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Design o f Air coo led evapo rator manual ly
Air cooling evaporators for cold rooms, blast freezers, air-conditioning, etc., will have
finned pipe coils in all but very small coolers, there will be fans to blow the air over the
coil. Construction materials will be the same as for air-cooled condensers. Aluminumfins on copper tube are the most common for the halocarbons, with stainless steel or
aluminum tube for ammonia. Frost or condensed water will form on the fin surface and
must be drained away. To permit this, fins will be vertical and the air flow horizontal,
with a drain tray provided under. The size of the tube will be such that the velocity of
the boiling fluid within it will cause turbulence to promote heat transfer. Tube
diameters will vary from 9 mm to 32 mm, according to the size of coil. Fin spacing
will be a compromise between compactness (and cost) and the tendency for the spaces
to block with condensed moisture or frost. Spacings will vary from 2 mm on a compact
air-conditioner to 12 mm on a low-temperature cold-room coil.
We will design manually and by Techinsolve software
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Evaporator Design :
From the psychrometric chart:
Inlet condition:
dbta in=380c & wbta in=33
0cha in=114.15kj/kg & Wa 1=0.01585 kgw/kga
TDP=21.20c
Outlet condition:
C.S.H.F=0.40 & RH=100%ha out=90 kj/kg
Cooling load:
Qc =a ha in ha out)
123 =a (114.15 90) a=
5.02kg/sec.
Coil design:
:side (ref.)TubeFor
( )
( )
:For air side
* + ( )
( )
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R=0.75 kj/kg.k
Ts1 √
√
Ts1 =30.56
0
c
Ts1 ˃TDP wet surface
Ts2 √
√
Ts2 =25.450
c
∆Trm=
=
= 20.9 0c
Ai=
=
= 3 m2
Ao=Ai*(18.5)= m2
Nr=6
ref =
0.898=
Nc 26
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NC=
H =26*0.0254 = 0.66 m
Aface=
=1.731 m2
Aface=H*LL = 2.62 m
Tube length:
L =
Nt = 24 tubes
Fin calculations
Assume
⁄
(
)
( )
From chart
Assume w=15cm
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)
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Techn isolv e Software for Evaporator coi l design
Manufactur ing design proc edure:
1st Step:
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2nd Step:
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3rd Step (Run Calculation from F9 button or button):
Coil Manufacturing Report
Recoil (5/8 inch - 38.1x50.8)
1016 x 1264 4r 6f 40c
DX 15938 / 20 / 04 / 6.00 / 1264 Cu/GI (40)
Areas and VolumesAo = 86.919 m²
Ao' = 16.921 m²/face m²-rows
Ai = 5.389 m²
Vi = 20.9 Litre
Pipe ConnectionsSize = 67 mm
Heat Transferho = 44.102 W/m²°C
Ui = 3.780 kW/m²°CUo = 36.800 W/m²°C
Ntu = 0.434
Cr = 0.000
Qt = e x Qmax
= 0.352 x 350.216 = 123.242 kW
Air Side DutyQt = ma (hao - hai)
= 3.504 (87.49 - 122.66) = -123.242 kW
Qs = ma x Cpa (dbo - dbi)
= 3.504 x 1.066 (28.3 - 38.0) = -36.308 kWRate = 39.156 kW/cms
Psychrometrics
Bypass factor = 0.358
Apparatus Dew Point = 22.8 °C
Refrigerant (R134a) DutySuperheat = 7.5 °C
Mass flow = 0.790 kg/s (approx)
Mass flux = 101.7 kg/sqm.s (approx)
Velocity = 0.080 m/s
Qt = mr x dh= 0.790 x 156 = 123.26 kW
Dimensions
Height 1016.0 mm
Length 1264.0 mm
Depth 152.4 mm
Rows 4
Fins 6.00 fpi
Weight 135.4 kg
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CircuitingTubes High 20
Tube Count 80
Circuits 40
Circuit Basis Tubes high
Tubes/Circuits 2
Unlinked tubes 0
Serpentine 2
Eq Length 3.8 mConnections Same end
Tube (Staggered Pattern)ID 15.723 mm
OD 16.586 mm
Sx 38.100 mm
Sy 50.800 mm
FinThickness 0.200 mm
Area factor 1.000 mm
MaterialFin Cu
Tube Cu
Casing GI
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Psychrometric Chart :
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Condenser
Condenser is an important component of any air conditioning system. In a typical
refrigerant condenser, the refrigerant enters the condenser in a superheated state. It is
first de-superheated and then condensed by rejecting heat to an external medium. The
refrigerant may leave the condenser as a saturated or a sub-cooled liquid, depending
upon the temperature of the external medium and design of the condenser.
Classif icat ion of con densers (Based on th e external f luid) : Air cooled condensers (will be used in our case study so we will concentrate on it).
Water cooled condensers (discussed before in chapter 2).
Evaporative condensers (discussed before in chapter 2).
Air cooled condensers:
The circulation of air over the condenser surface is maintained by using a fan or a
blower. These condensers normally use fins on air-side for good heat transfer. The fins
can be either plate type or annular type. This type of condensers is commonly used in
window air conditioners, water coolers and packaged air conditioning plants. The face
velocity is usually around 2m/s to 3.5 m/s to limit the pressure drop due to frictional
resistance. The coils of the tube in the flow direction are called rows. A condenser may
have two to eight rows of the tubes carrying the refrigerant. The moist air flows over
the fins while the refrigerant flows inside the tubes. The fins are usually of aluminum
and tubes are made of copper.
Holes of diameter slightly less than the tube diameter are punched in the plates and
plates are slid over the tube bank. Then the copper tubes are pressurized which expands
the tubes and makes a good thermal contact between the tube and fins.
Air Cooled Condenser design :We will design the Air cooled condenser by Software and manually
To design the Air cooled condenser by Software, we will use ( Technisolve air cooled
condenser software)
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Input values to Technisolve air cooled condenser software:
Barometer Pressure (101.325 kpa) Type of Refrigerant (R134a)
On Coil Temperature (dpt,wbt) (380
C,340
C)
Condensing temperature (54.50C)
Air Volume (9.582 m3/s )
Air Velocity (3 m/s)
Fin Height (1118 mm) Target duty (150 Kw)
Number of Rows deep (6)
Fin density (12 fpi)
Finned Length (2858 mm) Tube size (5/8 inch-38.1 ×50.8)
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Techniso lve Condenser coi l Manufactur ing design procedure:
1st Step:
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2nd Step:
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3rd Step (Run Calculation from F9 button or button):
Model
Recoil (5/8 inch - 38.1x50.8)
1118 x 2858 6r 12f 11c
CD 15938 / 22 / 06 / 12.00 / 2858 Cu/GI (11)
Areas and VolumesAo = 628.104 m²
Ao' = 32.762 m²/face m²-rows
Ai = 19.285 m²
Vi = 75.3 Litre
Pipe ConnectionsSize = 35 mm
Heat Transferho = 71.064 W/m²°C
Ui = 1.616 kW/m²°CUo = 29.092 W/m²°C
Ntu = 1.607
Cr = 0.000
Qt = e x Qmax
= 0.799 x 187.671 = 150.029 kW
Air Side DutyQt = ma (hao - hai)
= 10.672 (136.72 - 122.66) = 150.018 kW
Qs = ma x Cpa (dbo - dbi)
= 10.672 x 1.066 (51.2 - 38.0) = 150.029 kWRate = 15.651 kW/cms
Psychrometrics
Bypass factor = 0.020
Apparatus Dew Point = 33.1 °C
Refrigerant (R134a) DutySub-cooling = 5.0 °C
Mass flow = 0.827 kg/s (approx)
Mass flux = 1951.5 kg/sqm.s (approx)
Velocity = 1.809 m/sQt = mr x dh
= 0.827 x 181 = 150.029 kW
Dimensions
Height 1118.0 mm
Length 2858.0 mm
Depth 228.6 mm
Rows 6
Fins 12.00 fpi
Weight 775.7 kg
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CircuitingTubes High 22
Tube Count 132
Circuits 11
Circuit Basis Tubes high
Tubes/Circuits 12
Unlinked tubes 0
Serpentine 1/2
Eq Length 41.8 mConnections Same end
Tube (Staggered Pattern)ID 15.723 mm
OD 16.586 mm
Sx 38.100 mm
Sy 50.800 mm
FinThickness 0.200 mm
Area factor 1.000 mm
MaterialFin Cu
Tube Cu
Casing GI
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Psychrometric Chart:
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14.1. Design of Air cooled condenser manually:
Given Data
(1)
(2)
(3) ⁄ (4) *
(5) (6)
Where { ⁄ }
⁄
⁄ *
Assume
ε=
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Afrontal = L × H = 3 ×1 = 3
Assume 2.54
Check on
Tube side (ref.)
( )
( )
For air side
By using induced draught far
From tables
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[ ( )]
(
)
Fin calculations
Assume
⁄
(
)
( )
From chart
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Assume w=15cm
)