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Fans. Blowers

Date post: 08-Sep-2015
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  • FAN:-The basic purpose of a fan is to move a mass of gas or vapour at the desired velocity.

    Develop pressure in a few MM of W.G.

    Ceiling, Table and Ventilation fans are axial fan.

  • Blower:-

    It is also referred to as a fan.

    Delivers the gas or air with an appreciable rise in pressure.

    Develop pressures of the ordered of 1000 mm of W.G.

    Forced and induced draft fans terms as blowers.

    Blowers can achieve much higher pressures than fans, as high as 1.20 kg/cm2.

    They are also used to produce negative pressures for industrial vacuum systems.

    Major types are: (1)Centrifugal blower (2) Positive-displacement blower.

  • Compressor:-It is a mechanical equipment which takes air from atmosphere and increases its pressure by reducing its volume, the high pressure air is then stored in receiver for various uses.

    The energy stored in compressed air in form of pressure is utilized to do work in equipment and instruments in a industry.

    It develops to high pressures.

    Pressure expressed in pressure ratio.

  • Specific ratio:-The ratio of the discharge pressure over the suction pressure

    DIFFERENCES BETWEEN FANS, BLOWER AND COMPRESSOREquipmentSpecific Ratio Pressure rise (mmWg) FansBlowersCompressorsUp to 1.111.11 to 1.20more than 1.2011361136 2066 -

  • Fan Application:-Thermal power Plant.Cooling Tower.Cooling of motors & Generators.Air Circulation & Ventilation.Steel Plants.

  • Types of Fan-1.Axial Flow Fan:-Axial flow, in which the air flows axially through the impeller. (a) Propeller Fan. (b) Tube axial Fan.(c) Vane axial Fan.2. Centrifugal Fan:- -Centrifugal, in which the air flows radially through the impeller. -Centrifugal fans are classified according to wheel blading, (a) Forward curved (b) Backward curved (c) Radial (straight).

  • Propeller FanPropeller fans usually run at low speeds and moderate temperatures. They experience a large change in airflow with small changes in static pressure. They handle large volumes of air at low pressure or free delivery. Propeller fans are often used indoors as exhaust fans.Outdoor applications include air-cooled condensers and cooling towers.Efficiency is low approximately 50% or less.

  • Propeller Fan

  • Tube axial FanTube axial fans have a wheel inside a cylindrical housing, with close clearance between blade and housing to improve airflow efficiency.

    The wheel turn faster than propeller fans, enabling operation under high-pressures 250 400 mm WC.

    The efficiency is up to 65%.

  • Tube Axial fan (Fans without guide vanes)

  • Tube Axial fan

  • Vane axial Fan.Vane axial fans are similar to tube axial, but with addition of guide vanes that improve efficiency by directing and straightening the flow.

    As a result, they have a higher static pressure with less dependence on the duct static pressure.

    Such fans are used generally for pressures up to 500 mm WC.

    Vane axial are typically the most energy-efficient fans available and should be used whenever possible.

  • Vane Axial (Fans with guide vanes)Fans with upstream guide vanes

    (b) Fans with down stream guide vanes

  • Vane axial fan

  • Vane Axial (Fans with guide vanes)c) Fans with upstream and down stream guide vanes.

  • Performance of Axial fans:-

  • Centrifugal FansA centrifugal fan (also squirrel-cage fan) is a mechanical device for moving air or gases.gasesIt has a fan wheel composed of a number of blades or ribs mounted around a hub.

    The gas enters from the side of the fan wheel turns 90 degrees and accelerates due to centrifugal force as it flows over the fan blades and exits the fan housing.[1]

  • Centrifugal Fan

  • Centrifugal Fans:-

  • Main components of a centrifugal blower

  • Centrifugal impeller with double entry

  • Types of Centrifugal Fans:-Forward Curved Blades.Backward Curved Blades.Radial Blades.

  • Forward Curved BladesUse blades that curve in the direction of the fan wheel's rotation.

    These are especially sensitive to particulates.

    Forward-curved blades are for high flow, low pressure applications.

  • Backward Curved BladesBackward-inclined fansare more efficient than forward-curved fans. Backward-inclined fans reach their peak power consumption and then power demand drops off well within their useable airflow range. Backward-inclined fans are known as "non-overloading" because changes in static pressure do not overload the motor. Backward curved fans can have a high range of specific speeds but are most often used for medium specific speed applications-- high pressure, medium flow applications

  • Radial Blades.Radial fan blades, as in Figure 3(c), extend straight out from the hub. A radial blade fan wheel is often used on particulate-laden gas streams because it is the least sensitive to solids build-up on the blades, but it is often characterized by greater noise output. High speeds, low volumes, and high pressures are common with radial fans, and are often used in vacuum cleaners, pneumatic material conveying systems, and similar processes.

  • Radial blade Forward curved blades

    Backward Curved blades

  • Forward Curved blade fan

  • Backward Curved Blade fan

  • Radial Blade fan

  • Laws of Fan Performance

    Fan laws are used to predict fan performance under changing operating conditions or fan size.

    They are applicable to all types of fans. The symbols used in the formulas represent the following quantities.

  • Laws of Fan PerformanceQ -Volume rate of flow through the fan.

    N -Rotational speed of the impeller.

    P -Pressure developed by the fan, either static or total.

    HP -horsepower input to the fan.

    D -fan wheel diameter. The fan size number may be used if is proportional to the wheel diameter

    W -Air density, varying directly as the barometric pressure and inversely as the absolute temperature.

  • Fan Accessories:-Access door.Drains.Variable inlet vanes.Outlet Dampers.Vibration Isolator.

  • Fan dampers and Vanes Fan dampers are used to control gas flow into and out of the centrifugal fan.

    They may be installed on the inlet side or on the outlet side of the fan, or both. Dampers on the outlet side impose a flow resistance that is used to control gas flow

    Dampers on the inlet side (inlet vanes) are designed to control gas flow by changing the amount of gas or air admitted to the fan inlet.]

  • Fan Control

    Variable Speed motor Control.Outlet Damper Control.Variable inlet vane control.Fan drive change. Scroll volume control.

  • Fan drive change

  • Outlet Damper Control

  • Variable inlet vane control

  • Diffusers and VolutesStatic pressure is recovered from the kinetic energy of the flow at the impeller exit by diffusing the flow in a vane-less or vaned diffuser. The spiral casing as a collector of flow from the impeller or the diffuser is an essential part of the centrifugal blower.

    The provision of a vaned diffuser in a blower can give a slightly higher efficiency than a blower with only a volute casing.

  • Drum Type Fans:-

  • Centrifugal Fan losses:-Impeller entry lossesLeakage LossesImpeller LossesDiffuser and volute losses.Disc Friction

  • Fan Bearing:-

    Journal BearingsRoller BearingsSelf aligning bearings

  • Fan Drives:-Direct Coupled:-The fan wheel can be linked directly to the shaft of an electric motor. This means that the fan wheel speed is identical to the motor's rotational speed. With this type of fan drive mechanism, the fan speed cannot be varied unless the motor speed is adjustable.

    (b) V- belt drive :-A set of sheaves(V-groove pulley) are mounted on the motor shaft and the fan wheel shaft. The belts transmit the mechanical energy from the motor to the fan.

  • Fan Noise:-The main cause of aerodynamically generated noise. Flow at entry & exit of the fan.Turbulences of air.Passage of blades through wakes.Separation, stalling and Surging.Shedding of vortices from blades.Rotation of blades through air or gas.

    The frequencies and noise levels that occurs in fanand blower.Frequencies = 65-800 hz.Noise level = 40 and 50 db

  • Method of reducing noise:-Operation of fan at their max. efficiencies .Use of low speed and low pressure fan.Employment of uniform flow in ducts.Use of flexible fan mounting. Use of silencer at the suction and exhaust. Use of sound absorbing walls; ducts should also be lined by sound absorbing material.Enclosing the fan in a sound absorbing casing.

  • Dust erosion of fans When dust particles directly hit the moving blades, cause of cracking of blades and surface erosion.Aspect of dust erosion

    Eroded part may be fail any time.Rotor may be unbalance due uneven erosion of fan blade.High vibration reduce fan life.

  • Minimizing of Dust erosion

    Employing a more efficient dust removing apparatus.Regulating fan speed at part loadsProviding erosion shields on the blades. Employing large and low speed fans .Reducing stratification.Reducing stratification.

  • Fan & Blower Maintenance Introduction:-

    Dirty filters, dirty coils, or restriction of any kind will reduce the air quantity.

    Any major reduction in operating pressure may overload the motor by permitting the fan to handle more than rated capacity.

  • Fan & Blower MaintenanceCleaningFan BearingDirection of RotationAdjustment.AlignmentFan Coupling.Direct CouplingV-Belt DrumLubricating of bearing.

  • TROUBLE SHOOTING

  • VIBRATION DISPLACEMENT MILS

    Fan Speed RPMSmoothFairRoughVery Rough 6002.004.008.0015-209001.52.756.008-1012001.02.004.56-818000.751.53.55-7

  • COMPRESSORSUses of Compressed Air:-

    Acid and Chemical IndustriesAgricultureConstruction IndustryAircraft Industry Ammunition DepotsMining OperationsIn GeneralStarting of IC enginesSpraying of fuel into diesel enginesSpraying paintsGlass blowingIn Nuclear Power StationsMask AirInstrument AirService Air

  • Important Terms:-Before taking up the actual study of air compressors one must know the following terms which are very frequently used in connection with them.

    Air Compressor:- This may be regarded as a machine, which is used to increase the pressure of air reducing its volume.

    Reciprocating Compressor:- This is a machine, which compresses air b means of piston reciprocating inside a cylinder.

    Single acting Compressor:- this compressor is a machine, which compresses air in only one end of a cylinder.

  • Double acting compressor:- The double acting compressor is a machine, which compresses air in both ends of a cylinder.

    Single Stage Compressor:- This is a machine in which the air from atmospheric pressure is compressed to the desired discharge pressure in a single operation.

    Two stage Compressor:- In this machine the air from atmospheric pressure is compressed to the desired pressure in two stages. In the first stage the air is compressed to an intermediate pressure while in the second stage it is further compressed to the desired final pressure.

    Multistage Compressor:- This is compressor, which produces the desired final pressure through two or more stage.

  • Rotary Compressor:- This is a machine in which the compression is effected by a rotating vane or impeller that imparts velocity to the flowing air to give it the desired pressure.

    Inlet pressure:- This is the absolute pressure of air at the outlet of a compressor.

    Discharge pressure:- This is the absolute pressure of the air at the outlet of a compressor.

    Compression ratio:- This is the ration of the absolute discharge pressure to the absolute inlet pressure.

    Free Air delivered (FAD):- Free air delivered is the volume of air delivered under the conditions of temperature and pressure existing at the compressor intake, i.e. volume of air delivered at surroundings air temperature and pressure. In the absence of any given free air conditions, these are generally taken as 1.0332 kgf/cm2 abs and 15 C


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