PRESENTED BY:
DARSHAL VITHALANI
SUTARIYA ZEEL
RAMANI JAY
ROKAD DARSHIT
COLLEGE OF FOOD PROCESSING TECHNOLOGY AND BIO ENERGY,
ANAND AGRICULTURAL UNIVERSITY,
ANAND-388110.
SUBJECT:
REFRIGERATION AND AIR
CONDITION
FPT B.TECH. (4TH SEM.)
EVAPORATORS
•AT LOW PRESSURE
SIDE OF
REFRIGERATION
SYSTEM
•REFRIGERENT
CHANGES FROM
LIQUID PHASE TO
VAPOUR
•HEAT ABSOPTION
CAPACITY OF AN EVAPORATOR
THE AMOUNT OF HEAT ABSORBED BY IT OVER A GIVEN
PERIOD OF TIME.
HEAT TRANSFER CAPACITY OF AN EVAPORATOR:
Q = UA(T2 - T1) ….. W or J/s
WHERE;
U = OVERALL HEAT TRANSFER COIFICIENT
A = AREA OF EVAPORATOR SURFACE
T2 = TEMPERATURE OF MEDIUM TO BR COOLED
T1 = SATURATION TEMPERATURE OF
REFRIGERENT AT EVAPORATOR PRESSURE
FACTORS AFFECTING THE HEAT
TRANSFER CAPACITY OF AN
EVAPORATOR
1.
MATERIAL
2.
TEMPERATURE DIFFERENCE
3.
VELOCITY OF REFRIGERENT
4.
THICKNESS OF THE EVAPORATOR COIL WALL
5.
CONTACT OF SURFACE AREA
TYPES OF EVAPORATORS
According to type of construction
1.
Bare tube coil evaporator
2.
Finned tube evaporator
3.
Plate evaporator
4.
Shell and tube evaporator
5.
Shell and coil evaporator
6.
Tube in tube evaporator
According to the manner in which liquid refrigerant is fed
1.
Flooded evaporator
2.
Dry expansion evaporator
According to the mode of heat transfer
1.
Natural convection evaporator
2.
Forced convection evaporator
According to operating condition
1.
Frosting evaporator
2.
Non-frosting evaporator
3.
Defrosting evaporator
Bare tube coil evaporator
•Prime surface evaporator
•Easy to clean and defrost
Finned tube evaporator
•Over the bare tube metal fins are
fastened
•s/f contact area is less
•Shape, size, spacing can be
adapted for better rate of heat
transfer
•Limited applications
•Extended surface evaporators
Plate evaporator
•The bare coils are either welded on
the plate or between the two plates
which are welded together
•Used in household refrigerators,
beverage cooler, ice cream cabinets
Shell and tube evaporator
•Contraction is same as shell and tube
type of condenser
•Available in flooded as well as dry
expansion type
•Baffle plates are provided for good
turbulence of liquid
•Capacity 2TR to 250TR
Shell and coil evaporator
Tube in tube evaporator
•Generally dry expansion
evaporators for chilling water
•Used for small capacity
2TR to 10TR
•Restricted to operate above 5
degree calicoes to prevent freezing
problems
•Double tube evaporator
•Refrigerant can flow in outer pipe
and liquid to be cooled can flow in
inner pipe
•The flow of refrigerant can be
parallel or counter
Natural convection
evaporators
•Low velocity and min. hydration is
require
•Velocity of air depends upon temp.
difference
•Circulation of air around coil depends
upon its size shape and location
•The coil should occupy 2/3rd of width
of the path & 3/4th the length of the
box
Forced convection
evaporators
•Air is forced over refrigerant coils
•Fins are provided to increase heat
transfer rate
•More efficient than natural convection
evaporators
•Require less cooling surface and high
evaporator pressure can be used which
save power input to the compressor
Frosting evaporators
•Operates below 0°C
•The frost forms on the evaporator
comes from the moisture of the air
•Cooling efficiency is decreases until
the ice and frost is removed
Non-frosting evaporators
•Operates above 0°C therefore frost
does not forms on evaporators
•Temp. close to cooling 0.6°C to 1°C
•RH from 75-80 % in the cabinet
•This keeps the food fresh & stops
shrinking in weight
DEFROSTING EVAPORATORS
•Frost creates on the coils
when the compressor is
running & melts after the
compressor shuts off
•Temp. of about -7°C to -6°C
•It also keeps high RH of
about 90% to 95%
APPLICATIONS:
 EVAPORATORS ARE USED IN WIDE RANGE OF PROCESS INDUSTRIES, PAPER AND
PULP INDUSTRIES, WINERY, BEVERGARES, FOOD PRESERVATION, ICE PLANTS,
CHEMICAL, POLYMERS AND RESINS, INORGANIC SALTS, ACIDES AND VERITY OF
OTHER MATERIALS.