1. INTRODUCTION

1.1 Solar Energy - General

The sun is a sphere of immensely hot gaseous matter,

continuously generating heat by thermonuclear fusion

reactions, which convert hydrogen atoms. This energy is

radiated from the sun in all directions and a very small

fraction of it reaches the earth. This solar energy

represents non-polluting, inexhaustible renewable source of

energy that can be utilized economically to supply man's

needs for all the time. Increase in prices and reduced

availability of fossil fuels and public concerned about the

safety of nuclear reactors have led to surge of interest in

using the power of Sun. (Solar Energy Utilization – Rai

G.D.)

1.2 Utilization Of Solar Energy In India

The power from the sun intercepted by the earth is

approximately 1.8x1011 MW, which is many thousands of time

larger than the present consumption rate on the of all

commercial energy sources. In a tropical counties like India

where the sun shine with brilliance for more than 300 days

in the year and where solar radiation is as much as 650

calories per sq. cm per day, the utilization of solar energy

can be very effective.

As a frontier area ‘Ministry Of Non-Conventional

Energy Sources’ has taken up the identification and

implementation of solar energy projects on national basis.

The various way in which solar energy can be used are solar

cooking, solar drying, solar water pumping, solar air

heating, solar green houses, solar cooling, solar thermal

power generation, solar furnace and solar photo voltaic

cells.

1.3 Solar Energy For Cooking

Cooking is most energy intensive activity in domestic

sector increasing demand for energy, unchecked

deforestation, drudgery in fuel wood collection and

exponential population growth has aggravated cooking energy

problems. In this critical situation, solar energy offers

practical solution to the household energy problems.

1.4 Solar Energy For Drying Agricultural Produce

Traditional practice of drying agricultural produce in

the fields country yards and the roads by direct exposure to

sunshine involves the risk of weather damage, losses in

fields and losses during storage and transportation due to

improper and incomplete drying. As compared with sun

drying , solar dryers can generate higher air temperature

and consequences lower relative humidity's which are both

conductive to improved drying rates and lower final moisture

contents of the agricultural produce.

1.5 Objectives Of The Study

Cooking of the food requires tremendous amount of

energy in the form of fuel, wood, cow dung, crop wastes etc.

affecting the environment. Due to multiple cropping system

and increased crop intensity drying of crop also assumed

importance on small scale, village women and housewives in

urban area needs to cook food and dry food materials.

The present study was undertaken to develop a solar

dryer cum cooker with locally available material and simple

to operate with the following objectives:

1.To design and develop a solar cooker cum dryer.

2.To test the performance of the device for cooking

and drying.

2. REVIEW OF LITERATURE

Solar energy research programme in India has

multiplied many folds during recent years. Research work on

design, development and testing of solar cooker and solar

dryer has been done and under taken by some of the institute

in foreign countries as well as in India

2.1 General

Use of solar energy for post harvest processing has

been discussed by Brinidorfer et.al (1985), in common wealth

science councils. This publication provides basic

information and interaction on solar crop drying techniques

encompassing the range of discipline involved.

Shrivastava and Bhojwai(1981)has discussed the

preservation of fruits and vegetables by drying and

canning . methods of preserving fruits and vegetable ,B.I.S.

specification, drying time , temperature and expected yield

of some perishable commodities are expected in data .

2.2 Solar Energy

(Ranjeetsingh and Yadava, 1989) Sun gives 3.7 x 1026

watts energy of which earth intercept only 1.8 x 10 watts.

This means that the energy emitted by the sun within three

minutes is equivalent to the world energy consumption during

year. The 99% of the energy of the solar radiation is

contained in the wavelength bond from 0.15 to 4 micrometer

comprising the near ultraviolet, visible and near infrared

region of solar spectrum. The solar constant has a value of

1.36 kw/m2 or 1.95 cal/cm2/min.

2.3 Solar Cooker

There are 3 designs of solar cooker:

1.Flat plate box type solar cooker with or without

reflector

2.Multi reflector type solar oven.

3.Parabolic disc concentrator type solar oven.

(Solar energy utilization-Rai G.D.1997.) Flat mate box

type design is the simplest of all the designs based on the

above design aspects. (Solar Energy Utilization-Rai G.D.)

2.3.1 Box type cooker

Department of Rural Engineering, Gujarat (Rawal and

Varshneys-1984), conducted research on the performance of

commercially available box type Jyoti solar cooker and it

was evaluated with respect to inside cooker temperature and

cooker temperature for three insulating materials namely,

fiber glass, saw dust and Aak floss mixed with paddy husk

ash were measured. Modifications were made to increase the

effectiveness of absorbing surface and to make cooker

airtight. The maximum temperature in cooker was recorded for

the insulation of Aak floss mixed with paddy husk ash.

The agricultural tools Research center, Suruchi

campus, Bardoli (Anonymous,1978) developed a box type solar

cooker. It consisted of a double box with double glass

cover. The temperature inside the cooker raised to 90C in

winter and 105C in summer.

The Central Arid Zone Research Institute, Jodhpur (Garg

1975) developed fire types of solar cookers and their

comparative performance was tested. These are conventional

box type solar cooker, conventional solar oven solar stream

cooker, paraboiled (NPL) type and step reflector type. The

temperature in the first type of cooker reached 178c in

summer and 148c in winter

2.3.2 Reflector type solar cooker

The Mechanical Engineering Department, Punjab

Agricultural University (Annonymous,1974) Ludhiana in 1974,

designed and develop a solar oven providing theoretical

concentration of solar energy. Baking and cooking various

food tested the solar oven. It took about 2 hours about

cooking red beans and 35 minutes for rice.

Garg and Krishan (1974) reported that the drying time

for chilling simple cabinet solar dryer is 50% less compared

to open country yard drying.

An inclined dryer was developed and tested by Pande

and Thanvi (1982) to compute maximum radiation through out

the year. They reported that the dying time for chilling in

this dryer is reduced to 40% compared to simple cabinet

dryer. Moisture content of chilies can be reduced from 82%

to 72% within 5 to6 days. Maximum temperature 29.3C. The

efficiency of utilization of solar energy was about 13% in

this dryer.

Pannalal Singh (1978) studied the performance of three

solar cookers. He compared double reflector box type solar

cooker with PAU solar cooker and commercial solar cooker.

The double reflected CIAE solar cooker was found to be very

effective in terms of higher stagnant temperature and

reduction in water heating time.

Hans Rao (1964) reported that the optimum size of

reflector should be 1.1 m3 with maximum focal length of 0.9m.

A solar cooker of this size will be capable of to cook meal

for 6 persons.

Department of Applied Mechanics III New Delhi

(annonymous,1975) carried out research on application of

solar concentrator in domestic cooking. Concentrator was

composed of mirrors strips of 18.75cm X 3.75cm

approximately. The whole arrangement could be adjusted to

predetermined position giving maximum concentration for

different positions of the sun.

(Anonymous 2007). A paraboloid solar collector

having aperture diameter 1.3m depth 0.3m and focal length

0.35m was designed and fabricated at Department of Renewable

Energy Sources, College of Technology and Engineering

Udaipur (Rajasthan) India. The paraboloid solar cooker was

tested under no load conditions and attains maximum

temperature 326C and 319C on different day.

2.3.3 Insulation Material

Dahiwalkar and Galve (1981) developed three solar

cookers using groundnut hulls, glass wool and sawdust as

insulating materials. Maximum temperature of 90c was

obtained in cooker with groundnut hulls following by 81.5C

and 77.5C in solar cookers with saw dust and glass wool.

Solar cooker with ground nut hulls gave better performance.

2.4 Types Of Solar Dryers

The solar dryers have been classified on the following

criteria.

1. Whether or not the drying commodity is exposed to

isolation.

2. The mode of airflow through dryer.

3. The temperature of drying airflow circulated to drying

chamber.

2.4.1 Cabinet Dryer

The basic design consists of a rectangular container,

preferably insulated and covered with a roof or clear

plastics. There are holes in the base and upper parts of the

cabinet and rear panels. The interior of the cabinet was

blackened to act as a solar absorber. Perforated drying

trays are positioned within the cabinet. (Brenidorfer et al

1985).

McDowell (1973) working in Jamaica carried out an

considerable amount of work on the development of the

cabinet dryer. His basic dryer is made of clay, bricks mud

or locally produced compressed bricks of earth and cement.

Plastic sheet is used for a cabinet cover. The entry of air

to the bottom of the cabinet is by means of length of bamboo

with regularly spaced holes placed at intervals across the

width of dryer.

2.5 Solar Collector

Solar collectors are employed to gain useful energy

from the sun radiation. They are almost invariably used to

heat either air or water. Solar collectors may be either of

concentrating type or of the ( non concentrating) flat plate

type. Principle type of flat plate collectors are as shown

in fig.

Brenidorfer et al(1985) reported that for purpose of crop

drying, flat plate type air heating collectors can provide

the desired temperature elevation and are a most appropriate

solution than a more complex concentrating collectors. There

are several factors affecting the amount of energy

absorbedly the plate.

1. The level of insulation, clearly the higher the

insulation the greater the energy absorbed.

2. The angle between the incident insulation and the

absorber plate surface. Ideally the absorber plate should be

perpendicular toi the insulation.

3. The transmitivity of the cover material.

4. The absorptivity of the absorber surface.

2.6 Selection of Collector Type

The main factors governing the choice of the solar

collector type is the temperature increase required. Some

general guidelines to this choice are as follows

(Brenidorfer et al 1985 )

1.For temperature rise up to approximately 10c a bare plate

solar collector is most suitable due to it's simplicity. It

is recommended that a higher air velocity be used for bare

plates collectors than for collectors with cover plate

2. For greater temperature rise of up to approximately 35c

single cover plate collectors are more effective oveall than

double oe triple covers

2.7 Clear Cover Material

Desirable properties of clear cover are,

1. High transmissivity in the visible range of spectrum.

2. Low transmissivity of infrared radiation.

3. Stability at the operating temperature

4. Durability

5. Strength and resistance to breakage.

6. Low cost.

7. Low weight per unit area.

Glass is traditional clear cover and has good

transmissivity for visible radiation. Glass is also stable

at temperature encountered and durable.

2.8 Absorber Performance

Desirable properties of absorber in the solar

collector are high absorptivity of incident radiation, low

emissivity, good thermal conductivity, stability at the

temperature encountered, durability, low cost, low weight

per unit area. (Brenidorfer etal 1985)

Where

Q = Latitude at test sit, Q = 21.75N

Positive value of = collector should be south

facing.

Negative value of = Collector should be North

facing.

= ( 21.75 – (-2.41)) = 24.160

As the value of is +21.75, collector

should be south facing at an angle of 21.750

3.1.2 Intensity of insulation on collector surface (Ic)

Instantaneous insulation on surface is approximately

proportional to the cosine of the angle of incidence (θ).

Fig 3.1 shows the angle of incidence on a south-facing

roof at midday following equation was used to calculate the

angle of incidence for insulation falling on a surface

(Brenderfor et al 1985)

Cos = Sin. SinQ. Cos - Sin. CosQ. Sin. Cosr + Cos.

cosQ. Cos.Cosw + Cos. SinQ. Sin. Cosw + Cos. Sin. Cosw +

Cos. Sin. Sinr. Sinw ………………………………………………….(3.3)

Where

= Angle of incidence –2.41

Q = Latitude of test site 21.45N

= Slope of collector 24.16

r = surface azimuth angle, for this can be considered it’s

orientation wits respect to a north south axis. The angle

varies from -180 to +180, zero is due to south, east is

negative and west positive.

The value of r = 0 was used for the present calculation.

3. MATERIALS AND METHODS

The solar cooker cum dryer was Designed and fabricated

in the Department of Agricultural Process Engineering,

Dr.Ulhas Patil College Of Agricultural Engineering, Jalgaon,

Affiliated To M.P.K.V. Rahuri.

3.1 Design of solar collector

The solar collector is to be designed by following

assumptions:

1. The dryer is situated at latitude of 21.05N.

2. Average isolation on horizontal plane during March is

580w/m2.

3.1.1 Slope Of The Collector ()

In order to calculate the optimum slope of the

collector,march 16 was taken as mid point of the drying

season.

Angle of inclination (Q) is calculated from the

following equation (Brenidorfer et al 1985)

= 23.45 sin ( 0.9863 (284+n))…………………………………(3.1)

For March 16 , n = 75

= 23.45 sin (0.9863(284+75) …………………………………(3.2)

= -2.41

Slope of the collector () was calculated by

following formula, = (Q - )

w = It is the hour angle, is the angular displacement at

the sun east or west. It is zero at solar noon and changes

15 per hour. Morning is negative and afternoon is positive.

w = 0 is used for present calculation.

The intensity of radiation on horizontal surface θhwas calculated as follows:

Since slope is zero, equation (3.3) is simplified as

Cosθh = Sin SinQ + Cos.CosQ = Sin(-2.41). Sin(21.75) + Cos(-2.41).

Cos(21.75)

= 0.912

The equation (3.3) was used again to calculate the

angle of incidence upon collector surface

Cosθ=Sin(-2.41)Sin(21.75)Cos(24.16)–Sin(-2.41)Cos(21.75)Sin(24.16)Cos0+ Cos(-

2.41)Cos(21.75)Cos(24.16)Cos0+Cos(-

2.41)Sin(2175)Sin(24.16)Cos(0)Cos(0)

= 0.8484 + 0.1515

Cosθ = 1.00 Following equation is used to determine the

intensityof insulation on collector surface Ic

Ic = Ih (CosQ/Cosθh)……………..(3.5)

Where, Ih = Intensity of insolation of horizontal surface,

W/m2

Ic = 580(1.00/0.912

Ic = 635.96 W/m2

3.2 Drying Chamber

The drying chamber size is fixed as 750mm

X 600mm X 450mm and perforated wire mesh tray of size

650mm X 370mm is to be provided inside the drying

chamber. A plenum chamber of size 750mm X 450mm X 150mm

is to be provided with the drying tray for air

circulation. Drying chamber size is to be designed by

considering thin layer drying.

3.2.1 Air Circulation System:

Two pipes of size 25mm are to be extended

from solar cooker or solar collector to the bottom of

drying chamber. These pipes will be the hot air inlets

to the dryer. They will be provided with valves of size

25mm to control the air flow rate. Three inlet holes

will be provided on the sides of cooker with caps.

3.3 Fabrication of the cooker:

The cooker will be fabricated by using

wood, hard board, insulation material, G.I. sheet etc.

3.3.1 Frame

Wooden frame of size 750mm x 600mm will

be made using wood strips of size 50mm x 50mm. While

fabricating the frame, the collector angle will be

adjusted by providing slope of 21.75 to the wooden

strips.

3.3.2 Solar Cooker

A cooker box will be fabricated by

fitting hardboard (5mm thick) from the outside and G.I.

sheet (24SWG) from inside the cooker box. Coir mat

(30mm thick) will be fitted in between hardboard and

G.I. sheets as an insulating material to prevent the

heat loss. Using plain glass having 3mm thickness

covered the sloping portion of the box. The sheet was

painted black by using black mat paint enough room was

provided for cooking utensil in the cooker box. Four

cooking utensils made of aluminum can be placed. The

diameter and height of each utensils were 200mm and

62.5mm respectively. Box is provided with door of

placing the utensils. Three holes were provided on the

cooker box with caps of air inlet .two PVC pipes (25mm)

were extended frome the back side of box for hot air

outlet to the drying chamber .

3.4 Fabrication of drying chamber

The drying chamber will be fabricated by

using G.I. sheet (24SWG) of size 750mm x 600mm x 450mm.

A wooden frame will support the drying chamber. The

chamber will also be painted black from outside to

receive solar insulation. A tray having 650mm x 370mm

size is to be provided for supporting the material to

be dried. A plenum chamber of size 750mm x 450mm x

150mm has to be constructed and is to be connected to

the solar collector.the hot air from the the solar

cooker cum collector enters the plenum chamber, which

in turn enters the drying the chamber through the

materials. Two pipes extended from solar collector are

provided with valves to control the airflow rate. Two

pipes outlets were for the exhaust of air as shown in

fig 3.2

3.5 Parameters to study

Temperature: temperature will be measured by using

mercury in glass thermometer (0-110c). Dry bulb

temperature and wet bulb temperature of ambient air

will be measured. The air temperature inside the cooker

and inside the drying chamber is to be measured .

3.5.1 Solar Intensity

Solar Intensity is to be measured by using a solar

–intensity merter known as ‘Suryamapi’ (make- Central

Electronics Ltd., SM-203 Range- 0-120 mW/cm2). The

solar intensity is to be measured at predetermined

intervals during cooking and drying experiments.

3.5.2 Measurement of Weight Samples

Weight meausument is to be done by using

electronic balance (make- Adair Dutt & Co. (I)

Pvt.Ltd.) The least count of the electronic balance was

0.01gm and capacity 300gms.

3.6 Drying Rate

Drying rate in grams of moisture removed per hours

per 100 gms of dry matter is to be calculated by using

following formula.

(Chakraborty and De,1981)

amount of moisture removed (dry basis)Drying rate = -- - -- - - - - - - - -- - - - - -- - -- - - - - - - - - - -

time required (hr)x(amount of dry mattergm))

3.7 Performance of Drying System

Performance of drying system is to be evaluated by

using the data temperature, moisture content drying

time and drying rate the performance parameter like

drying efficiency , Heat utilization factor and

coefficient performance were calculated as discussed in

following paragraphs

3.7.1 Drying Efficiency (nd)

It is the ratio of energy required to evaporate

the moisture to the energy supplied to the dryer.

Drying efficiency is calculated by following formula

(Brenidorfer et. Al) 1985

w.H1

nd = - - - - -- - x 100 Ic.Ac

Where,

w = Mass of moisture evaporated (kg) in time

‘t’.

H1 = Latent heat of evaporation (KJ/Kg)

Ic = Isolations on collector surface, (KW/m2)

Ac = collector area, m2

3.7.2 Heat Utilization Factor (HUF)

This is defined as the ratio of temperature

decrease due to cooling air during drying and the

temperature increase due to heating of air (Brenidorfer

et. al 1985).

HUF is calculated by formula as

HUF = (t1 –t2)/(t1-t0)

Where;

to= Dry bulb temperature of a ambient air

t1 = Dry temperature of drying air

t2 = Dry bulb temperature of exhaust air

3.7.3 Coefficient of Performance

It is calculated by as follows,

COP = (t2-t0)/(t1-t0)

Where:

t0, t1, and t1 have the same meaning as mentioned

above.

HUF + COP = 1 (Brenidorfer et. al 1985).

4. REFERENCES Anonymous. (2007) A paraboloid solar collector fabricated at

Department of Renewable Energy Sources, College

of Technology and Engineering Udaipur (Rajasthan) India.

Anonymous. (1978) Solar Cooker Box Type. Directory of Solar

Energy Projects in India. Compiled By Tata Energy

Research Institute, New Delhi.

Brenidorfer B and other, (1985). Solar dryers; their role in

post harvest processing, Commonwealth Secretariat.

Marlborough house, London. SW1y 5hx.

Panna Lal Singh And G.C. Yadava. (1998). Performance Study Of

Double Reflector Box Type Solar Cooker. Journal Of

Agricultural Engineering,35(1),15-22.

Rai, G.D. (1993). Solar Energy Utilization (Fourth Edition).

Khanna Publishers Delhi 1-16.

Ranjeet Singh And O.P. Yadav. (1989). Design and testing of

parboiled surface concentrated type of solar cooker.

Renewable energy and Environment. Proceeding of

National Solar Energy Convention, Udaipur. India.

Dec.1-3.63.

Shrivastava A.K. And R. Bhojwani.(1981).Fruit and Vegetable

preservation by drying and canning. Small, medium and

large-scale industries.vol. (1).553-559.