PROJECT REPORT ON SOLAR DRYER

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MANUFACTURE OF SOLAR DRYER
INTAZUL BORAH
PRIYAM JYOTI BORAH
MEGHNA SAHARIAH
BORNALI MEDHI
DEPARTMENT OF CHEMICAL ENGINEERING
ASSAM ENGINEERING COLLEGE
GUWAHATI-781013
JANUARY-2020
MANUFACTURE OF SOLAR DRYER
SEVENTH SEMESTER B.E. PROJECT
Submitted in partial fulfillment of
The Requirements for the Degree of
BACHELOR OF ENGINEERING
in
CHEMICAL ENGNEERING
of
GAUHATI UNIVERSITY
by

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INTAZUL BORAH (Roll No. 16/112)
PRIYAM JYOTI BORAH (Roll No. 16/275)
MEGHNA SAHARIA (Roll No. 16/256)
BORNALI MEDHI (Roll No. 16/177)
ASSAM ENGINEERING COLLEGE,
GUWAHAHATI-781013
JANUARY 2020
ASSAM ENGINEERING COLLEGE
GUWAHATI-781013

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CERTIFICATE
This is to certify that Intazul Borah (Roll No. 16/112), Priyam Jyoti Bora (Roll No. 16/275), Meghna
Saharia (Roll No. 16/256) and Bornali Medhi (Roll No. 16/177) of B.E. 7th
Semester have jointly carried
out the project entitled “MANUFACTURE OF SOLAR DRYER” under my supervision and submitted
the report in partial fulfillment of the requirement for the Degree of Bachelor of Engineering in Chemical
Engineering of Gauhati University, which may be accepted.
Date:
Runjun Das
Associate Professor

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ACKNOWLEDGEMENT
We would like to express our sincere gratitude and respect to the people of Assam Engineering College,
faculty members of the Department who always helped & guided us in understanding various concepts,
which were unknown to us. We are also thankful to Runjun Das ma’am under whose visionary
enlightenment we were able to complete this project.
Submitted By,
Intazul Borah (16/112)
Priyam Jyoti Bora (16/275)
Meghna Sahariah (16/256)
Bornali Medhi (16/177)

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Chapter 1
Introduction
Drying is one of the methods used to preserve food products for longer periods. The heat
from the sun coupled with the wind has been used to dry food for preservation for several
years.
Drying is the oldest preservation technique of agricultural products and it is an energy
intensive process. High prices and shortages of fossil fuels have increased the emphasis on
using alternative renewable energy resources. Drying of agricultural products using
renewable energy such as solar energy is environmental friendly and has less environmental
impact.
Different types of solar dryers have been designed, developed and tested in the different
regions of the tropics and subtropics. The major two categories of the dryers are natural
convection solar dryers and forced convection solar dryers. In the natural convection solar
dryers the airflow is established by buoyancy induced airflow while in forced convection
solar dryers the airflow is provided by using fan operated either by electricity/solar module or
fossil fuel.
Solar thermal technology is a technology that is rapidly gaining acceptance as an energy
saving measure in agriculture application. It is preferred to other alternative sources of energy
such as wind and shale, because it is abundant, inexhaustible, and non-polluting. Solar air
heaters are simple devices to heat air by utilizing solar energy and it is employed in many
applications requiring low to moderate temperature below 80°C, such as crop drying and
space heating.
1.1 Literature Review
Crop drying is the most energy consuming process in all processes on the farm. The purpose
of drying is to remove moisture from the agricultural produce so that it can be processed
safely and stored for increased periods of time. Crops are also dried before storage or, during
storage, by forced circulation of air, to prevent spontaneous combustion by inhibiting

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fermentation. It is estimated that 20% of the world‘s grain production is lost after harvest
because of inefficient handling and poor implementation of post- harvest technology, says
Hartman‘s (1991). Grains and seeds are normally harvested at a moisture level between 18%
and 40% depending on the nature of crop. These must be dried to a level of 7% to 11%
depending on application and market need. Once a cereal crop is harvested, it may have to be
stored for a period of time before it can be marketed or used as feed. The length of time a
cereal can be safely stored will depend on the condition it was harvested and the type of
storage facility being utilized. Grains stored at low temperature and moisture contents can be
kept in storage for longer period of time before its quality will deteriorate. Some of the
cereals which are normally stored include maize, rice, beans.
Solar drying may be classified into direct and indirect solar dryer. In direct solar dryers the
air heater contains the grains and solar energy which passes through a transparent cover and
is absorbed by the grains. Essentially, the heat required for drying is provided by radiation to
the upper layers and subsequent conduction into the grain bed. However, in indirect dryers,
solar energy is collected in a separate solar collector (air heater) and the heated air then
passes through the grain bed, while in the mixed mode type of dryer, the heated air from a
separate solar collector is passed through a grain bed, and at the same time, the drying cabinet
absorbs solar energy directly through the transparent walls or the roof.
To reduce the impact of conventional energy sources on the environment, much attention
should be paid to the development of new energy and renewable energy resources. Solar
energy, which is environment friendly, is renewable and can serve as a sustainable energy
source. Hence, it will certainly become an important part of the future energy structure with
the increasingly drying up of the terrestrial fossil fuel. However, the lower energy density and
seasonal doing with geographical dependence are the major challenges in identifying suitable
applications using solar energy as the heat source. Consequently, exploring high efficiency
solar energy concentration technology is necessary and realistic.
Solar energy is free, environmentally clean, and therefore is recognized as one of the most
promising alternative energy recourses options. In near future, the large-scale introduction of
solar energy systems, directly converting solar radiation into heat, can be looked forward.
However, solar energy is intermittent by its nature; there is no sun at night. Its total available
value is seasonal and is dependent on the meteorological conditions of the location.
Unreliability is the biggest retarding factor for extensive solar energy utilization. Of course,

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reliability of solar energy can be increased by storing its portion when it is in excess of the
load and using the stored energy whenever needed.
Solar drying is a potential decentralized thermal application of solar energy particularly in
developing countries. However, so far, there has been very little field penetration of solar
drying technology. In the initial phase of dissemination, identification of suitable areas for
using solar dryers would be extremely helpful towards their market penetration.
Solar drying is often differentiated from ―sun drying by the use of equipment to collect the
sun‘s radiation in order to harness the radiative energy for drying applications. Sun drying is
a common farming and agricultural process in many countries, particularly where the outdoor
temperature reaches 30o
C or higher. In many parts of South East Asia, spice s and herbs are
routinely dried. However, weather conditions often preclude the use of sun drying because of
spoilage due to rehydration during unexpected rainy days. Furthermore, any direct exposure
to the sun during high temperature days might cause case hardening, where a hard shell
develops on the outside of the agricultural products, trapping moisture inside. Therefore, the
employment of solar dryer taps on the freely available sun energy while ensuring good
product quality via judicious control of the radiative heat. Solar energy has been used
throughout the world to dry products. Such is the diversity of solar dryers that commonly
solar-dried products include grains, fruits, meat, vegetables and fish. A typical solar dryer
improves upon the traditional open-air sun system in five important ways.
It is more efficient. Since materials can be dried more quickly, less will be lost to spoilage
immediately after harvest. This is especially true of products that require immediate drying
such as freshly harvested grain with high moisture content. In this way, a larger percentage of
products will be available for human consumption. Also, less of the harvest will be lost to
marauding animals and insects since the products are in safely enclosed compartments. It is
hygienic. Since materials are dried in a controlled environment, they are less likely to be
contaminated by pests, and can be stored with less likelihood of the growth of toxic fungi. It
is healthier. Drying materials at optimum temperatures and in a shorter amount of time
enables them to retain more of their nutritional value such as vitamin C. An added bonus is
that products will look better, which enhances their marketability and hence provides better
financial returns for the farmers. It is cheap. Using freely available solar energy instead of
conventional fuels to dry products, or using a cheap supplementary supply of solar heat, so
reducing conventional fuel demand can result in significant cost savings.

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1.2 Problem Statement
Food scientists have found that by reducing the moisture content of food to between 10 and
20%, bacteria, yeast, mold and enzymes are prevented from spoiling it. The flavor and most
of the nutritional value is preserved and concentrated.
Drying and preservation of agricultural products have been one of the oldest uses of solar
energy. The traditional method, still widely used throughout the world, is open sun drying
where diverse crops, such as fruits, vegetables, cereals, grains, tobacco, etc. are spread on the
ground and turned regularly until sufficiently dried so that they can be stored safely.
However, there exist many problems associated with open sun drying. It has been seen that
open sun drying has the following disadvantages. It requires both large amount of space and
long drying time. The disadvantages of open sun drying need an appropriate technology that
can help in improving the quality of the dried products and in reducing the wastage. This led
to the application of various types of drying devices like solar dryer, electric dryers, wood
fuel driers and oil-burned driers. However, the high cost of oil and electricity and their
scarcity in the rural areas of most third world countries have made some of these driers very
unattractive. Therefore interest has been focused mainly on the development of solar driers.
Solar dryers are usually classified according to the mode of air flow into natural convection
and forced convection dryers. Natural convection dryers do not require a fan to pump the air
through the dryer. The low air flow rate and the long drying time, however, result in low
drying capacity. One basic disadvantage of forced convection dryers lies in their requirement
of electrical power to run the fan. Since the rural or remote areas of many developing
countries are not connected, the use of these dryers is limited to electrified urban areas.

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1.3 Problem Statement Objectives
The objective of this study is to develop a solar dryer in which the grains are dried
simultaneously by the heated air from the solar collector. The problems of low and medium
scale processor could be alleviated, if the solar dryer is designed and constructed with the
consideration of overcoming the limitations of direct and indirect type of solar dryer. So
therefore, this work will be based on the importance of a solar dryer which is reliable and
economically, design and construct a solar dryer using locally available materials and to
evaluate the performance of this solar dryer.
1.4 Problem Justification and Outcomes
Drying is one of the methods used to preserve food products for longer periods. It has been
established as the most efficient preservation technique for most tropical crops.
This project presents the design, construction and performance of a solar dryer for food
preservation. In the dryer, the heated air from a separate solar collector is passed through a
glass, and at the same time, the drying cabinet absorbs solar energy directly through glass
arrangement. The results obtained during the test period revealed that the temperatures inside
the dryer and solar collector were much higher than the ambient temperature during most
hours of the day- light. The temperature rise inside the drying cabinet was up to 74% for
about three hours immediately after 12.00h (noon). The dryer exhibited sufficient ability to
dry food items reasonably rapidly to a safe moisture level and simultaneously it ensures a
superior quality of the dried product.

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Chapter 2
DESIGN APPROACH AND METHODOLOGY
Solar drying refers to a technique that utilizes incident solar radiation to convert it into thermal
energy required for drying purposes. Most solar dryers use solar air heaters and the heated air is
then passed through the drying chamber (containing material) to be dried. The air transfers its
energy to the material causing evaporation of moisture of the material.
2.1 Design approach
2.1.1 Drying Mechanism
There are two basic mechanisms involved in the drying process:
The migration of moisture from the interior of an individual material to the surface, and the
evaporation of moisture from the surface to the surrounding air. The drying of a product is a
complex heat and mass transfer process which depends on external variables such as
temperature, humidity and velocity of the air stream and internal variables which depend on
parameters like surface characteristics (rough or smooth surface), chemical composition
(sugars, starches, etc.), physical structure(porosity, density, etc.), and size and shape of
products. The rate of moisture movement from the product inside to the air outside differs
from one product to another and depends very much on whether the material is hygroscopic
or non-hygroscopic. Non-hygroscopic materials can be dried to zero moisture level while the
hygroscopic materials like most of the food products will always have residual moisture
content. This moisture, in hygroscopic material, may be bound moisture which remained in
the material due to closed capillaries or due to surface forces and unbound moisture which
remained in the material due to the surface tension of water.

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Figure 2.1 Moisture in the drying material
When the hygroscopic material is exposed to air, it will absorb either moisture or desorbs
moisture depending on the relative humidity of the air. The equilibrium moisture content
(EMC
= Me) will soon reach when the vapour pressure of water in the material becomes equal to the
partial pressure of water in the surrounding air [14]. The equilibrium moisture content in
drying is therefore important since this is the minimum moisture to which the material can be
dried under a given set of drying conditions. A series of drying characteristic curves can be
plotted. The best is if the average moisture content M of the material is plotted versus time.

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Figure 2.2 Rate of moisture loss
Figure 2.3 rate dM/dt versus moisture content M

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A
As is seen from Figure 2.3 for both non-hygroscopic and hygroscopic materials, there is a
constant drying rate terminating at the critical moisture content followed by falling drying
rate. The constant drying rate for both non-hygroscopic and hygroscopic materials is the same
while the period of falling rate is little different. For nonhygroscopic materials, in the period
of falling rate, the drying rate goes on decreasing till the moisture content become zero.
While in the hygroscopic materials, the period of falling rate is similar until the unbound
moisture content is completely removed, then the drying rate further decreases and some
bound moisture is removed and continues till the vapour pressure of the material becomes
equal to the vapour pressure of the drying air. When this equilibrium reaches then the drying
rate becomes zero.
The period of constant drying for most of the organic materials like fruits, vegetables, timber,
etc. is short and it is the falling rate period in which is of more interest and which depends on
the rate at which the moisture is removed. In the falling rate regime moisture is migrated by
diffusion and in the products with high moisture content, the diffusion of moisture is
comparatively slower due to turgid cells and filled interstices. In most agricultural products,
there is sugar and minerals of water in the liquid phase which also migrates to the surfaces,
increase the viscosity hence reduces the surface vapour pressure and hence reduce the
moisture evaporation rate.
2.1.2 Air Properties
The properties of the air flowing around the product are major factors in determining the rate
of removal of moisture. The capacity of air to remove moisture is principally dependent upon
its initial temperature and humidity; the greater the temperature and lower the humidity the
greater the moisture removal capacity of the air. The relationship between temperature,
humidity and other thermodynamic properties is represented by the psychometric chart. It is
important to appreciate the difference between the absolute humidity and relative humidity of
air. The absolute humidity is the moisture content of the air (mass of water per unit mass of
air) whereas the relative humidity is the ratio, expressed as a percentage, of the moisture
content of the air at a specified temperature to the moisture content of air if it were saturated
at that temperature.
The changes in condition of air when it is heated using the solar energy and then passed
through a bed of moist product are shown in Figure 2.4. The heating of air from temperature
TA to TB is represented by the line AB. During heating the absolute humidity remains

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constant at whereas the relative humidity falls. As air moves through the material to be dried,
it absorbs moisture.
Under (hypothetical) adiabatic drying; sensible heat in the air is converted to latent heat and
the change in the condition of air is represented along a line of constant enthalpy, BC.
Figure 2.4 Representation of drying process

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2.1.3 Classification of drying systems
All drying systems can be classified primarily according to their operating temperature ranges
into two main groups of high temperature dryers and low temperature dryers. However;
dryers are more commonly classified broadly according to their heating sources into fossil
fuel dryers (more commonly known as conventional dryers) and solar-energy dryers. Strictly,
all practically- realized designs of high temperature dryers are fossil fuel powered, while the
low temperature dryers are either fossil fuel or solar-energy based systems.
1. High temperature dryers
High temperature dryers are necessary when very fast drying is desired. They are usually
employed when the products require a short exposure to the drying air. Their operating
temperatures are such that, if the drying air remains in contact with the product until
equilibrium moisture content is reached, serious over drying will occur. Thus, the products
are only dried to the required moisture contents and later cooled. High temperature dryers are
usually classified into batch dryers and continuous-flow dryers. In batch dryers, the products
are dried in a bin and subsequently moved to storage. Thus, they are usually known as batch-
in-bin dryers. Continuous-flow dryers are heated columns through which the product flows
under gravity and is exposed to heated air while descending. Because of the temperature
ranges prevalent in high temperature dryers, most known designs are electricity or fossil-fuel
powered. Only a very few practically-realized designs of high temperature drying systems are
solar energy heated.
2. Low temperature dryers
In low temperature drying systems, the moisture content of the product is usually brought in
equilibrium with the drying air by constant ventilation. Thus, they do tolerate intermittent or
variable heat input. Low temperature drying enables products to be dried in bulk and is most
suited also for long term storage systems. Thus, they are usually known as bulk or storage
dryers. Thus, some conventional dryers and most practically-realized designs of solar-energy
dryers are of the low temperature type.

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2.2 Design Methodology
2.2.1 Types of solar driers
Solar-energy drying systems are classified primarily according to their heating modes and the
manner in which the solar heat is utilized. In broad terms; they can be classified into two
major groups, namely
• Direct (integral) type solar dryers.
• Indirect (distributed) type solar dryers.
• Direct solar dryers have the material to be dried placed in an enclosure, with a
transparent cover on it. Heat is generated by absorption of solar radiation on the product
itself as well as on the internal surfaces of the drying chamber. In indirect solar dryers,
solar radiation is not directly incident on the material to be dried. Air is heated in a solar
collector and then ducted to the drying chamber to dry the product. Specialized dryers are
normally designed with a specific product in mind and may include hybrid systems where
other forms of energy are also used. Although indirect dryers are less compact when
compared to direct solar dryers, they are generally more efficient. Hybrid solar systems
allow for faster rate of drying by using other sources of heat energy to supplement solar
heat.
• The three modes of drying are: (i) open sun, (ii) direct and (iii) indirect in the
presence of solar energy. The working principle of these modes mainly depends upon the
method of solar-energy collection and its conversion to useful thermal energy.

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Open sun drying (OSD)
Figure shows the working principle of open sun drying by using solar energy.
Figure 2.5: Open Sun Drying
Solar energy falls on the uneven product surface. A part of this energy is reflected back
and the remaining part is absorbed by the surface. The absorbed radiation is converted
into thermal energy and the temperature of product stars increasing. This results in long
wavelength radiation loss from the surface of product to ambient air through moist air. In
addition to long wave length radiation loss there is convective heat loss too due to the
blowing wind through moist air over the material surface. Evaporation of moisture takes
place in the form of evaporative losses and so the material is dried. Further apart of
absorbed thermal energy is conducted into the interior of the product. This causes a rise
in temperature and formation of water vapor inside the material and then diffuses towards
the surface of the and finally losses thermal energy in the end then diffuses towards the
surface of the and finally losses the thermal energy in the form of evaporation. In the
initial stages, the moisture removal is rapid since the excess moisture on the surface of
the product presents a wet surface to the drying air. Subsequently, drying depends upon
the rate at which the moisture within the product moves to the surface by a diffusion

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process depending upon the type of the product
2.2.2.1 Direct type solar drying (DSD)
Direct solar drying is also called natural convection cabinet dryer. Direct solar dryers use
only the natural movement of heated air. A part of incidence solar radiation on the glass
cover is reflected back to atmosphere and remaining is transmitted inside cabin dryer. . A
direct solar dryer is one in which the material is directly exposed to the sun‘s rays. This
dryer comprises of a drying chamber that is covered by a transparent cover made of glass
or plastic. The drying chamber is usually a shallow, insulated box with air-holes in it to
allow air to enter and exit the box. The product samples are placed on a perforated tray
that allows the air to flow through it and the material. Fig. 2.6 shows a schematic of a
simple direct dryer [15]. Solar radiation passes through the transparent cover and is
converted to low-grade heat when it strikes an opaque wall. This low-grade heat is then
trapped inside the box by what is known as the ‗greenhouse effect. ‘‘Simply stated, the
short wavelength solar radiation can penetrate the transparent cover. Once converted to
low-grade heat, the energy radiates.
Figure 2.6: Direct Type Solar
Figure 2.6: Direct Type Solar Drying

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2.2.2.2 Indirect type solar drying(ISD)
This type is not directly exposed to solar radiation to minimize discolorations and
cracking. The drying chamber is used for keeping the in wire mesh tray. A downward
facing absorber is fixed below the drying chamber at a sufficient distance from the
bottom of the drying chamber. A cylindrical reflector is placed under the absorber fitted
with the glass cover on its aperture to minimize convective heat losses from the absorber.
The absorber can be selectively coated. The inclination of the glass cover is taken as 45o
from horizontal to receive maximum radiation. The area of absorber and glass cover are
taken equal to the area of bottom of drying chamber. Solar radiation after passing through
the glass cover is reflected by cylindrical reflector toward an absorber. After absorber, a
part of this is lost to ambient through a glass cover and remaining is transferred to the
flowing air above it by convection. The flowing air is thus heated and passes through the
placed in the drying chamber. The exhaust air and moisture is removed through a vent
provided at the top of drying chamber.
Figure 2.7: Indirect Type Solar Drying

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2.3 Applications of solar driers
The change of main variables such as moisture content along the drying tunnel is considered
unlike in previous works where uniform distribution is assumed .This is a study of tunnel
green house drier which is continuous type. The conditions for improvement of efficiency are
evaluated. A linear relationship between the tunnel output temperature and incident solar
radiation is obtained. The drier production is presented by a performance parameter which is
defined as the ratio between the energy actually used in the evaporation and the total
available energy for the drying process.
A non-dimensional variable is also defined which has all the meteorological information. It
is found that, the average moisture content value of the tunnel can be considered to be
constant. The construction and working of solar tunnel drier is explained in detail. Three fans
run by a solar module are used to create forced convection. The drying procedure and the
instrumentation are also described. The major advantage of solar tunnel drier is that the
regulation of the drying temperature is possible. During high insulation periods, more energy
is received by the collector, which tends to increase the drying temperature and is
compensated by the increase of the air flow rate. The variation of voltage with respect to
radiation in a given day and variation of radiation with respect to time of the day are
presented. The comparative curves using the tunnel dryer and natural sun drying are
presented to show that, the tunnel drying time is less. A substantial increase in the average
sugar content is observed. The economics of the drier is worked out to show that, the payback
period is 3years.
2.4 Conclusions
The dependence of the drying on the characteristics of product remains still as a problem, for
comparison of drying efficiencies of various driers. Author presented 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. Two broad groups of
solar energy dryers can be identified, viz., passive or natural-circulation solar-energy dryers
and active or forced-convection solar-energy dryers (often called hybrid solar dryers). Three

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sub-groups of these, which differ mainly on their structural arrangement, can also be
identified, via integral or direct mode solar dryers, distributed or indirect modes. This
classification illustrates clearly how these solar dryer designs can be grouped systematically
according to their operating temperature ranges, heating sources and heating modes,
operational modes or structural modes. Though properly, designed forced-convection (active)
solar dryers are agreed generally to be more effective and more controllable than the natural-
circulation (passive) types. This chapter also presents some easy-to-fabricate and easy-to-
operate dryers that can be suitably employed at small-scale factories. Such low-cost drying
technologies can be readily introduced in rural areas to reduce spoilage, improve product
quality and overall processing hygiene.

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Chapter 3
THEORETICAL BACKGROUND
3.1 Design specifications and assumptions
3.1.1 Introduction
Solar drying may be classified into direct and indirect solar dryer. In direct solar
dryers the air heater contains the grains and solar energy which passes through a
transparent cover and is absorbed by the grains. Essentially, the heat required for
drying is provided by radiation to the upper layers and subsequent conduction into the
grain bed. However, in indirect dryers, solar energy is collected in a separate solar
collector (air heater) and the heated air then passes through the grain bed, while in the
mixed mode type of dryer, the heated air from a separate solar collector is passed
through a grain bed, and at the same time, the drying cabinet absorbs solar energy
directly through the transparent walls or the roof. The objective of this study is to
design a mixed-mode solar dryer in which the grains are dried simultaneously by both
direct radiation through the transparent walls and roof of the cabinet and by the heated
air from the solar collector.
The materials used for the construction of the mixed-mode solar dryer are cheap and
easily obtainable in the local market. Figure3.1 shows the main components of the
dryer, consisting of the solar collector (air heater), the drying cabinet and drying trays.
3.1.2 Solar Dryer Components
The solar dryer consists of the solar collector (air heater), the drying cabinet and drying trays.

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1. Collector (Air Heater):
The heat absorber (inner box) of the solar air heater was constructed using well seasoned
woods painted black. The solar collector assembly consists of air flow channel enclosed
by transparent cover (glazing). An absorber mesh screen midway between the glass
cover and the absorber back plate provides effective air heating because solar radiation
that passes through the transparent cover is then absorbed by both the mesh and back-
plate.
2. The Drying Cabinet:
The drying cabinet together with the structural frame of the dryer was built from well-
seasoned woods 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
convection flow of air through the dryer. Access door to the drying chamber was also
provided at the back of the cabinet. The roof and the two opposite side walls of the
cabinet are covered with transparent glass sheets of 4 mm thick, which provided
additional heating.
3. Drying Tray:
The drying tray are contained inside the drying chamber and was constructed from a
double layer of fine chicken wire mesh with a fairly open structure to allow drying air to
pass through the food items.
3.1.3 The orientation of the Solar Collector:
The flat-plate solar collector is always tilted and oriented in such a way that it receives
maximum solar radiation during the desired season of used. The best stationary
orientation is due south in the northern hemisphere and due north in southern hemisphere.
Therefore, solar collector in this work is oriented facing south and tilted at 45 to the
horizontal. This inclination is also to allow easy run off of water and enhance air
circulation.

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3.1.4 Materials required for making the solar dryer:
The materials which are used to make the solar dryer are used in our everyday life
.And they are found easily near our locality.
1) Plywood
2) Hammer
3) Nail And Glue
4) Glass
5) Thermometer
6) Black Paint

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3.2 Mathematical models and formulations
3.2.1 Operation of the Dryer
The dryer is a passive system in the sense that it has no moving parts. It is energized by the
sun‘s rays entering through the collector glazing. The trapping of the rays is enhanced by the
inside surfaces of the collector that were painted black and the trapped energy heats the air
inside the collector. The greenhouse effect achieved within the collector drives the air current
through the drying chamber. If the vents are open, the hot air rises and escapes through the
upper vent in the drying chamber while cooler air at ambient temperature enters through the
lower vent in the collector.
3.2.2 Drying mechanism
In the process of drying, heat is necessary to evaporate moisture from the material and a flow
of air helps in carrying away the evaporated moisture. There are two basic mechanisms
involved in the drying process:
1) The migration of moisture from the interior of an individual material to the surface.
2) The evaporation of moisture from the surface to the surrounding air.
The drying product is a complex heat and mass transfer process which depends on
external variables such as temperature, humidity and velocity of the air stream and
internal variables which depend on parameters like surface characteristics (rough or
smooth surface), chemical composition (sugars, starches, etc.), physical structure
(porosity, density, etc.), and size and shape of product.

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3.2.3 Basic Theory (Formulations)
Some important formulae used are given as follows:
1. Dryer efficiency(η d):
Dryer efficiency is the ratio of collection efficiency (ηc) and the system efficiency
(ηs). (ηc) = Qu/AcIs
Where, Qu= mCp∆t
Ac = collector surface area
Is = Insulation on tilted surface
Efficiency (ηs) =WL / AcIs
Where, W= mass of moisture evaporated.
L= latent heat of evaporation in the dryer temperature.
2. Determination of moisture
content :Mwb= (Mi– Md)/
Mi×100
Where, Mwb= moisture on wet
basis Mi= initial mass of the
sample
Md= final mass of the sample

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Chapter 4
DESIGN PROCEDURE AND IMPLEMENTATION
4.1 Design Procedures
In many parts of the world there is a growing awareness that renewable energy have
an important role to play in extending technology to the farmer in developing
countries to increase their productivity. Solar thermal technology is a technology that
is rapidly gaining acceptance as an energy saving measure in agriculture application. It
is preferred to other alternative sources of energy such as wind and shale, because it is
abundant, inexhaustible, and non-polluting. Solar air heaters are simple devices to heat
air by utilizing solar energy and employed in many applications requiring low to
moderate temperature below 80 C, such as crop drying and space heating. Drying
processes play an important role in the preservation of agricultural products.
They are defined as a process of moisture removal due to simultaneous heat and mass
transfer. According to two types of water are present in food items; the chemically
bound water and the physically held water. In drying, it is only the physically held
water that is removed. The most important reasons for the popularity of dried products
are longer shelf-life, product diversity as well as substantial volume reduction. This
could be expanded further with improvements in product quality and process
applications. The application of dryers in developing countries can reduce post harvest
losses and significantly contribute to the availability of food in these countries.
Estimations of these losses are generally cited to be of the order of 40% but they can,
under very adverse conditions, be nearly as high as 80%. A significant percentage of
these losses are related to improper and/or untimely drying of foodstuffs such as cereal
grains, pulses, tubers, meat, fish, etc.

29
4.1.1 The Experimental Set-Up
Figure 4.1: View of Solar Dryer
Figure 4.2: Complete Setup of Solar Dryer

30
The mixed-mode solar dryer with box-type absorber collector was constructed using
the materials that are easily obtainable from the local market.
4.2 Design Implementation
Ambient temperature was recorded during the course of experiments with the help of
digital sensor. This project presents the design, construction and performance of a
mixed-mode solar dryer for food preservation. The dryer exhibited sufficient ability to
dry food items reasonably rapidly to a safe moisture level and simultaneously it
ensures a superior quality of the dried product.
4.3.1 Object of the observation
Details of moisture removed during drying (in the month off Sept-Nov) both in outside
and the inside chamber are as shown below. Room temperature during drying period was
310
C and the comparing the percentage of moisture removed from the solar dryer and the
ordinary air (fruit present in the atmosphere) the following table is experimental based
data.
Also we take different fruit for calculation of experiment average dryer efficiency for one
day was found to be 13% while the moisture content for various samples like chilli,
ginger and turmeric were found 64%, 58% and 60% respectively. All the readings were
on a day basis i.e. for one day.
variation of temp over months.
35
30
25
20
15
10
5
0
Max temp. (°C) Min Temp. (°C) Avg. temp. (°C)

31
Below is the curves plotted between time and temperature inside and outside the
prototype machine.
Temperature(°C)
75
65
55
45
35
Outlet T°C
Inlet T°C
25
15
0
0 0-1515-2020-2530-3535-4545-5050-5555-6060-65
Time (Seconds)

Sample 1: Green Chilli
Reading-1
Location Reference Sample
Direction SW(226°) SW (217°)
Latitude 26.154507 26.154562
Longitude 91.755456 91.765624
Sl.
no.
Time Sample inside the prototype Sample under direct sunlight
Temperature
(°C)
Weight
(gm)
Moisture
removed
Temperature
(°C)
Weight
(gm)
Moisture
removed
1 11:00
AM
31.8 500 0.0 % 31.8 500 0.0 %
2 12:00
PM
58 461.5 7.7 % 31.3 484.2 3.16 %
3 01:00
PM
63 420.2 15.96 % 32.2 472.8 5.44 %
4 02:00
PM
64.3 378.4 24.32 % 32.1 466.8 6.64 %
5 03:00
PM
63.4 348.5 30.3 % 32.5 456 8.8 %
300
320
340
360
380
400
420
440
460
480
500
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM
Weight of the sample inside the prototype (gm)
Weight of the sample under direct Sunlight (gm)
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM
Moisture removed from the sample inside the prototype (wt. %)
Moisture removed from the sample under direct sunlight (wt. %)

Reading-2
Latitude 26.154507 26.154562
Longitude 91.755456 91.765624
Sl.
no.
Temperature
(°C)
Weight
(gm)
Moisture
removed
Temperature
(°C)
Weight
(gm)
Moisture
removed
1 11:00
AM
30.4 250 0.0 % 30.4 250 0.0 %
2 12:00
PM
58 232.7 6.92 % 32 243.5 2.6 %
3 01:00
PM
61 211.6 15.36 % 31.6 238.7 4.52 %
4 02:00
PM
63 192.3 23.08 % 30.2 232.8 6.88 %
5 03:00
PM
63 184.3 26.28 % 30 229.3 8.28 %
150
160
170
180
190
200
210
220
230
240
250
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM

34
Sample 2: Ginger
Reading-1
Latitude 26.141507 26.141634
Longitude 91.660495 91.661564
Sl.
no.
Temperature
(°C)
Weight
(gm)
Moisture
removed
Temperature
(°C)
Weight
(gm)
Moisture
removed
1 11:00
AM
31.3 500 0.0 % 31.3 500 0.0 %
2 12:00
PM
59.5 128.6 74.4 % 32 364.4 27.12 %
3 01:00
PM
62.2 74.5 85.1 % 31 182.6 63.48 %
4 02:00
PM
64.1 55.8 88.84 % 32 144.2 71.2 %
5 03:00
PM
63.4 46.3 90.74 % 30 124.6 75.08 %
0
50
100
150
200
250
300
350
400
450
500
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM

35
Reading-1
Direction SW(226°) SW (217°C)
Latitude 26.141507 26.141634
Longitude 91.660495 91.661564
Sl.
no.
Temperature
(°C)
Weight
(gm)
Moisture
removed
Temperature
(°C)
Weight
(gm)
Moisture
removed
1 11:00
AM
30.8 250 0.0 % 30.8 250 0.0 %
2 12:00
PM
58.3 62.3 37.54 % 31 167.2 33.12 %
3 01:00
PM
61.4 33 86.8 % 31.8 87.5 65 %
4 02:00
PM
64.2 26 89.6 % 31.8 68 72.8 %
5 03:00
PM
62.3 22.3 91.08 % 30.2 59.5 76.2 %
0
50
100
150
200
250
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM

36
4.3.2 Graphical Representation of Drying Rate:
The following graph represents total moisture % removed per every hour inside and the
outside of the chamber. The lower most and the middle graphical line represent moisture
content removed in % at inside the chamber. Lower most graphical lines represent the MC
removed in % outside the drying chamber. The following represents the MC removed in %
with respect to time and the temperature at that point. Since the solar drying does not give
constant temperature because of climatic condition; so the moisture % removed varies un-
uniformly with time and the varied temperature.
Figure 4.6: Graphical representation of drying rate
95
90
85
80
75
1st
Sample
2nd
Sample
Outside chamber
65
55
0
1 2 3 4 5 6

37
CALCULAION OF SOLAR DRYER EFFICIENCY
1. Dryer efficiency
➢ One day Dryer efficiency (η d) for Green Chilli = 13.6%
➢ One day Dryer efficiency (η d)for Ginger = 33.2%
The average dryer efficiency is found out to be 13% for one day.
2. Moisture content
➢ Moisture content for Green Chilli = 31 % (approx)
➢ Moisture content for Ginger = 90.76% (approx)
4.3.3 Result and Discussion
After study we have found that the solar dryer gives more than three-four times heat inside
the chamber than that of the outside atm temperature. In 6 hours continuous drying under the
same climatic condition and same time it removed 28.73 % (upper tray) and 27.28 % (lower
tray) moisture content from inside chamber chili whereas at outside only 12.75 % moisture
content was removed. Our experiment of average dryer efficiency for one day was found to
be 13% while the moisture content for various samples like chili, ginger and turmeric were
found 64%, 58% and 60% respectively. All the readings were on a day basis i.e. for one day.

38
Chapter 5
FEASIBIILITY STUDIES AND MARKET NEEDS
Cost Economics, of Food Solar dryer System enterprises are worked out for fruits and
vegetables. 1 Million For one unit of 10 dryers. It can transact 10 tons of fruits or fruit bars in
dehydrated form. This is an excellent income and profitable venture in rural Saudi Arabia.
The cost benefit analysis of our dryers indicates that a commercial venture of a project with
10 solar dryers will give the payback period of 2 - 2½years.
The profitability of the technology in terms of employment potential and income generation
is established and acceptability of the product in the market is evaluated from the proven
market demand. Our expectation about the feasibility of the technology for rural employment
has been realized.
The reasons for the success are:
1. The grass root level Non-Government and voluntary organizations have devotion for
service to rural people and have the ability to capacity building and skill development among
rural women.
2. Food Solar drying process is the integration of food science and technology and solar
drying technology disciplines. So the practice followed in solar food processing is based on
these two techniques. To make the solar food processing products, one needs rigorous
training in this technology by well qualified persons, close monitoring and supervision of the
operations and following the food safety, clean & hygienic practices, quality consciousness
and assurance in day to day production. The social entrepreneurs have proved very successful
in this respect.

39
Chapter 6
CONCLUSION AND RECOMMENDATIONS
6.1 Conclusion
From the test carried out, the following conclusions were made. The solar dryer can raise the
ambient air temperature to a considerable high value for increasing the drying rate of
agricultural crops. The product inside the dryer requires less attentions, like attack of the
product by rain or pest (both human and animals), compared with those in the open sun
drying. Although the dryer was used to dry Potato, it can be used to dry other crops like
yams, cassava, maize and plantain etc. There is ease in monitoring when compared to the
natural sun drying technique. The capital cost involved in the construction of a solar dryer is
much lower to that of a mechanical dryer. Also from the test carried out, the simple and
inexpensive solar dryer was designed and constructed using locally sourced materials. . In
this experiment we find that how much moisture removed from the sample which is present
in solar dryer and the sample which is present in ordinary air and we compare both of them
by mathematical calculation. In this paper we took green chili, some of the chili we put inside
the dryer and some in the ordinary air and then compare their moisture removed with respect
to time and temperature. We find that temperature inside the dryer is two times outside the
temperature. As per our experiment the maximum peak temperature inside the drying
chamber is 75°C during mid-day (3pm) and in an average approximately 60°
C-62°C in a full
sunny day (10:00AM to 03:00PM). In 6 hours continuous drying in one full sunny day under
the same climatic condition and in same time the solar dryer removed a maximum of 30- 40%
moisture content from drying chamber for drying of low moisture content food products.
Experimental observation shows that the solar dryer can be used as an alternative in case of
food preservation and the efficiency is also acceptable. The people can make it in their
homes, especially in the developing countries where the energy demand is skyrocketing. It
can be handy in times of recession .The food stuffs can be stored in this dryer and used for
days without wasting it .The data concluded while performing this experiment is shown in the
following table for different samples:

40
SAMPLES DRYER EFFICIENCY(one day) MOISTURE CONTENT
Green chilli 13.6 % 31 %
Ginger 33.2 % 90.76 %
6.2 Recommendations
The performance of existing solar food dryers can still be improved upon especially in the
aspect of reducing the drying time, and probably storage of heat energy within the system by
increasing the size of the solar collector. Also, meteorological data should be readily
available to users of solar products to ensure maximum efficiency and effectiveness of the
system. Such information will probably guide a local farmer on when to dry his agricultural
produce and when not to dry them.

41
REFERENCES
1 Ajayi, C., Sunil, K.S., and Deepak, D. 2009. “Design of Solar Dryer with Turbo
ventilator and Fireplace”. International Solar Food Processing Conference2009.
2 Brenidorfer B, Kennedy L, Bateman C O (1995). Solar dryer: their role in post harvest
processing, Commonwealth Secretariat Marlborough house, London, Swly5hx.
3. A.A. El-Sebaii; S.M. Shalaby (2012): Solar drying of agricultural products: A review,
Renewable and Sustainable Energy Reviews 16, 37– 43.
4. Fadhel; S. Kooli; A. Farhat; A. Bellghith (2005): Study of the solar drying of grapes by
three different processes, Desalination 185,535–541.
5. Gutti Babagana; Kiman Silas and Mustafa B. G. (2012): Design and Construction of
Forced/Natural Convection Solar Vegetable Dryer with Heat Storage, ARPN Journal of
Engineering and Applied Sciences, VOL. 7, NO.10.
6. B.K. Bala; M.R.A. Mondol; B.K. Biswas; B.L. Das Chowdury; S. Janjai (2003): Solar
drying of pineapple using solar tunnel drier, Renewable Energy 28,183–190.
7. Wang, Y., Zhang, M., Mujumdar, A.S., Mothibe, K.J., Roknul Azam, S.M. Effect of
blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying
chamber, (2012) Journal of Food Engineering, 113 (2), pp.177-185.
8. Zhonghua Dr., W., Long, W., Zhanyong, L., Mujumdar, A.S. Atomization and Drying
Characteristics of Sewage Sludge inside a Helmholtz Pulse Combustor (2012) Drying
Technology, 30 (10), pp.1105-1112.
9. Jiang, Y., Xu, P., Mujumdar, A.S., Qiu, S., Jiang, Z. A Numerical Study on the Convective
Heat Transfer Characteristics of Pulsed Impingement Drying (2012) Drying Technology, 30
(10), pp.1056-1061.

42
10. J. Kaewkiew; S. Nabnean; S. Janjai (2012): Experimental investigation of the
performance of a large-scale greenhouse type solar dryer for drying chili in Thailand.
Procedia Engineering 32, 433 –439.
11. J.K. Afriyie; M.A.A. Nazha; H. Rajakaruna; F.K. Forson (2009): Experimental
investigations of a chimney dependent solar crop dryer, Renewable Energy 34, 217– 222
12.Sharma, A., Chen, C. R., Vu Lan, N., 2009. Solar- energy drying systems: A review.
Renewable and Sustainable Energy Reviews, Vol.13, pp.1185-1210.

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