solar projectarticle
TRANSCRIPT
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1.0 INTRODUCTION
1.1 GENERAL INTRODUCTION
Solar dryer can be defined as a special structure that
enhances the drying power of the sun and protect the
agricultural produce or food from dust, rain, birds, insects and
domestic animals while drying.
Drying is an excellent way to preserve food and solar fooddryers are appropriate food preservation technology for
sustainable development. Drying was probably the first ever
food preserving method used by man, even before cooking. It
involves the removal of moisture from Agricultural produce so
as to provide a product that can be safely stored for longer
period of time without getting spoiled.
Sun drying is the earliest method of drying farm produce
ever known to man and it involves simply laying the
agricultural products in the sun on mats, roofs or drying floors.
This has several disadvantages since the farm produce are laid
in the open sky and there is great risk of spoilage due to
adverse climatic conditions like rain, wind, moist and dust, loss
of produce to birds insects and rodents. It is totally dependent
on good weather and very slow drying rate with danger of
mould growth, thereby causing deterioration and
decomposition of produce. The process also requires large area
of land, takes time and is labour intensive.
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With cultural and industrial development, artificial mechanical
drying came into practice but this process is highly energy
intensive and expensive which ultimately increase product cost.
Recently, efforts to improve "sun drying" have led to solar
drying.
In solar drying, specialized devices that control the drying
process and protect agricultural produce from damage by
insect pests, dust and rain are used. In comparison to natural
"Sun 'drying", solar dryer generates higher temperatures, lowerrelative humidity, lower product moisture content and reduced
spoilage during the drying process. In addition, it takes up less
space, takes less time and relatively inexpensive compared to
artificial mechanical drying method. Thus, solar drying is a
better alternative solution to all the drawbacks of natural drying
and artificial mechanical drying.
The solar dryer can be seen as one of the solution to the
world's food and energy crises. With drying, most agricultural
produce can be preserved and this can be achieved more
efficiently through the use of solar dryers.
1.2 USEFULNESS OF SOLAR DRYER
The solar dryer system is used as replacement to the
traditional sun-drying methods. It is mainly used for drying of
agricultural produce. It has an improved feature that eliminates
the shortcomings inherent in the traditional sun- drying
method. Produced or food being dried in this device is therefore2
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protected against: rain, dust, birds domestic animals etc. The
usefulnes~ of the drying can be outline as follows:
1. The solar dryer, dries faster in the sense that, inside thedryer, it is warmer than outside.
2. The solar dryer system offer less risk of spoilage because
of the speed of drying (if the drying process is slow the
fruit start to ferment and the product is spoilt)
3. The solar dryer system is labour saving.
4. The quality of food or products dried using this device is
better in terms of nutrients, hygiene, texture and colour.
1.3 AIMS AND OBJECTIVES
The primary aim of this project is to design system that
provides move improved features that overcomes and replace
the traditional sun-drying method and its limitations, which
includes protection against flies, protection against rain,
protection against dust, protection against domestic animals
etc. The summary of the objective can be stated as followings.
1. To design a solar dryer that extends shelf life of farm
produce.
2. Guarantees foods security through out the year.
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3. To ensure that the food or products is protected against
rain, dust birds, insects, domestic animals etc.
4. To know the principles behind the basic construction andoperation of a solar drying equipment.
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However reports abound in literature on the 18th century
works of Archimedes on concentrating the Sun's rays with flatMirrors, Antoine Lavoisier on solar furnace, Joseph priestly on
concentrating rays using lens. In the 19th century,
development of solar distillation unit covering 4750 sq meters
of land, operated for 40 years and producing 6,000 gallons of
water from salt water per day was reported and noted
alongside with John Ericson's work on conversion of solarenergy into mechanical energy through a device which
produced the (146W) for each 9.3m2 of collection surface.
Modern research on the use of solar energy started during
the 20th century. Development includes the invention of a solar
boiler, small powered steam engine and solar battery, but it
was difficult to market them in competition with engine running
on inexpensive gasoline. During the mid 1970's shortages of oil
and natural gas, increase in cost of fuels and the depletion of
other resources stimulated efforts in the United States to
develop solar energy into a practical power source. Thus,
interest was rekindled in the harnessing of solar energy for
heating.
As a result of this, in the 1970s, Kelin, Beckmann and Duffle
(1975, 1976) developed the F-chart methodology based on
TRNSYS software simulations. They established correlations
between dimensionless design parameters and solar fraction
(ratio of the energy supplied by the solar system to the energy6
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demand of: the process). This methodology was developed for
water and air heating system. However, the focus was not on
the drying of agricultural products. The main characteristic of
the F- Chart is its simple operation and accessibility to people
not skilled in solar energy engineering.
At the end of the 1970s and beginning of the 1980s, the first
Brazilian studies on application of solar energy in drying
processes were done" at UNICAMP by a drying research During
this period Santos (1980) studied the use of collectors withbeds made of pebbles in in-bin Soy drying. The advantages of
this over flat collectors were the lower cost per unit of area, the
smaller collector area and the capacity to store energy and to
avoid temperature peaks.
Modern variations in solar dryer are to build special
enclosed drying rack or cabinet to expose the food to a flow, of
dry air heated by electricity, propane or solar radiation. In
recent time, the design of solar dryer had improved to building
of special structure that enhance the drying power of the sun
radiation in drying of produce and as well protect the produce
from external influences.
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CHAPTER THREE
3.0 METHODOLOGY
This chapter is focused on the methods employed in the
construction of the solar dryer. It reviews the design
consideration, description of main components and design
analysis. It also discusses the factors guiding material used for
the construction, fabrication techniques and engineering
analysis and its evaluation as well.
3.1 DESIGN
(a) Design Consideration:
(i) Temperature: The minimum temperature for drying food
is 30c and the maximum is 60c. Therefore, the range of
temperature for effective function of the device is 30c-
60c and any temperature above is 60c, the produce get
burnt.
(ii) Reliable: Solar dryer is more reliable than any other '
dryers because it dries produce without change in the
texture and the nutritional value.
(iii) Availability of the materials: Mild steel metal and
reflective glasses are cheaply and readily found.
Therefore, the choice of using them for the project
becomes necessary.
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(iv) Flexibility: The parabolic reflector is made flexible to
face the rays for radiation of the sun at any given angle
and direction with the aid of an adjustable screw rig and
fixture.
(v) Portability: The movement of the object from one place
to another is possible with the aid of fitted rollers. The
rollers not only assist to enhance the portability of the
object but also contribute greatly to the setting of the
parabolic reflector at the needed direction for effectivefunctioning.
(vi) Air gap: It is suggested that for hot climate passive solar
dryer, gap or holes of 4mm diameter inlet and air passage
and also reduction of exceeds heating of the produce. This
enhances the prevention of the produce from being burnt.
(vii) Drying items: The device to be designed should be
capable to dry vegetables, fruits, roots, tuber crops or
chips crop seed and some other.
(viii) Availability of power source: Sun being a natural
renewable source of energy, not only using for heatingpurpose can also be applied for drying sake without
noticing the rate of consumption.
(ix) Choice of reflector: The utilization of aluminum plate as
a reflector which enhances the effective reflection of the
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radiation to the focal point for proper drying efficiency is
considered.
(b) Description of the main components
(i) Glass Box: As the name implies, this box is constructed
using glass with reflecting surface. It houses the food
produce to be loaded in the box for drying. The reflective
surface of the glass enables the box to retain the heat
needed for drying. I t is also provided with air vent at both
sides to allow air passage out of the cabinet, thereby
releasing the moisture from the produce to aid drying.
(See diagram of the box.)
(ii) Parabolic Reflector or Concentrator: This is
constructed to have a parabolic shape made possible by
assembling sectors (segments) of equal sizes to form a
circle. It is incorporated with reflectors made of aluminum
sheet that enhance the drying power of the sun by
concentrating the heat to a focal point. (See assembling
diagram for dimensions).
(iii) Box Stand or Hanger:The box stand is constructed witha mild steel pipe. It serves as the seating for the drying
box. It has an, adjustment to suit the focal point of the
concentrator.
(iv) Main Stand: This is the main stand of the device. It is
constructed to hold the parabolic reflector in position. It is
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constructed using two circular galvanized steel rod, held in
position by mounting rods and crossed side tense rods. It
has an elevation pole for adjusting reflector seating to be
tilted at the proper angle. The base of the stand is
incorporated with three rollers to allow the reflector to be
following the direction of the sun. (see assemblies
diagrams for more details and dimensions).
(c) Design Analysis
Calculation for the focal point of the parabolic reflector 296mm
Employed the formula
F = D2
16d
Where F =focal point of the parabolic reflector.
D = Diameter of the parabolic reflector
d = depth of the parabolic reflector
F = =
F = 684mm11
d = 296mm
D = 18000mm
(180002) 3240000
296 x 16 4,736
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Calculation for the stand of the reflector
For the angle
U sing Pythagoras theorem
[AB]2 + [BC] = [AC]2 =
8202 = [AB2
] + 6502
[AB]2 = 8202 - 6502
= 672400 - 422500
= 249900.
12
820mm 650mm
C
499.9mm
B
A
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AB = 249900 = 499.9mm
Cos A = 8202+ 6202 - 499.92 x 820 x 650
672400 + 455500 - 249900.01 = 0.7931066000
Cos A = 844999.99 = 0.7931066000
A = Cos-1 = 370,3"
Area of the Triangle
Cos A = 844999.991066000
Area = 2 x X L x b
= L x b = 650 x 499.9
= 324.94mm2
Area of the top circle i.e. reflector rim.
A= r2 = or
= = 212399.2mm2
13
C
A B499.9mm
650mm
820mm
d2
4d2
4
D
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Area of mounting bottom rim
= = 3.14(610)2
= 292284.55mm2
Area of the parabolic reflector
= = 2545020mm2
Total area of the whole body
AT = 324.94+212399.2+292284.55+2545020
= 3050028.69mm2
Weight of the device i.e. the parabolic reflector and its sta is =
35kg (i.e. the weight weighed by using electronic weighingmachine).
Thus, 35 x 9.81 = 343.35N.
Therefore stress, = = 1.96 x 10-4N/mm2
Now, taking 3 as the factor safety.
Recall that;
Factor of safety =
Ultimate Stress = Factor of Safety x Working Stress
14
d2
44
d24
3.14 x 18002
343.25
1745008.69
Ultimatestress
Workin stress
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Ultimate Stress = 3 x 1.96 x 10-4
= 7.9 X 10-4 N/mm2
Calculation for the dryer box
Area of fig. A = L x b = 302 x 100 = 30,200mm2
Area of fig. B = Lx b = 210 x 100 = 2100mm2
Area of fig. C = b x h = X 210 x 202 = 21,210mm2
:.'The area of the dryer box = 30,200 + 21,000 + 21,210
= 73, 250mm2
Mass of the box = 3kg
Weight of the box 3 x 9.81 = 29.43N
Mass of a piece of a meat = 0. 12kg
15
283mm
100mm
210
310mm
B
A C
302
100mm
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Mass of 20 piece of meat = 0.12 x 20 = 2kg .I
Weight of a piece of meat = 0.12 x 9.81 = 1.18N
Weight of 20 pieces of meat = 1.18 x 20 = 23.6N
Total weight =.weight of the box + weight of 20 pieces meat
= 29.43 + 23.544 = 52.974N
Area of the dryer stand = Area of the box seat + Area of pipe A+ pipe B.
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BOX SEAT
Area of box seat = L x B
= 320 x 320 = 102 400mm2
Curve surface area of pipe A= base circumference x height
Curve surface area A = 2r x h
= dh = 3.142 x 25 x 910
= 71480.5mm2
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320mm
320mm
Pipe A
25mm
910mm
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Note: r = d2
Curve surface area of pipe B = 2rh = dh
= 3.142 x 30 x 700 = 65982mm2
Area of the dryer stand = 102400 + 71480.5 + 65982
= 239862.5mm2
Total area = Area of dryer box "+ area of the dryer stand =
66575 + 239862.5 = 306437.5mm2
Mass of the dryer stand = 7kg
Weight of the dryer stand = 7 x 9.81= 68.67N
Stress = Weight/ Area
Stress weight on the stand =
Total weight = weight of box and 20pieces of meat + weight of
stand
18
Pipe B
700mm
30mm
Total weight on the stand
Total area
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Weight of box and 20 pieces of meat = 52.974N Weight of the
stand = 68.67N
Total weight on the dryer stand = 52.974N + 68.67N =121.644N
Recalling that total area = 306437.5mm2
:. The stress = 121.644 = 3. 969 x 10 -4 N/mm2
306437.5
Due to variation in the load i.e, items to be dried, let factor of
safety be 1.5.
Ultimate stress = allowable working stress x Factor of safety
Allowable working stress = 3.969x 10-4 N/mm2
Factor of safety = 1. 5
:. Ultimate (M) = 3.969 X 10-4 x 1.5
= 5.9535 X 10-4 N/mm2
Note: 3.969 x 10-4 N/mm2 = Allowable working stress.
3.2 Material Selection
For the construction of this device, the selection of
materials used was based on its availability and cost.
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As a result of this, two main materials were considered and
used for the construction of the device.
(a) Carbon steel: This is also called plain carbon steel. Itis a steel where the main interstitial alloying
constituents is carbon. According to American iron and
steel Institute (AISI) defines carbon steel as a steel in
which no minimum content is specified or required for
chromium, cobalt molybdenum etc. In the construction,
carbon steel was the stand of the box and the parabolicreflector, then carbon mild steel was used for the
construction of the sectors or segment that form the
parabolic reflector. Apart from the availability and
affordability of this carbon steel, it is a good choice for
construction because of its availability and hardness
though it has some disadvantages such as poorresistance to corrosion and less brittle.
Aluminium: It was used as a reflector because of its
shinning nature.
(b) Glass: This was used for the construction of the box. It
was considered because of its transparent nature and to allow
easy penetration of solar energy (heart from sun). It is
constructed with its reflective surface inside the box to allow
reflection of heat in the box thereby retaining the heat needed
for drying.
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3.3 THEORETICAL BACKGROUND OF THE STUDY
The movement of the sun's ray follows the laws of refraction.
This is illustrated as follows:
Movement of sun-rays
LAWS OF REFRACTION
The laws of refraction state as follows
21
Incident rays
Glass (medium of ray
Refracted rays in the solar
i i
^ ^
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(i) The incident and refracted rays are on opposite sides of
the normal at the point of incidence and all three are in
the same plane.
(ii) Also know as snell's law. The ratio of the sine of the angle
of incidence to the angle of the angle of; refraction is a
constant for a given pair of media.
22
N
Oi
r
Air
Glass
AO = incident rayOB = Refracted rayNNI = NormalI = Angel of incidentr =Angel of refraction
Refraction of Light (Sun)
N
S 1
TE 1
E 2
S
T
Refracted rays through the glassblock
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Straight line SS is representing the surface separation between
air and glass ,is drawn in a sheet of drawing paper on a
drawing-board together with a normal on and several lines at
various .angles to on to represent incident rays from the sun
(solar) generation power sources.
A line TT' to represent the lower edge of the glass block is now
drawn. Without moving the ruler, the block is now placed
carefully in contact with the ruler. The two lines SS' and If'
should now coincide exactly with the upper and lower verticalface of the block.
REFRACTIVE INDEX
The value of the constant sin i for a ray passing from one
medium to sin r another is called the refractive index of the
second medium with respect to the first, and is denoted by the
symbol n.
23
Sun (lightIncident rays
Refracted rays in thesolar box
Glassmedium
S1
SNELLS LAW OF REFRACTION
T1
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For simplicity, only one pair of rays has been shown, we see
that:
Sin i = AB and sin r = CDAO CO
Therefore sin i AB x COSin r AO CD
AO = CO (radii of circle)
Therefore sin i = ABSin r CD
For each pair of. rays, AB and CD are measured and recorded in
a table. The AB/CD Should be found constant, thus verifying
snell's law. Thus, if any ray passes from air into glass, the
refractive index of water = n = Sin i/Sin r.24
AB
S
P1
P
2
O S1
CE1T T1
=
E2D
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3.4 FABRICATION TECHNIQUES
Fabrication is simply the process of constructing a
mechanical structure or device by bringing together the various
components or parts using any of the method of joining. This
includes welding, bracing, soldering, bonding, riveting and
bolting.
(a) Joining Method: For the purpose of this design, the
joining methods of this device are:
(i) Welding
(ii) Bolt and nuts
(iii) Adhesive bonding
Welding process was applied for the; construction of the stands
using a welding machine and electrodes. However, the major
coupling and assembling was done with bolts and nuts cap
screws, and machine screw. They were used to fasten and hold
together the sectors (segments) that form the parabolic shape
reflector. The joining of the glass box was mainly done by
adhesive materials e.g. glue.
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(b) Machining Process: Greater part of this project was
achieved by machining. The machining process undertakenduring the construction of this device involves the cutting and
machining of the plain mild steel plate to form a parabolic
shaped sectors (segments) used for the reflector. Other
operation carried out is the cutting of the glass using diamond
cutter. During the machining processes, the materials (i.e. plain
glass and carbon mild steel plate) were measured, marked andcut to require sizes and shapes as presented in the working
diagrams. (see assembling diagram).
(c) Surface finishing: This refers to the general broad range
of industrial process that alters the surface of the manufactured
item to achieve a certain property. The finishing processes
'employed in this work are: sand papering, filing, internal and.:,
external cleaning and painting of the device (solar dryer). This
process was employed to improve the appearance and
smoothness of the manufactured solar drying device, as well as
to control the surface friction.
3.5 ENGINEERING ANALYSIS AND EVALUATION
(a) Cost analysis and Evaluation: the following cost
and Evaluations were made on the construction of
this solar dryer
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27
S/N QTY Description of material
Length &Thickness
Rate Cost
1. 1 Sheet of plain glass 1500mm x700mm 7,800 7,8002. 3 Sheet of mild
carbon steel platefull length
1800mm x900mm
4,730 14,190
3. 2 Galvanize pipe 200mm long 3,300 6,6004. 1 Pack of electrode 1,800 1,8004 Roll of sand paper 350 3505. Pack of bolt and
nuts
1,600 1,600
6. 4 Rubber roller stand 450 1,8007. 4 Tins of oil paint 375 1,5008. 2 Brush 300 3009. 1 Merge wire 900 90010. 2 Hinges 220 55011. 3 Aluminum
cardboard sheet1800mm x900mm
3,000 9,000
12. Machining shop 8,000 8,00013. Miscellaneous 4,000 4,000
Total N 58,390
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(b) Tools used
1. Hammer
2. Chisel
3. Drilling Machine
4. Drilling Bit
5. Diamond cutter
6. T-Square
7. Plier
8. Tape
9. Centre Punch
10. Riveting machine
11. Wood Bench
12. Screw driver
13. Hand file.
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FUNCTION OF THE TOOLS USED
29
TOOLS FUNCTIONHammer Used for striking the head of the chisels and
center punch
Center punch For creating dots on the work-piece to enabledrill bit centre itself for operation
Tape Used for the measurement of the variouscomponent
Diamond glass It is used for the cutting of the plane glass intotheir cutter required pattern.
Drilling machinedrilling bits
Generation of holes on the work-piece fixed inthe drilling chuck to generate the required holes
Hack saw for cutting and sawing aluminum framesVice Hold work-piece in position
Drawing set, Teesquare anddrawing board
Used for the preparation of working diagrams
Hand file Removal of small particles of metal from thework-piece
Riveting machine Used for the riveting of rivet screws
Sand paper For the smoothing of the ply-wood
Hand brush Used for the painting of the ply wood
Cutting machine Cuts the aluminum frames Into different
dimensioned partsComputer It is used for the Auto-card
System (laptop) Design of the drawing in the system
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CHAPTER FOUR
4.0 EXPERIMENTATION/TESTING AND DISCUSSION
OF RESULT
4.1 EXPERIMENTATION AND TESTING
The testing of the solar dryer was done in the month of
December for 3days. The solar dryer was placed outside with
the concentrator or reflector facing the direction of the sun. Theparabolic concentrator has been rigidly fixed to its stand at an
angle approximately 45c to the horizontal to obtain
approximately perpendicular beam of sun rays. A fresh fish
weighing 1.5 kg was cut into 3 pieces and arranged on the
drying bed in single layer. The dryer chamber door was closed
and placed in position. The result obtained for hourly reading of6 hours everyday is tabulated in the table 1-3.
4.2 RESULT
Result on 17th December, 2012
Table 1: Variation of temperature with time on the first
day.
DayTime 10am 11am 12pm 1pm 2pm 3pm 4pm
Ts (C0) 28 30 33 35 35 32 40Tp (C0) 40 48 51 55 58 54 56
MA 1.5 1.28
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(kg)
Ts (CO) = Temperature of the sun.
Tp (CO) = Temperature of the drying chamber.
M 1 = Mass of fish at 10am
M2 = Mass of fish at 4pm
Moisture removed = Ml- M2 = 1.5- 1.28 = 0.22kg.
Result on 18th December, 2012.
Table 2: Variation of temperature with time on the second Day.
Day 2Time 10am 11am 12pm 1pm 2pm 3pm 4pm
Ts (C0
) 25 27 30 32 32 31 30Tp (C0) 38 42 50 55 58 55 52MA(kg)
1.28 1.13
Ml = 1.28, M21.13
Moisture removed = 1.28 - 1.13 = 0.15kg
Result on 19th December, 2012.
Table 3: Variation of Temperature with time on the third Day.
DayTime 10am 11am 12pm 1pm 2pm 3pm 4pm
Ts (C0) 29 33 35 33 31 30 27Tp (C0) 40 42 47 48 55 49 50MA(kg)
1.13 1.03
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M1 = 1.13, M2 1.03
1.13 -1.03=0.10kg
4.3 DISCUSSION OF RESULTS
Based on the results obtained during the test of the solar
dryer, temperature a9ove 45c was recorded against ambient
temperature in the drying chamber, large quantity of moisture
O.22kg was removed on the first day because the fish was
fresh and full of moisture and it was easy for evaporation to
take place. As the fish dried, the skin becomes harden and rate
of evaporation reduced, so quantity of moisture removed on
the third day reduced to 0.10kg. Table 1 to 3 shows the
variations of inside temperature of the drying chamber with
respect to time.
4.4 MAINTENANCE AND SAFETY
The solar dryer should not be mishandled, over loaded and
never left out in the rain. The only maintenance it should need
is cleaning of the reflector surface. Since the aluminized
cardboard sheet used on the surface of reflector attracts dust,
it should be lightly wiped periodically with a soft, dry cloth. The
dryer's box should be cleaned always after use. It should also
be lightly wiped allover with a wet cloth.
The dryer's box should be handled with great care since it is
constructed with glass which makes it more fragile than any
other component of the device. When not in use, the solar32
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dryer should be stored out of the sun or covered with a
waterproof cover.
Other components such as the box stand and reflector standshould be inspected and painted from time to time to avoid
rust.
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CHAPTER FIVE
5.0 CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
In conclusion, the need for the construction of a solar
dryer arose as an alternative to ordinary sun-drying technique.
Base on the results obtained during test, temperatureabove 45c was recorded. This high temperature in the drying
chamber cause 0.22 kg" of moisture will be removed on the
first day, 0.15kg on the second day and 0.10kg on the third
day. At the end of the, third day, the mass of 1.5 kg of fresh
fish was reduced to 1.03kg. Total amount of moisture removed
was 0.47kg which is the required amount for safe storage of
fish.
5.2 RECOMMENDATION
To use the solar dryer, simply place the solar box on it's
stand facing the parabolic reflector and adjusts the tilted angle
of the parabolic reflector through the elevation pole until the
box shadow falls in the centre of the parabolic reflector for the
best focus to be obtained. This is about 684mm from the depth
of the reflector.
The parabolic reflector stand holds the reflector and allows it to
be rotated to follow the sun as it moves across the sky.
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The device should be use in area, where sunshine is plentiful.
The performance of the solar dryer can still be improved upon
especially in the aspect of reducing the drying time and
probably storage of heat within the system.
Also, meteorological data should be readily available to
designer, and users of solar products. Proper account of heat
loss, reflective power of the reflector and focal point of the
systems should be considered to ensure maximum efficiency
and effectiveness of the system on further design. Furtherrecommendation on usage is considered as follows:
1. Pre-treatment of the food such as blanching (boiling/
steaming) before drying is advisable.
2. Effective drying is accomplished with a combination of
heat and air movement.
3. Typical drying time ranges from 1 to 3 days depending on
sun, air movement humidity, quantity and type of food.
4. Food to be loaded in the box should be cut into thin slice
and spread out to allow free air movement.
5. Allow food to cool completely before storing.
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