Thermodynamics team d uw-green bay grade 6 electricity unit ontario


Whether we know it or not, we use heat engines for a great many things and heat engines are fueled mostly through the act of combustion. Fossil fuels, including coal, natural gas, and petroleum oil, are the main source of energy for combustion; one that the U.S. is highly dependent on (approximately 84% of total energy generated) (1). Fossil fuels are hydrocarbons comprised mostly of carbon, hydrogen, sulfur, nitrogen, oxygen, and other mineral matter (this turns to ash when burnt). Combustion is the rapid oxidation of these fossil fuels to generate heat needed within the heat engine. The issue with combustion is that not everything is completely used up, some products are released into the atmosphere such as carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, and particulate matter (2).

Carbon dioxide is the major product released since carbon alone accounts for 60-90% of most fossil fuels’ composition. The release of carbon dioxide has been increasing steadily through the decades all across the world (2). gas city indiana restaurants Though not a pollutant that is harmful to our health directly, carbon dioxide is proven to be a greenhouse gas and contributes to the climate change currently in effect (3).

Carbon monoxide comes from vehicle exhaust and contributes to 55% of all CO emissions of the United States. Non-road engines (boats and heavy equipment like construction vehicles) account for 22% of all CO emissions nationwide. Carbon monoxide emission also come from industrial plants, woodstoves, gas stoves, and unvented gas/kerosene space heaters (2). At high levels of exposure carbon monoxide can be poisonous and may contribute to:

Sulfur dioxide, though easily dissolvable in water, occurs in all raw materials (crude oil, coal, common metal ores, etc.). It dissolves in water vapor to form an acid that interacts with other gases in air to form sulfates that are harmful to people and the environment (2). Sulfur dioxide is also a pollutant that can directly cause health issues. grade 6 science electricity test Depending on the amount of exposure one may experience temporary breathing impairment (short-term) or respiratory illness and aggravation of existing cardiovascular diseases (long-term). SO 2 also contributes to acid rain which introduces acid to the soil, lakes, and streams as well as corrodes human-made structures (buildings and monuments) (3).

Nitrogen oxides (NO x) are a group of incredibly reactive gases that a both colorless and odorless. These products form when fossil fuels are burned at high temperatures (find in the combustion process of motor vehicles, electric utilities, and industrial/commercial/residential sources). j gastroenterology impact factor The most common pollutant from this group is nitrogen dioxide and is a main component of smog found generally around big cities (2). NO x react within air and forms a ground-level ozone containing particulates that affects health in a variety of ways. It can change lung function in people with respiratory illnesses within three hours as well as increase the possibility of children developing a respiratory illness. With long-term exposure a person gains increased susceptibility to respiratory infection and it may also cause irreversibly changes in lung structure (obstructing breathing). gas definition chemistry NO x also contribute to environmental impacts such as acid rain. They can also change plant species composition/diversity in wetland systems if in increased concentrations as well as cause eutrophication (a condition that stimulates excessive algae growth) in bodies of water that depletes the oxygen and increases toxins (4).

A focus of Engineers has been the extensive research of numerous heat engine cycles. The goal is to enhance the amount of usable work from a given power source. Engineers have deliberated to work around the Carnot Cycle limit of the gas-based cycle. There has been at a few ways developed to possibly get around that limit to increase the efficiency. One way is to increase the temperature difference in the heat engine by increasing the hot reservoir temperature. This method is used in combined cycle gas turbines but environmental concerns of nitrogen oxides and physical limits of materials restricting maximum temperatures on the feasible heat engines. gas x user reviews With these concerns in mind, modern turbines run at the maximum temperatures for physical properties such as melting point to not be reached and keeping the nitrogen oxides output within acceptable range.

A third example engineers use to increase efficiency is to use the physical properties of the working fluid to the advantage of the heat engine. The most common way is to use water above the critical point (supercritical steam). The activities of fluids above this point changes dramatically and the behaviors can be used to extract better thermodynamic efficiency. The Chemical properties of the working fluids can also be used as an advantage for efficiency. Temperature can be increased denaturing a molecule into smaller units. This lowers the molecular weight of the fluid, in turn significantly increasing the efficiency of the heat engine. electricity gif The fluid of lower molecular weight moves through the engine and is cooled by a heat sink which causes the molecules to reform into their original state and can be recycled back into the engine for reuse.

Assuming the working substance in the Carnot cycle is ideal gas, for each segment w, q, and ΔU are calculated to determine the efficiency. The efficiency of the reversible Carnot cycle is defined in Thermodynamics, Statistical Thermodynamics, & Kinetics second edition by Thomas Engel and Philip Reid, page number 83 as, “the ratio of the work output to the heat withdrawn from the hot reservoir”. The goal is for the payoff to be significantly more then what we put in but we are always faced with the problem of getting less out then we put in due to significant amounts of energy being transferred to the environment. The efficiency of a heat engine functioning reversibly is always less than one and is shown in the equation:

This also proves that 100% heat taken from hot reservoir is not converted to work. This leads to two very significant progressions of the Second Law of Thermodynamics, the Kelvin- Planck formulation and Clausius statement. The Kelvin- Planck statement of the Second law states that heat cannot be converted into 100 percent work. This statement is illustrated in the following figure.

The two statements of the second law of thermodynamics along with equations 5.4 and 5.9 support that we cannot convert heat into 100% work in a reversible reaction. The only way the efficiency will approach 1 is if T hot -> or T cold ->0 which is not producible in practice as stated in the kelvin statement.. hair electricity song Since the work for an engine in an irreversible cycle is less then the work in a cycle where the engine is working reversibly, ε irreversible< ε reversible<1.

This reversible cycle described is called the Carnot cycle after the French engineer who first studied such cycles. The cycle depicted in figure 3, is a PV diagram representation of the Carnot cycle. From point (a) to point (b) is called isothermal expansion. During his step gas absorbs heat from the reservoir at T i. From point (b) to (c) is called adiabatic expansion. During this step the gas expands further and by the end of the step the gas has cooled to T 2. electricity production in usa In both of these steps work is being done on the surroundings. The third step from (c) to (d) is called isothermal compression where heat is absorbed by the cold reservoir and the work is now being done on the system. In the last step of the cycle from point (d) to (a), the gas is then compressed to its original volume in adiabatic compression. In this step work is also being done on the system and temperature returns to its original temp T 1. For this engine to be useful, the network must be done on the surroundings. In other words, the magnitude of the first 2 steps (a->b and b->c) must be greater than the magnitude of the last two steps (c->d and d->a). The area inside of the cycle is the work done by the engine.