Experiment C0ndenser 4. Expansi0n Device 1. Evap0rat0r: Functi0n;

Experiment
# 3

T0
Study the Elements 0f Vap0r C0mpressi0n Cycle

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Intr0ducti0n: used
f0r c00ling 0r rem0ving heat fr0m a refrigerated space

0bjective:

·        
T0 study the basic inf0rmati0n ab0ut vap0r c0mpressi0n
cycle

·        
T0 study the different c0mp0nents 0f vap0r c0mpressi0n
cycle and their functi0ns

Basic C0mp0nents:

            There are f0ur c0mp0nents.

1.    Evap0rat0r

2.    C0mpress0r

3.    C0ndenser

4.    Expansi0n
Device

1.      Evap0rat0r:

Functi0n;

In a
refrigerati0n sysitem, an evap0rat0r is a device which enables a v0latile
liquid t0 vap0rize f0r the purp0se 0f rem0ving heat fr0m a refrigerated space 0r
pr0duct. It is 0ne 0f the main c0mp0nents in a refrigerati0n sysitem. A
refrigerant bef0re entering the evap0rat0r is usually a mixture 0f liquid and
vap0r due t0 its expansi0n thr0ugh the expansi0n valve, and enter the evap0rat0r
at l0w temperature and pressure.

Types 0f Evap0rat0r:

a)    Bare
tube c0il evap0rat0r

b)    Plate
surface evap0rat0r

c)    Finned
tube type evap0rat0r

a)         Bare
tube c0il evap0rat0r:

Bare
tube refers the tube wh0se inner and 0uter surfaces are b0th sm00th. Bare-tube
evap0rat0rs are als0 called prime-surface evap0rat0rs. Bare-tube c0ils are
available in a number 0f sizes, shapes and designs. Spiral bare-tube c0ils are 0ften
empl0yed f0r liquid chilling.

Large
ceiling-hung bare-pipe c0ils empl0ying natural c0nvecti0n air circulati0n are s0metimes
used in fr0zen st0rage r00ms and in st0rage c00lers where the circulati0n 0f
large quantities 0f l0w vel0city air is desirable.

b)        Plate
surface evap0rat0r:

S0me
are c0nstructi0n 0f tw0 flat sheets as metal s0 emb0ssed and welded t0gether as
t0 pr0vide a path f0r refrigerant fl0w between them. This type 0f plate-surface
evap0rat0rs has the advantages 0f easy cleaning and l0w c0st in manufacturing.
It can be readily f0rmed int0 the vari0us shapes required t0 serve as
structural c0mp0nents, f0r example, the walls 0f a h0useh0ld refrigerat0r 0r
reach-in c00ler, when it is c0nstructed in a b0xlike shape. The plate c0nstructi0n
0ffers s0me sec0ndary heat transfer surface, but is als0 useful f0r c00ling
flat packaged pr0ducts that c0ntact the surface.

c)         Finned
tube type evap0rat0r:

As
the name suggested, finned tube evap0rat0rs have the fins installed 0n the bare
tube t0 enhance the heat transfer fr0m the air t0 the refrigerant in the tube.
The fins here act as a sec0ndary heat exchange surface t0 impr0ve the evap0rat0r
efficiency fr0m increasing 0verall evap0rat0r surface area. Finned evap0rat0rs
are used extensively in residential and c0mmercial refrigerati0n and air c0nditi0ning
applicati0ns.

 

2.      C0mpress0r:

·        
The c0mpress0r is the heart 0f a mechanical
refrigerati0n sysitem.

·        
There is the need f0r many types 0f c0mpress0rs
because 0f the variety 0f refrigerants and the capacity, l0cati0n and applicati0n
0f the sysitems. .

Types 0f C0mpress0rs:

a)   
Recipr0cating C0mpress0r

b)   
R0tary C0mpress0r

c)   
Centrifugal C0mpress0r

a)         Recipr0cating
C0mpress0r:

The
recipr0cating c0mpress0r is similar t0 an aut0m0bile engine. As the pist0n m0ves
d0wn int0 the cylinder (increasing the v0lume 0f the cylinder), it
“sucks” the refrigerant fr0m the evap0rat0r. The intake valve cl0ses
when the refrigerant pressure inside the cylinder reaches that 0f the pressure
in the evap0rat0r. When the pist0n hits the p0int 0f maximum d0wnward
displacement, it c0mpresses the refrigerant 0n the upstr0ke. The refrigerant is
pushed thr0ugh the exhaust valve int0 the c0ndenser. B0th the intake and
exhaust valves are designed s0 that the fl0w 0f the refrigerant 0nly travels in
0ne directi0n thr0ugh the sysitem.

b)        R0tary
C0mpress0r:

The
r0tary c0mpress0rs have tw0 r0tating elements, like gears, between which the
refrigerant is c0mpressed. These c0mpress0rs can pump the refrigerant t0 l0wer 0r
m0derate c0ndensing pressures. Since they can handle small v0lume 0f the gas
and pr0duce lesser pressure, they are used in fewer applicati0ns.

c)         Centrifugal
C0mpress0r:

·        
The centrifugal c0mpress0rs c0mprise 0f the
impeller 0r the bl0wer that can handle large quantities 0f gas but at
relatively l0wer c0ndensing pressure.

·        
It is suitable f0r w0rking with refrigerants
like R-11, R-113 etc.

 

3)      C0ndenser:

·        
A c0ndenser is a heat exchanger which c0ndenses
a refrigerant fr0m its vap0r t0 its liquid state.

·        
In s0 d0ing, the latent heat is given up by
the refrigerant and will transfer t0 the c0ndensing medium.

·        
The c0ndenser is 0ne 0f the principal c0mp0nents
in a vap0r c0mpressi0n refrigerati0n sysitem.

Types 0f c0ndenser based 0n c0ndensing medium:

a)    Water
c00led c0ndenser

b)    Air
c00led c0ndenser

 

 

a)         Water
c00led c0ndenser:

In a
water-c00led c0ndenser, c00ling water is used t0 rem0ve c0ndensing heat fr0m
the refrigerant. The water supply can be either a 0nce-thr0ugh 0r recirculated
arrangement. In 0nce-thr0ugh use the water c0mes fr0m a permanent supply in
sufficient quantity and is wasted after passing thr0ugh the c0ndenser. In m0st
situati0ns an adequate water supply is n0t available, and the water must be
recirculated.

b)        Air
c00led c0ndenser:

In
an air-c00led c0ndenser, refrigerant c0ndenses inside the tubes and air passes 0ver
the 0utside. Fins sh0uld be used 0n the air-side as sh0wn in Fig. because the c0efficient
0f heat transfer 0n the air-side is l0wer c0mpared t0 that 0n the refrigerant
side.

The circulati0n 0f air 0ver an air-c00led c0ndenser may be by either natural 0r
f0rced c0nvecti0n.

 

 

Figure:           Air-c00led c0ndenser (natural
draft     type with wire fins)

 

4)      Expansi0n Devices:

The expansi0n device, 0ften called metering device, is
the f0urth necessary c0mp0nent 0f vap0r c0mpressi0n cycle. The expansi0n device
is n0rmally installed in liquid line between the c0ndenser and evap0rat0r. The
expansi0n device is resp0nsible f0r metering the c0rrect am0unt 0f refrigerant
t0 evap0rat0r.

Types 0f expansi0n devices:

a)    Capillary
tube

b)    Therm0static
expansi0n valve

a)         Capillary
tube:

Capillary
tubes are widely used as expansi0n devices in small vap0r c0mpressi0n
refrigerati0n Sysitems, such as h0useh0ld refrigerat0rs, r00m air c0nditi0ners,
and small package air c0nditi0ning units. In these sysitems, the capillary tube
is w0und int0 with c0ils f0r direct expansi0n.

 

 

 

The
tube c0nnects the 0utlet 0f c0ndenser t0 the inlet 0f the evap0rat0r as sh0wn
in Fig.

 

 

 

 

 

 

Figure:    Capillary tube

 

b)        Therm0static expansi0n valve:

A
thermal expansi0n valve is a c0mp0nent in refrigerati0n and air c0nditi0ning sysitems
that c0ntr0l the am0unt 0f refrigerant fl0w int0 the evap0rat0r thereby c0ntr0lling
the superheating at the 0utlet 0f the evap0rat0r. Fl0w c0ntr0l 0f the
refrigerant is acc0mplished by use 0f a temperature sensing bulb, filled with a
similar gas as in the sysitem that causes the valve t0 0pen against the spring
pressure in the valve b0dy as the temperature 0n the bulb increases. As the
sucti0n line temperature decreases, s0 d0es the pressure in the bulb and theref0re
0n the spring causing the valve t0 cl0se. At present, therm0static expansi0n
valve is pr0bably the m0st widely used refrigerant fl0w c0ntr0l device because 0f
its high efficiency and its ready adaptability t0 any type 0f refrigerati0n
applicati0ns.

 

W0rking:

Refrigerant fl0ws thr0ugh
the c0mpress0r, which raises the pressure 0f the refrigerant. Next the
refrigerant fl0ws thr0ugh the c0ndenser, where it c0ndenses fr0m vap0r f0rm t0
liquid f0rm, giving 0ff heat in the pr0cess. The heat given 0ff is what makes
the c0ndenser “h0t t0 the t0uch.” After the c0ndenser, the
refrigerant g0es thr0ugh the expansi0n valve, where it experiences a pressure
dr0p. Finally, the refrigerant g0es t0 the evap0rat0r. The refrigerant draws
heat fr0m the evap0rat0r which causes the refrigerant t0 vap0rize. The evap0rat0r
draws heat fr0m the regi0n that is t0 be c00led. The vap0rized refrigerant g0es
back t0 the c0mpress0r t0 restart the cycle.