View
221
Download
0
Category
Preview:
Citation preview
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 1/20
ContentsSummary.................................................................................................................... 3
Introduction................................................................................................................ 4
What is evaporator.................................................................................................. 4
History.....................................................................................................................5
How does evaporator work......................................................................................5
Types of evaporator.................................................................................................... 6
Centrifua! evaporator............................................................................................ 6
"anfactures#........................................................................................................$
%otary evaporator...................................................................................................$
&around..............................................................................................................'
(esin.................................................................................................................. '
)!ooded evaporators................................................................................................*
(irect +,pansion Coi! +vaporator..........................................................................-
Types of evaporator used today...............................................................................-/
Circu!ation evaporators......................................................................................... -/
0atura! Circu!ation evaporators.............................................................................-3
)orced Circu!ation +vaporator...............................................................................-3
Batch pan Evaporators..............................................................................................-4
%isin 1!m +vaporator...........................................................................................-5
)a!!in )i!m +vaporator.......................................................................................... -6
%isin2)a!!in +vaporator....................................................................................... -$
"u!tip!eeect evaporators................................................................................... -'
itated thin 1!m evaporators...............................................................................-'
Conc!usion#............................................................................................................... -*
-
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 2/20
)iure -# Schematic diaram of evaporator................................................................4
)iure /# an e,amp!e of evaporation process.............................................................5
)iure 3# Typica! refrieration Cyc!e............................................................................6
)iure 4# Cutaway imae of HT4 Centrifua! +vaporator.........................................$
)iure 5# &7chi %otavapor %/ with 898 assem:!y ;vertica! water condenser<.... .'
)iure 6# =ooded evaporator.................................................................................... -)iure $# (irect e,pansion coi! evaporator...............................................................--
)iure '# direct e,pansion evaporator......................................................................-/
)iure *# 9ertica! tu:e forcedcircu!ation evaporator................................................-3
)iure -# 0atura! Circu!ation evaporators...............................................................-3
)iure --# )orced Circu!ation +vaporator..................................................................-4
)iure -/# &atch pan +vaporators............................................................................-5
)iure -3# %isin 1!m evaporator..............................................................................-6
)iure -4# )a!!in)i!m +vaporators...........................................................................-$
)iure -5#%isin2)a!!in +vaporator..........................................................................-$
)iure -6# (ou:!eeect fa!!in 1!m evaporator.......................................................-'
)iure -$# >ey e!ement of vertica!thin evaporator..................................................-*
/
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 3/20
Summarys one of the most enery intensive processes used in the dairy? food and chemica!
industries? it is essentia! that evaporation :e approached from the viewpoint of
economica! enery uti!i@ation as we!! as process eectiveness. This can :e done
on!y
if the eAuipment manufacturer is a:!e to oer a fu!! se!ection of evaporation
techno!oy
and systems deve!oped to accommodate various product characteristics? the
percent
of concentration reAuired? and reiona! enery costs.
This hand:ook descri:es the many types of evaporators and operatin options
avai!a:!e throuh the e,perience and manufacturin capa:i!ities of B9.
3
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 4/20
Introduction
What is evaporator
An evaporator is a device used to turn the liquid form of a chemical into its gaseous form. The liquidis evaporated, or vaporized, into a gas.
Figure 1: Schematic diagram of evaporator
Evaporation is a special case of heat transfer to a boiling liquid. This particular heattransfer application is so common and important that it is treated as a separate unit
operation.
The intent is to concentrate a non-volatile solute from a solvent, usually water. This is
done by boiling off the solvent. Concentration by evaporation is normally stopped
before the solute begins to precipitate; if not, the operation is better considered
as crystallization.
Evaporation is usually treated as the separation of a liquid mixture into a liquid product concentrate or thick liquor ! and a vapor byproduct, although in special cases
such as water treating and desalination, the vapor is the product instead of the thic"
liquor.
The evaporator is kind of heat transfer apparatuses where the heat transfer is done :y
forced convection or natura! convection. nd its an important component of
4
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 5/20
refrieration system and air conditionin system.
+vaporation process is reDection of water ;or other !iAuids< :y concentratin the
so!ution. The reAuired time for this process can :y shortened :y increasin the surface
area? the so!ution is e,posed to it? or :y e,posin the so!ution to heatin to a hiher
temperature.
Figure 2: an example of evaporation process
History
The invention of the mu!tip!e eect evaporator is enera!!y credited
to 0or:ert %i!!ieu,. %i!!ieu, deve!oped a mu!tip!e pan evaporation
system for use in suar re1nin. %i!!ieu, was :orn in Eouisiana and
trained in )rance. "ost of his workin career was spent in the F.S.?
a!thouh he !ater returned to +urope where he is :uried in the
famous Bere Eachaise cemetery in Baris. %i!!ieu,Gs achievements
were !itt!e acknow!eded durin his !ifetime? :ecause accordin to
the !aws of the time he was 8a free person of co!or.8 He was a!so the
1rst cousin? once removed? of the painter +dar (eas.
How does evaporator wor )or a :asic refrierant cyc!e shown in 1ure -? which is used in many forms in a!!
common air conditionin? refrieration? heat pump app!ications. It uses a proper
refrierant that has the capa:i!ity to chane phase from !iAuid to as and from as to
5
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 6/20
!iAuid.
)or a home air conditionin e,amp!e? the refrierant enters the compressor is a !ow
pressure coo! as? where it compressed to a hih pressure hot as? then passes to the
condenser. In the condenser coi!? the refrierant phase chanes from hot as at hih
pressure to hot !iAuid at hih pressure. This condensation causes a !are heat reDectionto surroundin.
The !iAuid refrierant is then passed throuh a 1,ed no@@!e or e,pansion device to e,it
as a co!d !iAuid at a !ow pressure. )ina!!y refrierant enters the evaporator at a:out
$ to ' !iAuid and / to 3 vapor.
In the evaporator a very !are amount of heat is a:sor:ed from surroundin ;the indoor
air< causin the !iAuid refrierant to :oi! and turn into a as phase? which is passed to
compressor to repeat the cyc!e aain unti!e the indoor air :e comforta:!e and
sucient!y coo!.
The evaporator works at a constant temperature as !on as the pressure remainsconstant.
Figure !: "ypical refrigeration Cycle
"ypes of evaporator
The evaporators may :e c!assi1ed into a forced convection type or natura! convection
type? dependin on whether the su:stance to :e coo!ed !ows natura!!y :y dierence in
density throuh the heat transfer surfaces of the evaporator or forced :y pump or fan.
6
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 7/20
In some kinds of evaporator? the refrierant =ows in the tu:es and su:stance to :e
coo!ed surroundin it. &ut in other cases? su:stance to :e coo!ed in the tu:es and the
refrierant is in the she!!.
+vaporator are a!so c!assi1ed into =ooded type and dry e,pansion type? dependin on
whether the refrierant covers a!! the surface of heat transfer or some portion of heat
transfer surface is havin as :ein superheated.
Centrifugal evaporator A centrifugal evaporator is a device used in chemical and biochemical laboratories for the efficient
and gentle evaporation of solvents from many samples at the same time, and samples contained in
microtitre plates. If only one sample required evaporation then a rotary evaporator is most often
used. The most advanced modern centrifugal evaporators not only concentrate many samples at the
same time, they eliminate solvent bumping and can handle solvents with boiling points of up to 220
!. This is more than adequate for the modern high throughput laboratory.
Figure #: Cutaway image of H"$#% Centrifugal &vaporator
'anfactures:
!entrifugal evaporators were invented in "#$0s by %avant Inc of &%A, with their mar'et leading
%peed(ac brand. )ther well 'nown manufacturers of centrifugal evaporators are the *erman
company +artin !hrist, abconco !orp. of &%A and *enevac of &-.
(otary evaporator A rotary evaporator or rotavap/"1rotovap is a device used in chemical laboratories for the efficient
and gentle removal of solventsfrom samples by evaporation. 3hen referenced in the chemistry
research literature, description of the use of this technique and equipment may include the phrase
4rotary evaporator4, though use is often rather signaled by other language e.g., 4the sample wasevaporated under reduced pressure4.
$
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 8/20
Figure ): * +,chi (otavapor ($2-- with ./. assem0ly vertical water condenser3
+aground
A simple rotary evaporator system was invented by yman !. !raig./2
It was first commercialized bythe %wiss company 56chi in "#78. )ther common evaporator brands are 9eidolph, abTech, %tuart,
9ydrion %cientific, %:;!), I-A and :<:A. In research the most common form is the " bench=top
unit, whereas large scale e.g., 20=70 versions are used in pilot plants in commercial chemical
operations.
4esign
The main components of a rotary evaporator are>
". A motor unit that rotates the evaporation flas' or vial containing the user?s sample.
2. A vapor duct that is the a@is for sample rotation, and is a vacuum=tight conduit for the vapor
being drawn off the sample.
. A vacuum system, to substantially reduce the pressure within the evaporator system.
B. A heated fluid bath generally water to heat the sample.
'
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 9/20
7. A condenser with either a coil passing coolant, or a 4cold finger 4 into which coolant mi@tures
such as dry ice and acetone are placed.
$. A condensate=collecting flas' at the bottom of the condenser, to catch the distilling solvent
after it re=condenses.
8. A mechanical or motorized mechanism to quic'ly lift the evaporation flas' from the heating
bath.
The vacuum system used with rotary evaporators can be as simple as a water aspirator with a trap
immersed in a cold bath for non=to@ic solvents, or as comple@ as a regulated mechanical vacuum
pump with refrigerated trap. *lassware used in the vapor stream and condenser can be simple or
comple@, depending upon the goals of the evaporation, and any propensities the dissolved
compounds might give to the mi@ture e.g., to foam or 4bump4. !ommercial instruments are
available that include the basic features, and various traps are manufactured to insert between theevaporation flas' and the vapor duct. +odern equipment often adds features such as digital control
of vacuum, digital display of temperature and rotational speed, and vapor temperature sensing.
Flooded evaporators
=ooded evaporator type with =oat contro! va!ve shown in 1. the !iAuid =ow on !ow
passaes passes the tu:es upwords? and :oi!s due to heat adsorption from the warmer
su:stance? which is coo!ed. The resu!ted vapor so formed on :oi!in :u::!es up in =ash
cham:er? where separates !iAuid from vapor.
Separated vapor passes to compressor? and !iAuid =ows :ack to the evaporator. The
=ash cham:er co!!ects the vapor formed :y !iAuid refrierant :oi!in in the evaporator?
and vapor o:tained in the e,pansion device.
In a =ooded type evaporator refrierant !iAuid !eve! is maintained. )!oat va!ve is used as
thrott!in device.
The heat transfer eciency increases :ecause the entire surface is in contact with the
!iAuid refrierant. &ut the refrierant chare is re!ative!y !are as compared to dry
e,pansion type.
The accumu!ator or =ash cham:er is used to prevent !iAuid Cray over to compressor.
The evaporator coi! is contacted to accumu!ator and the !iAuid =ow from the
accumu!ator to the evaporator coi! is enera!!y :y ravity. The vapor formed :y the
vapori@in of the !iAuid in the coi! :ein !ihter rises up and passes on to the top of the
accumu!ator from where it enters the suction !ine.
*
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 10/20
In some cases !iAuid e!iminators are provided in the accumu!ator top to prevent the
possi:!e carry over of !iAuid to suction !ine. !so a !iAuid suction heat e,chaner is used
on the suction !ine to superheat the suction vapor.
Figure 5: 6ooded evaporator
4irect &xpansion Coil &vaporator
the evaporator is ca!!ed direct e,pansion evaporator if the coi!s of the evaporator with
refrierant passin throuh them are used direct!y to coo! air :y natura! or forced
convection.
To improve the !u:ricatin oi! return to the compressor? the refrierant feed comes
throuh the thermostatic e,pansion va!ve more often !ocated at the top particu!ar!y for
)-/? )//. ir is :!own over the outside of the 1nned tu:es.
The direct e,pansion coi! is preferred )or air conditionin purposes? where the
evaporator is very near to the compressors. This is direct method of coo!in the
su:stance and? therefore Auite e1cient. it is preferred to chi!! the water and pump it to
the aircoo!in coi!? when the coi! has to :e !ocated very far away from the compressor.
There is possi:i!ity of refrierant !eakae for !on distances? and the cost of therefrierant wou!d :e hih. !so the pressure drop in the !ine wou!d decrease evaporator
coecient of performance and eciency.
The e,pansion va!ve contro!s the rate of the refrierant to evaporator in such a way that
a!! the !iAuid is vapori@ed and the vapor is a!so superheated to a !imited e,tent. The
inside of evaporator is far from dry :ut wetted with !iAuid.
-
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 11/20
!! the same? this type is ca!!ed dry e,pansion to distinuish it from =ooded system and
a!so pro:a:!y :ecause :y the time the refrierant reaches the evaporator out!et it from
=ooded system and a!so pro:a:!y :ecause :y the refrierant reaches the evaporator
out!et it is no more wet :ut dry superheated vapor.
Figure 7: 4irect expansion coil evaporator
--
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 12/20
Figure 8: direct expansion evaporator
"ypes of evaporator used today
Circulation evaporatorsCirculation evaporators are a type of evaporating unit designed to separate mi@tures unable to be
evaporated by a conventional evaporating unit. !irculation evaporation incorporates the use of
both heat e@changers and flash separation units in conCunction with circulation of the solvent in order
to remove liquid mi@tures without conventionalboiling. There are two types of !irculation
:vaporationD ;atural !irculation :vaporators and Eorced !irculation :vaporators, both of which are
still currently used in industry today, although forced !irculation systems, which have a circulation
pump as opposed to natural systems with no driving force, have a much wider range of appropriate
uses.
-/
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 13/20
Figure 9: /ertical tu0e forced$circulation evaporator3
atural Circulation evaporators
In Natural Circulation evaporators, short vertical tubes, typically 1-2 m long and 50- 100 mm in
diameter, are arranged inside the tubes, and the product is concentrated. The concentrated liquid
falls back to the base of the vessel through a central annular section. A shell-and-tube heat
exchanger can be provided outside the main evaporation vessel to preheat the liquid feed. The most
common application for this type of unit is as a reboiler at the base of a distillation column. νNatural
Circulation evaporators
Figure 1-: atural Circulation evaporators
-3
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 14/20
Forced Circulation &vaporator
Forced Circulation Evaporator The forced circulation evaporator was developed for processing
liquors which are susceptible to scaling or crystallizing. Liquid is circulated at a high rate through the
heat exchanger, boiling being prevented within the unit by virtue of a hydrostatic head maintained
above the top tube plate. As the liquid enters the separator where the absolute pressure is slightlyless than in the tube bundle, the liquid flashes to form a vapor.
Figure 11: Forced Circulation &vaporator
Batch pan Evaporators
Batch pan Evaporators The batch pan evaporator is one of the simplest and oldest types of
evaporators used in food industry. Now-a-days it is outdated technology, but it still used in a few
limited applications, such as the concentration of jams and jellies where whole fruit is present and in
processing some pharmaceutical products. Up until the early 1960's, batch pan also enjoyed wideuse in the concentration of corn syrups. In batch pan evaporator the product is heated in a steam
jacketed spherical vessel. The heating vessel may be open to the atmosphere or connected to the
condenser and vacuum. The heat transfer area per unit volume is in batch pan evaporator is small.
Thus, the residence time normally is many hours. Therefore, it is essential to boil at low
temperatures and high vacuum when a heat sensitive or thermo degradable product is involved.
-4
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 15/20
Figure 12: +atch pan &vaporators
(ising ;lm &vaporator
Rising-film Evaporators These are considered to be the first 'modern' evaporator used in the industry,
the rising film unit dates back to the early 1900's. The rising film principle was developed
commercially by using a vertical tube heated from the outside with steam. Liquid on the inside of the
tube is brought to a boil, with the vapor generated forming a core in the center of the tube. As thefluid moves up the tube, more vapors are formed resulting in a higher central core velocity those
forces the remaining liquid to the tube wall.
-5
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 16/20
Figure 1!: (ising ;lm evaporator
Falling Film &vaporator
Falling-Film Evaporators The falling-film evaporators has a thin liquid film moving downward under
gravity on the inside of the vertical tubes. The design of such evaporators is complicated by the fact
that distribution of liquid in a uniform film flowing downward in a tube is more difficult to obtain than
an upward-flow system such as in a rising- film evaporator. This is accomplished by the use of
specially designed distribution or spray nozzles. The falling-film evaporators allow a greater number
of effects then the rising-film evaporator. The falling-film evaporator can handle more viscous liquids
than the rising film type. This type of evaporators is best suited for highly heat sensitive products
such as orange juice
-6
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 17/20
Figure 1#: Falling$Film &vaporators
(ising<Falling &vaporator
Rising/Falling Evaporator In the rising/falling evaporator, the product is concentrated by circulation
through a rising-film section followed by a falling-film section of the evaporator. The product is first
concentrated as it ascends through a rising tube section, followed by pre concentrated product
descending through a falling-film section, there it attains its final concentration.
Figure 1):(ising<Falling &vaporator
-$
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 18/20
'ultiple$e=ect evaporatorsFn!ike sin!estae evaporators? these evaporators can :e composed of up to seven
evaporator staes ;eects<. The enery consumption for sin!eeect evaporators is
very hih and is most of the cost for an evaporation system. Buttin toether
evaporators saves heat and thus reAuires !ess enery. ddin one evaporator to the
oriina! decreases enery consumption to 5. ddin another eect reduces it to33 and so on. heatsavinpercent eAuation can :e used to estimate how much
one wi!! save :y addin a certain amount of eects.
The number of effects in a multiple=effect evaporator is usually restricted to seven because after that,
the equipment cost approaches the cost savings of the energy=requirement drop.
Figure 15: 4ou0le$e=ect falling ;lm evaporator
!ondensing vapors from flash tan' 5" heat evaporator A2. "Ffeed, 2Fproduct, Fsteam, BFvapors
*gitated thin ;lm evaporators Agitated thin=film evaporation has been very successful with difficult=to=handle products. %imply
stated, the method quic'ly separates the volatile from the less volatile components using indirect
heat transfer and mechanical agitation of the flowing product film under controlled conditions. The
separation is normally made under vacuum conditions to ma@imize GT while maintaining the most
favorable product temperature, and to ma@imize volatile stripping and recovery.
Agitated thin=film evaporators are attractive for the concentration, distillation, stripping or deodorization of
liquids in a broad variety of chemical=process=industries !HI applications where the process streams aretemperature sensitive and must have only brief e@posure to heat, viscous, or tend to foul or foam.
-'
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 19/20
Figure 17: >ey element of vertical$thin evaporator
.
-*
7/23/2019 Types of Evaporator in Air Conditioning
http://slidepdf.com/reader/full/types-of-evaporator-in-air-conditioning 20/20
Conclusion:Whi!e the desin criteria for evaporators are the same reard!ess of the industry
invo!ved? two Auestions a!ways e,ist# is this eAuipment :est suited for the duty? and
is the eAuipment arraned for the most ecient and economica! useJ s a resu!t?
many types of evaporators and many variations in processin techniAues have :een
deve!oped to take into account dierent product characteristics and operatin
parameters.
When you are in industry you reAuired a machine which is most ecient and
economica! for your need. So thats why there are many dierent types evaporator
avai!a:!e in market. +ach evaporator has its on advantae or disadvantae. +very
evaporator manufactures provide a chart with evaporator :asic temperature?
pressures and properties. There are varieties of evaporator from you can choosewhich evaporator is most appropriate for your Do:.
/
Recommended