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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
2.7.2 Experimental results obtained by investigators after drying
untreated grapes using solar dryers 2.33
2.7.3 Experimental results obtained by investigators after drying
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
3.0 Introduction 3.1
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
3.9 Conclusions 3.21
References 3.21
CHAPTER - IV EXPERIMENTAL STUDY AND PERFORMANCE EVALUATION OF SOLAR CONCENTRATOR BASED DRYER
4.0 Introduction 4.1
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
4.9 Conclusions 4.36
References 4.38
CHAPTER - V KINETICS OF GRAPE DRYING
5.0 Introduction 5.1
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
5.10 Conclusions 5.24
References 5.25
CHAPTER - VI MATHEMATICAL MODELING AND VALIDATION WITH EXPERIMENTAL RESULTS OF THE PROPOSED SOLAR DRYER
6.0 Introduction 6.1
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
6.3 Conclusions 6.26
References 6.26
CHAPTER - VII TECHNO-ECONOMIC ANALYSIS OF SOLAR CONCENTRATOR BASED GRAPE DRYER WITH SENSIBLE HEAT STORAGE
7.0 Introduction 7.1
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
7.6 Conclusions 7.12
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
Table No. Particulars Page No.
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
Table No. Particulars Page No.
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
7.9 IRR calculation for solar concentrator based indirect grape drying system
of 5 kg capacity E.3
7.10 Projected profitability and cash flow statements of 5 kg capacity dryer E.5
7.11 IRR calculation for solar concentrator based indirect grape drying system
of 10 kg capacity E.6
7.12 Projected profitability and cash flow statements of 10 kg capacity dryer E.8
7.13 IRR calculation for solar concentrator based indirect grape drying system
of 20 kg capacity E.9
7.14 Projected profitability and cash flow statements of 20 kg capacity dryer E.11
7.15 IRR calculation for solar concentrator based indirect grape drying system
of 30 kg capacity E.12
7.16 Projected profitability and cash flow statements of 30 kg capacity dryer E.14
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
Figure No. Particulars Page No.
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
Figure No. Particulars Page No.
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
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.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
Figure No. Particulars Page No.
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
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.4
5.1 Drying characteristics of grapes at air temperature 60°C and
velocity 2 m/sec 5.16
5.2 Drying characteristics of grapes at air temperature 50°C and
velocity not mentioned 5.16
5.3 Drying characteristics of grapes at air temperature 60°C and
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
5.5 Drying characteristics of grapes at air temperature 60°C and
velocity 1.2 m/sec 5.16
5.6 Drying characteristics of grapes at air temperature 60°C and
velocity 0.5 m/s 5.16
5.7 Drying characteristics of grapes at air temperature and velocity
not mentioned 5.17
5.8 Drying characteristics of grapes at air temperature and velocity
not mentioned 5.17
5.9 Drying characteristics of grapes at air temperature 50°C and
velocity 1 m/s 5.17
5.10 Drying characteristics of grapes at air temperature and velocity
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
Figure No. Particulars Page No.
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
experimental solar dryer model 4.12
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
experimental solar dryer model 4.22
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
grapes using the proposed experimental solar dryer model 4.34
4.22 Photograph of raisins obtained after drying Thompson seedless
grapes using the proposed experimental solar dryer model 4.35
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