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FANS & BLOWERS

Presented By

Pranav

11MTFTFE009

Food Engineering

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Fans & Blowers

Introduction

Types of fans and blowers

Assessment of fans and blowers

Energy efficiency opportunities

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Fans

Fans generally add only a small amount of pressure to a gas.

Fluid compressibility can be ignored in the calculations.

They pull air from the atmosphere and discharge to a space

that is slightly above atmospheric pressure..

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Fan & Blower-Differences

Equipment Specific Ratio Pressure rise

(mmWg)

Fans Upto 1.11 1136

Blowers 1.11 to 1.20 1136-2066

Compressors More than 1.20 -

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Fans & blowers are differentiated by the method

used to move the air, and by the system pressure they

must operate against.

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Introduction-Fan Components

OutletDiffusers

Baffles

Heat

Exchanger

Turning Vanes

(typically used on short

radius elbows)

Variable Frequency Drive

Motor

Centrifugal

Fan

Inlet

Vanes

Filter

Belt Drive

Motor

Controller

Provide air for ventilation and industrialprocesses that need air flow

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System Resistance

Sum of static pressure losses in system

Configuration of ducts, pickups, elbows

Pressure drop across equipment

Increases with square of air volume

Long narrow ducts, many bends: more resistance

Large ducts, few bends: less resistance

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Static pressure

Static pressure is the potential energy put into the systemby the fan. It is given up to friction in the ducts and at the

duct inlet as it is converted to velocity pressure.

At the inlet to the duct, the static pressure produces an

area of low pressure.

Velocity pressure

Velocity pressure is the pressure along the line of the

flow that results from the air flowing through the duct.

The velocity pressure is used to calculate air velocity.

Total pressureTotal pressure is the sum of the static and velocity

pressure.

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Types of Fans & Blowers

Types of fans

Centrifugal

Axial

Types of blowers

Centrifugal

Positive displacement

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Centrifugal FansRotating impeller increases air

velocity

Air speed is converted topressure

High pressures for harsh

conditions

High temperatures

Moist/dirty air streams

Material handling

Categorized by blade shapes Radial

Forward curved

Backward inclined

.

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Centrifugal Fans Radial fans

Advantages

High pressure and temp

Simple design

High durability Efficiency up to 75%

Large running clearances

Disadvantages

Suited for low/medium airflow rates

only

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Radial blades

The most common fan found in

industry

Wide range of applicability

Can handle significant amounts of

particulates

Relatively low rpm

Stable throughout its range

Power increases with flow

Least efficient but still acceptable

.

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Forward curved

blades

Runs more slowly and quietly

Used for medium volumes at low

pressure rise

Power increases with flow

Theoretically pressure increases with

flow but practically these fans are

designed and used with a falling

pressure curve

.

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Centrifugal Fans Forward curved

Advantages

Large air volumes against low

pressure

Relative small size

Low noise level

Disadvantages

Not high pressure / harsh

service Difficult to adjust fan output

Careful driver selection

Low energy efficiency 55-65%

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Backward

inclined blades

Best mechanical efficiency

Quietest

Nonoverloading power characteristic

.

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Centrifugal Fans - Backward-inclined

Advantages

Operates with changing

static pressure

Suited for high flow and forced draft services

Efficiency >85%

Disadvantages

Not suited for dirty airstreams

Instability and erosion risk

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Axial Fans

Work like airplane propeller:

Blades create aerodynamic lift

Air is pressurized

Air moves along fan axis

Popular with industry: compact, low cost and light weight

Applications

Ventilation (requires reverse airflow)

Exhausts (dust, smoke, steam)

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Axial Fans Tube axial fans

Advantages High pressures to overcome duct losses

Suited for medium-pressure, high airflow

rates

Quick acceleration Space efficient

Disadvantages

Expensive Moderate noise

Low energy efficiency 65%

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Axial Fans Vane axial fans

(Canadian Blower)

Advantages

Suited for medium/high pressures

Quick acceleration

Suited for direct motor shaft connection

Most energy efficient 85%

Disadvantages

Expensive

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Blowers

Types

Centrifugal blower

Positive displacement

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Centrifugal Blowers

Gear-driven impeller that accelerates air

Single and multi-stage blowers

Operate at 0.35-0.70 kg/cm2 pressure

Airflow drops if system pressure rises

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Positive Displacement

Blowers

Rotors trap air and push it

through housing

Constant air volume

regardless of system pressure

Suited for applications prone

to clogging

Turn slower than centrifugal

blowers

Belt-driven for speed changes23

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Assessment of fans and blowers

Fan efficiency:

Ratio of the power conveyed to air stream and powerdelivered by the motor to the fan

Depends on type of fan and impeller

Fan performance curve

Graph of different pressures and corresponding required

power

Supplier by manufacturers

Fan Efficiency and Performance

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Step 1: Calculate air/gas density

Step 2: Measure air velocity and calculate

average

Step 3: Calculate the volumetric flow in theduct

t= Temperature of air/gas atsite condition

Cp= Pitot tube constant, 0.85(or) as given by the

manufacturer

p= Average differential

pressure

= Density of air or gas at

test condition

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Fan Efficiency

Step 4: Measure the power drive of the motor

Step 5: Calculate fan efficiency

Fan mechanical efficiency

Fan static efficiency

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Energy Efficiency Opportunities

Choose the right fan

Reduce the system resistance

Operate close to BEP

Maintain fans regularly

Control the fan air flow

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Choose the Right Fan

Considerations for fan selection

Noise

Rotational speed

Air stream characteristics

Temperature range

Variations in operating conditions

Space constraints and system layout

Purchase/operating costs and operating life

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Reduce the System Resistance

Increased system resistance reduces fan

efficiency

Check periodically

Check after system modifications

Reduce where possible

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Control the Fan Air flow

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

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Control the Fan Air flow

Pulley change: reduce motor/drive pulley size

Advantages

Permanent speed

decrease

Real energy reduction

Disadvantages

Fan must handle capacity change

Only applicable if V-belt system or motor

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Control the Fan Air flow

Dampers: reduce flow and increase upstream pressure

Advantages

Inexpensive

Easy to install

Disadvantages

Limited adjustment

Reduce flow but not energy consumption

Higher operating and maintenance costs

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Fans & Blowers

THANK YOU FOR YOUR ATTENTION