Final Icaer

5th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

Paper Code: xxxxx

Performance Evaluation of Natural Convection V groove Solar Dryer for Drying of Potato slices

D.V.N.Lakshmi1*, S. S. Mohapatra2, H.Das2

1 Department of Mechanical Engineering, C.V. Raman College of Engineering, Bhubaneswar, Odisha-752054, India

2 Department of Mechanical Engineering, ITER, SOA University, Bhubaneswar, Odisha-751030, India * Corresponding Author. Tel: (+91) 8763760530, E-mail: [email protected]

Abstract: A natural convection V groove solar dryer has been fabricated with locally available material and tested for drying of two different thickness potato slices under the meteorological conditions of Bhubaneswar, Odisha, India. The System consists of a V grooved aluminum absorber plate, glass, insulation material and a drying chamber. Paraffin wax grade –II used as a thermal energy storage material to store excess energy and supply during off shine hours and cloudy condition during drying. The solar air heater was tilted about an angle of 20° horizontal. The set up is oriented to face south to maximize the solar radiation incident on the solar collector. The experiments were carried out in day time from morning 9.00 AM to evening 8.00 PM. Experiments were conducted to dry the two different thicknesses of the potato slices of 8 mm and 4mm .The experiments were performed for drying of 2 kg of potato slices as in a single batch. The time taken for drying of potato slices thickness of 4 mm was 600 min and similarly for drying of 8 mm thickness potato slices was 780min respectively from initial moisture content of 84% to 11 %.

Keywords: Drying chamber, Natural convection, Potato Slices, V groove aluminum absorber plate, Paraffin wax.

1. INTRODUCTION

India is an agro based country where more than half of the population depends on agriculture as their main source of income and livelihood. India holds the second position in the agricultural production in the World. Since Independence, India has made immense progress towards food security, Indian population has tripled, but food-grain production more than quadrupled: there has thus been substantial increase in available food-grain per capita. Potato is a major food crop in India after rice, wheat. It will be consumed by ¾th population of the country. According to the Central Institute of Post-Harvest Engineering and Technology (CIPHET), Ludhiana, approximately 18 per cent of the country’s fruits and vegetables, worth of INR 133 billion, go to waste annually because of the lack of proper storage facilities. India wastes more fruit and vegetables than any other food product, mostly due to inadequate post harvesting technologies. Drying is one of the best processes to store the grains, vegetable and fruits. Drying is a method of food preservation that works by removing water from the food, which inhibits the growth of bacteria and has been practiced since ancient times to preserve food. Industrial drying is very good solution for storing and minimizing the losses but the main disadvantage of this process is cost and this type of drying systems consumes fossil fuels. Drying under direct sunlight is known as open solar drying which is the oldest drying technique to preserve food products in many countries. In the open solar drying the crops spread on the large area where they receive solar energy the amount of moisture removed by natural circulation of air. The OSD method does not fulfill the required quality standards this is mainly due to improper moisture removal from the product and insects, rain et al. To avoid the disadvantages in OSD one more method suggested by using the solar energy is known as Solar drying. Based on the air motion solar dryers are classified in to two types: Natural and forced convection dryers. In natural convection mode the induced air motion is created by buoyancy difference, in forced convection mode an extra blower is used to blow the air. Recently so many works are published in drying by using solar dryers either natural or forced convection for drying of food products [1-5]. E. Akpinar et al[6] investigated a single layer drying behavior of sliced potatoes in a convection cyclone type dryer the authors carried out the experiments two different thickness of potato slices of 12.5 mm and 8 mm at a temperatures of 60, 70 and 80 °C and they found that drying time required for 12.5 mm thickness was about in the range of 460-740 min. P.P.Tripathy [7] developed a mathematical model for developing for comparing a drying rate in cylindrical and slices and they concluded that the drying rate is faster. Using simply solar dryers are not sufficient to dry the products due to bad weather conditions so we have to store solar energy during peak hours and utilizes when required. Samira Chouicha et al [8] developed a solar hybrid dryer with a photo voltaic module for drying of potato slices and also they compared the results with conventional dryer. With the use of one solar PV panel the drying time was 3 hours and with two panels the

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5th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

drying time was reduced to 2 hours 30 min. Esakkimuthu et al [9] investigated the feasibility of HS 58 material in solar air heater for improving the efficiency. Many works have been reported in literature for drying of different food products by using forced convection mode. However, very few literatures are available on natural convection solar dryers due to low heat transfer coefficient of air. Natural convection solar air dryers are suitable in rural areas where electricity is not available. In the present research work, a V-grooved natural convection solar dryer with thermal energy storage material is designed and developed with locally available materials and performance of the dryer has been analyzed under the meteorological conditions of Bhubaneswar 20.27°N and 85.84°E, Odisha, India.

2. EXPERIMENTAL SET UP

The picture of experimental set up of natural convection V-grooved solar heater with dryer assembly is shown in Fig1. The main components in this system are solar air heater, absorber, and dryer. The solar air heater is made up of plywood frame, a glass cover, absorber with fins (v-grooves) and insulating material. A rectangular box of 2 m length and 1 m width and 25 cm height has been used with an aluminum absorber 0.8 mm thickness, 1.9 m length and 0.9 m wide and it consists of 10 v-grooves. The absorber plate is placed just below the glass cover. The thickness of the glass cover is 6 mm. The air flows between the glass cover and absorber plate. To increase the mass flow rate of air, a modification in design of the collector has been done. After 1.3 m length of the absorber, the rest part is of conical cross section. The inlet of the duct cross section is rectangular but the outlet of duct is circular in cross section. The fabrication of stand is such that we can change the angle and keep the solar air heater at various angles as required .The solar air heater was tilted about an angle of 20° horizontal. The set up is oriented to face south to maximize the solar radiation incident on the solar collector. A pipe is connected at the exit of the wooden block and another end of the pipe is connected to the dryer. Dryer is made up of mild steel and it has three tray to keep the objects which are to be dry. At the bottom tray thermal energy storage material chosen as paraffin wax grade II placed in copper tubes. Fifty no of copper tubes are used in this experiment for storing of 5 kg of grade-II paraffin wax. The blanched potato slices were placed in tray II and Tray II holes were drilled on the drying chamber to inserting the probes for measuring temperatures and humidity. The air is heated in the heater and it is passes in to the drying chamber due to the buoyancy force and then passes to the trays at the top air vent is provided to exit the heated air. The experiments were carried out in day time from morning 9.00 AM to evening 8.00 PM. The specification details of the collector are given in table 1. Experiments were conducted with solar air heater from morning 9 AM to evening 8 PM during Jan 2015 to May 2015 at C.V. Raman College of engineering, Bhubaneswar, Odisha, India. The solar radiation, temperature and air velocity were measured and recorded for every one hour. The Temperature was recorded by using K-type (Chromel and Alumel), Temperature range-0~1350 °C,Sensitivity-40.6 μV/ °C,1.5 mm dia×200 mm L with port seal 40mm L, SS 316 Sheath, grounded with 0.5 mm. The air velocity at exit was measured by using the hot wire anemometer and mass flow was calculated. The solar radiation was measured with the help of Solari meter (Model: KM-SPM-11).

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Fig.1. Experimental set up of v groove natural convection solar dryer

5th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

Table.1: Technical specifications of the collector

Materials Dimension

Glass plate Plane glass 2 m ×1 m

Absorbing material Aluminum 1.9 m × 0.9 m

No of v-grooves Aluminum 10

Angle of V. Groove Aluminum 34°

Drying Chamber Mild steel .75mx0.5m

3. THEORITICAL ANALYSIS

Thermal energy analysis plays an important role for performance evaluation of any system. In solar air heater mainly the analysis is based on the solar radiation, absorbed and the mass flow rate of the fluid Energy incident on the Collector is given by,

Qc= AI(Eq.1)

where, Qc (watt) is the energy incident on the collector and A is the area projected to the radiation of sun and I (W/m2) is the intensity of solar radiationThe Useful energy gain in the solar air heater (Qu )

(Eq.2)

where, is the mass flow rate of fluid in (kg/s ) and Cp is the specific heat of the fluid (kJ/kg-K) and T5 and

T1 are the outlet and inlet temperatures of the fluid (K).

The moisture ratio (MR) of the potato slices during the experiment was calculated by using the following formula

(Eq.3)

Me is the equilibrium moisture content on dry basis, Mo is the initial moisture content on dry basis And Mt is the moisture content of slices at given time.

4. RESULTS AND DISCUSSIONS

Experiments were performed on a single pass natural convection v grooved solar dryer for drying of potato slices at C.V. Raman College of Engineering, Bhubaneswar, and Odisha, India between Jan 2015 to May 2015 for drying of different agricultural products. The present paper explains about the drying kinetics of two different thicknesses of potato slices placed in the dryer. Fig.2 explains about the variation of solar radiation intensity and ambient temperature on 11 May 2015 climatic conditions of Bhubaneswar. The maximum intensity of solar radiation was found 935W/m2 at 11 am. The average ambient temperature throughout the day was found to be 34C. Temperature T1 is the inlet fluid temperature at the entry of the collector and T 4 is the exit fluid temperature from the collector. The Thermocouples are placed at four different positions, Fig.3 explains about the temperature of the air inside the collector with respect to time. The maximum temperature was recorded at the exit section was 102C at 11 am at a solar radiation intensity of 935W/m2. This hot air passes through a pipe the drying chamber. In the present experiment the drying chamber consisting of three trays. At the ground level

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5th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

thermal energy storage material was placed in a 50 number of copper tubes. The energy storage material was selected as paraffin wax grade –II due to its low cost and ease of availability. The hot air passes through the ground and the paraffin wax stores energy during peak hours and it supplies heat after the sunshine hours to dry the given product. The main use of TES are to get uniform heating inside the drying chamber and at the top trays the potato slices were placed in tray 1 the 8 mm thickness of potato slices are spread evenly. The temperatures were measured with the help of thermocouples. Similarly 4 mm thickness of potato slices was placed at the tray 2. At the top vent was provided to remove the exit air. Fig 4 shows the average temperatures inside the drying chambers with respect to time. Temperatures inside the drying chamber was recorded as Td ground means temperature of the drying chamber at ground level similarly Td tray1, Td tray2 are the temperatures at the tray 1 and tray2 It was observed that after sunshine hours the temperature inside the drying chamber was maintained averagely 60C which was sufficient to dry the product. Fig 5 shows the moisture content as a function of time. During the drying of potato slices both heat and mass transfer takes place simultaneously. Heat is transferred from the drying air to the potato slices and increase the temperature of moisture and water vapor in the slice, whereas mass is transferred out of the slice in the form of vapor (evaporated liquid) due to the vapor pressure difference between the water present in the potato slices and the ambient.

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9am 10am 11am12noon 1pm 2pm 3pm 4pm 5pm 6pm 7pm 8pm

0

200

400

600

800

1000Date 11/05/15

Solar radiation intensity Ambient temperature

Time (hrs)

Sola

r ra

diat

ion

inte

nsity

(W

/m2 )

25

30

35

40

45

50

Am

bien

t tem

pera

ture

(C

)

Fig.2. Variation of ambient temperature and solar radiation intensity with respect to time

9am 10am11am12noon1pm 2pm 3pm 4pm 5pm 6pm 7pm 8pm30

40

50

60

70

80

90

100

110

Date:11/05/15

Colle

ctor

tem

pera

ture

at v

ario

us p

ositi

ons (

deg

C)

Time (hrs)

T1 T2 T3 T4

Fig.3. Variation of temperatures at different positions of the v grooved air collector

5th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

Initially when heat is transferred, the surface moisture will evaporate. The moisture content initially high and reduces to desired level with respect to time. Initial moisture content of two different thickness of potato slices were 83% are placed inside the drying chamber and the moisture content reduces gradually, initially mass transfer takes place rapidly once if they reaches equilibrium moisture content the mass transfer takes place slowly. From the fig.5 the drying time for thickness of potato slices 4 mm was 600 min and similarly for drying of 8 mm thickness potato slices was 780min respectively.

5. CONCLUSIONS

5

9am 10am11am12noon1pm 2pm 3pm 4pm 5pm 6pm 7pm 8pm30

40

50

60

70

80

90Date:11/05/2015

Tem

per

atu

res

insi

de

the

dry

ing

cham

ber

(C

)

Time (hrs)

Td ground

Td tray1

Td tray2

Fig.4. Average temperatures inside the drying chamber at different positions

0 100 200 300 400 500 600 700 800 900

10

20

30

40

50

60

70

80

90

Moi

stur

e co

nten

t (%

)

Time (min)

Potato slice thickness 4 mm) Potato slice thickness 8 mm

Fig.5 Moisture content curves for different thickness of potato slices

5th International Conference on Advances in Energy ResearchIndian Institute of Technology Bombay, Mumbai

5. CONCLUSIONS

A natural convection V-grooved solar air heater is designed and fabricated and the performance analysis is carried out for drying of potato slices using thermal energy storage materials from morning 9 AM to 8 PM in different months and temperatures and solar radiation were measured in hourly basis. The collector produced on an average 20-35C above the ambient temperature. Paraffin was used as an energy storage material to get uniform drying and do the drying after sunshine hours. The average relative humidity of the air was found to be 39% inside the drying chamber and the moisture transfer analysis of two different thickness of the potato slices were reported and the time required for 4 mm thickness of slices are 600 min whereas for 8 mm thickness of potato slices the time consuming is more this mainly due to more thickness of the slices.

6. ACKNOWLEDGEMENTS

The authors gratefully acknowledge the authority of C. V. Raman College of Engineering, Bhubaneswar for providing the facilities to carry out the experiments

7. REFERENCES

[1] A. Duffie and William A. Beckman, Solar Engineering of Thermal Processes, 4th edition .[2] [3] Akpinar .E, Midilli.A, Bicer Y. (2003) Single layer ,drying behaviour of potato slices in a convective

cyclone dryer and mathematical modeling, Energy Conversion and Management , 44,pp. 1689–1705.[4] Tripathy, P. P. and Kumar, Subodh (2009)Modeling of heat transfer and energy analysis of potato slices and

cylinders during solar drying ,Applied Thermal Engineering, 29 (5-6), pp.884-891 [5] Samira Chouicha, Abdelghani Boubekri, Djamel Mennouche, Mohamed Hafed Berrbeuh (2013)

solar drying of sliced potatoes. an experimental investigation, Energy Procedia ,36 , pp. 1276 – 1285.[6] Esakkimuthu S. Abdel Hakim Hassabou Palaniappan , C. Markus Spinnler , Jurgen Blumenberg , Velraj R

(2013) Experimental investigation on phase change material based thermal storage system for solar air heating applications, Solar energy, 88,pp 144-153.

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