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REVIEW OF SOLAR COOKER

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 88 0Cwas achieve. In 1837, John Herchel used a solar over whose temperature was recorded at 116 0C.


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)

(3)

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.

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 100 0c. 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 F 1: So obtain the first figure of merit F 1, the stagnation temperature, ambient temperature and global radiation are required equation F1=

T ps −Ta Ig

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) 14th January 2008.

Local time

Absorbe r temperat ure

Average stagnation temperatur e

Ambient temperat ure

0

0

Ta0c

c

9.30 9.40 9.50 10.00 10.10 10.20 10.30 10.40 10.50 11.00 11.10 11.20 11.30 11.40 11.50 12.00 12.10 12.20 12.30 12.40 12.50 01.00

24 32 49 58 67 82 89 91 92 93 93.5 94 95.5 96 97 98 98 97 97 96 94 93

c

83.39

26 26 26 26.5 26.5 26.5 27 27 27 27 27 27 28 28 28 28 28 28.5 28 27 27 27

Average global Global radiation at radiati stagnation on condition Ig(w/m Ig(w/m2) 2 ) 625 570 552 612 606 624 624 630 630 654 27.14 654 642 649 558 558 547 544 544 538 537 532 531

Average global radiation at Sky condition stagnation condition Clear

605

Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear Clear 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 14th 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 83.39 0c 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 14th 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 F 1

calculated from F1=

=

T ps −Ta Ig

=

83.39 − 27.14 = 605

56.25 = 0.093 605

4.3 Analytical studies for Determining the Second Figure of Merit, F 2 The Second Figure of merit F2 determined from the expression.


F2=

( MC ) w ∆Tw AJ

Tw2

∑ Tw1

    1   I − 1 (T −T )  g w a   F1  

For the computation, the value of F 1 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=ρv= (1gm/cc) (1000cc) =1000gm= 1kg and C=heat capacity of water = 4.21KJ/ Kg 0c =4216J/0c. The rest of the quantities of Tw1, Tw2, Ta and τ 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=27.23 0C and the time interval between the temperature Tw1 and Tw2, τ=5400 sec. We found average, global radiation Ig between the temperatures Tw1. and T w2 = 297.5 w/m2. Aperture area of the glass 0.49 m 2 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) 14th January 2008. Local time 10.30 10.40 10.50 11.00 11.10 11.20 11.30 11.40 11.50 12.00 12.10 12.20 12.30 12.40 12.50 01.00 01.10

Average Water Ambient ambient temperature temperature temperature 0 0 c c Ta0c 25.5 26 31 26 37 26 46 26.5 51.5 26.5 56 27 59 27 66 27 671 27 78 27.5 80 27.5 27.23 82 27.5 84 28 84.5 28 85 28 86 28 87 28

Global radiation Ig(w/m2) 417 417 945 965 440 932 446 412 472 465 447 458 462 463 468 457 390

Average global radiation Ig(w/m2)

Sky condition Clear

411.93


01.20 01.30 01.40 01.50 02.00 02.10

87.5 88 889 89.5 90 90.5

28 28 27 27 27 27

376 340 320 306 294 285

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 = 27.23 0c and the time interval between the temperature T w1 and Tw2, τ = 5400 sec. We found average global radiation (Ig) between the temperatures Tw1. and Tw2 =297.5 m/m2. Aperture area of the glass 0.49 m2. F2 was determined by using these above numerical values. from the equation.

 1  T − Ta   1 −  w 2   F1 ( MC ) w  F1  I g  ln  F2=  AJ 1 − 1  Tw1 − Ta    F1  I g   


=

F1 ( MC ) w  F1 × I g − ( Tw 2 − Ta )  ln   AJ  F1 × I g − ( Tw 2 − Ta ) 

=

0.093 ×1× 4216  0.093 × 297.5( 280 − 27.23)  ln   0.49 ×5400 0.093 × 297.5 − (78 − 27.23) 

 27.67 − 0.77   =0.1482 ln   27.67 − 50.77  = 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, F 2 for different cookers with load of 2 Kg

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

water

19.11.07 16.11.07 20.11.07

Cooker no- 1 Cooker no-2 Cooker no-3

60 60 60

90 90 90

28.2 28.5 28.5

5100 4440 4200

534 599 605

0.41 0.29 0.30

10.0 9.5 9.0

0.55 0.60 0.62


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

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

water

22.11,07 20.11.07 22.11.07

Cooker no- 1 Cooker no-2 Cooker no-3

60 60 60

90 90 90

28.8 28.5 28.0

3300 4500 2934

647 587 648

0.41 0.29 0.30

10.0 9.5 9.0

0.26 0.33 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/m 2 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/m 2 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/m 2 over the when water temperature was between 60°C and 90°C for cooker no.-l and 522 w/m 2 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/m 2 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)

Average Amount of ambient Average G water added temperature (w/m2) (cc) (OC)

Vegetables

150

350

28.0

515

Rice

250

400

25.2

640

Condition of Cooking the sky Time (hour) Semi-Cloudy, 3 Clurdy Semi-Cloudy, 2 Clear


Pluses Rice

200 250

400 500

25.0 25.0

580 580

Clear Clear

1.5 1.5

Rice

250

400

24.6

585

Clear

1.7

Dal

200

400

24.3

550

Clear

1.5

Vegetables Rice

250 250

300 400

24.1 24.3

560 700

Rice

250

400

23.5

535

Clear 1.7 Clear 1.3 Clear, Semi1.3 Cloudy,

Rice

250

400

23.0

300

Semi-Cloudy, 2.5 Cloudy

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 Sky condition Clear

No. of pots

Period

1 pot- 0.75 Kg

Oct-Feb Mar - May Jun – 3/4 Sep iV2 i'/4

22 2

2 pot-1.50Kg

Oct - Feb Mar - May Jun – 2 Sep iV2 i'/2

2'/2 2 2

3 pot-2.25 Kg

Oct-Feb Mar - May Jun – 2V4 Sep 22

23/4 2'/2 2

4 pot-3.00Kg

Oct-Feb Mar - May Jun – Sep

3

Semi – Cloudy

21/, 2V4 2

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 February March April May June July

28 25 23 26 23 9 5

3 2 1 1 1 -

3 1 6 3 7 20 26


August September October November December Total

13 12 18 30 27 239

1 5 3 2 19

17 13 10 2 108

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 Jessore Barishal

239 250 242

19 5 6

108 111 118

Sylhet Chittagong

236 282

4 3

126 81

Bogra

260

9

97

Table-5.5: Monthly Global Solar Insolation at different cities of Bangladesh (in KWh/m 2/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/rn 2 and the ambient temperature is 26°C or so, we obtain the value of F 1 as F1=

T ps − Ta Is

=

111 − 26 = 0.15 550

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 F 1 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 F 1 appears to decrease by a small amount. I have found from my experimental results that the value of F 1 for my cookers satisfy the minimum requirements. The second figure of merit F 2 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 F 1 = 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 F 2 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 F 2 appears to decrease by a small amount. The decreasing F 1 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 F 1 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 (F 1=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/m 2 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 Glass wool (3Kg) G.I. sheet absorber tray G.I. sheet made trolley (with making charge) Two glass covers Black paint Four cooking pots (blackened) Making charge including gasket foam, soft foam, etc. Booster mirror Total = Tk. 3000.00 Cooker No.-2

= = = = = = = = =

Tk. 800.00 Tk. 350.00 Tk. 250.00 Tk. 500.00 Tk. 300.00 Tk. 100.00 Tk. 200:00 Tk. 300.00 Tk. 200.00

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

= = = = = = = = = =

Tk. 300.00 Tk. 200.00 Tk. 325.00 Tk. 250,00 Tk. 500.00 Tk. 300.00 Tk. 100.00 Tk. 200.00 Tk. 300.00 Tk. 200.00

= = = = = = = = = =

Tk. 300.00 Tk. 200.00 Tk. 350.00 Tk. 350.00 Tk. 500.00 Tk. 300.00 Tk. 100.00 Tk. 200.00 Tk. 300.00 Tk. 200.00

Cooker No.-3 G.I. sheet frame Wooden frame Glass wool (3Kg) G. I Sheet absorber tray G. I Sheet made trolley (with making charge) Two glass covers Black paint Four cooking pots (blackened) Making charge including gasket foam, soft foam, etc. Booster mirror Total = Tk. 2700.00

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61.

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62.

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Profile for Md Papon

Review of solar cooker  

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” i...

Review of solar cooker  

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” i...

Profile for md.papon
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