Heat transfer from this water is a complex process see Figure 3. Steam, produced in the steam generator, is used to drive the turbine-generators. Calculate the maximum theoretical efficiency for a heat engine operating between these two temperatures. Figure 3. Schematic diagram of a pressurized water nuclear reactor and the steam turbines that convert work into electrical energy.
Heat exchange is used to generate steam, in part to avoid contamination of the generators with radioactivity. Two turbines are used because this is less expensive than operating a single generator that produces the same amount of electrical energy. The steam is condensed to liquid before being returned to the heat exchanger, to keep exit steam pressure low and aid the flow of steam through the turbines equivalent to using a lower-temperature cold reservoir. The considerable energy associated with condensation must be dissipated into the local environment; in this example, a cooling tower is used so there is no direct heat transfer to an aquatic environment.
Note that the water going to the cooling tower does not come into contact with the steam flowing over the turbines. Those temperatures must first be converted to kelvins. The cold reservoir temperature in any of these power stations is limited by the local environment. Figure 4 shows a the exterior of a nuclear power station and b the exterior of a coal-fired power station. Both have cooling towers into which water from the condenser enters the tower near the top and is sprayed downward, cooled by evaporation.
Figure 4. Both have cooling towers in which water evaporates into the environment, representing Q c. The nuclear reactor, which supplies Q h , is housed inside the dome-shaped containment buildings. Since all real processes are irreversible, the actual efficiency of a heat engine can never be as great as that of a Carnot engine, as illustrated in Figure 5a.
Even with the best heat engine possible, there are always dissipative processes in peripheral equipment, such as electrical transformers or car transmissions. Entropy is a measure of the amount of unavailable energy in the universe, or so as to say waste energy. The crucial point is, it always increases, it can never decrease. So, when heat is lost, it is actually energy that cannot be converted to useful work, and is thus unavailable energy.
This increases entropy, and so, there HAS to be an amount of heat rejected to the sink. Happy Reading! Born and brought up in Dehradun, India, I completed my schooling in my hometown itself. Graduated in Physics from Univ. It has been my dream and aim since childhood to be an astrophysicist, and because of the same I have deep interest in knowing more about space, the world around us and everyday scientific achievements.
I love to read books. Currently, I am an astronomy educator fan-boying about his obsession to little curious kids, and adults alike. View all posts by Shantanu. Like Liked by 1 person. All engines are designed as reversible in order to obtain maximum efficiency.
As far as efficiency goes, the 4-stroke certainly wins. This is due to the fact that fuel is consumed once every 4 strokes. But yes, heat engines are generally quite inefficient. Doing that removes energy from the gas so it cools and loses pressure. By repeating the compression of a hot gas and extracting energy using a piston, we can get continuous work. No machine is free from the effects of gravity, and even with wonderful lubrication, friction always exists. The energy a machine produces is always less than the energy put into it energy input.
Machines cannot multiply energy or work input. Energy transformation, also known as energy conversion, is the process of changing energy from one form to another. Energy can be converted from one form to another. Examples: Gasoline chemical is put into our cars, and with the help of electrical energy from a battery, provides mechanical kinetic energy.
Nuclear Fuels. Acid Rain. Climate Change. Climate Feedback. Ocean Acidification.
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