1

(Project Term January-May 2015)

PROJECT ON SOLAR DRYER

Submitted by

SARVASINDHU MISHRA : 11107851

RISHABH YADAV : 11102399

ANUGRAH SOY : 11103846

MD. ISMIL : 11101103

PROJECT GROUP NUMBER……….

Under The Guidance Of

Mr. RAHUL WANDRA

LOVELY SCHOOL OF SCIENCE AND TECHNOLOGY

CAPSTONE PROJECT REPORT

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DECLARATION:

We hereby declare that the project work entitled SOLAR CABINET DRYER is an authentic

record of our own work carried out as requirements of Capstone Project for the award of degree

of Bachelor Of Technology in MECHANICAL ENGINEERING from Lovely Professional

University, Phagwara, under the guidance of Mr.RAHUL WANDRA, during January to May,

2015.

PROJECT GROUP MEMBER:

Sarvasindhu Mishra

( 11107851)

Rishabh Yadav

(11102399)

Anugrah Soy

(11103846)

Md. Ismil

(11101103)

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CERTIFICATE:

This is to certify that the declaration statement made by this group of students is correct to the

best of my knowledge and belief. The Capstone Project Proposal based on the technology / tool

learnt is fit for the submission and partial fulfillment of the conditions for the award of Bachelor

Of Technology in MECHANICAL ENGINEERING from Lovely Professional University,

Phagwara.

Name: ……………………………………………..

U.ID: ………………………………………………

Designation: ……………………………………….

Signature of Faculty Mentor

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Acknowledgement:

We would like to express our sincere gratitude to the H.O.D “Mr. GurpreetPhool” of School of

Mechanical Engineering, Lovely Professional University Punjab for his help and support which

was vital in the completion of this report. We also want to express our sincere gratitude &

respect to the people at LOVELY PROFESSIONAL UNIVERSITY who always helped &

guided us in understanding various concepts, which were unknown to us. We are also thankful to

“RAHUL WANDRA” under whose visionary enlightenment we were able to complete this

project.

Submitted By:

Sarvasindhu Mishra

( 11107851)

Rishabh Yadav

(11102399)

Anugrah Soy

( 11103846)

Md.Ismil

(11101103)

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TABLE OF CONTENTS

1. INTRODUCTION

1.1 Literature Review…………………………………………………………….8 1.2 Problem Statement …………………………………………………………..11

1.3 Problem Statement Objectives ………………………………………………12

1.4 Problem Justification and Outcomes…………………………………………12

2. DESIGN APPROACH AND METHODOLOGY

2.1 Design Approach

2.1.1 Drying Mechanism…………………………………………………………13

2.1.2 Air Properties ……………………………………………………………..16

2.1.3 Classification Of Drying Systems ………………………………………….18

2.2 Design Methodology

2.2.1 Types Of Solar Dryers………………………………………………………19

(i) Open Sun Drying ………………………………………………………20

(ii) Direct type Solar Drying ………………………………………………21

(iii) Indirect Type Solar Drying …………………………………………...22

2.2 Applications Of Solar Dryers …………………………………….23

2.4 Canclusion…………………………………………………...23

3. THEORETICAL BACKGROUND

Design Specifications And Assumptions

3.1.1 Introduction …………………………………………………………….25

3.1.2 Solar Dryer Components ……………………………………………….25

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3.1.3 The Orientation Of Solar Collector ………………………………………26

3.1.4 Materials Required For Making Solar Dryer …………………………….27

3.2 Mathematical Models And Formulations

3.2.1 Operation Of Dryer ………………………………………………………..28

3.2.2 Drying Mechanism……………………………………………………… 28

3.2.3 Basic Theory (Formulations)……………………………………………….29

4. Design Procedure And Implementations

4.1 Design Procedure ……………………………………………………………..30

4.2 The Experimental Set Up ……………………………………………………..31

4.3 Design Implementation ……………………………………………………….31

4.3.1 Object Of The Observation ……………………………………………….32

4.3.2 Graphical Representation Of Drying Rate ………………………………..34

4.3.3 Result And Discussions …………………………………………………...34

5. Feasibility Studies And Market Needs………………………...36

6. Conclusion And Recommendation……………………………....37

References…………………………………………………………………….38

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LIST OF FIGRUES

1) Figure 2.1 Moisture In The Drying Materials………………………………….14

2) Figure 2.2 Rate of moisture loss……………………………………………….15

3) Figure 2.3 Rate Vs Moisture Content………………………………………….15

4) Figure 2.4 Representation Of Drying Process…………………………………17

5) Figure 2.5 Open Sun Drying ………………………………………………….20

6) Figure 2.6 Direct Type Solar Drying………………………………………….21

7) Figure 2.7 Indirect Type Solar Drying ………………………………………..22

8) Figure 3.1 View Of Solar Cabinet Dryer……………………………………...27

9) Figure 3.2 Tray Arrangement Of Solar Dryer ………………………………..27

10) Figure 3.3 Front View Of Solar Dryer ………………………………………. 27

11) Figure 4.1 Solar Dryer Making ……………………………………………....31

12) Figure 4.2 Complete Setup Of Solar Dryer …………………………………..31

13) Figure 4.3 Chili Before Drying……………………………………………….33

14) Figure 4.4 Chili Inside Dryer …………………………………………………33

15) Figure 4.5 Chili After Drying ………………………………………………...34

16) Figure 4.6 Graphical Representation Of Drying Rate ………………………..34

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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 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%

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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

mixedmode 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.

Energy is important for the existence and development of human kind and is a key issue in international

politics, the economy, military preparedness, and diplomacy. 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, 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

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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 30 oC 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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1.2Problem 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.

1.4Problem 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

2.1.1Drying 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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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 reduce 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.

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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 constant at A

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. Both absolute

humidity and relative humidity increase from B and C and from to C, respectively, but

air temperature decreases to, TC. The absorption of moisture by the air would be the difference

between the absolute humidities at C and B. ( C - A). If unheated air is passed through the bed,

the drying process would be represented by the line AD. Assuming that the air at D to be at the

same relative humidity, C , as the heated air at C, then the absorbed moisture would be(( D -

A), considerably less than that absorbed by the heated air (( C - A).

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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(i)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 process depending

upon the type of the product.

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(ii)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 Drying

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(iii)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 3 years.

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

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forced-convection solar-energy dryers (often called hybrid solar dryers). Three 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 Trays:

The drying trays are contained inside the drying chamber and were 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.

27

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) Wired Mess

5) Glass

6) Thermometer

7) Black Paint

(3.1) (3.2)

(3.3)

28

Figue:(3.1): view of solar cabinet dryer,(3.2): trey arrangement of solar dryer

(3.3): front view of solar dryer

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.

29

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 evapourated.

L= latent heat of evapouration 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

30

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.

31

4.2 The Experimental Set-Up

Figure 4.1: View Of Solar Dryer

Figure 4.2: Complete Setup Of Solar Dryer

The mixed-mode solar dryer with box-type absorber collector was constructed using the

materials that are easily obtainable from the local market.

4.3 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.

32

4.3.1 Object Of The Observation

Details of moisture removed during drying (in the month off fab-march) both in outsideand the

inside chamber are as shown below. Room temperature during drying periodwas 310c.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, grapes and apple were found

64% ,58% and 60% respectively. All the readings were on a day basis i,e for one day.

The following data is given bello:

TABLE 1 Temperature, weight and %moisture removed in different

condition

SI.

No

Time

Upper Tray

Lower Tray

Outside

Chamber

Temperature

oc

Weight

(gm)

Moisture

Removed

Temperature

oc

Weight

(gm)

Moisture

Removed

Weight

(gm)

Moisture

Removed

1.

10:00(AM)

31

250

0.00%

31

250

0.00%

250

0.00%

2.

11:00(AM)

58

225.00

10.00

56

228

8.8

247

1.20

33

3.

12:00(AM)

63

202.01

19.20

63

206.45

17.42

236.03

5.58

4.

01:00(PM)

66

177.02

29.20

65

184.66

26.13

226.54

9.38

5.

02:00(PM)

71

125.00

50.00

68

128.20

48.72

199.04

20.38

6.

03:00(PM)

75

90.03

64.00

73.97

93.44

62.66

150.00

40.00

physical appearance of (chili) before and after 6 hours of drying in a full sunny

day.

Figure 4.3: chili before dry

Figure 4.4: chili after dry

34

Figure 4.5: chilli inside dryer

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

0

10

20

30

40

50

60

70

1 2 3 4 5 6

upper tray

lower tray

outside the chamber

35

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 grapes = 14.19 %

One day Dryer efficiency (η d) for apples = 13.78%

The average dryer efficiency is found out to be 13% for one day.

2 Moisture content

Moisture content for green chilli = 64%

Moisture content for grapes = 58%

Moisture content for apple = 60%

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, grapes and apple were found 64% ,58% and 60% respectively. All the readings

were on a day basis i,e for one day.

36

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 - 2½ years.

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.

37

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:

38

SAMPLES DRYER

EFFICIENCY(one day)

MOISTURE

CONTENT

Green chilli 13.6% 64%

Grapes 14.19% 58%

Apple 13.78% 60%

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.

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