This document discusses the development of a solar dryer for post-harvest treatment of cereals. It begins with an introduction to food waste and losses in India. It then discusses sources of grain losses at different stages and the need for proper drying. Existing solar dryer designs have limitations. The proposed dryer uses mixed-mode solar drying and space heating principles to allow drying during cloudy weather and at night. Key features of the dryer include the solar collector, drying cabinet, and trays. The dryer was found to dry cereals faster than open sun drying and maintain product quality.

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Development of Solar Dryer for post harvest Treatment of Cereals -
Review
Sumit S. Dharmarao1
1
PG Student ,Department of Mechanical Engineering, Bramhadevdada Mane Institute Of Technology, Solapur,
Maharashtra
sumitdharmarao@gmail.com
Abstract—although in many parts of India certain crops
can be produced at certain period of year, the major part of
the produce such as cereals & other crops are seasonal. Food
produced in one harvest period lasts only for few weeks. This
which must be stored for gradual consumption until next
harvest and seeds must be held for next season crops. Also
the market value of any crop tends to rise during off season.
Therefore it is important to minimize losses and prepare the
food for long lasting storage. This paper consist of various
requirement of storage of cereals as cereals covers larger part
of diet, for proper storage includes needs study of various
properties of grains of cereals. This study shows that proper
drying is required for proper storage, the solar dryer
development details are presented in the paper.
Index Terms— food storage, grain properties, post harvest,
solar Dryer
INTRODUCTION
“Food waste” refers to food that is of good quality and fit
for human consumption but that does not get consumed
because it is discarded either before or after it spoils. Food
waste is the result of negligence or a conscious decision to
throw food away. Food loss is the unintended result of an
agricultural process or technical limitation in storage,
infrastructure, packaging, or marketing. [1] Technological
limitations are basically faced by the developing nations
such as India, Africa, Brazil etc.
As per a news published in The Economics Times dated
12.Feb.2014 which is based on Food Corporation of India
(FCI) replied RTI query asked by social activist Om
Prakash Sharma in last few years 19,40,502 MT food
cereals worth crores of rupees are wasted in India.
The Food and Agriculture Organization of the United
Nations (FAO) estimates that 32 percent of all food
produced in the world was lost or wasted in 2009. This
estimate is based on weight. When converted into calories,
global food loss and waste amounts to approximately 24
percent of all food produced.
“Food loss and waste” refers to the edible parts of plants
and animals that are produced or harvested for human
consumption but that are not ultimately consumed by
people. Food loss and waste have many negative economic
and environmental impacts. Economically, they represent
a wasted investment that can reduce farmers’ incomes and
increase consumers’ expenses. Environmentally, food loss
and waste inflict a host of impacts, including unnecessary
greenhouse gas emissions and inefficiently used water and
land, which in turn can lead to diminished natural
ecosystems and the services they provide.
Grains may be lost in the pre-harvest, harvest and post-
harvest stages. Pre-harvest losses occur before the process
of harvesting begins, and may be due to insects, weeds and
rusts. Harvest losses occur between the beginning and
completion of harvesting, and are primarily caused by
losses due to shattering. Post-harvest losses occur between
harvest and the moment of human consumption. They
include on-farm losses, such as when grain is threshed,
winnowed and dried & losses along the chain during
transportation, storage and processing. Important in many
developing countries, particularly in India, are on-farm
losses during storage, when the grain is being stored for
auto-consumption or while the farmer awaits a selling
opportunity or a rise in prices. There is probability of loss
throughout the grain harvesting and agricultural marketing
chains. During stripping of cereals (maize grain) from the
cob, known as shelling, losses can occur when mechanical
shelling is not followed up by hand-stripping of the grains
that are missed. Certain shellers can damage the grain,
making insect penetration easier. For crops other than
maize, threshing losses occur as a result of spillage,
incomplete removal of the grain or by damage to grain
during the threshing. They can also occur after threshing
due to poor separation of grain from the chaff during
cleaning or winnowing.
The major reasons stated are the un-proper drying &
storing methods in our country for food losses.[2] With a
high moisture content, grain is susceptible to mould,
heating, discoloration and a variety of chemical changes.
Ideally, most grains should be dried to acceptable levels
within 2–3 days of harvest.[3]
The main cause of loss during drying is the cracking of
grain kernels that are eaten whole, such as rice. Some
grains may also be lost during the drying process.
However, failure to dry crops adequately can lead to much
higher levels of loss than poor-quality drying, and may
result in the entire harvest becoming inedible. Adequate
drying by farmers is essential if grains are to be stored on-
farm and poorly dried grains for the market need to be sold
quickly to enable the marketing-processing chain to carry
out adequate drying before the grains become spoilt. One
of the problems in assessing levels of post-harvest loss is
in separating weight loss caused by the very necessary
drying operations from weight loss caused by other,

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controllable, factors. From FAO report it is observe that
various commodities which are loss due to improper
drying the loss is by weight & 100% = 1.3billion tones.
Fig.1various commodities which are lost due to improper drying
Grains are produced on a seasonal basis. In many places
there is only one harvest a year. Thus most production of
maize, wheat, rice, jawar, bajra etc. must be held in storage
for periods varying from a few days up to more than a
year. Drying & storage therefore plays a vital role in grain
supply chains. For all grains, storage losses can be
considerable but the greatest losses appear to be of cereals,
particularly in India. Losses in stored grain are determined
by the interaction between the grain, the storage
environment and a variety of organisms. Hence there is
need to develop proper/ suitable drying method for studyis
undertaken & reported in following points.
LITERATURE STUDY
Sun Drying: Drying using the sun under the open sky for
preserving low value foods and agricultural crops may be
the most inexpensive and extensively used option since
early times. Major disadvantage of this method is
contamination of the products by dust, birds, animals and
insects, spoiling due to rain, wind and moisture, and the
method totally depends on good weather conditions.
Further, the process is labor intensive, unhygienic,
unreliable, time consuming, non-uniform drying, and
requires a large area for spreading the produce out to dry.
[4]. Drying using the sun under the open sky for
preserving low value foods and agricultural crops may be
the most inexpensive and extensively used option since
early times.The current energy scenario clearly depicts that
the available fossil fuel resources and its derivatives may
not satisfy the future demands. The need for alternate
energy resources is the need of the day. India is a tropical
country and we receive solar radiation throughout the year
for most of the days in a year(360 days in year)[5]. Our
country is an agricultural country and the utilization of
solar power for drying of agricultural produces is a boom
to our country’s economy. Especially in rainy days
without drying facilities a vast amount of agricultural
produces gets wasted and it affects the farmer’s life.Most
parts of the country receive mean solar radiation in the
range of 5-7 kwh/m² and has more than 300 sunny days in
a year. India is the fifth largest energy consumer.
Use of Other Energies:India is experiencing an acute
shortage of electric power that is likely to be worsening
day by day which stresses the need for deployment of
renewable energy resources to extenuate this energy crisis
use of renewable energy sources in the form of solar,
biomass, biogas, and wind energy must be done.
Present Solar Dryers: In India most common method to
dry the cereals is sun drying which has many drawbacks as
mentioned above solar Dryer is just a method to avoid
contamination of food with unwanted things.[6] As solar
Dryer involves some problems like no drying during
cloudy weather & at nights. Researchers & scientists have
suggested Electro solar Dryer but countries like India
which are facing deficiency of of electric power can’t go
for such substitute, Another option available is hybrid
solar Dryer which is combination of biogas & solar Dryer
which increases cost & require separate set up of biogas
plant.[7] There has no work done to build a more efficient
solar dryer by adding principles of solar space heating
which will useful in cloudy weather & even at time when
there is no sun. As we know current scenario of world
energy requirements & diminishing fossil fuels all over the
world which forces us to choose the non traditional energy
sources for completing our needs. In India about 60% of
electrical energy is generated by using coal which is kind
of fossil fuel .Today India is facing the energy crisis & the
Dryers which run on electrical power and used for drying
the cereals is not affordable by farmers also there are many
villages in our nation which are still waiting for the
electricity so the best option to dry out the cereals is to use
solar Dryer, but again it has problem of non working in
rainy, cloudy season and at nights.
PROPOSED DRYER FOR FOOD DRYING
Many researchers has provided the solution of combining
the another energies along with solar energy like electrical,
biogas, direct heating but they require auxiliary set up &
another source to run it which results into the hike in
capital cost of Dryer. There is another concept of solar
space heating which must be looked to solve the above
mentioned problem. In solar space heating floors, walls are
designed to collect, store & distribute solar energy in the
form of heat in sunny days and fortunately almost 320
days of year India has bright sunny days.
PROPOSED SOLAR DRYER FOR FOOD DRYING
A solar dryer is an enclosed unit to keep the food safe
from damage from birds, insects, microorganism,
pilferage, and unexpected rainfall. The produce is dried
using solar thermal energy in a cleaner and healthier
fashion. Basically, there are four types of solar dryers:

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1. Direct solar dryers. In these dryers, the material to be
dried is placed in a transparent enclosure of glass or
transparent plastic. The sun heats the material to be dried,
and heat also builds up within the enclosure due to the
‘greenhouse effect.’ The drier chamber is usually painted
black to absorb the maximum amount of heat.
2. Indirect solar dryers. In these dryers, the sun does not
act directly on the material to be dried thus making them
useful in the preparation of those crops whose vitamin
content can be destroyed by sunlight. The products are
dried by hot air heated elsewhere by the sun.
3. Mixed-mode dryers. In these dryers, the combined
action of the solar radiation incident on the material to be
dried and the air preheated in solar collector provides the
heat required for the drying operation.
4. Hybrid solar dryers. In these dryers, although the sun is
used to dry products, other technologies are also used to
cause air movement in the dryers.
THE DRYING PROCESS IN PROPOSED DRYER
The process of dehydration consists of removal of
moisture from the produce by heat usually in the presence
of a controlled flow of air. Cereals are placed on flat
bottomed trays that are placed into the dryer. The solar
rays enter the cabinet through the cover material. Upon
reaching the solar collector or tray surface, they are
converted into heat energy, raising the inside temperature.
The heat energy is transferred to the produce to be dried.
The heated produce gives out water vapor and dries up.
Gradually the heated moist air goes up and leaves the
drying chamber through the air outlet at the high end of
the drier. The efficiency of drying of the solar dryer is
influenced by relative humidity in the air, the moisture
content of the materials to be dried and their amount and
thickness. The solar radiation intensity on the materials
varies with seasons, time of the day, and length of
exposure, ambient air temperature, and wind speed, which
are important factors.
Fig.2 General drying preocess
DESIGN CONSEDERATIONS
Points to be consider while designing the natural
convection solar dryer system:
1. The amount of moisture to be removed from the
given quantity of cereals
2. Harvesting period during which drying is needed
3. The daily sunshine hours for the selection of the
total drying time
4. The quantity of air needed for drying
5. Daily solar radiation to determine energy
received by the dryer per day and
6. Wind speed for the calculation of air vent
dimensions.
CONSTRUCTION OF PROPOSED DRYER
Construction of mixed-mode solar dryer: The materials
used for the construction of mixed-mode solar dryer were
inexpensive and easily obtainable in the local market.
Figure 2 shows the essential features of the dryer
consisting of the solar collector (air heater), drying
cabinets, and drying trays. Solar collector setup: The
experimental setup is an open-flow loop that consists of a
test duct with entrance and exit sections, a blower unit,
control valve, orifice plate, and various devices for
measurement of temperature, and fluid head. The flow
system consists of an entry section, a test section, exit
section, a flow meter, and a centrifugal blower. The setup
consists of two identical wooden ducts: one is rough
absorber duct and other one is smooth absorber duct. As
shown in figure 3. The absorber plate which is made up of
an aluminum sheet which is painted black to increase the
absorbing capacity. Another absorber plate is roughed with
strips to provide obstacle to the path of air to obtain the
maximum temperature. The solar collector assembly
consisted of airflow channels enclosed by transparent
cover (glazing). The glazing is a single layer of 4-mm
thick transparent glass sheet. The outlet of duct is
connected to the orifice meter with an inclined manometer
to measure the mass flow rate of air. The outlet of the
orifice meter is connected to the inlet of the blower. The
outlet of blower is connected to the inlet of the cabinet
dryer.
Fig.3 Mixed mode solar type

4. NCETSTM 2K14, MREC
The drying cabinet: The drying cabinet, together with the
structural frame of the dryer, was built from well-seasoned
wood which could withstand termite and atmospheric
attacks. An outlet vent was provided toward the upper end
at the back of the cabinet to facilitate and control the
convective flow of air through the dryer. The roof and the
two opposite side walls of the cabinet are covered with
transparent glass sheets of 4-mm thick, which provided
glass. The dryer skeleton was formed with wood raised
200 mm from the ground.
Drying trays: The drying trays are contained inside the
drying chamber and are constructed from a double layer of
fine wire mesh with a fairly open structure to allow drying
air to pass through the food items. The three trays were
separated with a gap of 100 mm.
The orientation of solar collector: The flat plate solar
collector is kept horizontally and oriented in such a way
that it receives maximum solar radiation during the desired
season of use. The best stationary orientation is south in
the northern hemisphere and north in the southern
hemisphere. Therefore, solar collector in this work is
orientation facing south.
OPERATION OF PROPOSED DRYER
The dryer was a passive system in the sense that it had no
moving parts. The sun rays entering through the collector
glazing energizes it. The absorption of the rays is enhance
by the inside surface of the collector that were painted
black and the absorbed energy heats the air further weight
loss occurred were known. The dryer performance was
evaluated and comparison was made with the result
obtained with natural drying process and by forced
convection with smooth and rough absorber plate.
CONCLUSIONS
1. A simple and inexpensive mixed-mode solar
dryer was designed and constructed using locally
sourced materials.
2. The hourly variation of the temperatures inside
the cabinet and air heater is much higher than
ambient temperature during the most hours of
the day.
3. The temperature increase inside the drying
cabinet was up to 60 to 80°C for most the hours
in the noon time. The drying rate, collector
efficiency, and percentage of moisture removed
for drying cereals were 0.52 kg/h, 67.5%, and
88%, respectively.
4. The dryer exhibited sufficient ability to dry food
items at a reasonable rapid time to a safe moisture
level and simultaneously ensured a superior
quality of the dried product
5. The drying of cereals in the open sun takes 7 to 8
days during clear sunny weather conditions.
However, it only takes 3 to 4 days in the solar
cabinet dryer under similar weather conditions.
Also, the quality of dried grapes is remarkably
better in cabinet dryer compared to open sun
drying as the product is protected from dust and
insects.
6. The dryer is easy to build and required only
semiskilled laborer and limited facilities to
fabricate. Thus, the dryer is suitable for use in
urban as well as rural areas of the country.
REFERENCES
[1] Brian Lipinski & et all, “ Installment two of creating a
sustainable food future reducing food loss & waste” World
Resource Insitute
[2] News based on RTI report published in Economics Times
dated 12.feb.2014
[3] Harris, kentel L and carl J. lindblad, eds.- “ Post harvest
drain loss assessment methods a manual of methods for
evaluation of post harvest losses” American association of
cereals chemists, 1976.
[4] A report on “food processing in Bihar the road ahead ”
IL&FS analysis; RAU and state government publications.
Pp. 28-31
[5] “Krishidarshini 2014”, Mahatma Jothiba Fule krishi
vidyapeeth, Rahuri, Maharashtra, India.
[6] M.G. Campos “Good practices in grain Storage” 9th
International Working Conference on Stored product
protection, France 2007.
[7] K gunkesaran, sannugam & P. suresh. “modeling &
analytical Experimental study of hybrid solar dryer
integrated with biomass dryer for drying” IPCSIT, vol.28
(2012), IACSIT, press, Singapore.
[8] Paul artiuch & Samuel kornstein “ sustainable Approaches
to Reducing Food Easte in India” MIT Independent
activities period research project, February 2012
[9] Chandrakumar pardhi,and jiwanlal Bhagoria “ Development
and Performance evaluation of Mixed mode solar dryer
with forced convection” International Journal of Energy &
Engineering 2013.