TRANSCRIPTS
pumping water out of mines or pumping air in. Now, a lot of mechanical engineers work on refrigeration and central heating systems.
Unit 1, Lesson 1.4, Exercise E ≤1.7
Lecture 2 Have you ever played with a paper clip? If you try to straighten a paper clip, it’s quite difficult. But with enough force you can do it and, with some more force, you can bend it back to the original shape. If you try to straighten the clip again, it’s much easier. Finally, you can move the metal backwards and forwards with almost no effort. And it is at this point that if you put a small force on the paper clip, it breaks. We can call the weakening of the paper clip metal fatigue.
So, metal fatigue is caused by repeated stress loading on part of a machine or a vehicle. Stress loading means some kind of force or pressure. Repeated, of course, means again and again. Finally, the metal fails under a very weak stress loading. The effects of metal fatigue can be very serious, including the collapse of buildings, and accidents involving planes, trains and factory machinery.
The term metal fatigue was invented in the 19th century. But it really came to public notice in 1954. On the 10th of January that year, one of the new British passenger jet planes, the Comet, crashed near Italy. Thirty-five people died. Three months later, on the 8th of April 1954, another Comet crashed, again near Italy. All 21 people on board were killed. Scientists examined thousands of fragments of the first crashed plane. They eventually identified the cause as metal fatigue. Apparently, one of the cabin windows failed. In this case, mechanical engineers had the answer. From that day on, all aeroplane windows were made with rounded instead of square corners. However, it is still not possible to predict exactly when and where metal fatigue will occur. One solution is to overengineer products so they can bear much greater stress loading than will ever occur in use. But this solution is very expensive.
Unit 1, Lesson 1.4, Exercise E ≤1.8
Lecture 3 So, let’s move on to the history of air conditioning. We could say that cooling the air around us is simply the opposite of heating it. And yet, the second process, space heating, has been known and understood for thousands of years, ever since
people discovered how to make and control fires, whereas space cooling is relatively new. Some ancient civilizations had primitive methods. In ancient India, for example, they hung wet mats made of grass over the windows. The hot wind blowing through the wet grass was cooled by evaporation. But the first true air-conditioning machine was built in 1922 and installed in a theatre in Los Angeles, in the United States. It was invented by Willis Carrier. In the 1930s, scientists discovered freons, and these were used to make more efficient air conditioners. By 1935, there was air conditioning on American trains. In 1950, people started to install window ACs to cool single rooms in apartment blocks. Nowadays, economic development in many countries depends on air conditioning because it enables people to work and study in cooled buildings when the ambient or outside temperature exceeds 40 degrees centigrade.
How do air conditioners work? Well, just like the grass mat method in ancient India, the process depends on evaporation. One kind of air conditioner is called a heat pump. The refrigerant – water or some other fluid – is passed through a set of coils. Air from the space to be cooled passes over the coils. The refrigerant evaporates and takes heat from the passing air. We say it absorbs the heat – A-B-S-O-R-B-S. The cooled air is then recycled into the space. Meanwhile, the vaporized refrigerant passes into a compressor. It is pressurized and passed through another set of coils. These coils are in contact with the ambient air. Once again, there is a heat transfer – this time from the refrigerant to the outside air. The refrigerant condenses into a liquid and passes back into the evaporator coils again.
Unit 1, Lesson 1.4, Exercise E ≤1.9
Lecture 4 The Industrial Revolution began in England in the early part of the 18th century. The revolution introduced the use of machines to do work which, until then, had all been done by hand. Some early machines were powered by running water but, in 1712, Thomas Newcomen, an Englishman, used a steam engine to pump water out of a coal mine. The new source of power – steam – revolutionized machinery. In 1765, James Watt, another Englishman, improved Newcomen’s engine, and within a hundred years, steam engines were everywhere: on rails, on water and even on the roads. A new kind of engineer was needed for all these machines – the mechanical engineer.
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