M. Ibbotson - Professional english in use engineering (794233), страница 22
Текст из файла (страница 22)
This allows the heat from the gas to be(11] absorbed/emitted by the cool water that's returning to the boiler after passing through theradiators in the home's (12] cooling/heating system - heat transfer takes place from hot gas tocool water by (13) conduction/radiation through the metal of the heat exchanger. In addition, whenthe temperature of the gas has fallen to a certain point, the water vapour within it (14) condenses/solidifies. And it is th is process that enables significant amounts of heat to be transferred, due tothe prin cip le of (15)1atent/specific heat0V~r01':fOLA ~Think about some appliances, machines or structures where heat transfer is an importantconsideration. How is the heat transferred, and how does this affect the design?.f-oProfessional English in Use Engineering79liD Fluid containmentPipes, ducts and hosesA pipeAn air ductA hosePipes are rigid tubes, made from materials such as steel and plastic.
They carry fluids (liquidsor gases). Pipes can be fitted together with different pipe fittings (see Appendix IX on page111). Assemblies of pipes are often referred to as pipework.Mains are underground pipes for water and natural gas. Water mains and gas mains runbeneath the streets of cities to supply buildings.Pipelines are long-distance pipes, often above ground, for crude oil or natural gas.Drains are underground pipes that carry waste water.
Large drains, as found below the streetsin cities, are called sewers. Drains and sewers rely on gravity to allow them to flow. Theytherefore have a downward slope, called a fall .Ducts are pipes used for moving air that is not under pressure- usually for heating or airconditioning. Ductwork often consists of rectangular cross-section ducts.Hoses are flexible tubes, often made from plastic, for liquids and gases. They are fittedtogether using hose fittings (or hose couplings). Examples of hoses are fuel hoses andcompressed air hoses - sometimes called fuel lines and air lines.Note: In everyday English, fluid usually means a liquid. In physics and engineering, the word refers toboth liquids and gases.TanksA tank is a container for liquid or gas.
It may be watertight (will not leak water) and open atthe top. It may also be enclosed and airtight (will not leak gas), and may contain gas that isunder pressure.A pressure vessel is a tank for storing gas- or a mixture of liquid and gas- that is underpressure. The vessel must therefore be sealed -with no openings, so that gas cannot escape.It must also be strong enough to withstand the pressure inside. Pressure vessels include smallportable gas cylinders (also called gas bottles).
Some pressure vessels also function as boilers- they heat the liquid inside them in order to boil it and increase pressure -for example, awater boiler that produces high-pressure steam.-Pumps, fans and turbinesLiquids can be forced to flow (move) along pipes bymechanical devices called pumps. For example, in cars,fuel is pumped from the fuel tank to the engine bya fuel pump. The flow of fluids can be controlled byvalves (see Appendix IX on page 111).
A pump used toincrease the pressure of gas is called a compressor.A device powered by a motor which rotates in order tomove air or gas - for example, along a duct - is calleda fan. A turbine has the opposite function to a fan - itis designed to be moved by a flow of air or gas. Forexample, a wind turbine revolves due to the wind, andcan be used to drive a generator (to generate electricity}.80Professional English in Use EngineeringThis compressor produces compressed airfor powering tools.37.1Complete the emails about the design of a new manufacturing plant using words from Aopposite.CJNew MessageAir temperature will be high in this area , due to the presence of four large-diametersteel steam (l) ................................
running along the ceiling. This opens up the possibility ofextracting hot air and transferring it, via (2) ................................ , to other areas of the plant,for heating use.New MessageGiven that this machine will move to an extent, due to vibration, it should be connected tothe water supply using a flexible (3) ................................ , rather than a rigid (4) ................................
.The pressure of the supply may also need to be increased, depending on the pressure ofwater coming into the plant from the (5) ................................................................ .New Me ssageWaste water will exit the plant via a (6) ................................ on the western edge of the site.This will run into the (7) ................................ under the street on the north side of the plant.The survey has confirmed that the level of the site, relative to the street, will allow anadequate (8) ................................ .31.2One sentence in each pair is false. Choose the truesentence.
Look at A and B opposite and Appendix IXon page 111 to help you.1 a All gas cylinders are pressure vessels.b All pressure vessels are gas cylinders.2 a Elbows are types of pipe or hose fitting.b3 ab4 ab5 ab31.3Pipe or hose fittings are types of elbow.Any watertight tank will also be airtight.Any airtight tank will also be watertight.All pressure vessels are types of tank.All tanks are types of pressure vessel.A pipe is a specific sort of pipeline.A pipeline is a specific sort of pipe.A propane gas tankChange one word in each of the sentences below to make them correct.
Look at C oppositeand Appendix IX on page 111 to help you.1 A fa n is designed to be driven by a flow of air or gas.2 A pump used to increase the pressure in a vessel is called a turbine.3 A safety valve is an inlet which releases excess pressure.4 A non-return valve is also called a safety valve.5 Some valves can be partly closed to stop a flow, reducing its rate.Ove.,r .f-o t:foa~Think about a machine or installation you're familiar with, in which liquid or gas is stored,supplied or circulated. What equipment is used to contain the gas or liquid? How are flowand pressure managed?Professional English in Use Engineering81Fluid pressureGauge pressure and absolute pressurePressure is the amount of force acting on an area.
When fluids (liquids or gases) are underpressure they exert pressure on the surfaces of the tanks, pipes, etc., that hold them.Examples of pressurized fluids are compressed air inside air hoses, compressed gases such aspropane in gas cylinders, and water in water mains. The SI measurement of pressure is thePascal. One Pascal is equal to one newton per square metre (1 Pa = 1 N/m 2 ). However, manypressure gauges (devices which measure pressure) use the imperial measurement poundsper square inch (psi).
Pressure can also be measured in bars. One bar is roughly equal toatmospheric pressure- that is, the pressure of the air in the atmosphere- at sea level. Forexample, four bars, or four bar- which can also be described as four atmospheres - is fourtimes atmospheric pressure.When engineers calculate the pressure of a fluid inside a vessel, they usually calculate itsgauge pressure. This is the pressure differential - the difference in pressure - between thefluid inside the vessel and atmospheric pressure outside. Therefore, with gauge pressure, itis assumed that the atmosphere has a pressure of zero Pascals - even though this is not true(see below).
Engineers use gauge pressure because they need to know if a fluid inside a vesselis at a higher pressure or at a lower pressure than the outside air (the air in the atmosphere),and if it is, by how much. This allows them to design tanks and pipes so that they do not faildangerously by exploding if their gauge pressure is positive, or by imploding if their gaugepressure is negative.Pressure can also be measured by comparing it with a vacuum - a void containing nogas or liquid, as in space, where pressure is truly zero Pascals. Pressure compared with avacuum is called absolute pressure. The absolute pressure of the atmosphere at sea level isapproximately 100,000 Pascals (or 100 kilo-Pascals).
Therefore a partial vacuum- which isbelow atmospheric pressure but is not a perfect vacuum - has a positive pressure when it ismeasured as an absolute pressure, because it has a higher pressure than a perfect vacuum.But it has a negative pressure when it is measured as a gauge pressure, because it has a lowerpressure than the atmosphere.Note: See Appendix Ill on page 100 for more on imperial measurements.Hydrostatic pressure and siphonic actionIn liquids- most often in waterpressure and flow can be generatedby hydrostatic pressure.An example is a water tower whichsupplies drinking water to homes.Water is stored in the tower at a highlevel, so that the water pushes down.This is called a head of water.
It putsthe water at lower level (in the watermain) under pressure. If the height ofthe water tower is increased, this willincrease the water pressure at lowlevel. Smaller tanks located at a highlevel to generate hydrostatic pressure- at the tops of buildings, forexample - are called header tanks.Note: See Appendix X on page 112 fora description of siphonic action.82Professional English in Use Engineeringwater levelwater towerhead of water-- water main flowsunder hydrostaticpressure38.1Complete the sentences using the words positive, negative and zero.12In a perfect vacuum, absolute pressure is ................................ and gauge pressure is ................................ .In a partial vacuum, absolute pressure is ................................
and gauge pressure is ................................ .3 At atmospheric pressure, absolute pressure is ................................ and gauge pressure is4 In compressed air, absolute pressure is ................................ and gauge pressure is ................................ .38.2Use the expressions in the box to complete the article about pressurized aircraft cabins, takenfrom an engineering journal.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
