Effect of Air Recirculation in the Energy Saving During Drying Process of Fruits, Vegetables and Grains: A Review

(1)

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)

_______________________________________________________________________________________________

ISSN (Print): 2319-3182, Volume -6, Issue-1-2, 2017 154

Effect of Air Recirculation in the Energy Saving During Drying Process of Fruits, Vegetables and Grains: A Review

1Hitesh Singh Waskale, ²Snehal Bharat Bhote, ³Mahesh Ganpat Bhong

1,2,3Department of Mechanical Engineering, Indira College of Engineering and Management, Pune Savitribai Phule Pune University, India

Email: ¹[email protected], ²[email protected], ³[email protected]

Abstract- Drying of fruits and vegetables always been a part of human food culture. This not only reduce the growth of fungus but also increase the shelf life of food.

Nowadays various methods are available to dry food in expense of external energy use. During convective drying of fruits, vegetables and grains, the exhaust air from the dryer are still at higher temperature and unsaturated. It means that the exhaust air could be recirculate to achieve drying of eatables. This review paper emphasis the study of experimental papers where the air is recirculated and its effect on the energy saving.

Index Terms—Air recirculation, Drying, Eatables, Energy saving

I. INTRODUCTION

Globalization leads to development of food supply chain so to make food available to the places where there is no land to harvest or the place where population density is very high. Urbanization could not be possible without good food supply chain. [1] The food undergoes storage and transport needs to have high shelf life. The basic way to increase the shelf life of any food is to reduce the moisture contain of it.[2] Methods like hot air drying, microwave drying, infrared radiation and freeze dryingare currently used commercial process to reduce the moisture contain.[3]

The food are classified into two category namely perishable and non-perishable.[4] The perishable food items are those whichget spoil, decay and unsafe to consume if they are not kept refrigerated. [5] Where else non-perishable are those food which have high shelf life.

[6] During food transport the shelf life of perishable food is increases by removing moisture of from it. It leads to slow down the decay rate of food and also its weight to volume ratio decreases and food become easier to handle and transport.[7]

II. MAJOR TERMSAND CONCEPTS

A. Food drying method

Various methods are present to dry the fruits and vegetables. Some method are traditional like natural convection drying process where eatables are kept under direct sunrays.[8]To increase the rate of drying process advance method was evolve where heated air was forced to remove the moisture of eatables known as force convection drying method or hot air drying.[9]

Vacuum drying is another drying process come under category of contact drying. The wall of dryer was drum type in which eatables are place to dry up. The wall of drum dryer was maintain at certain temperature to achieve the drying ofeatables.[10]

Nowadays dielectric drying in which radiofrequency or microwaves is usedbeen topic of research.[11] Many researcher have found that it increases the drying speed of fruits and vegetables as compare to classic drying method.

One of the most popular technique used commercial is freeze drying.[12] The solvent is frozen prior to drying and then sublimed. The biological properties like protein and vitamin are well maintain in this drying process.

B. Air recirculation ratio During force convection drying process, the exhaust gasses still possess capacity to remove moisture as it’s not fully saturated. To reuse the exhaust air, the air is recirculated to the drying chamber. This is known as air recirculation. The air recirculation ratio is the ratio of air recirculated to the drying chamber upon the fresh heated air recirculated in the drying chamber.

The concept of air recirculation leads to drying of fruits and vegetables with lesser amount of running cost as compare to convectional drying process where air not recirculated.

C. Energy saving during drying process

Running cost plays an important role in any manufacturing or food processing process. High food processing cost leads to high product cost which affect the sale of the item. The time when many company are present for processing same eatable, it is necessary to keep the processed food item as low as possible to maintain the sale or increase the sale of the processed eatables.[13]

The recirculation of exhaust air provide mean to save fuel used to generate the thermal energy to heat air.[14]

The saving of input energy to heat air can be electric saving or solid fuel saving depending on the type of heater use to heat the air. This helps to lower down the processing cost and ultimately lowering the processed food cost.

(2)

_______________________________________________________________________________________________

III. STUDIES OF EFFECT OF AIR RECIRCULATION IN ENERGY SAVING IN

FRUITS DRYING PROCESS

Many researcher had done experiments to achieve the optimum air recirculation ratio to save energy during fruit drying process. Fig. 1 shows various results obtain from different researcher who used air recirculation to dry fruits. Liu [15] used forced convection drying process to dry peach and apple ring. At 70% of air recirculation, 46% of energy saving was achieved for peach and at 80% air recirculation, 50% energy saving was achieved.

Vagenas et al. [16] dried sultana grapes and at 76% air recirculation they obtained 28% energy saving. Jain et al. [17] at 75% air recirculation obtain 30% energy saving in drying of green mango. Walker [18] studied drying of peach and apple and obtain 53% and 46%

energy saving respectively at 70% and 80% air recirculation ratio. Young [19] carried experiment to dry peanuts and achieved 26% energy saving at 92% air recirculation ratio. Rumsey et al. [20] dried walnuts and obtained 30% energy saving at 60% air recirculation ratio.

Walnuts (Rumsey et al.) Peanuts (Young) Apple (Walker) Peach (Walker) Green mango (Jain et al.) Sultana grapes (Vagenas et al.) Apple ring (Liu) Peach (Liu)

0 20 40 60 80

Percentage (%) Energy Saving Air Recirculation Ratio

Figure 1 Energy saving during fruits drying process

IV. STUDIES OF EFFECT OF AIR RECIRCULATION IN ENERGY SAVING IN

VEGETABLES AND GRAINS DRYING PROCESS

Cauliflower (Singh) Cabbage (Singh) Onion (Pelegrina et al.) Onion (Singh) Maize (Giner et al.) Maize (Meiering et al.) Forage (Schoenau et al.) Paddy (Meiering et al.)

0 20 40 60 80

Percentage (%) Energy Saving Air Recirculation Ratio

Figure 2 Energy saving during vegetables and grains drying process

Vegetables and grain drying always been an area of interest for many researcher. Fig. 2 shows results achieved by different researcher who dried vegetables

and grains using air recirculation. Meiering et al. [21]

dried paddy and obtained 28% energy saving at 80% air recirculation ratio. Schoenau et al. [22] achieved 27%

energy saving at 30% air recirculation ratio. Meiering et al. [20] dried maize and obtained 24% energy saving at 86% air recirculation.

Giner et al. [23] achieved 26% energy saving at 70% air recirculation ratio for drying maize. Singh [20] obtained 30%, 30% and 28% energy saving during drying of onion, cabbage and cauliflower respectively at 75% air recirculation for all. Pelegrina et al. [24] dried onion and achieved 30% energy saving at 84% air recirculation.

V. RANGE OF AIR RECIRCULATION FOR MAXIMIZING ENERGY SAVING

Various researcher experimented different air recirculation ratio to achieve the maximum energy saving for fruits, vegetables and grains. Fig. 3 shows result obtain from all different experiments done by different researchers. The value of air recirculation ratio observed for getting maximum energy saving seemto be ranging from 70% to 86%.This clearly indicates that the maximum energy saving was achieved at higher air recirculation ratio.

Walnuts (Rumsey et al.) Peanuts (Young)

Apple (W alker) Peach (W alker)

Green mango (Jain et al.) Sultana grapes (Vagenas et al.)

Apple ring (Liu) Peach (Liu)

Cauliflower (Singh) Cabbage (Singh) Onion (Pelegrina et al.)

Onion (Singh) Maize (Giner et al.)

Maize (Meiering et al.) Forage (Schoenau et al.)

Paddy (Meiering et al.) 30

40 50 60 70 80 90 100

Air Recirculation Ratio (%)

A

Air Recirculation Ratio

Figure 3 Range of air recirculation ratio

VI. CONCLUSION

Air recirculation proved to be agood option to use waste heat energy. It also helps to maximize the profit by decreasing the food processing cost. Drying fruits, vegetables and grains not only increases there shelf life but also make them easy to handle and transport as the dried product are less in weight as compared to fresh items. The value of air recirculation ratio seems to be high where maximum energy saving was achieved. This suggest that the exhaust air from the drying chamber contain high amount of heat energy which thereafter used in air recirculation and result in energy saving for air that to be heated. The use of air recirculation in forced convective drying not only decrease thefood processing cost but also save fuel used to heat up the air and motive for waste heat recovery.

REFERENCES

[1] D. Satterthwaite, G. McGranahan and C. Ta,

"Urbanization and its implications for food and farming," Philosophical transactions of the royal society B, vol. 365, p. 2809–2820, 2010.

(3)

_______________________________________________________________________________________________

[2] S. S. Nielsen, Food Analysis, West Lafayette, IN, USA: Springer Science+Business Media, 2010.

[3] F. Sellami, R. Jarboui, S. Hachicha, K. Medhioub and E. Ammar, "Cocomposting of oil exhausted olive-cake, poultry manure and industrial residues," Bioresource Technology, vol. 99, p.

1177–1188, 2008.

[4] S. V. Jangam, C. L. Law and A. S. Mujumd, Drying of Foods, Vegetables and Fruits.

[5] "What foods are perishable," 2 July 2014.

[Online]. Available:

https://askkaren.custhelp.com/app/answers/detail/

a_id/486/~/what-foods-are-perishable%3F.

[Accessed 2017 January 24].

[6] "What is a nonperishable food item," Refrences,

https://www.reference.com/food/nonperishable- food-item-5cd142e00ec47f02. [Accessed 24 January 2017].

[7] C. L. Hii, S. V. Jangam, C. L. Chiang and A. S.

Mujumdar, Processing and Drying of Foods, Vegetables and fruits, 2013.

[8] B. K. Bala and J. L. Woods, "Optimization of natural-convection, solar drying systems,"

Energy, vol. 20, no. 4, pp. 285-294, 1995.

[9] S. Prvulovic, D. Tolmac and M. Lambic,

"Convection Drying in the Food Industry,"

Agricultural Engineering International: the CIGR Ejournal, vol. 9, no. 9.

[10] D. M. Parikh, "Vacuum Drying: Basics and Application," Chemical Engineering, vol. 122, no. 4, 2015.

[11] "Drying," Wikipedia, 4 December 2016.

https://en.wikipedia.org/wiki/Drying. [Accessed 26 January 2017].

[12] "Freeze-drying," Wikipedia, 24 January 2017.

https://en.wikipedia.org/wiki/Freeze-drying.

[Accessed 26 January 2017].

[13] T. Andreyeva, M. W. Long and K. D. Brownell,

"The Impact of Food Prices on Consumption: A Systematic Review of Research on the Price Elasticity of Demand for Food," Am J Public Health, vol. 100, no. 2, pp. 216-222, 2010.

[14] T. Jokiniemi, K. Kautto, E. Kokin and J. Ahokas,

"Energy efficiency measurements in grain drying," Agronomy Research Biosystem Engineering Special Issue, no. 1, pp. 69-75, 2011.

[15] X. Lui, "Energy conservation by recirculation of

drying air," University of Tennesse, Knoxville, TN, 1995.

[16] K. D. Marinos and V. K. G, "The design and optimization of an industrial dryer for sultana raisins," Drying Technology, vol. 9, no. 2, pp.

439-461, 2007.

[17] S. Das, T. Das, S. P. Rao and J. K. R,

"Development of an air recirculating tray dryer for high moisture biological materials," Journal of Food Engineering, vol. 50, no. 4, p. 223–227, 2001.

[18] H. T. Walker, "Drying cut fruits with recirculated air for energy," The University of Tennesse, Knoxville,, 1992.

[19] J. H. Young, J. C. Tutor and G. J. Cain,

"Recirculation and solar energy collection to assist peanut drying," American Society of Agricultural and Biological Engineers, 1988.

[20] A. Iguaz, B. López and P . Vı́rseda, "Influence of air recycling on the performance of a continuous rotary dryer for vegetable wholesale by- products," Journal of Food Engineering, vol. 54, no. 4, p. 289–297, 2002.

[21] S. Soponronnaritl and S. Pnchayawankornz,

"OPTIMUM STRATEGY FOR FLUIDIZED BED PADDY DRYING," Drying Technology, vol. 12, no. 7, pp. 1667-1686, 1994.

[22] G. J. Schoenau and S. Sokhansanj, "Forage drying with exhaust air recirculation," University of Saskatchewan, [Online]. Available:

https://www.usask.ca/agriculture/plantsci/winter_

cereals/winter-wheat-production-manual/chapter- 23.php. [Accessed 26 January 2017].

[23] S. A. Giner and A. d. Michelis, "Evaluation of the thermal efficiency of wheat drying in fluidized beds: Influence of air temperature and heat recovery," Journal of Agricultural Engineering Research, vol. 41, no. 1, pp. 11-23, 1988.

[24] A. H. Pelegrina, M. P. Elustondo and M. J.

Urbicain, "Rotary semi-continuous drier for vegetables: effect of air recycling," Journal of Food Engineering, vol. 41, no. 3-4, pp. 215-219, 1999.

[25] J. F. Thompso, "Reducing Enerly Costs of Walnut Dehydration," Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA, 1981.

[26] M. Jayeeta and S. L. S, "Onion dehydration: a review," J Food Sci Technol, vol. 493, no. 3, p.

267–277, 2012.

