Experimental Investigation of a Box-Type Solar Cooker with Finned Pot

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					                              GCREEDER 2009, Amman-Jordan, March 31st – April 2nd 2009                              1

 Experimental Investigation of a Box-Type Solar Cooker with Finned Pot
 Thermal Performance in Jordan
 Tariq A. Al-Azaba, M. Q. Al-Odatb* and F. M. Al-Hussienc
   Mechanical Engineering Department, Al-Salt Community College
 Al-Balqa Applied University, Al-Salt-Jordan
   Mechanical Engineering Department, Yanbu Industrial College
 Saudi Arabia
   Mechanical Engineering Department, Al-Huson University College
 Al-Balqa Applied University, Irbid-Jordan

           In this study, a box type solar cooker was designed, fabricated and tested under Irbid prevailing
           climate conditions. The cooker is of the hot box type with two plane mirror reflectors. The thermal
           performance of the cooker is experimentally investigated. Testing was performed during over a two-
           month period between May and July 2007, with 2 l water load. The testing was conducted at Irbid city
           in accordance with the International Standard Procedure for Testing Solar Cookers. Two types of
           cooking pots with and without fins were tested in this work. It was found that, the maximum
           temperature obtained in the un-finned and finned pots containing 2 lit of water was reached 90 oC and
           98 oC, respectively. Also many factors that affect the cooking performance were examined. This
           study shows the present cooker is able to cook most kinds of food with an overall utilization
           efficiency of 45% with the finned pot.

           Keywords: Solar Energy, Box solar cooker, Finned pot, Thermal performance

                                                                 order to generate the necessary energy to supply the
 Nomenclature                                                    increasing energy demand and also to comply with the
                                                                 regulations related to environmental pollution, use of solar
 A         Absorber area, m2                                     energy as a renewable energy source is becoming more
 Cp        Specific heat of water (4186 J/kg. °C)                and more important.
 I         Solar radiation, W/m2                                 As a result, energetic search of alternative energy sources
 m1        Mass of water in cooking pot, kg                      has followed and led to extensive research efforts in the
 mw        Mass of cooking, kg                                   field. Solar Energy received attention at a global scale
 mw        mass of water (kg)                                    because it is renewable, widely dispersed, and is pollution
 Q         average cooking power (W)                             free. However, solar, compared to the convectional energy
 Qs        Standardize cooking power                             sources (fossil fuel), has disadvantages as a source of
 t         Period of test, h                                     energy including its generally lower thermal density,
 Ta         Average ambient temperature (°C)                     intermittent, and nonhomogeneous form. Each of these
 Tw         Average water or pot content temperature (°C)        characteristics has its consequences on the feasibility and
                                                                 economy of solar energy as an alternative source and must
Greek symbols                                                    be taken into account when considering any solar energy
  θ1, θ2   Inclination angle of the reflector mirrors            system.
θ2         Tilt angle of the collecting surface                  Solar cooking offers a simple, effective, low cost and
  η        Efficiency of the solar cooker                        practical method of utilization solar energy for meeting a
                                                                 considerable demand for cooking energy and, hence,
                                                                 protecting the environment. Considerable efforts have
      1.   INTRODUCTION                                          gone into the development and performance testing of a
 In Jordan, energy resources are almost nonexistent, and the     variety of solar cooking and their suitability for cooking
 country imports most of its energy. The unstable imported       different food.
 supply consumes a significant proportion of the GNP.            For utilizing solar energy to be useful for cooking a solar
 Consequently, research in the renewable energy sector has       cooker designed for that purpose. Solar cookers are mainly
 emerged. The demand on the available but limited                of two types: box types and concentrating types. Box type
 traditional energy sources (oil and coal) has been              solar cookers are simple and suitable for limited cooking
 dramatically increasing due to the increase in population       due to their relatively low heat collection capacity, while
 and economic development. In addition, fossil fuels have        concentrating type solar cookers are capable of generating
 caused serious pollution problems throughout the world. In

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                               GCREEDER 2009, Amman-Jordan, March 31st – April 2nd 2009                           2

higher temperatures and can efficiently be used for variety   down. The tilt of the reflectors can be varied from 0
of cooking applications [1].                                  (closed lid) to 120° from the horizontal plane, depending
A large number of solar cookers have been developed in        upon the season.
many countries. These cookers are broadly divided into          10

direct or focusing type [2, 4], indirect or box-type 5, 6],
and advanced solar cookers [7, 8]. Using the advanced           8
cookers, the problem of cooking outdoors is avoided to
some extent. Using phase change materials as storage
media inside solar cookers [9, 10] has solved the problem       6

of cooking in the evening or during low intensity solar
radiation periods.                                              4

The objective of the present work is to experimentally
investigate the thermal performance of a box- type solar
cooker with finned cooking pot. The experimental results        2

show that the tested solar cooker can be successfully used
to cook several foods.
                                                                     0.1              1.0                  10.0

As shown in Fig (1), the box type solar cooker under Figure (2): Detailed Working Drawing of the solar cook
consideration is a double-walled hot box, i.e. a box under consideration (All dimensions in cm)
within a box. The inner box (absorber plate) is made of Two cooking cylindrical pots (finned and un-finned)
steel sheets and the outer box is made of wood. The were made of aluminium with diameter of 16cm and
dimensions of the outer box are 61.5cm×40.5cm×21cm. depth 8cm and are attached to the center of the
and of the inner box are 56cm×35cm×19.5cm. The upper absorber plate to achieve the desired contact between
surface of the absorber plate is painted by dull black the pots and the absorber plate; in order to increase
coating; thus, increasing it is capability of absorbing the rate of heat transfer by conduction between the
incident solar radiation. The space between the outer tray absorber plate and the cooking pots. Finally, the
and outer box is filled with foam thermal insulation layer cooker is equipped with a four wheels to facilities its
with about 1.5cm in thickness                              movement.
                                                           When the solar cooker was placed in the sun, the
The detailed working drawing of the present box
                                                           cooking pots started absorbing the solar radiation
type solar cooker, with the required dimensions            coming through the glass cover. The inside
is depicted in Figure (2).                                 temperature began rising rapidly, because the input
                                                           energy is much greater than the loss of heat.
                                                           However, after a short time the equilibrium
                                                           temperature will be reached. The amount of incident
                                                           energy was increased by the reflectors, which could
                                                           focus an additional amount of solar energy inside the
                                                           solar cooker.

Figure (1): A filed photograph of the box-type solar
 cooker under-consideration
The top of the box is covered with a clear window glass
(with thickness 4 mm) and rubber gasket is provided to
prevent air leakage. Furthermore, there are a two
reflector mirrors attached to the solar cooker. These
reflecting mirrors can be adjusted to any angle with the
help of two slotted hinges on either side of the box, and Figure (3): Two cooking pots used in the present study
there are two moving arms to fix the mirrors in the
desired angle and another arm to move one mirror up or

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                            GCREEDER 2009, Amman-Jordan, March 31st – April 2nd 2009                                                                               3

3. EXPERIMENTAL METHODOLOGY                                                          (m Cp                      ΔTw + m p Cp P ΔTP )
   NUMBERS                                                        η=
                                                                                                    w       w
Experiments were conducted outdoors in AL-Huson                                                                  A∫ I t dt
University College, Irbid city; Northern Jordan located at                                                         0
32.55oN Latitude and 35.85 Longitude on May and June
2007 to evaluate the performance of the solar cooking           4. RESULTS AND DISCUSSION
system. The solar cooker was loaded with two liters of
water for three days May, 13th and June 7th of the year         The results of the present experimental study are
2007.                                                           shown in Figures (4) to (9).
During each test the two cooking pots were placed side by       Fig (4) shows the variation of solar radiation
side on the absorber of the solar cooker and loaded with        intensity with time on the full load test days at Al
the same mass of water at the same initial temperature.         Huson University College, Irbid– Jordan with a load
Temperature measurements were taken at interval of 30           of 2 liter of water. It is clear that the solar radiation
minutes during the day (From 8–17) with K-type
                                                                intensity increases with time until it reaches a
thermocouples. The solar radiation intensity was measured
by a Kipp and Zonen CM-11 type Pyranometer.                     maximum value at about 13 clocks (Solar Noon). In
Two thermocouples were immersed centrally in each pot           addition the solar radiation in June is greater than that
and secured above the pot bottom and 100 mm below the           in May.
water level. The thermocouple wires were passed through         The experimental performance of the cooker with the
a hole drilled in the pot lid and sealed using an epoxy resin   two cooking pots for the testing days is shown in
to reduce vapor loss. The following data were taken every       Figures (5) and (6), (θ1= θ2= 45°) at Al Huson–
30 minuets: water temperature in each pot, the ambient          Irbid– Jordan with two liter water load. The water
temperatures, absorber plate temperature, temperature of        temperature inside the finned pot was higher than
air inside the cooker and the solar radiation intensity.        that of the unfinned counterpart, this due to the
During the experiments, the cooker was manually aligned
                                                                increase of the heat transfer area resulting from fins
hourly or when shadows appear on the absorber plate in
order to track the sun.                                         addition to the external surface. It can be seen that
Tests were conducted according to the International             the water temperature reaches a maximum at about
Standard for Testing Solar Cooker and Reporting                 13 h. Also, it is obvious that the water temperature
performance [10]                                                increasing with time rapidly in early morning.
To calculate the average cooking power, the total mass of                                1000

water in each pot was multiplied by the temperature raise
in each 30-minute and the specific heat capacity of water.

The result was divided by 1800 s (30 minutes), and thus
                                                                     Solar Radiation (W/m2)

the cooking power in Watt can be calculated as:
       mW C P ΔT mW C P (Tw − Ta )                                                            700

 Q=             =                              (1)
           t         1800                                                                     600

Where:                                                                                        500
                                                                                                                             Solar Radiation

Q: average cooking power (W)                                                                                                      13 th May, 2007
                                                                                                                                  7 th June, 2007
Ta: Average ambient temperature (°C)                                                          400

Tw: Average water or pot content temperature (°C)
mw: mass of water (kg)                                                                        300

Cp: specific heat of water (4186 J/kg. °C)                                                    200
t: testing time (sec)                                                                                   8   9     10   11    12      13        14   15   16   17

Standardizing cooking power can be calculated by                                                                        Local time (hr)
multiplying the interval observed cooking power by 700
W/m2 and the result divided by the interval average
                                                                Figure (4): Measured Solar Radiation on 13th May and 7th
isolation recorded during the corresponding interval, thus
                                                                June 2007 at Al-Huson College.
       Q × 700
Qs =                                                    (2)
In this study the solar cooker was tested under different
angles of inclination.
The average sensible efficiency of the solar cookers was
obtained by the following relation:

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                               GCREEDER 2009, Amman-Jordan, March 31st – April 2nd 2009                          4

Fig (5): The relationship between the ambient temperature
                                                              Fig (7): Variation of Standardized cooking power
and water temperature inside both pots with time, [load 2     with temperature difference between pot contents
liter of water; θ1= θ2= 45°; in 13th May 2007; Huson-         and ambient [2 liter; θ1= θ2= 45°; 7th June, 2007,
Irbid- Jordan]                                                Huson- Irbid- Jordan]
                                                              Comparing the performance curves in Figure 5 and 6,
                                                              it can be seen that the water temperature in 7th June is
                                                              higher that in 13th May. This is due to higher solar
                                                              intensity in June compared to May.
                                                              Variation of Standardized cooking power with
                                                              temperature difference between pot loads and
                                                              ambient for finned and unfinned pots is depicted in
                                                              Fig (7). The cooking power increases continuously
                                                              with the temperature difference between the pot load
                                                              (water) and ambient. In addition, the cooking power
                                                              for the finned pot is much higher that the unfinned
                                                              pot specially at high values of temperature
                                                              Fig (8 and 9) shows the efficiency variation with time
                                                              for both pots. The cooker efficiencies are calculated
                                                              for 30 minuet period and assumed to be constant
                                                              during this period. It can be seen that the efficiencies
                                                              are high at early periods of tests and decreases as
                                                              time elapses. This behavior is due to the decrease in
Fig (6): Loaded water and ambient temperature variation       the rate of increase in temperature and solar radiation
with time [Load 2 liter of water; θ1= θ2= 45°; in 7th June,
                                                              with time.
2007; Huson- Irbid- Jordan]

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                          GCREEDER 2009, Amman-Jordan, March 31st – April 2nd 2009                             5

                                                           5.   CONCLUDING REMARKS
                                                           An experimental study was conducted to investigate the
                                                           thermal performance of box type solar cooker with
                                                           different cooking pots. The cooker temperature depends on
                                                           the solar intensity. The present solar cooker is inexpensive,
                                                           easy to fabricate locally and simple to use. It was found
                                                           that cooker temperature can be increased by using a finned
                                                           cooking pot. The cooker efficiency can reach 45% for
                                                           finned pot and 40% for unfinned pot. Further study is
                                                           required to optimize the developed solar cooker.

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Fig (9): Solar cooker efficiency variation with time for
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45°; 13th May, 2007; Huson- Irbid- Jordan]

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