thompson - coolingucce.ucdavis.edu/files/datastore/234-2224.pdf · jim thompson biological &...
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6/15/2012
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Initial Cooling
Chapter 11 andCommercial Cooling of Fruits, Vegetables
and Flowers
Jim Thompson
Biological & Agricultural Engineering, UC Davis
2
Cooling Begins in the Field
• Prevent heating in the field.
• Shorten time before cooling begins.
3
Shade product to reduce heat gain & moisture loss
4
water spray
Carrot Receiving
5
Use frequent, scheduled pick up
6
Product temperature drop is rare in trailers.
Transport Cooling
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7
Slow cooling in marine transport
8
Vertical Airflow
Marine Container
product
Stack to ceiling
Prevent air from bypassing the load– Cover floor
– Stack to ceiling at the rear of the load10
Room Cooling
11
Room Cooling
• 100 cfm per ton of product.
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Ceiling fans
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3
13
Room Cooling
• 100 cfm per ton of product.
• Space stack product.
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4 -6” between lanes
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Room Cooling
• 100 cfm per ton of product.
• Space stack product.
• Well vented boxes.
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Sloped sidesVents
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Room Cooling
• 100 cfm per ton of product.
• Space stack product.
• Well vented boxes.
• Lowest possible air temperature.
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Highest Freezing Temperature
°C °F
Apples -1.5 29.3
Cherries -2.1 28.8
Pear -1.7 29.2
Asparagus -0.6 30.9
Lettuce -0.2 31.7
Cauliflower -0.8 30.6
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Room Cooling
Pallets of tight fill plums in corrugated boxes
Vents Box spacing
Stacking Longest cooling time (hr)
none none cross 84
4% none register 22
4% 1” register 18
Room CoolingHalf Cooling Time in Days for palletized
d’Anjou Pears
Wrapped Tray packed
Location outside inside outside inside
top 2.0 4.9 1.7 4.2
middle 7.0 15.0 4.6 7.2
bottom 2.1 3.3 1.8 2.1
Kader & Fabion
21
Forced Air Cooling
Pallets of tight fill plums in corrugated boxes
Vents Box spacing
Stacking Longest cooling time (hr)
4% none register 3 - 6
Forced Air - Tunnel
Tarp
Exhaust fan
23 24
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25 26
Reversing Airflow Direction
openclosedopen closed
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Portable Fan & Tarp
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Small Scale Forced Air
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Airflow
30
Forced Air - Serpentine
Cloth strips
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31
Gravity operated louver
Seal
32
Operating serpentine cooler
33
Forced Air - Cold Wall
Damper
Evaporator
Fan
34
35 36
30
40
50
60
70
80
90
100
Tem
per
atu
re (。F
)
0.0 1.0 2.0 3.0 4.0 5.0
Hours of Cooling
30
20
10
Tem
per
atu
re (。C
)
most shielded
mass average
most exposed
1/2 3/4 7/8 15/16 Cool
0
Peaches at 0.5 cfm/lb.
Forced Air Cooling
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37
0
1
2
3
4
5
7/8
Co
olin
g T
ime
(hr)
0 1 2 3 4
Air Flow Rate (cfm/lb or l/s-kg)
Cantaloupe, dia.=6.0
Peaches, dia.=3.25"
Cherries, dia.=1.0"
Forced Air Cooling High Capacity Cooling
• High airflow rate (strawberries in <60 min)
• Airflow reversal
• Modular
• Energy efficient
0
1
2
3
7/8
Co
olin
g T
ime
(h
r)
0 1 2 3 4Air Flow Rate (cfm/lb)
Peaches
Cherries
MACS - Semi-continuous Flow
Inside cold room
Conveyor
Airflow reverses
www.macscooler.com
American Cooling - Field-side Cooler
Refrigeration trailer
Generator
Forced air cooler w/ flow reversal Bobtail
reefer truck
Refrigerated dock
Enclosed outfeed conveyor
American Cooling - Fieldside Cooler Vertical Airflow Cooler
http://ne-postharvest.com
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43
Pressure Drop vs. Airflow
Air Flow (cfm/lb)
0
1
2
3
4
0 1 2 3
Pre
ssu
re D
rop
(in
.)
Grape
Pear
44
Venting
Good - 5%
Poor
45
Box Venting
L12
LL
14
L12
L12L
14
L14
L14
L32
46
Bagged Grapes
47
0
0.5
1.0
1.5
0 5 10 15 20 25 °CTemperature drop during cooling
Wei
gh
t lo
ss a
t 80
% c
oo
l(%
)
10 20 30 40°F
Carrots without tops
Moisture Loss in Forced Air Cooling
48
Fiberboard Strength
0
50
100
20 40 60 80 100
Relative Humidity (%)
moisture
0
15
30strength
Ret
aine
d S
tren
gth
(%)
Moi
stur
e C
onte
nt (
%)
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49
Electricity Use in Forced Air Cooling
Electricity Use (%)
Product 36
Fans 30
Lights 16
Walls 14
Lifts 450
Electricity Use vs. Throughput
y = 0.0008x + 0.1181
R2 = 0.9096
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 200 400 600 800 1000 1200 1400 1600
Ener
gy C
oefic
ient
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Hydrocooling
52
53 54
Evaporator
Immersion Hydrocooler
Water circulation
Immersion tank
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55
asparagus
carrot
0
20
40
60
80packed corn with husk
potato
radish
tomatocantaloupe
peach
citrus
apple
0 1 2 3 4 5
Product diameter (inches)
cantaloupe
7/8t
hs
Co
olin
g T
ime
(min
)
Hydrocooling Time
56
Cherry Hydro-cooling
0
5
10
15
20
25
30
Tem
per
atu
re (。C
)
0 5 10 15 20
Time (min)
15 GPM/ft^2
7 GPM/ft^2
57
Moisture Loss in Hydrocooling
Gain 0.5 % to lose .05%
58
Water Beating Damage
59
Control pH and Chlorine Levels
60
Package Icing
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61
Ice solidifies & melts away from product
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Liquid Ice Machine
63
Manual Liquid Icing
64
Iced Boxes at Market
65
Small Ice Machine
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Vacuum Cooling
At 25mm Hg water boils at 20°C
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67
12 Pallet Vacuum Cooler
68
Cools product that can release moisture quickly
69
Moisture Loss in Vacuum Cooling
• Lose 2.0 to 4.0 %
• 1%moisture loss for each 11°F (6°C) of temperature drop
70
Water Spray Vacuum Cooling
71
Cold Rooms
72
Selecting a Cooling System
• Product requirements.
• Product mix.
• Temperature requirements.
• Cooler cost.
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