PROJECT REPORT ONICE CUBE MAKING MACHINESubmitted in partial
fulfillment for the award of the Degree of BACHELOR OF ENGINEERING
INMECHANICAL ENGINEERINGBYSAGAR REVALESURESH CHOUDHARYRISHITOSH
BHANDARYROSHVEL BARRETTO NIPUN BHATIA
UNDER THE GUIDANCE OF Prof Mrs K.H DHANAVDE
LOKMANYA TILAK COLLEGE OF ENGINEERINGKOPARKHAIRANE NAVI MUMBAI
400 709UNIVERSITY OF MUMBAI 2014-15ICE CUBE MAKING
MACHINEDissertationSubmitted by SAGAR REVALESURESH CHOUDHARYROSHVEL
BARRETTONIPUN BHATIARISHITOSH BHANDARYIn partial fulfillment for
the award of the Degree of BACHELOR OF ENGINEERING IN MECHANICAL
ENGINEERINGUnder the guidance of Prof Mrs K.H DHANAVDELOKMANYA
TILAK COLLEGE OF ENGINEERING,NAVI MUMBAI
DEPARTMENT OF MECHANICAL ENGINEERING LOKMANYA TILAK COLLEGE OF
ENGINEERINGKOPARKHAIRANE, NAVI MUMBAIMAHARASHTRA, INDIA 400709
2014-15
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This is to certify that the project report on, ...........
submitted by ........, Bachelor of Engineering student of Lokmanya
Tilak College Of Engineering, Navi Mumbai, towards partial
fulfillment of the requirements for the award of the Degree of
Bachelor of Engineering in Mechanical Engineering as prescribed by
the University Of Mumbai, is a bona fide record of the work carried
out by him under my supervision and guidance. The matter contained
in this dissertation has not been submitted to any other University
for award of any Degree or Diploma.
Date of Submission: _________________
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APPROVAL OF PROJECT REPORTThis is to certify that the thesis
entitled project title, submitted by student name in partial
fulfillment of the requirements for the award of the Degree of
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ICE CUBE MAKING MACHINE
INTRODUCTIONS:Ice cube makers use more water than just the water
contained in the ice. This equipment can often be very inefficient
in water use. The typical icemaker uses 2 or 3 times more water
than needed to make the ice we consume. These water using machines
can be found everywhere; hospitals account for 39.4 percent of all
commercial ice-maker purchases, followed by hotels (22.3 percent),
restaurants (13.8 percent), retail outlets (8.5 percent), schools
(8.5 percent), offices (4.3 percent) and grocery stores (3.2
percent).There are two basic equipment designs: air-cooled
refrigeration units and water cooled refrigeration units. The
air-cooled units are usually more water efficient; while the water
cooled units are usually more energy efficient. Both types vary
greatly in water efficiency, even within its own design type. The
water efficiency is measured by the industry in gallons of water
per 100 lbs (45.36 kg) of ice. Perfect water efficiency would
equate to 11.97 gallons (45.3 L) of water to produce 100 lbs
(45.36kg)of ice. Most ice makers water use ranges between 18 to 200
gallons (68 L to 756.9 L) of water per 100 lbs (45.36 kg) of ice.
This represents a water efficiency range of 66% to only 5%. Thus,
34% to 95% of the water used is dumped down the drain. The water
varies for several reasons.As the ice is formed in the freezing
trays, minerals in the water collect in the equipment. These
minerals must be occasionally rinsed off the freezing trays and the
water reservoirs. Ice makers have a variable setting to initiate a
rinse cycle at desired frequencies. The frequency of rinse is to be
determined by local water quality and site requirements. Some new
model actuate the rinse cycles based on sensor readings of
minerals. Often the ice maker is set to rinse more often than
necessary, resulting in water waste.The quality of the ice can also
affect water use. Some ice makers are designed to produce clearer
and smoother ice by using a repeated freezing and partial thawing
cycle while the ice is produced. This results in ice cubes that are
smoother, without air bubbles and more crystalline like.
Unfortunately, this aesthetic quality wastes a lot of water and
serves no useful purpose; frosty ice cools just as well as clear
ice.Water cooled ice makers are often the most inefficient in water
use, although sometimes providing significant energy savings at the
point of use. Itis important to note that there are many air-cooled
ice machinesmoreenergy efficient than some water-cooled ice
machines.Water cooled machines generally use potable water to
remove heat from the refrigeration equipment. In years past, most
of these machines used single-pass cooling dumping the water into
the sewer as it exited the machine.Fortunately, many manufacturers
are started to abandon thiswasteful design. Some newer designs
re-circulate the water after it passes through a cooling tower or
heat exchanger, but these still require large amounts of make up
water. While air-cooled machines generally have a water efficiency
of 40% to 66%, water cooled machines are usually less than 15%
water efficient.
Problem Statement:Nickel- or tin-plated copper is most commonly
used for the ice forming pockets in cube ice machines today. Such
pockets may be formed by fitting notched strips of copper together
in an "egg crate" relationship to form a grid of four sided
pockets. The strips are then soldered to a backing pan. At the same
time a serpentine piece of copper tubing (forming the evaporator
section of the refrigeration system) can be soldered to the back of
the pan. The entire evaporator/ice forming assembly is then nickel
or tin plated. The plating is required by National Sanitation
Foundation (NSF) codes, which prohibit the use of copper parts in
contact with food products.While plated copper assemblies work well
in cube ice machines, they have several drawbacks. One of the
primary problems is that the plating operation itself is costly,
and typically produces sludge that is costly to dispose of in an
environmentally safe manner. Also, copper is relatively expensive.
Further, though it has very good heat conduction properties, copper
is dense, so that it has a high heat capacity per unit volume. The
duration of the production/harvest cycle is thus longer than
desired because, at each change in the cycle, the copper ice
forming pockets have to be either heated or cooled.Another
disadvantage of assemblies made from bonded parts, including plated
copper assemblies, is that structures made from bonding different
parts together usually suffer a heat transfer impediment. Usually,
two elements may not be perfectly joined because the elements are
not perfectly flat or otherwise matched in profile, and the
presence of dust particles or oxides may cause surface
irregularities decreasing thermal conduction at those locations.
Further, because air has poor conducting properties, the presence
of air pockets in two bonded elements may also reduce thermal
conduction.In attempting to overcome these disadvantages, a cast
aluminum grid was experimented with. Cast aluminum was found to
present several drawbacks. Primarily, even though the ice cube
pockets could easily be formed in the casting, the evaporator
system tubing had to be attached after the casting operation. This
proved to be unworkable because the cast aluminum was so porous
that the tubing could not suitably be brazed to the casting
VAPOUR COMPRESSION REFRIGERATION CYCLE: Most of the modern
refrigerators work on this cycle. In its simplest form there are
four fundamental operations require to complete one cycle.
Compression Condensation Expansion Vaporization
Compression: The low pressure vapors in dry state are drawn from
the evaporator during the suction stroke of the compressor. During
Compression stroke the pressure and temperature increase until
vapour temperature is greater than the temperature of condenser
cooling medium.
Condensation : When the high pressure refrigerant vapour enters
the condenser heat flows from condenser to cooling medium thus
allowing the vapourized refrigerant to return to liquid state.
Expansion : After condenser the liquid refrigerant is stored in
the liquid receiver until needed. From the receiver it passes
through an expansion valve where the pressure is reduced
sufficiently to allow the vapourization of liquid a low temperature
of about -10C.
Vaporization : The low pressure refrigerant vapour after
expansion in the expansion valve enters the evaporator or
refrigerated space where a considerable amount of heat is absorbed
by it and refrigeration is furnished.
Vapour-compression cycle for Refrigeration system
Vapour-compression cycle with T-S Diagram & P-V Diagram
Components of Compression cycle requires four components :The
vapour compression cycle requires four components : Compressor : To
raise the pressure of low-pressure low temperature gas to
high-pressure high temperature gas. The Condenser : To change the
state of high-pressure, high temperature gas to high-pressure, high
temperature LIQUID. This is achieved by passing ambient air (known
as air-cooled) or water (known as water-cooled) over the condenser
tubes. The Expansion Device : The purpose of the device is to
change the state of the refrigerant from high-pressure, high
temperature liquid to low pressure low temperature saturated
liquid. This is achieved by passing the liquid through an orifice.
The Evaporator : To absorb the heat from room air or water, which
in the case of a chiller is circulated around the evaporator coil.
This will change the state of low-pressure, low temperature
saturated liquid to low pressure, low/medium temperature gas .
COMPRESSORSIntoduction : A refrigerator compressor is the center
of the refrigerator cycle . Compressor may be called as a heart of
any vapour compression system . It works as a pump to control the
circulation of the refrigerant, and it adds pressure to the
refrigerant, heating it up . The compressor also draws vapour away
from the evaporator to maintain a lower pressure and lower
temperature before sending it to the condenser.
CLASSIFICATION OF COMPRESSORS :According to the method of
compression : Reciprocating compressors Rotary compressors
Centrifugal compressors
HERMATICALLY SEALED :A small hermatically sealed compressor in a
common consumer refrigerator or freezer; it typically has a rounded
steel outer shell that is permanentaly welded shut, and which seals
operating gases inside the system. There is no route for gases to
leak, such as around motor shaft seals. On this model, the plastic
top section is part of an auto-defrost system which uses motor heat
to evaporate the water. Compressers are often described as being
either open , hermatic, or semi-hermatic, to describe how the
compressor and motor drive is situated in relation to the gas or
vapour being compressed. The industry name for hermatic is
hermatically sealed compressor, while a semi- is commonly called a
semi-hermatic compressor. In hermatic and most semi-hermatic
compressors, the compressor and motor driving the compressor are
integrated, and operate within the pressurized gas envelope of the
system. The motor is designed to operate and be cooled by the gas
or vapour being compressed. The difference between the hermatic and
semi-hermatic, is that the hermatic uses a one-piece welded steel
casing that cannot be opened for repair; if the hermatic fails it
is simply replaced with an entire new unit . A semi-hermatic uses a
large cast metal shell with gasketed covers that can be opened to
replace motor and pump components. The primary advantage of a
hermatic and semi-hermatic is that there is no route for the gas to
leak out of the system. Open compresser rely on either natural
leather or synthetic rubber seals to retain the internal pressure,
and these seals require a lubricant such as oil to retain their
sealing properties. An open pressurized system such as an
automobile air conditioner can leak its operating gases, if it is
not operated frequently enough. Open systems rely on lubricant in
the system to splash on pump components and seals. If it is not
operated frequently enough, the lubricant on the seals slowly
evaporates, and the seals begin to leak until the system is no
longer functional and must be recharged. By comparison, a hermatic
system can sit unused for years, and can usually be started up
again at any time without requiring maintenance or experiencing any
loss of system pressure.The disadvantage of hermatic compressors is
that the motor drive cannot be repair or maintained, and the entire
compressor must be removed if a motor fails. A further disadvantage
is that burnt out windings can contaminate whole systems requiring
the system to be entirely pumped down and the gas replaced.
Typically hermatic compressors are used in low-cost
factory-assembled consumer goods where the cost of repair is high
compared to the value of the device , and it would be more
economical to just purchase a new device.An advantage of open
compressors is that they can be driven by non-electric power
sources, such as an internal combustion engine or turbine. However,
open compressors that drive refrigeration systems are generally not
totally maintenance free throughout the life of the system, since
some gas leakage will occur over time.
Compressor Lubrication In order to lubricate the moving parts of
the compressor, an oil is added to the refrigerant during
installation or commissioning. The type of oil may be mineral or
synthetic to suit the compressor type, and also chosen so as not to
react with the refrigerant type and other components in the system.
In small refrigeration systems the oil is allowed to circulate
throughout the whole circuit, but care must be taken to design the
pipework and components such that oil can drain back under gravity
to the compressor. In larger more distributed systems, especially
in retail refrigeration, the oil is normally captured at an oil
separator immediately after the compressor, and is in turn
redelivered, by an oil level management system, back to the
compressor(s). Oil separators are not 100% efficient so system
pipework must still be designed so that oil can drain back by
gravity to oil separator or compressor.Some newer compressor
technologies use magnetic bearings and require no lubrication, for
example the Danfoss Turbocor range of centrifugal compressors.
Avoiding the need for oil lubrication and the design requirements
and ancillaries associated with it, simplifies the design of the
refrigerant system and reduces maintenance requirements.
APPLICATION: Refrigerators Deep freezer Water cooler Bottle
coolers Room air conditioners
CONDENSOR
Introductions :Condensors and evaporators are basically heat
exchangers in which the refrigerant undergoes a phase change. Next
to compressors, proper design and selection of condensers and
evaporators is very important for satisfactory performance of any
refrigeration system. Since both condensers and evaporators are
essentially heat exchangers, they have many things in common as far
as the design of these components is concerned. In condensers the
refrigerant vapour condenses by rejecting heat to an external
fluid, which acts as a heat sink. Normally, the external fluid does
not undergo any phase change, except in some special cases such as
in cascade condensers, where the external fluid (another
refrigerant) evaporates. In evaporators, the liquid refrigerant
evaporates by extracting heat from an external fluid (low
temperature heat source). The external fluid may not undergo phase
change, for example if the system is used forsensibly cooling
water, air or some other fluid. There are many refrigeration and
air conditioning applications, where the external fluid also
undergoes phase change. For example, in typical summer air
conditioning system, the moist air is dehimidised by condensing
water vapour and then, removing the condensed liquid water. In many
low temperature refrigeration applications freezing or frosting of
evaporators takes place. These aspects have to be considered while
designing condensers and evaporators.
Classification of condensers:Condensers may be classified on the
following basis: On the basis of cooling medium used:(a) Air cooled
condenser(b) Water cooled condenser(c) Evaporative condenser
On the basis of construction:(a) Shell type condenser(b) Shell
and coil condenser(c) Double pipe condenser(d) Finned condenser
Purpose of a Condenser:The purpose of a condenser in the cycle
of compression refrigeration is to change the hot gas being
discharged from the compressor to a liquid prepared for use in the
evaporator. The condenser accomplishes this action by the removal
of sufficient heat from the hot gas, to ensure its condensation at
the pressure available in the condenser. The heat is shifted to
another medium, like water or air, to cool the condenser.
AIR COOLED FIN TYPE CONDENSER
Air-cooled finned condenser is widely used in refrigeration and
air conditioning application. For same amount of heat transfer, the
operation of air cooled condenser is more economic as compared with
water cooled condenser typically air cooled condenser are of the
round tube and fin type. To improve the performance of air cooled
condensers multiple techniques can be achieved such as enhancement
on inner pipe surface, changing the tube geometry from round to
flat shape and external fins. A micro-channel flat tubes that heat
exchanger is one of the potential alternatives for replacing the
conventional finned tube heat exchanger. This kind of heat
exchanger is made of a flat tube with several independent passages
in the cross section and formed into a serpentine or a parallel
flow arrangement. In these heat exchangers, a multitude of
corogated fins with louvers are inserted into the gaps between the
flat tubes. The flat tube design offers higher thermal performance
and lower pressure drop then the finned round heat exchangers.
EXPANSION DEVICES Introduction: An expansion device is another
basic component of a refrigeration system. The basic functions of
an expansion device used in refrigeration system are to:1. Reduce
pressure from condenser pressure to evaporator pressure, and2.
Regulate the refrigerant flow from the high-pressure liquid line
into the evaporator at a rate equal to the evaporation rate In the
evaporator.
The expansion devices used in rerfrigeration system can be
divided into fixed opening type or variable opening type. As the
name implies, in fixed opening type in the flow area changes with
changing mass flow rates. There are basically seven types of
refrigerant expansion devices. These are:1. Hand (manual) expansion
valves 2. Capillary Tubes 3. Orifice 4. Constant pressure or
Automatic Expansion Valve (AEV)5. Thermostatic Expansion Valve 6.
Float type Expansion Valvea) High Side Float Valveb) Low Side Float
Valve7. Electronic Expansion Valve
Capillary Tube:A capillry tube is long narrow tube of constant
diameter. The word capillry is a misnomer since surface tension is
not important in refrigeration application of capillary tubes.
Typical tube diameters of refrigerab=nt capillary tubes range from
0.5mm to 3 mm and the length ranges from 1.0m to 6m. The pressure
reduction in capillary tube occurs due to the following two
factors:1. The refrigerant has to overcome the frictinal resistance
offered by the walls. This leads to some pressure drop, and2. The
liquid refrigerant flashes (evaporates) into mixture of liquid and
vapours its pressure reduces. The density of vapour is less than
that of the liquid. Hence, the average density of refrigerant
decreases as it flows in the tube. The mass flow rate and the tube
diameter (hence area) being constant, the velocity of refrigerant
increases since. The increse in velocity or acceleration of the
refrigerant also requires pressure drop. Several combinations of
length and bore are available for the same mass flow rate and
pressure drop. However, once a capillary tube of some diameter and
length has been installed in a refrigeratin system, the mass flow
rate through it will vary in such a manner that the total pressure
drop through it matches with the pressure difference between
condenser and the evaporator. Its mass flow rate is totally
dependent upon the pressure difference across it; it cannot adjust
itself to variation of load effectively.
Selection of Capillary Tube: For any new system, the diameter
and the lenghth of capillary tube have to be selected by the
designer such that the compressor and the capillary tube achieve
the balanced point at the desired evaporator temperature. There are
analytical and graphical methods to select the capillary tube. The
fine-tuning of the length is finally done by cut-andtry method.
Atube longer than the design (calculated) vaue is installed with
the expected result that evaporating temperature will be lower than
expected. The tube is shortened until the desired balance point is
achieved. This is done for mass production. If a single system is
to be designed then tube of slightly shorter length than the design
length is chosen. The tube will usually result in higher
temperature than the design value. The tube is pinched at a few
apots to obtain the required pressure and temperature.
Advantages and disadvantages of capillary tube: Some of the
advantages of a capillary tube are:1. It is Inexpensive.2. It does
not have any moving parts hence it does not require maintenance.3.
Capillary tube provides an open connection between condenser and
the evaporator hence during off-cycle, pressure equalization occurs
between condenser ans evaporator. This reduces the starting torque
requirement of the motor starts with same pressure on the two sides
of the compressor. Hence, a motor with low starting torque
(squirrel cage Induction motor) can be used.4. Ideal for hermatic
compressor based systems, which are critically charged and factory
assembled.Some of the disadvantages of the capillary tube are:1. It
cannot adjust itself to changing flow conditions in response to
daily and seasonal variation in ambient temperature and load. Hence
, COP is usually low under off design conditions.2. It is
susceptible to clogging because of narrow bore of the tube, hence,
utmost care is required at the time of asembly. A filter-drier
should be used ahead of the capillary to prevent entry of moisture
or any solid particles.3. During off-cycle liquid refrigerant flows
to evaporator because of pressure difference between condenser and
evaporator. The evaporator may get flooded and refrigerant may flow
to compressor and damage it when starts.Therefore critical charge
is used in capillary tube based compressor systems. Further, it is
used only with hermatically sealed compressors where refrigerant
does not leak so that critical charge can be used. Normally an
accumulator is provided after the evaporator to prevant slugging of
compressor.
EVAPORATORSIntroductions:An evaporators, like condenser is also
a heat exchanger. In an evaporator, the refrigerant boils or
evaporates and in doing so absorb heat from the substance being
refrigerated. The name evaporator refers to the evaporation process
occuring in the heat exchanger.Copper Condenser CoilsThe most
common use of copper alloy tube bundles are for condensers and
auxiliary heat exchangers. If you need to turn steam into water
minimal back flow and high efficiency, then copper tubing is one of
your best bets.Reaching your particular fluids dew point is not
hard with copper and a moderate amount of air moving over the coil.
Coppers high thermal transfer rate makes it ideal for condensing
operations.Copper Evaporator CoilsWhen intense heat is required for
your application or pressurized fittings are needed. CTCG has you
covered! Our end tube manipulation services allows you to customize
your any way you want. Cannot find the end fixture you need? We can
buil it in house for you.When pressurized gas is depressurized at
the expansion valve, it becomes far cooler than it was before. In
other words, as pressurized gas is able to expand in an evaporator
coil, its temperature decreases and it becomes a colling agent.
Usually, this process is used either to cool the air outside the
coil or to turn a pressurized or liquid medium into gas.
Refrigeration technician choose copper because of its thermal
conductivity, which is eight times greater than aluminium tube. The
lightweight and durable properties of copper make it easy to work
with during and after installation. Coppers long life span and
resistance to corrosion make it a maintenance free choice that will
likely last the lifetime of the building.Removing heat is a process
greately helped by coppers highly heat sensitive nature. Using
tubing with fluid is a very efficient way to transfer haet, and can
be utilized in diverse ways to accommodate your projects
needs.Unlike other industries, copper tubes used for air
conditioning and refrigeration purposes are designated by their
outside diameter. Other industries use the inside diameter of the
tube.
REFRIGERANTSA refrigerants is a substance used in heat cycle
usually including, for enhanced efficiency, a reversible phase
change from a liquid to a gas.Traditionally, fluorocarbons,
especially chlorofluorocarbons, were used as refrigerants, but they
are being phased out because of their ozone depletion effects.
Other common refrigerants used in various applications are ammonia,
sulphur dioxide, and non- halogenated hydrocarbons such as
methane.
Introductions: The thermodynamic efficiency of a refrigeration
system depends mainly on its operating temperatures. However,
important practical issues such as the system design, size, initial
and operating costs, safety, reliability, and servicebility etc.
depend very much on the type of refrigerant selected for a given
application. Due to several envirnment issues such as ozone layer
depletion and global warming and their relation to the various
refrigerants used, the selection of suitable refrigerant by a
completely new refrigerant, for whatever reason, is an expensive
proposition as it may call for several changes in the design and
manufacturing of refrigeration system. Hence it is very important
to understand the issues related to the selection and use of
refrigerants. In principle, any fluid can be used as a refrigerant.
Air used in an air cycle refrigeration system can also be
considered as a refrigerant. However, in this lecture the attention
is mainly focused on those fluids that can be used as refrigerants
in vapour compression refrigeration systems only.
Physical properties:The ideal refrigerant has a favorable
thermodynamic properties, is unrective chemically, and is safe. The
desired thermodynamic properties are boiling point somewhat below
the target temperature, a high heat of vaporization, a moderate
density in liquid form, a relatively high density in gaseous form,
and a high critical temperature. Since boiling point and gas
density are affected by pressure, refrigerants may be made more
suitable for a particular application by choice of operating
pressure. These properties are ideally met by the
chlorofluorocarbons, but environmental science regards stability as
being an undesirable property of a refrigerant, leading to
recommendations such as Supercritical carbon dioxide as a possible
future cooling agent for use in vehicles.Corrosion properties are a
matter of materials compatibility with the mechanical components:
compressor, piping, evaporator, and condenser. Safety
considerations include toxicity and flammability.
Primary and Secondary refrigerants:Fluids suitable for
refrigeration purposes can be classified into primary and secondary
refrigerants. Primary refrigerants are those fluids, which are used
directly as working fluids, for example in vapour compression and
vapour absorption refrigeration systems. When used in compresson or
absorption systems, these fluids provide refrigeration by
undergoing a phase change process in the evaporator. As the name
implies, secondary refrigerants are those liquids, which are used
for transporting thermal energy from one location to other.
Secondary refrigerants are also known under the name brines or
antifreezes. Of course, if the oprating temperatures are above 0oc,
then pure water can also be used as secondary refrigerant, for
example in large air conditioning systems. Antifreezes or brines
are used when refrigerantion is required at sub-zero temperatuers.
Unlike primary refrigerants, the secondary refrigerants do not
undergo phase change as they transport energy from one location to
other.
Refrigerant selection criteria:Selection of refrigerant for a
particular application is based on the following requirements:i.
Thermodynamic and thermo-physical propertiesii. Enviromental and
safety properties, and iii. Economics
Refrigerant R-134a:
Refrigerant R134a is a hydrofluorocarbon (HFC) that has zero
potential to cause the depletion of the ozone layer and very little
greenhouse effect. Let us see the various properties of this
refrigerant and how it replaces R12.Refrigerant R134aThe
refrigerant R134a is the chemical compound tetrafluoroethane
comprising of two atoms of carbon, two atoms of hydrogen and four
atoms of fluorine. Its chemical formula is CF3CH2F. The molecular
weight of refrigerant R134a is 133.4 and its boiling point is -15.1
degree F.Refrigerant R134a is a hydrofluorocarbon (HFC) that has
zero potential to cause the depletion of the ozone layer and very
little greenhouse effect. R134a is the nonflammable and
non-explosive, has toxicity within limits and good chemical
stability. It has somewhat high affinity for the moisture. The
overall physical and thermodynamic properties of refrigerant R134a
closely resemble with that of refrigerant R12. Due to all the above
factors, R134a is considered to be an excellent replacement for R12
refrigeran
INSULATIONInsulation is the reduction of heat transfer between
objects in thermal contact or in range of radiative influence. Heat
transfer is the transfer of thermal energy between objects of
differing temperature. The means to stem heat flow may be
especially engineered methods or processes, as well as suitable
static objects and materials.
Purpose of Insulation:A thermal insulator is a poor conductor of
heat and has a low conductivity. Insulation is used in buildings
and in manufacturing processes to prevent heat loss or heat gain.
Although its primary purpose is an economic one, it also provides
more accurate control of process temperatures and protection of
personnel. It prevents condensation on cold surfaces and the
resulting corrosion. Such materials are porous, containing large
number of dormant air cells. Thermal insulation delivers the
following benefits: Reduces over-all energy consumption. Offers
better process control by maintaining process temperature. Prevents
corrosion by keeping the exposed surface of a refrigerated system
above dew point. Provides fire protection to equipment. Absorbs
vibration.
Insulation material:Insulation materials can also be classified
into organic and inorganic types.Inorganic insulation is based on
Siliceous/Aluminous/Calcium materials in fiberous, granular or
powder forms. Example: Mineral wool, Calcium silicate etc.Organic
insulations are based on the hyocarbon polymers, which can be
expanded to obtain hogh void structures. Example Thermocol
(Expanded Polystyrene) and Poly Urethane Foam (PUF).Puf stands for
poly Urethene Foam. Polyurethane (PUF) is used extensively in
applications of lower temperatures.
BRAZINGBrazing is metal-joining process whereby a filler metal
is heated above melting point and distributed between two or more
close-fitting parts by capillary action. The filler metal is
brought slightly above its melting (liquids) temperature while
protected bya suitable atmosphere, usually a flux. It then flows
over the base metal (known as wetting) and is then cooled to join
the work pieces together. It is similar to soldering, except the
temperatures used to melt the filler metal are higher.
Fundamentals:In order to obtain high-quality brazed joints,
parts must be closely fitted, and the base metals must be
exceptionally clean and free of oxides. In most cases, joint
clearances of 0.03 to 0.08mm (0.0012 to 0.0031in) are recommended
for the bestcapillary actionand joint strength.However, in some
brazing operations it is not uncommon to have joint clearances
around 0.6mm (0.024in). Cleanliness of the brazing surfaces is also
important, as any contamination can cause poor wetting (flow). The
two main methods for cleaning parts, prior to brazing, are chemical
cleaning and abrasive or mechanical cleaning. In the case of
mechanical cleaning, it is important to maintain the proper surface
roughness as wetting on a rough surface occurs much more readily
than on a smooth surface of the same geometry.Another consideration
that cannot be overlooked is the effect of temperature and time on
the quality of brazed joints. As the temperature of the braze alloy
is increased, the alloying and wetting action of the filler metal
increases as well. In general, the brazing temperature selected
must be above the melting point of the filler metal. However, there
are several factors that influence the joint designer's temperature
selection. The best temperature is usually selected so as to: (1)
be the lowest possible braze temperature, (2) minimize any heat
effects on the assembly, (3) keep filler metal/base metal
interactions to a minimum, and (4) maximize the life of any
fixtures or jigs used.In some cases, a higher temperature may be
selected to allow for other factors in the design (e.g. to allow
use of a different filler metal, or to control metallurgical
effects, or to sufficiently remove surface contamination). The
effect of time on the brazed joint primarily affects the extent to
which the aforementioned effects are present; however, in general
most production processes are selected to minimize brazing time and
the associated costs. This is not always the case, however, since
in some non-production settings, time and cost are secondary to
other joint attributes (e.g. strength, appearance).
Torch brazingTorchbrazing is by far the most common method of
mechanized brazing in use. It is best used in small production
volumes or in specialized operations, and in some countries, it
accounts for a majority of the brazing taking place. There are
three main categories of torch brazing in use:manual, machine, and
automatic torch brazing.Manual torch brazingis a procedure where
the heat is applied using a gas flame placed on or near the joint
being brazed. The torch can either be hand held or held in a fixed
position depending on whether the operation is completely manual or
has some level of automation. Manual brazing is most commonly used
on small production volumes or in applications where the part size
or configuration makes other brazing methods impossible.The main
drawback is the high labor cost associated with the method as well
as the operator skill required to obtain quality brazed joints. The
use of flux or self-fluxing material is required to prevent
oxidation. Torch brazing of copper can be done without the use of
flux if it is brazed with a torch using oxygen and hydrogen gas,
rather than oxygen and other flammable gases.Machine torch
brazingis commonly used where a repetitive braze operation is being
carried out. This method is a mix of both automated and manual
operations with an operator often placing brazes material, flux and
jigging parts while the machine mechanism carries out the actual
braze.The advantage of this method is that it reduces the high
labor and skill requirement of manual brazing. The use of flux is
also required for this method as there is no protective atmosphere,
and it is best suited to small to medium production
volumes.Automatic torch brazingis a method that almost eliminates
the need for manual labor in the brazing operation, except for
loading and unloading of the machine. The main advantages of this
method are: a high production rate, uniform braze quality, and
reduced operating cost. The equipment used is essentially the same
as that used for Machine torch brazing, with the main difference
being that the machinery replaces the operator in the part
preparation.
ELECTRIC MOTORAn electric motor is an electromechanical device
that converts electrical energy to mechanical energy. In normal
motoring mode, most electric motors operate through the interaction
between an electric motor'smagnetic fieldandwinding currentsto
generate force within the motor. In certain applications, such as
in the transportation industry withtraction motors, electric motors
can operate in both motoring andgenerating or brakingmodes to also
produce electrical energy from mechanical energy.Found in
applications as diverse as industrial fans, blowers and pumps,
machine tools, household appliances, power tools, and disk drives,
electric motors can be powered bydirect current (DC)sources, such
as from batteries, motor vehicles or rectifiers, or byalternating
current (AC)sources, such as from the power grid,invertersor
generators. Small motors may be found in electric watches.
General-purpose motors with highly standardized dimensions and
characteristics provide convenient mechanical power for industrial
use. The largest of electric motors are used for ship propulsion,
pipeline compression andpumped-storageapplications with ratings
reaching 100 megawatts. Electric motors may be classified by
electric power source type, internal construction, application,
type of motion output, and so on.Electric motors are used to
produce linear or rotary force (torque), and should be
distinguished from devices such as magnetic solenoids and
loudspeakers that convert electricity into motion but do not
generate usable mechanical powers, which are respectively referred
to as actuators and transducers.
Parts of an Electric Motor:
RotorIn an electric motor the moving part is the rotor which
turns the shaft to deliver the mechanical power. The rotor usually
has conductors laid into it which carry currents that interact with
the magnetic field of the stator to generate the forces that turn
the shaft. However, some rotors carry permanent magnets, and the
stator holds the conductors.
StatorThe stationary part is the stator, usually has either
windings or permanent magnets. The stator is the stationary part of
the motors electromagnetic circuit. The stator core is made up of
many thin metal sheets, called laminations. Laminations are used to
reduce energy losses that would result if a solid core were
used.
Air gapIn between the rotor and stator is the air gap. The air
gap has important effects, and is generally as small as possible,
as a large gap has a strong negative effect on the performance of
an electric motor.
Windings Windings are wires that are laid in coils, usually
wrapped around a laminated soft ironmagnetic coreso as to form
magnetic poles when energized with current.Electric machines come
in two basic magnet field pole configurations:salient-polemachine
andnonsalient-polemachine. In the salient-pole machine the pole's
magnetic field is produced by a winding wound around the pole below
the pole face. In thenonsalient-pole, or distributed field, or
round-rotor, machine, the winding is distributed in pole face
slots.Ashaded-pole motorhas a winding around part of the pole that
delays the phase of the magnetic field for that pole.Some motors
have conductors which consist of thicker metal, such as bars or
sheets of metal, usuallycopper, although sometimesaluminumis used.
These are usually powered byelectromagnetic induction.
CommutatorAcommutatoris a mechanism used toswitchthe input of
most DC machines and certain AC machines consisting of slip ring
segments insulated from each other and from the electric motor's
shaft. The motor's armature current is supplied through the
stationarybrushesin contact with the revolving commutator, which
causes required current reversal and applies power to the machine
in an optimal manner as therotorrotates from pole to pole.In
absence of such current reversal, the motor would brake to a stop.
In light of significant advances in the past few decades due to
improved technologies in electronic controller, sensorless control,
induction motor, and permanent magnet motor fields,
electromechanically commutated motors are increasingly being
displaced by externally commutated induction andpermanent-magnet
motors.
WELDING
Weldingis afabricationorsculpturalprocessthat joins materials,
usuallymetalsorthermoplastics, by causingcoalescence. This is often
done bymeltingthe workpieces and adding a filler material to form a
pool of molten material (theweld pool) that cools to become a
strong joint, withpressuresometimes used in conjunction withheat,
or by itself, to produce the weld. This is in contrast
withsolderingandbrazing, which involve melting a
lower-melting-point material between the workpieces to form a bond
between them, without melting the work pieces. It is often used in
construction engineering.Many differentenergy sourcescan be used
for welding, including a gasflame, anelectric arc, alaser,
anelectron beam,friction, andultrasound. While often an industrial
process, welding may be performed in many different environments,
including in open air,under water, and inouter space. Welding is a
hazardous undertaking and precautions are required to
avoidburns,electric shock, vision damage, inhalation of poisonous
gases and fumes, and exposure tointense ultraviolet radiation.Until
the end of the 19th century, the only welding process wasforge
welding, whichblacksmithshad used for centuries to join iron and
steel by heating and hammering.Arc weldingandoxyfuel weldingwere
among the first processes to develop late in the century,
andelectric resistance weldingfollowed soon after. Welding
technology advanced quickly during the early 20th century as World
War I and World War II drove the demand for reliable and
inexpensive joining methods. Following the wars, several modern
welding techniques were developed, including manual methods like
SMAW, now one of the most popular welding methods, as well as
semi-automatic and automatic processes such as GMAW, SAW, FCAW and
ESW. Developments continued with the invention oflaser beam
welding, electron beam welding,magnetic pulse welding(MPW),
andfriction stir weldingin the latter half of the century. Today,
the science continues to advance.Robot weldingis commonplace in
industrial settings, and researchers continue to develop new
welding methods and gain greater understanding of weld quality.
CORE WIREAwireis a single, usuallycylindrical, flexible strand
or rod of metal. Wires are used to bear mechanicalloads
orelectricityand telecommunications signals. Wire is commonly
formed bydrawingthe metal through a hole in adieordraw plate.Wire
gaugescome in variousstandardsizes, as expressed in terms of agauge
number. The termwireis also used more loosely to refer to a bundle
of such strands, as in 'multistranded wire', which is more
correctly termed awire ropein mechanics, or acablein
electricity.Wire comes in solid core, stranded, or braided forms.
Although usually circular in cross-section, wire can be made in
square, hexagonal, flattened rectangular, or other cross-sections,
either for decorative purposes, or for technical purposes such as
high-efficiencyvoice coils inloudspeakers. Edge-wound coil springs,
such as theSlinkytoy, are made of special flattened wire.
Uses:Wire has many uses. It forms the raw material of many
importantmanufacturers, such as thewire nettingindustry, engineered
springs,wire-clothmaking andwire ropespinning, in which it occupies
a place analogous to atextilefiber. Wire-cloth of all degrees of
strength and fineness of mesh is used for sifting and screening
machinery, for draining paper pulp, for window screens, and for
many other purposes. Vast quantities
ofaluminium,copper,nickelandsteelwire are employed for telephone
anddata cables, and as conductors inelectric power transmission,
andheating. It is in no less demand for fencing, and much is
consumed in the construction ofsuspension bridges, and cages, etc.
In the manufacture of stringed musical instruments and scientific
instruments wire is again largely used. Carbon and stainless spring
steel wire have significant applications for engineered springs for
critical automotive or industrial manufactured parts/components.
Among its other sources of consumption it is sufficient to mention
pin andhairpinmaking, the needle andfish-hookindustries, nail, peg
and rivet making, and carding machinery; indeed there are few
industries into which it does not enter.Not all metals and
metallicalloyspossess the physical properties necessary to make
useful wire. The metals must in the first place beductileand strong
in tension, the quality on which the utility of wire principally
depends. The metals suitable for wire, possessing almost equal
ductility, areplatinum,silver,iron,copper, aluminium andgold; and
it is only from these and certain of theiralloyswith other metals,
principallybrassandbronze, that wire is prepared (For a detailed
discussion oncopper wire, see main article:Copper wire and
cable.).By careful treatment extremely thin wire can be produced.
Special purpose wire is however made from other metals
(e.g.tungstenwire forlight bulbandvacuum tubefilaments, because of
its high melting temperature). Copper wires are also plated with
other metals, such as tin, nickel, and silver to handle different
temperatures, provide lubrication, provide easier stripping of
rubber from copper.
INNOVATIONS:
WORKING PRINCIPLE:
In this system, the metal ice tray is connected to a set of
coiledheat-exchanging pipeslike the ones on the back of your
refrigerator. If you've readHow Refrigerators Work, then you know
how these pipes work. A compressor drives a stream of refrigerant
fluid in a continuous cycle of condensation and expansion.
Basically, the compressor forces refrigerant through a narrow tube
(called thecondenser) to condense it, and then releases it into a
wider tube (called theevaporator), where it can expand.Compressing
the refrigerant raises its pressure, which increases its
temperature. As the refrigerant passes through the narrow condenser
coils, it loses heat to the cooler air outside, and itcondensesinto
a liquid. When the compressed fluid passes through theexpansion
valve, it evaporates -- it expands to become a gas. This
evaporation process draws in heat energy from the metal pipes and
the air around the refrigerant. This cools the pipes and the
attached metal ice tray.The icemaker has a water pump, which draws
water from acollection sumpand pours it over the chilled ice tray.
As the water flows over the tray, it gradually freezes, building up
ice cubes in the well of the tray. When you freeze water layer by
layer this way, it forms clear ice. When you freeze it all at once,
as in the home icemaker, you get cloudy ice . After a set amount of
time, the icemaker triggers asolenoid valveconnected to the
heat-exchanging coils. Switching this valve changes the path of the
refrigerant. The compressor stops forcing the heated gas from the
compressor into the narrow condenser; instead, it forces the gas
into a widebypass tube. The hot gas is cycled back to the
evaporator without condensing. When you force this hot gas through
the evaporator pipes, the pipes and the ice tray heat up rapidly,
which loosens the ice cubes.Typically, the individual cube cavities
areslantedso the loosened ice will slide out on their own, into a
collection bin below. Some systems have acylinder pistonthat gives
the tray a little shove, knocking the cubes loose.This sort of
system is popular in restaurants and hotels because it makes ice
cubes with a standard shape and size. Other businesses, such as
grocery stores and scientific research firms, need smallerice
flakesfor packing perishable items