.  [c.46]

To reduce drying time, maximum airflows are used during the first portion of the kilning cycle until the exit air is no longer saturated with moisture. Airflow then is reduced or recirculated to conserve energy. Average fuel consumption for a United States kiln is ca 5.9 x 10 kJ/t (1.4 x 10 kcal/t) ) malt, with a range of 2.9-10 X 10 kJ/t of malt.  [c.481]

Another problem, prevalent ia areas where severe icing conditions are met, is referred to as galloping of power lines. When ice forms on a power line, there is frequently a prevailing wiad which causes the ice to take a teardrop or airfoil shape. This foil provides an aerodynamic lift to the conductors and under certain conditions the conductors can go iato a resonant vibration such that large standing waves are created that exert enormous forces on the system. Miles of power lines and the towers along them have been destroyed by this phenomenon.  [c.465]

Mechanical Mills with Mir Classifiers. To improve the end fineness and achieve a sharper topsize cutoff point, many mechanical impact mills are fitted with integral air classifiers (Fig. 13). These can be driven separately from the mill rotor or share a common drive. The material to be ground is introduced into the mill section of the machine, where impact size reduction takes place. The airflow through the machine carries the partially ground product to the air classifier, which is usually some form of rotating turbine. The speed of rotation determines which particle size is internally recycled for further grinding and which is allowed to exit the machine with the airflow. Machines are available up to 375 kW and can achieve products with essentially all material <20 fim.  [c.144]

Product falls to bottom of cone. Airflow may be spiral or straight-line flow  [c.252]

For heat transfer directly to solids, predictive equations give directly the volume V or the heat-transfer area A, as determined by heat balance and airflow rate. For devices with gas flow normal to a fluidized-solids bed,  [c.1059]

Using 285 m (1000 fU) of airflow at normal temperature and pressure at 40 percent relative humidity to cariy off 0.45 kg (1 lb) of  [c.1059]

Operating co.sts. Power requirements for air-cooled heat exchangers can be lower than at the summer design condition provided that an adequate means of air-flow control is used. The annual power requirement for an exchanger is a function of the means of airflow control, the exchanger seiwice, the air-temperature rise, and the approach temperature.  [c.1082]

G. R. Nickerson and co-workers, M Computer Program for the Prediction of Solid Propellant Motor Peformance, Vols. 1, 2, and 3, AREPL-TR-80-34, AFRPL, Dayton, Ohio, Apr. 1981.  [c.53]

B. D. Nahloosky and G. A. Zimmerman, Thermoplastic Elastomers for S olid Propellant Binders, AERPL-TR-86-069, Aerojet Tactical Systems Co., Sacramento, Calif., Dec. 1986.  [c.55]

Tube-Axia.IFa.ns, The tube-axial fan is a refinement of the propeller fan ia both wheel design and mechanical strength, having improved capacity, pressure level, and efficiency. Designs are often capable of operating over a greater range of speeds. The cheapest fans may have an open-type propeller wheel with the motor enclosed ia a tube if directly coimected. Belt-drive models are also available. In more refined types, the blades are shorter and of airfoil cross section mounted on a large diameter hub which may approach 50% of the wheel diameter. The hub and motor tube are normally of the same diameter and reduce the back flow of higher pressure air, which might recycle through less effective central portions of the wheel if a smaller hub were utilised. The performance curve (Fig. 10) may have a dip to the left of the pressure peak which would constitute an unstable region for fan operation and which should be avoided. Commercial models are available having static pressures up to 750 Pa (3 ia. of H2O). The general range of appHcation is for  [c.111]

D. L. Endicott and L. H. Donahue, E>evelopment and Demonstration of Criteria forEiquid Eluorine Eeed System Components, Report AERPL-TR-65-133, McDonnell Douglas Astronautics Co., St. Louis, Mo., 1965.  [c.134]

L. A. Dee, Analysis of Nitrogen Trifluoride, AERPL-TR-76-20 (AD-A022887), Air Eorce Rocket Propulsion Laboratory, Edward Air Eorce Base,  [c.218]

One problem inherent in space stmctures (9) is vibration, which can impact on the function of space experiments and the accuracy of instmments. Large flexible stmctures, once put in motion by some external or internal force or shift of mass, have by themselves no substantial damping, operating in the vacuum of space. In essence, a smart material is one which can change its characteristics in such a way as to correct a condition which degrades its performance. These systems have incorporated into their stmctures sensors (qv), controllers, and actuators. The detector, sensing a vibration, sends a signal to a microprocessor—controller that in turn energizes some form of actuator to change the local stmctural dynamics, causing the vibration to decrease or be canceled. Shape-memory wires and ribbons embedded in the composite materials of constmction have proved to be very effective. The wire or ribbon is prestrained before being embedded and then held under constraint while the composite, typically a graphite epoxy, is cured. When these SMA actuators are electrically heated, they attempt to recover their original dimensions. Owing to the constraint offered by the composite to which the SMAs are bonded, however, they can only produce an in-plane stress that alters the modal response of the stmcture, reducing its vibrational ampHtude. In addition to acoustic and vibration control, SMA actuators are also used in smart materials for shape control, for example, changing the contour of an airfoil or hydrofoil, fine-tuning the contour of an antenna, and changing the focal point of microwave reflectors.  [c.465]

Turbine Construction. Large steam turbines are generally designed as a rotor inside one or two cylinders or casings. The low pressure nuclear turbine having a partial integral rotor (Fig. 26) illustrates many of the features of both older and newer turbines. The rotor carries multiple rows of blades (or buckets) the cylinder acts as a pressure vessel and carries the same number of diaphragms of stationary blades. The stationary blades may also be called vanes or nozzles. A row of stationary blades followed by a row of rotating blades is called a stage. A typical turbine has 20 to 25 stages varying in height from approximately 2 cm at the inlet to more than 130 cm at the exhaust. The low pressure stages may be multipbed in a double, quadmple, or sextuple flow. Each blade row, stationary and rotating, contains from 80 to 150 blades. This amounts to thousands of blades, each of which is a precision airfoil. The stationary blades direct the expanding steam in the proper directions so that the rotating blades efficiently convert the energy into torque. The difference between the rotating and stationary blades is significant. The rotating blades experience centrifugal stress, whereas the stationary blades do not. Because the principal source of operating stress in the rotating parts is usually the rotation, stress corrosion cracking thus occurs more in rotating parts than in stationary ones.  [c.364]

T. J. Haley, / Pharm. Sci. 54, 663 (1965) T. J. Haley, ia Ref. 2, Chapt. 40 P. Arvela, Prog. Pharmacology 2(3), 69 (1979).  [c.372]

Two types of floater aozzles are curreafly ia use and they are based on two different principles. The Bernoulli principle is used ia the airfoil flotatioa aozzles, ia which the air flows from the aozzle parallel to the web and the high velocities create a reduced pressure, which attracts the web while keeping the web from touching the nozzles. The Coanda effect is used to create a flotation nozzle when the air is focused and thus a pressure pad is created to support the web as shown ia Figure 19.  [c.315]

Another important characteristic property of cotton fibers is their fineness, or linear density, or weight per unit length. The normal units for fineness are millitex. Eineness is directiy related to the amount of cellulose in the fiber, which is a function of the fiber wall area, excluding the hoUow center (lumen), and the fiber length. Developments in computerized microscopic image analysis (18) allow for rapid and accurate measurements of fiber wall area and perimeter. The term fiber maturity relates to the degree of development or thickening of the fiber wall relative to its perimeter. Acceptable range of maturity for mill usage is from 75 to 80%. The most common measure of fiber fineness is the Micronaire reading, an airflow measurement performed on a 3.25-g test specimen, which is compressed to a specific volume in a porous chamber. Air is forced through the specimen and the resistance to the airflow is proportional to the linear density. The Micronaire reading is affected by a combination of both fiber fineness and maturity to the extent that for the same genetic variety with a constant perimeter, the Micronaire will directly correspond to maturity. Depending on acceptable maturity, a good range of Micronaire is between about 3.5 and 4.8 (19).  [c.311]

Vanes may be used to improve velocity distribution and reduce frictional loss in bends, when the ratio of bend turning radius to pipe diameter is less than 1.0. For a miter bend with low-velocity flows, simple circular arcs (Fig. 6-37) can be used, and with high-velocity flows, vanes of special airfoil shapes are required. For additional details and references, see Ower and Pankhurst The Mea.surement of Air Flow, Pergamon, New York, 1977, p. 102) Pankhurst and Holder Wind-Tunnel Technique, Pitman, London, 1952, pp. 92-93) Rouse Engineering Hydraulics, Wiley, New York, 1950, pp. 399 01) and Joreensen Fan Engineerinp, 7th ed., Buffalo Forge Co., Buffalo, 1970, pp. Ill, 117, 118).  [c.659]

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]

Figure 10-77 shows a typical axial-flow compressor. The rotating element consists of a single drum to which are attached several rows of decreasing-height blades having airfoil cross sections. Between each rotating blade row is a stationaiy blade row. All blade angles and areas are designed precisely for a given performance and high efficiency. The use of multiple stages permits overall pressure incrases up to 30 1. The efficiency in an axial flow compressor is higher than the centrifugal compressor.  [c.927]

The axial flow compressor has three distinct stall phenomena. Rotating stall and individual blade stall are aerodynamic phenomena. Stall flutter is an aeroelastic phenomenon. Rotating stall (propagating stall) consists of large stall zones covering several Blade passages and propagates in the direction of the rotor and at some fraction of rotor speed. The number of stall zones and the propagating rates vaiy considerably Rotating stall is the most prevalent type of stall phenomenon. Individual blade stall occurs when all the blades around the compressor annulus stall simultaneously without the occurrence of the stall propagation mechanism. The phenomena of stall flutter is caused by self-excitation of the blade and is aeroelastic. It must be distinguished from classic flutter, since classic flutter is a coupled torsional-flexural vibration that occurs when the freestream velocity over an airfoil section reaches a certain critical velocity. Stall flutter, on the other hand, is a phenomenon that occurs due to the stalling of the flow around a blade. Blade stall causes Karman vortices in the airfoil wake. Whenever the frequency of the vortices coincides with the natural frequency of airfoil, flutter will occur. Stall flutter is a major cause of compressor-blade failure.  [c.927]

A nominal resiilt of this techniqne is that the reqnired airflow rate and eqnipment size is abont two-thirds of that when evaporative cooling is not nsed. See Sec. 20 for eqmpmeut available.  [c.1060]


See pages that mention the term Airflow : [c.200]    [c.192]    [c.442]    [c.442]    [c.452]    [c.281]    [c.105]    [c.113]    [c.218]    [c.227]    [c.23]    [c.486]    [c.311]    [c.1060]   
See chapters in:

Industrial ventilation design guidebook  -> Airflow


Industrial ventilation design guidebook (2001) -- [ c.0 ]