AN ORAL PRESENTATION ON

DESIGN AND CONSTRUCTION OF A TUNNEL DRYER FOR FOOD CROPS

21st SAAFoST BIENNIAL INTERNATIONAL CONGRESS & EXHIBITION 6 – 9 September 2015, Southern Sun Elangeni /

Maharani Complex, Durban, South Africa

SEPTEMBER, 2015

BY

A.S. AJALA, P.O. NGODDY & J.O. OLAJIDE

Department of Food Science and Engineering Faculty of Engineering and Technology LADOKE AKINTOLA UNIVERSITY OF TECHNOLOGY, OGBOMOSO, NIGERIA

OUTLINE OF PRESENTATION

Introduction/Background of the Study

Statement of Research Problem

Research Aim and Objectives

Design methodology for the Dryer

Results and Discussion

Contribution to Knowledge

3

Nigeria is the most populous nation in Africa with an

estimate of 160 million people

Background of the Study

Figure 1: Geographic Distribution of Nigeria

4

Different Geographic areas in Nigeria is known for the

production of different crops

Background of the Study (contd)

Figure 2: Farming System in Nigeria

5

Background of the Study (contd)

Table 1: Some farm produce in Nigeria

Product Metric tons (millions)

References

Cassava 37.5 +_ FAOSTAT, 2012

Maize 10 + Nigeria Bureau of

Statistics, 2012

Yam 38 + Ibitoye and Onimisi

(2013)

Tomatoes 1.7 + Donkoh et al., 2013

6

Cassava

Background of the Study (contd)

Figure 3: Woman in Cassava Farm

7

Maize

Background of the Study (contd)

Figure 4: Man in a Maize Farm

8

Background of the Study (contd)

Figure 4: Woman selling pepper and tomatoes in Oshodi Market, Lagos

Pepper & Tomatoes

9

Due to large expanse of fertile lands, many people are into farming and at the end of the year we can boast of excess supply of agricultural products more than we need or can consume.

Despite all these production almost 70% of these products are wasted

Statement of the Problem

10

Statement of the Problem (Contd.)

Table 2: Wastages of farm produce

in Nigeria

Product Wastages (%) References

Cassava 13.3 P. E International, 2013

Maize 13.7 P. E International, 2013

Yam 10 FAO, 2013

Tomatoes 70 Umeofia, 2015

11

Statement of the Problem (Contd.)

Some reasons for these wastages

includes:

Unavailability of storage facilities

Poor processing methods

Poor preservation methods

12

Drying has been adopted by many farmers as a

means of preserving their farm products.

The types of drying available includes:

Sun Drying Natural Artificial

Mechanical dryers

Cabinet Infrared Vacuum Drum Tunnel

Statement of the Problem (Contd.)

13

Natural sun drying Most adopted

It’s the cheapest

Its not effective as its weather dependent

Hence,

Mechanical dryers is considered to be a preferable and better alternative

Statement of the Problem (Contd.)

This work introduces a general purpose tunnel dryer for food crop dehydration

AIM OF STUDY

Design Features of the Constructed Tunnel Dryer

• It has both counter-current and co-current mode of drying

• Expected Production rate: 32.5kg/batch

• Expected number of trucks: 6

• Expected number of trays per truck: 6

• Air temperature before entering dryer: 32oC

Description of major components and materials of construction

• Drying Chamber (Tunnel) • Heaters • Blower (fan) • Trucks • Trays • Return channel (pipe or duct) • Fasteners (bolts and nuts) • Lagging material (fiber glass) • Electrical/electronic components (wire, thermocouple,

and temperature regulator, humidity sensor and velocity regulator)

Description of major components and materials of construction

• Drying Chamber (Tunnel) • Heaters • Blower (fan) • Trucks • Trays • Return channel (pipe or duct) • Fasteners (bolts and nuts) • Lagging material (fiber glass) • Electrical/electronic components (wire, thermocouple,

and temperature regulator, humidity sensor and velocity regulator)

Front View of the Tunnel Dryer

Figure 5: Front view of the tunnel dryer

Isometric view of the tunnel dryer

Figure 6: Isometric view of the developed dryer

20 Figure 7: Isometric view of the developed Truck

Isometric View

21

Truck design cont’d

Figure 8: Front view of the developed Truck

Front view

Design of Trays • Length of tray=0.25m • Breadth of the tray= 0.20m • Height of the tray= 0.015m

• Design of Trucks • Height of the truck = 0.25m • Length of the truck = 0.30m • Breadth of the truck =0.2m

• Design for drying chamber of the tunnel

• Length of the drying chamber =3.25m

• Breadth of the drying chamber =0.35m

Design Specifications

• Feed rate (mw) = 32.5 kg/hr

• Intended drying time = 6 hours

• Initial moisture content of the cassava chips = 75%

• Desired final moisture content = 14%

• Therefore, weight loss from wet to dried chips is calculated thus

where mw is the mass of wet cassava chips, m0 =initial moisture content (%) md is the mass of dried cassava chips, mf =final moisture content (%)

)

100

100( 0

f

wdm

mmm

)14100

75100(5.32

dm

Heater Design

Quantity of heat required to remove the water = quantity of heat on the cassava • chips + latent heat of evaporation of • water inside the chips • Specific heat of cassava chips = 3.41kJ/kgoC (Hahn and Keyer, 1985)

• Latent heat = 4.186 x103 {(597- 0.56(Tpr)} (Youcef-Ali et al., 2001) • where Tpr is the product temperature

• Q = mass of cassava chips x specific heat of the chips x temperature difference + • Mass of water x 4.186 x103 {(597- 0.56(Tpr)} • = 32.5 x 3.41 x (80-30) + 23.05 x 4.186 {(597- 0.56 (60)} • = (5541.25 +57485.81) kJ • = 63025.06kJ • Power of heater to be used = Quantity of heat /Time • = 63025.06/ (6 x 3600) • = 2.905 kW • From the above calculation, a heater of about 3kW was used.

Heater Design

• Length of the drying chamber (previously calculated) = 3.25 m

• Breadth of the drying chamber (previously calculated) = 0.35m

• Height at which chips fill each tray = 0.05m

• Total depth of chips for 36 trays = 36 x 0.05 =1.8m

• Volume of the material in the tunnel (m3) = 3.25 x 0.35 x 1.8 = 1.134m3

• Minimum required range of air velocity necessary for drying food products as recommended is 0.5 m/s (Bulent et al 2007; Ndukwu, 2009)

Fan Design

Fan horse power (P) = volume air flow rates x total static pressure

6320 x fan efficiency

Most industrial fan have efficiency between 70- 85% (Adzimah and Seckley, 2009), Hence,

85.06320

638.101156.607

x

xP

= 2.29 Hp

A centrifugal fan with 2.5 Hp and 3.64 inches water pressure was used.

Fan Design

Insulation Design

xg xs xa

T1 = 32oC

T2 =100oC

Aluminium

Sheet

Fibre Glass

Aluminium Sheet

Thermal Efficiency

The thermal efficiency is given as

Tamb= ambient air temperature (30oC) Tout= outlet air temperature (40oC) Tin=inlet air temperature (70oC)

cov = 100T-T

T-T

in

outinx

amb

The thermal efficiency of the dryer was 75%

29 Figure 9: Drying rate against time

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10

Drying time (hr)

Dry

ing

rate

(kg

/hr)

Drying Rate Pattern

30 Figure 6: Truck distance against time

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10

Tru

ck d

ista

nce co

vere

d (m

)

Drying time (hr)

Truck Movement Pattern in the Dryer

31 Figure 10: Temperature against time

50

55

60

65

70

75

0 2 4 6 8 10

Tem

pera

ture

pro

file

(o

C)

Drying time (hr)

Temperature Pattern in the Dryer

32 Figure 11: Air velocity against time

2

2.5

3

3.5

4

4.5

5

5.5

0 2 4 6 8 10

Air

velo

cit

y p

att

ern

(m

/s)

Drying time (hr)

Air Velocity Pattern in the Dryer

• Processing relatively large volume of product

• Better control of drying parameters

• Cost effective drying and maximum product quality.

• Adaptable to drying tubers, fruits and vegetables

• Simplicity in construction

Advantages of using this tunnel dryer

Samples of Products Dried

Picture of the constructed tunnel dryer

Samples of the dried cassava chips packaged in polythene film

Figure 12 : Dried Cassava Chips

Samples of Products Dried

Figure 13 : Dried Egg

Conclusions

• This dryer has catered for most deficiencies experiences with sun drying

• The maintenance cost is minimal because air (instead of gas) is used as drying agent

• The fans and heaters are capable to deliver the required heat needed for the drying operation

Recommendations

• Further study on automation of the machine trucks will be a great advantage for drying of food products

References

Adzimah K.S. and Seckley E. (2009). “Improvement on the design of a cabinet grain dryer”.

American Journal of Engineering and Applied Sciences 2 (1): 217-228.

Ajala, A.S., Ngoddy, P.O. and Olajide, J.O. (2013). Study of Drying Parameters in Tunnel

Drying. International Journal of Advanced Scientific and Technical Research, Issue 3 volume 2,

pp 265-266

ASTM (2005). “Standard temperature for measuring humidity with a psycrometer (the

measurement of wet & dry bulb temperature)”. Annual book of ASTM standards, section 11

volume 11.03 designation E337-02. American Society for Testing and Materials, International,

West Conshohocken, pp.1226-1249

References contd

Hahn, S.K. and Keyer, J. (1985). “Cassava: A basic food for Africa”. Outlook Agriculture, 14

(9): 5-9.

Kiranoudis, C.T., Maroulis, Z.B. Tsami E. and Marinos-Kouris D. ( 1993) Equilibrium moisture

content and heat of desorption of some vegetables. Journal of Food Engineering, vol. 20, p. 55-

74.

Youcef-Ali, S., Messaoudi, H., Desmons, J. Y., Abene, A. and Le Ray, M. (2001).

“Determination of the average coefficient of internal moisture transfer during the drying of a thin

bed of potato slices”. Journal of Food Engineering, 48(2): 95-101.

ACKNOWLEDGMENT

• The Management of Ladoke Akintola University of Technology, Ogbomoso, Nigeria

Thanks for

Listening