Solar D Dryer
Solar D Dryer
Solar D Dryer
ENGINEERING
SOLAR DRYER
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ABSTRACT
Different commodities are dried locally using different methods including
natural drying in open area, solar drying. Different solar dryer designs
can be found in various parts of india and a suitable design can be
selected for the prototype depending on the type of drying contents,
climatic condition, etc.
Open air drying was reported as most common method of drying agro-
commodities. The farmers were not happy with with uncontrolled open air
method and desired to design a simple and easy to use low cost dryer
suitable for drying any agro commodities in a clear or /rainy day.
The purpose of this project was to study, design, fabricate and test a
solar cabinet type of dryer for drying mango. Main emphasis was givenin
designing a simple dryer to be made from locally available materials and
different products or materials are dried like cereals,legumes,
condiments, fruites, vegetables, meat and fish mostly in open air or
under shade. A prototype dryer was designed for 1kg of mango slices to
be dried by means of direct solar heat in conjunction with an auxiliary
heater. Mango pulp is perfectly suited for conversion to juices, nectars,
jams, bakery fillings, fruit meals to children, flavours for food industry, to
make ice-cream& yog hurt. Processed mangoes enable exporters to
serve their market even during off season period for fresh mangoes.
Having gained the confidence on the dryer performance, detailed tests
were conducted to study the effects of drying modes. From performance
and graphs it is seen that the percentage moisture removal desired at the
design stage was achieved.
INDEX
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Particulars Page no
Certificate………………………………………………………….3
Acknowledgement……………………………………………….4
Abstreact…………………………………………………………..5
List of Table……………………………………………………….9
List of Fifure……………………………………………………...10
1.Introduction………………………………………………..11
1.2 Objective……………………………………………….16
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Solar Dryer for mango slices……………………………..24
Sun’s warmth…………………………………….36
6. References……………………………………………..……….55
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LIST OF TABLES
31
3.1 Design of Conditions & Assumptions
32
3.2 Value of Design Parameters
38
4.1 Drying characteristics of Some Products
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LIST OF FIGURE
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1. INTRODUCTION
Drying has been used to preserve food throughout the world since
prehistoric times. When people learned that dried foods left out in the
sun remain wholesome for long periods. The dried foods industry has
greatly expanded after World War II but remained restricted to dried
foods, including milk, soup, eggs fruits, yeast some meats and instant
coffee etc. several mechanical drying units were built on experimental
basis and a few commercial units were in operation primarily for
dehydration of fruits, vegetables, and hay and seed corn. Much of the
research in agriculture product up to 1955 was concerned mainly with
field result. Since 1955 considerable research has dealt with theory
and principles of drying in the design of farm level of commercial
driers.
Drying in one of the oldest user of solar energy. The practice has
been cheaply and successfully employed all over the world for
thousands of years. The basics philosophy of drying foods is to
remove water for prevention of micro organisms to grow and limit
food enzymatic activity. It reduces an item to roughly 50% of its
original volume and 20% of its original weight through gradual
elimination of water. Three basic methods of drying are used today (i)
sun drying, a traditional method in which foods dry naturally in the
sun, (ii) hot air drying in which foods are exposed to a blast of hot air
and (iii) freeze drying in which frozen foods are placed in a vacuum
chamber to draw out the water. Removing the water preserves foods
because micro
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Figer 1.1 annual mean global irradiance on a horizontal plane
at the surfaceof earth W/m averaged over 24 hours (Source:
Budyko, 1958)
Recent work on solar drying has been devoted in two directions. There has
been work on direct drying where in the material is exposed to direct solar
heat and the product moisture is evaporated to the atmosphere to the other
method drying is indirectly accomplished by the use of some type of
collector, which furnishes hot air to a separate drying unit . Since solar heat
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is not a constant source of heat due to weather conditions. Systems that
are more effective are possible in some cases if a supplemental oil/gas or
electric heater is used when the weather is cloudy.
The methods of utilizing solar energy for drying to date have largely been
based on open air-drying. However to better utilize this abundant source of
energy effectively. Systems need to be developed based on specific needs.
Crop dryers that can be used active dryers and passive dryers. Active
dryers use an external device operated for example a fan to circulate the
air, but passive dryers do not. Although a passive system tends to be more
realistic for application in developing countries because of the relatively
low initial capital and operating costs, it is possible to use active system for
relatively large-scale applications. There are various needs in which solar
energy can be used for drying.
The open air-drying method use solar insulation, wind velocities, ambient
air temperatures and relative humidity of the air to reduce the moisture
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content of crops. The crop is generally spread on clean ground in a thin
layer. The mechanism by which the incident solar radiation. The solar
radiation heats the ground and the surrounding air. Heat is transferred to
the crop by conduction from the ground, by conduction and convention
form the air close to the crop and by radiation from the sun. The moisture at
or near the surface of the crop is thus heated
And is vaporized, which causes movement of moisture to the surface. The
heat transferred to the croup may also be transmitted to the inner core by
conduction, which will in turn liberate further vapour. Thus the rate of drying
depends upon the available radiation and ground temperature. Because
there is little or no vertical circulation of air through the croup, they have to
be spread thinly, which required large land area.
Another method is to use trays slacked one above the other with their base
of wire mesh. This process increases the drying rate and reduces the
space needed for the crop spreading. Direct drying use dryers that consist
of an enclosure with a transparent cover. The crops are placed on trays in
the enclosure and elevated temperatures cause evaporation of water from
crops. The moist laden air through dryer. The design of direct dryers is
such that the croup is directly beneath the transparent top cover that is
sloped at the appropriate angle to collect maximum solar radiation. The
recommended value of this angle is α = latitude + 15۬۬ . indirect dryers
however , use heated air in a solar air collector to dry out commodities
without direct contact of solar energy with commodities. The heated air
could be circulated using a fan or just natural convection.
1.2 OBJECTIVES
1.to design and fabricate a suitable prototype for drying common agro-
commodities usually dried traditionally in open air
2.to evaluate the performance of the prototype using some common
agro-commodities with different loads and drying modes.
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1.3 MATERIAL THICKNESS & DRYING
Moy et designed three type of dryers. Direct absorption solar dryer with
reflector and combined mode solar dryers models. The second group of
dryers had a collector attached to the main drying units.
The experimental solar drying of taro roots in slice and shredded forms
indicated that the direct absorption dryer with plastic mirrors as reflectors
and two mixed mode solar dryers were reasonably efficient in drying taro
into stable forms of storage. With taro slices at loading density at 7.3 Kg/m3
, the direct dryer with reflector was very efficient , the mixed mode dryer
and the direct cage dryer were equally efficient, but slightly less than the
direct dryer with reflectors, the indirect mode of solar drying was least
efficient.
While preparing the taro roots into shredded from resulted in larger surface-
to-volume ratio and could be useful for making flour after the shred were nit
necessarily effective for solar drying because the pieces tended to clump
together thereby impending air passage through the shreds.
The quality of dried product was found was found acceptable to consumers
and nutritionally satisfactory. The storage of dried product for 32 weeks at
room temperature showed no adverse effect on quality or change in
chemical composition. The dried product had a moisture content of 10-13%
Drying experiments over two years showed that if the drying rate due to
high air velocity, was too great the product tended to dry mainly from the
surface layers and after being removed from the dryer, the surface become
monist again.
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The collector and drying chamber were made of A-5 aluminum. The
collecting surface was 2.32 x 1m with a cover glass thickness of 3 mm and
insulation (6 cm of glass wool) on the sides and bottom of the collector. The
drying chamber of three trays 15 cm apart each. The trays were made from
1 x 1 cm wire mesh to allow easy flow of air. Measurement were taken
every six minutes on temperature of air entering and leaving the collector.
The glass plates the collector plate and the air entering and drying chamber
and the global radiation with the use of a Hewlett data acquisition system.
The results obtained from the limited number of tests were found
encouraging.
2. LITERATURE REVIEW
Excel (1979) worked vat the Asian institute of technology and built a rice
dryer to be constructed by the local farmers at low cost using indigenous
materials. In this dryer sunlight passed through the clear plastic sheet and
warmed the air inside aided by a layer of burnt rice hunks that covered the
ground below to absorb the radiation. The warm air passed through the
bad off the paddy and dried it. The chimney provided a tall column of warm
air that increases the flow of heat through the bad by natural convection.
The air inlet when faced the wind direction increase the flow further.
Djokoto et al developed and tested solar tunnel dryer for drying weight at
international rise research institute (IRRI) Philippines. The dryer consisted
of a collector and tunnel drying chambers arranged parallel to each other.
A centrifugal blower with backward curved drying air through the collector.
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Tyuirn et al (1989) designed and developed a simple solar powered dryer
for fruits. A layer of produce was spread in a solar heated chamber on a
lattice through which air was forced. Roof ventilators regulated inside
temperature and humidity within 6 days, grapes could be dried sufficiently
for further processing, whereas onions were dried within 24 hours.
Once the dryer was closed the fans were switched on. The maximum drying
temperature was selected 65 ۬C to avoid significant quality losses. The
performance of the dryer was examined and it was found that 60 kg of dry
apricots could be obtained forma harvest of 3000 kg.
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2.1TRY STACKING AND DRYING EFFICIENCY
Fuller et al (1994) developed and tested a solar rotary tray system for use
in solar tunnel dryer. The system was designed to replace and overcome
the main limitation which occurred with stacked try system. The system
offered advisor even drying and easy on and off loading compared with
stacked trays. The anther pointed out that trials conducted in 1989 shoed
uneven exposure of the bottom trays, solar radiation attenuation was
approximately 70%, 30%, 10%, and 5% respectively.
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2.2MISCELLANEOUS DRYING ACTIVITIES
Abidov et al (1990) designed and tested a solar fruit-drying unit with a solar
chamber divided into three section with heat-insulated walls. The internal
walls were colour black. Convention was provided by holes and intensified
by a ventilation pipe. In the period of passive radiation the outlet holes were
closed.
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Miah [1993] reviewed the present situation regarding grain-drying technology
in Bangladesh. Various drying methods were discussed including sun drying
and drying rooms with ceiling fans, and a recently developed batch dryer
was also mentioned briefly. It was concluded that while arterial dryers were
not cost-effective during sunny wither, they were found essential during
prolonged period of rain.
Relative humidity, wind velocity and mass of material per unit try area
[loading] on the sun drying rate of cassae chips were investigated. The
factors that directly influenced the internal temperature inside the food were
low, such that a simple lumped-capacity models that predicted a uniform
internal food temperature inside the food were low, such that predicated a
uniform internal food temperature could be used in combination with the
moisture field.
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Updraft solar dryer deigns are the most frequently see cabinet from. In this
design, the hot air flows upward through a solar heat collection trough the try
and the bottom of cabinet underneath the food. The dry air rises through the
tray and around the food, exiting through a vent at the top or near the top of
the shadowed side. The theoretical basis for this design is that hot air rises
and therefore when heated , the air flows naturally upward through the trays
of food.
Three major components were considered for the design of the dryer.
These included
A. The main drying unit called “Main dryer”
B. An auxiliary collector called “Booster”
C. Fossil fuel heater called “Heater / stove ” for article heating in cloudy
/rainy days
Carpio (1981) and Boston et al (1992) pointed out than sun drying
depended upon total surface area exposed to sunlight. Therefore,
emphasis was given to load the material in the trays stacked one above
the other to provide maximum surface area to let escape the moisture from
the commodity through maximum surface area.
Duffie and beckhan [1974] noted that flat plat collector could be designed
for applications requiring energy delivery at moderate temperature and
those they do not require qriatation towards sun. agrawal [1983] pointed
out that in northern hemisphere , the most favorable oriatation is that the
surface facing south should be inclined at an angel to latitude + 15 ° in
winer and latitude - 15 ° in summer , wheres stine and harridam [1985]
suggested the most logical tilt angel for fixed flate plate collectors with a
tilted surface from horizontal at an angel equal to the latitude angel.
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2.3.1 USE OF AUXILIARY COMPONENTS
A chimney of was fabricated from iron sheet 1 mm thick. The shape of the
chimney resembled a rectangular block with top cover of a hut shape
structure 45 ° included with horizontal and properly reverted with the body
of the chimney. The top cover had sufficient clearance to allow escape of
moist laden air from the chimney to the open atmosphere. The entire
chimney was painted black to further increase the temperature of the moist
laden air in chimney for fast escape under buoyancy effect through natural
convection , without the use of a fan or a blower.
We have taken help of the design prepared and use in Sudan by admin
omda, Mohamed okay, Mohamed ayosub Ismail. The geographical and
climatic condition of India and Sudan are almost same, hence the
assumption made were taken up into the calculation. Sudan and India are
both situated at 20 ° latitude (center) and both are typical countries. The
average ambient condition are 30 ° C air temperature 25 % R,H. in month
of April with daily global solar radiation incident on horizontal surface of
about 20 MJ/m2 per day.
OBJECTIVE:
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To designed a natural convection solar dryer to dry mango slices. Solar
dryer to be constructed to dry 1 kg of mango slice. Initial moisture content
of mangoes is 85% & final moisture content desired is 6%.
The solar dryers has the shape of a home cabinet with tilted transparent
top. The angle of the slope of the dryer cover is 37 ° for the latitude location
it provided with air inlet and outlet holes at the front and back respectively.
The outlet vent is higher level. The vents have sliding covers which control
air and outflow.
The movement of air through the vents, when the dryer is placed in the
path of air flow , brings about a thermo siphon effect which creates an
updraft of solar heated air laden with moisture out of the drying chamber.
3.3.1DESIGN CALCULATION
TO carry out design calculation and size of the dryer, the design condition
applicable to jaipur are required. The condition and summarized in Table 1
are used for the design of the mango dryer. From the condition, assumption
and relationship, the values of the design parameters were calculated.
The result of calculation are summarized in table 5.2.
i-Amount of the moisture to be removed from a given quality of wet mango
slice to bring the moisture content to safe storage level in a specified time.
Where :
-mp is the initial mass of product to be dried, kg ;
-M is the initial moisture content, % wet basis,
-Mf is the final moisture content, % wet basis.
mw = 1(0.85-0.06)/(100-0.06)
=0.79 kg of water /kg of mango.
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aw =1-exp[-exp(0.914+0.5639lnM)] ------------------------- (2)
where
0.89729=2.610 x RH/100
RH = 34.37
= 079 x 23255.74
= 18372.0346 KJ
Where :
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= 232555.74 kJ/kg.
Where:
Moreover , the total heat energy, E (kg) required to evaporate water was
calculated as follows:
=6.475(78.18-29.764) x 10
=3.1349 MJ
Where:
The enthaphalpy (h) of moist air in J/kg dry air temperature T(°C)can be
approximated as (Brooker el al.,1992);
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iv- Average drying rate
average drying rate, mdr, was determined from the mass of moisture to be
removed by solar heat and drying time by the following equation:
=079/10
The mass OF AIR needed for drying was calculated using equation given
by sodha et al. (1987) as follows:
Where:
Wf & wi = find and initial humidity ratio, respectively , kg H2O / kg dry air
From the total useful heat energy required to evaporate moisture and the
net radiation received by the tilted collector, the solar drying system
collector area Ac, in m2 can be calculated from the following equation.
=3.134/20 x 0.35
=0.447 m2
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Width of collector =0.5 mts
Where :-
E is the total useful energy received by the drying air , kj;
i is the global radiation on the horizontal surface during period, kj /m2 =
20 kj /m2
&
ή is the collector efficiency , 35 % (sodha et al.,1987)
volumetric airflow rate , va was obtained by dividing ma by density of air
which is 1.2 kg/ m3
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Item Condition or assumption
Crop Mango
Variedty Totapuri
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PARAMETER VALUE DATE OF EQUATION
USED
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a natural convection solar dryer of a box – type ( cabinet was designed and
constructed. The constructed dryer (cabinet –type) consisted of drying
chamber and solar collector combined in one unit as shown in fig. 9.
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Figure 3.5.2 model of solar dryer
A simple box frame 90cm long, 51 cm wide and 34cm hight at the back
and 10 cm high in front made of mild steel plates (16 guages ) 1.6mm was
fabricated. Sheets of mild metal sheet 0.16cm thick were welded onto three
sides and bottom of the fabricated frame. Glass wood was used as
insulator with a thickness of 1 cm and placed the bottom mild metal sheet.
Try holders made of angle iron were welded in such away to hold try inside
drying chamber. The lower holder was 15cm above the absorber glass
wool and the upper was 15. Asbestos sheet of 0.3 cm thick were used as
insulator and fitted to the three inner sides of the
frame. Aluminum foil sheets were glued to asbestos sheet and used as
moisture barrier and to reflect incident solar radiation to absorber from
sides.
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One panel of a 5-mm thick transparent glass (84.5 cm x 44.5 cm ) was
glued to the top part of the frame with sealant. The glass used was
toughened glass, low in iron content (water white glass) because of its
good transmissivity for solar radiation. The glass was inclined at an angle
of 37° due south, which is the angle of the experimental site.
In side the drying chamber there were four movable wire mesh trays that
can be placed on their hiders. The frame of each try was constructed from
wood. Each tray was made of wood and stainless steel wire mesh. For
loading and unloading of material to be dried, a hinged door was made for
this purpose.
The hinged door was constructed from M.S. metal sheet (0.16 cm thick ) ,
0.3 cm asbestos was use as insulator. The door was sealed to prevent air
leakage between the surrounding and drying chamber.
Two air vents for ventialation were provided. Intel air hole (front air vent)
located above the base of absorber plate; 60cm legth and 6 cm width,
provided with adjustable cover that was tow level of operating; full and half
opening for dryer temperature control.
The outlet vent (rear air vent); 60 cm x 6 cm was locked top edge and
provided with adjustable cover for dryer temperature control. It has two
levels of opening; full and half opening.
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Size :- 80 x 80 x 25
Voltage :- 12 V
Bearing :- sleeve
Current :- 0.12 mA
RPM :- 2500
Air flow rate :- 32CFM
As the crop is warmed up , including the air between the plant fibers , the
water it contains quickly evaporates. Pretty soon the air within and
surrounding the croup is saturated with water vapour. Fortunately the air
moving alongside, warm and unsecured can take up this moisture and
transport it away. A small fan will of course help this process, but it is not
strictly necessary.
At a certain moment the air in the room has taken up so much moisture
from the croup that the windows suddenly mist up ( though this will depend
on the outside temperature ); the air against the could window has been
cooled to below the ‘dew point’. In this way the water in the croup is
transferred to the window panes, where it can be wiped off, or allowed to
fall into a gutter which leads outsides the room.
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Solar drying is technique particulary suited the warmer parts of world
since:
MOISTURE
SR. PRODUCT FORM DRYING CONTENT(W.B) %
NO. TEMP. (°C)
INITIAL FINAL
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1 Amla Pieces 67 81.0 15.0
2 Carrot slices 56 91.0 8.0
3 Green chilly pieces 73 86.0 7.0
4 Mango slices 74 85.0 6.0
5 Mango bar pulp 62 40.0 14.0
6 Potato slices 58 82.0 6.0
7 Sweet mango slices 62 34.5 4.0
8 Tomato pieces 80 94.0 5.5
The warmth in the drier actually encourages rotting in product that are not
yet compliantly dried. For this reason the speed at which the drying takes
place is important. The fastest drying is brought about by strong ventilation
with dry air.
Under such circumstances the difference between the internal and external
temperature is less important than simply getting rid of the moisture as fast
as possible. At a later stage the evaporation is les abundant, and much
more temperature dependent. If the ventilation is now limited, the air in the
dried will be warmed up, and the drying process improved further.
These consideration apart, the quality of the original product ( its freshness
and cleanliss. ) and of the drying air both exert a critical on the quality of
the end product.
Electric fans strongly increase the transfer of warmath to the drying air.
This is especially true if the product is stacked close together, impending
the air circulation. It is important, therefore, to rack and shelve the product
in such a way that the products in such a way that the air circulation is
impeded as little as possible. Forced air circulation is only worthwhile if
sufficient energy can be taken in by the drier; this supposes a large enough
( with regard to the mass to be dried) and efficient enough absorbent
surface ( for example, porous material), and special glass for covering.
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If this factors are not taken into account, the temperature within the drier
will not be much higher than that outside it – which of coerce does not
promote efficient drying, and certainly not at the last drying stage. Forced
air circulation becomes economics in larger installation drying 50-10 kg per
day more. In non-forced air circulation, or natural ventilation a site is
chosen which makes best use of prevailing wides, the air inlet and outlet
being oriented accordingly, or a chimney is added to improve the draught.
In drying, the relative and absolute humidity are of great importance. Air
can take up moisture, but only up to a limit. This limit is the absolute
(=maximum) humidity, and is temparature dependent.
In practice, however, the air is very rerely fully saturated with moisture. The
degree of saturation at a given temparature is called the relative humidity
and express as a percentage of the absolute humidity at that temparature.
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If air is passed over a moist substance it will take up moisture until it is
virtually fully saturated, that is to say until absolute has been reached.
However, the capacity of the air for taking up this moisture is dependent on
its temparature. The higher the remparature, the higher the absolute
humidity, and the larger the uptake of moisture.
If air is warmed the amount of moisture in it remains the same, but the
relative humidity falls; and the air is therefore enabled to take up more
moisture from its surrondings.
A transparent cover which admits sunlight and limits heats loss (glass
or plastic)
An absorbent surface, made dark in colour, which takes up sunlight
and converts it to warmth then giving this can also be the product
that needs drting it self.
An insulating layer underneath.
An air intake and an outlet, by which means the damper air can be
replaced with fresh drier air.
The four elements can be modifieds if necessary, and/or othe element
added, for example a fan or chimney.
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5. TYPES OF SOLAR DRYER
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Figure 5.2 solar drver indirectly employed
Moreover, certain sessitive products can become overheated and
evantually charred. Dried fruits so spoiled necessary loses its sale value.
However, its use demands some care. Faulty stacking of the product to be
dried can lead to condensation; rising hot air in the lowest layers becomes
saturated, but cool so quickly as it rises that the water condense out again
in the upper layers.
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angle of the absorber is also specified by the latitude. Take care
that the collector is facing the sun and that it is out of shadow as far
as possible.
The air must not cool – this causes a reverse airflow, a wooden chimney is
suitable. A chimney less than 40 cm height will in this case suffice.
Despite the many experiment carried out in almost every tropical area, it
still appears to be impossible to design the ‘ideal’ solar drier. Depending on
the building materials used, the product that need drying, and the season in
which the drying must take place, the ‘ideal ‘ dryer take many forms.
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Such as installation makes it possible to control the air temperature in the
drying room, and thus to ensure that the different drying stages work well (
for example, for sowing-seeds). In the first drying stage higher temperature
are allowable because the considerable free water still in the product.
Dust on the cover reduces its efficiency, and should be removed as often
as possible. If than collector is strongly titled, this favors the airflow and
therefore promotes good heat transfer. However , the further it is titled
below the sun the less sunlight it receive. For this reason the indirect dryers
are often better in practice.
Watch out for excessive surrounding air humidity, for instance during misty
early mornings. It is vital that the drier is only set into operation. ( by
opening the air intake and outlet) after the mist has risen and the air
humidity has fallan. Otherwise there is a risk that in the weak early morning
sunshine product, instead of being dried, attracts condensation.
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PAULUDHIANA
Function : Natural convection type device used to dry product like fruits,
vegetables, spice etc. for domestic use under hygienic conditions.
SPRERI V.V.NAGAR
Performance: efficiency of the packed bed type solar air heater was
found around 40% more than commercial heater, very good quality finished
product and agro-product retain their colour and flavor to a large extent.
Approximate cost:- packed bed type and unglazed type flute plate
solar air heaters cost RS. 3,500(US $ 77) & Rs.2000/- (US $ 44 ) per
square meter area, respectively. A 200 kg/d capacity solar of the onion
flakes cost two that of the electric fired dryers. However, cost of the drying
per kg product of the solar dryer is less than half that of the electrical dryer.
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Present status: A few installations are under operation for drying onion
flakes, tomatoes mushroom etc. the design, installation and commixing and
commission of the oral dryer system can be taken up on consultancy basis.
Function: Natural walk –in type dryer useful for bulk drying of agriculture
& industrial products at moderate air temperature.
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calcium phosphate is reduced to around 15 % from an initial value of 35-
40% in 2-3 solar days depending upon the solar insulation.
Design features:- batch type stiffer, portable, eases loading & unloading
of cocoons, glass wool insulation, double glass glazing back-up of 2 kW
rating with thermostat, collector are of 2m2 and loading capacity of 10 kg
cocoons per batch.
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silk reeling center was found to be 20-60 kg / day depending upon season.
The remittal of solar stifled and electric oven stifled cocoons was almost
same.
Cost: the stiffer costs around Rs. 15,000/-(US $ 330). Solar stifling of
cocoons costs around 35% lower than stifling by electric c oven method.
the mango ( mangifera indicia )is a tropical fruit, original from the south of
asia, and ot is avlible worlwide today. The calture of mango, although still
concentrated asia, was become enlarged for some countries, in all the
continets, being important in africa and americas and with lesser presence
in the Europ, where it is caltivated in small scale in spain. From the annual
world production of 18 milion tones, asia accounts for 75% , americas 14%,
africa 10% and 1 % remain in other areas, as austalia and europe.
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Drying lowers weight and volume of the product hence lower costs in
trasportation and storage. However, drying allows some lowering in
natrition value of the product e.g. loss of vitamin C, and changes of colour
and appearance that might not be desirable.
FRUITS:
Fruits like mangoes, paw paws, guavas and bananas can easily be
dried. However, they should be harvested at the right stage and ripeness.
Hard ripe stage in mangoes, paw paws and bananas gives best result.
Avoid overripe, under mature fruits in order to obtain good products. To
prepare the fruits for drying, wash then throughly with clean water.
Scrubbing with a brush might be necessary like in case of mango fruit with
a lot of latex cover. The fruits are placed if necessary and cut into smaller
uniform pieces to ensure faster drying. Stainless steel knives are
recommed for peeling and cutting of the slice or pieces. To avoid
discolaration and exessive vitamin losses, tretment with anti-oxidant like
cirtrus(lemon) juice is done . fruits like pineapples may require pre-cooking
to soften fibros tissue hence drying. Drying is done on trys, which should be
made of wood , fabric, plastic or sisal material. This is because metal
materials may affect the drying product negatively e.g. copper destroys
vitamin C, iron rusts, aluminium discolours fruits and corrodes.
VEGETABLES
BLANCHING
MANGO
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Several option have become available for large scale processing of mango
products.
Mango pulp
Juice
Nectar
Fruit sauces
Fruit sauces
Fruit cocktails
Mango wine
Glazing
Dryer around the world are using improved methods to make all sorts of
new dried fruit products. Many of these make great natural snacks. Mango
is delicious as a snack, in a sauce or in a salad. Snacks are packed in
transparent plastic bags. Mangoes are dried in the from of pieces, powders,
and flakes. Drying procedure such as sun drying, try drying tunnel
dehydration, vacuum drying, and osmotic dehydration may be used.
Packaged and stored properly, dried mango product are stable and
nutritious.
Canned mangoes do not have to meet any specific standards, but CODEX
Alimentations ( Latin, meting, food law or code, UN Commission for food
standards) is developing international facts written on containers. Mangoes
are the common product name of the canned food that is made from
properly prepare fresh mango varieties, that have the peel ( rind), stems
and pits (stones) removed; shall be packed in packing medium consting of
water, with or without a sweating ingredient, or natural reconstituted,
concentrated fruit juice or juices, or fruit puree or nectar, with or without a
sweetening ingredient; and many contain: pectin, a suitable acid ingredient,
calcium-based firming agent, and beta-carotene.
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REFERANCES
BOOKS:
1 SOLAR DRYING SYSTEM BY B.K.BALA
WEBSITES:
1. http://www.tropentag.de
2. http://www.se-project.com/sito/home/index_uk.html
3. http://www.the-green-company.com/
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