Summer Internship Report (National Engineering Services Pakistan)-2014

SUMMER INTERNSHIP

REPORT - 2014

Mechanical Section

National Engineering Services Pakistan-NESPAK

6/27/2014

Prepared by:

Danial Sohail ME-089

Muhammad Bilal Javaid ME-120

Syed Irfan Ali ME-076

Sagar P. Jesrani ME-122

Zohaib Azhar Mallick ME-178

NED University of Engineering &Technology

Batch 2011-12

ii

Acknowledgements

All praise to ALMIGHTY ALLAH, the creator of the universe and all

thing in this universe. He made us super creature, blessed us to

accomplish this work. We are very thankful to Allah Almighty, Who has

provided us such an opportunity to gain knowledge in National

Engineering Services Pakistan (NESPAK). It was a great experience of

getting trained here. We learnt many things practically which we have

learnt theoretically earlier. We also pay our gratitude to the Almighty for

enabling us to complete this Internship Report within due course of time.

We would like to thank all staff, especially Mr. Saeed Ahmed Soomro,

for helping us and for their kind behavior towards us throughout our

internship. We acknowledge that we were unable to learn this much on

our own.

Thank you!

With warm regards;

Danial Sohail

Muhammad Bilal Javaid

Syed Irfan Ali

Sagar P. Jesrani

Zohaib Azhar Mallick

iii

Table of Contents

Executive Summary ....................................................................................................................................... I

Lifts / Elevators ............................................................................................................................................. 1

Types of Lifts ................................................................................................................................... 2

Advantages and Disadvantages of Different Types of Elevator ....................................................... 3

Components of Elevator System ...................................................................................................... 4

Elements of Lift Design .................................................................................................................... 7

Famous Lift Manufacturers .............................................................................................................. 8

Visit to NICL Elevator System ........................................................................................................... 9

Fuel Storage Tanks ..................................................................................................................................... 10

Orientation of Storage Tanks ......................................................................................................... 11

Basic Components of Storage Tanks .............................................................................................. 13

Fuel Storage Tank Designing .......................................................................................................... 14

Designing of 10000 Liter Fuel Storage Tank................................................................................... 15

Fire Suppression System ............................................................................................................................ 16

Classes of Fire................................................................................................................................. 17

Fire Ingredients .............................................................................................................................. 17

Fire Suppression Techniques ......................................................................................................... 18

Fire Suppression Using Gases ........................................................................................................ 19

HVAC ........................................................................................................................................................... 21

Goal of an HVAC System ................................................................................................................ 22

Components of an HVAC System ................................................................................................... 23

Split Air Conditioner System .......................................................................................................... 24

Packaged Air Conditioner............................................................................................................... 25

Cooling Tower Technology ............................................................................................................. 27

Chillers ........................................................................................................................................... 29

Air Handling Units .......................................................................................................................... 30

Pumps ............................................................................................................................................ 32

Positive Displacement Pumps ........................................................................................... 32

Kinetic Pumps ................................................................................................................... 38

iv

Welding Techniques ................................................................................................................................... 41

Gas Welding ................................................................................................................................... 42

Arc Welding .................................................................................................................................... 42

Shielded Metal Arc Welding .......................................................................................................... 43

Gas Shielded Arc Welding .............................................................................................................. 43

Weld Joints ..................................................................................................................................... 44

v

Preface

Internship is one of the keys for understanding more deeply the concepts

learned from formal education by going through practical practices

adapted by industries. And this rationale brought us to National

Engineering Services Pakistan NESPAK.

During our internship we have learned a lot about building services and

HVAC systems. Every topic from crust to core was explained to us and

this report is an overview of what we learned. Information in this report

is gathered from different sources like instruction manual, project

proposals, online websites and notes provided by instructors.

This document gives reader an insight of design techniques for lifts,

storage tanks, and HVAC systems along with introduction to

international standards. Interactive visuals provide an ease to reader for

understanding cyclic process and don’t let reader to get bored as

traditional technical text does.

We have tried our best to eliminate all mistakes and misrepresentation of

facts but since its natural for humans to make mistakes, so we ask your

pardon in advance for any such mistake.

Thank you!

vi

Executive Summary

Introduction: During our internship at Mechanical Section NESPAK, we have gone through a lot

of stuff related to Building Services and HVAC system. We have studied and

discovered functioning of lifts, designing of fuel storage tanks, fire suppression

systems, welding techniques, HVAC systems and components, pumps and

Window and Split air conditioning systems.

Following is a brief topic wise detail of subjects we have studied during our

internship.

Lifts / Elevators: Starting from basic types of lifts, area of application, advantages, disadvantages of

each type, our study have been extended to techniques of lift selection for

residential buildings, offices and medical facilities. Also visit to N.I.C.L building

Elevator system gave us an insight of working procedure of elevators.

Fuel Storage Tanks: Demand of fuel storage tank is increasing day by day because of installation of

high power output standby generators in residential buildings, therefore during our

study of fuel storage tanks we were taught about tank orientation, tank’s basic

components and their significance. Techniques for designing tank following

international standards were taught by our instructors and a task of designing

10000 liter tank was assigned to us, which was successfully completed.

Fire Suppression System: One of our internship course outline topic was Fire Suppression System. Our

instructors taught about fire ingredients (factors necessary for fire initiation). We

also have studied about 4 common classes of fires, ways to tackle with them. Our

training included Fire suppressions through Clean Gas Technology and Fire

suppression using water.

HVAC: NESPAK has its expertise in designing HVAC systems for residential buildings,

offices, medical facilities. During our posting in HVAC systems we have learned a

lot about HVAC system, from the main reason for employing HVAC to goals

HVAC should be accomplished, we have learned about components found in every

HVAC system along with types of air conditioning systems for better

vii

understanding of working of each component. Not just study of systems but also

the study of their governing refrigeration cycle gave us an insight of purpose of

each component. Special attention was given to study of pumps because it has its

application not only in HVAC but also in Waste Water Treatment, Fuel

transportation, Industrial purposes. Therefore we have studied all pump types and

area of their application.

Welding Techniques: Welding is most used method for making parts in industry, from seamless pipes to

chases of cars, most structures are joined by weld. Welding techniques includes

preparation of work piece before welding, pre heating of work piece and

electrodes. Welding techniques also includes selection of appropriate welding

mechanism according to application and purpose of weld.

Conclusion: Internship at NESPAK is one of most knowledgeable period in our professional

lives. We have learned a lot here, all staff specially engineers helped us throughout

our internship and we hope that this knowledge we are taking from here will help

us throughout our life.

SUMMER INTERNSHIP REPORT - 2014

1 | P a g e

LIFTS / ELEVATORS

Lift – British English

Elevator – American English


2 | P a g e

Nowadays buildings are becoming taller and taller to confine large population into

a small piece of land, but access to floors above ground is inconvenient if done by

staircase because they are both time consuming and tiring, therefore lifts and

escalators are employed for transporting people from one floor to another.

Types of Lifts

Lifts are of two types

Traction Lifts

Hydraulic Lifts

Traction lift:

Works on the principle of pulling whereas hydraulic powered lifts works by

lifting through pushing action. In traction lifts pulling is done by electric motors

which rotate the pulley over which wire controls the motion of lift

corresponding to motion of balancing weights.


3 | P a g e

Hydraulic Powered Lifts:

Hydraulic powered lifts have telescoping plunger/piston being pushed by

pressurized fluid.

Advantages and Disadvantages of Different

Types of Elevators

Hydraulic Lifts:

Each lifting mechanism has its own advantages and drawbacks.

Hydraulic powered lifts are less costly.

They have a larger lifting capacity.

They have limitation of height up to which they can push lift cabin

(maximum 3-4 floors).

They have lesser speeds.


4 | P a g e

Traction Lifts:

They can lift up to greater heights.

They have greater speeds

They are more costly than hydraulic elevators.

Components of Elevator System

Elevator systems have following components:

Elevator Car:

Elevator Car is the vehicle that travels between the different elevators stops

carrying passengers and/or goods, it is usually a heavy steel frame surrounding

a cage of metal and wood panels.

Shaft:

A vertical shaft in a building that gives passage to elevator to travel from floor

to floor

Guides:

Guides provide ways for traveling of cabin and counterweight and avoid

unnecessary vibration, providing a fixed path.


5 | P a g e

Counter weight:

Counterweight balances the elevator car and provides an ease in functioning of

lifts. Initially during no load condition counter weight is equal to weight of

elevator car and then 50% weight of total lifting capacity of lift is added in

counterweights.

Machine Room:

Machine room consists of different components necessary for elevator system.

These include:

PCB’s for controlling actions and reactions of lifts during a lift call.

Motor drive which gives power to lift car.

Governor and brake lever: as ELD (emergency landing device)


6 | P a g e

Governor: It is an independent device which in case of failures acts and applies brakes

on guides to stop lift immediately.

Buffer: Buffer is a device used to absorb kinetic energy. Buffers are places at the

bottom of shaft at certain depth below floor, in case if cables supporting lifts

cuts off and lift fall then elevator car falls onto buffer and it reduces much of

its speed before striking ground.


7 | P a g e

Elements of lift design:

NESPAK has its expertise in lift design, lift designing is not as simple as it

seems by just installing a lift, there are numerous factors which should be

considered before designing lift system, these factors include building type,

either residential or commercial, approximate numbers of occupants, available

space and factors which should be viewed while designing including lift speed,

lift size, secure operation provision, comfort ability of passengers etcetera.

Mr. Zaki of Building services section instructed us about designing lifts by

presenting their ongoing project of designing lift system for crescent bay emmar

tower. He provided us floor plan of crescent bay indicating shaft for lift and

MCR (machine control room) along with his calculations of specification of lift

based on following assumed factors:

Each tower comprises of 30 occupiable floors.

20% of total population of building is using lifts every time.

Specific number of occupants for each flat.

Peak usage hours will be 7 a.m. - 10 a.m. & 4 p.m. - 6 p.m.

Based on above assumptions there were number of choices of lifting system

like

System Car speed Car capacity Remarks

System 1 1.5 m/s 1250 kg Poor

System 2 2.5 m/s 1250 kg Good

System 3 1.5 m/s 1600 kg Good

System 4 2.5 m/s 1600 kg Recommended

These systems can be installed / employed having different specification of

speed, area, lifting capacity and waiting time with corresponding

grades/remarks so management will not face trouble while selecting one.


8 | P a g e

Famous Lifts Manufacturers:

Various companies manufactures lifts these includes brands from Korea,

China, Japan and from Western countries. Prices of lifts from eastern and

western brands vary significantly. While going through catalogues from

different brand we got an insight of sizes of traction elevators. Residential

elevators may be small enough to only accommodate one person while some

are large enough for more than a dozen. Wheelchair, or platform elevators, a

specialized type of elevator designed to move a wheelchair 12 feet (3.7 m) or

less, can often accommodate just one person in a wheelchair at a time with a

load of 750 pounds (340 kg). And freight elevators can lift up to 4500 kg

mass.

Some common lift manufacturer includes:

Doppler Lift manufacturer

Thyssen Krupp Aufzüge

Schindler

Hyundai Elevators


9 | P a g e

Not only speed, lifting capacity is important but elevator car appearance is

important if installed in corporate buildings and shopping malls, so

manufacturer pays special attention to its appearance and sometimes to

bring more fantasy capsule lifts are installed.

Visit to N.I.C.L Elevator System:

After studying all standard practices for installing lifts and all safety

provisions which are given, Mr. Saeed Soomro of BSS have organized a

visit to N.I.C.L building lift system. He took us to Machine room, there were

PCB’s, Governors, Motors, Pulleys and also learned that incase of power

breakup how one can bring lift to nearest stop using brake release panel and

manually through pulley. One noticeable thing was presence of air

conditioning room in machine room and this was clarified as that it is used

to keep cool all electrical and electronic components so they don’t get

damaged.


10 | P a g e

FUEL STORAGE

TANKS


11 | P a g e

Continuous supply of fuel is required in all equipment’s like generators, HVAC

plants, fabric industry machinery, boilers etc. Therefore instead of laying long

underground supply pipelines from large reservoirs which is complicated, costly

and dangerous in case of fuel. Storage tanks are employed for storage of these

fluids capacitive enough to provide nonstop supply according to requirement up to

certain number of days.

Tanks are manufactured having storage capacity from few hundred liters for small

residential building to thousands of gallons for storing fuel for generators and

HVAC chillers in skyscrapers.

Orientation of Storage Tanks:

There are two possible orientations of storage tanks:

Horizontal storage tanks

Vertical storage tanks

These orientations are employed according to applications and space

availability of site where it is going to be placed.

Horizontal Storage Tanks:

Horizontal storage tanks are used when;

Liquid stored is not required to be heated before extraction, because a larger

bottom fluid area takes more time to reach to a certain temperature before

extraction.

When there is enough ground space but have limitation of height.


12 | P a g e

Vertical Storage Tanks:

Vertical storage tanks are employed when;

Liquid stored in storage tank is required to be heated before extraction,

because of lesser cross section are, heat is more concentrated on bottom than

rest of tank therefore resulting in higher bottom temperature and thus hot

liquid is extracted from bottom.

When there is limitation of available are but not any restriction on height.


13 | P a g e

Basic Components of Storage Tanks:

Basic components of fuel storage tank include:

Shell:

It covers majority of storage capacity of tank. It is simply a cylindrical shell

with dished ends to store any kind of liquid.

Dished Ends:

Dished ends closes shell opening so fuel can be confined in it, it is made dished

shape so forces developing on its surface will be distributed on a larger area

thus reducing its effect.

Air Vent:

Air vent is placed at top of tank on higher side of slope to prevent air trap.

Operating Valves:

Operation valves present in fuel storage tanks include:

Inlet/input valve

Outlet/output valve

Drainage valve

Lifting Lug:

It helps lifting tank during installation and other maintenance operations.

Manhole:

It is a provision/space for workers to enter tank for cleaning and maintenance

purposes.

Level Indicator:

It is a glass tube whose one end is linked to tanks bottom and other end to tank

tops, it indicates fuel level in tank.


14 | P a g e

Saddles and Supports:

Tanks are placed on saddles; these saddles are designed and placed according to

tank size. Saddles themselves stands on supporting plates.

Fuel Storage Tank Designing:

To ensure proper and safe functioning of storage tanks they should be designed

and manufactured following international standards. These standards are

available in form of codes and norms published by different engineering

societies. These codes guide designer from setting up basic parameters to the

thickness and number of coats of paintjob. Societies which publish such codes

includes;

ASME (American Society of Mechanical Engineers)

UL (Underwriters Laboratories)

DIN (DeutschesInstitutfürNormung)

EN (European Standards)

BSI (British Standards Institution)


15 | P a g e

Designing of 10000 Liter Fuel Storage Tank:

After spending enough time studying international standards for tank designing

and tank drawing, we were able to design our own tank. So Mr. Saeed Ahmed

Soomro gave us a task for designing a fuel storage tank with 10000 liter storage

capacity following European standards EN-12286-1 and EN-12285-2 entitled

“WORKSHOP FABRICATED STEEL TANKS”. After finding all design

parameter we designed that tank on CAD. Following is the 3D design of tank

on Pro-Engineer wildfire 4.0.


16 | P a g e

FIRE SUPPRESSION

SYSTEM


17 | P a g e

In 2012, National Fire Protection Association-United States responded to

1,375,000 fires, which caused 2,855 civilian fire fatalities, 16,500 civilian fire

injuries and a total estimated loss of $12,427,000,000. (source:

http://www.nfpa.org)

From above given statistics we can understand the necessity of firefighting. These

fires are caused when the temperature rises and crosses flash point of surrounding

material. In order to deal with fire effectively and to avoid any major loss Fire

Suppression Systems are adapted. These automated system fights with fire until

firefighting crew arrives to deal with it. It uses fire extinguishing material like

foams, water and gases depending upon surrounding area and cause of fire.

Classes of Fires:

Fires are divided into four basic classes depending on material which causes

initiation of fire and each fire class has its own coping strategy. Four classes

of fires are:

Class Causes / fuel type

Class A Household and office items: Wood, Paper, Plastics etc.

Class B Fuels: Petrol, Alcohol, Ethanol, Diesel

Class C Electrical Items: Short circuits, Over heated electric panels

Class D Exotic materials: Manganese, Potassium, Sulphur etc.

Fire Ingredients:

Fire Triangle also known as combustion triangle tells us about necessary

ingredients of fires. The triangle illustrates the three elements a fire needs to

ignite: heat, fuel, and oxygen. A fire naturally occurs when the elements are

present and combined in the right mixture. And a fire can be prevented and

extinguished by any of these elements. And this is what a fire extinguisher /

fire suppression system do. Different types of system attacks on different

ingredient like water attacks heat whereas gas based suppression system

attacks on oxidizing agent.


18 | P a g e

Fire Suppression Techniques:

Following are the techniques used for fire suppression nowadays.

Fire suppression using water

Fire suppression using gases

Fire Suppression Using Water:

Fire suppression through water is one of the oldest ways of extinguishing fire;

it eliminates heat from effected area. It is used for Class A fires and is the

cheapest way of extinguishing fire. These extinguishers are heat activated and

are mostly used in homes, hotels, smoking lounges and kitchens. It uses a

glass bulb type sprinkler head which sprays water into the room if sufficient

heat reaches the bulb and causes it to shatter and water continues to sprinkle

until someone closes valve from water source. Bulb is initially filled with

colored alcohol which represents its design temperature and upon reaching

that temperature it shatters.


19 | P a g e

.

Fire Suppression Using Gases:

In case of fires in offices and control rooms having important documents and

costly electronic appliances, water is not used for extinguishing fire because it

damages all appliances and ruins all documents. Therefore for such fires

Halon and inert gases are used and cleanly extinguishes fire;

Halon Based Fire Suppression System:

Systems based on halons are smoke activated, as smoke enters smoke detector

and crosses a predetermined level, it activates and gives an alarm beep for

occupants to leave and after a fixed time period it releases halon gas into

environment which attacks heat and reduces room temperature thus

suppressing fire.

FM-200, Ecaro-25, Novec and Saphirecomes under the category of halon.

FM-200 is commercially most commonly used halon gas for firefighting and

is chemically hepta-fluoro-propane.

A separated pressurized piping system is required for halon based system and

is more costly than water sprinkler system.

Many organizations with such firefighting systems conduct fire drill regularly

to keep their staff prepared for any future happening.


20 | P a g e

Inert Gas Based Fire Suppression System:

Another way of firefighting is to reduce amount of oxygen from surroundings

of fire, so fire extinguished because of lack of one of its ingredient i.e.

oxygen. Inert gases are preferred for this purpose because they don’t react

easily with materials around it and all materials tend to be more reactive at

high temperatures therefore other gases fails. Likewise halon based system

this system is also smoke activated and uses Imergen-55 (carbon-dioxide,

nitrogen, argon) Imergen-101 (nitrogen, argon) and pro-inert gasses. Since

inert gas don’t liquefy at high temperatures therefore cylinders with higher

schedule is required for their storage at high pressure. Inert gas based system

are more costly than water and halon based systems. Special vents are

provided in coverage area so pressure doesn’t buildup when nozzle releases

high pressure gas.


21 | P a g e

HVAC


22 | P a g e

Air quality is an essential consideration in maintaining productivity, comfort and

health of occupants of a building and should not be trivialized. If air quality and

temperature are not maintained occupants comfort in the workplace can suffer,

directly effecting productivity and morale.

Therefore modern commercial building along with other sophisticated systems

includes HVAC system. HVAC stands for

H- Heating

V- Ventilation

AC- Air-conditioning.

GOAL of an HVAC System:

Following are the goals of an HVAC system:

HVAC system keeps occupants comfortable by controlling room

temperature.

HVAC system keeps occupants comfortable by supplying fresh air to zones.

If HVAC introduces significant proportion of fresh exterior air and alleviate

carbon dioxide buildup occupants experience better health and performance

grows. Study shows direct relation between CO2 levels and short term sick

leaves in office work forces.

HVAC systems job includes removal of contaminants and dust from air

using filters because in heavily air-conditioned energy efficient

environments re-circulated conditioned air can carry contaminants which

contribute to occupant’s respiratory illness. Compared to average office

building this feature is critical in facilities like clean rooms, medical

facilities and laboratory with hazardous material.

HVAC system must also be efficient and economical because of increasing

cost of fuel. Energy efficient HVAC system might incorporate;

Variable air volume design

Components operating at low pressure

Digital control systems

Mechanisms for reclaiming heating and cooling benefits from

recirculate air


23 | P a g e

High efficiency ECM (Electrical control module) motors.

Components of an HVAC System: Following are basic components found in every HVAC system.

Furnace: The furnace pushes the cold or hot air outward into the ducts that run through

every room in the building. Throughout the ducts, there are vents that allow the

warm or cool air to pass into rooms and change their interior temperature. The

furnace unit is typically fairly large, requiring its own space within a building.

Heat Exchangers:

When the furnace is activated by the thermostat, the heat exchanger begins to

function as well. Air is sucked into the heat exchanger, either from the outside

or from a separate duct that pulls cool air out of the building’s rooms then heats

it before pushing it back out into the ductwork.

Evaporator Coil: Evaporator coils performs the opposite function of the heat exchanger. It

supplies chilled air which is forced through ducts when required.

Condensing Unit: In this unit, refrigerant liquid exchanges heat with air outside and cools. It is

then transmitted to the evaporator coil where it can be distributed throughout

the home.

Refrigerant Lines:

Refrigerant lines are series of tubes that contains refrigerant and transmits it

from the condensing unit to the evaporator coil and back.

Thermostat: The thermostat controls the function of the furnace. A thermostat is usually

positioned somewhere within the building where it can easily discern

temperature and remain accessible to users. If the air in the room or building is

too cold, the heat exchanger kicks in and blows heat through the vents. If the

room is too warm, the condensing unit and evaporator coil start to function, and

the air conditioning system sends cool air throughout the building or to one

particular section of the building.

http://www.ebay.com/sch/Business-Industrial-/12576/i.html?_from=R40&_nkw=thermostat


24 | P a g e

Ducts:

Heating ducts are put in during the construction of a home or a building. They

are often run through the ceiling. In each room, at least one rectangular opening

is cut into the duct so that a vent or vents can be installed.

Vents Vents are usually rectangular in shape. They are placed in the ceiling, with their

edges corresponding to the opening in the duct above. As warm or cool air

pours through the ducts, vents allow it to disperse into the rooms below.

Split Air Conditioner System:

Split air conditioners are used for small rooms and halls, usually in places

where window air conditioners cannot be installed.

There are two main parts of the split air conditioner;

Outdoor unit: This unit houses important components of the air conditioner like the

compressor, condenser coil and also the expansion coil or capillary tubing. This

unit is installed outside the room or office space which is to be cooled.

Indoor unit: It is the indoor unit that produces the cooling effect inside the room or the

office. This is a beautiful looking tall unit usually white in color, though these

days a number of stylish models of the indoor unit are being launched.

http://www.ebay.com/sch/Business-Industrial-/12576/i.html?_from=R40&_nkw=Heating+ducts


25 | P a g e

Air Conditioning and Refrigeration Cycle:

Following are the basis of air conditioning and refrigeration;

Liquids absorb heat when changed from liquid to gas

Gases give off heat when changed from gas to liquid.

For an air conditioning system to operate with economy, the refrigerant must be

used repeatedly. For this reason, all air conditioners use the same cycle of

compression, condensation, expansion, and evaporation in a closed circuit. The

same refrigerant is used to move the heat from one area, to cool this area, and to

expel this heat in another area.

The refrigerant comes into the compressor as a low-pressure gas, it is compressed and then moves out of the compressor as a high-pressure gas.

The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its heat to the outside air.

The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of the fluid, and lowers its pressure as it leaves the expansion valve.

The low-pressure liquid then moves to the evaporator, where heat from the inside air is absorbed and changes it from a liquid to a gas.

As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is repeated.


26 | P a g e

Packaged Air Conditioner:

Packaged Air Conditioner is one kind of the split air-conditioning, commonly

used in home and small office; usually it is applied to a larger area of the room,

whether as hanging air conditioning or cabinet air conditioning to be

determined according to the actual needs of the user.

The packaged air conditioners are available in the fixed rated capacities of 3, 5,

7, 10 and 15 tons.

As the name implies, in the Packaged Air Conditioners all the important

components of the air conditioners are enclosed in a single casing like Window

Air Conditioner. Thus the compressor, cooling coil, air handling unit and the air

filter are all housed in a single casing and assembled at the factory location.

Depending on the type of the cooling system used in these systems, the

packaged air conditioners are divided into two types;

Packaged Air Conditioner with water cooled condenser

Packaged Air Conditioner with air cooled condensers


27 | P a g e

Packaged Air Conditioners with Water Cooled Condenser:

In Water cooled condenser Packaged air conditions the condenser is cooled by

the water. The condenser is of shell and tube type, with refrigerant flowing

along the tube side and the cooling water flowing along the shell side. The

water has to be supplied continuously in these systems to maintain functioning

of the air conditioning system.

Packaged Air Conditioners with Air Cooled Condensers:

In Air cooled condenser packaged air conditioners the condenser of the

refrigeration system is cooled by the atmospheric air. There is an outdoor unit

that comprises of the important components like the compressor, condenser and

in some cases the expansion valve (refer the figure below). The outdoor unit

can be kept on the terrace or any other open place where the free flow of the

atmospheric air is available. The fan located inside this unit sucks the outside

air and blows it over the condenser coil cooling it in the process.

Cooling Tower Technology: In all of the air conditioning systems we've described so far, air is used to

dissipate heat from the compressor coils. In some large systems, a cooling

tower is used instead. The tower creates a stream of cold water that runs

through a heat exchanger, cooling the hot condenser coils. The tower blows air

through a stream of water causing some of it to evaporate, and the evaporation

cools the water stream. One of the disadvantages of this type of system is that

water has to be added regularly to make up for liquid lost through evaporation.

The actual amount of cooling that an air conditioning system gets from a

cooling tower depends on the relative humidity of the air and the barometric

pressure.

Common application includes;

Cooling the circulating water used in oil refineries

Petro-chemical plants

Thermal power stations

HVAC systems for buildings.

http://en.wikipedia.org/wiki/Oil_refineries

http://en.wikipedia.org/wiki/Thermal_power_station

http://en.wikipedia.org/wiki/HVAC


28 | P a g e

Cooling towers can be classified on the basis of the type of air induction into the tower. The main types of cooling towers are; Induced draft cooling towers Natural draft cooling towers

Induced Draft:

An induced draft cooling tower is provided with a top mounted fan that

induces atmospheric air to flow up through the tower, as warm water falls

downward. An induced draft tower may have only spray nozzles for water

break up or it may be filled with various slat and deck arrangements.

Natural Draft:

The natural draft cooling tower is designed to cool water by means of air

moving through the tower at the low velocities prevalent in open spaces

during the summer. Natural draft towers are constructed of cypress or red

wood and have numerous wooden decks of splash bars installed at regular

intervals from bottom to the top. Warm water from the condenser is flooded

or sprayed over the distributing deck and flows by gravity to the water

collecting basin.

http://en.wikipedia.org/wiki/Forced_convection

http://en.wikipedia.org/wiki/Natural_convection


29 | P a g e

Chillers: A chiller is a machine that removes heat from a liquid via a vapor-compression

or absorption refrigeration cycle. This liquid can then be circulated through a

heat exchanger to cool air or equipment as required. As a necessary byproduct,

refrigeration creates waste heat that must be exhausted to ambient or for greater

efficiency, recovered for heating purposes. Concerns in design and selection of

chillers include performance, efficiency, maintenance, and product life cycle

environmental impact.

Vapor Compression Chillers:

Vapor compression chillers operate on the reverse-Rankine cycle, using

mechanical energy to compress the refrigerant, and may include:

Reciprocating action – uses pistons for compression

Screw – uses two counter rotating screws for compression

Scroll – uses two interlocking spirals or scrolls to perform the compression

Centrifugal – uses rotating impeller blades to compress the air

Following is the working cycle of Centrifugal type chiller.


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Absorption Chillers:

Absorption chillers uses heat to vaporize a working fluid (usually either

ammonia or lithium bromide)

Single Effect Absorption – use a single generator & condenser.

Double Effect Absorption – use two generators/concentrators and

condensers, one at a lower temperature and the other at a higher temperature.

It is more efficient than the single effect, but it must use a higher

temperature heat source.

Following is the working cycle of Absorption chiller;

Air Handling Units:

An air handler, or air handling unit (often abbreviated to AHU), is a device used

to condition and circulate air as part of a heating, ventilating, and air-

conditioning (HVAC) system. An air handler is usually a large metal box

containing a blower, heating or cooling elements filter racks or chambers, sound

attenuators, and dampers. Air handlers usually connect to ductwork

ventilation that distributes the conditioned air through the building and returns it

http://en.wikipedia.org/wiki/HVAC

http://en.wikipedia.org/wiki/Fan_(mechanical)

http://en.wikipedia.org/wiki/Air_filter

http://en.wikipedia.org/wiki/Damper_(architecture)


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to the AHU. Sometimes AHUs discharge (supply) and admit (return) air

directly to and from the space served without ductwork.

Small air handlers, for local use, are called terminal units, and may only include

an air filter, coil, and blower; these simple terminal units are called blower

coils or fan coil units. A larger air handler that conditions 100% outside air, and

don’t re-circulate air, is known as a makeup air unit (MAU). An air handler

designed for outdoor use, typically on roofs, is known as a packaged unit (PU)

or rooftop unit (RTU).

An air handling unit; air flow is from the right to left in this case. Some

AHU components shown are

1 – Supply duct

2 – Fan compartment

3 – Vibration isolator ('flex joint')

4 – Heating and/or cooling coil

5 – Filter compartment

6 – Mixed (re circulated + outside) air duct

http://en.wikipedia.org/wiki/Blower_coil

http://en.wikipedia.org/wiki/Blower_coil

http://en.wikipedia.org/wiki/Fan_coil_unit


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Pumps: The storage of liquids is necessary for their usage. It is also necessary that the

liquids from the storage tanks may easily approach the places where they are to

be used. To make sure that the liquid approach its target easily with the required

flow rate, pumps are used. The basic purpose of pumps is to maintain the flow

by keep on injecting kinetic energy in it, because the liquid loses its flow with

the passage of time because of the friction in the pipes and viscous forces.

Different type of pumps has different usage but there are only 2 basic type of

pumps which are: Positive Displacement Pumps

Kinetic Pumps

Positive Displacement Pumps: The working principle of positive displacement pump is that it traps a fixed

amount of fluid and then forces it to the discharge pipe. The main advantage of

positive displacement pumps is that they can give same discharge as their

ability is no matter what the discharge pressure is and can also suck the air.

These pumps should be provided a bypass line by which if the pressure

increases the liquid may come back without causing any damage because if by

mistake they are operated against a closed valve than the pump will keep on

supplying the liquid at the discharge resulting in increase of pressure causing

the pump are the line or both to damage.


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The positive displacement pumps mainly work either on reciprocating action or

on rotary action therefore the 2 branches of positive displacement pumps are:

Reciprocating positive displacement pumps

Rotary positive displacement pumps

Reciprocating Positive Displacement Pumps:

Reciprocating positive displacement pumps traps a known amount of liquid

either by using a diaphragm or a piston/plunger. Therefore there are two

types of reciprocating pumps i.e.

Piston/Plunger pumps

Diaphragm pumps

Piston/Plunger Pumps:

A piston/plunger pump consists of a piston or plunger reciprocating in a

cylinder.In the cylinder there are 2 or more than 2 ports which may allow

uni directional flow.One port is the inlet and the other is discharge. When

the pump compresses the liquid then only discharge port opens while the

inlet remains closed because of the presence of uni directional valve.

While the piston moves backwards the inlet port experiences a negative

pressure and opens while discharge remains closed. If the pump is double

acting than there will be 4 ports 2 at either ends of the piston.


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Diaphragm Pumps:

The diaphragm pumps or pneumatic diaphragm pumps use a flexible

diaphragm to trap and discharge the liquid rather using piston/plunger. It

also works on reciprocating action but the discharge and suction is with

the help of a diaphragm. The diaphragm may be of rubber, thermoplastic

or Teflon.

Rotary Positive Displacement Pumps: Rotary pumps is another type of positive displacement pumps which also

works on the principle of trapping liquid and supplying but in it there is no

piston/plunger but there is a rotor which while rotating traps and discharges

the liquid. The discharge is not on the centrifugal phenomenon because of

the critical design of rotor and its surrounding.

Single Rotor:

If the rotary pump uses a single rotor than it is single rotor rotary pump.

Vane Pump:

It is positive displacement pump in which there is a vane that is mounted on

a rotor. The rotor and the stator are not concentric so the liquid is pressurized

near the outlet where the area decreases. It consists of following

components;


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Stator

Rotor

Vanes

Spring

Piston Pumps:

In case of rotary piston pumps there are several piston connected with

the rotor instead of diaphragms. The rotor shaft is eccentric with stator

center line as a result of which the piston moves in axial direction and

pushes the liquid out of the pump.

Flexible Member Rotary Pumps:

The pump uses an elastomer rotating member with enlarged vane tips that

form a pumping chamber in conjunction with a casing when the rotor is

placed with the shaft centered in the substantially circular casing that

incorporates an eccentric section. Discharge forcing action is accomplished


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as the vane bends in the eccentric section, effectively squeezing liquid from

the discharge chamber.

Screw Rotary Pump:

Screw rotary pump consists of a screw. In each revolution of the screw it

traps the liquid in its threading and pushes it forward. Its threading is in the

form of worm which pulls, traps and pushes the liquid.

Multiple Rotor Positive Displacement Pumps:

The working principle is similar to single rotor pump, but the difference is that

in these pumps two or more than two pumps mesh together and pushes the

liquid.


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Gear Pumps: Gear pumps are also widely used in chemical installations to pump high

viscosity fluids. They work on the principle that as the gears rotate they

separate on the intake side of the pump, creating a void and suction which is

filled by fluid. The fluid is carried by the gears to the discharge side of the

pump, where the meshing of the gears displaces the fluid.

Lobe Pumps: Lobe pumps are used in a variety of industries including pulp and paper,

chemical, food, beverage, pharmaceutical, and biotechnology. They are

popular in these diverse industries because they offer superb sanitary

qualities, high efficiency, reliability, corrosion resistance and good clean-in-

place and steam-in-place (CIP/SIP) characteristics. There are lobes present

inside the goosing of the pump which while rotating traps the liquid and

discharges the pressurized liquid.

http://en.wikipedia.org/wiki/Fluid


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Circumferential Piston Pumps

In these pumps inside the housing there is a flexible member present. The

piston is in contact with the member during compression stroke delivers the

pressurized liquid while during the other strike it creates suction and pulls

the liquid.

Multiple Rotor Screw Pumps It is similar to screw pump except in it liquid is raped by the use of multiple

rotors. Two rotors trap it together and then discharge the pressurized liquid.

Kinetic Pumps: Kinetic pumps can be divided into two classes, centrifugal and peripheral.

In kinetic pumps a velocity is imparted to the fluid. Most of this velocity head is

then converted to pressure head. The disadvantage of these pumps is that, if

head increases at the outlet than it can’t give the desired flow.

Kinetic pumps are classified into two main branches namely:

Centrifugal pumps.

Peripheral pumps.

Centrifugal Pumps: Centrifugal pumps are those pumps which work on the centrifugal action of

the rotor. As the rotor rotates the impeller applies centrifugal forces on the

liquid in contact with it. The housing is made in such a way that inner area is

not constant throughout.as the area decreases pressure increases near the


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discharge this area increases and the pressure head of the liquid converts into

the velocity head.

Radial Flow: These pumps totally on the centrifugal action and discharges the liquid in the

radial.

Mixed Flow: These pumps are normally used in multistage where one impeller discharges

the pressurized liquid to the other and so on.The final discharge is obtained in

the radial direction. As the flow is both in the radial and axial direction

therefore it is known as mixed flow.


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Axial Flow Pump: An axial-flow pump, or AFP, is a common type of pump that essentially

consists of a propeller (an axial impeller) in a pipe. The propeller can be driven

directly by a sealed motor in the pipe or by electric motor or petrol/diesel

engines mounted to the pipe from the outside or by a right-angle drive shaft

that pierces the pipe.

Single Suction/Double Suction Pumps: The peripheral pumps are only present in single suction i.e.They can only

suck from one point whereas centrifugal pumps are present in single suction

as well as in double suction.

Single Stage/Multi Stage Pumps: Centrifugal and peripheral pumps both are present in single stage and multi

stage. Multi stage pumps are used where we have to pull liquid from the

great depth while single stage pumps are used to just energize the liquid.

Peripheral Pumps:

The Peripheral pump is a niche product between the Displacement and the

Centrifugal pump, in which the medium is pumped in a Peripheral channel.

Following are the types of peripheral pumps;


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WELDING

TECHNIQUES


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Welding is a fabrication or sculptural process that joins materials,

usually metals or thermoplastics, by causing coalescence. This is often done

by melting the work pieces and adding a filler material to form a pool of molten

material (the weld pool) that cools to become a strong joint,

with pressure sometimes used in conjunction with heat, or by itself, to produce the

weld. This is in contrast with soldering and brazing, which involve melting a

lower-melting-point material between the work pieces to form a bond between

them, without melting the work pieces.

The most common types of welding are oxyfuel gas welding (OFW), arc welding

(AW), and resistance welding (RW). As a Steelworker, your primary concern

is gas and arc welding. The primary difference between these two processes is the

method used to generate the heat.

.

Gas Welding One of the most popular welding methods uses a gas flame as a source of heat. In

the oxy-fuel gas welding process, heat is produced by burning a combustible gas,

such as MAPP (methylacetylene-propadiene)or acetylene, mixed with oxygen.

Arc Welding Arc welding is a process that uses an electric arc to join the metals being welded. A

distinct advantage of arc welding over gas welding is the concentration of heat.

In gas welding the flame spreads over a large area, sometimes causing heat

distortion. The concentration of heat, characteristic of arc welding, is an advantage

because less heat spread reduces buckling and warping.

Shielded Metal Arc Welding Shielded metal arc welding is performed by striking an arc between a coated-metal

electrode and the base metal.

http://en.wikipedia.org/wiki/Fabrication_(metal)

http://en.wikipedia.org/wiki/Welded_sculpture

http://en.wikipedia.org/wiki/Process_(science)

http://en.wikipedia.org/wiki/Metal

http://en.wikipedia.org/wiki/Thermoplastic

http://en.wiktionary.org/wiki/coalesce

http://en.wikipedia.org/wiki/Melting

http://en.wikipedia.org/wiki/Weld_pool

http://en.wikipedia.org/wiki/Pressure

http://en.wikipedia.org/wiki/Heat

http://en.wikipedia.org/wiki/Soldering

http://en.wikipedia.org/wiki/Brazing


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Gas Shielded Arc Welding The primary difference between shielded metal arc welding and gas shielded arc

welding is the type of shielding used. In gas shielded arc welding, both the arc

and the molten puddle are covered by a shield of inert gas. The shield of inert gas

prevents atmospheric contamination, thereby producing a better weld.

Weld Joints The weld joint is where two or more metal parts are joined by welding. The five

basic types of weld joints are;

Butt joint- used to join two members aligned in the same plane.

Corner joint- used to join two members located at right angles to each other.

Tee joint- used to join two members located at right angles to each other.

Lap joint- made by lapping one piece of metal over another.

Edge joint- used to join the edges of two or more members lying in the same

plane.

Corner and tee joints are used to join two members located at right angles to

each other.


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Date post:	16-Jan-2017
Category:	Engineering
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