Investigation of solar cooker with pcm heat storage

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online) IJMET
Volume 3, Issue 3, September - December (2012), pp. 555-564
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2012): 3.8071 (Calculated by GISI)
©IAEME
www.jifactor.com

INVESTIGATION OF SOLAR COOKER WITH PCM HEAT
STORAGE FOR HIGH ALTITUDE PLACES (TAIF CITY)
Talal K. Kassem
Department of Mechanical Engineering, College of Engineering, Taif University, P.O.
Box 888 Zip Code 21974, Taif, Saudi Arabia.
Permanent Address: Department of Mechanical Engineering, Faculty of Mechanical and
Electrical Engineering, Damascus University, P.O. Box 86, Syria.
E-Mail: t.kassem3@yahoo.com
Mobile: +966564401827

Abstract

In this paper, an experimental investigation is carried on a box solar cooker with
heat storage. The cooker is connected to solar water heating system compound of
evacuated tubes solar collectors and a storage tank of hot water. The base of this box
(the absorber plate) is incorporated by welding with a spiral copper tubes heat
exchanger and cylindrical pot inside it filled with paraffin as a PCM. Some parameters
affecting on the performance of this system, such the solar radiation, air humidity,
orientation of solar cooker and the ambient temperature were investigated. This study
highlights the ability of using this system with high performance in the conditions of
high altitude (high insulation, partly clouding and moderate temperature) for cooking
and heating the food.

Keywords: solar cooker, solar heating system, evacuated tubes solar collectors, PCM
heat storage

1. Introduction

Solar energy is free, environmentally clean, and therefore is recognized as one of the
most promising alternative energy resources options. Therefore, solar cooking has
proved to be one of the simplest and attractive options for solar energy utilization.
Basically there are different types and designs of solar cookers. For each design of
them different performance parameters has been used. The available solar cookers are
mainly classified into two groups. The first group is solar cookers without storage and
the second one is solar cookers with storage.

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

Solar cookers without storage are classified into direct and indirect solar cookers
according to the heat transfer mechanism to the cooking vessel [1]. In direct type solar
cookers, solar radiation is used directly in the cooking process, while, in the indirect
solar cookers a heat transfer fluid is used to transfer the heat from the collector to the
cooking vessel.

Direct type cookers are box and concentrating type cookers. Many designs of
each type have proposed and tested to investigate the thermal performance parameters
for each type. Among the direct solar cookers, box type solar cookers are more popular
due to their simplicity of handling and operation. Different designs of box type solar
cookers are available to enhance the thermal performance of solar cooker. Cooker pot
design also helps in improving the thermal performance of the cooker. A solar box
cooker has been designed, constructed and tested by Alozie et al. [2] to investigate its
workability of cooking food in most tropical regions where the sun's radiation is
abundant.

An experimental study was conducted at Irbid city, Jordan by Al-Azab et al. [3]
to investigate the thermal performance of box type solar cooker with two different
cooking pots (finned and un-finned pots).
Guar et al. [4] designed and fabricated the pot lid in concave shape and carried out
water heating test and stagnation test with conventional pot lid and concave shaped lid.
A comparative experimentally study of a box type solar cooker with two different
cooking vessels has been carried out by Harmim et al. [5]. In most recent review article
for box type solar cookers, some of the performance parameters and the related test
procedures have been reviewed by Lahkar and Samdarshi [6].

Cooking outdoors and impossibility of cooking food in late evening hours are
the main problems associated with solar cooking systems. There are three methods for
storing thermal energy, namely; latent, sensible, and thermo-chemical heat storage [7].
Many Solar Cookers with Latent Heat Storage Materials have been investigated where;
the thermal performance of a prototype solar cooker based on an evacuated tube solar
collector with phase change material (PCM) storage unit has been studied by Sharma et
al. [8] at Mie, Japan. Buddhi et al. [9] tested acetanilide as a PCM with a melting point
of 118.9 oC for night cooking in a box type cooker with three reflectors.
In sensible heat storage, thermal energy is stored by raising the temperature of a solid or
liquid. Ramadan et al. [10] designed a simple flat-plate solar cooker with focusing
plane mirrors and energy storage capabilities constructed by the locally available
materials.

2. Theoretical model

The thermal performance of the box solar cooker can be evaluated according to [11-
12] by calculating: The consumed thermal energy on cooking Qh and The efficiency th.
The thermal energy used in the cooking process is done by:

mw Cw ∆T
Qh = (1)
∆t

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The efficiency of the cooker is defined by the ratio of heat uses for cooking to the
insolation of solar energy incident on the base of cooker:
m w C p ∆T
ηth = t
(2)
A c ∫ G t dt
0
The efficiency of evaporation can be defined by the ratio of the thermal energy used in
the evaporation process ( m w .e . h fg ) to the insolation of solar energy incident on the
base of cooker:
m w .e h fg Q solar − Q lost
ηe = = (3)
t
Q solar
Ac ∫ G t dt
0
Heat lost from the cooker to the surrounding can be done by:
Qsolar = U system (T100 − Tamb ) (kJ) (4)

By knowing the experimental value of ηe , the total coefficient of heat transfer Usystem
can be calculate by:
(1 − ηe ) A c G t
Usystem = (5)
T100 − Tamb

The maximum temperature can be reached when ηe = 0. This means that the gained
thermal energy from the solar radiation was dissipated in two ways:
- Evaporation of water from the pot inside the cooker.
- Heat loses to the surrounding.

3. Experimental Work:

Figure 1 . Outlines the experimental system which composed of the solar heating
system (evacuated tubes solar collectors with a storage tank of hot water) and the solar
cooker. The solar cooker consists of two boxes designed in the form of parallel
rectangles join between them a layer of thermal insulation (wool thermal) thickness of 5
mm. The reflector support, made of iron, has been used for making the reflector rigid
and adjusting the reflector in an angle calculated according to the place, date and time.
One layer of glass (mm) as transparent cover.
The internal box of the cooker was made of galvanized iron of dimensions (45 x 60 x 40
cm). The base of this box is connected by welding on the one hand with a spiral copper
tubes heat exchanger, and on the other hand with a cylindrical pot, where the heat
exchanger includes inside the cylindrical pot which filled with paraffin of density of
0.75 kg/l (in the case of fluid).

Paraffin melts at 27 ⁰C and it can store a lots of heat energy. In this system, the storage
tank of the solar heating system feeds hot water to the heat exchanger, where the
thermal energy will be stored in paraffin which heats the cooking pot and accelerates the
cooking process, and then hot water returns to the storage tank.

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Fig. 1: A schematic diagram showing the arrangement of the cooker-collector
systems.

All edges and corners of the box solar cooker were well filled with silicon to prevent any
leakage of heat or air infiltration.
The south faced solar water heating system is installed on the roof of the Fluid Mechanics
Laboratory, Mechanical Engineering Department, College of Engineering, Taif University, Taif
city, Saudi Arabia.
The total intensity of solar radiation has been measured by using Pyranometer - LP 02 with
Amplifier - AC 420 and Hand held readout unit- LI 18, which mounted in parallel manner to the
transparent cover of the cooker. The inner box of the cooker receives the total solar radiation
(beam and diffuse) and the reflected radiation from the mirror of reflector which fixed on an
iron framework in the east-west and north sides of the cooker. The cooker box is kept
horizontal.
Reflector was oriented southwards with a tilt angle of 60 to 105 degrees. This angle depends on
the solar altitude angle and the hour angle as shown in Fig. 2.

120

100
Reflector tilt angle

80

60

40
0 10 20 30 40 solar angle 80 90 100
Altitude 50 60 70

Fig. 2: Variation of reflector tilt angle with altitude solar angle.
The thermal performance of the solar cooker was evaluated under Taif weather conditions (1450 m above
sea level). So, a series of experiments were performed with and without connection of the solar cooker to
the solar heating system (with and without heat storage).
In this study absorber plate temperature, internal temperature of the solar cooker and the temperature of
water in the cooking vessel were measured as shown in table (1) by using K-type thermocouples, whilst,
the ambient temperature and the relative humidity were measured by a hygrometer.

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Table. 1. Variation of the absorber plate temperature, pot water temperature and
ambient temperature with solar radiation intensity on 30/06/2012.

Solar radiation
Temperatures (◦C)
intensity on
Time (h)
horizontal surface Ambient Absorbent
(W. m-2) water
Temperature plate
11:00 968 31 112 52
11:30 1011 31.5 119 58
12:00 1026 32.5 127 62
12:30 1037 33 133 72
13:00 1046 33 135 79
13:30 1025 33.5 136 83
14:00 998 32.5 137 88
14:30 936 32 139 97
15:00 846 31.5 136 98
15:30 763 31 134 98
16:00 605 31 131 98
16:30 469 30 127 95
17:00 358 29.5 123 92

4. Results and Discussion

The incident solar radiation variation on a horizontal surface for Taif city during day
time on Sunday 16/09/2012 is shown in Fig. 3.

Fig. 3: Variation of the incident solar radiation on Taif city during day
time on Sunday (16/ 09/2012).

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a- Investigation of solar cooker without heat storage:

The solar cooker was not connected to the solar heating system. So, the absorber
plate of the cooker will be heated only by the total solar radiation (beam and diffuse)
which is affected by the climatic conditions especially in the cloudy and partly cloudy
days and in the cold climate.

I- The solar cooker has one position

The solar cooker was oriented southwards while the tilt angle of the reflector
was 85 degrees. The cooking pot was loaded by 2 liter water. Measurements were taken
at intervals of 1 hour during the period of effective sunshine from 09:00 am to 17:00
pm. (15 – 19 /09/ 2012), and the pot water temperature inside the cooker cannot exceed
90 ◦C. The results were plotted in Fig. 4 on Sunday (16/09/2012) where, the maximum
value of the solar radiation intensity decreases to below 820 W.m-2. Temperature of the
absorbed plate increases during the day until it achieves its maximum value (82 ◦C) at
13:30 pm, where the cooking process cannot be started.

Fig. 4: Variation of the absorber plate temperature, the pot water temperature and
the ambient temperature with time of day for one position (16 /09/ 2012).

For the same case where, the solar cooker has one position from 09:00 am to 18:00 pm
and its reflector facing the south. The solar cooker was investigated for a few typical
days (12- 17/05/2012). The variation of temperature of the absorber plate of cooker, pot
water temperature and ambient temperature are given in Fig. 5 on Wednesday
(16/05/2012) when the solar radiation intensity was about 910 W/m2. It is seen that the
maximum attainable temperature of the absorber plate of the cooker is about 125 ◦C at
14:00 pm.

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140
120

Temperature (°C) 100
80
Absorber
60 plate

40
20
0
8 10 12 14
Time (hr) 16 18

Fig. 5: Variation of the absorber plate temperature, the pot water temperature and the
ambient temperature with time of day for one position (16/05/2012).

II- The solar cooker has two positions

The solar cooker was investigated during two periods (from 09:00 am to 12:00 pm) and
(from 12:00 pm to 17:00 pm) for the period of (09 – 13/06/2012). On Monday (11/06/2012) the
maximum value of the solar radiation exceeded 1050 W.m-2. The solar azimuth angle will be
varied between ßs = 25◦ north- east for the first period (09:00 – 12:00) and ßs = 24◦ north- west
for the second period (09:00 – 12:00). The reflector tilt angle was 85◦ for the two periods.

ambient temperature with time of day for two positions (11/06/2012).

Figure 6 shows that the temperature of the absorber plate has two tops at 11:00 am and 15:00
pm (131 and 134.2◦C) respectively, while the temperature of water in the cooking pot reaches its
maximum value (97.4 ◦C) at 15:00 pm and continues to be constant approximately.

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III- The solar cooker has a permanent setting (ßs= 0):

In this case the reflector tilt angle (δ) of the solar cooker can be defined by rapport to
the altitude solar angle (h) by the relation 3δ – 2h = 180◦ during the period between 08:00 am to
16 pm (26 – 30/08/2012), with approximately the same maximum daily average value of the
solar radiation intensity (986 W.m-2) for the period of (09 – 13/06/2012). The variations of the
absorber plate temperature, the pot water temperature, and the ambient temperature on Tuesday
(28/08/2012) with solar radiation of (1032 W. m-2) were plotted in the Fig. 7. The absorber plate
temperature increases rapidly to the maximum value on 15 PM.

Fig. 7: Variation of the absorber plate temperature, the pot water temperature and the ambient
temperature with time of day for permanent setting (28/08/2012).

b- Investigation of solar cooker with heat storage:

The solar cooker was connected to the solar heating system, where the hot water flows from
the storage tank to the heat exchanger where it loses some of its thermal energy to heat the
paraffin in the cylindrical pot, and the absorber plate temperature increases rapidly to reach its
maximum value (about 140 ◦C) on Monday (15/10/2012) where, the maximum value of the
solar radiation intensity was in the order of 790 W.m-2. In this case the cooking process can be
started at 13:00 pm as shown in the Fig. 8.
150

100
Temperature (°C)

Absorber
plate
50

0
11 13 Time (hr)15 17

ambient temperature with time of day (15/10/2012).

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5- Conclusion

An experimental investigation on the performance of box solar cookerg has been
carried out. Therefore, to enhance the efficiency of the proposed solar cooker system, a
series of experiments have been implemented during two periods with and without heat
storage to evaluate the performance of the solar cooker under outdoor weather
conditions of Taif city. This experimental study and the different obtained
measurements lead to the following conclusions:
- The performance of the solar cooker with heat storage is much better than that of
without heat storage ones in all climate conditions, where the thermal energy
storage is essentially needed to increase the utility and reliability of the solar
cookers.
- The solar heating system coupled with the solar cooker can maintain the stability
of the absorber plate temperature of the cooker in the cloudy and partly cloudy
days.
- The solar cooker without heat storage can’t be used for cooking in the cold and
cloudy days.
- Using the heat storage can accelerate the cooking process which can be started at
12:00 PM. At the same time, the solar heating system decreases the falling of the
internal temperature of the cooker.
- The results show that the best time to cook with the solar box cooker is between
the hours of 11.00 am and 4:00 pm (K.S.A. locale time) on sunny days and is
not possible to cook on cloudy or rainy days or at night unless effective solar
storage devices are incorporated.

Nomenclature

mw mass of heated water in the pot of cooking (kg)
Cp thermal capacity of water (KJ. kg-1 K-1)
o
∆T water Temperature Difference (35 – 95) ( C)
t period of time of heating (sec)
Gt intensity of solar energy (W. m-2)
Ac area of solar collectors (m2)
m w.e mass of the measured evaporated water (kg)
h fg evaporation latent heat of water (kJ. kg-1)

References

[1] Muthusivagami .R.M., et. al. (2010), “Solar cookers with and without thermal
storage: A review”, Renewable and Sustainable Energy Reviews, Vol. 14, No. 2,
pp. 691-701.
[2] Alozie .G.A., et. al. (2010), “Design and construction of a solar box cooker as an
alternative in Nigerian kitchens”, ISESCO Science and Technology Vision, Vol. 6,
No. 9, pp. 57- 62.

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[3] Al-Azab .T.A., et. al. (2009), “Experimental investigation of a box-type solar
cooker with finned pot thermal performance in Jordan”, GCREEDER, Amman,
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[4] Gaur .A, et. al. (1999), “Performance study of solar cooker with modified utensil”,
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[10] Ramadan .M.R.I., et. al. (1998), “A model of an improved low cost indoor solar
cooker in Tanta”, Solar and Wind Technology, journal, Vol. 5, No 4, pp. 387-
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[11] Pejak .E.R. (1991), “Mathematical model of the thermal performance of box type
solar cookers”, Renewable Energy, journal, Vol. 1, No 5-6, pp. 609 – 615.
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families and institutions”, Solar Energy, journal, Vol. 75, No 1, pp. 35 – 41.

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Investigation of solar cooker with pcm heat storage

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