Environmental Physics RSPH 467 PDF

Enviromental Physics RSPH 467 Dr. Hanan ALZahrani ENERGY RESOURCES AND ENVIRONMENTAL POLLUTION 1.0 INTRODUCTION The sun is the ultimate source of the energy that sustains life on the earth. In this Chapter, you will be introduced to the principal techniques by which energy...

Enviromental Physics RSPH 467 Dr. Hanan ALZahrani ENERGY RESOURCES AND ENVIRONMENTAL POLLUTION 1.0 INTRODUCTION The sun is the ultimate source of the energy that sustains life on the earth. In this Chapter, you will be introduced to the principal techniques by which energy is transformed from one form to a more useful form. You will also learn how each of these energy resources impacts on the environment. 2.0 OBJECTIVES At the end of this Chapter, you should able to describe: the source of air, thermal and chemical pollution seven energy-generating mechanisms the adverse effects of energy resources on the environment.  3.1 Physics and the Environment Environmental physics is the application of the laws and techniques of physics in order to provide a description of the natural environment. Today, there are many environmental problems facing mankind. Some of these problems are global warming, ozone layer depletion, energy crisis, nuclear and electronic waste disposal complications. Others are air, soil, water and thermal pollution. These problems and their solutions can be understood from the perspective of physics. This explains why environmental physics is a very important discipline. The ultimate aim of the environmental physicist is to understand these issues and provide solutions using the principles and techniques of physics  3.2 Air Pollution Air is polluted when fossil fuel is burned. Fossil fuels include coal, oil, gas and fire-wood. Air pollution can result from burning the fossil fuel in cars, in industrial furnaces for smelting, and in electric generating plants. The situation is worse if the burning takes place so quickly that the combination is incomplete. That is why the internal combustion engines of automobiles are especially hostile to the environment. Because of the incomplete nature of the combustion in automobile engines, more noxious gases are produced. Even when the combustion is complete, the situation still remains bad since the carbon-dioxide (CO2) released into the atmosphere absorbs some of the natural infrared radiations emitted by the warm earth (and prevents them from escaping). The resulting build up of atmospheric CO2 and the consequent heating of the atmosphere is known as the green house effect. Scientists have projected that the green house effect is capable of raising the average temperature of the atmosphere by several celsius degrees within this century. Such rise in the temperature of the atmosphere is of serious concern due to the fact that it can cause a shift in rainfall patterns and melt polar ice caps. The enormous amounts of water resulting from the melted polar ice caps will be dumped into the oceans thereby raising the sea-level and flooding the low-land areas. There is, therefore, an urgent need for humans to limit the rate at which fossil fuel is burned.  3.3 Thermal Pollution Every heat engine exhausts heat to the environment. Automobiles and power plants are good examples of heat engines. Electricity- generating power plants use a heat engine to convert thermal energy into electrical energy. The exhausted heat is generally absorbed by a coolant such as water. The basic idea behind a heat engine is that thermal energy can be transformed into mechanical energy only when heat is allowed to flow from a high-temperature reservoir to a low-temperature reservoir. In the process, some of heat can then be used to do mechanical work. The efficiency h of the heat engine is given by h=1-QL , QH whereQH is the heat input at the high temperature TH , and QL is the heat condemned at a low temperature TL. For an ideal Carnot engine, the heat Q is proportional to the corresponding temperatureT. Thus, the efficiency h of the ideal Carnot engine is given by h=1-TL × TH This means that the efficiency of the heat engine can be increased by reducing the value ofTL. Hence, for greater efficiency, a large quantity of water must flow as coolant through a power plant in order to keep the temperature TL as low as possible. Of course, this water has to come from the environment. The water (which may come from a nearby river, a lake, a sea or an ocean) is ultimately recycled back to where it came from. As more and more heat is transferred to the water, its temperature continues to rise. The resulting warm water holds less oxygen. As a result, this process can cause significant damage to aquatic life in the environment. Sometimes, large cooling towers are used to exhaust heat at an electric– generating plant. The cooling towers discharge the heat into the atmosphere. The heated air resulting from this process can adversely affect the weather of the region. Thus, this method gives rise to serious environmental pollution. In what follows; you will be introduced to some of the energy resources and their negative effects on the environment.  3.4 Fossil-Fuel Steam Plants ◦ A fossil-fuel steam plant burns coal, oil or natural gas in order to boil water and produce high pressure steam that turns the turbine. These steam plants are very useful to man. However, they also create serious environmental problems. The product of their combustion creates air pollution; the heat condemned at the lower temperature reservoir creates thermal pollution; the extraction of the minerals creates environmental disasters and oil spills create environmental nightmares. These problems ◦ have the capacity to destroy every possible means of livelihood in the affected places.  3.5 Nuclear Energy Nuclear energy may be released through the process of nuclear fusion or through the process of nuclear fission. Nuclear fusion involves the coming together of two or more light nuclei (like hydrogen nuclei) to form a more massive nucleus. Nuclear fission involves the splitting of a massive nucleus (like uranium or plutonium nucleus) to form smaller nuclei. In both cases, huge amounts of nuclear energy are released. The nuclear fusion process has two major difficulties. The first is the difficulty encountered in generating the extremely high temperatures needed to initiate the thermonuclear reaction. The second is the problem of containment. For this reason, all the present-day nuclear power plants make use of the fission process to generate energy. A nuclear power plant may, therefore, be regarded as a steam engine that makes use of uranium as its fuel. Under normal conditions, a nuclear power plant produces practically no air pollution. It does not release any carbon-dioxide (CO2) into the environment. Thus, neither the fusion process nor the fission process contributes to the greenhouse effect. However, nuclear accidents can deal a devastating blow to the environment. For instance, the 1979 nuclear accident at three mile island, and the 1986 nuclear disaster at Chernobyl readily come to mind. More recently, the 2011 catastrophic meltdown of some of the Japanese reactors at Fukushima is still fresh in mind. In all, three reactors experienced total meltdown in Japan. Today, the Japanese authorities are still struggling to gain control of that nuclear crisis.  3.6 Geothermal Energy In some places, the underground water makes contact with the hot interior part of the earth. This causes the temperature of the water to rise significantly. When this happens, the hot water may come to the surface as hot springs or steam vents. These natural vents can be used to produce the steam needed to drive a turbine. Sometimes, scientists and engineers drill holes from the surface of the earth to the steam beds trapped below the ground. Cold water may also be heated by causing it to make contact with the hot dry rock. Geothermal energy is largely clean. It produces practically no air pollution. However, any non-steam emission from a geothermal plant may still be harmful to the environment. But, the more serious problem is the thermal pollution resulting from the spent water. The mineral content of the spent water maybe hostile to the environment. In particular, such minerals may be corrosive.  3.7 Hydroelectric Power Plant In hydroelectric power stations, falling water is used to turn the turbines of the electric generators directly. For this reason, hydroelectric power plants do not need heat engines. Usually, the turbines are located at the base of a dam. Hydroelectric power plants are almost 100% efficient. However, the reservoirs behind the dams inundate lands that may otherwise be used for agricultural (as well as other) purposes. As a result, the environment also suffers. 3.8 Tidal Power Plants The adverse effect of tidal power on the environment is minimal. Yet, the abrupt changes in water level, as the tidal power plant operates between high-tide and low-tide sessions, can have a negative effect on wildlife. 3.9 Wind Power Plants Wind mills of various shapes and sizes may be used to turn turbines in order to generate electrical energy. Generally, windmills are regarded as a clean source of energy. However, a large array is required to meet a significant portion of a country’s energy needs. Such large arrays might affect the weather and damage the beauty of the affected place. 3.10 Solar Energy Solar energy can be harnessed by means of active solar heating, passive solar heating and photovoltaic cells. Like heat engines, the efficiency of this cells lies somewhere between 30% and 40%. Solar energy is extremely useful to man. For instance, photovoltaic cells might be placed at rooftops for home use. Solar energy is, to a large extent, considered ‘‘clean’’. However, the chemical pollution resulting from large scale manufacture of solar cells impacts adversely on the environment..  4.0 CONCLUSION In this Chapter, you have been introduced to some of the energy resources such as steam plants, nuclear energy, geothermal energy, hydroelectric power, tidal energy, wind power and solar energy. You have also seen how each energy-generating mechanism impacts negatively on the environment  5.0 SUMMARY The chapter has so far discussed the following: Environmental physicists apply the principles and techniques of physics in order to provide a description of the natural environment. The ultimate aim of the environmental physicist is to provide solution to the problem of environmental degradation. Air is polluted when fossil fuel is burned. The heat exhausted by heat engines and cooling towers creates thermal pollution. Nuclear wastes and nuclear accidents are a great threat to the environment. Geothermal power plants creates thermal pollution resulting from the spent water. A large array of windmills might distort the weather pattern and damage the beauty of the environment. Chemical pollution is produced in the process of manufacturing large quantities of solar cells.