Vocabulary. Heat production and transfer

Transcription

1 Kick off 1 Heat is the transfer of energy between objects that are usually at different temperatures. Match the types of energy with the pictures. 1 chemical 3 mechanical 2 nuclear 4 electrical 2 Heat is transferred in three major ways (called means). Look at the pictures. Then match the means to the path ofthe heat. Means 2 What things do people use in everyday life to try to slow down or speed up this transfer of energy? Think about things we do to keep ourselves, buildings, cars, etc. warm or cool. 3 The opposite of an insulator is a conductor. Suggest materials for making (a) a frying pan and (b) the handle. Choose from wood,plastic, aluminium, cast iron. Which are conductors and which are insulators? Vocabulary Heat production and transfer 1 Complete the sentences with the words in the list. burning cooling energy hot temperature thermal 1 Heat is a form of 2 Heat can be measured by 3 Heat flows from something to something cold. 4 Heating is the opposite of 5 Heat from an object can be seen by imaging. 6 Heat can cause Path a through the metal pan handle b from the fire to the bottom of the pan c through water in the pan 3 Read the text. Underline the nouns that end in -tion. For each underlined noun, write the verb that it comes from. We use insulation to slow down the flow of heat. We do this to conserve heat and energy stop water condensation and corrosion protect ourselves from hot or cold surfaces or weather. We use different means of insulation for the different types of heat transfer. Here are some examples: radiation - reflective foil on the outside of a hot water tank conduction - plastic handles on a cooking pot convection - insulation in the roof of a house. EXAMPLE insulation - insulate 4 Read the text again. Find two verbs and one adjective that can be made into a noun ending in -tion.

2 Number talk Saying temperatures 1 Q Listen. Circle the numbers that you hear. 1 a 273 K b -273 C 2 a 40 b a -273 F b -273 C 4 a 100 C b 100 K 2 Work in pairs. Student A, go to p.109. Student B, go to p.115. Listening A tour of a power station 1 Read the text and think about the missing words. Then look at the diagram and complete the text. A gas-fired power plant converts heat energy into mechanical energy and then into electricity. The ' turbine turns an = and it also creates hot. J as a result of combustion. The exhaust gases are a by-product (something that is produced as a result of producing something else). The tour guide will explain how the Heat Recovery Steam Generators (HRSGs) collect the exhaust gases to feed into a steam turbine so they are not wasted. 2 ((fi Listen to the introduction to a power plant tour and check your answers. 3 Q Listen to the second part ofthe explanation. Complete the fact file. I Number of gas turbines in the plant:. Gas turbine electrical production: Exhaust gas temperature: Steam turbine electrical production:. Temperature of cooled water returned to river: Power station efficiency: ^ % 4 Listen again. Discuss the questions. _ megawatts _" megawatts 1 How is the heat energy from the exhaust gases transferred to the water - by convection, conduction, or radiation? Explain your answer using the diagram. 2 Why do you think the plant cools the water before returning it to the river? What might happen if they pumped very hot water into the river? 3 The tour guide says that the power plant is over 50% efficient. What does this plant reduce that makes it more efficient than other plants? 5 What other methods of electrical generation do you know about? Name a few good and bad points about each one. 5 1 air filter generator im II gas turbine r^l I

3 78 Unit 11 Absolute zero A system at zero K or C lias no thermal energy. It is impossible to achieve but the current world record for the lowest temperature was set in 1999 at 100 picokelvin (pk). Reading Dealing witli heat Answer the questions. 1 Think of things that you use every day. Which ones generate heat? What sort of heat do they generate - mechanical, chemical, electrical? 2 What machines or appliances create heat as a product? What machines or appliances create heat as a by-product? 3 How is unwanted heat dealt with? When you're looking for specific information, you don't always need to read a text carefully. Try looking at the texts quickly to find the figures to complete the information. 3 Match each text with a type of heat. 1 chemical 3 mechanical 2 nuclear 4 electrical 4 Answer the questions. 1 What is the cause of heat in a microprocessor? 2 What negative effect does heat have on brakes? 3 Why does convection help to transfer heat? 4 In a nuclear power plant, is heat a product or a by-product of nuclear reactions? 5 Give reasons why engineers work hard to reduce waste heat. A safe microprocessor temperature: ' C A hot motorcycle brake: ^ C A gas flame: ^ C A nuclear reactor cooling water temperature: " C The pressure in a nuclear reactor: 'bar Dealing with heat Heat can be an important factor - and a big problem - in almost any engineering project. Here are four very different examples of the role of heat in engineering. Micropiocessors Computer chips generate heat because of the electrical resistance in their circuits. In fact, it's this heat problem rather than microprocessor size that currently limits the speed of CPUs. A safe operating temperature is in the range of C. Computer design engineers keep computers cool by installing fans that increase air circulation, heat sinks (solid materials that transfer heat away from hot spots), and by trying to reduce the amount of waste heat that is generated by making CPUs as efficient as possible. Motorcycle brakes When the brakes are applied, the friction ofthe brake pads on the brake disc creates heat. When brakes become very hot - around 400 C - friction is reduced. This means that the brakes are less effective, which is dangerous. Engineers design brake discs with holes in them. The holes allow the air to circulate more freely around the disc to dissipate the heat. They also help remove rain water. Gas-fired boilers Gas-fired boilers are used in homes and industry for space heating and hot water. Chemical heat is generated by burning gases such as propane or butane. The temperature of a gas flame burning in air is almost 2000 C. At this high temperature, heat is easily transferred to heat exchangers and water pipes to heat air and water between 20 and 60 C. Heat transfer is aided by convection; as the air or water is heated from the bottom, it rises, and the colder fluid sinks. This forms a circulating flow so that the cooler fluid is constantly heated. Nuclear reactors Heat is generated in the reactor core when uranium-235 is split into lighter elements. The heat turns water into steam, which turns turbines. The turbines turn generators and make electricity. Most reactors operate with a water temperature of around 315 C and pressure of around 155 bar. In these extreme conditions, engineering design is critical particularly of safety and shutdown systems. The 2011 Fukushima plant disaster in Japan was made worse by the failure of water pumps that were needed to cool the reactor core.

4 Although the degree Celsius ( C) is commonly used in engineering, certain formulae, particularly those involving expansion and gases, require the use ofthe Kelvin (K). The degree Fahrenheit ( F) is still used extensively in the USA. It's my job 1 Read the specifications and the numbers. Think about the information and try to match each specification with the most likely number. 1 gas turbine operating temperature ( C) a exhaust temperature ( C) b turbine insulation thickness (m) c 10 4 power generated (mw) d number of homes supplied e number of years Adrian has worked in f 1 the plant g 30 7 temperature at which cooled water is returned to the river ( C) 2 Read and check your answers. 3 Read again. Answer the questions. 1 What powers the generators in Adrian's station? 2 Why are special alloys used for the turbine blades? 3 Why are the turbines heavily insulated? 4 Why do you think the coal-fired plant was replaced with a gas-fired one? 5 What was Adrian's first job at this plant? 6 What two things does Adrian like the most about his work? 7 How does the power station try to keep an open and positive relationship with the community? 8 What's the plant's biggest environmental challenge? 4 Would you like to do Adrian's job? Why / why not? Adrian lanescu I work in a gas-fired power station. We have two gas turbines and a steam turbine. It's known as a CCGT plant. Combined Cycle Gas Turbine. That way we get as much useful heat from burning the gas as possible. The gas turbines operate at around 1400 C with the exhaust around 540 C. The turbine blades are made of special alloys to withstand that sort of temperature. Insulation covering the turbines is over one metre thick in places. The exhaust gases from the gas turbine are fed into the steam turbine. We don't want to waste any heat from the burning gas. We generate up to 700 megawatts of electricity. That's enough to supply over homes. At university, I studied mechanical engineering. In my final year, I specialized in thermodynamics. I visited several power stations for my final project. I joined the company ten years ago. They had just demolished an old coal-fired station here and I came in when the new plant was being built as a commissioning engineer for start up, so I know the plant quite well. I really like the idea that I'm contributing to the local community, keeping everybody warm in winter and cool in summer. I also enjoy training and mentoring our three engineering apprentices. We have an open day every year and invite everybody to tour the plant. We show them what we do to protect the environment. Our main concern is cooling water. The river water in the cooling towers leaves at around 30 C into ponds to cool naturally before going back to the river.

5 In everyday language, work might be writing an essay or digging the garden. But to scientists and engineers, work has a precise meaning: work is done whenever a force makes something move. The greater the force or the greater the distance moved, the more work is done. Language spot Cause and result 1 Decide which part of these sentences talks about the cause and which part talks about the result. EXAMPLE The gases from combustion cause the turbine to turn, (cause) (result) 1 Computer chips generate heat because of the electrical resistance in their circuits. 2 The friction of the brake pads on the brake disc creates heat. 3 The turbine creates exhaust gases as a result of combustion. 4 The turbine turns the main generator, which produces electricity. 5 Combustion causes the gases to expand. 6 When the brakes become very hot, friction is reduced.» Go to Giammai lefeience p.l23 2 Complete the sentences with the words in the list. a result of because of causes creates when which produces 1 Increasing heat gases to expand. 2 Brakes become hot as friction. 3 The problem became worse equipment failure. 4 the generator turns, electricity is produced. 5 Splitting uranium atoms heat. 6 The water is heated from the bottom, convection. 3 Use the notes below to write sentences to explain the cause and result relationships. 1 the car to slow down / applying the brakes (cause) 2 resistance in the circuits / the CPU becomes hot (as a result of) 3 the project was delayed / an accident (because of) 4 steam is produced / water boils (when) 5 combustion / exhaust gases (creates) 6 heat / the gases are burned (which produces) Pronunciation 1 Listen. Repeat the words. Notice which syllables are stressed. combustion compression convert converted engine exhaust expand ignited intake piston released turbine 2 Put the words from 1 in the correct place in the table according to stress. engine convert combustion 3 (if) Listen and check your answers. Spealcing Describing heat engine cycles 1 Read the text and look at the pressure-volume diagram. Answer the questions. Petrol, diesel, jet engines (gas turbines), and the turbines i and steam plant in power stations are all heat engines. They convert heat into work. Heat naturally flows from a higher to a lower temperature. All heat engines take heat from one material at high temperature (e.g. burning petrol-air mixture) and pass on less heat to a material at a lower temperature (e.g. the atmosphere). The difference is converted into work. A pressure-volume (PV) diagram shows how the energy is transferred in four stages: 2 compression Volume

6 Heat 81 1 Which of these is an example of a heat engine in use - a train, a motorcycle, an electric heater, a rocket, an oven? 2 Can you name other examples of heat engines that we use in everyday life? 3 What are the four stages in converting heat into work? 4 What are two by-products of the heat-to-work conversion? Look at the diagram of a gas turbine. Use it and the cycle diagram on p.80 to complete the explanation. INTAKE COMPRESSION COMBUSTION EXHAUST Checklist Assess your progress in this unit. Tick (/) the statements which are true. I can talk about heat production and transfer I can use units of heat I know how to talk about cause and result I can explain heat engine cycles and PV diagrams Key words Adjective thermal Nouns by-product combustion conduction convection efficiency exhaust friction generator heat engine intake piston pressure-volume (PV) diagram radiation compressor combustor turbine Verb dissipate air in natural gas in exhaust gases In stage 1, the intake stage, ' is drawn into the compressor. In stage 2 - compression - the ' compresses the air. In stage 3, the air and gas mix is ignited in the \This is the " stage. Combustion causes the gases to expand. The expanding gases turn the 5 blades. Finally, in the exhaust stage - stage 4 - the hot ' are released. 3 Work in pairs. Take turns explaining the cycles of two other heat engines. Go to p.l09.