M. Ibbotson - Professional english in use engineering (794233), страница 21
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by an external energy(2) ................................ , most often via overheadelectric lines. This differs from a diesel-electriclocomotive, which has an onboard fuel tank anda diesel-powered generator to provide electricityfor its motors. Purely electric power hasnumerous advantages over diesel-electric power,explaining the choice of electric locomotives foruse in high-speed trains.powerfulsourcestoredthermalusefulwastewattagework.... An electric locomotiveFirstly, an electric locomotive needs to carry neither a generator nor fuel.
Its mass istherefore lower than a diesel-electric equivalent. This results in a significant efficiency(3) ................................ ,as the electric locomotive's smaller mass means less (4) ................................is done - measured as a total number of (5) ................................ - on a given journey. For acomparable rate of acceleration, its motors are also required to provide less(6) ................................ . As they use a lower (7) ................................ ,this means less (8) ..............................
..motors can be used, making them smaller, thus further reducing weight and improving(9) ................................. In addition, electric locomotives use only (10) ................................ energy.This means there is no need to (11) ................................ energy from one (12) ................................ toanother on board the train (electricity can be generated more efficiently in power stations).In a diesel-electric unit, the energy conversion process starts with (13) .............................. ..energy, which is (14) ................................ within the hydro-carbon compounds of diesel. This fuel isburned to produce (15) ................................ energy, and the heat is then converted by the engineinto (16) ................................
energy, which provides the movement to drive the train. This processis a very long way from being 100% (17) ................................ - only a small percentage of theinitial chemical energy is converted to the (18) ................................ energy that is actually used todrive the train, with a significant percentage being (19) ................................ into the air in the formof heat, constituting (20) ................................
energy.Ove,r .f-o':fOtc{J1Think about some machines or appliances you're familiar with. What sources of energy dothey convert? What forms of useful energy and waste energy arc produced?Professional English in Use Engineering77ll!J Heat and temperature-Changes of temperature and stateThe two extracts below are from a basic technical training course for the customer servicestaff of a manufacturer of heating boilers.As 'jOU k-now, Te.mpe.ratuce. Is me.asufe.d in de.g"~Ce.b.tu:s. (• C.).
!Ju-t he.a.:tis e.ne.fg'j• so i-t'smeasufe.d in ~oule.s . To calcula-te. -the. amoun-t of e.ne.fg'j ne.e.de.d -to false. -the. -te.mpe.fa-tuce. ofa subs-tance., 'jou ne.e.d -to k-now -the. mass of -the. subs-tance. be.ing he.a.-te.d, and also i-ts.spe.c.~flc heaTc.apac.ltlj -in o-the.c weeds, -the. amoun-t of e.ne.fg'j• in jOUie.s, fe.<jUife.d -to caise.-the. -te.mpe.fa-tufe. of one.
k..ilogcam of -the. subs-tance. b'j one. de.gfe.e. C.e.lsius.Wna-t happe.ns wren subs-tances change_ sta-te..? We.\\, hea-t e.ne.c3'j is ne.e.de.d TO mak..e. a solidmel-t and be.ccme. a li<jUicl. IT 's also ne.e.de.d -to -tum liq-lid in-to vapc:u- - rt -tak..e.s e.ne.cg'j -to mak-e.a liqlid boll, so -tha-t rt e.vaporate..s (oc vaponz...u.) and be.ccme.s a gas.
lha-t 's because. me.11-rsand e.vapora11crl ace. e.rdcrthe.rmk:- pca::.e..sse.s. lha-t me.ansThe.'j -tak-e. jQ hea-t e.ne.f9'j - The.'jAnd rt 's The. opposiTe. wren ane.e.d -to ab:scxb hea-t fran a hea-t ~ce.. ~h as a flame..subs-tance. coob. As a gas ~ -to be.ccme. a liqJicl, oc as a liqJid ~ -to be.ccme. asolid, The. pca::.e..ss is e.xcthe.rmlc -hea-t is e.mttte.d. lre amoun-t of e.ne.c3'j ab:SOCbe.d oc e.mrt-te.dwhile. a subs-tance. changes sta-te., in ~ou\e.s pe.f k..ilogcam, is cal\e.d la-tent hea-t. Wing me.Hing iT 'scal\e.d la-tent hea-t of fusion, and d<King vapoclz...lng iT's cal\e.d la-tent hea-t of vap:xlz.a.:tlooNote: See Appendix Ill on page 100 for other units of temperature, and Appendix VII on page 109for notes on vapour and steam.-Heat transferThe textbook extract below looks at heat transfer- how heat travels.To help understand heat transfer, homes provideeveryday examples.
The heating systems in homesoften have electric convector heaters. These heatthe air and make it circulate, so that it moves in acircle- first rising, then cooling and sinking beforerising again. This is called convection, where warmgas or liquid moves around and dissipates heat,transferring it to the rest of the gas or liquid.Alternatively, the heating system in a home maycirculate hot water through radiators. The radiatorsAn electric convector heateract as heat exchangers - devices that transfer heat-in this case, from the hot water inside to the cooler air outside. This happens by conduction- heattransfer through solid material. After the heat has been conducted through the metal of the radiator,the heat is dissipated by convection.The third way that heat is transferred is by radiation.
This is heat that travels as electromagneticwaves. An example is the heat from the sun. So the radiators that circulate water have a misleadingname, as they don't really function by radiation.Notes: See Unit 19 for more on the thermal properties of solid materials.See Appendix VII on page 109 for more on radiators in cooling systems, and thermal inertia.See Appendix VIII on page 110 for specific types of electromagnetic wave.78Professional English in Use Engineering36.1Complete the sentences about water using words from A opposite.
Sometimes there is morethan one possible answer.2345636.2When the temperature of ice reaches 0 oc, it changes ................................ - it ................................ tobecome water.At 100 oc, water ................................ .When water is ................................ to 0 oc or below and ................................ to become ice, it is said tofreeze.In gas form, water is called ................................ or ................................ ................................
.Between 100 oc and 374 oc water is a ................................ because it is below its criticaltemperature.Extremely hot water vapour is called ................................ ................................ .Match the two parts to make correct sentences. Look at A and B opposite, and Appendix Vllon page 109 to help you.1 A liquid pumped onto a workpiece that is being machined, to stop it overheating, is called a2 The form of heat transfer that occurs with infrared heat- a form of electromagnetic wave-is called3 The metal fins (plates) around air-cooled engines, intended to maximize the surface area ofthe hot engine that is in contact with the cooler air, are designed to act as a4 Thick, dense, internal walls inside an energy-efficient house, which are intended to absorbheat energy during the day and store some of it to be emitted at night, function as a5 The soil and rocks on the surface of the earth remain warm at night in summer, due to theprinciple ofa radiation.b coolant.36.3c heat sink.d thermal inertia.e heat exchanger.Circle the correct words to complete the article about condensing boilers.
Look at A and Bopposite to help you. The first one has been done for you.Condensing boilers are becoming increasingly popular in homes, as they use up to 40% less gasthan traditional boilers. How do they work? By exploiting the fact that when a liquid condenses, dueto the principle of latent heat of (1) fusion~orizat@, the process is (2) endothermic/exothermic.This means heat is (3) absorbed/emitted, and can thus be (4) circulated/conducted via the waterinside the radiators in the home.A condensing boiler burns natural gas (hydrocarbon fuel) to (5) heat/cool water, just like aconventional boiler.
However, it ach ieves greater efficiency by recovering energy from water vapour.This is present in the hot, waste gas that's produced when natural gas is burned . In a traditionalboiler the (6) heat/temperature energy from the gas, which is at a (7) heat/temperature of 180or more, would be (8) dissipated/radiated into the atmosphere by (9) conduction/convection, andocthe water vapour within it would condense in the outside air. But in a condensing boiler the hotgas passes through a (1 0) heat/temperature exchanger.
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