ABSTRACT
This study was carried out to generate a design data, design and fabricate a
maize corn-on-cob tray dryer used by maize farmers. Ripped maize corns with
husks were bought from the market and preserved to retained its moisture
content, dehusked and thereafter, dried to a given percentage moisture content
of 15%. This was done by laboratory dryer. The drying rate data was generated
and the high rate of 2.0g/hr was used afterwards to design and fabricate the
corn-on-cob dryer. From the results, drying of a sample of maize corn-on-cob
by the laboratory dryer took a period of three days and six hours to reach the
15% moisture content (wet basis) needed. A test run was carried out on the
fabricated dryer and seventeen hours was used to dry a sample of maize cornon-cob
to the same 15% moisture content. This implies that design data is
satisfactory as its application in the fabrication of the dryer resulted in an
increased flow rate of air in the dryer thereby increasing the rate of drying at the
same drying temperature of 40oC.
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NOMENCLATURE
Twb Wet bulb temperature
Tdb Dry bulb temperature
Mwb Moisture content on wet basis
Mdb Moisture content on dry basis
MO Initial moisture content (Dry basis)
Wo initial weight of undried product (kg)
W Weight of water removed (kg)
Wd Weight of dry matter in product (kg)
A Total area of the drying surface (m2
)
Ha
Heat transfer coefficient
Ta
Inlet temperature of air after being heated up
Td
Drying chamber temperature
? Latent heat of vaporization of moisture at Td
0C(Cal/mol)
G Mass velocity of air (Kg/ s.m2
)
De
Equivalent diameter of the air flow channel (m)
1
TABLE OF CONTENT
Title page- – – – – – – – – – -i
Certification- – – – – – – – – -ii
Dedication- – – – – – – – – – -iii
Acknowledgement- – – – – – – – -iv
Abstract- – – – – – – – – – -vi
Nomenclature- – – – – – – – – -vii
Table of content- – – – – – – – – -viii
CHAPTER ONE
INTRODUCTION
1.1 Background of study– – – – – – – -1
1.2 Statement of the problem- – – – – – – -2
1.3 Objective of the research project- – – – – – -3
1.4 Significance of the research- – – – – – -4
1.5 Scope of the research- – – – – – – -4
2
CHAPTER TWO
LITERATURE REVIEW
2.1 Maize farming in Nigeria- – – – – – – -5
2.2 Drying- – – – – – – – – – -5
2.2.1 Some basic definitions on drying- – – – – -8
2.2.2 Drying rates– – – – – – – – -12
2.2.3 Classification of dryers- – – – – – – -18
2.2.4 Tray dryer- – – – – – – – – -20
CHAPTER THREE
MATERIALS AND METHODS
3.1 Sourcing and preservation of the raw material- – – – -22
3.2 Drying- – – – – – – – – – -22
3.2.1 Maize corn-on-cob bone drying– – – – – -23
3.2.2 Generation of dryer design data from maize corn-on-cobs– -24
3.3 Dryer design and materials of fabrication- – – – -24
3.4 Design considerations- – – – – – – -27
3
3.5 Test running of the dryer- – – – – – – -31
CHAPTER FOUR
RESULT AND DISCUSSION
4.1 Result- – – – – – – – – – -33
4.2 Discussion- – – – – – – – – -35
CHAPTER FIVE
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
5.1 Summary- – – – – – – – – -37
5.2 Conclusion- – – – – – – – – -37
5.3 Recommendation- – – – – – – – -38
REFERENCES- – – – – – – – – -40
APPENDICES- – – – – – – – – -41
Appendix A (Graphs) – – – – – – – – -41
Appendix B (Tables) – – – – – – – – -55
Appendix C (Calculations) – – – – – – – -58
CHAPTER ONE
4
INTRODUCTION
1.1. BACKGROUND OF STUDY
Cereal grains have been and will continue to be a major source of food for
humans and animals throughout the world. Amongst all cereals, the most
important is the maize grain. (Leonard et al, 1963). Maize corn and products can
be used for various purposes; human food, alternative medicine, chemicals, bio
fuels, ornamentals, fodder, to mention but a few (Leonard, Warren H., and John
H. Martin). Maize crop is intensively and extensively cultivated in all the geopolitical
zones of Nigeria. Early maize is planted between late March and late
May while the late maize is planted between August and September. The
harvest time for the early maize is usually between late July and September.
During this period, corns are harvested fresh and cannot be preserved by drying
owing to the unavailability of sunshine during the rainy season. It is usually
roasted or cooked fresh. This practice does not encourage maize farmers as they
would sell the maize corn at a give-away prices and this does not guarantee
returns on their investment. In addition to this, dried maize grains will guarantee
food sufficiency during the scarce period. Notably, corn of high moisture
content does not stored very well and is usually vulnerable to damage due to
deterioration, molds, and insects during the period of storage.
However, open air-sun drying as practiced in most rural areas often yields poor
quality dried corn, since the product is not protected against dust, moisture,
wind, rodents as well as other domestic animals while carrying out the drying.
As a result, they are often contaminated with pathogens. Another common
practice in maize corn-on-cob drying is drying over a fire place. This has its
own problems as the maize grains are contaminated with smoke. Moreover, the
temperature of drying is not properly controlled such that grains become dead
after drying. There are various research works that have been carried out on
grain drying (Zare et al, 2006; Mellmann, et al 2011; Adzimah and Seckley,
2009). These works were silent on drying and dryer design for maize corn-oncobs.
There are four major drying techniques; open air sun drying, fire wood /fuel
drying, electrical drying and solar drying(Anyanwu et al 2006, Scanlin 1997
and Whitefield 2000). This research project will address these problems
associated with postharvest handling of maize corn-on-cobs, in particular
drying, by designing and fabricating electrically operated tray dryer that will be
simple but very robust in operation.
1.2 STATEMENT OF THE PROBLEM
Maize corns are usually stored when dried to certain percentage moisture
content. In Nigeria, maize corn drying is done in dry season because of low
humidity of atmospheric air and adequate sunshine. However, it is a common
place to see peasant maize farmers dry their maize corn-on-cobs over fire place,
but this practice contaminates the dried maize corn with smoke and usually
small quantity of maize corn-on-cob are dried. The reverse is the case during the
rainy season. Unfortunately, bulk of the maize corn is harvested in the rainy
season and farmers can not dry the fresh maize corn rather they sell them at
very cheap prices to corn roasters and for other delicacies. To give value to
farmers and also to guarantee maize corn sufficiency during scarce period, it
becomes necessary that a simple but robust corn-on-cob dryer should be
designed and fabricated to assist farmers have good returns on their investment
especially during post-harvest handling of maize corn during rainy season.
1.3 OBJECTIVES OF THE RESEARCH
The aims of this research include:
i. To develop a drying rate curve for maize corn-on-cob at constant drying
condition.
ii. To generate design data for tray dryer to be used to dry maize corn-oncob.
iii. To develop and draw working diagrams for the tray dryer.
iv. To fabricate a tray dryer.
v. To test run the tray dryer.
1.4 SIGNIFICANCE OF THE RESEARCH
Some of the benefits derivable from this research project include:
i. It will encourage maize farmers by giving them good returns on
their labour and enhance maize corn production.
ii. It will provide Nigerian populace with a cleaner dried maize grains.
iii. It will attract foreign exchange for Nigeria as cleaner dried maize
can be export.
iv. It will ensure maize grain sufficiency during the scarce period.
1.5 SCOPE OF THE RESEARCH
This research will be restricted to the following areas;
i. Generation of design data for corn-on-cobs.
ii. Designing the corn-on-cob dryer.
iii. Fabrication of the dryer.
iv. Test run