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1

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

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Room Cooling

• 100 cfm per ton of product.

12

Ceiling fans

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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.

16

Sloped sidesVents

17

Room Cooling

• 100 cfm per ton of product.

• Space stack product.

• Well vented boxes.

• Lowest possible air temperature.

18

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

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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

28

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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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

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Bagged Grapes

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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

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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

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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

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Moisture Loss in Hydrocooling

Gain 0.5 % to lose .05%

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Water Beating Damage

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Control pH and Chlorine Levels

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Package Icing

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Ice solidifies & melts away from product

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Liquid Ice Machine

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Manual Liquid Icing

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Iced Boxes at Market

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Small Ice Machine

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Vacuum Cooling

At 25mm Hg water boils at 20°C

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12 Pallet Vacuum Cooler

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Cools product that can release moisture quickly

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Moisture Loss in Vacuum Cooling

• Lose 2.0 to 4.0 %

• 1%moisture loss for each 11°F (6°C) of temperature drop

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Water Spray Vacuum Cooling

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Cold Rooms

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Selecting a Cooling System

• Product requirements.

• Product mix.

• Temperature requirements.

• Cooler cost.

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73

Capital Cost

Cos

t ($

/lb-d

ay)

4

3

2

1

0Liquid

iceVacuum Forced

airHydro

74

Energy Use

Ene

rgy

Coe

ffici

ent

3

2

1

0Liquid

iceVacuum Forced

airHydro Hydro

Vac