International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
Review on Research and Development in Solar Banana Dryer
Application
P. S. Patil#1, D.R.Pangavane#2, D.S.Deshmukh#3
1
Assistant Professor Department of Mechanical Engineering, R.C.Patel Institute of Technology Shirpur,
Dhule, M.S.India
2
Principal K. J. Somaiya Institute of Engineering And Information Technology Vidyanagar,
Mumbai M.S.India
3
Professor and H.O.D.S.S.B.T College of Engineering Bambhori Jalgaon M.S.India
Abstract— Demand for dried tropical fruits such
as mango, banana, papaya and pineapple are
increasing Day by day. There is plenty of extra
sunshine available to dry food and vegetables. On
clean day approximately 800 Watts of solar energy
are available for use per square metre area of earth
surface. Typical operating conditions for solar dryer
will vary depending upon weather. There is variety of
solar dryer available for farmers according to their
needs. Selection of dryer for particular application
depends upon the countries situated in tropical and
subtropical region. A systematic study of different
types of solar drying system invented earlier is
presented in this paper. Groups of solar-energy
dryers are studied, viz. passive or natural-circulation
solar-energy dryers and active or forced-convection
solar-energy dryers. We also highlight some recent
developments in solar banana drying systems.
Keywords - solar dryer, passive circulaion,
the process is labor intensive, time consuming and
banana drying systems ,solar radiation
the fuel energy required. Solar dryer technology can
Small farmers in developing countries
produce vegetables, fruits as major products. In case
of overproduction, tremendous losses occur because
farmers have neither access to markets in big cities
due to poor food product quality and absence of
good marketing. As an alternative to the marketing
of fresh fruits and vegetables, small farmers can
The process of banana drying has been carried
out from ancient days there are many demerits of
open drying products spoil due to rain, wind,
moisture and dust; loss due to birds and animals;
the
development, is energy intensive and high cost and
ultimately increases the product price. Solar-drying
offers an alternative
which can process
the
vegetables and fruits in clean, hygienic and sanitary
conditions to national and international standards
with zero energy costs. It saves energy, time,
occupies less area, improves product quality, and
makes the process easier. Solar drying can be used
for the complete drying process or as a supplement to
artificial drying systems, in the latter case reducing
produce hygienic, good Quality food products. In this
context, one of the possible areas of immediate
intervention in developing countries appears to be the
solar drying of cash crops such as tobacco, tea,
coffee,
grapes
raisin,
small
cardamom,
chili,
coriander seeds, ginger, turmeric, black pepper,
onion flakes etc. For such crops, even with the
capital intensive nature of solar dryers, the unit cost
produce dried products.
in
Artificial mechanical drying, a relatively recent
be used in small-scale food processing industries to
I. INTRODUCTION
deterioration
requires more space or drying.
harvested
crops
due
to
decomposition, insect attacks and fungi, etc. Further,
of solar drying is expected to be a small fraction of
the selling price of the dried product. In this paper, an
attempt has been made towards potential assessment
of solar drying of some cash crops in India. Solar
drying is often differentiated from „„sun drying‟‟ by
the use of equipment to collect the sun‟s radiation in
order to harness the radioactive energy for drying
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applications. Sun drying is a common farming and
quality product. But the equipment is expensive and
agricultural process in many countries freely
requires substantial quantities of fuel or electricity to
available sun energy while ensuring good product
operate.
quality via judicious control of the radioactive heat.
R. Baini, T.A.G. Langrish
[17]
in their work
Solar energy has been used throughout the world to
has assessed the dominant type of diffusion in drying
dry food products. Such is the diversity of solar
bananas, together with performing an analysis of the
dryers that commonly solar-dried products include
effect of temperature and moisture content on the
grains, fruits, meat, vegetables etc.
[1]
diffusivity, investigating the variations in the
Many of these fruits and vegetables contain a
diffusivities within and between the bananas, and
large quantity of initial moisture content and are
studying the effect of the degree of ripeness on the
therefore
diffusivity.
highly
susceptible
to
rapid
quality
degradation, even to the extent of spoilage, if not
A number of designs are proven technically and
kept in thermally controlled storage facilities.
while none are yet in widespread use, there is still
Therefore, it is imperative that, besides employing
optimism about their potential. Solar drying is a
reliable storage systems, post-harvest methods such
potential decentralized thermal application of solar
as drying can be implemented hand-in-hand to
energy particularly in developing countries [2–5].
convert
these
perishable
products
into
more
stabilized products that can be kept under a minimal
controlled Environment for an extended period of
time. Many food industries dealing with commercial
products employ state-of-the-art drying equipment
such as freeze dryers, spray dryers, drum dryers and
II. WORKING OF SOLAR DRYER
Direct solar dryers expose the substance to be
dehydrated
to
direct sunlight.
They
have
a black absorbing surface which collects the light and
converts it to heat; the substance to be dried is placed
directly on this surface. These driers may have
steam dryers. The prices of such dryers are
enclosures, glass covers or vents to in order to
significantly high and only commercial companies
increase efficiency. [7]
generating substantial revenues can afford them.
Therefore, because of the high initial capital costs,
most of the small-scale companies dealing directly
with farmers are not able to afford the price of
employing such high-end drying technologies that
are known to produce high quality products. Instead
cheaper, easy-to-use and practical drying systems
become appealing to such companies or even to the
rural farmers.
Atul Sharma et al.
presented
using only solar energy. The crops are generally
spread on the ground, mat, cement floor where they
receive short wavelength solar energy during a major
part of the day and also natural air Circulation. A part
of the energy is reflected back and the remaining is
absorbed by the surface depending upon the color of
the crops. The absorbed radiation is converted into
thermal energy and the temperature of the material
[1]
reported previously is
A comprehensive review of the various
designs, details of construction and operational
principles of the wide variety of practically realized
designs of solar-energy drying systems.
starts to increase. However there are losses like the
long wavelength radiation loss from the surface of
crop to ambient air through moist air and also
convective heat loss due to the blowing wind through
moist air over the crop surface. The process is
Mechanized drying is faster than open-air
drying, requires less space and usually gives a better
ISSN: 2231-5381
Fig 1 shows working principle of open drying
independent of any other source of energy except
sunlight and hence the cheapest method however has
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a number of limitations. In general, the open sun
operational principles of the wide variety of
drying method does not fulfill the required quality
practically-realised designs of solar-energy drying
standards and sometimes the products cannot be sold
systems. The constructional and oprating features
in the international market. With the awareness of
may vary according to the design of solar dryer. The
inadequacies involved in open sun drying, a more
classification of solar dryer primarily according to
scientific method of solar-energy utilization for crop
their heating modes and the manner in which the
drying has emerged termed as solar drying.
solar heat is utilised. In broad terms, they can be
classified into two major groups, namely
1.active solar-energy drying systems (most types of
which are often termed hybrid solar dryers); and
2.
passive
solar-energy
(conventionally
termed
drying
systems
natural-circulation
solar
drying systems).
Three distinct sub-classes of either the active or
passive solar drying systems can be identified (which
vary mainly in the design arrangement of system
components and the mode of utilisation of the solar
Fig. 1 working principle of open sun drying.
heat, namely [7]
[1]
III. CLASSIFICATION OF SOLAR
integral-type solar dryers;
DRYERS
Dryers are more commonly classified broadly
distributed-type solar dryers; and
according to their heating sources into fossil fuel
mixed-mode solar dryers.
dryers (more commonly known as conventional
Natural
convection
dryers
can
be
used
all
independent from electricity supply. However, the
practically-realised designs of high temperature
airflow in this type of dryer is not sufficient to
dryers are fossil fuel powered, while the low
penetrate higher crop bulks. Furthermore the air flow
temperature dryers are either fossil fuel or solar-
comes to a standstill during night and adverse
energy based systems.
weather conditions. The risk of product deterioration
dryers)
and
solar-energy
dryers.
Strictly,
To classify the various types of solar dryers, it
is necessary to simplify the complex constructions
due to mould attack and enzymatic reactions is high.
Furthermore
the
mode
of
drying
can
be
and various modes of operation to the basic
differentiated into direct and indirect, depending
principles. Solar dryers can be classified based on
whether the product is directly exposed to solar
the following criteria:
radiation or dried in the shade. In direct mode, the
product itself serves as absorber, i.e. the heat transfer
Mode of air movement
is affected not only by convection but also by
Exposure to insulation
radiation according to the nature of the product
Direction of air flow
surface. Therefore, the surface area of the product
Arrangement of the dryer
being dried has to be maximized by spreading the
Status of solar contribution
crop in thin layers. To obtain uniform final moisture
O.V. Ekechukwu, B. Norton
[6]
has given Review
content, the crop has to be turned frequently.
of the various designs, details of construction and
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Follwing table provideslittle detail explaination of
used on the wall facing away from the sun. The food
the above maintioned dryer, according to there heat
to be dried is placed on a rack above the ground.
uilisation and design arrangment.
Drying times are however not always much lower
than for open-air drying (-25 %). (Probably,
Table 1: Classification of solar dryers. [8]
Types Of
Dryers
insufficient attention has so far been paid to utilizing
natural convection.) The main purpose of the dryers
Active Dryers
Passive Dryers
may be to provide protection from dust, dirt, rain,
wind or predators and they are usually used for fruit,
fish, coffee or other products for which wastage is
otherwise high. Tent dryers can also be taken down
Integral
and stored when not in use. They have disadvantage
Direct Type
of
being
easily
damaged
by
strong
winds.
Distributed
(Indirect)
Type
Mixed
Mode Type
A.Passive Solar Dryers
Passive solar dryers are also called natural
circulation or natural convection systems. They are
generally of a size appropriate for on-farm use. They
can be either direct (e.g. tent and box dryer) or
indirect (e.g. cabinet dryer). Natural-circulation solar
dryers depend for their operation entirely on solar-
Fig. 2: Solar tent dryer
[9]
energy. In such systems, solar-heated air is circulated
2.
through the crop by buoyancy forces or as a result of
The box-type solar dryer has been widely used for
wind pressure, acting either singly or in combination.
small scale food drying. It consists of a wooden box
1. Tent Dryers
with a hinged transparent lid. The inside is painted
Tent solar dryers, as shown in Fig. 2, are cheap and
black and the food supported on a mesh tray above
simple to build and consist of a frame of wood poles
the dryer floor. Air flows into the chamber through
covered with plastic sheet. Black plastic should be
holes in the front and exits from vents at the top of
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Box Dryers
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trays should be propped up with wooden supports.[12]
the back wall.
Drying temperatures in excess of about 80 °C
were reported for the dryer.[12]
Fig. 3: Box dryer
[12]
Fig. 4: Seesaw dryer
4. Cabinet Solar Dryers
3. Seesaw Dryer
The traditional seesaw dryer
[12]
has a rigid,
rectangular frame, the length of which being 3 times
the width' resting on a support with an axis. This
support is oriented north-south and is sufficiently
high to allow the frame to be tilted 30° towards east
in the morning and towards west in the afternoon.
The material for drying is placed on a number of
trays, which have a wooden frame 100 x 50 cm and a
mesh bottom, which can be made of a variety of
materials, such as wire netting, old fishing nets,
bamboo lattice or any other material that will allow
Here, the crop is located in trays or shelves
inside a drying chamber. If the chamber is
transparent, the dryer is termed an integral-type or
direct solar dryer. If the chamber is opaque, the dryer
is termed distributed-type or indirect solar dryer Fig.
5indicates Mixed-mode dryers combine the features
of the integral (direct) type and the distributed
(indirect) type solar dryers. Here the combined action
of solar radiation incident directly on the product to
be dried and pre-heated in a solar air heater furnishes
the necessary heat required for the drying process.
vertical air circulation and maximum evaporation.
The bottom of the improved seesaw dryer is made
of galvanised corrugated iron sheets reinforced
crosswise by wooden planks and lengthwise by two
wooden planks, about 15 cm high. The upper surface
of the bottom is painted black. Good thermal
insulation can be provided by attaching insulation
plates made of lignified wood fibre, expanded
polystyrene various layers of corrugated cardboard
etc. to the underside of the bottom.
The removable trays are placed on top of the
corrugated iron bottom either in a continuous row or
with space between them, which will result in better
Fig. 5: Features of a typical distributed (indirect) mode natural
heating of the air above the blackened surface of the
corrugated iron bottom. In this case the edges of the
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convection cabinet dryer.
[12]
In most cases the air is warmed during its flow
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through a low pressure drop thermosyphonic solar
Fans may be powered with utility electricity if it is
collector and passes through air ducts into the drying
available, or with a solar photovoltaic panel.
chamber and over drying trays containing the crops.
The moist air is then discharged through air vents or
Almost all types of natural convection dryers can
be operated by forced convection as well.
a chimney at the top of the chamber.
The cabinet is a large wooden or metal box. It
1. Active Ventilated Cabinet Solar Dryers
should be insulated properly to minimize heat losses
If utility electricity is available it is cheaper to
and made durable (within economically justifiable
connect the fans to the grid, compared to a
limits). Construction from metal sheets or water
connection to a PV installation. Besides the fans also
resistant
an electronic controller may be connected to the grid,
cladding,
e.g.
paint
or
resin,
is
which is able to adjust the appropriate temperature by
recommended.
Inside the box internal runners are fitted to support
variable speed of
the fan.
the trays of food being processed. A general rule of
thumb is that one m² of tray area is needed to lay out
10 kg of fresh food stuff to be produced at a time.
Flat collector
Access to the inside of the dryer is via hinged doors
at the rear of the cabinet. The drying trays slide on
rails on the inside of the cabinet so that they can be
removed from the dryer for loading, unloading and
cleaning. [17]
B.Active Solar Cabinet Dryers
Fig.6: C/S of the active ventilated cabinet dryer.
Active solar dryers are also called forced
convection or hybrid solar dryers. Optimum air flow
can be provided in the dryer throughout the drying
process to control temperature and moisture in wide
ranges independent of the weather conditions.
Furthermore the bulk depth is less restricted and the
air flow rate can be controlled. Hence, the capacity
and the reliability of the dryers are increased
2. Hybrid IAE-Type-Solar-Biomass Dryer
The Institute of Agricultural Engineering (IAE)
and the University of Philippines Los Banos (UPLB)
conducted a number of laboratory experiments under
controlled conditions to determine the optimum
drying parameters such as drying air temperature and
the flow rate, thickness of fruit slices, etc., to achieve
considerably compared to natural convection dryers.
It is generally agreed that well designed forced-
best quality products within a short period.
.
convection distributed solar dryers are more effective
Based on these studies, IAE/UPLB decided to
and more controllable than the natural-circulation
develop a cabinet type hybrid solar-biomass dryer
types.
suitable for small-scale drying applications with a
The use of forced convection can reduce drying
time by three times and decrease the required
capacity of about 50 kg/batch, referred to as Model
FD-50.
collector area by 50 %. Consequently, dryer using
The drying chamber has 30 aluminium wire screen
fans may achieve the same throughput as a natural
trays to hold the products. The flat plate solar
convection dryer with a collector six times as large.
collector used has a single Plexiglas cover positioned
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about 5 cm above a matt black painted metal
system. The roof and wall of this solar dryer can be
absorber sheet. All collector walls except for the
made of transparent materials such as glass, fibre
transparent glass cover are insulated to 8 cm
glass, UV stabilized plastic or polycarbonate sheets.
thickness to reduce heat losses. The solar collector is
The transparent materials are fixed on a steel frame
attached to the backside of the drying chamber at an
support or pillars with bolts and nuts and rubber
angle of 15°. A 45 W exhaust fan fixed in the
packing to prevent humid air or rain water leaking
chimney of the drying chamber forces the ambient
into the chamber other than those introduced from
air to pass through the collector and rise up through
the inlet opening. To enhance solar radiation
the fruits being dried. The biomass gasifier stove
absorption, black surfaces should be provided within
assists
the structure. Inlet and exhaust fans are placed at
drying
whenever
solar
radiation
is
insufficient.
proper position within the structure to ensure even
The design of the gasifier was adopted from the
gasifiers
developed
at
the
Asian
distribution of the drying air.
Institute
Designed properly, greenhouse dryers allow a
Technology. It consumes about 2.0 kg of coconut
greater degree of control over the drying process
shell or wood charcoal per hour and is capable of
than the cabinet dryers and they are more appropriate
providing drying temperatures up to 60°C. The
for large scale drying.
performance tests showed that a batch of 50 kg of
1. Natural Convection Greenhouse Dryer
sliced pineapple with an initial moisture content of
The earliest form of practically-realised natural-
85% (wet basis) could be dried to a final moisture
circulation solar greenhouse dryers reported was the
content of 20% in about 18 hours at a drying
Brace Research Institute glass-roof solar dryer in
temperature of 60°C. A recovery rate of 10 kg of
The dryer consisted of two parallel rows of drying
pineapple fruits was obtained. The total cost of the
platforms (along the long side) of galvanised iron
finished dryer was about P 56,000 (US$ 1,120 as of
wire mesh surface laid over wooden beams is shown
[10]
[12]
.
in Fig. 8. A fixed slanted glass roof over the platform
Feb 2002).
allowed solar radiation over the product. The dryer,
aligned lengthwise in the north-south axis, had black
coated internal walls for improved absorption of
solar radiation. A ridge cap made of folded zinc sheet
over the roof provides an air exit vent. Shutters at the
outer sides of the platforms regulated the air inlet.
Fig. 7: Drying chamber and biomass stove of the FD-50 Dryer
[10]
IV. GREENHOUSE DRYERS
The idea of a greenhouse dryer is to replace the
function of the solar collector by a green house
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Fig. 8: Natural convection glass roof greenhouse dryer.[6]
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A simplified design of the typical greenhouse-type
natural-circulation
solar
dryer
consists
of
2. Tunnel dryers
a
More than ten years of research and field testing
transparent semi-cylindrical drying chamber with an
has resulted in the development of a solar tunnel
attached cylindrical chimney, rising vertically out of
dryer well suited to medium sized farms or small
one end, while the other end is equipped with a door
cooperatives.
for air inlet and access to the drying chamber (see
developed
Fig. 9). The chimney (designed to allow for a
Germany , and has been duplicated successfully
varying height) has a maximum possible height of
throughout the world. A key to this success has been
3.0 m above the chamber and a diameter of 1.64 m.
the adaptation of the dryer design to the local climate
The drying chamber was a modified and augmented
and manufacturing possibilities in multiple countries.
version of a commercially-available poly-tunnel type
By 2003 over 1,000 Hohenheim type solar dryers
greenhouse.
were in use in 60 countries. Over half of these dryers
at
The
the
non-patented
University
of
design
was
Hohenheim,
The dryer operates by the action of solar-energy
were manufactured in the country of use; the rest
impinging directly on the crop within the dryer. The
were supplied by Innotech, a German corporation
crop and a vertically-hung, black absorbing curtain
manufacturing prototypes of the dryers. Innotech
within the chimney absorb the solar radiation and are
supplies the dryers in kit form for roughly 5,500
warmed. The surrounding air is, in turn, heated. As
US$
this heated air rises and flows up the chimney to the
manufacturing has not yet been established. Innotech
outside of the dryer, fresh replenishing air is drawn in
also offers a consultancy for quality assurance and
from the other end of the dryer.
marketing of dried products for export to industrial
Apart from the obvious advantages of passive solar-
countries.
(2000),
for
use
in
locations
where
energy dryers over the active types (for applications
The Hohenheim-type dryer results in faster drying
in rural farm locations in developing countries), the
and higher quality than traditional open-air methods.
advantages of the natural-circulation solar -energy
In Turkey, for example, apricots can be dried in 2
ventilated greenhouse dryer over other passive solar-
days – half the time required by traditional methods.
energy dryer designs include its low cost and its
An important feature contributing to consistent
simplicity in both on-the-site construction and
quality is the use of photovoltaic powered fans for
operation. Its major drawback is its susceptibility to
forced convection. The controlled drying process
damage under high wind speeds.
[12]
results in high-quality. The acceptable load for the
dryer ranges from 1.5 kg/m² for medicinal herbs to
25 kg/m² for rice or coffee. For a standard dryer with
a 20 m² drying area, this corresponds to 30 to 500 kg
per batch.
Some dryers made in Thailand are equipped with a
gas powered air-heating unit to allow drying during
the six-month rainy season. In contrast, Turkish
weather is dry enough to allow the all-solar dryers to
operate well with twice the standard drying area.
Local manufacture of the Turkish models allowed a
Fig. 9: Natural convection greenhouse dryer with chimney
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[12]
total installation cost of less than 1000 US$ in 1997,
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resulting in a payback period of only one year. The
or in a portable construction. When introduced in a
models used in Thailand were more expensive due to
new region, the tunnel dryer often requires
the gas-powered back-up heating unit
customization
to
suit
the
local
climate
and
Three major dryer components, as shown in Fig.
manufacturing possibilities. Often a prototype is
10, are the solar collector, food dryer compartment,
adapted and tested before proceeding with local
and the airflow system. Air is circulated by fans,
manufacture.
which use from 20-40 W of power from a
V. APPLICATIONS
photovoltaic panel, a generator, a
OF
SOLAR
DRYERS
Direct solar dring is most useful for small farmers
in of rural areas, where avalilabilty of electrical
power is very less. Solar dryers used in agriculture
for food and crop drying, for drying agricultural
products within less period of time, dryers can be
proved to be most useful device from energy
conservation point of view. The mixed-mode dryer is
having less cost, easily available, and can be easily
made by local farmers. Tomatoes, mango slices, and
food grains can be dried using this dryer It not only
save energy but also save lot of time, occupying less
area, improves quality of the product, make the
process more efficient and protects environment also.
the low-cost indirect- type natural convection solar
dryers are used for drying cassava, bananas, and
rough rice.Solar drying can be used for the entire
Fig. 10: Solar Tunnel Dryer
or central utility. Air is forced into the solar
drying process or for supplementing artificial drying
collector by the fans where it is heated by the sun,
systems, thus reducing the total amount of fuel
and then flows on to the food dryer section. An
energy required.
advantage of the PV powered system is that,
depending on the solar radiation, the air throughput is
automatically adjusted by the speed of the fans. The
plastic cover may be constructed from a sheet of
greenhouse type UV-stabilized polyethylene (PE).
Access to the drying chamber is gained by
removing the plastic covering using the hand crank.
The crop is placed on a polyester mesh suspended by
a grid of galvanized wire. This arrangement allows
air to flow on all sides of the food, preventing the
VI. CONCLUSION
This paper focuses on a study on the design,
performance, and application of various types of
solar dryers available nowdays. We also focus on
solar dryer models useful for producing good quality
of dried product. In this review paper, design and
development of active and passive solar dryer has
been reviewed. Scholars have also sugested different
easy methods to make solar dryer for farmers of rural
area.
need to turn it during the drying process. Depending
on local circumstances a dryer may be built in a
permanent installation (with concrete, for example),
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Acknowledgement
I would like to thank my Research Guides for the
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inspiration and support they have given time to time.
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