Review of Solar Cooker

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3.01
Introduction:

Solar energy is the gift of merciful
Allah for us. The devices in which food is easily an conveniently cooked with
solar energy the “fuel” instead of other fuels such as, coal, fire wood,
fissile fuels, natural yes, electricity are called solar cookers (or solar
evens). Solar cookers are an ideal addition to any kitchen wherever there are
predictable hours of sun many days of the year. For millions of people living
in and, fuel-scarce regions of the world.

Though at present solar devices are
general expensive, for Bangladesh some solar alternatives may have excellent
prospects and should give better value for money even now. In supplying low
temperature heat in the form of hot water for industry at the such places where
natural gas in not available. Since food is to be cooked and in the absence of
any alternative cooking fuel, it is impossible to step the rural people used of
the fuel wood, agricultural waste and dried cattle dung fro the purpose. If we
can make available solar cooker and suits the requirements it can offer a
partial solution to the multiple problem faced by the poor and the people
living in the Surry bell of the developing countries. It we can solar cooker is
properly developed, engineered and studies, introduced and proper education and
training provided can be used or a mass scale and will therefore relative hundreds
of millions of people f the world from suffering and hardship.

3.02
History of Solar Cooking:

 Initial people died not know how to make
cooking of food. They ate food in the condition in which they found it. When
the initial people contrived the devised of inflaming the fire, then they filed
to control it and used to cook food. Fire is essentially solar power stored in
the form of wood.

Looking for the beginnings of what
are now call solar cooking, we find some isolated history in the distant past. The
first known person to build a box to cook food by solar satiation was Hoare do Assure,
a Sunnis naturalist. He cooked fruits in a primitive box type solar cooker that
reached temperatures of 1990⁰F. He is known to be grand father of
solar cooking. During this time, others also started using solar coopers. In
India, a British solder patented a fairly sophisticate solar cooker that looked
a lot like the solar chef. In 1894 there was a restaurant in China that served
solar cooked food. Cookers we see today started evolving in the 1950s. Our
world was till reeling from the intensity of war. People were looking for ways
to create a stable and peaceful future. The worldwide nature of the previous
war should, in some ways for the first time, that we are a world community
facing global problems that affect all us.

One of these global problems was the
growth of deserts around arid communities. The United Nations and other major
funding agencies initiated many studies to design solar cookers that could elevate
some of the reliance or plant life for fuel. Many top engineers of the 1950’s
were hired to study different aspects of solar cooking designs. The UN then
sponsored studies and programs to introduce these cookers into cultures where
the need was most apparent. These efforts proved mostly unsuccessful. In one
study, 500 wooden solar cookers were given to a refuge camp. There months later
they had been chopped up and used for fire wood. The social scientist concluded
that traditional cooking method, were too, culturally ingrained, and people
were unwilling to adapt.

The UN did note one success, In a
Northern Mexican community lacking fuel wood; they found that the cookers were
still in use five years later. This showed that it was possible to get cookers
out to people in need.

Others felt that the promotion
techniques used in the UN studies were also flared. Social scientists, who had
never integrated solar cooking into their own lives, were in charge of the UN
studies. The cookers were promoted as a solution to poor peoples problems. But
certainly not as cooking tools that would be useful in developed countries.
This cased solar cookers to be looked upon as a second class – 1001 by those
buying asked to use them. Solar cook sought new wags to promote solar cookers
that were more sensitive to the cultures they were trying to there them with.

3.03
Review of previous works or Solar Cooker:

The first deference in the use of
solar every for food preparation relates to even Horase de Saussure, a Suiss
naturalist (1740-1790). The temperature of 88⁰Cwas achieve.

In 1837, John Herchel used a solar
over whose temperature was recorded at 116⁰C.

In 1876, Adams made a solar cooker
using flat-glass mirrors managed in an 8-suded paramedical structure. Abbot
(1939) built a solar over using a cylindrical parabolic reflect for to focus
sunlight or to a blacker pipe enclosed in a glass tube.

Telkes in U.S.A, designed a solar
oven. The talkes cylindrical solar over was considerably improved by Pardya and
Gary and extensive trials have been conducted or the same both at Ahmedabad and
Jodhpur in India.

Ghosh undertook the development of a
simple box cooker in India and the temperature of 120⁰C were
reported.

The German Approximate technology
exchange (GATE) published a report in 1978 describing 17 solar cookers together
with an evaluation of their usefulness in the view of the consumer.

In 11 July 1987, the Solar Coker
International (SCI) was formed in Sacramento USA, which

• is
  an international clearinghouse for information or solar cooking devices,
  uses and dissemination.
• Provides
  training an develops educational materials.
• Consults
  or the adoption of devices and cooking methods to local conditions.
• Facilities
  regional collaboration among 500 independent groups that promote solar
  cooking through conferences, periodicals and electronic media.
• Rarely
  funds or manage solar cooking projects in the field, except occasional
  research and pilot demonstration projects.

SCI support
comes mostly from individual donations: others sources are soles of cooker and
education materials, fees for training, and grants from private foundations.

The Archives of
Solar Cooker International

Figure-3.1:
Joe Froese’s large institutional oven

Figure-3.2: A
Collapsible Solar Box Cooker

 

 Figure-3.3: The Heaven’s Flame Cooker

Figure-3.4: The
Reflective Open Box Cooker

 Figure-3.5: Panel Cooker

 

 Figure-3.6: Box Cooker

  Figure-3.7: Parabolic Cooker

3.4
Reasons for Deserving Attention of Solar Cooker:

(1)   One-fourth of humanity suffers fuel
scarcities. Half of the world cooks with wood. Accelerating wood shortage in
many countries add new burdens to families, particularly in eastern and
southern Africa, Families must be fed every day.

Rural women of all ages including
those whose are pregnant and have infants, the elderly and very young girls who
should in school spend more time and walk ever longer distances to find, than
carry, heavy loads of wood.

Many families are unable to cook
nutritious foods such as beans and maize, which require hours of cooking, and
substitute less nutritious, faster cooking foods such as pasts.

Families are
also less able to heat/ pasteurize their water and milk to reduce water borne-diseases,
the major killers of children. Solar cookers easily cook most foods and
pasteurize milk and water. Fuel gathering is one factor in the tide of
migration to cities. A rural Zimbabwean summed up the possibilities. “Today
many young Zimbabwe women don’t want to stay in rural areas because gathering
fuel wood is so difficult and time consuming. Solar cookers can make rural life
easier for women so they’ll want to stay there.” The annual per capita wood
consumption for cooking in most parts of the world is about .5 ton (1.32 kg per
day), or about 3 tons per family of six people. A solar cooker can save on ton
of wood per year.

The cost to
replace cut trees in India is double the market price of cut wood. Many
governments including Zimbabwe and Kenya import and subsidize less sustainable
fuels at great expense.

(2)   Current cooking methods are unhealthy,
unsustainable and unavailable to future generations.

* Cooking with fire means fire hazards
and dangers of burns for small children.

* Smoke causes lung and eye diseases.

* Future generations will have fewer
options.

(3)   Improved solar cookers and training

Historically most solar cookers were
either curved parabolic reflectors focusing intense heat onto a single pot, or
heat trap boxes with a window on the top or one or several flat reflectors.
Both types were too expensive for most people, cumbersome and sometimes even
dangerous to use.

A wide variety of new solar cookers
are more convenient, much lower-priced, and now competitive with alternatives
such as wood, charcoal, and woo stoves, one such model, an open reflector, has
been widely tested and has proven useful in the USA, Kenya and Zimbabwe. It
pays for itself in fuel savings in two months or less and becomes a recurrent
economic benefit to individual households.

Developed in 1994 by an
international team of volunteers and dubbed the “Cook it”, it is ideal for
introducing the basics of solar cooking. It is easily hand-made and also is being
mass-produced in USA, Kenya and Zimbabwe with modifications to suit local needs
and climates.

Participative
instruction quickly teaches solar cooking skills and trains local women to
solar teach their neighbors.

Many
millions are waiting for the simple, life-long skill that they can pass on to
future generations.

2.6
Reduction of inequities through the use of solar box cookers:

Many of the world’s people are
confronted by staggering inequities in matters of health, environmental
quality, economics and personal and political freedoms. The inequities tend to
be interrelated; consequently many people are forced to live in abject poverty.

Inequities
Health:

The general
unavailability of health care and family planning services in the third world has
exacerbated many chronic health conditions. Several billion people suffer
regular bouts of diarrheal illness because of the lack of clean water. Many
suffer respiratory and eye ailments because of the extremely smoky cooking
conditions, which are equivalent to smoking 10-20 packs of cigarettes per day.
A great deal of malnutrition is caused by the lack of food, the under-cooking
of food (because of the shortage of fuel) and the practice of single pot
cooking which means that separate weaning foods cannot be prepared. As a
result, 14 million young children die each year and the life expectancy in many
countries is less than 50 years.

Environment

Unequal
distribution of energy sources is causing environmental degradation in the
third world. Even though- the third world consumes little energy compared to
the first world, 90% of its energy is used for cooking food. Already, 1/4 of
humanity is affected by a fuel wood shortage; by the year 2000 the shortage
will affect at least 2.4 billion people (UN/FAO estimate). The ensuing
deforestation causes soil erosion, water pollution, a loss of soil fertility,
and ultimately, desertification. Sub-Saharan Africa is a graphic example of the
process.

Economics

Many of the
third worlds people are trapped in a vicious economic cycle of poverty because
of their low income and lack of land ownership. Many families are forced to
spend more on cooking fuel than they are able to spend on food. Third world
governments are unable to assist their poor citizens because of the high interest
rates attached to their foreign debts accumulated in the past decade.

Freedoms

The poor of the
world are further impoverished because of a lack of personal and political
freedoms. In our terms, they endure a subhuman existence. Many people suffer at
the hands of oppressive governments and are victimized by the prevailing (male)
attitudes and cultural practices. Almost universally, the poor of the world,
and especially the women, are enslaved to the processes of fuel collection and
cooking. Very few are literate; most receive less than a third-grade education.

Solutions

Gloomy as the
above situation may seem, there is hope for the poor of the world. There must
be hope, or else humanity will perish. Many of the more fortunate people in the
world are developing programs and strategies to balance the scales and reduce
the inequities, which
separate humans.

We have learned
in the past 14 years that a simple cooking device, the Solar Box Cooker (SBC),
can ameliorate each of the inequities cited above. SBCs can serve as focal
point to catalyze the attainment of many objectives in international
development programs.

Health

The SBC can
improve health in the third world in numerous ways. It can be used to
pasteurize water, by heating it to 65C (150F), thereby reducing the incidence
of diarrheal illnesses. The SBC is smokeless; its use will reduce the incidence
of respiratory and eye ailments. It can even be used to disinfect medical
instruments, as such it could be of significant benefit in many poor areas; it
can even destroy the AIDS virus. Importantly, several pots of food can be
cooked simultaneously, permitting separate preparation of weaning foods. All
foods can be thoroughly cooked, thereby aiding digestion and enhancing nutrient
absorption. Breadstuffs can be baked in an SBC, yielding foods, which have some
degree of stability.

Environment

Use of the SBC
will reduce dependence on fuel wood and charcoal. Reduced rates of
deforestation will yield reduced rates of soil erosion. In many villages there
is a complete lack of fuel wood and the people have resorted to burning dried
animal dung or crop residues. These practices deprive the soil of much of its
potential fertility. Use of the SBC minimizes the burning of dung and crop
residues, thereby permitting those materials to be used as natural fertilizers.

Economics

Much of the
expense of fuel wood, charcoal or kerosene can be eliminated through the use of
an SBC. The SBC also requires a low capital outlay; it can be built for about
$20, an amount equivalent to one or two weeks of cooking fuel purchases. The
SBC should be a useful tool to stimulate economic development in poor areas. It
is ideally suited to low -technology cottage industries. Because of its
relatively low cost, revolving loan funds could help spread the SBCs quickly.

Freedom

For many, the
SBC is a significant labor-saving device since less time would need to be spent
in accumulating and transporting fuel wood or dung. A project leader in
Guatemala said, The Solar Box Cooker can liberate women from millennia of
slavery. The saved time can be used for education, better family care, and food
production. In turn, greater economic and political freedoms will follow.

We are living
and participating in a very strange system. Humanity has one foot stepping towards
the stars, while the other is mired in a sinking sea of poverty. The distance
between humanity’s two feet is growing. We can help reverse the process by
teaching several billion people in the Third World how to build and use solar
box cookers.

Analytical and Comparative Studies for Box-type Solar
Cooker

4.1
Introduction:

Foods
are easily and conveniently cooked with solar energy as the “fuel” in device
called solar cookers (or solar ovens). Solar cookers are an ideal addition to
any kitchen wherever there are predictable hours of many days of the year.
Although solar cookers have been there topic of research forever the last 200
years, there has been standard last provide for thermal rating of solar
cookers. Exact thermal analysis of the Box & Trolley Type Solar Cooker is tedious.
The complete thermal analysis is complex due to the 3-dimensional transient
heat transfer involved.

Box and Trolley type solar cookers
are suitable mainly for the boiling type of cooking the cooking temperature in
this case is close to 100⁰c. A large function of the mass of most
food presents is water and more water may be added in the boiling type of
cooking.

Performance of the cookers has been
made using the analytical technique is terms of the Figures of merit of cookers.
F₁ and F₂. Relative performances of the cookers have also
been studied by testing a member of cookers on the same over the same period of
time results of such studies are described below.

4.2
Analytical studies for Determining the First Figure of Merit F₁:

So obtain the first figure of merit
F₁, the stagnation temperature, ambient temperature and global
radiation are required equation

 F₁=

The stagnation temperature was
measured with the help of a thermocouple thermometer inside the cooker without
any load under different conditions of the sky of different days. The ambient temperature
was measured by another alcohol thermometer. The global radiation was measured
by an Eppley PSP Pyrarometer.

The below table-4.1 shows a set of
typical data determining the stagnation temperature of a Box type cooker i.e.,
the stagnation temperatures of the black painted absorber tray inside the
cooker without load obtained or 14 January 2008.

Table-4.1:
Typical data for the determination of the stagnation temperature (Cooker – Box
type) 14^th January 2008.

Local time	Absorber temperature	Average stagnation temperature	Ambient temperature	Average global radiation at stagnation condition	Global radiation	Average global radiation at stagnation condition	Sky condition
	0c	0c	Ta0c	Ig(w/m2)	Ig(w/m2)		Clear
9.30	24		26		625		Clear
9.40	32		26		570		Clear
9.50	49		26		552		Clear
10.00	58		26.5		612		Clear
10.10	67		26.5		606		Clear
10.20	82		26.5		624		Clear
10.30	89		27		624		Clear
10.40	91		27		630		Clear
10.50	92		27		630		Clear
11.00	93		27		654		Clear
11.10	93.5	83.39	27	27.14	654	605	Clear
11.20	94		27		642		Clear
11.30	95.5		28		649		Clear
11.40	96		28		558		Clear
11.50	97		28		558		Clear
12.00	98		28		547		Clear
12.10	98		28		544		Clear
12.20	97		28.5		544		Clear
12.30	97		28		538		Clear
12.40	96		27		537		Clear
12.50	94		27		532		Clear
01.00	93		27		531		Clear

For
cooker-1

  Absorber
Temperature

  Global Radiation

 
Ambient Temperature

Figure- 4.1:
Variation of the temperature of the black painted pot (without load) with time
of the day 14^th January 2008.

For the experiment,
the solar cooker was kept facing the sun at 9.30 and the date collection of the
experiment started at the time. From the table 4.1, it is seen that the maximum
temperature remains practically near the hour and the average stagnation
temperature was 83.39⁰c the Global radiation was on the average 605
w/m² and the average ambient temperature was 27.140c over the same
time period.

The figure 4.1 indicates the
variation of the inside temperature of the empty, cooker with time of the day
or 14^th January 2008. The Global radiation as well as the ambient
temperature at different time of the day is also shown in fig 4.1.

The table shows the values of the
stagnation of the cooker and corresponding ambient temperature and irrolation.
The figure of merit temperature and insolation. The figure of merit F₁
calculated from F₁==

=

4.3
Analytical studies for Determining the Second Figure of Merit, F₂

The Second Figure of merit F₂
determined from the expression.

F₂= 

For the computation, the value of F₁
has been taken from the above calculation, and the produce of mass and heat
capacity of water (MC) was kept always the same for a set of measurement with,
M=mass of water, V=1000ml = 1000cc, m=rv=
(1gm/cc) (1000cc) =1000gm= 1kg and C=heat capacity of water = 4.21KJ/ Kg ⁰c
=4216J/⁰c.

The rest of the quantities of T_w1,
T_w2, T_a and t
have determined from experimental data of the day and corresponds to the aperture
area of each cooker. The upper limit of water temperature T_w2 could
have been taken 100⁰c the boiling temperature.

In the same way we have tabulated of
the data local time water temperature, ambient temperature and Global radiation
in the table 4.2 or 21^st November 2007.

The below Figure 4.2 shows the
global radiation with local time of the day or 21^st November 2007. I
have taker from the figure the average ambient temperature was found to be
Ta=27.23⁰C and the time interval between the temperature T_w1
and T_w2, t=5400
sec. We found average, global radiation I_g between the temperatures Tw1.
and T_w2 = 297.5 w/m². Aperture area of the glass 0.49 m²
F₂ was dtermined by using these above numarical vales. From the
equation.

Table-4.2:
Typical data for the determination of the stagnation temperature (Cooker – Box
type) 14^th January 2008.

Local time	Water temperature	Ambient temperature	Average ambient temperature	Global radiation	Average global radiation	Sky condition
	0c	0c	Ta0c	Ig(w/m2)	Ig(w/m2)
10.30	25.5	26		417		Clear
10.40	31	26		417
10.50	37	26		945
11.00	46	26.5		965
11.10	51.5	26.5		440
11.20	56	27		932
11.30	59	27		446
11.40	66	27		412
11.50	671	27		472	411.93
12.00	78	27.5		465
12.10	80	27.5	27.23	447
12.20	82	27.5		458
12.30	84	28		462
12.40	84.5	28		463
12.50	85	28		468
01.00	86	28		457
01.10	87	28		390
01.20	87.5	28		376
01.30	88	28		340
01.40	889	27		320
01.50	89.5	27		306
02.00	90	27		294
02.10	90.5	27		285

  Water in one pot 0.3 kg

Global radiation

Figure- 4.2:
Carves for the variation of water temperature in the utensils with time of the
day, on 21^st November 2007

The below Figure
4.2 shows the global radiation with local time of the day or 21^st
November 2007. I have taken from the figure the average ambient temperature was
found to be Ta = 27.23⁰c and the time interval between the
temperature T_w1 and T_w2, t
= 5400 sec. We found average global radiation (I_g) between the
temperatures T_w1. and T_w2 =297.5 m/m².
Aperture area of the glass 0.49 m².

F₂ was determined by
using these above numerical values. from the equation.

F₂=

=

=

=0.1482 ln

= 0.1482 ´ (-0.152293527)

=-0.023

This result
depends on the amount of load (water), performance of the cooker (i.e., stop
the heat loss), sky condition and the condition of the weather.

Table-4.3: Determination of the second
figure of merit, F₂ for different cookers with load of 2 Kg water

Date	Cooker Number	Lower temperature Tw1 (0C)	Upper temperature Tw2 (0C)	Average ambient temperature, Ta (0C)	Time interval l to reach from Tw1 to Tw2. (Sec)	Average global radiation for the time interval, Is (w/m2)	Aperture area of the glass, A (m2)	Depth of cooker (absorber tray)	Second figure or merit , F2
19.11.07	Cooker no- 1	60	90	28.2	5100	534	0.41	10.0	0.55
16.11.07	Cooker no-2	60	90	28.5	4440	599	0.29	9.5	0.60
20.11.07	Cooker no-3	60	90	28.5	4200	605	0.30	9.0	0.62

Table-4.4: Determination of the second Figure of merit, F₂ for different
cookers with load of 2 Kg water

Date	Cooker Number	Lower temperature Tw1 (0C)	Upper temperature Tw2 (0C)	Average ambient temperature, Ta (0C)	Time interval l to reach from Tw1 to Tw2. (Sec)	Average global radiation for the time interval, Is (w/m2)	Aperture area of the glass, A (m2)	Depth of cooker (absorber tray)	Second figure or merit , F2
22.11,07	Cooker no- 1	60	90	28.8	3300	647	0.41	10.0	0.26
20.11.07	Cooker no-2	60	90	28.5	4500	587	0.29	9.5	0.33
22.11.07	Cooker no-3	60	90	28.0	2934	648	0.30	9.0	0.38

4.4. Comparative Studies on Box & Trolley-type Solar Cookers

Comparative
studies on different box-type solar cookers
with a load of 2Kg/ 1Kg of water
were made by using a graphical representation.

Fig. 4.5:
Curves for the variation
of water temperature -with time,
of the day, on 20-11-2007, Cookers no. 1 & 3. 2007, (Coolers
no.-1 & 3)

Local time of the day, (Hours) ®

Fig. 4.3 shows the curves for the variation of water temperature
of cooker nos. 1 and 2 with time of the day as measured on 16-11-2007 with 2Kg
of water. It is evident that the rise in temperature of water of cooker no. l
is faster than that of cooker no. 2. The time required to reach the water
temperature from 60°C to 90°C is 70 min. for cooker no. l and 77 min. for
cooker no. 2. The global radiation was on the average 606 w/m² over
the time when water temperature was between 60°C and 90°C for cooker no. l and
599 w/m² for cooker no. 2.

Fig. 4.4 shows the curves for the variation of water temperature
of cooker no. l and 3 with time of the day as measured on 20-11-2007 with 2kg
of water. It is evident that the rise in temperature of water of cooker no. 3
is faster than that of cooker no. l.

The time required to reach the water temperature from 60°C to 90°C
is 70 min. for cooker no.-3 and 80 min. for cooker no. l.

The global radiation was on the average 605 w/m² over
the time when water temperature was between 60°C and 90°C for cooker no. 3 and
597 w/m² for cooker no. l

Fig. 5.6: Curves for the variation of
water temperature with time, of the day, on 09-11-2007, Coolers no. 1 & 2.

Fig, 4.5 shows the
curves for the variation of water temperature of cooker nos. 1 and 2 with time
of the day as measured on 09-11-2007 with 1kg of water. It is evident that the
rise in temperature of water of cooker on,-l is faster than that of cooker
no.-2. The time required to reach the water temperature from 60°C to 90°C is 35
min. for cooker

no.-l and 40 min. for cooker no.-2. The global radiation was on the average 578
w/m² over the when water temperature was between 60°C and 90°C for
cooker no.-l and 522 w/m² for cooker no. 2.

Fig. 4.7: Curves for the variation of
water temperature with time, of the day, on 22-11-2007, (Coolers no. l &
3).

Fig. 4.6 shows the curves for the variation of water temperature
of cooker no.-l and cooker no.-3 with time of the day as measured on 22-11-2007
with 1Kg of water. It is evident that the rise in temperature of water of
cooker no.-3 is faster than that of cooker no.-l. The time required to reach
the water temperature from 60°C 90°C is 48 min. for cooker no. 3 and 55 min.
for cooker no.-l. The global radiation was no the average 648 w/m²
over the time when water temperature was between 60°C 90°C for cooker no.-3 and
647 w/m² for cooker no.-l.

Fig. 4.6 shows that the rise in temperature of water of cooker
no.-3 is faster than that of cooker no.-l when 1Kg of water is kept in each pot
as has been shown before. But Fig. 5.12 shows that the rise in temperature of
water of cooker no.-l is faster than that of cooker no.-3 when 1Kg of water was
placed in two pots inside cooker no.-l while the same amount of water was
placed in one pot in cooker no.-3.

Cooking Tests for the Box & Trolley-type solar Cooker

5.1.
Cooking Tests

Different
articles of food (vegetables, rice and dal) were cooker on different days and
the time taken for cooking was obtained. Generally, cooking started between
9:30 and 11:00 a.m. During the determination of cooking time, the global
radiation and the ambient temperature were also measured. Table-5.1 shows that
the time required for cooking different items. It has been found that 400 gm of
water should be added to 250 gm of rice and to 200 gm of pluses, 300 gm of
water might well be used with 250 gm of vegetable. No attempt was made to cook
meat but one expects that this would not take much longer to cook. From 93
cooking tests over the year time schedule given Table-5.2 is recommended for
cooking rice, vegetables and pulses.

Table-5.2
indicates that for sunny days cooking generally should not required more than 2
hours and for semi cloudy days it should be within 3 hours. Dhaka has an annual
average daily insolation of around 4.7 KWh/m
and even with the medium level of radiation solar cooking is practical
in Bangladesh.

From
the sunshine date of the Meteorological Department of Bangladesh for one year,
it is seen that sunny days are very common for eight months of the year as shown
in Table-5.3. The other four months of the year (i.e. June to September) are
often cloudy, that is radiation remains bad and cooking is hardly possible with
the help of our box-type solar cookers in these months.

From
our experience we find that cooking is generally not possible if sunshine
duration is less than 3 hours from 10 a.m. to 3 p.m. and 4 hours from 9 a.m. to
3 p.m. Table-5.3 shows that for around 100 days in a year cooking may not be
possible. For around 240 days cooking of two meals per day should be possible
in Dhaka.

Table-4.4
gives the sunshine availability for the different stations in Bangladesh. It is
found that cooking should be possible for nearly number of days all over
Bangladesh. However, for Sylhet region the sunshine availability is a bit less
while for Chittagong region it is a bit higher. Table-5.5 shows the global
solar insolation at different cities in Bangladesh.

Table-5.1:
Cooking Time for different Items Under Various Conditions

Item	Quantity (gm)	Amount of water added (cc)	Average ambient temperature (OC)	Average G (w/m2)	Condition of the sky	Cooking Time (hour)
Vegetables	150	350	28.0	515	Semi-Cloudy, Clurdy	3
Rice	250	400	25.2	640	Semi-Cloudy, Clear	2
Pluses	200	400	25.0	580	Clear	1.5
Rice	250	500	25.0	580	Clear	1.5
Rice	250	400	24.6	585	Clear	1.7
Dal	200	400	24.3	550	Clear	1.5
Vegetables	250	300	24.1	560	Clear	1.7
Rice	250	400	24.3	700	Clear	1.3
Rice	250	400	23.5	535	Clear, Semi-Cloudy,	1.3
Rice	250	400	23.0	300	Semi-Cloudy, Cloudy	2.5
Rice	250	400	21.0	535	Clear	1.5
Rice	250	500	27.0	655	Clear	2

Table-5.2:
Recommended Cooking Time in Hours

No. of pots	Period	Sky condition
		Clear	Semi – Cloudy
1 pot- 0.75 Kg	Oct-Feb Mar – May Jun – Sep	3/4 iV2 i’/4	2 2 2
2 pot-1.50Kg	Oct – Feb Mar – May Jun – Sep	2 iV2 i’/2	2’/2 2 2
3 pot-2.25 Kg	Oct-Feb Mar – May Jun – Sep	2V4 2 2	23/4 2’/2 2
4 pot-3.00Kg	Oct-Feb Mar – May Jun – Sep	21/, 2V4 2	3

Taable-5.3:
The Sunshine Availability Over the Months (Station of Dhaka – 2007)

Month	No. of good days S.S. hrs > 3 hrs. (10 am to 2 pm) S.S.hrs.>4hrs. 9 am to 3 pm	No. of fair days S.S. hrs. < 3 hrs. (10 am to 2 pm) S.S, hrs. < 4 hrs. (9 am to 3 pm)	No. of bad days S.S. hrs. < 3 hrs. (10 am to 2 pm) S.S. hrs. < 4 hrs. (9 am to 3 pm)
January	28	–	3
February	25	3	1
March	23	2	6
April	26	1	3
May	23	1	7
June	9	1	20
July	5	–	26
August	13	1	17
September	12	5	13
October	18	3	10
November	30	–	–
December	27	2	2
Total	239	19	108

Table-5.4:
The Sunshine Availability in Bangladesh (2007)

Metrological Department Stations	No. of good days S.S. ks.> 3 hrs. (I’O am to 2 pm) S.S. hrs.> 4 hrs. (9 am to 3 pm)	No. of fair days   S.S. hrs. <3 hrs. (10am to 2 pm) S.S. hrs. < 4 hrs, (9 am to 3 pm)	No. of bad days S.S. hrs. < 3 hrs. (10 am to 2 pm) S.S. hrs. < 4 hrs. (9 am to 3 pm)
Dhaka	239	19	108
Jessore	250	5	111
Barishal	242	6	118
Sylhet	236	4	126
Chittagong	282	3	81
Bogra	260	9	97

Table-5.5:
Monthly Global Solar Insolation at different cities of Bangladesh (in KWh/m²/dav)

Month	Dhaka	Rajshahi	Sylhet	Bogra	Barishal	Jessore
January	4.03	3.96	4.00	4.01	4.17	4.25
February	4.78	4.47	4.63	4.69	4.81	4.85
March	5.33	5.88	5.20	5.68	5.30	4.50
April	5.71	5.24	5.24	5.87	5,94	5.23
May	5.71	6.17	5.37	6.02	5.75	5.09
June	4.80	5.25	4.53	5.26	4.39	5.12
My	4.41	4.79	4.14	4.34	4.20	4.81
August	4.82	5.16	4.56	4.84	4.42	4.93
September	4.41	4.96	4.07	4.67	4.48	4.57
October	4.61	4.88	4.61	4.65	4.71	4.68
November	4.27	4.42	4.32	4.35	4.35	4.24
December	3.92	3.82	3.85	3.87	3.95	3.97
Average	4.73	5.00	4.54	4,85	4.71	4.85

Source:
Dr. Shahida Rafique, Dhaka University, recorded from 1988 to 1998.

5.2.
Discussions

In the Several box type solar
cookers have built and analytical and comparative studies were made and cooking
tests have also been performed.

According
to S.C. Mullick et al. has specified that suitable minimum value of the first
figure of merit fi would be
probably between 0.12 and 0.16, depending on the climatic condition of the
country.

For
Bangladesh a lower permissible limit of the value of fi may be specified to ensure a minimum level of thermal
performance. To rise the plate temperature of the cooker up to 11TC, in winter
season, when the radiation around noon for a semi cloud) day is generally above
550 W/rn² and the ambient temperature is 26°C or so, we obtain the value
of F₁ as

F₁=

following
the prescription of Mullick for the stagnation temperature T_ps (111⁰C).
This gives the minimum value of F₁
for the cooker to work throughout the year. The measured value of F₁ is 0.17 for cooker no.-2 & 3 and
0.16 for cooker no.-l.

To
find the effect of the number of glass covers on the performance of the cover
measurements of fi were made also
with a single glass cover for cooker no.-2 in place of usual double covers. The
value of fi was found to be lower
0.16, for cooker no.-2. This F₁ appears to decrease by a small
amount.

I
have found from my experimental results that the value of F₁ for my
cookers satisfy the minimum requirements.

The
second figure of merit F₂ is equal to F₁ (FUO, where F’ is the heat exchange
efficiency factor and ul is the
heat joss co-efficient. S.C. Mullick et al. obtained a value of F₁ =
0.254 using 1Kg of water in. 4 cooking pots for their cooker.

My
experimental results for the cookers (no.-l, 2 and 3) gave the value of F₂
between 0.44 and 0.62 using 2Kgmass of water in two cooking pots. The results
have been show in Table-4.4.

It
found that F₂ values for 1kg of water are nearly half of that for
2Kg. This shows from equation- 12 that the heat capacity of water, utensil and
inside cooker parts (MC)’_W is doubled when water mass is doubled.
This happens as the heat capacity of utensil and cooker parts are small
compared to that of 1Kg water.

Measurements
of F₂ were also made with 2Kg of water in 1 pot for a few cookers
(no.-l, 2 & 3). The results have been presented in Table-4.5. The values
are between 0.26 and 0.38.

To
find the effect of the number of glass covers on the performance of the cooker
measurements of F₂ were made with a single glass cover for cooker
no.-2 with 1Kg of water in 1 pot. The value of F₂ was found to be
0.31 for cooker no.-2 in place of 0.3″ with two covers. This F₂
appears to decrease by a small amount. The decreasing F₁ and F₂ may be considered due
to increase in heat loss for a single glass cover.

From
a perusal of comparative studies of all the cookers it has

found
in chapter 5 that for cooker no.-l the temperature of water increases more
rapidly compared to the cooke-no,-2. The temperature of water increases faster
for cooker no.-3 than cooker no.-l. I was also found that if 1Kg of water is
placed in two pots in place of 1 pot, the temperature of water increases
faster.

It
is found from analytical studies that F₁ and F₂ values
are highest for cooker no.-3 and comparative studies show that it could
fastest. It is seen from analytical studies that cooker no.-2 has higher F₁ and F₂ values (F₁==0.17,
F₂=0.60) compared to those for cooker no.-l (F₁=0.l6, F₂=0.53).
But from comparative studies it is well visualized that cooker no.-l is better
than cooker no.-2 as it cooks faster.

From
Table-5.4, it is seen that time taken to reach the water temperature from 60°C
to 90°C was 5100 seconds, while the global radiation and the ambient
temperature were 534 W/m² and 28.2°C. Now if we compute the time
taken (equatioh-10) by cooker no.-2 to reach 90°C from 60°C for the same
radiation and ambient temperature we find tfetat the time required is 5854
seconds.

Rice,
vegetables and dal were cooked on different days by using cooker no,-2 & 3
occasionally while 53 cooking tests were successfully completed over the year
by using cooker no.-1 in the Govt.
Bangla College Solar Park.

From
the study of the chapter 4 it can be concluded that the performance of the
cooker no.-3 is good compared to cooker no.-1 & 2 when there will be bright
sunshine hour.

In
the conclusion I would like to suggest that cooker no.-3 is most suitable to
use when bright sunshine prevails. It is recommended that cooker no.-3 may be
manufactured for remete areas in Bangladesh where electricity is not available.
For saving energy, ensuring clean and unproved living environment Government,
semi-government, non­ government and public Ltd. Organizations should take
efficient steps to sncourage and use solar cooking.

The
cost of fabrication of my suggested cooker is too cheap compared to its
longevity that most people can Use it without any financial help from any
organizations. It is our duty to ensure healthy -and potential world for the
next generation, which requires clean energy consumption.

APPENDIX-A

Approximate
cost of cookers

Cooker
No.-l

Wood for casing	=	Tk. 800.00
Glass wool (3Kg)	=	Tk. 350.00
G.I. sheet absorber tray	=	Tk. 250.00
G.I. sheet made trolley (with making charge)	=	Tk. 500.00
Two glass covers	=	Tk. 300.00
Black paint	=	Tk. 100.00
Four cooking pots (blackened)	=	Tk. 200:00
Making charge including gasket foam, soft foam, etc.	=	Tk. 300.00
Booster mirror	=	Tk. 200.00
Total =   Tk. 3000.00

Cooker
No.-2

G.I. sheet frame	=	Tk. 300.00
Wooden frame	=	Tk. 200.00
Glass wool (2.75Kg)	=	Tk. 325.00
G.I. sheet absorber tray	=	Tk. 250,00
G.I. sheet made trolley (with making charge)	=	Tk. 500.00
Two glass covers	=	Tk. 300.00
Black paint	=	Tk. 100.00
Four cooking pots (blackened)	=	Tk. 200.00
Making charge including gasket foam, soft foam, etc.	=	Tk. 300.00
Booster mirror	=	Tk. 200.00
Total = Tk. 2675.00

  Cooker
No.-3

G.I. sheet frame	=	Tk. 300.00
Wooden frame	=	Tk. 200.00
Glass wool (3Kg)	=	Tk. 350.00
G. I Sheet absorber tray	=	Tk. 350.00
G. I Sheet made trolley (with making charge)	=	Tk. 500.00
Two glass covers	=	Tk. 300.00
Black paint	=	Tk. 100.00
Four cooking pots (blackened)	=	Tk. 200.00
Making charge including gasket foam, soft foam, etc.	=	Tk. 300.00
Booster mirror	=	Tk. 200.00
Total = Tk. 2700.00

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