design and development of an evaporative cooling system for tropical fruits and vegetables on...

DESIGN AND DEVELOPMENT OF AN EVAPORATIVE COOLING SYSTEM DESIGN AND DEVELOPMENT OF AN EVAPORATIVE COOLING SYSTEM FOR TROPICAL FRUITS AND VEGETABLES ON TRANSPORT VEHICLES FOR TROPICAL FRUITS AND VEGETABLES ON TRANSPORT VEHICLES

Food Engineering and Bioprocess TechnologyFood Engineering and Bioprocess Technology

Prof. Athapol Noomhorm (Chairperson)Prof. Athapol Noomhorm (Chairperson)

Present byPresent by

Nattriya SupmoonNattriya Supmoon

Asian Institute of TechnologyAsian Institute of Technology

Presentation Outlines

RationaleRationale

Material and MethodsMaterial and Methods

Results and DiscussionsResults and Discussions

ConclusionConclusion

RecommendationsRecommendations

1. R1. Rationaleationale

General background

fruits and vegetables

risk of post-harvest losses

physiologicalbiochemical microbiological activities

increases the vapor pressure of the air decreases physiological weight loss

COLD CHAIN

low temperature high relative humidity

decreased

higher relative humidity

perishable

Statement of Problems

highly weight loss 15-20% fruits

20-25 % vegetables

Postharvest loss(Truck from Chiang Mai)

60% for cabbage and tomato50% for head lettuce 30% for bell pepper

17% for Chinese cabbage

tropical country hot and humid

more stress and hastens the decay

high water content and respiration rate tropical produce

transport without regard for heat


heavy initial cost and demand high input of energy

low investment and less energy input

Evaporative cooling

Refrigeration and other commercial cold storage systems

TEMPERATURE MANAGEMENT

Motivation of this thesis

Direct evaporative cooling system

have also been interesting for storage fruits and vegetables

but there is still no system yet on transport system

Cooling efficiency (η)


Sensible heat in the air is used to evaporate water

(transferred to latent heat in the moist air) %1001

21

stt

tt

11 22

Thailand HOT AND HUMIDDirect evaporative cooler

How to maximize temperature drop

limitation in dry bulb temperature drop (Jain, 2008)lower than the T_wb of the ambient air (Dessouky, 2004)


TRAFFIC CONDITIONTRAFFIC CONDITIONCAR SPEED VARIATION CAR SPEED VARIATION

Factors effect on cooling efficiency

2. Material and Methods

Objective

Design and construct a lab-scale evaporative cooler

Evaluate the effect of operating condition on cooling efficiency

Develop mathematical model of cooling efficiency

based on the steady state heat and mass transfer balance

Design and construct a modified evaporative cooling unit

used for storage tropical fruits and vegetables on transport vehicle

Experimental study and data collection to investigate

system performance of modified evaporative cooling unit

Objective 1

Objective 2


Procedure steps Dry bulb temperature: 21.6, 23.7, 24.6, 25.7, 26.7 C

Wet bulb temperature: 18.5, 19.6, 21, 21.3, 21.5 C

Thickness of cooling media:5, 10, 15, 20, 25 cm. (5 levels)

Inlet air velocity:5 levels depend on capability of fan

Design and construct

a lab-scale evaporative cooling lab-scale evaporative cooling systemsystem

Experimental Test

Vary operating condition

Data collection

Parameter

•T_db and T_wb

•Cooling efficiency

•Air velocity

Experimental results

Objective1: To determine the effect of operating conditions on the cooling efficiency



Construction of a lab-scale evaporative cooler unit



Construction and instrumentation of a lab-scale evaporative cooler unit

•Dry-bulb temperature (2-5)using K-type thermocouple

•Wet-bulb temperature (1)using K-type thermocouple kept moist by a wick dipped in a glass of water

•Air velocity (6)using vane anemometer

•Water flow rateusing volumetric method reading the time and a volume of water corresponding to valve adjustment

Water stream Air stream

Hot & dry air Cool & moist air



Cooling media

Distribution pad

Cooling pad

RIGID MEDIA (CelDek 7090)

3. Results and Discussions

Effect of temperature of entering air


No effect on cooling efficiency

Thickness of cooling media =20cm

Inlet air velocity =1.2m/s

Relative humidity =57%


Inlet air velocity =1.2m/s

T_db =26C

3. Results and Discussions

Effect of the inlet air velocity


0

10

20

30

40

50

60

70

80

90

100

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Inlet air velocity (m/s)

Coo

ling

Eff

icie

ncy

(%)


Effect of thickness of cooling media

0

10

20

30

40

50

60

70

80

90

100

0.000 0.050 0.100 0.150 0.200 0.250 0.300

Thickness of cooling media (m)

Co

oli

ng

Eff

icie

ncy

(%

)

Inlet air velocity =1.86±0.018 m/s

Cooling efficiency Temperature drop

Increased contact time and surface area

Heat and mass transfer

cooling efficiency

Thickness of cooling media

Inlet air velocity

3. Results and DiscussionsMathematical models as applied to evaporative cooling system

Wu, et al. (2008) Heat and mass balance of direct evaporative cooler

sensible heat removed from air = latent heat gain by air through water

3/18.0

12.0

PrRe10.0

llNu e

0

20

40

60

80

100

120

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

thickness of cooling media

Co

oli

ng

eff

icie

ncy

v=1

v=2

v=3

v=4

v=5

v=10

3. Results and DiscussionsObjective1: To determine the effect of operating conditions on the cooling efficiency

)34.10exp(12.0

88.0

V

Mathematical model of cooling efficiency

2. Material and MethodsObjective2: To design and develop an evaporative cooler used for transport tropical

fruits and vegetables on moving vehicles

Procedure stepsEvap configurations

-Single-stage EC

-Two-stage EC

Car velocity

40, 50, 60, 70, 80 km/hr

Design and construct

a modified evaporative cooling modified evaporative cooling systemsystem

Experimental Test

Vary Evap configuration & Car velocity

Data collection

•Parameter

•T_db and T_wb

•Cooling efficiency

•Relative inlet air velocity

Experimental results

3. Results and DiscussionsObjective2: To design and develop an evaporative cooler used for transport tropical


Selection of the operating condition

thickness of cooling media

air velocity

25 cm

As low as possible

The more thickness of cooling media, the higher cooling efficiency

The lesser inlet air velocity, the more cooling efficiency



Construction of a modified evaporative cooler unit




Single-stage EC Two-stage EC



Cooling efficiency

70

75

80

85

90

95

100

105

110

40 45 50 55 60 65 70 75 80 85

Car velocity (km/hr)

Cool

ing

effic

ienc

y (%

)

Single-stage EC

Two-stage EC



Temperature drop

0

5

10

15

20

25

30

35

40 45 50 55 60 65 70 75 80

car velocity (km/hr)

T(C

)

T_inlet Single-stage EC

T_outlet Single-stage EC

T_inlet Two-stage EC

T_outlet Two-stage EC

One-stage EC

Temperature drop about 7C

Two-stage EC

Temperature drop about 10C



Adjustment the area of inlet air to control the air velocity

00.5

11.5

22.5

33.5

44.5

5

40 50 60 70 80 90

car velocity (km/hr)

rela

tive

air

velo

city

(m/s

)

air entering (2 stage EC)

leaving (2 stage EC)

entering (1 stage EC)

leaving (1 stage EC)

This equation may be taken as a constant

when the variation range of air condition is small and the cooling media is given. For the different material and configuration of cooling media, the number will take a different value.

main effectsmain effects Thickness of cooling media () & inlet air velocity (V)

4. Conclusions

Objective 1

The predicted cooling efficiency model for a direct evaporative cooler with rigid media as a cooling pad based on heat and mass balance analysis of air and moisture.

)34.10exp(12.0

88.0

V

4. Conclusions

Objective 2

Single-stage evaporative cooling system temperature drop by 7C cooling efficiency ranged from 84% to 96%.

Two-stage evaporative cooling system temperature drop by 10C cooling efficiency ranged from 104% to 107%

Effect of car velocity on the relative inlet air velocity Two-stage EC is less than Single-stage EC results in less variation in temperature gradients

5. Recommendations

Some fruit and vegetable located in the north or northeastern part of Thailand should be considered to be the testing for the evaporative cooling system on

moving vehicle.

The cost analysis of the evaporative cooling system on moving vehicle should be done

to check the energy costs and efficiency of the system.

5. Recommendations

Desiccant DehumidificationReduce moisture of ambient air before

passing through direct evaporative cooling system

Actual sizeFactor to be considered is relative inlet air

velocity

Thank you

design and development of an evaporative cooling system for tropical fruits and vegetables on...

Documents

cooling efficiencyconstruction

c thickness of cooling

humiddirect evaporative

effect of operating

temperature droplimitation

c wet bulb temperature

storage tropical fruits

storage fruits