Comparative performance of solar cabinet, vacuum assisted solar and open sun drying methods.pdf

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COMPARATIVE PERFORMANCE OF SOLAR CABINET,
VACUUM ASSISTED SOLAR AND OPEN SUN DRYING
METHODS
By
Rajkumar Perumal
Department of Bioresource Engineering
McGill University, Montreal, Canada
February, 2007
A thesis submitted to McGill University in partial fulfillment of
the requirements for the degree of Master of Science
© Rajkumar Perumal 2007
ABSTRACT
RAJKUMAR PERUMAL
.Sc.
ioresource Engineering
COMPARATIVE PERFORMANCE OF SOLAR CABINET,
VACUUM ASSISTED SOLAR AND OPEN SUN DRYING
METHODS
Tomato ( Lycopersicon esculentum L.var ) is one of the most important vegetables
in our diet and dried tomato products are becoming popular for the preparation of various
food items. Though sun drying has been used for the preservation, it is a slow process and
the quality of the dried product is often inferior due to contaminations. Therefore, a lab
model solar cabinet and vacuum assisted solar dryers were developed to study the drying
kinetics of tomato slices (4, 6 and 8 mm thicknesses) and the results were compared
individually with open sun drying under the weather conditions of Montreal, Canada. The
drying kinetics using thin layer drying models and the influence of weather parameters
such as ambient air temperature, relative humidity, solar insolation and wind velocity on
drying of tomato slices were evaluated.
During drying, it was observed that the temperatures inside the solar cabinet and
vacuum chamber were increased to 63 and 48 o C when the maximum ambient temperature
was only 30 o C. The tomato slices of 4, 6 and 8 mm thicknesses could be dried from 94.0
to 11.5% wet basis moisture content, respectively in 300, 420 and 570 min using solar
cabinet, in 360, 480 and 600 min using vacuum assisted solar dryer and it took 435, 615
and 735 min under open sun drying method.
The quality of tomato slices in terms of physicochemical parameters such as
colour retention, water activity, rehydration capacity and ascorbic acid retention were
evaluated and the overall study concluded that good quality dehydrated tomato slices
could be produced by using vacuum assisted solar dryer compared to solar cabinet and
open sun drying methods. The Page model was found to be better in describing the drying
kinetics of tomato slices in all the drying methods studied.
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RÉSUMÉ
RAJKUMAR PERUMAL
.Sc.
ioresource Engineering
ANALYSE COMPARATIVE DE LA PERFORMANCE DU
SÉCHAGE AVEC UN SÉCHOIR SOLAIRE, UN SÉCHOIR
SOLAIRE SOUS-VIDE ET PAR SÉCHAGE NATUREL
La tomate ( Lycopersicon esculentum L. var ) est une importante source nutritive
de notre alimentation et les tomates séchées gagnent en popularité dans de nombreuses
préparations alimentaires. Le séchage naturel est la méthode traditionnelle utilisée pour
la production de tomates séchées, cependant c’est un processus lent et la qualité du
produit séché est variable et sujette à la contamination. Un séchoir solaire et un séchoir
solaire sous-vide furent donc développés afin d’étudier le séchage solaire de tranches de
tomates (4, 6 et 8 mm d’épaisseur) en comparaison au séchage naturel sous les conditions
météorologiques de Montréal, Canada. La cinétique du séchage des tranches de tomates
suivant des modèles en couches minces a été établie en fonction de l’influence des
conditions météorologiques telles que la température ambiante, l’humidité relative, le
rayonnement solaire et la vitesse du vent.
Lors du séchage dans le séchoir solaire et le séchoir solaire sous-vide, la
température interne des deux séchoirs a atteint 63° et 48°C respectivement alors que la
température ambiante était de 30°C. Les tranches de tomates de 4, 6 et 8 mm d’épaisseur
ont pu être séchées d’un taux d’humidité de 94% à 11.5% (état humide) et ce après 300,
420 et 570 minutes en utilisant le séchoir solaire, en 360, 480 et 600 minutes grâce au
séchoir solaire sous-vide, alors qu’il en a pris 435, 615 et 735 minutes par séchage
naturel.
La qualité des tranches de tomates a été évaluée en fonction de certains
paramètres physico-chimiques tels que la stabilité de la couleur, l’activité de l’eau, la
capacité de réhydratation, et la conservation de l’acide ascorbique. Des tranches de
tomates séchées de meilleure qualité peuvent être produites par séchage solaire sous-vide
en comparaison avec le séchage solaire et le séchage naturel. La modélisation de Page
offre une très bonne représentation de la cinétique du séchage des tranches de tomates et
ce pour les trois méthodes de séchage étudiées.
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ACKNOWLEDGEMENTS
I have a great pleasure to express my whole hearted deep sense of gratitude to my beloved
Supervisor Dr.G.S.V.Raghavan, James McGill Professor, Department of Bioresource Engineering,
for his expert guidance, sustained interest, constructive suggestions, continuous encouragement,
personal affection and care bestowed throughout the course of this study and my stay period in
Canada.
I express my sincere and heartfelt thanks to Dr. Yvan Gariepy, Dr. Valerie Orsat and
Dr.R.Venkatesh Sosle, CIDA group under the Project Director of Dr. G.S.V. Raghavan, Department
of Bioresource Engineering, Macdonald Campus of McGill University, Canada, for their constant
encouragement and helps extended during my study period.
I wish to sincerely thank Dr.Ning Wang, Dr.M.Ngadi, Dr.H.S.Ramaswamy and Dr.Sam
Sotocianal for their helps at various stages during my study programme.
I place on record my sincere thanks to my Dean Dr.A. Sampathrajan and Former Dean
Dr.R.Manian, AEC&RI, Tamil Nadu Agricultural University (TNAU), Coimbatore, for their
encouragement and constructive ideas extended for this study programme.
I take this opportunity to acknowledge and thank Dr. S. Kulanthaisamy,
Dr. S. L. Jagadeesh, Dr.V.Palanimuthu, Er.R.S.Satya, Er.M.Arun, Er.Simona Nemes and all my
friends (Badminton group) for their valuable helps rendered both morally and personally for me.
I thank all my department colleagues and friends at TNAU Coimbatore for their helps in
updating the latest news and morally supported my family at Coimbatore during this long study
period.
I gratefully acknowledge the Canadian International Development Agency (CIDA)
funded UPCD Tier-I Project “Consolidation of Food Security in South India” for providing me
this opportunity to study in Canada.
On my personal note I owe to my parents Tmt. and Th. T.Perumal, parent-in-laws Tmt. &
Th.S.Gunasekaran, wife Tmt.J.G.Anitha Rajkumar, sons R.A.Rajakash; R.A.Nikhilesh and all
my family members for their inspiration and forbearance during my stay period in Canada.
(P.RAJKUMAR)
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CONTRIBUTIONS OF AUTHORS
The authors for both the articles in this thesis are P.Rajkumar, G.S.V.Raghavan
and Y.Gariepy. The research work submitted here was performed by the candidate and
supervised by Dr.G.S.V.Raghavan of the Department of Bioresource Engineering,
Macdonald campus of McGill University, Montreal, Canada. The entire fabrication and
experimental study were carried out in the post harvest technology lab, Department of
Bioresource Engineering, McGill University. Mr. Y.Gariepy provided technical
assistance in the design and fabrication of solar dryers which was used to collect the data
during the entire experimental period.
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