ABSTRACT
In recent years there has been an increased awareness to conserve energy through efficient use of fuels, energy saving devices and insulation against heat losses. Consequently, the construction of a rocket stove was undertaken in this research and the thermal property tests for ash and clay-sawdust insulation materials were carried out, after which the effect of these insulation materials on the thermal efficiency of the rocket stove was experimentally determined using cooking tests (water boiling test, control test and kitchen performance test). Both the ash and the clay-sawdust showed the ability to be used as insulators in the rocket stove; having low thermal conductivities (0.2W/mK and 0.16W/mK respectively), high specific heat (889J/kgK and 910J/kgK respectively) and low thermal diffusivity (3.67e-7/m2s and 1.58e-7/m2s respectively). When the ash and clay-sawdust were used in the rocket stove the thermal efficiency of the stove has a value of 21.6% and 22.28% respectively (for cold start), 46.34% and 44.06 % respectively (for hot start) and 20.00% and 23.91% respectively (simmering phase). This shows a great improvement when compared with the stove without insulation 10.86% (cold start), 17.70% (hot start) and 14.50% (simmering). The burning rate (5.30g/min, 5.24g/min for ash and clay-sawdust respectively, 10.72g/min for the stove without insulaion), firepower (2.36Watt and 2.34Watt for ash and clay-sawdust respectively, 5.25Watt for the stove without insulation) and specific fuel consumption (0.038 and 0.039 for ash and clay-sawdust respectively, 0.13 for the stove without insulation) all improved when there was insulation around the rocket stove. This shows that both ash and the clay-sawdust can be used as insulation material in the rocket stove and they improve the thermal efficiency of the rocket stove. The clay-sawdust insulated stove performed better than the ash insulated stove, having better thermal properties as shown above and gave better results when the water boiling tests were carried out.
TABLE OF CONTENTS
Content Page
DECLARATION ……………………………………………………………………………………………… II
CERTIFICATION ……………………………………………………………………………………………. III
ACKNOWLEDGEMENT ………………………………………………………………………………… IV
ABSTRACT …………………………………………………………………………………………………….. V
TABLE OF CONTENTS ………………………………………………………………………………….. VI
LIST OF TABLES …………………………………………………………………………………………… IX
LIST OF FIGURES …………………………………………………………………………………………… X
LIST OF PLATES ………………………………………………………………………………………….. XII
LIST OF APPENDICES ………………………………………………………………………………… XIII
NOMENCLATURE ………………………………………………………………………………………. XIV
CHAPTER ONE ……………………………………………………………………………………………….. 1
INTRODUCTION ……………………………………………………………………………………………… 1
1.1 BACKGROUND OF STUDY …………………………………………………………………………….. 1
1.2 STATEMENT OF PROBLEM ……………………………………………………………………………. 3
1.3 PRESENT RESEARCH …………………………………………………………………………………… 4
1.4 AIM AND OBJECTIVES …………………………………………………………………………………. 4
1.5 JUSTIFICATION …………………………………………………………………………………………… 5
1.6 SCOPE OF STUDY ……………………………………………………………………………………….. 5
CHAPTER TWO ……………………………………………………………………………………………….. 7
LITERATURE REVIEW ……………………………………………………………………………………. 7
2.1 INTRODUCTION ………………………………………………………………………………………….. 7
2.2 TYPES OF COOK STOVES ……………………………………………………………………………… 8
2.3 COMPONENTS OF ROCKET STOVE ……………………………………………………………….. 10
2.3.1 Combustion chamber …………………………………………………………………………. 10
2.3.2 Fuel Magazine ………………………………………………………………………………….. 11
2.3.3 Pot Seat ……………………………………………………………………………………………. 12
2.3.4 Grate ……………………………………………………………………………………………….. 12
2.4 ENERGY BALANCE IN A COOKING STOVE …………………………………………………….. 12
2.5 TYPES OF EFFICIENCIES IN A STOVE ……………………………………………………………. 13
2.6 REVIEW OF RELATED LITERATURES ……………………………………………………………. 14
2.7 RESEARCH GAP ……………………………………………………………………………………….. 21
CHAPTER THREE ………………………………………………………………………………………….. 22
MATERIALS AND METHODS ……………………………………………………………………….. 22
3.1 INTRODUCTION ………………………………………………………………………………………… 22
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3.2 THE STOVE DESCRIPTION ………………………………………………………………………….. 22
3.3 DESIGN SPECIFICATION …………………………………………………………………………….. 23
3.3.1 Considerations ………………………………………………………………………………….. 23
3.3.2 Material Selection for fabrication………………………………………………………… 23
3.4 EQUIPMENT FOR TESTING ………………………………………………………………………….. 24
3.5 DETERMINATION OF THERMAL PROPERTIES OF INSULATION MATERIALS …………. 24
3.5.1 Thermal Conductivity ……………………………………………………………………….. 24
3.5.2 Specific Heat Capacity ………………………………………………………………………. 25
3.5.3 Thermal Diffusivity …………………………………………………………………………… 26
3.6 DESIGN EQUATIONS …………………………………………………………………………………. 26
3.6.1 Combustion Chamber area (Ac) ………………………………………………………….. 26
3.6.2 Perimeter of the combustion chamber ………………………………………………….. 27
3.6.3 Gap between pot and combustion chamber (Gap A) ……………………………… 27
3.6.4 Pot Circumference (Cp) ……………………………………………………………………… 27
3.6.5 Gap at the edge of the Pot (Gap C) ……………………………………………………… 27
3.6.6 Gap between pot side and Stove body …………………………………………………. 27
3.6.7 Height of Combustion Chamber …………………………………………………………. 28
3.6.8 Thermal Efficiency ……………………………………………………………………………. 28
3.6.9 percentage Heat Utilised ……………………………………………………………………. 28
3.6.10 Burning rate ……………………………………………………………………………………. 29
3.6.11 Specific fuel consumption ………………………………………………………………… 29
3.6.12 Duration of phase ……………………………………………………………………………. 30
3.7 DESIGN CALCULATIONS ………………………………………………………………………… 30
3.8 METHODS ……………………………………………………………………………………………….. 32
3.8.1 Construction …………………………………………………………………………………….. 32
3.8.2 Material Testing (Thermal Conductivity and Specific Heat Tests) ………….. 33
3.8.3 Cooking test ……………………………………………………………………………………… 34
3.8.4 Water boiling test ……………………………………………………………………………… 35
3.8.5 Controlled Cooking Test (CCT) ………………………………………………………….. 39
3.8.6 Kitchen performance evaluation test ……………………………………………………. 40
CHAPTER FOUR ……………………………………………………………………………………………. 41
RESULTS AND DISCUSSION ………………………………………………………………………… 41
4.1 MATERIAL TEST ……………………………………………………………………………………….. 41
4.1.1 Results for material test ……………………………………………………………………… 41
4.2 WATER BOILING TEST ………………………………………………………………………………. 43
4.2.1 Cold Start …………………………………………………………………………………………. 43
4.2.2 Hot Start Phase …………………………………………………………………………………. 47
4.2.3 Simmering phase ………………………………………………………………………………. 50
4.3 DISCUSSION OF RESULTS FOR WATER BOILING TEST …………………………………….. 55
4.3.1 Percentage Heat Utilised (PHU)………………………………………………………….. 55
4.3.2 Firepower ………………………………………………………………………………………… 56
4.3.3 Burning rate (g/min) ………………………………………………………………………….. 57
4.3.4 Turn down ratio ………………………………………………………………………………… 59
4.4 VARYING OTHER VARIABLES ……………………………………………………………………… 60
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4.4.1 Different quantity of water …………………………………………………………………. 60
4.4.3 Varying the sizes of the wood …………………………………………………………….. 63
4.5 CONTROL COOKING TEST ………………………………………………………………………….. 67
4.6 KITCHEN PERFORMANCE TEST ……………………………………………………………………. 70
4.6.1 User Acceptability …………………………………………………………………………….. 70
4.6.2 External Need …………………………………………………………………………………… 70
CHAPTER FIVE ……………………………………………………………………………………………… 72
SUMMARY, CONCLUSION AND RECOMMENDATIONS ……………………………… 72
5.1 SUMMARY ………………………………………………………………………………………………. 72
5.2 CONCLUSION …………………………………………………………………………………………… 73
5.3 RECOMMENDATIONS ………………………………………………………………………………… 74
5.4 CONTRIBUTION TO KNOWLEDGE ………………………………………………………………… 74
REFERENCES ………………………………………………………………………………………………… 75
APPENDIX A: SPECIFIC HEAT FOR SELECTED FOODS (KULLA, 2011) ………. 78
APPENDIX B: WOOD SPECIES AND THEIR CHARACTERISTICS (KULLA, 2011) ………………………………………………………………………………………………………………. 78
APPENDIX C: PLATE 1 AND 2 ………………………………………………………………………. 79
APPENDIX D: DIFFERENT VIEWS OF THE ROCKET STOVE ………………………. 80
CALCULATION OF RESULTS ……………………………………………………………………….. 81
CHAPTER ONE
INTRODUCTION
1.1 Background of Study
With a global human population exceeding six billion people, a lot of food is being cooked using a lot of energy. In the industrialised world, that energy usually takes the form of a stove that is heated by electricity or by burning a gaseous fuel such as natural gas or liquefied petroleum gas (Zube, 2010). While in the developing world, the cooking device is rarely powered by electricity, and is far more likely to be powered by burning liquefied petroleum gas, kerosene or biomass such as wood, dung, or charcoal. The large preference for wood as fuel is predicated upon the fact that apart from wood and coal the other primary non-renewable sources of energy such as petroleum, natural gas and liquefied natural gas are no longer easy to come-by in terms of cost and availability. The lifetime for these other alternatives is estimated to range from 15 years for natural gas to nearly 300 years for coal (Yawas, 2003). Estimate put the total number of people throughout the world who rely on solid biomass fuels at three billion, or roughly one-half of the world‘s human population (Desai et al., 2004). The problems that surround burning biomass for cooking purposes affect a very large number of people, and this number is not likely to be reduced significantly in the near future (Zube, 2010). Even in areas where governments are actively attempting to displace the use of biomass fuels by subsidising the cost of electricity, people continue to use biomass for cooking because it tends to be less expensive, and electricity is valued for its ability to power television sets and other devices that cannot be powered with wood (Madubansi and Shackleton, 2007).
Nearly 2.7 billion people use solid biomass fuels for household cooking and heating in open fires and simple stoves (Legros et al., 2009). The users of these stoves live almost
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entirely in the developing world, and the individual, community, and global impacts of these small biomass cook stoves is significant. It has been estimated that indoor air pollution from solid fuel use is responsible for nearly 4 million deaths annually and approximately 4% of the global burden of disease, representing the second leading cause of death for women globally (Lim et al., 2012). The fine particulate matter, carbon monoxide, polycyclic aromatic hydrocarbons, and other emissions due to incomplete combustion within poorly ventilated spaces contribute to acute lower respiratory infections, pneumonia, and chronic obstructive lung disease; as well as adverse pregnancy outcomes and cataracts (Legros et al., 2009). In many cases, the use of biomass fuel for household energy is exacerbated by deforestation and desertification around communities, leading to increased time and energy spent in gathering fuel, and it poses a significant opportunity cost to education, health, and income-generating activities, primarily for women and children (Rehfuess, 2006). The ‗vicious circle‘ of energy poverty and environmental deterioration, health degradation, and opportunity costs inhibits the capacity to move from the use of energy for simply meeting basic survival needs to productive or income-generating energy use. Poor families spend one-fifth or more of their income on wood and charcoal, devote one quarter of household labour collecting fuel wood, and then suffer the life-endangering pollution that results from inefficient combustion (Sovacool, 2012).
Stove dissemination programmes have been met with varying levels of success (Schreiner, 2011). As is true with any development initiative, the sustainability of an improved stove research is not driven by the technology alone. Social, cultural, and economic factors have a significant effect on stove use and adoption rates. The most successful improved stoves are easy to construct in local settings using existing
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techniques and materials and have clear advantages with respect to fuel economy, ease of use, durability, and cleanliness (Barnes, 1994). The Rocket stove as first designed by Winiarski, introduced insulation around the fire to improve thermal efficiency of the stove (Bryden, 2010). Rocket Stove is a stove with flexible design that produces virtually no smoke and uses very little fuel. Rocket Stoves features ”elbow” fuel magazines which produce cleaner, more complete combustion and insulated combustion chambers which maintain high cooking temperatures. Rocket stoves are small efficient stoves that can produce a hot flame with only a few small pieces of wood. The reason it is called a rocket stove is because when wood is added to the fire the flames create an internal draft. As the draft is created, the fire begins to produce a jet of fire coming through the stove pipe. The rocket stove has become widely recognized as the world leader in high efficiency, intermediate technology stove, (Scott, 2006). Insulators due to their low thermal conductivity are able to retard the flow of heat energy. There are varieties of insulating materials which come in various forms like loose fill, rigid boards, pipe and foam. Proper selection of the insulating material to be used is based on the thermal properties which include the thermal conductivity, specific heat capacity and thermal diffusivity.
1.2 Statement of Problem
With a large population of the world relying on woodstove for cooking, wood fuel will continue to be in high demand. Felling of trees harm the environment and there are many health challenges associated with cooking with wood. An open fire is often 90% efficient in turning wood into energy, but only a small proportion (10% to 40%) of the released energy makes it to the pot (heat exchanger) hence, more wood is burnt (Bryden, 2010). Hence, combustion efficiency does not appreciably help the stove use less fuel. Heat transfer is currently underutilised as a means of increasing stove thermal
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efficiency and opportunities exist that could change this. Hence, this is the area of research offering the greatest potential to enhance performance and provide more people with improved cooking procedures (Ebiega, 2012).
Also, most improved stoves have the problem of absorbing some of the heat produced into the stove body thereby reducing heat reaching the heat exchanger, even though they may have low specific fuel consumption.
1.3 Present Research
The present research investigated experimentally the thermal properties of wood ash and clay-sawdust mixture for use as insulators in a rocket stove, with the aim of improving heat transfer efficiency in the rocket stove and studied how they affect the thermal efficiency of the rocket stove, and the stove was tested under different conditions to ascertain the best condition for its usage.
1.4 Aim and Objectives
The aim of this research is to investigate experimentally the thermal properties of wood-ash and clay-sawdust mixture insulating materials and to determine their effect on the thermal efficiency of a rocket stove. The specific objectives of this research work are to:
i. develop wood ash and clay-sawdust mixture insulating materials and test their thermal properties: thermal conductivity, specific heat capacity and thermal diffusivity.
ii. construct three prototypes of a designed rocket stove with wood ash and clay-sawdust mixture as insulation materials for the two stoves and one without insulation.
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iii. determine experimentally the effects of each insulating material on the efficiency of the stoves.
iv. carry out control cooking tests on the stoves.
1.5 Justification
With over 2 billion of the world‘s population using biomass to cook every day, the possibility of improved stoves helping to mitigate climate change is generating increasing attention. Laboratory results have shown that some improved stoves with rocket-type combustion or fan assistance can reduce the overall warming impact from the products of incomplete combustion (PICs) by as much as 50-65% (Karekezi, 1992). The use of insulators is one way of improving heat transfer efficiency as heat loss to the stove body which is a major challenge in improved stoves is reduced greatly hence more heat gets to reach the heat exchanger. Hence if the stove performance can be improved using local materials like wood-ash and clay-sawdust mixture as insulatorsthen health, economic and environmental concerns will be greatly reduced in Nigeria
If it is ascertained that wood-ash and clay-sawdust mixture are good enough insulators for the rocket stove, this will be a boost economically, as people can go into stove manufacturing and both health and environmental challenges will be reduced eventually and there are large quantities of these materials (wood ash and the clay-sawdust).
1.6 Scope of Study
This present research is focused on constructing an already designed rocket stove. The thermal properties of the insulating materials were determined experimentally and water boiling test and cooking tests were carried out to find the effects of the thermal
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property of wood-ash and clay-sawdust mixture on the thermal efficiency of the rocket stove.
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