Refrigeration is a process of producing low temperatures as compared to the surrounding temperatures. It will be possible only if heat is transferred...
Project Report on Solar Powered Vapour Absorption Refrigeration SystemFull description
Full description
Project Report on ATM System
Project Report on ATM SystemDescripción completa
A project report based on the most successful sport format which came out of India. Indian Premier League (IPL)Full description
RETAIL STORE MARKETING ACTIVITY (IN STORE TIE-UPS FOR LOYALTY PROGRAM TO ACHIEVE GREEN CARD TARGET, TIE-UPS FOR EOSS AND DENIM EXCHANGE) AT PANTALOON RETAIL INDIA LTD.
Full description
ngo
India's craze for films has not been fully exploited by the "Film Exhibition" industry due to the lack of screen density in the country coupled with the poor quality of screens. "Multiplex C…Full description
Biogas cncept
civil engineeringFull description
uiu9io7u/97/9Full description
About the consumer perception
this document states how the pharma and health sector will take a boom in coming yearsFull description
Full description
Detailed Reporting and Snapshots for Airlines Reservation System. Objective,System Analysis etc. all steps are included.Full description
Its a project report...specially fo d technical student....Full description
A PROJECT REPORT ON
Adv REFRIGERATION SYSTEM Submitted in partial fulfilment of the requirements For the award of BTEC! EN"#NEER#N" #N $$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$ EN"#NEER#N" S%B&#TTE' B( ))))))))))))))))))))
'EPART&ENT OF $$$$$$$$$$$$$$$$$$$$$$$ EN"#NEER#N" $$$$$$$$$$CO,,E"E $$$$$$$$$$CO,,E"E OF EN"#NEER#N" AFF#,#ATE' TO $$$$$$$$$$$ %N#-ERS#T(
1
CERTIFICATE
This is to .ertif/ that the dissertation wor0 entitled 1REFRIGERATION SYSTEM ” is the wor0 done b/ $$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$submitted $$$$$submitted in partial fulfilment for the award of 2BTEC! #N EN"#NEER#N"3 in $$$$$$$$$$$$$$$$$$$$$$$$$$En4 $$$$$$$$$$$$$$$$$$$$$$$$$$En4ineerin4 ineerin4 from$$$$$$$$$$$$$$ from$$$$$$$$$$$$$$ SC!OO, of En4ineerin4 affiliated to $$$$$$$$$ %ni5ersit/6
________________ ________________
____________
(Head of the department,______ department,__ ____
(A!!"!tant (A!!"!t ant #rofe!!or
2
AC$NO%&E'GEMENT
The satisfa.tion and euphoria that a..ompan/ the su..essful .ompletion of an/ tas0 would be in.omplete without the mentionin4 of the people whose .onstant 4uidan.e and en.oura4ement made it possible 7e ta0e pleasure in presentin4 before /ou6 our pro8e.t6 whi.h is result of studied blend of both resear.h and 0nowled4e
7e e9press e9press our earnes earnestt 4ratit 4ratitude ude to our intern internal al 4uide6 4uide6 Assista Assistant nt Profess Professor or $$$$$$$$$$$$$$6
'epartment
of
$$$$$$$$$$6
our
pro8e.t
4uide
$$$$$$$$$$$$$$$$$$$$$6 for his .onstant support6 en.oura4ement and 4uidan.e 7e 7e are 4rateful for his .ooperation and his 5aluable su44estions
Finall/6 we e9press our 4ratitude to all other members who are in5ol5ed either dire.tl/ or indire.tl/ for the .ompletion of this pro8e.t
3
'EC&ARATION
7e6 the undersi4ned6 de.lare that the pro8 ro8e.t entitled A')ANCE REFRIGERATION REFRIGERATION SYSTEM*6 bein4 submitted in partial fulfilment for the award of B)te.h in En4ineerin4 in $$$$$$$$$$$$$$$$$$$$$$$$$En4ineerin46 affiliated to $$$$$$$$$ %ni5ersit/6 is the wor0 .arried out b/ us
$$$$$$$$$$
$$$$$$$$$
$$$$$$$$$
$$$$$$$$$$
$$$$$$$$$
$$$$$$$$$
4
A+!trat The 8ob of a refri4eration plant is to .ool arti.les or substan.es down to6 and maintain them at a temperature lower than the ambient temperature Refri4eration .an be defined as a pro.ess that remo5es heatThe oldest and most well)0nown amon4 refri4erants are i.e6 water6 and air #n the be4innin46 the sole purpose was to .onser5e food The Chinese were the first to find out that i.e in.reased the life and impro5ed the taste of drin0s and for .enturies Es0imos ha5e .onser5ed food b/ free:in4 it All we are usin4 Refri4eration s/stem now a da/s be.ause of this hi4h heat as well as 4lobal warmin4 Refri4eration is a pro.ess in whi.h wor0 is done to mo5e heat from one lo.ation to another Refri4eration has man/ appli.ations6 in.ludin46 but not limited to; household refri4erators6 industrial free:ers6 .r/o4eni.s6 and air .onditionin4 .
5
Introd-t"on Refri4eration is a pro.ess of produ.in4 low temperatures as .ompared to the surroundin4 temperatures #t will be possible onl/ if heat is transferred from the low temperature re4ion to a hi4h temperature re4ion Ob5iousl/ it is not possible in the natural manner be.ause heat flows from hi4h temperature to low temperature li0e fluid flows from hi4h pressure to low pressure< .urrent flows from hi4h 5olta4e to low 5olta4e< 4as flows from hi4h .on.entration to the re4ion of low .on.entration #t means in refri4eration one is tr/in4 to 4o a4ainst the natural pro.ess as well as a4ainst the se.ond law of thermod/nami.s whi.h states that heat .annot flow from low temperature re4ion to a hi4h temperature re4ion without the use of an e9ternal a4ent The e9ternal a4ent in refri4eration is the .ompressor whi.h introdu.es the most .ommon method of refri4eration
The most commonly used closed vapour compression refrigeration system consists of six main parts namely compressor, condenser, expansion device, evaporator, piping and circulating working substance called the refrigerant.
6
INTRODUCTION
1.1 Introduction: Refrigeration is dened as the science of maintaining the temperature of particular space lower than the surrounding space. This process is called refrigeration system.
1.2 Background: • n 1!34" an #merican in$entor named %aco& 'er(ins o&tained the rst patent for a $apor)compression refrigeration system. t uses ether in a $apor compression cycle. • The $apor compression type refrigeration system plays a great role in domestic and industrial area. • t controls mainly temperature * relati$e humidity of air to (eep food at initial condition without changing nutrition * taste. • t protects food from &acteria and (eeps the li$ing place neat * healthy. • t is used in sectors li(e 'harmaceutical companies" +hemical industries" ce+ream factories" +old storages" ,otels e.g. -T, /0T ,## etc.
1.3 Objective: • To &uild a low cost &ut eecti$e $apor compression type refrigeration system. • To ma(e it a$aila&le for commercial use.
1.4 et!odo"og#: • +ollection of data and technical information from the manuals of 0#078" ',9'0" /#9T: . • 'urchase of the discrete components from local mar(et. • ;isit of ,otels -T, /0T ,##.
C$%&T'R ( )2
&RINCI&*' O+ R'+RI,'R%TION <
2.1 &re--ure: 'ressure is the force on an o&=ect that is spread o$er a surface area. The e>uation for pressure is ' ? @A#. 'ressure can &e measured for a solid is pushing on a solid" &ut the case of a solid pushing on a li>uid or gas re>uires that the Buid &e conned in a container. The force can also &e created &y the weight of an o&=ect. 0o that" '?@A# /here" '?'ressure is new tons per s>uare meter -AmC or 'ascalDs -'a. @?The force in new tons -. #?The area in s>uare meters -mC. #nother common unit of pressure measure is the &ar. :ne &ar is e>ual to 1EEEEE pa or AmC.
2.2 &a-ca"- *a/: To honor the scientist 'ascal" the 0 metric system uses the term F'ascalF as a unit of pressure. # 'ascal is a ewton per s>uare meter -A mC.# ewton is the metric unit oorce. :ne ewton is e>ual to the mass of 1 (ilogram &eing accelerated at rate of 1 meterper second per second. 'ascal low states that pressure applied upon a conned Buid is transmitted e>ually in all di rections. t is the &asis of operation of most hydraulic and pneumatic system.
2.3 &re--ure gage: # pressure gage is an instrument" which used to measure Buid -8aseous or li>uid pressure in a closed $essel. 'ressure gages commonly used in the refrigeration industry are of two principle types. 0uch as manometer and &ourdon tu&e.
2.4 %t0o-!eric re--ure: The earth is surrounded &y an en$elope of atmosphere or air eGtends upward from the surface of the earth to a distance of some 5E miles or more. 0ince air has mass and is su&=ect to the actions of gra$ity. t eGerts a pressure that is (nown as the atmospheric pressure.
2. %b-o"ute re--ure: #&solute 'ressure is the sum of the a$aila&le atmospheric pressure and the gage pressure in the pumping system.
!
2. $eat: 12,eat is a from of energy. This is e$ident from the fact that heat can &e con$erted in to other forms of energy and that other forms of energy can &e con$erted in to heat. Thermodynamically heat is the dened as energy in transit from one &ody to another as the result temperature dierence &etween the two &odies. #ll other transfers occur as wor(.
2. 5eci6c !eat: 0pecic heat is the amount of heat per unit mass re>uired to raise the temperature &y one degree +elsius. The specic heat of water is 1 calorie A gram H+. 0o that "I ? c m dT /here" I ? ,eat added. c ? 0pecic heat. m ? ass. dT ? +hange in temperature.
2.7 5en-ib"e !eat: 0ensi&le heat is the heat a&sor&ed or gi$en o &y a su&stance that is not in the process of changing its physical state. 0ensi&le heat can &e sensed or measured with a thermometer and the addition or remo$al of sensi&le heat will always cause a change in the temperature of the su&stance.
2.8 *atent !eat: 9atent heat is the heat a&sor&ed or gi$en o &y a su&stance while it is changing its physical state. The heat a&sor&ed or gi$en o does not cause a temperature change in the su&stance the heat is latent or hidden. n other words" sensi&le heat is the heat that aects the temperature of things latent heat is the heat that aects the physical state of things.
2.1) 5uer!eat: :nce a li>uid has &een $aporiJed" the temperature of the resulting $apor can &e further increased &y the additional of heat. The heat added to a $apor after $aporiJation is the sensi&le heat of the $apor" more commonly called super heat.
2.11 Te0erature:
K
Temperature is a measurement of the a$erage (inetic energy of the molecules in an o&=ect or system and can &e measured with a thermometer or a calorimeter. t is a means of determining the internal energy contained within the system.
2.12 %b-o"ute te0erature: The temperature $alue relati$e to a&solute Jero. The a&solute Jero is the theoretical temperature at which molecular motion $anishes and a &ody would ha$e no heat energy the Jero point of the el$in and Ran(in temperature scales. #&solute Jero may &e interpreted as the temperature at which the $olume of a perfect gas $anishes or more generally as the temperature of the cold source" that would render 1EEL eMcient.
2.13 5aturation te0erature: 130aturation temperature means &oiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a li>uid &oils into its $apor phase. The li>uid can &e said to &e saturated with thermal energy. #ny addition of thermal energy results in a phase transition.
2.14 T!er0o0eter: #n instrument for measuring and indicating temperature typically one consisting of a narrow hermetically sealed glass tu&e mar(ed with graduations and ha$ing at one end a &ul& containing mercury or alcohol that eGpands and contracts in the tu&e with heating and cooling.
2.1 9ork: /or( is the transfer of energy. :therwise wor( is dened -in calculus terms as the integral of the force o$er a distance of displacement. The 0 units for wor( are the =oule -% or ewton)meter - N m" from the function. / ? @ N s /here" /?s wor(. @?s force. s ? s the displacement.
2.1 &o/er: 'ower is the time rate at which wor( is done or energy is transferred. n calculus terms" power is the deri$ati$e of wor( with respect to time. The 0 unit of power is the watt -/ or =oule per second -%As. ,orsepower is a unit of power in the Oritish system of measurement. The dimension of power is energy di$ided &y time.
2.1 'nerg#:
1E
nergy is the capacity of a physical system to perform wor(. nergy eGists in se$eral forms such as heat" (inetic or mechanical energy" light" potential energy" electrical" or other forms. The 0 unit of energy is the =oule -%.
2.17 5aturation te0erature: The temperature and pressure of the atmosphere must &e at that point or in an inter$al of $alues for the su&stance to &e saturated.
2.18 5uer!eated vaor: The present in$ention in$ol$es a system and method for superheating the refrigerant gas in a motor $ehicle air conditioning system in order to minimiJe the amount of wor( re>uired to &e performed &y the compressor. n an em&odiment of the present in$ention" the refrigerant gas is di$erted through the eGhaust manifold immediately after passing through the compressor. #s the refrigerant gas passes through the eGhaust manifold. 14The surrounding hot eGhaust gases there&y increasing the refrigerant gas pressure to reduce the amount of wor( done &y the compressor superheat it. Refrigerant $apor at a temperature that is higher than its &oiling point at a gi$en pressure.
2.2) 5ub coo"ed "iuid: # compressed Buid -also called a su&cooled Buid or su&cooled li>uid is a Buid underthermodynamic conditions that force it to &e a li>uid. t is a li>uid at a temperature lower than the saturation temperature at a gi$en pressure. n a plot comparing a&solute pressure and specic $olume -commonly called a ')$ diagram" of a real gas" a compressed Buid is to the left of the li>uid)$apor phase &oundaryP that is" it will &e to the left of the $apor dome.
2.21 ;aoriuid phase into a gaseous phase./ater &oiling into steam is an eGample of $aporiJation.
2.22 'vaoration: $aporation is the process &y which water is con$erted from its li>uid form to its $apor form and thus transferred from land and water masses to the atmosphere. $aporation from the oceans accounts for !EL of the water deli$ered as precipitation with the &alance occurring on land" inland waters and plant surfaces.
2.23 T!e coo"ing e=ect o> evaoration: $aporation is the remo$al of water molecules from the surface of a li>uid. f alcohol is splashed on the &ac( of the hand" it produces a cooling eect. /hen a 11
li>uid e$aporates" this in$ol$es a change of state from li>uid to gas. This change re>uires heat energy called latent heatA hidden heat. #s plants transpire" water is e$aporated from the lea$es. $aporation has a cooling eect in this situation as well. 'lants are cooled during transpiration. $aporation is used &y the &ody to regulate its temperature. /hen the temperature of the &ody rises we &egin to perspire more. 0weat glands in the s(in will produce more sweat. This sweat e$aporates and the result is a cooling eect on the s(in. The rate at which the e$aporation ta(es place depends on the rate of air o$er the s(in and this is why we fan oursel$es to speed up the process. /hen the surroundings are cold" the &lood $essels contract" to pre$ent heat loss. n these circumstances the su&cutaneous fat ser$es as insulation and is sometimes &urnt to pro$ide heat. ,airs may also &ecome erect to trap air as further insulation. n circumstances where the temperature is high" our meta&olic rate falls so that less heat is generated &y our &ody. n cold temperatures eGtra heat is produced &y an increase of the meta&olic rate" mainly of the li$er and muscles. This sometimes causes rhythmical in$oluntary contractions of the s(eletal muscles-shi$ering.
2.24 Conden-ation: t is the change of the physical state of matter from gaseous phase into li>uid phase" and is the re$erse of e$aporation. 15/hen the transition happens from the gaseous phase into the solid phase directly" the change is called deposition. 7pon the slowing)down of the molecules of the material" the o$erall attraction forces &etween these pre$ail and &ring them together at distances compara&le to their siJes. 0ince the condensing molecules suer from reduced degrees of freedom and ranges of motion" their prior (inetic energy must &e transferred to an a&sor&ing colder entity either a center of condensation within the gas $olume or some contact surface.
2.2 Critica" te0erature: The temperature at which some phase change occurs in a metal during heating or cooling" i.e. the temperature at which an arrest or critical point is shown on heating or cooling cur$es.
2.2 Critica" re--ure: +ritical pressure is the lowest pressure at which a su&stance can eGist in the li>uid sate at its critical temperature.t is the saturation pressure at the critical temperature.
2.2 'nt!ra"#: nthalpy is a measure of the total energy of a thermodynamic system. t includes the internal energy" which is the energy re>uired to create a system" and the amount of energy re>uired to ma(e room for it &y displacing its en$ironment and esta&lishing its $olume and pressure. 12
0o that", ? 7 Q p ; /here", ? s the enthalpy of the system.7 ? s the internal energy of the system.p ? s the pressure at the &oundary of the system and its en$ironment. ; ? s the $olume of the system.
2.27 'ntro#: # thermodynamic >uantity representing the una$aila&ility of a systems thermal energy for con$ersion into mechanical wor( often interpreted as the degree of disorder or randomness in the system. 16+,#'TR S E3 T, ,0T:R :@ R@R8R#T:
3.1 Re>rigeration !i-tor#: n 'rehistoric times" man found that his game would last during times when food was not a$aila&le if stored in the coolness of a ca$e or pac(ed in snow. n +hina" &efore the rst millennium" ice was har$ested and stored. ,e&rews" 8ree(s" and Romans placed largeamounts of snow into storage pits dug into the ground and insulated with wood and straw. The ancient gyptians lled earthen =ars with &oiled water and put them on their roofs" thus eGposing the =ars to the nightDs cool air. n ndia" e$aporati$e cooling was employed. /hen a li>uid $aporiJes rapidly" it eGpands >uic(ly. The rising molecules of $apor a&ruptly increase their (inetic energy and this increase is drawn from the immediate surroundings of the $apor. These surroundings are therefore cooled. The intermediate stage in the history of cooling foods was to add chemicals li(e sodium nitrate or potassium nitrate to water causing the temperature to fall. +ooling wine $ia this method was recorded in 155E" as were the words Fto refrigerateU. +ooling drin(s came into $ogue &y 16EE in @rance. nstead of cooling water at night people rotated long nec(ed &ottles in water in which saltpeter had &een dissol$ed. This solution could &e used to produce $ery low temperatures and to ma(e ice. Oy the end of the 1
uors and froJen =uices were popular in @rench society. The rst (nown articial refrigeration was demonstrated &y /illiam +ullen at the 7ni$ersity of 8lasgow in 1<4!.+ullen let ethyl ether &oil into a partial $acuum he did not howe$er" use the result to any practical purpose. ce was rst shipped commercially out of +anal 0treet in ew or( +ity to +harleston" 0outh +arolina in 1uic(ly and cheaply cutting uniform &loc(s of ice that 13
transformed the ice industry" ma(ing it possi&le to speed handling techni>ues in storage"transportation and distri&ution with less waste. n 1!E5" an #merican in$entor" :li$er$ans" designed the rstrefrigerationmachine that used $apor instead of li>uid. $ansne$er constructed his machine" &ut one similar to it was &uilt &y an #merican physician"%ohn 8orrie. n 1!42" the #merican physician %ohn 8orrie" to cool sic(rooms in a @loridahospital designed and &uilt an air)cooling apparatus for treating yellow fe$er patients.,is &asic principle that of compressing a gas" cooling it &y sending it through radiatingcoils" and then eGpanding it to lower the temperature further is the one most often used inrefrigerators today. 8i$ing up his medical practice to engage in time consumingeGperimentation with ice ma(ing" he was granted the rst 7.0. patent for mechanicalrefrigeration in 1!51. +ommercial refrigeration is &elie$ed to ha$e &een initiated &y an #merican &usinessperson" #leGander +. Twinning" in 1!56. 0hortly afterward an#ustralian" %ames ,arrison eGamined the refrigerators used &y 8orrie and Twinning and introduced $apor)compression refrigeration to the &rewing and meatpac(ing industries. @erdinand +arrW of @rance de$eloped a somewhat more compleG system in 1!5K.1<7nli(e earlier compression machines" which used air as a coolant" +arrWs e>uipmentcontained rapidly eGpanding ammonia -#mmonia li>uees at a much lower temperature than water and is thus a&le to a&sor& more heat. +arrWs refrigerators were widely used" and $apor compression refrigeration &ecame and still is" the most widely used method of cooling. ,owe$er" the cost" siJe and compleGity of refrigeration systems of the time" coupled with the toGicity of their ammonia coolants pre$ented the general use of mechanical refrigerators in the home. ost households used ice&oGes that were supplied almost daily with &loc(s of ice from a local refrigeration plant. Oeginning in the 1!4Es"refrigerated cars were used to transport mil( and &utter. Oy 1!6E" refrigerated transportwas limited to mostly seafood and dairy products. The refrigerated railroad car was patented &y %.O. 0utherland of etroit" ichigan in 1!6<. ,e designed an insulated car with ice &un(ers in each end. #ir came in on the top passed through the &un(ers and circulated through the car &y gra$ity controlled &y the use of hanging Baps that created dierences in air temperature. The rst refrigerated car to carry fresh fruit was &uilt in 1!6< &y 'ar(er arle of llinois" who shipped straw&erries on the llinois +entral Railroad. ach chest contained 1EE pounds of ice and 2EE >uarts of straw&erries. t wasnot until 1K4K that a refrigeration system made its way into the truc(ing industry &y way of a roof)mounted cooling de$ice" patented &y @red %ones. Orewing was the rst acti$ity in the northern states to use mechanical refrigeration eGtensi$ely" &eginning with an a&sorption machine used &y 0. 9ie&mannDs 0ons Orewing +ompany in Oroo(lyn" ew or( in 1!uipped with refrigerating machines. atural ice supply &ecame an industry unto itself. ore companies entered the &usiness" prices decreased and refrigeration using ice &ecame more accessi&le. Oy 1!
/alden 'ond" where 1"EEE tons of ice was eGtracted each day in 1!4<. ,owe$er" as time went on ice" as a refrigeration agent" &ecame a health pro&lem. 0ays Oern agengast" co)author of ,eat and +old astering the 8reat ndoors -pu&lished &y the #merican 0ociety of ,eating" Refrigeration and #ir)conditioning ngineers" V8ood sources were harder and harder to nd. Oy the 1!KEDs" natural ice &ecame a pro&lem &ecause of pollution and sewagedumping.U 0igns of a pro&lem were rst e$ident in the &rewing industry. 0oon the meatpac(ing and dairy industries followed with their complaints. Refrigeration technology pro$ided the solution ice" mechanically manufactured gi$ing &irth to mechanical refrigeration. +arl -'aul 8ottfried $on 9inde in 1!K5 set up a large)scale plant for the production of li>uid air. 0iG years later he de$eloped a method for separating pure li>uid oGygen from li>uid air that resulted in widespread industrial con$ersion to processes utiliJing oGygen -e.g." in steel manufacture. Though meatpac(ers were slower to adopt refrigeration than the &reweries" they ultimately used refrigeration per$asi$ely. Oy 1K14" the machinery installed in almost all #merican pac(ing plants was the ammonia compression system" which had a refrigeration capacity of well o$er KE"EEE tonsAday. espite the inherent ad$antages" refrigeration had its pro&lems. Refrigerants li(e sulfur dioGide and methyl chloride were causing people to die. #mmonia had an e>ually serious toGic eect if it lea(ed. Refrigeration engineers searched for accepta&le su&stitutes until the 1K2Es" when a num&er of synthetic refrigerants called halocar&ons or +@+s -chloroBuorocar&ons were de$eloped &y @rigidaire. The &est (nown of these su&stances was patented under the &rand name of @reon. +hemically @reon was created &y the su&stitution of two chlorine and two Buorine atoms for the four hydrogen atoms in methane -+,4 the result" dichlorodiBuoromethane -++l2@2 is odorless and is toGic only in eGtremely large doses.1!Though ice" &rewing" and meatpac(ing industries were refrigerationDs ma=or &eneciaries" many other industries found refrigeration a &oon to their &usiness. n metal wor(ing" for instance mechanically produced cold helped temper cutlery and tools.ron production got a &oost" as refrigeration remo$ed moisture from the air deli$ered to &last furnaces" increasing production.#llied ghting ships held car&on)dioGide machines to (eep ammunition well &elow temperatures at which high eGplosi$es &ecame unsta&le.n 1K<3" 'rof. %ames 9o$eloc( reported nding trace amounts of refrigerant gases in the atmosphere. n 1K<4" 0herwood Rowland and ario olina predicted that chloroBuorocar&on refrigerant gases would reach the high stratosphere and there damage the protecti$e mantle of the oGygen allotrope" oJone. n 1K!5 the FoJone holeF o$er the #ntarctic had &een disco$ered and &y 1KKE Rowland and olinas prediction was pro$edcorrect. The &asic components of todayDs modern $apor)compression refrigeration system are a compressor" a condenser" an eGpansion de$ice" which can &e a $al$e" a capillary tu&e" an engine" or a tur&ineP and an e$aporator. The gas coolant is rst compressed" usually &y a piston" and then pushed through a tu&e into the condenser. n the condenser" the winding tu&e containing the $apor is passed through either circulating air or a &ath of water" which remo$es some of the heat energy of the compressed gas.The cooled $apor is passed through an eGpansion de$ice to an area of much lower pressure as the $apor eGpands" it draws the energy of its eGpansion from its surroundings or the medium in contact 15
with it. $aporators may directly cool a space &y letting the $apor come into contact with the area to &e chilled or they may act indirectly)i.e. &y cooling a secondary medium such as water. n most domestic refrigerators" the coilcontaining the e$aporator directly contacts the air in the food compartment. #t the end of the process" the warmed gas is drawn toward the compressor.
1K+,#'TR S E4 C*%55I+IC%TION O+ DI++'R'NT T?&' R'+RI,'R%TION 5?5T' 4.1 Re>rigeration -#-te0: Refrigeration is dened as the science of maintaining the temperature of a particularspace lower than the surrounding space. Thermodynamically" when the &ody at certain temperature is (ept in the atmosphere it tends to attain the temperature of the atmosphere. Out with the process of refrigeration it can &e (ept at temperature much lower than the atmospheric temperature. # refrigerator uses the e$aporation of a li>uid to a&sor& heat. The li>uid or refrigerant used in a refrigerator e$aporates at an eGtremely low temperature creating freeJing temperatures inside the refrigerator. ts all &ased on the following physics a li>uid is rapidly $aporiJed -through compression the >uic(ly eGpanding $apor re>uires (inetic energy and draws the energy needed from the immediate area which loses energy and &ecomes cooler. +ooling caused &y the rapid eGpansion of gases is the primary means of refrigeration today.
4.2 et!od- o> re>rigeration -#-te0: /e can classication se$en types of refrigeration systen from principle and operation. 1 ry)+ Refrigeration system. 2 0team)%et Refrigeration system.
4.3 Dr#@IC' Re>rigeration -#-te0: ry ice is the solid car&on dioGide ha$ing the temperature of )
2)+igure: Dr#@Ice re>rigeration -#-te0. This methods of refrigeration system can &e used only in places where small amount of refrigeration is re>uired in places li(e la&oratories" wor(shops" water coolers" small old drin( shops" small hotels etc. n fact the ordinary ice and dry ice used for the refrigeration purposed ha$e to &e manufactured &y the cyclic methods of refrigeration which we shall see in the neGt article. ,owe$er" in the earlier days the ice used for the cooling purposes was usually har$ested during the winter seasons from the ponds and la(es and stored in large insulated ice houses for the use throughout the year.
4.4 5tea0 jet re>rigeration -#-te0: f water is sprayed into a cham&er where a low pressure is maintained a part of the water will e$aporate. The enthalpy of e$aporation will cool the remaining water to its saturation temperature at the pressure in the cham&er. :&$iously lower temperature will re>uire lower pressure. /ater freeJes at Eo+ hence temperature lower than 4o+ cannot &e o&tained with water. n this system" high $elocity steam is used to entrain the e$aporating water $apor. ,igh)pressure moti$e steam passes through either con$ergent or con$ergent)di$ergent noJJle where it ac>uires &oth sonic or supersonic $elocity and low pressure of the order of E.EEK ('a corresponding to an e$aporator temperature of 4o+. The high momentum of moti$e steam entrains or carries along with it the water $apor e$aporating from the Bash cham&er. Oecause of its high $elocity it 1<
mo$es the $apors against the pressure gradient up to the condenser where the pressure is 5.6 to <.4('a corresponding to condenser temperature of 35)45o+. The moti$e $apor and the e$aporated $apor &oth are condensed and recycled. t can &e seen that this system re>uires a good $acuum to &e maintained. 0ometimes &ooster e=ector is used for this purpose. This system is dri$en &y low) grade energy that is process steam in chemical plants or a &oiler.
21+igure: 5c!e0aticre>rigeration -#-te0.
diagra0
o>
-tea0
jet
n 1!3!" the @renchman 'elletan was granted a patent for the compression of steam &y means of a =et of moti$e steam. #round 1KEE" the nglishman +harles 'arsons studied the possi&ility of reduction of pressure &y an entrainment eect from a steam =et. ,owe$er" the credit for constructing the steam =et refrigeration system goes to the @rench engineer" aurice 9e&lanc who de$eloped the system in 1KE<)E!. n this system" e=ectors were used to produce a high $elocity steam =et -X 12EE mAs. Oased on 9e&lancDs design the rst commercial system was made &y /estinghouse in 1KEK in 'aris. $en though the eMciency of the steam =et refrigeration system was low" it was still attracti$e as water is harmless and the system can run using eGhaust steam from a steam engine.@rom 1K1E onwards" stem =et refrigeration systems were used mainly in &reweries" chemical factories" warships etc. n 1K26" the @rench engineer @ellahin impro$ed the machine &y introducing multiple stages of $aporiJation and condensation of the suction steam. Oetween 1K2!)1K3E" there was much interest in this type of systems in 70#. n 70# they were mainly used for air conditioning of factories" cinema theatres" ships and e$en railway wagons. 0e$eral companies such as /estinghouse" ngersoll Rand and +arrier started commercial production of these systems from 1K3E. ,owe$er" gradually these systems were replaced &y more eMcient $apor a&sorption systems using 9iOrwater. 0till" some east uropean countries such as +Jechoslo$a(ia and Russia manufactured these systems as late as 1K6Es. The e=ector principle can also &e used to pro$ide refrigeration using Buids other than water" i.e." refrigerants such as +@+)11" +@+)21" +@+)22" +@+)113" +@+)114 etc. The credit for rst de$eloping these closed $apor =et refrigeration systems goes to the Russian engineer" .0. Oadyl(es around 1K55.
4.5 #ir cycle refrigeration systemY #ir cycle refrigeration systems &elong to the general class of gas cycle refrigeration systems in which gas is used as the wor(ing Buid. The gas does not under go any phase change during the cycle" conse>uently" all the internal heat transfer processes are sensi&le heat transfer processes. t applications in air craft ca&in cooling and also in the li>uefaction of $arious gases. #ir cycle refrigeration systems use air as their refrigerant compressing it and eGpanding it to create heating and cooling capacity. 22#ir cycle is not a new technology. #ir cycle or Zcold air machinesD were a$aila&le from +ompanies such as % * ,all in the early 1KEEs. These were used on &oard ships and &y food producers and retailers to pro$ide cooling for their food stores. ,owe$er" the de$elopment of $apor 1!
compression cycles &ased initially on ethyl ether ammonia or sulphur)dioGide &ut superseded &y chloroBuorocar&ons -+@+s led to the gradual replacement of the ma=ority of air cycle systems eGcept in the eld of aircraft air conditioning. n$ironmental concerns a&out +@+s" oJone depletion" glo&al warming and the resulting increasingly stringent legislation ha$e renewed interest in alternati$es to the current standard of $apor)compression refrigeration technologies. The use of air cycle is one of these oering a &enign su&stitute for +@+ refrigerants as well as reduced energy consumption and capital costs for targeted applications. #ir cycle refrigeration wor(s on the re$erse Orayton or %oule cycle. #ir is compressed and then heat remo$ed this air is then eGpanded to a lower temperature than &efore it was compressed. /or( must &e ta(en out of the air during the eGpansion otherwise the entropy would increase. /or( is ta(en out of the air &y an eGpansion tur&ine which remo$es energy as the &lades are dri$en round &y the eGpanding air. This wor( can &e usefully employed to run other de$ices such as generators or fans. :ften though it is used to power a directly connected -&ootstrap compressor which ele$ates the compressed -hot side pressure further without added eGternal energy input essentially recycling the energy remo$ed from the eGpanding air to compress the high pressure air further. The increase in pressure on the hot side further ele$ates the temperature and ma(es the air cycle system produce more usea&le heat -at a higher temperature. The cold air after the tur&ine can &e used as a refrigerant either directly in an open system or indirectly &y means of a heat eGchanger in a closed system. The eMciency of such systems limited to a great eGtent &y the eMciencies of compression and eGpansion as well as those of the heat eGchangers employed. :riginally slow speed reciprocating compressors and eGpanders were used. The poor eMciency and relia&ility of such machinery were ma=or factors in the replacement of such systems with $apor compression e>uipment. ,owe$er" the de$elopment of rotary compressors and eGpanders -such as in car tur&ochargers greatly impro$ed the isentropic eMciency and relia&ility of the air cycle. #d$ances in tur&ine technology together with the de$elopment of air &earings and ceramic components oer further eMciency impro$ements. +om&ining these ad$ances with newly a$aila&le compact heat eGchangers which ha$e greatly impro$ed heat transfer characteristics ma(es competition with many eGisting $apor compression >uite feasi&le. @igureY 0chematic of a simple aircraft refrigeration cycle.23n gure shows the schematic of a simple aircraft refrigeration system and the operating cycle on T)s diagram. This is an open system. #s shown in the T)s diagram the outside low pressure and low temperature air -state 1 is compressed due to ram eect to ram pressure -state 2. uring this process its temperature increases from 1 to 2. This air is compressed in the main compressor to state 3" and is cooled to state 4 in the air cooler. ts pressure is reduced to ca&in pressure in the tur&ine -state 5" as a result its temperature drops from 4 to 5. The cold air at state 5 is supplied to the ca&in. t pic(s up heat as it Bows through the ca&in pro$iding useful cooling eect. The power output of the tur&ine is used to dri$e the fan which maintains the re>uired air Bow o$er the air cooler. This simple system is good for ground 1K
cooling -when the aircraft is not mo$ing as fan can continue to maintain airBow o$er the air cooler.
4. ;aor co0re--ion re>rigeration -#-te0: Refrigeration systems are also used for pro$iding cooling and dehumidication in summer or personal comfort -air conditioning. The rst air conditioning systems were used for industrial as well as comfort air conditioning. astman oda( installed the rst air conditioning system in 1!K1 in Rochester" ew or( for the storage of photographic lms. #n air conditioning system was installed in a printing press in 1KE2 and in a telephone eGchange in ,am&urg in 1KE4. any systems were installed in to&acco and teGtile factories around 1KEE. The rst domestic air conditioning system was installed in a house in @ran(furt in 1!K4. # pri$ate li&rary in 0t 9ouis" 70# was air conditioned in 1!K5" and a casino was air conditioned in onte +arlo in 1KE1. orts ha$e also &een made to air condition passenger rail coaches using ice. The widespread de$elopment of air conditioning is attri&uted to the #merican scientist and industrialist /illis +arrier. +arrier studied the control of humidity in 1KE2 and designed a central air conditioning plant using air washer in 1KE4. ue to the pioneering eorts of +arrier and also due to simultaneous de$elopment of dierent components and controls air conditioning >uic(ly &ecame $ery popular especially after 1K23. #t present comfort air conditioning is widely used in residences" oMces" commercial &uildings" air ports" hospitals and in mo&ile applications such as rail coaches" automo&iles" aircrafts etc. ndustrial air conditioning is largely responsi&le for the growth of modern electronic" pharmaceutical" chemical industries etc. ost of the present day air conditioning systems use either a $apor compression refrigeration system or a $apor a&sorption refrigeration system. The capacities $ary from few (ilowatts to megawatts. #s shown in the gure the &asic system consists of an e$aporator" compressor" condenser and an eGpansion $al$e. @igureY ;apour compressoion refrigeration system. 24The refrigeration eect is o&tained in the cold region as heat is eGtracted &y the $aporiJation of refrigerant in the e$aporator. The refrigerant $apor from the e$aporator is compressed in the compressor to a high pressure at which its saturation temperature is greater than the am&ient or any other heat sin(. ,ence when the high pressure high temperature refrigerant Bows through the condenser" condensation of the $apor into li>uid ta(es place &y heat re=ection to the heat sin(. To complete the cycle the high pressure li>uid is made to Bow through an eGpansion $al$e. n the eGpansion $al$e the pressure and temperature of the refrigerant decrease. This low pressure and low temperature refrigerant $apor e$aporates in the e$aporator ta(ing heat from the cold region. t should &e o&ser$ed that the system operates on a closed cycle. The system re>uires input in the form of mechanical wor(. t eGtracts heat from a cold space and re=ects heat to a high temperature heat sin(. # refrigeration system can also &e used as a heat pump" in which the useful output is the high temperature heat re=ected at the condenser. #lternati$ely a refrigeration system can &e used for
2E
pro$iding cooling in summer and heating in winter. 0uch systems ha$e &een &uilt and are a$aila&le now.
Vapor-Compression Refrigeration Compression refri4eration ./.les ta0e ad5anta4e of the fa.t that hi4hl/ .ompressed fluids at a .ertain temperature tend to 4et .older when the/ are allowed to e9pand #f the pressure .han4e is hi4h enou4h6 then the .ompressed 4as will be hotter than our sour.e of .oolin4 *outside air6 for instan.e+ and the e9pand ed 4as will be .ooler than our desired .old temperature #n this .ase6 fluid is used to .ool a low temperature en5ironment and re8e.t the heat to a hi4h temperature en5ironment -apour .ompression refri4eration . /.les ha5e two ad5anta4es First6 a lar4e amount of thermal ener4/ is required to .han4e a liquid to a 5apor6 and therefore a lot of heat .an be remo5ed from the air).onditioned spa.e Se.ond6 the isothermal nature of the 5apori:ation allows e9tra.tion of heat without raisin4 the temperature of the wor0in4 fluid to the temperature of whate5er is bein4 .ooled This means that the heat transfer rate remains hi4h6 be.ause the .loser the wor0in4 fluid temperature approa.hes that of the surroundin4s6 the lower the rate of heat transfer
Vapor-Compression Refrigeration
condenser
21
Compressr
evaporator
Refrigeration Cycle A brief review of the vapour-compression refrigeration cycle will help to relate that Components which is used in refrigeration system.
22
A diagram of a typical vapor-
compression refrigeration cycle can be superimposed on a pressure-enthalpy !- h" chart to demonstrate the function of each component in the system. The pressure-enthalpy chart plots the properties of a refrigerant # refrigerant pressure vertical axis" versus enthalpy hori$ontal axis". Enthalpy is a measure of the heat content, both sensible and latent, per pound %kg& of refrigerant.
The cycle starts with a cool, low-pressure mixture of li'uid and vapor refrigerant entering the evaporator " where it absorbs heat from the relatively warm air, water, or other fluid that is being cooled. This transfer of heat boils the li'uid refrigerant in the evaporator, and this superheated refrigerant vapour is drawn to the compressor ".
23
The compressor draws in the superheated refrigerant vapor " and compresses it to a pressure and temperature " high enough that it can re(ect heat to another fluid. This hot, high-pressure refrigerant vapour then travels to the condenser.
24
)ithin the condenser, heat is transferred from the hot refrigerant vapor to relatively cool ambient air or cooling water. This reduction in the heat content of the refrigerant vapour causes it to desuperheated, condense into li'uid, and further sub cool before leaving the condenser " for the expansion device.
25
*inally, the high-pressure li'uid refrigerant " flows through the expansion device, causing a large pressure drop that reduces the pressure of the refrigerant to that of the evaporator. This pressure reduction causes a small portion of the li'uid to boil off, or flash, cooling the remaining refrigerant to the desired evaporator temperature. The cooled mixture of li'uid and vapour refrigerant then enters the evaporator " to repeat the cycle.
Refrigeration System Components Condensers+ The first ma(or component to be discussed is the condenser. The condenser is a heat exchanger that re(ects heat from the refrigerant to air, water, or some other fluid. The three common types of condensers are air-cooled, water-cooled, and evaporative.
26
Air-Cooled Condensers A typical air-cooled condenser uses propeller-type fans to draw outdoor air over a finned tube heat transfer surface. The temperature difference between the hot refrigerant vapour that is flowing through the tubes and the cooler outdoor air induces heat transfer. The resulting reduction in the heat content of the refrigerant vapour causes it to condense into li'uid. )ithin the final few lengths of condenser tubing the sub cooler ", the li'uid refrigerant is further cooled below the temperature at which it was condensed. The air-cooled condenser is very popular in both residential and commercial applications because of its convenience. t re'uires very little maintenance and does not re'uire the free$e protection and water treatment that is necessary with a watercooled condenser. Additionally, it is favoured in areas that have an inade'uate or costly water supply, or where the use of water for air conditioning is restricted.
2<
The benefit of sub cooling on system performance can be demonstrated by comparing the performance of a system with and without sub cooling. The change in enthalpy the line from to " that occurs in the evaporator is called the refrigeration effect. This is the amount of heat that each pound %kg& of li'uid refrigerant will absorb when it evaporates. n comparison, the same system without sub cooling produces less refrigeration effect the line from I to ". The system without sub cooling must evaporate substantially more refrigerant within a larger coil to produce the same capacity as the system with sub cooling. nstead of sub cooling in the condenser, some packaged refrigeration e'uipment, such as water chillers, may use an economi$er or li'uidvapour separator to increase this refrigeration effect.
An alternative air-cooled condenser uses a centrifugal fan to draw or blow air over the condensing coil. The principal advantage of this design is that the centrifugal fan is capable of overcoming the higher static-pressure losses associated with ductwork. Therefore, if the condenser is to be located indoors and uses a duct system to deliver air to and from the condenser coil, the centrifugal fan air-cooled condenser is probably best suited for this application.
2!
Evaporative Condensers A modification of the air-cooled condenser is the evaporative condenser . )ithin this device, the refrigerant flows through tubes and air is drawn or blown over the tubes by a fan. The difference is that water is sprayed on the tube surfaces. As the air passes over the coil, it causes a small portion of the water to evaporate. This evaporation process absorbs heat from the coil, causing the refrigerant vapor within the tubes to condense. The remaining water then falls to the sump to be recirculated and used again. ub cooling of the refrigerant can be accomplished by piping the condensed li'uid back through another few rows of coil tubing, located either in the condenser airstream or in the water sump, where additional heat transfer reduces the temperature of the li'uid refrigerant.
2K
A cooling tower is a device commonly used to cool condensing water. n this design, warm water is sprayed over fill in the cooling tower while a propeller fan draws outdoor air upward through the fill. The movement of air through the spray causes some of the water to evaporate, a process that cools the remaining water. This cooled water then falls to the tower sump to be returned to the condenser. The final temperature of the water leaving the tower is determined, in part, by the humidity of the outdoor air. f the outdoor air is dry, the final water temperature can be considerably lower than the ambient dry-bulb temperature. f the outdoor air is humid, however, the final temperature will be near the ambient dry-bulb temperature. )hile a cooling tower can reclaim much of the condensing water, it cannot reclaim it all. The evaporation process uses up water to dissipate heat contributed by the cooling load plus the heat of compression. n addition, as the water evaporates, the dissolved minerals and water treatment chemicals become concentrated in the sump. To prevent this solution from becoming concentrated and possibly corrosive, water is periodically bled from the sump and an e'ual amount of fresh water is added. n the past, some water-cooled condensers used water from either a municipal or a natural water supply as the condensing water. After re(ecting the condenser heat to this water, it was dumped into the sewer or back into the body of water. /nvironmental and economic restrictions have made this method uncommon. *inally, a geothermal well system can be used to re(ect the heat from the condenser by circulating the condensing water through a series of underground pipes. This method takes advantage of the naturally-cool ground temperatures.
3E
Condenser Control Condenser capacity is influenced by: 0
Temperature difference between refrigerant and cooling media
0
*low rate of cooling media through condenser
0
*low rate of refrigerant through condenser
Condenser Control The heat re(ection capacity of a condenser is influenced by 1" the temperature difference between the refrigerant and the cooling media air, water, or other fluid", 2" the flow rate of the cooling media through the condenser, and 3" the flow rate of the refrigerant through the condenser. To balance the rate of heat re(ection in the condenser" with the changing system load, at least one of these variables may be controlled.
/vaporators+ The second ma(or component to be discussed is the evaporator . The evaporator is a heat exchanger that transfers heat from air, water, or some other fluid to the cool li'uid refrigerant.
Two common types of evaporators are the finned-tube and the shell-and-tube.
31
Finned-ube Evaporators A finned-tube evaporator includes rows of tubes passing through sheets of formed fins. Cool, li'uid refrigerant flows through the tubes, cooling the tube and fin surfaces. As air passes through the coil and comes into contact with the cold fin surfaces, heat is transferred from the air to the refrigerant. This heat transfer causes the refrigerant to boil and leave the evaporator as vapor.
32
To provide uniform heat transfer throughout the coil, the li'uid refrigerant distributed to the coil tubes in several parallel circuits. A distributor is used ensure uniform refrigerant distribution through these multiple coil circuits. distributes the li'uidvapour refrigerant mixture to the coil through several tubes e'ual length and diameter.
is to t of
As the refrigerant passes through the tubes of the coil, the li'uid refrigerant absorbs heat from the air, causing it to boil off into vapor. The refrigerant vapor leaves the coil tubes and collects in a suction header . /ach distributor has an allowable range of refrigerant flow rates that define its stable operating range. As the si$e of the evaporator coil increases, it may be necessary to use more than one distributor to feed li'uid refrigerant to the coil.
33
nside the final length of tubes#the location where the temperature difference between the refrigerant and the air is highest#this larger temperature difference accelerates the rate of heat transfer and the refrigerant vapour absorbs even more heat. )hen the li'uid refrigerant has completely evaporated, this additional heat gain to the vapour is called superheating. uperheating the refrigerant vapour to " shifts it away from the li'uidvapor region and ensures that the refrigerant vapour is completely free of li'uid prior to travelling to the compressor.
Evaporator Control Evaporator capacity is influenced by: 0
Temperature difference between refrigerant and air or water being cooled
0
*low rate of air or water through evaporator
0
*low rate of refrigerant through evaporator
34
Evaporator Control The rate of heat exchange within an evaporator is governed by 1" the temperature difference between the refrigerant and the air or water being cooled, 2" the flow rate of the air or water through the evaporator, and 3" the flow rate of the refrigerant through the evaporator. n comfort-cooling applications, it is necessary to balance the capacity of the system with the ever-changing load. The flow rate and temperature of the air or water being cooled are typically controlled to respond directly to the system load. A constantvolume system delivers a constant 'uantity of air to the space and, to maintain the re'uired space temperature at all load conditions, varies the temperature of this air. n contrast, a variable air- volume 4A4" system delivers air at a constant temperature and varies the airflow to maintain the re'uired space temperature at all load conditions. These are variables that the evaporator must respond to rather than directly control. The most common method of controlling the capacity of the evaporator at part load is to control the temperature andor flow rate of the refrigerant through the system by unloading or cycling compressors. To provide stable part-load operation and balance compressor unloading with the capacity of the evaporator, some direct form of evaporator capacity control may also be re'uired.
CO&R'55OR Introduction: The purpose of the compressor in the $apor compression cycle is to compress the low pressure dry gas from the e$aporator and raise its pressure to that of the condenser. +ompressors may &e di$ided into two types positi$e displacement and dynamic as 'ositi$e displacement types compress discrete $olumes of low pressure gas &y physically reducing the $olumes causing a pressure increase whereas dynamic types raise the $elocity of the low)pressure gas and su&se>uently reduce it in a way which causes a pressure increase. # compressor is the most important and often the costliest component -Typically 3E to 4E percent of total cost of any $apor compression refrigeration system -;+R0. The function of a compressor in a ;+R0 is to continuously draw the refrigerant $apor from the e$aporator so that a low pressure and low temperature can &e maintained in the e$aporator at which the refrigerant can &oil eGtracting heat from the refrigerated space. The compressor then has to raise the pressure of the refrigerant to a le$el at which it can condense &y re=ecting heat to the cooling medium in the condenser. # typical refrigeration system consists of se$eral &asic components such as compressors" condensers" eGpansion de$ices" e$aporators" in addition to se$eral accessories such as controls" lters" driers" oil separators etc. @or eMcient operation of the refrigeration system it is essential 35
that there &e a proper matching &etween $arious components. Oefore analyJing the &alanced performance of the complete system it is essential to study the design and performance characteristics of indi$idual components. Gcept in special applications the refrigeration system components are standard components manufactured &y industries specialiJing in indi$idual components. 8enerally for large systems depending upon the design specications components are selected from the manufacturersD catalogs and are assem&led at site. $en though most of the components are standard o the shelf items sometimes components such as e$aporator may &e made to order. 0mall capacity refrigeration systems such as refrigerators room and pac(age air conditioners water coolers are a$aila&le as complete systems. Doub"e acting a00onia co0re--or and -tea0 engine.
n this case the manufacturer himself designs or selects the system components" assem&les them at the factory" tests them for performance and then sells the complete 3!system as a unit. The rst refrigeration piston compressors were &uilt in the middle of the 1Kth century and e$ol$ed from the steam engines which pro$ided the prime mo$er. +onstruction at rst was dou&le acting &ut there was diMculty in maintaining gas tightness at the piston rod so the design e$ol$ed further into a single acting machine with the cran(case at suction inlet pressure lea$ing only the rotating shaft as a possi&le source of lea(age and this was sealed with a pac(ed gland. Today" the ma=ority of compressors are completely sealed with the motor enclosed.
C"a--i6cation o> co0re--or-: +ompressors used in refrigeration systems can &e classied in se$eral waysY #. Oased on the wor(ing principleY 1. 'ositi$e displacement type. 2. Rotor dynamic type. n positi$e displacement type compressors compression is achie$ed &y trapping a refrigerant $apor into an enclosed space and then reducing its $olume. 0ince a Ged amount of refrigerant is trapped each time its pressure rises as its $olume is reduced. /hen the pressure rises to a le$el that is slightly higher than the condensing pressure then it is eGpelled from the enclosed space and a fresh charge of low)pressure refrigerant is drawn in and the cycle continues. ,owe$er" since the operating speeds are normally $ery high the Bow appears to &e almost steady on macroscopic time scale. 0ince the Bow is pulsating on a microscopic time scale positi$e displacement type compressors are prone to high wear $i&ration and noise le$el. epending upon the construction positi$e displacement type compressors used in refrigeration and air conditioning can &e classied intoY a. Reciprocating type.
36
&. Rotary type with sliding $anes -Rolling piston type or multiple $ane type. c. Rotary screw type -0ingle screw or twin)screw type. d. :r&ital compressors. e. #coustic compressors. n Rotor dynamic compressors the pressure rise of refrigerant is achie$ed &y imparting (inetic energy to a steadily Bowing stream of refrigerant &y a rotating mechanical element and then con$erting into pressure as the refrigerant Bows through a di$erging passage. 7nli(e positi$e displacement type the rotor dynamic type compressors are steady Bow de$ices hence are su&=ected to less wear and $i&ration. epending upon the construction rotor dynamic type compressors can &e classied intoY i. Radial Bow type. ii. #Gial Bow type. +entrifugal compressors -#lso (nown as tur&o)compressors are radial Bow type rotor dynamic compressors. These compressors are widely used in large capacity refrigeration 3Kand air conditioning systems. #Gial Bow compressors are normally used in gas li>uefaction applications. O. Oased on arrangement of compressor motor or eGternal dri$eY 1. :pen type. 2. ,ermetic -or sealed type. 3. 0emi)hermetic -or semi)sealed type. n open type compressors the rotating shaft of the compressor eGtends through a seal in the cran(case for an eGternal dri$e. The eGternal dri$e may &e an electrical motor or an engine -e.g. diesel engine. The compressor may &e &elt dri$en or gear dri$en. :pen type compressors are normally used in medium to large capacity refrigeration system for all refrigerants and for ammonia -ue to its incompati&ility with hermetic motor materials. :pen type compressors are characteriJed &y high eMciency BeGi&ility &etter compressor cooling and ser$icea&ility. ,owe$er" since the shaft has to eGtend through the seal refrigerant lea(age from the system cannot &e eliminated completely. ,ence refrigeration systems using open type compressors re>uire a refrigerant reser$oir to ta(e care of the refrigerant lea(age for some time and then regular maintenance for charging the system with refrigerant changing of seals gas(ets etc. /e use the ,ermetic piston compressor type in our pro=ect.
$er0etic co0re--or-:
3<
# hermetic compressor is a direct compressor a direct)connected motor compressor assem&ly enclosed within a steel housing. t is designed to pump low)pressure refrigerant gas to a higher pressure. # hermetic container is one that is tightly sealed so no gas or li>uid can enter or escape. /elding seals the container. Tecumseh hermetic compressors ha$e a low)pressure shell or housing. This means that the interior of the compressor housing is su&=ect only to suction pressure. t is not su&=ect to the discharge created &y the piston stro(e. This point is emphasiJed to stress the haJard of introducing high pressure gas into the compressor shell at pressures a&o$e 15E psig. #. otor rotor. O. otor stator. +. +ompressor cylinder. . +ompressor piston. . +onnecting rod. @. +ran(shaft. 8. +ran( throw. ,. +ompressor shell. . 8lass sealed electrical connection. The suction is drawing into the compressor shell then to and through the electric motor that pro$ides power to the cran(shaft. The cran(shaft re$ol$es in its &earings" dri$ing the piston or pistons in the cylinder or cylinders. The cran(shaft is designed to carry oil from the oil pump in the &ottom of the compressor to all &earing surfaces. Refrigerant gas surrounds the compressor cran(case and the motor as it is drawn through the compressor shell and into the cylinder or cylinders through the suction mu[er and suction $al$es. The gas is compressed &y the mo$ing piston and is released through the discharge $al$es discharge mu[er and compressor discharge tu&e. The hermetically compressors can &e mo$ed easily from one place to the other place they are highly porta&le. :ne does not ha$e to disassem&le the compressor from the motor and no coupling" &elt and pulley arrangement is in$ol$ed. The whole condenser unit of the refrigeration or the air conditioning unit comprising of the condenser and the compressor can &e mo$ed easily from one place to the other. ts location can &e changed easily. 0ince no coupling" &elt or pulley is in$ol$ed" the maintenance is lesser. The lu&rication system of the hermetically sealed compressor is inherent and no eGternal lu&rication is re>uired unless the fresh gas charging is done. The installation of the hermetically sealed compressor is $ery easy. The suction and discharge connections and the electrical connections are a$aila&le eGternally.
3!
/xpansion 5evices+
An e!pansion device is used to maintain a pressure difference between the highpressure condenser" and low-pressure evaporator" sides of the system established by the compressor. This pressure difference allows the evaporator temperature to be low enough to absorb heat from the air or water to be cooled, while also allowing the refrigerant to be at a high enough temperature in the condenser to re(ect heat to air or water at normally available temperatures.
3K
There are several types of expansion devices, including expansion valves thermostatic or electronic", capillary tubes, and orifices. This clinic will limit its discussion to thermostatic expansion valves T64s". 7ther expansion devices perform essentially the same function.
n addition to maintaining a pressure difference, the thermostatic e!pansion valve controls the 'uantity of li'uid refrigerant entering the evaporator. t ensures that the refrigerant will be completely vapori$ed within the evaporator " and maintains the proper amount of superheat in the system.
4E
Accessories+
Solenoid Valve A solenoid valve is used to stop the flow of refrigerant within the system. These valves are magnetically operated, and an electric winding controls the opening and closing of the valve. The valve is typically a normally-closed type of valve so that it is closed when it is denergi$ed.
41
7ne common use of a solenoid valve is to control the flow of li'uid refrigerant to multiple sections of the evaporator. n this application, a valve is installed in the li'uid line, upstream of the expansion valve for each individually controlled section of the evaporator coil. 8sing the example of a face-split evaporator coil, at lower loads a solenoid valve may be used to shut off the flow of li'uid refrigerant to the top section of the coil. A portion of the air passes through the active lower section and is cooled, while the rest of the air passes through the inactive top section and remains unconditioned. The two airstreams mix downstream of the coil. At higher loads, both sections of the coil are activated.
42
Another common use of a solenoid valve is to enable system pump-down and prevent the refrigerant from migrating through the system when the compressor is shut off. n this application, a single solenoid valve is installed in the li'uid line, upstream of all expansion valves. )hen the compressor is shut off, the evaporator contains a large 'uantity of li'uid refrigerant. This can present a problem if some of the refrigerant drains into the suction line and slugs the compressor when it starts up again. To prevent this from occurring, many systems pump the refrigerant out of the evaporator and suction line before shutting the compressor off. This is called a pump-down cycle. nstead of shutting the compressor off right away, the solenoid valve is closed to stop the flow of li'uid refrigerant into the evaporator, and the compressor is allowed to run for a short period of time. The compressor pumps the refrigerant from the low-pressure side of the system evaporator and suction line" to the high-pressure side of the system discharge line, condenser, and li'uid line." 43
As the low-pressure side of the system is pumped free of refrigerant, the pressure in that part of the system drops. To end the pump-down cycle, a pressure sensor is used to shut the compressor off when this pressure reaches a predetermined set point. !rior to starting the compressor again, the solenoid valve is opened, allowing the pressure on the low pressure side of the system to increase again. The solenoid valve should be installed as close to the expansion valve as possible. This will minimi$e the pump-down time and allow the li'uid line to be used for storing refrigerant when the system is off.
"i#uid-"ine Filter $rier The next accessory to be discussed, the li#uid-line filter drier , is installed upstream of the solenoid valve and the expansion valve. t prevents moisture water" and foreign matter, introduced during the installation process, from entering the expansion valve and the solenoid valve. Reali$e, however, that there is no substitute for cleanliness during system installation. 9oisture and foreign matter can cause problems in any refrigeration system. )hen water is mixed with refrigerant and oil, and heat is added by the compressor, acids are formed that can damage the valves or compressor. Additionally, certain foreign 44
materials such as copper and brass particles can act as a catalyst in chemical reactions that result in the formation of acids. These acids can corrode system components and cause the oil to sludge. The filter drier should be installed close to the solenoid valve to provide the most protection for the solenoid and expansion valves.
%oisture-&ndicating Sight 'lass A moisture-indicating sight glass is installed in the li'uid line, upstream of the expansion valve, and permits the operator to observe the condition of the refrigerant prior to entering the expansion valve. The value of the sight glass is in its moisture indication ability#the sight glass should not be used to determine system refrigerant charge or sub cooling. Actual temperature and pressure measurements are re'uired to determine proper charge and subcooling. )ith the sight glass installed directly ahead of the expansion valve, it can also be used to detect the presence of bubbles in the li'uid line. This would indicate that some of the li'uid refrigerant has flashed into vapor upstream of the expansion 45
valve. ince the expansion valve is designed to control the flow of li'uid refrigerant only, the presence of refrigerant vapor results in a reduction in the 'uantity of li'uid refrigerant being fed to the evaporator. There are many potential causes of li'uid refrigerant flashing. The sight glass can alert the operator to the condition.
Suction "ine Filter imilar to the li'uid-line filter drier, the suction line filter performs the task of removing foreign matter from the refrigeration system. t is installed in the suction line, (ust upstream of the compressor. The suction filter contains filter media to remove copper filings, flux, dirt, and other foreign matter that may have been introduced during the installation process or as the result of a compressor failure. t protects the compressor parts from the abrasive action that could result if these materials enter the compressor. 5irt can obstruct oil passages, robbing the compressor bearings of lubrication.
46
imilar to the li'uid-line filter drier, the two common types of suction line filters are replaceable core and sealed. The replaceable core type allows the core to be easily changed. The sealed type is completely closed, reducing the chances of refrigerant leaks. Replaceable core suction filters are commonly installed after a compressor failure has occurred. The core is replaced after the foreign matter or acid has been removed from the system. Additionally, suction filters should be installed in all field-assembled systems. 4<
Shutoff Valve Shutoff valves are used to isolate one part of the refrigeration system from the rest. Additionally, they can be used to trap the refrigerant charge in one component of the system, the condenser for example, to permit service or repair to another part of the system. Common uses of shutoff valves include+
• solating the li'uid-line filter drier and suction filter to allow easier core or unit" Replacement
• solating the compressor from the rest of the system to allow for repair or replacement 4!
• solating the charge within the condenser or a receiver to allow access to the rest of the system
Access (ort An access port is used to add refrigerant to the system or for measurement. 7ne access port is typically installed in the li'uid line in a convenient location and is used to charge the system with li'uid refrigerant. t is also used to measure the amount of sub cooling in the system. The suction line typically includes two access ports. 7ne is installed near the compressor and is used to measure suction pressure. The other is located near the
4K
external e'uali$er line connection for the expansion valve, and is used to measure superheat when checking or ad(usting the expansion valve setting.
Review+ )e will now review the main concepts that were covered in the components in a vapour-compression refrigeration system.
!eriod 7ne reviewed the vapour-compression refrigeration cycle using the !- h chart. A cool, low-pressure mixture of li'uid and vapour refrigerant enters the evaporator " and absorbs heat from the relatively warm air or water that is being cooled. This transfer of heat boils the li'uid refrigerant in the evaporator and superheated refrigerant vapour " is drawn to the compressor. The compressor raises the pressure and temperature " high enough that the refrigerant vapour can re(ect heat to another fluid. This hot, high-pressure refrigerant vapour then travels to the condenser where heat is transferred to relatively cool ambient air or cooling water.
5E
This reduction in the heat content of the refrigerant vapour causes it to de superheat, condense into li'uid, and further sub cool before leaving the condenser " for the expansion device. *inally, the high-pressure li'uid refrigerant flows through the expansion device, causing a large pressure drop the line from to " that reduces the pressure of the refrigerant to that of the evaporator. This pressure reduction causes a small portion of the li'uid to boil off, or flash, cooling the remaining refrigerant to the desired evaporator temperature. This cooled refrigerant then enters the evaporator " to repeat the cycle.
!eriod Two discussed the different types of condensers and methods of condenser control. The condenser re(ects heat from the refrigerant to air, water, or some other fluid. The three common types of condensers are air-cooled, water-cooled, and evaporative.
51
!eriod Three presented the different types of evaporators and methods of evaporator control. The evaporator transfers heat from air, water, or some other fluid to the cool li'uid refrigerant. The two common types of evaporators are finned-tube and shelland-tube.
52
!eriod *our reviewed the operation of the expansion device, specifically the thermostatic expansion valve. The expansion device is used to maintain the pressure difference between the high-pressure condenser" and low-pressure evaporator" sides of the system established by the compressor.
n addition, the thermostatic expansion valve T64" controls the 'uantity of li'uid refrigerant entering the evaporator. t ensures that the refrigerant will be completely vapori$ed within the evaporator and maintains the proper amount of superheat in the system.
53
!eriod *ive discussed several accessories commonly used in comfort-cooling applications, including+ solenoid valve, li'uid-line filter drier, moisture-indicating sight glass, suction line filter, hot gas muffler, shutoff valve, and access port. The solenoid valve is used to stop the flow of refrigerant within the system. A li'uidline filter drier prevents moisture and foreign matter from damaging the valves and compressor. The moisture-indicating sight glass permits the operator to observe the condition of the refrigerant within the li'uid line before it enters the expansion device. A suction line filter protects the compressor from foreign matter in the suction line. The hot gas muffler is used to reduce noise and vibration associated with reciprocating compressors. hutoff valves are used to isolate one part of the 54
