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DESIGN OF HANDMADE SOLAR BOILER AND
EFFECT OF THERMAL INSULATIONS IN HEAT CONSERVATION
Abdul Karim Pouya
Asia University, Faculty of Engineering, Civil Department
Ferdowsi Street, Herat, Afghanistan.
https://doi.org/10.5281/zenodo.17688061
Abstract.
This paper report the results of an experiment on a handmade solar boiler
focusing on the effect of thermal insulations for better heat conservation and better efficiency of
the device by using a concave downward dish covered by aluminum sheets, the dish used to
reflect the solar radiation to the water tank. The boiler div is a box mad of polystyrene foam
boards with length, width and height of 45cm, 43cm and 28.5cm respectively. The purpose of this
research was to reach the 60⁰C water temperature, but handmade boiler reached a temperature
about 10⁰c more than the target.
Key words:
solar boiler, thermal insulation, heat conservation.
1. Introduction
The idea of using solar energy collectors to harness the sun’s power is recorded from the
prehistoric times when at 212 BC the Greek scientist/physician Archimedes devised a method to
burn the Roman fleet. Archimedes reputedly set the attacking Roman fleet afire by means of
concave metallic mirror in the form of hundreds of polished shields; all reflecting on the same
ship.
The most widely-used solar thermal applications is the solar water heating (SWH) system
[8]. In the nineteenth century, heating was a big problem. People generally used a cook stove for
this purpose. They were using wood or heavy hods of coal lifted, then the fuel had to be kindled
and the fire periodically stocked. In cities, the wealthier heated their water with gas
manufactured from coal. To circumvent these problems, many handy farmers or prospectors or
other outdoors men devised a much safer, easier, and cheaper way to heat water – placing into
the sun a metal water tank painted black to absorb as much solar energy as possible. These were
the first solar water heaters on record. The downside was that even on clear, hot days it usually
took from morning to early afternoon for the water to get hot. And as soon as the sun went down,
the tanks rapidly lost their heat because they had no protection from the low air temperature in
the night.
Nowadays many kinds of insulations are in researchers’ service to save the collected solar
energy in a better manner. Thermal insulators have been used in heat storage systems to prevent
temperature gradient thereby minimizing heat losses to the surroundings [4]. The thermal
insulation is provided by embedding insulation materials at least on the roof areas and the
vertical walls of the system [5]. New heat insulation material has been widely used in aerospace,
energy, chemical and metallurgical industries, an important development trend is the research
and development of composite function of heat insulation materials with low thermal
conductivity [2].
In order to obtain the high strength and low thermal conductivity of composite insulation
materials, The species and the composition of material need to change [3].
Because of the global concern about reducing carbon emissions, different policies could
be applied to reduce carbon emissions, such as enhancing renewable energy deployment and
encouraging technological innovations [6].
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According to the Renewable Energy Policy Network (2010), approximately 70 million
houses use SWH systems worldwide [9]. Many countries started to use facilities which uses
renewable energy, but this technology is young and novel in Afghanistan, that need research
investigation.
The solar energy has a very insignificant usage in heating water. The regional distribution
of residential water heating fuel type in USA in as follows, 54% of the residential water heated
by natural gas. 39% or the water heated by electricity, 6% of the demanded hot water heated by
other sources of energy, but only 1% of the water heated by using the solar energy [1]. In
America, with power accounting for 40% of CO2 emissions, the U.S. faces challenges in
producing electricity cleanly [7]. The usage of renewable energy is felt to be increased, because
the organic sources of energy will be finished and now it is the main cause of the air pollution.
The appropriate design of SWH systems is important to assure good performance and
maximize the economic benefits of these systems. These design methods can be broadly
classified into two categories, namely, correlation-based methods and simulation-based methods
[10].
2. Methodology
2.1 Synopsis of boiler information
Figures 1 (a) and 1(b) show the 3D views, and dimensions of the boiler, and figure 2 show the
material used, wall section and detailed dimensions of walls and floor. To prevent the heat loss
in three possible ways by radiation, convection, and conduction, we insulated the box as
following techniques. The device is a box shaped boiler made of polystyrene foam boards of
3cm thickness, which polystyrene foam boards prevent the heat loss by conduction. Also the
boiler walls and floor was insolated by aluminum foil to prevent heat loss by radiation, and to
keep at minimum the heat loss by convection the box was air tighten as much as possible. A 2
letter capacity PET bottle was used as a water tank for the boiler, the bottle was painted black for
better absorption of the solar heat.
a)
Box dimensions b) 3D view of Boiler
Figure 1 a) Shows the dimensions of the boiler and b) Shows the 3D view of the boiler
To increase the efficiency of the
device, a concave down aluminum covered plastic dish was used to reflect the solar radiation to
the back side of the PET bottle.
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Also to absorb more heat by device it was covered by a black paper. The top surface of
the boiler was covered by a transparent acrylic sheet to pass the solar radiation and also keep the
box airtight.
a)
Material used in boiler b) Detailed dimensions
Figure 2 a) show the material used in solar bioler, and b) show the detailed dimensions of
walls and floor of the box shaped handmade solar bioler.
After completing design and building of the solar boiler, two days experiment has been
done and temperature data was recorded accurately for further studying on the efficiency of the
device. To give more strength to the research the temperature of the water inside the bottle also
calculated by formulas and finally the results was compared.
2.2. Formulas used for calculations
In existence of deferent insulations used in the handmade solar boiler still there are some
heat losses in the system.
As per energy conservation law the amount of energy entered to a boiler is equal to the
amount of energy stored in device plus heat loss form the system. The Energy balance equation
of a solar boiler is as follows:
(Input Heat) = (storage Heat) + (heat loss from device)
The parts of formula explained as below:
: Solar absorptivity (0.99), I: solar radiation incoming into the transparent sheet
(W/m2)
: Specific heat capacity of water (j/ (kg
(4186),
: Mass of the water within the
bottle (kg) (2)
,
: Water temperature (
),
: Water temperature,
: earlier temperature, t: time (s)
: Outside air temperature (
),
: Area of wall,
: thermal transmittance of wall i
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: Area or thermal transmittance of transparent part,
: Area or thermal
transmittance of transparent of thermal insulation board,
solar permeability of transparent
sheet (0.99)
: Reflectivity of aluminium cover (0.3),
: Area of bottle face (m2)
Calculation of water temperature by formulas:
( Ka ) ( kb ) ( kc )
( kd )
.
=
+
.
+
.
=
(1)
Thermal transmittance coefficient of insulation sides and back (2)
Thermal transmittance coefficient of transparent sheet (3)
(2)
(3)
: Thickness of polystyrene foam (m) (0.06),
: Thermal conductivity of
polystyrene foam(w/m.
)(0.037)
: Thickness of transparent sheet (m) (0.0001),
: Thermal conductivity of
transparent sheet(w/m.
)(0.19)
: Exterior surface coefficient of heat transfer (w/m.
) (11) (Close as tightly as factory
product)
: Interior surface coefficient of heat transfer (w/m.
) (11)
: Thermal resistance of closed air gap (m.
) (0.09) (Close as tightly as handcraft
double wall)
The temperature of the water inside the bottle can be calculated from equation (1) and the
thermal transmittance coefficient of box walls and transparent sheet was calculated by equation
(2) and equation (3) respectively.
2.3 Thermometers and Data Logger arrangement
In this study a correlation method was used. By using Excel program for calculation of
the formulas and experiment on boiler under the direct sunlight, the correlation of the two ways
of calculation has been compared together. To calculate and record the temperature inside the
bottle, outside of the bottle and air temperature outside of the box, three thermometers used and
connected to the data logger to record the temperature data during the experiment. The data
logger recorded the temperature in a minute base.
3. Results and discussion
Two days of experiment has been don on the solar boiler after it was completed and
assembled together and the tilt angle for solar boiler was 30 degrees. The thermal sensors such as
thermocouple, pyrometer and data logger was connected to the surface of the bottle, back of the
bottle, inside the water, surface of the boiler, and back of the boiler and the data was recorded in
each minute.
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Also the water temperature was calculated from equation 1 and finally the results was
plotted in excel program and graphs was compared together.
Figure 3 show the comparison of estimated water temperature and experiment based
water temperature together.
The data has been recorded from 3:00 am till 17:00 pm in each minute. The water
temperature has been derived both from the practical experiment and from the equation (1) and
the result has been drawn in the Fig.3.
As it’s visible in the Fig.3, the water temperature recorded during the experiment is about
69.3˚C approximately 70˚C, and the highest temperature value which has derived from the
formula is 71.86
approximately 72
at 13:53 pm. The difference between the experimental
value and estimated value from the formula is not so much high, therefore it shows that the
formula have enough accuracy and also make sure that expected temperature of the water by
using thermal insulations in such manner is realistic and trustworthy.
4. Conclusion
From the experiment data and calculated data it can be concluded that the best boiler is
that one which can conserve heat energy and site recorded data be very close to the data
calculated by the formula. The different layers of the insolation prevented the heat transfer and
energy loss of the boiler very well. Different experiment has been done in designing the solar
boiler, but after when the results collected from the experiments, the solar boiler which has the
concave down dish inside had the best result in comparison to other solar boilers. This boiler rise
up the water temperature by about 10
degree more than ordinary solar boiler. Also it was
cleared that the formula for estimation of water temperature have a satisfactory and reliable
value, so it is possible to calculate the expected water temperature without doing experiment.
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In addition, the concave down dish used in the handmade solar boiler increased the
efficiency of the boiler by glinting the solar radiation to the opposite side of the water tank.
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