Fans and Blowers Session Objectives This session is

Fans and Blowers

Session Objectives This session is intended to discuss the following: • Types and working principle of fans and blowers • Applications of various fans and blowers • Pressure rise, flow coefficient and efficiency • Velocity triangles • Performance characteristics • Fan laws

What is a Fan? Any device that produces a current of air by the movement of broad surfaces can be called a fan. Fans fall under the general classification of “turbomachinery” and have a rotating impeller at least partially encased in a stationary housing. Fans are similar in many respects to pumps. Both are turbomachines that transfer energy to a flowing fluid. It is easy to distinguish between fans and pumps: pumps handle liquids; fans handle gasses. Broadly speaking, the function of a fan is to propel, displace, or move air or gas.

Fans, Blowers and Compressors . Fans, blowers and compressors are differentiated by the method used to move the air, and by the system pressure they must operate against. Difference Between Fans, Blower and Compressors Equipment Specific Ratio Pressure Rise (mm. WC) Fans Up to 1. 11 1136 Blowers 1. 11 to 1. 20 1136 to 2066 Compressors More than 1. 20 As per American Society of Mechanical Engineers (ASME) the specific ratio – the ratio of the discharge pressure to the suction pressure – is used for defining the fans and blowers

Components of Fan/Blower System Turning Vanes (typically used on short radius elbows) Outlet Diffusers Provide air for ventilation and industrial processes that need air flow Filter Heat Exchanger Baffles Inlet Vanes Motor Controller Centrifugal Fan/Blower Belt Drive Variable Frequency Drive Motor .

. Parts of a Fan / Blower 1. 2. 3. 4. 5. 6. 7. 8. • • Centrifugal housing include side plate and scroll sheets. Axial housing includes the outer and inner cylinder, belt tube. Impeller Blade Shroud Hub Housing Inlet Outlet Guide Vanes

Fan Types . Fans are classified according to the direction of flow through the impeller: Axial Flow: Air flows through the impeller parallel to, and at a constant distance from the axis. The pressure rise is provided by the direct action of the blades Centrifugal or radial flow: Air enters parallel to the axis of the fan and turns through 900 and is discharged radially through the blades. The blade force is tangential causing the air to spin with the blades and the main pressure is attributed to this centrifugal force Mixed flow: Air enters parallel to the axis of the fan and turns through an angle which may range from 300 to 900. The pressure rise is partially by direct blade action and partially by centrifugal action Cross Flow: air enters the impeller at one part of the outer periphery flows inward and exits at another part of the outer periphery.

Centrifugal Fans Rotating impeller increases air velocity Air speed is converted to pressure High pressures for harsh conditions • High temperatures • Moist/dirty air streams • Material handling Categorized by blade shapes • Radial • Forward curved • Backward inclined .

Centrifugal Fan Impeller Types . Open Type Backward inclined Radial Tip Blades Backward inclined Radial tip Blades Airfoil Blades with Higher Efficiency Backward inclined radial blade Open Type Backward inclined Radial Tip Blades Forward Curved Blades Type

. Centrifugal Fans Forward-curved fans are used in clean environments and operate at lower temperatures. Well suited for low tip speed and highairflow at lower pressures Paddle blade or radial fan Radial fans have high static pressures (up to 1400 mm WC) and can handle heavily contaminated airstreams. Well suited for high temperatures and medium blade tip speeds Backward curved Forward curved or multi-vane radial fan ©M. chhool ©S. M. R S. am Raah aima. Sia Scohfo. Aodl voafnce Addv. Satud nciees, d. B Staundgiaelore s Backward-inclined fans are more efficient than forwardcurved fans. Also known as "non-overloading" because changes in static pressure do not overload the motor

• • • • • Applications of Centrifugal Fans Augmenting Air Fan Scanner Air Fan Booster Air Fan Burner Air Fan Degasser Blower Combustion Air Fan Oil Vapour Exhaust Fan Purge Gas Blowers Inline Fans Supply Air Fan Exhaust Air Fan Ventilation Fan Radial Blowers Turbo Blowers (Centrifugal) FD Fan In-series Blowers Igniter Air Fan Seal Air Fan .

Centrifugal Fans Type Radial Characteristics . Typical Applications High pressure, medium flow, Various industrial applications, efficiency close to tube axial fans, suitable for dust laden, moist power increases continuously air/gases Medium pressure, high flow, dip Low pressure HVAC, packaged Forward curved in pressure curve, efficiency units, suitable for clean and blades higher than radial fans, power rises dust laden air/gases continuously Backward curved blades High pressure, high flow, high efficiency, power reduces as flow increases beyond the point of highest efficiency HVAC, vaious industrial applications forced draft fans etc Airfoil type Same as backward curve type, highest efficiency Same as backward curved, but for clean air application

Fan/Blower Blade Types Impeller blades are manufactured either laminar (flat, constant thickness) or aerofoil shape and generally hollow Aerofoil blades have greater efficiencies (up to 90%) compared to constant thickness blades, with the advantages of efficiency spread over the characteristic and lower noise generation However with careful attention to design of blade curvature, inlet eye detail and impeller shrouding, comparable efficiencies can be achieved with constant thickness blades Aerofoil blades are freely used particularly when blade stresses are high and extra stiffening is required constant thickness blades Aerofoil blades .

. Axial Flow Fans Less efficient, large airflow and low speeds Vane axial fan Tube axial fan Propeller fan Higher speeds than propeller fans, highpressures 250 – 400 mm WC and efficiency up to 65%. Pressures upto 500 mm. WC and are highly energy-efficient

Axial Flow Fans – Applications • • • • Ventilation Fan Airscrew Fan Wall mounted Supply Fan Wall mounted Exhaust Fan Bifurcated Fan Roof Exhaust Fan Inline Fan Spark proof Fans Inline Fans Fresh Air Unit Ventilation Unit Air washer Unit Smoke Exhaust Unit Toilet Exhaust Fans CPU Fans .

Propeller Fan Propeller fan also known as panel fan is commonly used to exhaust hot or contaminated air or corrosive gases from factories, welding shops, foundries, furnace rooms, laboratories, laundries, stores or residential attics or windows 24”propeller fan with belt drive .

Axial Fans Type Propeller Tube Axial Vane Axial . Characteristics Typical Applications low pressure, high flow, low Air circulation, efficiency, peak efficiency ventilation, close to point of free air exhaust delivery (zero static pressure) Medium pressure, high flow, HVAC, higher efficiency than drying ovens, propeller type, dip in pressure exhaust systems flow curve before peak pressure point High pressure, medium flow, High pressure dip in pressure-flow curve, applications including use of guide vanes improves HVAC systems efficiency exhausts

Mixed Flow Fan Mixed flow fan with barrel shaped spun housing for small diameters of inlet and outlet ducts. Direct drive, the fan wheel has a conical back plate. Outlet guide vanes prevent excessive air spin at the small outlet diameter. .

Axial-Centrifugal Fan Types Single inlet single width impeller Double inlet double width impeller Single inlet single width fan wheel with six radial blades welded to a back plate .

Belt Drive versus Direct Drive Belt drive • Flexibility in operating speeds • The air stream passing over the motor cools it • Large size fans can be operated at low speeds while motor is operated at higher speeds resulting in economical operation A 30 increase in blade angle will result in 10 -15% increase in flow . Direct drive • Lower number of components resulting in lower costs • Requires no regular checkups for adjustment of belt • Higher fan efficiency since no slippage due to belt drive • Results in more flow since motor does not obstruct flow • Performance flexibility of belt drive can be obtained by adjustable pitch blades and increasing number of blades

Blower Types . Centrifugal blowers typically operate against pressures of 0. 35 to 0. 70 kg/cm 2, but can achieve much higher pressures Also used to produce negative pressures for industrial vacuum systems Major types are; centrifugal blower and positive-displacement blower The impeller is typically gear-driven and rotates as fast as 15, 000 rpm Efficiency drops with multi-staging due to the path taken from stage to stage One characteristic is that airflow tends to drop drastically as system pressure increases Positive-displacement blowers have rotors, which "trap " air and push it through housing. Positive-displacement blowers provide a constant volume of air even if the system pressure varies. They are especially suitable for applications prone to clogging, They turn much slower than centrifugal blowers (e. g. 3, 600 rpm), and are often belt driven to facilitate speed changes.

Fan Efficiency Calculation . • Before calculating fan efficiency measure operating parameters Air velocity, pressure head, air stream temp, electrical motor input, etc. , • Ensure that Is efficiency Fan is operating at rated speed the only Operations are at stable condition criteria for fan • Methodology selection? 1. Calculate air/gas density 2. Measure air velocity and calculate average 3. Calculate the volumetric flow in the duct 4. Measure the power drive of the motor 5. Calculate fan efficiency (Mechanical and Static efficiency)

. Centrifugal Fans Schematic sketch of a typical centrifugal fan wheel with ten backward-curved airfoil blades d 1 = blade inner diameter d 2 = blade outer diameter b = blade width l = blade length = blade angle U = blade velocity W = relative air velocity V = Absolute air velocity 1 is usually 10 o to 30 o

Scroll Casing Schematic sketch of typical scroll housing assembly for a 36. 5 inch centrifugal fan with airfoil, backward curved blades for general ventilation .

Airflow versus Blade Width Airflow versus blade width for a centrifugal fan with airfoil blades .

Control of Fan/Blower Airflow Speed change by pulley change Dampers Inlet guide vanes Variable pitch fans Variable speed drives (VSD) Multiple speed drive Disc throttle Operating fans in parallel Operating fans in series Flow control dampers Inlet vane dampers . Pulley Driven Inlet guide vanes

Control of Fan/Blower Airflow • Pulley change: reduce motor/drive pulley size Speed Change Permanent speed decrease Real energy reduction Fan must handle capacity change Only applicable if V-belt system or motor • Dampers: reduce flow and increase upstream pressure Inexpensive Easy to install Limited adjustment Reduce flow but not energy consumption Higher operating and maintenance costs . Dampers

Control of Fan/Blower Airflow . • Inlet guide vanes Create swirls in fan direction Reduce angle air and fan blades Lowering fan load, pressure, air flow Improve efficiency: reduced load and airflow Cost effective at 80 -100% of full air flow Less efficient at <80% of full air flow • Variable pitch fans: changes angle incoming airflow and blades – Axial fan only High efficiency at range of operating conditions No resonance problems No stall problems at different flows Applicable to axial fans only Risk of fouling problems Reduced efficiency at low loads Lets look at this in detail in subsequent slides

Control of Fan/Blower Airflow . • Variable speed drives (VSDs): reduce fan speed and air flow – Two types; Mechanical VSDs and Electrical VSDs (including VFDs) Most improved and efficient speed control Speed adjustments over continuous range high costs • Variable frequency drives (Change motor’s rotational speed by adjusting electrical frequency of power) Effective and easy flow control Improved efficiency over wide operating range Can be retrofitted to existing motors Compactness No fouling problems Reduced energy losses and costs ©M. chhool ©S. M. R S. am Raah aima. Sia Scohfo. Aodl voafnce Addv. Satud nciees, d. B Staundgiaelore s 3399

Control of Fan/Blower Airflow • Multiple speed drive (Changes fan speed from one to other) Efficient control of flow Suitable if only 2 speeds required Need to jump from speed to speed High investment costs • Disc throttle (Sliding throttle that changes width of impeller exposed to air stream) Simple design Feasible in some applications only • Operate fans in series Lower average duct pressure red Less noise Lower structural / electrical support requi Not suited for low resistance systems. Fans in series .

Control of Fan/Blower Airflow • Operate more fans in parallel (instead of one large fan) High efficiencies at varying demand Less expensive and better performance than one large fan Risk of downtime avoided Can be equipped with other flow controls Only suited for low resistance system Comparing Fans in Parallel and Series Comparing the impact of different types of flow control on power use .

Merits of Axial and Centrifugal Fans . Axial fans offer better efficiency over a wider range of duties whereas the centrifugal fans can have a higher efficiency, albeit over a smaller range, on a single performance curve. The performance of a single speed axial fan can be altered simply by adjustment to the impeller blade pitch angle. The performance of a single speed centrifugal fan requires the installation of variable inlet vanes. Axial fans are generally considered to be more easily accessible for maintenance. Axial fans generally run faster than centrifugal as a consequence are much noisier. Axial fan impellers are generally manufactured from aluminum in an effort to keep weight to a minimum. As a consequence the potential for erosion is greater, particularly if there is water in the shaft.

Merits of Axial and Centrifugal Fans . The light material used in the blades along with the high rotational speed of axial fans make them prone to erosion, and even in good (dry) conditions it is reasonably expected that this erosion will have significantly reduced the fan performance within five years. Centrifugal fan impellers are fabricated from plate and are generally hollow. As a consequence when there is water in the shaft the nose of the blade is prone to pitting allowing water to enter the hollow section. Sufficient water in this section will cause the impeller to become unbalanced, and if allowed to continue it will result in high vibration and eventual failure of the impeller shaft. Centrifugal fans traditionally require the construction of large concrete foundations for the motor and ductwork. The cost of these foundations significantly increases the capital cost of the fan.

Merits of Single and Multiple Fans . Single fan installations are generally less expensive than multiple fan installations. Multiple fan installations have the advantage of airflow redundancy, i. e. a percentage of airflow will always be available whilst a fan is off line for maintenance or component change out. Single fan options do not provide any capacity for redundancy airflow. The purchase of spares (motor, impeller, shafts, bearings, blades etc) is good management and should be included as upfront capital expenditure.