a solar concentrator based indirect drying system...

A SOLAR CONCENTRATOR BASED INDIRECT DRYING SYSTEM FOR

GRAPES

A THESIS SUBMITTED

FOR THE AWARD

OF

THE DEGREE OF

DOCTOR OF PHILOSOPHY (ENERGY)

BY

K.S. JAIRAJ

UNDER THE GUIDANCE OF

DR. S.P. SINGH PROFESSOR AND HEAD

SCHOOL OF ENERGY AND ENVIRONMENTAL STUDIES

FACULTY OF ENGINEERING SCIENCE DEVI AHILYA VISHWAVIDYALAYA

INDORE

2015

CERTIFICATE OF THE SUPERVISOR

This is to certify that the work entitled “A SOLAR CONCENRATOR BASED INDIRECT

DRYING SYSTEM FOR GRAPES” is a piece of Research work done by Mr. K S Jairaj,

under my guidance and supervision for the award of degree of Doctor of Philosophy

(Energy) of Devi Ahilya University, Indore (M.P), India. The candidate has put in an

attendance of more than 200 days with me.

To the best of my knowledge and belief the thesis:

(i) embodies the work of the candidate himself;

(ii) has duly been completed;

(iii) fulfils the requirements of the ordinance relating to the Ph.D. Degree of the

University; and

(iv) is up to standards both in respect of content and language for being referred

to the examiner.

(Dr. S P Singh) (Dr. S P Singh) Signature of Supervisor Signature of the Head UTD

DECLARATION BY THE CANDIDATE

I hereby declare that the thesis entitled “ A SOLAR CONCENTRATOR BASED

INDIRECT DRYING SYSTEM FOR GRAPES ” is my own work conducted under the

supervision of Dr. S P Singh, at School of Energy and Environmental Studies, Faculty of

Engineering Sciences, Devi Ahilya University, Indore (M.P), India, approved by Research

Degree Committee. I have put in more than 200 days of attendance with the supervisor at the

center.

I further declare that to the best of my knowledge the thesis does not contain any part of any

work, which has been submitted for the award of any degree either in this university or in any

other University without proper citation.

(Dr. S.P.Singh) (K.S.Jairaj) Signature of Supervisor Signature of Candidate

(Dr. S.P.Singh) Signature of the Head UTD

ACKNOWLEDGEMENT

Guru Brahma, Guru Vishnu, Guru Devo Maheshwaraha, Guru Sakshath Parabrahma,

Tasmai Shri Sadguruve Namaha

It is only due to the Holy blessings of my spiritual Sadguruji

His Holiness, Shri Parama Poojya Gurupadeshwara Shivmath Maharaj ji

that I was destined to be in Indore for pursuing this most coveted Doctoral Course without

any hurdles.

This unique research work would not have seen the light of the day but for the innovative

idea and intellectual efforts of my Great Guruji, the unparalleled genius, greatly gifted and

widely respected Dr. Satendra Pal Singh Sir.

Words on paper have a severe limitation and fail to speak the language of my sincere feelings

of love, respect, and admiration towards Sir. Since the first day of my long standing

association with Sir, I have always been mesmerized by the multi dimensional and

exceptional qualities of this towering personality. His simplicity, his frankness, his spiritual

bent of mind and most importantly his over whelming zeal to help students without denting

their self respect made me look up at this academic colossus with awe and admiration. My

conscience always kept on telling me that this research acquaintance with Sir was only a

prelude to a greater spiritual and divine association with this spiritual yogi in the years to

come.

Sir’s approach towards his students can set up new benchmarks for anybody who is

passionately involved in teaching and research. He literally led me through this wild,

unpredictable and frightful jungle of research by holding my little finger, like my mother did

when I was a kid. This assured and confident guidance of Sir which pulled me out of several

complicated problems in a jiffy, made me feel that research was more of a pleasure than

torture.

Respected Sir, it is so kind of you for having accepted me as your student and making me

what I am today. It was only your ingenuity that has made me achieve what I once thought

was impossible. Sir, I do not know how I can repay this noble favor you have done to me, due

to which I am able to stand tall with my head held high in the field of technical education. A

Big, Big Thank You Sir !!!

I would definitely be cheating my conscience if I do not apologize and profusely thank

Madam Anjali Singh, Sir’s better half, for whole heartedly allowing Sir to spend late

evening hours with me in the department during the course of my research journey. Madam,

Thank You so much !!! for your gracious sacrifice. I also thank Yash Pratap Singh for

bearing and cooperating with me when his dear daddy could not find time for him as Sir

would be spending long hours at the department helping me in my research work.

I take this great opportunity to convey my heartfelt thanks to the legendary personality, who

is none other than the most revered, Dr. Mahendra Singh Sodha Sir, who was solely

responsible for bringing into existence our School of Energy and Environmental Studies,

Devi Ahilya Vishwavidyalaya, due to which it was possible for me to register and pursue this

Doctoral program.

Our School of Energy and Environmental Studies, DAVV, has one of the richest academic

atmospheres in DAVV where all staff members are ever ready to help students and tutor them

with great dignity.

Special regards to Dr. R.N.Singh Sir, who was so very resourceful and helpful during my

Ph.D. Course Work and thesis writing. Heartfelt thanks to Dr. Rubina Choudhary Madam

for the encouragement and assistance at crucial moments.

I would like to thank all the teaching and non-teaching staff of SEES, DAVV, Indore, for

their kind cooperation and assistance during my enjoyable and memorable sojourn in the

department.

I would like to place on record the dedicated service of my hard working son Mr. K S

Sangamesh, who spent several sleepless nights in the laboratory and several days in the

scorching heat, assisting me in conducting field experiments. Thank You Sonny !!! for

showing amazing grit and perseverance during this testing time. Your amicable company

chased away solitude and made research work enjoyable.

I could not have wished for a better brother and well wisher than Prof. K.Srikant, who stood

by me during the ups and downs of my life and career. His moral support, useful hints and

awesome editing made my work of publishing research papers and completing my thesis a

pleasurable experience.

I express my deep sense of gratitude and indebtedness to Hon’ble Shri. Vinod Kumar

Agarwal ji, Chairman, Chamelidevi Group of Institutions, Indore, for constantly motivating

me and whole heartedly supporting me in all possible ways to achieve this academic

milestone.

I sincerely thank CA. Pramodji Shrivastava, Co-ordinator, Chamelidevi Group of

Institutions, Indore, who actively supported me to carry out my research work along with my

day-to-day administrative responsibilities at CDGI.

I am too very glad to appreciate the expertise of Mr. Vijay Bhat in using MS Excel and

thank him for helping me in making mathematical modeling an easy track for me to run into

the final conclusions.

I would also like to thank the Management, Director, Staff and Students of Chamelidevi

Group of Institutions, for the assistance in one way or the other during this entire work.

The Staff of Mechanical Engineering department needs special mention for the unflinching

assistance rendered at crucial junctures of fabricating my dryer systems.

Special thanks with a deep sense of gratitude to my friends and colleagues Dr. H.N. Ramesh,

Dr. B.M. Rajprakash, Mr. Deepak Phalke, Mr. Manish Gome, Mr. Swapnil Bhurat,

Mr. Vipul Jain, Mr. Govind Hanotia, Mr. Gourishankar Kose, Mr. Sudhakar Dhote, Mr. Israr

Ahmad Sheikh and Mr. Prerit Mishra,

Special Thanks to Mr. Sahajram Yadav, who would get stuck in the department for late

long hours when Sir would be embroiled in solving my research problems. Special thanks to

Mr. Rana Pratap Singh, Mr. Mohan Rawat, Mr. Jai Bahadur Balwanshi, Mr. A.H. Pathan,

Mr. Rajesh Singhadiya, Mr. Vimlesh Shrivastava, Ms. Manju Soni, Ms. Nilam Shrivastava,

Mr. Ramcharan Kapoor, Mr. Kamal Hirve and all my research mates for their co-operation

and help during the course of this research work.

My Godly Mom and Dad to whom this work is dedicated, have been my leading lights during

moments of darkness. Their divine blessings and prayer for me has sustained my motivation

thus far and made me achieve this glory.

Success is just impossible without the steadfast support and cheerful love of your family. I

feel distinctly lucky to have been blessed with such a well knit family, who would sport

smiling faces even when I could not find time for their outings and pleasure trips on holidays.

I sincerely appreciate the sacrifice and caring support of my better half, Anita, my dear sonny

Sangamesh and adorable daughters Roopashree, Deepashree, Laxmi and Bhabhi ji Gouri.

Last but not the least; I would like to thank all those who directly or indirectly supported me

in the successful completion of this research work.

K.S.JAIRAJ.

This Work is Dedicated to

My most beloved, caring, inspiring and motivating parents,

Smt. GIRIJAMMA S. KALAVEERAKKANAVAR,

My First Teacher, who helped me put my first steps on this Earth

and taught me the Basic Lessons of Hard Work, Sincerity,

Morality and Spirituality

AND

Late Shri. SANGAPPA B. KALAVEERAKKANAVAR,

My Real Life Hero and Role Model, who imbibed in me the time

tested values of Uprightness, Honesty, Dedication, Self Discipline

and Self Respect

It is the Selfless Sacrifice and Tutelage of these two great

souls that has made me what I am Today

CONTENTS

Title Page No.

Certificate --

Declaration --

Acknowledgement --

Contents i

Executive Summary vi

List of Tables xxvi

List of Figures xxix

List of Plates xxxiv

List of Abbreviations xxxvi

CHAPTER - I INTRODUCTION

1.0 Background 1.1

1.1 Hypothesis 1.5

1.2 Objectives 1.6

1.3 Organization of the thesis 1.6

References 1.8

CHAPTER - II REVIEW OF LITERATURE - SOLAR DRYERS AND KINETICS OF GRAPE DRYING

2.0 Introduction 2.1

2.1 Working principle of solar drying 2.3

2.1.1 Open sun drying 2.4

2.1.2 Direct sun drying 2.5

2.1.3 Indirect sun drying 2.6

2.2 Traditional methods of grape drying 2.7

2.3 Solar dryers developed for grape drying 2.8

2.3.1 Direct type solar dryers 2.8

2.3.1.1 Solar cabinet dryer 2.8

2.3.1.2 Staircase solar dryer 2.9

2.3.1.3 Glass roof solar dryer 2.9

2.3.2 Indirect type solar dryers 2.10

2.3.2.1 Natural circulation type 2.10

2.3.2.1.1 Indirect type conventional solar dryer 2.10

2.3.2.1.2 Indirect natural convection solar dryer with chimney 2.10

2.3.2.1.3 Multipurpose natural convection solar dryer 2.12

2.3.2.1.4 Indirect natural convection solar dryer with chimney

and storage material 2.12

2.3.2.2 Forced circulation type 2.13

2.3.2.2.1 Solar dryer with green house as collector 2.13

2.3.2.2.2 Geodesic dome fruit dryer 2.13

2.3.2.2.3 Solar tunnel dryer with integral collector 2.14

2.3.2.2.4 Solar air flat plate collector with obstacles 2.14

2.3.2.2.5 Solar multiple layer batch dryer 2.16

2.3.2.2.6 Indirect type solar fruit and vegetable dryer 2.16

2.3.3 Hybrid photovoltaic-thermal greenhouse dryer 2.17

2.3.4 Hybrid solar dryer 2.18

2.4 Properties of grapes 2.18

2.5 Pretreatment of grapes 2.22

2.6 Factors affecting drying of grapes 2.24

2.7 Results obtained after grape drying 2.27

2.7.1 Experimental results obtained by investigators after drying

untreated and pretreated grapes by traditional methods 2.28


untreated grapes using solar dryers 2.33


pretreated grapes using solar dryers 2.34

2.7.4 Summary 2.37

2.8 Conclusions 2.38

References 2.38

CHAPTER - III DESIGN AND DEVELOPMENT OF SOLAR CONCENTRATOR BASED GRAPE DRYER WITH SENSIBLE HEAT STORAGE


3.1 Design criteria for experimental solar dryer model 3.2

3.1.1 Design procedure 3.3

3.1.2 Collection of data 3.4

3.1.3 Design calculations 3.5

3.2 Characteristic parameters of solar concentrating collectors 3.7

3.3 Types of solar concentrating collectors 3.9

3.3.1 Parabolic dish type solar concentrator 3.10

3.3.2 Parabolic dish type solar cooker 3.11

3.4 Initiative for this research 3.13

3.5 Specifications of parabolic solar concentrator 3.15

3.6 Experimental dryer model design details 3.15

3.7 Constructional details of experimental dryer model 3.16

3.8 Working of the experimental dryer model 3.19


References 3.21

CHAPTER - IV EXPERIMENTAL STUDY AND PERFORMANCE EVALUATION OF SOLAR CONCENTRATOR BASED DRYER


4.1 Drying performance compared with that of flat plate type 4.2

4.2 Drying rate 4.2

4.3 Initial moisture content 4.3

4.4 Moisture ratio 4.3

4.5 Materials and methods 4.4

4.6 Experimental procedure 4.8

4.6.1 Drying of Sharad seedless grapes 4.11

4.6.2 Experimental results and discussion 4.12

4.6.3 Drying of Thompson seedless grapes 4.21

4.6.4 Experimental results and discussion 4.23

4.7 Quality parameter of raisins 4.32

4.7.1 Parameters affecting qualities of raisins 4.33

4.7.2 Summary 4.33

4.8 Quality of raisins produced during experimentation 4.34


References 4.38

CHAPTER - V KINETICS OF GRAPE DRYING


5.1 Drying kinetics of food material 5.1

5.2 Drying models 5.2

5.2.1 Theoretical models 5.3

5.2.2 Semi-theoretical models 5.4

5.2.3 Empirical models 5.6

5.3 Drying characteristics of grapes 5.9

5.4 Proposed kinetic model : Universal drying rate constant 5.11

5.5 Models for grape drying characteristics 5.14

5.6 Drying curves fitted into Exponential model by curve fitting 5.17

5.7 Realization of drying rate constant values by curve fitting 5.18

5.8 Variation of drying rate constant with different drying

parameters 5.20

5.8.1 Summary 5.22

5.9 Verification of results obtained from drying experiment 5.23


References 5.25

CHAPTER - VI MATHEMATICAL MODELING AND VALIDATION WITH EXPERIMENTAL RESULTS OF THE PROPOSED SOLAR DRYER


6.1 Modeling of the drying system 6.2

6.2 Mathematical models to determine temperatures in dryer 6.4

6.2.1 Temperature at lower end of aluminum container

filled with sand - TB 6.8

6.2.2 Temperature at vertical sides of aluminum container

filled with sand - TVS 6.12

6.2.3 Temperature of sand filled in aluminum container at

lower end - TSB 6.16

6.2.4 Temperature of sand filled in aluminum container near

top surface - TST 6.18

6.2.5 Temperature of air above the aluminum container

filled with sand - TT 6.22


References 6.26

CHAPTER - VII TECHNO-ECONOMIC ANALYSIS OF SOLAR CONCENTRATOR BASED GRAPE DRYER WITH SENSIBLE HEAT STORAGE


7.1 Fabrication cost of solar concentrator based dryer 7.1

7.2 Economic analysis of solar concentrator based dryer 7.4

7.3 Internal rate of return (IRR) 7.5

7.4 Cost economics of drying systems with higher capacity 7.5

7.5 New type of indirect drying system proposed for

commercial grape drying 7.11


References 7.13

CHAPTER - VIII CONCLUSIONS AND RECOMMENDATIONS 8.0 Introduction 8.1

8.1 Conclusions 8.1

8.2 Recommendations 8.4

8.3 Scope for future work 8.4

List of publications P.1

Annexure - A A.1 - A.4

Annexure - B B.1

Annexure - C C.1 - C.7

Annexure - D D.1

Annexure - E E.1 - E.14

Annexure - F F.1

EXECUTIVE SUMMARY

Agriculture is still a major occupation in India as majority of its population is

concentrated in rural areas [1]. As population explosion is creating a heavy demand for

agricultural products in the country, the role of farmers in improving the food situation in the

country acquires considerable prominence. Hence, it is very much essential to support

farmers in all possible ways to make them financially self reliable and sustainable.

In today’s modern developing world, Agriculture is not only restricted to production

of crops and live stock on farm as defined in the Webster’s Dictionary but in the broader

perspective also includes various related activities like, forestry, horticulture, floriculture,

silk, dairy and poultry farming, bee keeping and other economically viable activities [2].

Majority of the farmers are adopting hi-tech methods of crop production, food processing and

preservation, fast and economic transportation and effective marketing to reap rich dividends

from their farming activities.

India basically is an agricultural country in which the occupation of a large section of

the working population has been agriculture and allied activities. With more than 60 % of its

total land area being arable, India is the second largest country in the world in terms of its

arable land [3]. As per statistics made available by the Ministry of Agriculture during the year

2014-15, agricultural sector employed 54.6 % of the total potential work force in the country

[4] and contributed about 16 % to the country’s total GDP and 10 % to total exports [3].

India is a country dominated by small and marginal farmers with poor financial status.

Lack of storage facilities, compulsion on repayment of loans and immediate financial

requirements are major causes, which force farmers to rush their farm products to the market

immediately after the harvesting season. With a majority of farmers trying to sell their

products during harvesting season, middlemen and market players exploit the surplus

situation to pull down prices of the farm products and deprive farmers of their actual benefit.

On the contrary, if facilities are extended to preserve and store farm products to be sold at a

later stage, the market glut which causes price reduction can be avoided and thus enable the

farmer to sell his produce at a later stage when it can fetch him higher prices.

With larger emphasis on variety and quality of agricultural products, there has been

large-scale improvement in their yield. Production of grains, fruits and vegetables per acre

has increased drastically due to improved methods of farming and pest control. This rapid

improvement in present day agricultural technology has enhanced production of food grains,

fruits and vegetables to a large extent resulting in surpluses during harvesting seasons. This

enhanced agricultural output has posed a serious challenge to technologists to research for

improved methods of harvesting and preserving surplus agricultural products. It is of utmost

importance to ensure that the processes employed shall be practically feasible and

economically viable.

As per limited data available on post harvest losses in fruits and vegetables, the

minimum reported loss is 21 % while some references indicate estimates in excess of 40 -

50 %; however, actual losses are much higher than the specified statistics [5]. The financial

status of farmers could be brightened if economical methods of cold storage and appropriate

food processing techniques could be adopted to increase the shelf life of fruits and vegetables

that are available in surplus during harvesting season.

Energy requirement becomes a major concern if shelf life of farm products has to be

extended for improving the economic situation of farmers and the country. As per the report

of 2014-15, energy consumption towards agriculture was 18.45 % of India's national

consumption and was the third highest behind industry and domestic consumption [6]. There

is a close nexus between energy consumption and agricultural productivity.

Since early days, one of the most widely practiced methods used for preserving fruits

and vegetables has been open sun drying. Drying is a preliminary process adopted in most of

the food producing countries. Drying of fruits and vegetables to a safe level of moisture

content enhances their shelf life, lowers their weight, enhances their appearance, reduces their

packing and transportation cost, while concurrently allowing the products to retain their

flavor and also their nutrition value. Huge demand for dried fruits and vegetables in local and

global markets has accelerated research in the field of quality oriented drying in most of the

developing countries. If the surplus quantity of fruits and vegetables produced during

harvesting season are dried for long term storage then it would provide handsome economic

returns for the farmers.

Grape being one of the world’s largest fruit crops has enormous demand in its dried

form throughout the world. According to the website of Agricultural and Processed Food

Products Export Development Authority, India, the country produced 2,584,600 tonnes of

grapes during 2013-14 [7] and exported 31,602.24 MT of dried grapes [8]. As per data

available on the website of Agricultural and Processed Food Products Export Development

Authority, India, the country exported about 3,16,059.43 MT of processed fruits and

vegetables worth Rs. 2,56,991.86 lakhs during 2014-15 [9]. Growing demand for superior

quality dried fruits and vegetables, has initiated intensive research in the field of quality

oriented drying of agriculture and farm products.

After going through a large number of research publications related to grape drying, it

was quite evident that traditional methods adopted for grape drying resulted in dried grapes of

inferior quality, which were unable to meet specifications and requirements of local and

international markets. Usage of industrial dryers for grape drying helped in improving the

quality of dried grapes, but huge initial investments and exorbitant running costs due to use of

electricity or alternative fossil fuel in these dryers posed considerable financial barriers for

small farmers to adopt them. Several disadvantages associated with open sun drying, shade

drying as well as mechanical drying, forced farmers in many countries to explore alternate

cost-effective and hygienic drying methods to preserve fruits and allied farm products.

One of the most cost effective and hygienic method suitable for drying farm products

is by using the inexhaustible and freely available solar energy. Solar dryers are definitely cost

effective with zero fuel costs and use a clean form of renewable energy with an advantage of

hygienic conditions that are suitable for drying and preserving farm products obtained in

surplus during the harvesting season. Introduction of solar dryers has reduced crop losses and

improved the quality of dried products significantly when compared to traditional methods of

drying [10].

Solar dryers, provide the required amount of heat to the drying air by using solar

energy. This is one of the most viable options for drying farm products in most of the

developing countries that lie within the belt of good solar radiation, like India [11]. Methods

of obtaining thermal energy from solar radiation are improving day by day. Researchers are

on the lookout for effective methods to precisely control drying air temperature in order to

increase the effectiveness and efficiency of drying systems. Detailed studies conducted by

many researchers have proved the superiority of solar dried grapes over naturally sun dried

grapes [12-14].

During the exhaustive literature survey conducted in the field related to solar drying

of grapes, it was observed that most of the researchers while using the indirect system for

drying had used flat plate collectors [10, 15-18]. Some of them worked with solar tunnel

dryers [19-21] and green houses [22-24], which could dry grapes in bulk quantities. Few

researchers have worked with evacuated tube collectors and obtained encouraging results

[25]. A solar drying system using parabolic dish, was used to dry bananas [26] as well as

grapes [27], although the system appeared to be a bit complicated, it was able to provide

satisfactory results. A solar dryer using six square parabolic reflectors was used to dry apples,

pears and peaches [28] with encouraging results.

During literature survey, it was observed that apart from the above-mentioned

research publications, not much work related to either improving or simplifying the process

of solar drying methods was carried out for drying grapes. Most of the indirect type solar

drying systems developed by researchers for drying grapes had used flat plate collectors.

After a detailed analysis of these existing indirect type-drying systems, certain drawbacks,

which have been listed below were observed -

Lack of portability of the drying system

Requirement of precautions to maintain the glass covering fixed over the flat plate

Inability of flat plate collectors to provide nearly constant drying air temperature

throughout the sunshine period

Limitation on maximum drying air temperatures (not more than 60 °C) obtained using

flat plate collectors (indirect mode)

Limitation on the difference between drying air temperature at outlet of flat plate

collector and ambient air temperature in indirect mode flat plate collectors

Limitation on reduction of drying time for any product due to difficulty in generating

maximum drying air temperatures in excess of 60 °C

Requirement of enhancement in area of flat plate collector to augment the capacity of

any dryer

The use of evacuated tube collectors posed specific problems similar to those

associated with flat plate collectors, but unlike flat plate collectors, they could provide higher

range of operating temperatures. Research was carried out to design and develop solar drying

systems that could perform much better than the existing drying systems. One of the major

requirements essential to accelerate the drying process without compromising on quality of

the dried final product was to maintain a constant drying air temperature close to the

maximum permissible temperature for drying grapes and this constant temperature had to be

maintained throughout the sunshine period in a day.

Several alternatives for achieving the required objective were investigated and one of

the best suitable alternatives was making use of a parabolic solar concentrator to obtain the

required level of thermal energy essential for drying grapes. A parabolic solar concentrator

was able to provide substantially higher values of temperatures than that required for grape

drying for a longer duration of time during the sunshine period. Temperature values available

at the focal point of parabolic solar concentrator depend on its concentration ratio. Parabolic

solar concentrators with higher values of concentration ratio produce higher temperatures.

Hence, the concentration ratio of the parabolic solar concentrator under consideration would

decide the dryer size and its capacity.

As per the design calculations carried out for drying 1 kg grapes, the value of aperture

area of solar concentrator obtained was 1.53 m2. After conducting an extensive market

survey, it was observed that parabolic dish type solar concentrators used for cooking purposes

were commercially available with a diameter of 1.4 m and an aperture area of 1.54 m2.

Hence, SK-14 solar concentrator was chosen for the proposed indirect drying system. SK-14

is able to provide an encouragingly high temperature of 50 °C during early mornings and late

evenings and a temperature as high as 200 °C during mid noon. Researchers all around the

globe have estimated that temperatures conducive for grape drying had to be maintained in

the range of around 60 °C to produce raisins of fairly good quality. In order to maintain

drying air temperatures in the specified range, a heat storage material in the form of sand was

used to absorb the reflected and concentrated solar radiation obtained from the solar

concentrator. In addition to effectively stabilizing the temperature of drying air in the

specified range of 60 to 70 °C, the hot sand was able to continue the drying process even

beyond sunshine hours, thus expediting the drying process and effectively reducing the total

number of hours required to dry grapes.

An indirect dryer suitable to be used along with SK-14 solar concentrator was

designed and fabricated. An aluminum sheet of 3 mm thickness was used to fabricate the

rectangular inner chamber of the dryer. Another concentric rectangular chamber was

fabricated using one mm thick GI sheet, so as to have a peripheral gap of 25 mm between this

outer GI chamber and the inner aluminum dryer chamber. This 25 mm peripheral gap

between the two rectangular chambers was then tightly stuffed with glass wool. The outer GI

sheet clad was then perfectly sealed to provide excellent thermal insulation for the inner

aluminum-drying chamber to avoid unnecessary heat loss. Fabrication of the proposed

indirect dryer is categorized into two sections:

The lower section

The upper section

The dryer lower section consists of a square aluminum container, which is used to fill

the heat storage material (sand). This sand filled container is rigidly fixed at the bottom of the

upper rectangular aluminum-drying chamber and placed at the focal point of the SK-14

parabolic solar concentrator, so that it receives the reflected and concentrated solar radiation

during sunshine hours. The size of the rectangular aluminum container is such that there is a

gap of 30 mm all around the periphery of the container to allow flow of hot air from the

bottom towards the drying tray.

The dryer upper section consists of a rectangular aluminum drying chamber cladded

with a layer of glass wool and the outer GI sheet covering. A drying tray was fabricated using

1 × 1 mm size iron wire mesh and bordered with GI sheet for stability. Provision is made for

hanging this drying tray from the top opening of the drying chamber. Height of the drying

tray from the bottom aluminum sand container is adjustable and this height will decide the

drying air temperature used to dry grapes. Higher drying air temperatures can be obtained by

lowering the drying tray closer to the bottom aluminum sand container. Drying air

temperature can be reduced by elevating the drying tray farther away from the bottom

aluminum sand container. During the experimental process, the drying tray was hung at a

suitable height to obtain a drying air temperature of around 70 °C. The drying chamber was

then covered on the top with a tight fitting square GI sheet cover having a small opening at

the centre, for allowing exit of moist air from the top. The outer surface of the top cover was

coated with a one inch thick layer of thermocol insulation sheet to maintain it at a lower

temperature for enhancing the exit of moist air.

Drying experiments were repeatedly conducted during the grape harvesting months of

April, May and June 2015 using pretreated Sharad seedless grapes (Black). One kg of

handpicked, uniformly sized grape samples were dried in a total time duration of 28 hours,

i.e. 14 hours during sunshine hours of two consecutive days and 14 hours during one night

spanning between the two sunshine days. During the experimentation process, 51.33 % of

initial moisture content present in Sharad seedless grapes was evaporated using reflected and

concentrated solar radiation from the parabolic solar concentrator within a time duration of

14 sunshine hours on two consecutive days. Bulk of the evaporation during this period was

due to convective mode of heat transfer. The entire drying chamber unit would then be stored

inside a close fitting, one inch thick air tight, plywood enclosure immediately after sunshine

hours to exploit the advantage of thermal energy stored in the sand for drying grapes. It was

possible to evaporate 13.7 % of moisture content through radiative mode of heat transfer in

14 hours using sensible heat stored in sand during the night time spanning between the two

consecutive sunshine days.

Similarly, drying experiments were repeatedly conducted using Thompson seedless

grapes (Green). One kg of handpicked, uniformly sized grape samples were dried in a total

time duration of 25 hours, i.e. 11 hours during sunshine hours of two consecutive days and

14 hours during one night spanning between the two sunshine days. During the

experimentation process, 43.56 % of initial moisture content present in Thompson seedless

grapes was evaporated using reflected and concentrated solar radiation from parabolic solar

concentrator within a time duration of 11 sunshine hours on two consecutive days. Bulk of

the evaporation during this period was due to convective mode of heat transfer. The entire

drying chamber unit would then be stored inside a close fitting, one inch thick air tight,

plywood enclosure immediately beyond sunshine hours to exploit the advantage of thermal

energy stored in the sand for drying grapes. It was possible to evaporate 20.44 % of moisture

content through radiative mode of heat transfer in 14 hours using sensible heat stored in sand

during the night time spanning between the two consecutive sunshine days.

Dried samples of both grape varieties were observed using images captured by a high-

resolution camera. It was observed that their surface structures were uniform without any

cracks on their outer skin; outer surfaces of dried grapes had nearly soft texture and were

neither sticky nor damaged. They possessed better-collapsed structure, better skin integrity as

well as small and uniform wrinkles. The dried grapes of both varieties were able to meet all

the quality parameters as per market requirements. The dried grape samples were also

subjected to color test in Food Laboratory, Centre for Technology Alternatives for Rural

Areas (CTARA), Indian Institute of Technology, Mumbai. The color properties of Thompson

seedless grapes showed higher value of L and lower value of a/b ratio which indicated that

the dried grapes were quite close to internationally acceptable levels.

The effective drying time required for drying Sharad seedless grapes using solar

energy to the required level of moisture content suitable for long time storage was found to be

14 hours while that for Thompson seedless grapes the drying time was 11 hours. The fairly

low value of drying time for Thompson seedless grapes is mainly due to two reasons -

smaller size and higher skin permeability and porosity of Thompson seedless grapes when

compared to Sharad seedless grapes. These two factors are responsible for higher mass

transfer. Results obtained through repeated drying experiments support the fact that Sharad

seedless grapes take a longer time to get dried to the required level of moisture content than

Thompson seedless grapes.

From the drying tests carried out on Sharad and Thompson seedless grapes it was

possible to show that the exponential model satisfactorily describes their drying

characteristics. Further, it was shown that the drying rate constant of seedless grapes obtained

from the drying characteristics of both variety seedless grapes was dependent solely on the

properties of the product to be dried and properties of the drying air.

All the proposed mathematical models that have been developed to estimate the

temperatures at different locations inside the dryer were experimentally validated. It can be

concluded that the estimated theoretical values of temperatures at different locations along

the height of the dryer chamber using mathematical models are in close agreement with the

experimental values obtained, thus proving validity of the proposed models. The up scaling

of solar drying systems has been proposed for value addition and increasing the shelf life of

the product (raisins).

Techno-economic analysis of indirect drying systems with drying capacities varying

from 5 to 40 kg grapes per batch (14 hours/batch for Sharad and 11 hours/batch for

Thompson grapes) was carried out to investigate the feasibility and viability of the systems.

These systems with capacities to dry 585 to 4680 kg fresh grapes per annum produced 116 to

930 kg raisins per annum. The calculated Internal rate of return (IRR) values for all these

indirect drying systems varied from 25 to 29 % per annum.

Hence, it can be concluded that the proposed experimental drying model, designed

and developed primarily for the benefit of small and marginal farmers in rural areas can dry

grapes in an effective and efficient manner. The experimental drying model can be up scaled

for drying large quantity of grapes in a single batch (14 hours/batch for Sharad and

11 hours/batch for Thompson grapes) to provide higher returns.

Chapter - 1 Introduction

Drying is one of the most widely used methods to reduce post harvest losses in fruits

and vegetables. Specific methods, which can provide ideal hygienic conditions during the

entire drying process, are necessary for drying fruits. This chapter consists of three sections -

The chapter starts with a brief background related to grapes and the most commonly used

drying processes. It provides information related to different varieties of grapes and their

cultivation along with information related to post harvest losses and their remedial measures.

It deals with the most prevalent modes of drying along with important features in the

development of solar dryers used for grape drying. The first section deals with the hypothesis

of this research work and the second section lists the prime objectives. In other words, it

states the aim of the presented research work, which is to develop an innovative approach

towards solar drying of grapes. It concludes with a brief description of organization of the

thesis and its significance.

Chapter - 2 Review of Literature - Solar dryers and kinetics of grape drying

A critical review of more than 150 research articles, books, journals and related useful

topics from several websites was carried out. Relevant and essential information from nearly

80 research articles was utilized in identifying the grey areas, which could be focused and

sorted out to achieve the end result. This chapter comprises of eight sections - The chapter

starts with a brief history related to grapes. It provides information about Thompson seedless

grapes and certain statistics pertaining to export and import of dried grapes. It also provides

some important information about availability of solar energy. The first section covers

different modes of solar drying and deals with working principle of all the three modes in

detail. The second section deals with traditional drying methods for grapes. The third section

deals with most of the prominent solar dryers developed for grape drying and have been

covered in detail. The fourth section provides detailed information related to properties of

grapes, their structural composition, nutritive values in fresh form as well as in dried form.

The fifth sections deals with pretreatment of grapes, pretreatment solutions and procedures

of dipping treatment adopted. The sixth section covers all the prominent factors that affect the

drying phenomena of grapes, all the contributions of prominent researchers are covered, the

effect of certain parameters on drying time and quality of grapes are sequentially discussed.

The seventh section deals with results published by prominent researchers who have worked

in the field of grape drying. Results obtained by investigators while drying grapes using

traditional methods are also presented. This is followed by results published by prominent

researchers while working with solar dryers to dry untreated as well as pretreated grapes and

discussed sequentially in detail. After reviewing the performance of existing solar dryers

developed for grape drying, all advantages that could be utilized and all the disadvantages

that could be improved upon were listed out to be adopted in the design and development of

the proposed dryer. The summary presented at the end, highlights specific issues to be

considered in the proposed research work. The chapter ends with conclusions that shall be

partially adopted in the design and development of the proposed dryer.

Chapter - 3 Design and development of solar concentrator based grape dryer with sensible

heat storage

The idea of concentrating solar radiation on to a target area and achieving the desired

result has been practiced since ancient times. The universal fossil fuel crisis created

tremendous chaotic situation which forced technologists to shift towards alternate sources of

renewable energy, more prominently towards using the abundantly and freely available solar

energy. Detailed information related to solar concentrators, their applications and advantages

are presented. This chapter comprises of nine sections - The chapter begins with details

related to use of solar concentrators during the early period. Details related to different types

of existing solar concentrators and their advantages are listed. The first section deals with the

preliminary design aspects of the solar dryer. Details of local weather data as well as both

variety grapes collected are presented and finally design calculations required for deciding

the solar concentrator size has been presented. The second section deals with important

characteristic parameters of solar concentrating collectors, which are defined to provide

clarity about each one of them. The third section deals with various types of solar

concentrating collectors, which provide an insight into the variety of solar collectors

available. It also provides details related to a parabolic solar concentrator and a parabolic type

solar cooker. The fourth section explains the initiative taken to carry forward this research

work. The fifth section presents technical specifications of the solar concentrator used in this

research work. The sixth section deals with a sequential presentation of the basic idea that

helped in designing the proposed dryer. The seventh section provides constructional details of

the proposed grape dryer along with figures showing step-by-step fabrication. The eighth

section explains operation of the proposed grape dryer and the step-by-step procedure to be

adopted for drying grapes. The chapter ends with conclusions related to the proposed dryer.

Chapter - 4 Experimental study and performance evaluation of solar concentrator based

dryer

Results obtained from experimental studies will be helpful to validate the

mathematical models developed for any drying system. Any newly developed system has to

be tested in order to evaluate its performance. This chapter has nine sections - The chapter

highlights the need of using renewable energy sources to meet energy requirements of the

agricultural sector. It stresses the need of simple and financially viable food processing

systems developed by researchers so that they can be used by small and marginal farmers

with advantage. The first section highlights notable difference in temperature made available

by a solar concentrator based dryer in comparison with that of a flat plate collector.

Temperatures available at the drying tray in case of solar concentrator based dryer is more

than 60 °C for a prolonged duration during sunshine period. This high value of almost

constant temperature available at the drying tray specifically reduces the drying time. The

second section defines drying rate and equations used for calculating the drying rate. The

third and fourth sections provide relations used to calculate certain basic parameters before

and during the experimentation. The fifth section deals with materials and methods used for

conducting the drying experiment. Composition of dipping solution used in the pretreatment

of grapes, temperature at which it was maintained and time duration for which grapes were

dipped in the solution are presented. All preparations made before starting the experiment

under the sun are also presented. Details of technical specifications of all measuring

instruments used in the experimental process have been presented. The sixth section explains

the procedure adopted for conducting the experiment using Sharad seedless grapes conducted

on 27th and 28th of May 2015, the results thus obtained were analyzed and discussed. A

glance at the tabulated values portray that the drying tray temperature was above 60 °C for

nearly 10 hours out of the accumulated drying time of 28 hours over two consecutive days.

The drying rate constant obtained for Shard seedless grapes was 0.0187 h-1. The overall

drying rate for drying Sharad seedless grapes was 0.0273 kg/hr.

The next sub-section deals with the drying experiment details using Thompson

seedless grapes conducted on 02nd and 3rd June, 2015. Further, the results thus obtained were

analyzed and discussed. A glance at the tabulated values portray that the drying tray

temperature was above 60 °C for nearly 10 hours out of the accumulated drying time of

25 hours over two consecutive days. The drying rate constant obtained for Thompson

seedless grapes was 0.0228 h-1. The overall drying rate for drying Thompson seedless grapes

was 0.0304 kg/hr. The color properties of dried Thompson seedless grapes showed higher

value of L and lower value of a/b ratio which indicated that the dried grapes were quite close

to acceptable levels. Dried grapes of both varieties were able to meet all the quality

parameters as per the market standards. It is finally inferred that by using solar energy for

14 hours, Sharad seedless grapes were dried to have a final moisture content ideal for long-

term storage. Thompson seedless grapes required solar energy for 11 hours to get dried and

reach final moisture content ideal for long-term storage. The seventh section deals with the

quality of raisins and parameters affecting quality of raisins. The eighth section deals with the

quality of raisins produced after drying both variety grapes using the proposed solar

concentrator based indirect drying experimental model for grapes. This chapter finally

concludes with the results obtained after drying both varieties of grapes.

Chapter - 5 Kinetics of grape drying

Drying kinetics of any agricultural product provides vital information related to its

behavior when subjected to varying drying conditions and parameters. This chapter consists

of ten sections - The chapter begins with brief information related to drying of farm products.

The first section provides a brief introduction to drying kinetics of food products and its

mathematical modeling. It highlights the importance of a mathematical model used to

describe the drying kinetics of food products. The second section covers vital information

related to drying models, with emphasis on thin layer drying model for fruits and vegetables.

Prominent categories of thin layer drying models are listed and each approach is elaborately

presented. Some important theoretical models published by researchers applicable to

moisture movement during drying of agricultural products have been presented. Semi-

theoretical models developed to describe the drying characteristics of food products, which

help to determine the drying rate as well as the drying rate constant are presented and

discussed. Empirical models, which do not explain the drying process but assist in

determining relevant variables and quantifying the kinetics, are presented. Several researchers

have developed empirical models for different agricultural products under specific

conditions; such models have also been presented. Some important empirical models used to

calculate specific drying parameters have been presented and discussed. The third section

deals with the drying characteristics of grapes. The fourth section deals with the proposed

kinetic model for seedless grapes, which leads to determination of the universal drying rate

constant. The fifth section deals with drying characteristics published by prominent

researchers, which are analyzed using Curve fitting software in order to find the curve of best

fit. The sixth section deals with the drying characteristics of seedless grapes fitted into the

Exponential model and the results obtained. The seventh section deals with the realization of

drying rate constants by curve fitting. The eighth section discusses about the different

parameters that affect the value of drying rate constant and finally sums up their effects. The

ninth section deals with verification of results using curve fitting for both variety grapes that

have been dried using the proposed dryer. This chapter finally concludes that the exponential

model satisfactorily describes the drying characteristics of seedless grapes and the drying rate

constant depends solely on the properties of the material to be dried as well as properties of

the drying air over wide ranging parameters.

Chapter - 6 Mathematical modeling and validation with experimental results of the

proposed solar dryer

Modeling is a mathematical representation of any system using mathematical

equations comprising of vital system parameters. It is one of the methods used for designing

thermal systems to study their performance. Some prominent models usually utilized are

listed out. This chapter comprises of three sections - The chapter begins with a brief

introduction about mathematical models and the most prominent models used by scientific

researchers. The first section deals with details of the system used and initial steps adopted in

modeling the proposed drying system. Assumptions made and relations used in estimating

certain important parameters have been discussed. The second section presents mathematical

models that have been developed to determine temperatures at five different points along the

height of the dryer chamber. All the proposed models have been experimentally validated.

The experimental results are in close agreement with values obtained by mathematical

modeling. This chapter finally concludes that the estimated theoretical values of temperatures

at different locations along the height of the dryer chamber using mathematical models are in

close agreement with the experimental values obtained, thus proving validity of the proposed

models.

Chapter - 7 Techno-economic analysis of solar concentrator based grape dryer with sensible

heat storage

Any system that has been designed to perform a specific task has to be technically

feasible and economically viable to be widely accepted by the industrial sector for bulk

production. The payback period of any proposed system will decide its economic viability.

Internal rate of return (IRR) assesses whether the project will achieve targeted rate of return

or not.

This chapter has six sections - The chapter begins with a brief introduction related to

systems required to perform a specific task. Any proposed system needs to be user friendly,

technically feasible and economically viable. The first section deals with the task of

estimating the total cost of the experimental drying model developed for grape drying. The

total cost of the experimental drying model worked out to be Rs. 11,400/-. The second section

deals with different type of costs that would help in carrying out economic analysis of the

experimental drying model developed. The payback period worked out to be 1.6 years, when

farmers would personally work with the experimental drying model to dry 117 kg fresh

grapes per annum, after the drying process they could get 23 kg raisins. The experimental

drying model when analyzed for its cost economics reflected a considerable margin of profit.

The third section defines IRR and discusses about its significant features. It is used to deal

with the economic analysis of higher capacity indirect grape drying systems to understand

their extent of economic viability. The fourth section deals with the analysis of higher

capacity indirect drying systems, which can dry grapes ranging from 585 to 4680 kg per

annum. Techno-economic analysis carried out for all the systems with higher drying capacity

resulted in IRR values ranging from 25 to 29 %. The fifth section presents an indirect drying

system, which has been planned and proposed for future work and can be adopted for grape

drying as a commercial venture. The chapter finally concludes that the experimental drying

model can be up scaled to dry grapes ranging from 585 to 4680 kg grapes per annum, so that

farmers would be benefitted with fairly good returns on their investments and produce

superior quality raisins which can fetch higher price.

Chapter - 8 Conclusions and recommendations

In this chapter, conclusions related to the research work carried out are drawn

and recommendations have been proposed for further development. The conclusions are -

The quantity of dried fruits and vegetables exported every year is observed to be on

the rise. By using the proposed drying system for commercial activity, the demand

can be met to a large extent.

The huge demand for superior quality dried fruits and vegetables, which are seasonal,

can be fulfilled by using this proposed drying system.

The large quantity of heat generated by a parabolic solar concentrator was effectively

stored and efficiently utilized beyond sunshine hours to expedite the drying process.

Whenever the drying process extends beyond a day, there is a major problem of

moisture re-absorption by the product during the night. This problem is eliminated

because of the extended drying period using stored energy after sunshine hours.

The method and material used to store heat in the proposed drying system is cost

effective and could be used in other drying systems.

The proposed drying system substantially reduces drying time, which helps in saving

considerable time and enhancing production of dried seasonal fruits.

Sensible heat stored in sand was able to evaporate an appreciable amount of moisture

content from both varieties of grapes beyond sunshine hours.

The proposed solar drying experimental model is technically feasible to dry fruits and

vegetables whose maximum drying temperatures lie in the range of 60 to 70 °C.

The initiative to maintain pre-treatment solutions above ambient temperature at 40 °C

was mainly responsible for reduction in drying time to a notable extent.

Both varieties of dried grapes are able to meet all the physical appearance parameters

required as per standards.

Dried Thompson seedless grapes when subjected to color analysis test were able to

meet required standards.

The required cumulative drying time over two consecutive days, using solar energy

for pre-treated Thompson seedless grapes and pre-treated Sharad seedless grapes to

reach the final moisture content ideal for long term storage were 11 hours and

14 hours respectively.

Reduction in drying time of Thompson seedless grapes when compared to Sharad

seedless grapes is mainly due to two prominent reasons -

higher skin permeability and porosity

smaller size grape berries

The experimental drying model with small drying capacity, when used to dry 117 kg

grapes per annum during the grape season, yielded a profit of Rs. 7,800/- per year

The IRR value of large drying systems used to dry grapes ranging from 585 to

4680 kg per annum using drying systems with capacities ranging from 5 to 40 kg per

batch (14 hours/batch for Sharad and 11 hours/batch for Thompson grapes) varied

between 25 to 29 %.

In order to make the indirect solar drying system for grapes commercially viable, a

new system has been proposed for future work whose capacity can be enhanced easily

to dry 50 to 100 kg grapes in each batch.

Recommendations for further development and suggestions related to scope for future work

have also been mentioned.

LIST OF TABLES

Table No. Particulars Page No.

2.1 Nutritive value in grapes and raisins 2.22

2.2 Details of drying natural grapes by open sun drying A.1

2.3 Details of drying natural grapes in solar dryers A.1

2.4 Details of drying grapes after pre-treatment by open sun drying A.2

2.5 Details of drying grapes after pre-treatment in solar dryers A.3

3.1 Relevant weather data collected for designing the solar concentrator

based indirect drying system 3.4

3.2 Relevant details of fruit to be dried - Sharad seedless grapes 3.4

3.3 Relevant details of fruit to be dried - Thompson seedless grapes 3.5

3.4 Basic design calculations for drying Sharad seedless grapes 3.5

3.5 Basic design calculations for drying Thompson seedless grapes 3.6

4.1 Experimental results of drying Sharad seedless grapes using proposed

experimental solar dryer model with heat storage material 4.15

4.2 Experimental results of drying Thompson seedless grapes using proposed

experimental solar dryer model with heat storage material 4.25

4.3 Colour analysis of Thompson seedless grapes dried in the proposed

experimental solar dryer model 4.36

4.4 Initial moisture content in Sharad seedless grapes on wet basis C.1

4.5 Initial moisture content in Thompson seedless grapes on wet basis C.1

4.6 Experimental results of drying Sharad seedless grapes using proposed

experimental solar dryer model with heat storage material C.5

4.7 Experimental results of drying Thompson seedless grapes using proposed

experimental solar dryer model with heat storage material C.6

4.8 Color analysis of raisins produced from Thompson seedless grapes dipped

for 3 minutes in solutions maintained at temperatures of 20°C, 30°C,

40°C, without dipping treatment and dried at a temperature of 60°C.

C.7

4.9

Organoleptic qualities using sensory evaluation of raisins produced from

Sharad seedless grapes dipped for 3 minutes in alkaline solutions

maintained at temperatures of 20 °C, 30 °C, 40 °C, without dipping

treatment and dried at a temperature of 60 °C

C.7

5.1 List of investigators with details of experiment carried out on grapes

using solar dryer 5.13


5.2 List of investigators with details of experiment carried out on grapes

using laboratory scale dryer 5.14

5.3 Parameters of Exponential model obtained by non-linear regression for

thin layer drying of grapes 5.18

5.4 Drying rate constant and statistical parameters obtained after fitting Log

MR Vs Time in a Linear model 5.19

5.5 Drying rate constant values for grapes published by investigators 5.19

5.6 Parameters of Exponential model obtained by non-linear regression for

Sharad and Thompson seedless grapes 5.23

5.7 Drying rate constant and statistical parameters obtained after fitting Log

MR Vs Time in a Linear model for Sharad and Thompson seedless

grapes

5.24

5.8 Parameters of Exponential model obtained by non-linear regression

analysis for thin layer drying of Sharad seedless grapes using curve

expert version 1.3

D.1

5.9 Parameters of Exponential model obtained by non-linear regression

analysis for thin layer drying of Thompson seedless grapes using

curve expert version 1.3

D.1

5.10 Drying rate constant of Sharad seedless grapes and statistical

parameters obtained by fitting Log MR Vs Time in a linear model

using curve expert version 1.3

D.1

5.11 Drying rate constant of Thompson seedless grapes and

statistical parameters obtained by fitting Log MR Vs Time in a linear

model using curve expert version 1.3

D.1

6.1 Thermal properties of air 6.5

6.2 Excel sheet to determine temperature at lower end of aluminum container

filled with sand 6.13

6.3 Excel sheet to determine temperature at vertical sides of aluminum

container filled with sand 6.13

6.4 Excel sheet to determine temperature of sand at lower end of container 6.19

6.5 Excel sheet to determine temperature of sand at the top surface of

container 6.19

6.6 Excel sheet to determine temperature of air above the aluminum

container filled with sand 6.24


7.1 Cost of components used in the fabrication of proposed experimental

dryer model and wooden almirah 7.3

7.2 Variation of different costs with dryer capacity 7.6 7.3 Calendar for drying of grapes 7.6

7.4 IRR calculation for solar concentrator based indirect grape drying system

of 40 kg capacity 7.8

7.5 IRR values obtained after Techno-economic analysis of solar

concentrator based indirect grape drying systems of different capacity 7.9

7.6 Projected profitability and cash flow statements of 40 kg capacity grape

dryer 7.10

7.7 Calculations to find cost of proposed experimental dryer model per

Sq.cm. E.1

7.8 Calculations to find cost of parabolic dish per Sq.m. E.1


of 5 kg capacity E.3

7.10 Projected profitability and cash flow statements of 5 kg capacity dryer E.5










LIST OF FIGURES

Figure No. Particulars Page No.

2.1 Working principle of open sun drying 2.4

2.2 Working principle of direct sun drying 2.5

2.3 Working principle of indirect sun drying system 2.6

2.4 Open sun drying without cover 2.7

2.5 Open sun drying with cover 2.7

2.6 Natural rack dryer 2.7

2.7 Classification of solar dryers 2.7

2.8 Solar cabinet dryer 2.11

2.9 Staircase solar dryer 2.11

2.10 Glass roof solar dryer 2.11

2.11 Foldable solar grape dryer 2.11

2.12 Indirect type conventional solar dryer 2.11

2.13 Indirect natural convection solar dryer with chimney 2.11

2.14 Multipurpose natural convection solar dryer 2.15

2.15 Indirect natural convection solar dryer with chimney and storage

material 2.15

2.16 Solar dryer with green house as collector 2.15

2.17 Geodesic dome fruit dryer 2.15

2.18 Side view of solar tunnel dryer 2.15

2.19 Solar air flat plate collector with obstacles 2.15

2.20 Solar multiple layer batch dryer 2.17

2.21 Schematic layout of indirect multi-shelf solar fruit and

vegetable dryer 2.17

2.22 Hybrid PV- Thermal greenhouse 2.17

2.23 Hybrid solar dryer 2.17

3.1 Characteristic parameters of solar concentrator 3.9

3.2 Parabolic type solar cooker 3.12

3.3 Aluminum drying chamber 3.17


3.4 Aluminum drying chamber with glass wool insulation and GI

sheet covering 3.17

3.5 Drying tray 3.18

3.6 Bottom container 3.18

3.7 Top lid 3.18

3.8 Drying chamber with bottom container and top lid 3.18

3.9 Dryer bottom part covered with wooden box 3.19

3.10 Complete drying unit placed in almirah 3.19

3.11 CAD image showing front view of proposed experimental solar

dryer model B.1

3.12 CAD image showing the exploded front view of proposed

experimental solar dryer model B.1

4.1

Variation of Direct beam solar radiation, Temperature at lower

end of aluminum container, Temperature of sand in aluminum

container, Temperature of outlet air, Temperature of ambient air

with Time during drying of Sharad seedless grapes using solar

energy and sensible heat in the proposed experimental solar

dryer model on 27th and 28th May 2015. All values used are

average values.

4.16

4.2

Variation of Relative humidity of drying air in the dryer,

Relative humidity of dryer outlet air and Velocity of dryer outlet

air with Time during drying of Sharad seedless grapes using the

proposed experimental solar dryer model on 27th & 28th May

2015

4.17

4.3

Variation of Moisture Ratio with Time during drying of Sharad

seedless grapes using the proposed experimental solar dryer

model on 27th and 28th May 2015 4.18

4.4 Curve fitting of Log (MR) Vs Time for drying Sharad seedless

grapes using the proposed experimental solar dryer model 4.20


4.5

Variation of Direct beam solar radiation, Temperature at lower

end of aluminum container, Temperature of sand in aluminum

container, Temperature of outlet air, Temperature of ambient air

with Time during drying of Thompson seedless grapes using

solar energy and sensible heat in the proposed experimental solar

dryer model on 02nd and 03rd June 2015. All values used are

average values

4.26

4.6

Variation of Relative humidity of drying air in the dryer,

Relative humidity of dryer outlet air and Velocity of dryer outlet

air with Time during drying of Thompson seedless grapes using

the proposed experimental solar dryer model on 2nd and 3rd June

2015

4.27

4.7

Variation of Moisture Ratio with Time during drying of

Thompson seedless grapes using the proposed experimental solar

dryer model on 2nd and 3rd June 2015

4.28

4.8

Curve fitting of Log (MR) Vs Time for drying Thompson

seedless grapes using the proposed experimental solar dryer

model

4.30

4.9

Variation of Direct beam solar radiation, Temperature of outlet air and

Temperature of ambient air with Time during drying of Sharad

seedless grapes using solar energy in the proposed experimental

solar dryer model

C.2

4.10

Variation of Temperature of outlet air and Temperature of ambient air

with Time during drying of Sharad seedless grapes using sensible heat

in the proposed experimental solar dryer model during off sunshine

hours

C.2

4.11


Temperature of ambient air with Time during drying of Sharad


solar dryer model

C.3

4.12

Variation of Direct beam solar radiation, Temperature of outlet air and Temperature of ambient air with Time during drying of Thompson seedless grapes using solar energy in the proposed experimental solar dryer model

C.3


4.13

Variation of Temperature of outlet air and Temperature of ambient air

with Time during drying of Thompson seedless grapes using sensible

heat in the proposed experimental solar dryer model during off

sunshine hours

C.4

4.14


Temperature of ambient air with Time during drying of Thompson


solar dryer model

C.4

5.1 Drying characteristics of grapes at air temperature 60°C and

velocity 2 m/sec 5.16


velocity not mentioned 5.16


velocity 0.5 m/sec 5.16

5.4 Drying characteristics of grapes at air temperature 39.6°C and

velocity 1 m/sec 5.16


velocity 1.2 m/sec 5.16


velocity 0.5 m/s 5.16

5.7 Drying characteristics of grapes at air temperature and velocity

not mentioned 5.17


not mentioned 5.17


velocity 1 m/s 5.17


not mentioned 5.17

6.1 Proposed experimental solar dryer model showing position of temperature sensors at which the temperature is considered during modeling

6.8

6.2 Graph of Theoretical and Experimental values of temperature at

lower end of bottom aluminum container 6.11


6.3 Graph of Theoretical and Experimental values of temperature at

vertical sides of bottom aluminum container 6.15

6.4 Graph of Theoretical and Experimental values of temperature in

sand near bottom of aluminum container 6.18

6.5 Graph of Theoretical and Experimental values of temperature in

sand near top surface of aluminum container 6.22

6.6 Graph of Theoretical and Experimental values of temperature

above the sand filled aluminum container 6.25

7.1 Exploded isometric view of experimental dryer model 7.2

7.2 Proposed solar concentrator based indirect drying system to dry

100 kg grapes 7.12

7.3 Equation obtained for dryer cost varying with capacity of dryer E.1 7.4 Equation obtained for dish cost varying with capacity of dryer E.2 7.5 Equation obtained for labor cost varying with capacity of dryer E.2

8.1 Proposed solar concentrator based indirect drying system to dry

100 kg grapes F.1

8.2 Rear view of drying chamber of the proposed solar concentrator

based indirect drying system to dry 100 kg grapes F.1

8.3 Side view of drying chamber of the proposed solar concentrator

based indirect drying system to dry 100 kg grapes F.1

LIST OF PLATES

Plate No. Particulars Page No.

2.1 Photographs of selected varieties of vineyards cultivated under a

variety of soil conditions 2.2

2.2 Photographs of Thompson seedless and Sharad seedless grape

vineyards before harvesting 2.20

2.3 Photographs of rack drying Thompson seedless grapes during

early stages of drying 2.29

2.4 Photographs of rack drying Thompson seedless grapes during the

later stages of drying 2.30

2.5 Photograph of dried Sharad seedless grapes using rack dryer

prior to cleaning 2.32

2.6 Photograph of dried Thompson seedless grapes using rack dryer

after cleaning 2.32

3.1 Photograph of parabolic solar concentrator 3.14

3.2 Photograph of proposed experimental dryer model 3.18

3.3 Photograph of system with experimental dryer model used for

drying grapes in convective mode during sunshine hours 3.20

4.1 Photograph of chemical containers used for preparing pre-

treatment dipping solution 4.5

4.2 Photograph of water bath used to maintain dipping solution at a

constant temperature of 40°C 4.5

4.3 Photograph of hot air oven and dessicator used to determine the

initial moisture content of grapes 4.5

4.4 Photograph of shadow indicator fixed on platform of the outer

rim of solar concentrator 4.5

4.5

Photograph of Data logger used to measure temperatures and

Humidity meter used to measure drying air relative humidity

below the drying tray

4.6

4.6 Photograph of weighing scales used during experimentation 4.6

4.7 Photograph of humidity meter used to measure relative humidity

of inlet air and outlet air from dryer 4.7

Plate No. Particulars Page No.

4.8 Photograph of hot wire anemometer used to measure velocity of

moist air flowing out of dryer 4.7

4.9 Photograph of anemometer used to measure ambient air velocity

close to the dryer 4.7

4.10 Photographs of Hunter lab color flex spectrophotometer used to

measure color parameters L, a, b 4.8

4.11 Photographs of weather station from which direct beam solar

radiation data was obtained 4.9

4.12 Photograph of proposed experimental dryer model with aluminum

container at bottom covered by a tight fitting wooden box 4.10

4.13 Photograph of proposed experimental dryer model placed in tight

fitting wooden almirah 4.10

4.14

Photograph of almirah with proposed experimental dryer model

inside it when drying process was in progress using sensible heat

stored in sand during off sunshine hours

4.10

4.15 Pretreated Sharad seedless grapes spread on wire mesh tray prior

to drying in the proposed experimental solar dryer model 4.12

4.16 Sharad seedless grapes after being dried in the proposed


4.17 Pretreated Thompson seedless grapes spread on wire mesh tray

prior to drying in the proposed experimental solar dryer model 4.22

4.18 Thompson seedless grapes after being dried in the proposed


4.19

Photograph showing aerial view of complete setup and dish

being aligned for proper focusing of concentrated reflected solar

radiation at bottom of aluminum container of the proposed

experimental solar dryer model

4.31

4.20 Photograph of best quality raisins 4.33

4.21 Photograph of raisins obtained after drying Sharad seedless


4.22 Photograph of raisins obtained after drying Thompson seedless


LIST OF ABBREVIATIONS

AD Anno Domini - Designates years since traditional date of birth of Jesus Christ

BC Before Christ

DGCIS Directorate General of Commercial Intelligence and Statistics

GI Galvanized Iron

IRR Internal rate of return

IU International Units

Kcal Kilo-calorie

K2CO3 Pottasium carbonate

KHCO3 Potassium Hydrogen carbonate or Potassium bicarbonate

M Moisture content

MT Metric Ton

NGO Non-Governmental Organization

NaOH Sodium hydroxide

SK 14 Solare Kookar of 1.4 meter in diameter

TSS Total Soluble Solids

USDA United States Department of Agriculture

UV Ultraviolet

W/m2 Watt per square meter

cm Centimeter

d.b. Dry basis

g Grams

h-1 Per hour

kg Kilogram

kg/m2 Kilogram/meter2

kWh/m2day Kilo-watt-hour/meter2 day

m Meter

mm Millimeter

mg Milligram

mL Milli-liter

m/s Meter per second

µg Microgram

mg/cm2 Milligram per square centimeter

m3/h Meter cube per hour

m3/minute Meter cube per minute

ton/ha Ton per hectare

w.b. Wet basis

° Degree

°C Degree centigrade

Aa Aperture area of dish in m2

AB Area of lower end of aluminum sand container in m2

AC Contact area between lower end and vertical sides of aluminum sand

container in m2

AT Area of top surface of aluminum sand container in m2

AVS Area of vertical sides of aluminum sand container in m2

CAL Specific heat of Aluminum in J/kg°C

CP Specific heat at constant pressure in J/kgK

CS Specific heat of sand in J/kg°C

DR Drying rate in kg/hour

dM/dt Drying rate

E Energy required for evaporation of moisture in kJ

g Acceleration due to gravity in m/s

hCB Heat transfer co-efficient of bottom in W/m2 K

hCT Heat transfer co-efficient of top in W/m2 K

hCVS Heat transfer co-efficient of vertical sides in W/m2 K

hf Enthalpy at product temperature in kJ/kg

hfg Latent heat of water in kJ/kg of water

hi Enthalpy at ambient temperature in kJ/kg

Idb Average direct beam solar radiation in W/m2

K Thermal conductivity in W/mK

KAL Thermal conductivity of aluminum in W/m°C

KS Thermal conductivity of dry sand in W/m°C

k Drying rate constant in h-1

L Characteristic length in m

LBSB Distance between the points where temperature is measured at the lower end

of aluminum sand container and sand at the lower end in m

LBST

Distance between the points where temperature is measured at lower end of

the aluminum sand container and in sand at a depth of 1 cm measured

from top surface of the aluminum sand container in m

LBVS Distance between the points where temperature is measured at lower end of

aluminum sand container and its vertical sides in m

LVSST Vertical distance between the points where temperature is measured along

vertical sides of aluminum sand container and in sand at the top surface in m

mi Initial mass of grapes to be dried in kg

mw Mass of water to be removed in kg

Ma Mass of air required for drying in kg/hour

Me Equilibrium moisture content

Mf Final moisture content in %

Mi Initial moisture content in %

Mt Moisture content at any instant of time t

MAL Mass of Aluminum container in kg

MS Mass of sand in kg

MR Moisture ratio

Nu Nusselt’s number

Q Heat required for removal of moisture in kJ

Ra Rayleigh’s number

td Drying time in hours

Ta Ambient temperature in °C

Tpr Product temperatures in °C

TA Temperature of ambient air surrounding the outer walls of the dryer chamber

in °C

TB Temperature at lower end of aluminum sand container in °C

TD Temperature of the drying tray over which grapes to be dried are spread in °C

TT Temperature at top surface of aluminum sand container in °C

TSB Temperature of sand at a height of 8 cm measured from lower end of

aluminum sand container in °C

TST Temperature of sand at a depth of 1 cm measured from the top surface in

aluminum sand container in °C

TVS Average temperature at vertical sides of aluminum sand container in °C

UB Overall heat loss factor from lower end of aluminum sand container in

W/m2°C

UT Overall heat loss factor from top surface of aluminum sand container in

W/m2°C

UVS Overall heat loss factor from vertical sides of aluminum sand container in

W/m2°C

wi Initial humidity ratio in kg/kg

wf Final humidity ratio in kg/kg

Wd Final weight in g

Wf Final weight in g

Wi Initial weight in g

Wt Weight at any time 't' in g

β Coefficient of thermal expansion in 1/K

ρ Density in kg/m3

ηo Optical efficiency of solar concentrator

ηd Efficiency of dryer

ν Kinematic viscosity in m2/s

ΔT Rise in temperature in °C

a solar concentrator based indirect drying system...

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