1. You should carry out this experiment using the technique developed in our laboratory.
2. Everyone must do his duty.
3. I have to do some extra work now because one of my colleagues is having a holiday and I have taken over his part of our joint research.
4. We can carry out this experiment now because we have all the necessary equipment. Last year we did not have it and therefore could not do the job.
5. May I use your device for the experiment? Yes, of course, you may.
III. Translate the following sentences paying attention to the Modal Verbs and their equivalents:
1. The designers can always improve the operation of these receivers.
2. He could use any transmitter for this system.
3. The scientists are able to construct a new device by using semiconductors.
4. We have to increase the current strength by decreasing the resistance of the circuit.
5. After finishing the experiment scientists will have to discuss the results.
6. The students didnt have to conduct experiments in this field of science.
7. They didnt have to analyze these data.
8. We may say that photoelectric properties of transistor are largely used in TV sets.
9. In order to see certain stars we must use a telescope.
10. He will be able to arrive tomorrow. We shall be able to translate these English texts.
11. He must study this rule. Engineers must create new technology.
12. Our plant is to increase its output. The workers of this plant are to increase the productivity of labour.
13. You should know the subject better. Workers should apply new methods of production.
IV. Explain the use of modal verbs with different Infinitive forms and translate the sentences.
1. To be detected the electron must have an interaction with the detector.
2. He cannot have made such a serious mistake in his experiment.
3. All the preparations for the experiments used in air navigation have to be small and light in weight.
4. According to the law of conservation of energy, the energy spent in starting the body must be equal to that when it is stopped.
5. Surface tension may be expressed in any unit of energy per unit of area.
POWER STATION (PLANTS)
A power station (also referred to as a generating station, power plant, powerhouse or generating plant) is an industrial facility for the generation of electric power. Each power station contains one or more generators, a rotating machine that converts mechanical power into electrical power by creating relative motion between a magnetic field and a conductor. The energy source harnessed to turn the generator varies widely. Most power stations in the world burn fossil fuels such as coal, oil, and natural gas to generate electricity, and some use nuclear power, but there is an increasing use of cleaner renewable sources such as solar, wind, wave and hydroelectric.
Thermal power stations
In thermal power stations, mechanical power is produced by a heat engine that transforms thermal energy, often from combustion of a fuel, into rotational energy. Most thermal power stations produce steam, so they are sometimes called steam power stations. Not all thermal energy can be transformed into mechanical power, according to the second law of thermodynamics; therefore, there is always heat lost to the environment. If this loss is employed as useful heat, for industrial processes or district heating, the power plant is referred to as a cogeneration power plant or CHP (combined heat-and-power) plant. In countries where district heating is common, there are dedicated heat plants called heat-only boiler stations. An important class of power stations in the Middle East uses by-product heat for the desalination of water.
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The efficiency of a steam turbine is limited by the maximum steam temperature produced. The efficiency is not directly a function of the fuel used. For the same steam conditions, coal-, nuclear- and gas power plants all have the same theoretical efficiency. Overall, if a system is on constantly (base load) it will be more efficient than one that is used intermittently (peak load). Steam turbines generally operate at higher efficiency when operated at full capacity.
Rotor of a modern steam turbine, used in power station.
Besides use of reject heat for process or district heating, one way to improve overall efficiency of a power plant is to combine two different thermodynamic cycles. Most commonly, exhaust gases from a gas turbine are used to generate steam for a boiler and a steam turbine. The combination of a "top" cycle and a "bottom" cycle produces higher overall efficiency than either cycle can attain alone.
Cooling tower
All thermal power plants produce waste heat energy as a byproduct of the useful electrical energy produced. The amount of waste heat energy equals or exceeds the amount of energy converted into useful electricity. Gas-fired power plants can achieve 50% conversion efficiency, while coal and oil plants achieve around 3049%.
The waste heat produces a temperature rise in the atmosphere, which is small compared to that produced by greenhouse-gas emissions from the same power plant. Natural draft wet cooling towers at many nuclear power plants and large fossil fuel-fired power plants use large hyperboloid chimney-like structures (as seen in the image at the right) that release the waste heat to the ambient atmosphere by the evaporation of water.
However, the mechanical induced-draft or forced-draft wet cooling towers in many large thermal power plants, nuclear power plants, fossil-fired power plants, petroleum refineries, petrochemical plants, geothermal, biomass and waste-to-energy plants use fans to provide air movement upward through down coming water, and are not hyperboloid chimney-like structures. The induced or forced-draft cooling towers are typically rectangular, box-like structures filled with a material that enhances the mixing of the up flowing air and the down flowing water.
In areas with restricted water use, a dry cooling tower or directly air-cooled radiators may be necessary, since the cost or environmental consequences of obtaining make-up water for evaporative cooling would be prohibitive. These coolers have lower efficiency and higher energy consumption to drive fans, compared to a typical wet, evaporative cooling tower.
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Where economically and environmentally possible, electric companies prefer to use cooling water from the ocean, a lake, or a river, or a cooling pond, instead of a cooling tower. This type of cooling can save the cost of a cooling tower and may have lower energy costs for pumping cooling water through the plant's heat exchangers. However, the waste heat can cause the temperature of the water to rise detectably. Power plants using natural bodies of water for cooling must be designed to prevent intake of organisms into the cooling machinery. A further environmental impact is that aquatic organisms which adapt to the warmer discharge water may be injured if the plant shuts down in cold weather.
Water consumption by power stations is a developing issue.
Hydroelectricity
Dams built to produce hydroelectricity impound a reservoir of water and release it through one or more water turbines, connected to generators, and generate electricity, from the energy provided by difference in water level upstream and downstream. Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing around 17 percent of domestic electricity use.
