Chapter 0 -Cover page to certificates - JJTshodhganga.inflibnet.ac.in/bitstream/10603/37646/10/10... · · 2015-03-19The minimum efficiency requirements are based on the function

“Studies on Radial Tipped Centrifugal Fan” 1

CHAPTER – 1 INTRODUCTION

1.1 Preamble

The world is facing serious challenges in energy. A global revolution is

needed in the ways that energy is produced, supplied and used. Total Energy

consumption by various sectors is shown in Figure 1.1. It shows that industries

consume almost 70% of total energy generated.

Figure 1.1 Energy Consumption by Various Sectors [1]

Manufacturing industries consumes about 85% of total industrial energy

usage. The non-manufacturing industries like agriculture, mining, oil and gas

extraction, and construction accounts for the remainder.

One of the biggest electricity consumers in the industrial sector is the motor

system, which is critical to both production process and facility end-users. For

example, material processing and handling, refrigeration, and compressed air, all use

motor drives to some extent. Figure 1.2, as given below shows the study of electricity

consumption of fan and pump systems in the industries, compared to other motor’s

applications.

Chapter – 1: Introduction


Figure 1.2 Electricity Consumption of Motor [2]

Within the motor drive sub-set, pumps and fans are significant electricity

consumers and generally account for about 40% of motor system consumption.

Energy is also lost due to inefficiencies in the wide range of equipment used for pre-

process and manufacturing process activities using motors, mechanical drives, process

heaters and coolers and others. Compressors typically lose as much as 80 percent of

energy inputs, pumps and fans typically lose 35 to 45 percent, and motors lose 5 to 10

percent [1].

Electricity consumption by the installed industrial fans and blowers is

estimated at 45–55 terawatt-hours (TWh) per year. Centrifugal fans dominate among

total fan and blower market by consuming 90% of sector energy. Initial field research

suggests that substantial further reductions in industrial fan and blower electricity

consumption are possible at equipment, speed control and system design level as

quantified in Table 1.1.

Table 1.1 Energy Savings Potential for Specific Fan and Blower Systems [2] Equipment 5–15%

Speed Control* 20–50%*

System Design* 5–25%

* Applies to variable flow systems and includes ASDs as well as staging multiple fans to serve a load

response to varying air needs.

All industrial fans can be classified primarily as centrifugal and axial flow

fans. These types are characterized by the path of the airflow through the fan.

Centrifugal fans use a rotating impeller to increase the velocity of an airstream. As the

air moves from the impeller hub to the blade tips, it gains kinetic energy. This kinetic

energy is then converted to a static pressure increase as the air slows before entering

the discharge. Centrifugal fans are capable of generating relatively high pressures.



They are frequently used in “dirty” airstreams (high moisture and particulate content),

in material handling applications, and in systems at higher temperatures.

Centrifugal fans have the largest market share at 34%, while axial-flow fans

account for about a 23% of the market, and mixed flow and propeller fans have a

combined market share of about 43% as shown in Figure 1.3. In terms of fan

applications, general application is the largest at about 46% [3].

Figure 1.3 Market Shares of Centrifugal, Axial and Other Fans [3] Figure 1.4 and Table 1.2 shows sales market forecast of number of axial,

centrifugal, cross and box type of fans from the year 1995 to 2020 presenting their

growth trend. It utilizes advanced econometric techniques for short-term and long-

term growth trends. The sales value of the 2005 fan sales was around 5.5 billion euro

(industry turnover).

Figure 1.4 Unit Sales (Million) by Fan Type during 1995-2020 [4]



Table 1.2 Fan Sales by Their Types [4]

Fan Type Sales [number of millions]

1995 2000 2005 2010 2015 2020 2025

Axial < 300 Pa 0.90 2.25 2.40 2.62 3.00 3.39 3.78

Axial > 300 Pa 0.93 2.51 2.70 2.86 3.01 3.17 3.33

Centr. FC 0.46 0.66 1.12 1.04 1.20 1.36 1.52

Centr. BC-Free 0.14 0.21 0.33 0.31 0.35 0.39 0.43

Centr. BC 0.14 0.23 0.37 0.34 0.39 0.44 0.49

Cross Flow 0.13 0.23 0.19 0.26 0.30 0.34 0.37

Box 1.53 2.58 2.30 2.91 3.13 3.35 3.57

Roof all 1.99 3.87 3.40 4.10 4.33 4.55 4.78

Total 6.23 12.54 12.81 14.44 15.72 16.99 18.27

100% 113% 123% 133% 143%

This impact assessment identified a stock of 143 million units in 2005, rising

to 227 million in 2020. Figure 1.5 shows the relative stock increase of fan sales

against the 2005 situation.

Figure 1.5 Fan Stocks 1990 – 2025 [4]



1.2 Need of Energy Efficient Fan

Further advancement and research study and government measures in the field

of energy efficient fans are carried out all around the globe. On 27 May 2008, the

meeting of the Eco-design Consultation Forum took place and presented a working

document (CSWD) on eco-design requirements related to fans. The technical scope of

axial, centrifugal, cross-flow, box and roof fans is in the power range of

125 W – 500 kW was selected due to their major market share. Improvements in the

energy efficiency of fans should be achieved by applying existing nonproprietary

cost-effective technologies that can reduce the total combined costs of purchasing and

operating them [4].

The eco-design consultation forum considered and proposed the following

minimum efficiency levels by fan type and year of implementation (all referring to

static efficiency) as shown in Table 1.3.

Table 1.3 Average Efficiency and CSWD Minimum Efficiency Requirements (at Base Case Power) [4]

Fan category kW Avg.

Efficiency2010 2011 2012 2020

Axial, ≤ 300 Pa 0.8 30.9% 26.4 26.4 26.4 30.4

Axial, > 300 Pa 1.32 37.1% 30.4 30.4 30.4 34.4

Centrifugal / FC 0.44 32.1% 26.4 26.4 26.4 30.4

Centrifugal / plug 3.76 56.4% 53.4 53.4 53.4 57.4

Centrifugal / BC-AF 3.82 53. 7% 50.6 50.6 50.6 55.6

Cross flow fans 0.42 7.3% 8.0 26.3 26.3 30.3

Box fans 0.37 23.1% 18.2 18.2 18.2 22.2

Roof fans 1.2 43.6% 37.7 37.7 38.1 42.1

The minimum efficiency requirements are based on the function performed by

a fan. The proposed minimum energy performance requirements and the timing for

their introduction of first phase start from the year 2010. Now it is a time to redesign

and manufacture more efficient fans.

Energy-efficiency improvement options specifically on use of fans in cement,

refineries, fertilizers, chlor-alkali and textile industries of India are identified [5]. The

Indian textile industry contributes about 14% to the national industrial output and



about 25% to the total national export earnings. Their feasibility report has suggested

that technological up gradation of installed fan or their replacement with use of

improved efficiency fan with variable drive can save maximum energy. Improved

energy efficiency is an important component to increasing national energy security,

reducing the cost of energy, and combating climate change and environmental

degradation.

Above assessment indicates the need of improving design to achieve energy

efficient centrifugal fan used in textile industry. Hence this research work is based on

an industrial requirement of re-designing fume extraction centrifugal fan used in SDS-

9 texturising machine of medium scale textile industry.

1.3 Turbomachines

The word turbo or turbine is of Latin origin and implies that which spins or

whirls around. Turbo-machines are defined as “A device in which energy is

transferred to or from a continuously moving fluid by the dynamic action of a moving

blade row. The blade row rotates and changes the stagnation pressure of the fluid by

either doing work on the fluid (as a fan/ pump) or by having work done on the blade

row by the fluid (as a turbine)” [6,7].

According to the Compressed Air Institute, fans are used where low pressures

(from few mm of water to nearly 7-kPa gauge pressure) and comparatively large

volumes are required to handle. They run at relatively low speeds, the casing and

impeller are usually built from iron sheets. Blowers are defined where a final pressure

is not exceeding 240 kPa. Blower is having higher flow resistance on delivery side

while fan is having such resistance on suction side. Similarly, a centrifugal

compressor is used to compress air or gas to a final pressure above 240 kPa.

Turbo machines are classified based on principal flow directions such as axial

flow machines, radial flow machines and mixed flow machines. They are also

classified based on specific speed. Sayers [8] have given a much generalized

classification of these machines as shown in Figure 1.6 while Figure 1.7 gives specific

rotor designs with their dimensionless specific speeds.

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The centrifugal machines are further classified based on blade geometry which

governs the loss and their performance, too.

Forward curved blade tips are inclined towards the direction of rotation and

exit blade angle β2 is greater than 90°. This results in large blade angles and higher

flow rate and higher stage pressure rise. Exit whirl component Vu2 is large and is

leading to a higher stage pressure rise. This type of blade is normally used for low

pressure heating, ventilating and air conditioning of domestic furnaces and packaged

air conditioning equipment.

Radial blade has tip (or even the whole blade in the case of paddle bladed

fans) in radial direction at exit having exit blade angle β2 is equal to 90°. Radial blade

with curved surface is known as radial tipped blade. This type of blades is generally

used in material handling applications having dirty or erosive environment.

Backward curved blade tip has its inclination away from the direction of

rotation which causes exit blade angle β2 less than 90°. The blade passage expands

gradually so airflow will decelerate gradually and will have minimum turbulence.

Hydraulic performance of centrifugal fan is governed by inlet and exit velocity

triangle. Velocity triangles for a turbo machine contain peripheral velocity (U) of

rotor blades, the absolute velocity (V) and relative velocity vector (W). These velocity

vectors and blade and flow angles are shown in Figure 1.8 at impeller entry and exit

with tangential direction taken as reference direction, for each case of forward, radial,

and backward curved impeller.



Figure 1.8 Velocity Triangles for Different Blade Profiles [9]

1.4 Fan Selection and Performance Characteristic Curves

[10, 11, 12]

In manufacturing, fan reliability is critical for plant operation. The importance

of fan reliability often causes system designers to design fan systems conservatively

by over sizing.

The choice of fan type for a given application depends on the required

magnitudes of flow, static pressure and rotational speed. High speed units are

generally more economical because of their higher hydraulic efficiency and relatively

low cost and smaller in size. However, for low pressure ratios, large sized low-speed



units are preferable. The use of a “systems approach” in the fan selection process will

typically yield a quieter, more efficient, and more reliable system.

The operating costs of large fans are often high enough and hence improving

fan system efficiency can offer a quick payback.

Fan characteristics can be represented in form of fan curves. The fan curve is a

performance curve for the particular fan under a specific set of conditions. It is a

graphical representation of a number of inter-related parameters like fan volume,

system static pressure, fan speed and shaft power/BHP required to drive the fan under

the stated conditions. An important aspect of a fan performance curve is the best

efficiency point (BEP). At BEP a fan operates most cost-effectively in terms of both

energy efficiency and maintenance considerations. Operating a fan near its BEP

improves its performance and reduces wear.

The intersection of the system resistance curve and the static pressure curve

defines the operating point. A horizontal line drawn through the intersection with the

power curve will lead to the required power on the right vertical axis. Figure 1.9

shows graphical representation of manufacturer’s test data for a typical fan. In this

Figure, the fan efficiency curve is also presented. It is important to note that a fan

operates along a performance given by the manufacturer only for a particular fan

speed.

Figure 1.9 Manufacturer’s Fan Characteristic/Performance Curves [12]



Typical static pressure and shaft power with respect to volume flow for

forward, backward and radial blade type fans are given in the Figure 1.10.

Figure 1.10 Static Pressure, Shaft Power V/s Volume Flow Curves for Different

Types of Blades [12]

Figure 1.11 shows effect of impeller rotational speed on head developed, shaft

power required, total efficiency and discharge. These curves are plotted as a set of

constant speed lines.

Figure 1.11 Centrifugal Fan Characteristic Curves [10]



Non dimensional performance parameters like power coefficient

λ P/ρ N3D5), and pressure coefficient (ψ gH/ N2D2), flow coefficient

(φ Q / ND3) as well as efficiency (η) are used to analyze standard fan performance.

These curves, based upon non - dimensional parameters can be plotted for a family of

geometrically similar fans operating under dynamically similar conditions. These non

dimensional performance curves are shown in Figure 1.12.

Figure 1.12 Centrifugal Fans Non-Dimensional Performance Curves [10]

1.5 Cordier Diagrams

[7, 13]

In the early of 1950s, Cordier had carried out an intensive empirical analysis

of “good” turbo-machines by using extensive experimental data. He had converted

these performance parameters into dimensionless correlations. He has used

dimensionless specific speed Ns and diameter coefficient δ (or Ds) as their

performance yardsticks.

He has made graphical presentation of these correlations and categorized all

axial, centrifugal and mixed flow turbo machines on the basis of these correlations. A

trend line of best efficiency performance of various turbo machines is prepared in the

form of curve. He found that subject to uncertainty and scatter in data, those

turbomachines which have excellent efficiencies, adhere close to the mean curve. So

it represents a fairly broad spread of results on either side of line. These curves are

very well known as Cordier diagrams and they are very useful tool for any designer to

specify that which class and type of turbo machine will serve their requirement



efficiently. These curves will not give exact solution but will lead to approximate

solution so that design process can start in right direction. Performance of actual fans

which is falling away to Cordier line is defined as moderate or less efficiency fans.

Specific speed is a criterion at which a fan of unspecified diameter would run

to give unit volume flow and pressure. This applies to all fans in a homologous series.

This is derived from the fan laws by elimination the diameter term, thus:

Discharge Q based specific speed is used for pumps, compressors, fans and blowers.

/

Power P, based specific speed is used for all types of turbines.

Cordier diagrams relating specific speed versus diameter coefficient and speed

coefficient versus diameter coefficient with total efficiency selection are shown in

Figures 1.13 and 1.14, respectively.

Figure 1.13 Cordier Diagrams Correlating Specific Speed Ns and Diameter

Coefficient δ For Pump and Fan Selection [13]

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1.6 Laboratory Methods for Performance Testing of Fans and Blowers - An Overview of Test Codes

[16, 17, 18, 19] Theoretical estimation of fan performance and associated slip and other losses

cannot be done accurately. Proven design must be validated by accurate test results.

The performance of any fan can be affected by many variables at suction and

discharge. Real performance characteristics of a fan or blower can only be truly

ascertained by accurate tests.

Field tests are considered less reliable than laboratory tests, because at field,

the flow conditions may not be identical as prescribed in test standards. If the

laboratory tests are conducted strictly in accordance with the relevant standard, the

performance data will accurately reflect fan performance within the appropriate

tolerances for efficiency, pressure and flow when tested in the defined configuration.

Fan test standards have been prepared in order to establish a clearly defined test

procedure that allows for comparison of different fan designs, and also allows for the

independent verification of test data.

Internationally recognized standards are AMCA210, BS848, IS4894 and

ISO5801. These are highly prescriptive, and precisely specify test duct configurations,

measurement procedures, measurement planes and instrumentation to be used.

• AMCA 210 Standard for fan testing

This standard provides rules for testing fans under laboratory conditions to

provide rating information. It was prepared by a joint committee consisting of the Air

Movement and Control Association Inc review committee (AMCA 210) and the

American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc

(ASHRAE) standard 51-75R committee. This joint committee unanimously decided

that AMCA standard 210-74 and ASHRAE standard 51-75 could be reaffirmed with

minor revisions and published as ANSI/AMCA STANDARD 210-85

ANSI/ASHRAE STANDARD 51-1985 titled as “American National Standard

Laboratory Methods of Testing Fans for Rating”. This standard includes

description of units of measurement, definitions, instruments and methods of

measurement, equipment and test setups, calibration corrections, observations and

conduct of test, testing by various flow sections, similarity and fan laws and

uncertainty analysis.



Fig. 1.16 shows schematic inlet duct test setup arrangements as suggested by

this standard.

• Location 1 stands for fan inlet, 2 stands for fan outlet, 3 stands at pitot transverse station

• Psr= Fan static pressure reading, Pvr= Fan velocity pressure reading • D= Diameter and equivalent diameter, L= Length of duct • Td= Dry bulb temperature, PL= Plane

Figure 1.16 Schematic Inlet Duct Test Setup Configurations as per ANSI/AMCA 210-85 [16]

• BS 848 Standard for fan testing

This international standard is the result of almost thirty years of discussion,

comparative testing and detailed analyses by leading specialists from the fan industry

and research organizations throughout the world.ISO/TC 117 committee had started

its work in 1963 and published subsequent revisions of various national standards.

British Standard BS 848: Part 1: 1997 “Fans for General Purposes –

Part 1: 1997, Performance Testing Using Standardized Airways” is now

reaffirmed by a Technical Committee ISO/TC 117, Industrial fans, Subcommittee

SC 1, Fan performance testing using standardized airways, as ISO 5801 “ Industrial

Fans – Performance Testing Using Standardized Airways” (First Edition 1997-06-01).

This standard includes A to D types of standardized installation to be tested where

type A is free inlet and outlet, type B is free inlet and ducted outlet, type C is ducted

inlet and free outlet and type D is for ducted inlet and outlet. Fan pressure is defined

as total pressure difference across the fan and compressibility of air is taken care if



high accuracy is required. Simplified methods can be used if Mach number does not

exceed 0.15. It explains standard methods to calculate average pressure in airway

duct, measurement of temperature, speed, input power and flow-rate. It includes

uncertainty analysis in measurements with maximum allowable uncertainties in

measurements and calculated results. This standard employs SI units of measurement.

Fig. 1.17 shows schematic inlet duct test setup arrangements as suggested by

this standard.

• Pe= Gauge pressure reading at pressure measurement section • D3= Internal diameter of a circular conduit at pressure measurement section • P= Differential pressure

Figure 1.17 Schematic Inlet Duct Test Setup Configurations as Per BS 848:

Part 1: 1997 [18]

• IS : 4894-1987 Standard for fan testing

The Indian Standard IS: 4894-1987 reaffirmed in 1994 is titled as “Indian

Standard - Specification for Centrifugal Fans” (First Revision) is published by

Bureau of Indian Standards (BIS), New Delhi for the testing of centrifugal fans. The

centrifugal fans covered by this standard are capable of working against pressure. In

preparing this standard, some assistance has been drawn from BS 848: Part 1:1980,

"Fans for General Purposes: Part 1 Methods for Testing Performance”. It (IS: 4894-

1987) describes terminology, performance rating, and point of rating, type of routine

and acceptance tests and sizes covered. It also includes general and electrical safety

requirements. Air delivery tests includes norms for airway inlet duct, manometers and

square blocks, values of coefficient of discharge for conical inlet with respect to

Reynolds number, use of resistance screens and locations for pressure tapping are

unique features of this standard. This standard facilitates formulae for computing and

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ability to study system variables and its effect without conducting experiments or

where it is very difficult to perform experiments. CFD gives feasible solution of the

problem which is under hazardous conditions in real. It also extends its solution

beyond the workable boundaries of the problem. It allows checking solution optimally

by offering wide range of variable parameters for a problem under study.

From the mid-1970's, the complex mathematics was generalized by the

algorithms developed. Afterwards in the early 1980's algorithms were well developed

and need of powerful computer processors was emerged. Recent advances in

computing power, together with powerful graphics and interactive 3D manipulation of

models, have made the process of creating a CFD model and analyzing results offer

better flow visualization at reduced time and cost.

3-D CFD analysis of various flow phenomenons occurring inside

turbomachine can be numerically analyzed with the help of commercially available

CFD softwares. The set of equations which describe the processes of momentum, heat

and mass transfer are known as the Navier-Stokes equations. These partial differential

equations were derived in the early nineteenth century and had no analytical solution

but it can be only discretized and solved numerically. In recent time, there are three

different types of numerical solution techniques available to solve governing

equations by computational fluid dynamics known as FDM, FEM and FVM. They

differ from each other due to difference in approximation of flow variables and

discretization method. Finite difference method (FDM) solves the governing

equations at node points of generated grids. This method is simple but it has more

approximation compare to other two methods. Finite element method (FEM) uses

elements of generated grid for describing local variations of unknown flow variables.

The governing equations are precisely satisfied by the exact solution by this method.

Finite volume method (FVM) integrates governing equations of fluid flow all over the

control volume. It converts integral equations into a system of algebraic equations.

These algebraic equations can be solved by iterative methods.

Centrifugal fan design performance can be truly ascertained by experimental

evaluations, but CFD analysis can greatly help in reducing number of experimental

iterations. CFD can also help to understand profile distribution of mass flow, pressure

and velocity at infinitesimal planes of centrifugal fan geometry under study. This

could not be possible merely by experiments and hence CFD analysis and

experimental evaluation are equally important and mutually exclusive.



1.8 Scope of Present Work

Fans are widely used in industrial and commercial applications. Centrifugal

fans have the largest market share as 34% amongst all other type of fans. Centrifugal

fans dominate among total fan and blower market by consuming 90% of sector

energy. Accordingly, the focus of present work is towards evolution of energy

efficient fans used in textile industries. It aims at redesigning fume extraction

centrifugal fan used in SDS-9 texturising machine of medium scale textile industry.

This application demands fume extraction at constant head. Radial vaned

centrifugal fans being ideal choice for such application [9, 20, 21, 22], the work is

focused towards evolution of energy efficient radial tipped centrifugal fan. The

process of energy efficient design requires understanding of influence and

optimization of number of blades, assessment of existing design methodologies,

evaluation of slip factor and losses and there after proposing design process which is

there after validated through experiments and 3-D CFD studies. This in general

demands extensive studies on centrifugal fan.

These aspects defines the scope of work in the direction of compilation and

experimental evaluation of existing design methodologies for radial tipped centrifugal

fan, optimization of finite number of blades through experimental studies at design

and off design conditions, determination of experimental values of slip factor at

different volute locations and along blade width to verify empirical correlations of slip

factor, experimental evaluation of hydraulic, leakage and power losses to ascertain

designed fan performance and finally offer a unified design methodology thoroughly

validated by experiments and numerical approach by 3-D CFD analysis which

ultimately meets or surpasses the CSWD minimum efficiency requirements for

centrifugal fans [4].

Documents

Chapter 0 -Cover page to certificates - JJTshodhganga.inflibnet.ac.in/bitstream/10603/37646/10/10... · · 2015-03-19The minimum efficiency requirements are based on the function