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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp.1931-1938. Article ID: IJMET_10_04_196
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
DESIGN AND TESTING OF COOKING VESSELS
OF SOLAR BOX COOKER FOR EVENING
COOKING
Ajeet Kumar Rai and Sanjay Kumar Srivastava
Mechanical Engineering Department, VIAET, SHUATS, Prayagraj, 211007, (U.P.) India
ABSTRACT
In the present work, an attempt has been made to design and test the performance
of box type solar cooker with cooking pots of different materials filled with latent heat
energy storage mediums to perform the cooking in sun shine and off sun - shine
conditions. The box type solar cookers are not common in use due to limited availability
of solar energy. Latent heat energy storage materials are used to store solar energy
available in day time to use in evening and off sunshine hours. Paraffin wax is used as
energy storage material (PCM) to improve the performance of the system in off sunshine
conditions. PCM filled aluminium pots are suitable for day time cooking. It is observed
from full load test that the water temperature in PCM filled steel pots are maintained
above 950C for more than 3 hours than PCM filled aluminium pots in off sunshine
conditions.
Keywords: Box Type solar cooker, Latent heat energy storage, cooking vessel.
Cite this Article: Ajeet Kumar Rai and Sanjay Kumar Srivastava, Design and Testing
of Cooking Vessels of Solar Box Cooker for Evening Cooking, International Journal
of Mechanical Engineering and Technology, 10(3), 2019, pp. 1931-1938.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3
1. INTRODUCTION
Energy is essential to sustain life on the earth. Energy is available in various forms on the earth.
A major amount of total available energy is utilized for cooking. Heat energy is the most
suitable form of energy to cook food. Heat generation by burning of fossil fuels is common
practice for cooking applications in developing countries. But fast depletion of resources and
environmental problems associated with use of fossil fuels has restricted its use. Utilization of
renewable energy based technologies is the most promising options for cooking applications.
Since cooking requires 36% of total primary energy consumptions in India [1]. In present days
14% of total world energy demand is supplied by renewable energy sources [2]. Therefore,
there is a rising attention concerning the renewable energy options to meet the cooking
requirements of people in developing countries. Since it is free of cost and environment
friendly, the solar energy is recognized as one of the most promising choice among other clean
Design and Testing of Cooking Vessels of Solar Box Cooker for Evening Cooking
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energy technologies. The earth receives 3.85 million EJ of solar energy each year [3]. It is well
known that most of the thickly populated countries from the developing part of the world are
blessed with abundant solar radiation with mean daily illumination in the range of 5-7 kW h/m2
and have more than 275 sunny days in a year [4]. From this point of view, it can be easily said
that solar cookers have a big potential in these countries in order to meet the energy demand
especially in the domestic sector. In addition, utilization of solar cookers provides many
advantageous like no recurring costs, high nutritional value of food, potential to reduce
drudgery and high durability [5].
Since solar energy is not continuously available with same maximum intensity. Thermal
energy storage mediums may be used to make solar cookers working for longer periods.
Thermal energy can be stored as sensible heat, latent heat or combination of these two.
Materials that can store latent heat during the phase transition are known as phase change
materials. Latent heat of phase change material is many orders higher than the specific heat of
materials. Therefore PCM can share 2-3 times more heat or cold per volume or per mass as can
be stored as sensible heat in water in a temperature interval of 20 0C. Rai et al have reviewed
work on PCMs and their wide range of applications [6]. They have also suggested a wide range
of PCMs that can be selected as a storage media. In order to select the most suitable PCM as a
storage media some criteria are also mentioned. Abhat, Dincer and Rosen have given a detailed
classification of PCMs with their properties [7,8]. Shukla et al have used PCM as a energy
storage medium to study the performance of a solar still [9]. Rai et al constructed novel
continuous single stage solar still with PCM. They reported that the productivity of a solar still
can be greatly enhanced by the use of a PCM integrated to the still [10]. Paraffin are chemically
known as hydrocarbons which are generally found to be as wax at room temperature. Paraffin
consists of a mixture of mostly straight chain n-alkanes CH3–(CH2)–CH3. The crystallization
of the (CH3)- chain release a large amount of latent heat. Both, the melting point and latent heat
of fusion, increase with chain length. Paraffin qualifies as heat of fusion storage materials due
to their availability in a large temperature range. System-using paraffin usually has very long
freeze–melt cycle. Apart from some several favorable characteristic of paraffin, such as
congruent melting and good nucleating properties, they show some undesirable properties such
as low thermal conductivity, non-compatible with the plastic container and moderately
flammable. All these undesirable effects can be partly eliminated by slightly modifying the wax
and the storage unit.
In this present experimental work, the attention is mainly focused on the exploring
possibility of use of solar cooker for evening cooking. PCM are used for latent heat energy
storage in sun shine hours which can later be used during off-sunshine hours. Sensible energy
storage is ensured with the use of cooking pots of Steel. Steel pots with PCM are tested and its
performance is compared with the Aluminium cooking pots integrated with PCM.
2. THERMAL TEST PROCEDURE FOR BOX TYPE SOLAR COOKERS
The energy balance for the horizontally placed empty solar cooker at stagnation (quasi-steady
state) is given as [11,12]
o s L ps as
H U T T

(1)
Where
o
is the optical efficiency,
ps
T
is the plate stagnation temperature,
s
H
and
as
T
are,
respectively, the insolation on a horizontal surface and the ambient temperature at the time
stagnation temperature is reached. The first figure of merit, F1, is defined as
Ajeet Kumar Rai and Sanjay Kumar Srivastava
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1ps as
s
TT
FH
(2)
And can be obtained from the simple stagnation test without load. Lower permissible limit
of the value of F1 may be specified to ensure a minimum level of thermal performance. It is
stipulated that F1 should equal or exceed 0.12.
The second figure of merit F2 is therefore obtained from sensible heating test. The proposed
figure of merit is based on following analysis.
2
1
'0
1
() 1
1
w
w
T
ww
T
Rwa
MC T
AF C H T T
F



 




(3)
Where,
w
T
is the average water temperature over an interval. Insolation may be assumed
constant and equal to average value (
) over the time interval.
2
1
20
1
() 1
'1
w
w
T
w
Rw
Twa
MC
F C F T
AH T T
F







(4)
The temperature interval ∆Tw can be gradually reduced until the computed values of F2
attain the desired degree of convergence.
3. DESIGNING OF THE STORAGE UNIT FOR COOKING POT
Mass of the latent heat storage material may be calculated using the following equation and the
assumptions taken are as given by Sharma et al [14] as
Mf CW (Tf – Tm) + MPCM CPCM (TPCM – Tm) + MPCML = ULA (Tf –Ta) ∆t (5)
Considering
1. Average solar radiation (9 AM to 3 PM) - 640 W/m2.
2. Average ambient temperature - 200C
3. PCM temperature at 3 PM (before evening loading) - 1200C
4. Food temperature at 3 PM (before loading) - 200C
5. Evening food is loaded at 3 PM
6. Solar cooker is closed to the solar radiation at 4 PM
7. PCM temperature at 4 PM - 970C
8. Food temperature at 4 PM - 970C
9. PCM temperature at 6.00 PM - 850C
10. Food temperature at 6.00 PM - 850C
It may be assumed that PCM initially is at ambient temperature, and the specific heat will
be the same for both the solid and liquid phases. The thermo-physical properties of PCM and
various cooker parameters are used. To have the food temperature at the solidifying point of
the PCM at 6.00 PM, the energy released by the PCM and food should be equal to the energy
loss from the cooker.
Design and Testing of Cooking Vessels of Solar Box Cooker for Evening Cooking
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4. EXPERIMENTAL SETUP
The standard size box type solar cooker is used in the present experiment with aluminium and
steel pots integrated with latent heat energy storage material. Paraffin Wax is used as latent heat
energy storage material. Figure 1 shows the photograph of box type solar cooker used in
experiments. PCM filled cooking pots of aluminium and steel are designed and assembled with
the available cooking pots in the solar cooker. Box type solar cooker is constructed using GI
sheet and insulated by a layer of styro-foam insulating material of thermal conductivity = 0.033
W/m-K. For the box type solar cooker, the absorber plate consists of GI sheet painted black of
a surface area (47.5cm × 47.5cm) with 8.75 cm height and outer surface area (57.5cm× 57.5cm)
with 17.5 cm height.
Figure 1 photograph of the PCM filled cooking vessel and box type solar cooker
Aluminium pots of two different sizes, one of 1.5 liter capacity and another of 0.75 liter
capacity are taken. Small pot of diameter of 157 mm is kept inside the bigger pot of diameter
212 mm concentrically. Height of small pot is 40 mm and that of the bigger pot is 55 mm.
Thickness of the pots material is 1 mm. PCM storage unit in aluminium pot is made by filling
paraffin Wax in the annulus space between the two concentric pots of different sizes. Similarly
energy storage unit in Steel pots are also made. Holes at the top cover are made to insert the
thermocouple wire to measure the PCM and water (when loaded) temperatures. Pots are
blackened from outside to absorb maximum insolation.
Experiments were conducted in the Solar Energy Laboratory of Mechanical Engineering
Department of the SHUATS Prayagraj U.P. India in the month of June 2018. Experiments were
started at 6:00 AM and continued till 7:00 AM next morning. During all the experiments solar
radiation intensity on the horizontal surface was measured using Solarimeter with least count
of 20 (W/m²). Digital temperature recorder with copper-constantan thermocouples is used to
measure the temperature of different locations on the box type solar cooker for example,
absorber plate, cooking pots, cooking fluid, PCM temperature, ambient temperature.
5. RESULTS AND DISCUSSION
Experimental studies are carried out on box type solar cooker with two different types of pot
materials, one is steel and other is aluminum. Fig 2 shows the variation of solar intensity with
Ajeet Kumar Rai and Sanjay Kumar Srivastava
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respect to the time of the day. Solar intensity starts increasing at steady rate before noon till it
reaches the maximum, and then rate of decrease is fast. Maximum value of 840 W/m2 is
obtained at around 2.00 P.M.
Figure 2 Variation of solar intensity with time of the day
To obtain the value of F1, the first figure of merit, stagnation tests were performed as per
international test procedures. Cooker was placed in the sun with covered reflector. Experiments
were conducted in the Solar Energy Laboratory of SHUATS Prayagraj, U.P. India. Maximum
stagnation temperature of absorber plate was obtained as 142 0C at around 1 PM. At this time
ambient temperature was 360C. The value of F1 is obtained as 0.13. According to Mullick et al,
1987 the first figure of merit F1 varies between 0.12 and 0.16. Value of F1 indicates good optical
efficiency and low heat loss factor. Box type solar cooker is of grade A as per BIS standard.
Before tests for second figure of merit, temperature variation of pots of aluminium and steel
were recorded. It was observed that once the steel pot crosses the aluminium pot temperature
during day time heating, temperature of steel pot remains at higher value than the aluminium
pot temperature. This is due to higher thermal conductivity of aluminium which cools it fast,
and thermal inertial effect and lower thermal conductivity of steel pot which keep it hot for
longer duration. For evening cooking using box type solar cooker, steel pots are of good choice
Varshney et al [23]. Figure 3 shows the variation of temperature of PCM filled steel and
aluminium pots with cavity temperature and ambient temperature. Trend of cavity temperature
during the day time is similar to that of the solar intensity variation as expected. After sunset
aluminium pot cools down faster than the steel pot. The maximum temperature in unloaded
condition of PCM filled aluminium pot was about 9% higher than PCM filled steel pot. In
unloaded condition temperature of steel pot is maintained above 800C after 8 hours of sunset.
It is concluded that the PCM Filled steel pots are most suitable for boiling type of cooking.
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