Well, the plant produced a chemical called caprolactam, which was used to manufacture nylon. The process involved another substance, cyclohexane, a flammable and dangerous chemical. Cyclohexane is actually a combination of hydrogen and carbon and has the chemical formula C6H12. It is used as a solvent and ...
Extract 4
By the way, the explosion that occurred as a result of this disaster was equivalent to 15 tons of TNT, and the resulting fires burned for ten days. So, who was responsible? The official inquiry at the time concluded that the pipe had failed due to unforeseen stresses, and that inexperienced engineers were at fault. However, later research has shown that it was more than just a simple mechanical fault, and that ignorance and a series of problems, including the presence of water in the reactors, contributed to the accident.
Unit 11, Lesson 11.2, Exercise B ≤2.16
Part 1 Good morning everyone, and welcome to today’s talk on wind turbines. As you no doubt know, wind turbines are devices that extract energy from the wind, turning it into mechanical energy or electrical energy. In some form or other, wind turbines, or windmills, as they have been known, have existed for hundreds of years, and were used in the distant past, for example, to drain marshlands in areas of Holland. But in view of the world’s need for cleaner, renewable sources of electricity, wind turbines have become a feature of modern power generation, and MacKay, in his excellent analysis of sustainable energy options, has no doubt that wind power will form a significant part of the answer to our future energy needs. Today, however, we’re going to talk about the factors which must be taken into account by mechanical engineers when designing and installing wind turbines to generate electricity.
Don’t misunderstand me. I don’t want to imply that only engineering factors affect the widespread use of wind turbines. There are many other factors related to public opinion, such as the impact on wildlife and the visual effect on the environment. To some degree, I think engineers must take into account these aspects, but in this lecture, I am only going to consider design. In particular, I’m going to look at the theory behind wind power and then consider some of the practical aspects.
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Unit 11, Lesson 11.2, Exercise C ≤2.17
Part 2 So, I want to begin by examining the theoretical maximum power extraction from the wind – a key consideration in wind turbine design. First of all, it is fair to say that the higher the wind speed, the more energy can be extracted. However, no matter how high the wind speed is, not all of the wind’s energy can be extracted, as I will explain. The problem is … we have to slow the wind down in the turbine in order to extract energy from it. Of course, we do not slow the wind down to zero, because then we could not extract any energy. But there is an optimum point at which the maximum energy can be extracted. It turns out that this theoretical limit is just under 60%. This is called the Lanchester-Betz-Joukowsky limit, but let’s just call it the Betz limit for short! (That’s spelt B-E-T-Z.) Let me reiterate: it is impossible to build a wind energy extraction device that converts more than 60% of the energy in the wind. Not only that, but real-world conditions limit the power conversion even more. Real wind turbines suffer further losses with respect to real-world conditions, and, therefore, with a real turbine, one can only expect to extract perhaps a maximum of 40% of the energy in the wind.
So far, I’ve been talking about the theoretical limit for wind power compared with the practical limit for real-world wind turbines. Now let’s talk about wind turbine design. Why do most modern wind turbines have three blades and point into the wind? To understand this, we need to talk about an important number called the tip speed ratio, that is to say, the ratio between the speed at the tip, or end, of the wind turbine blades and the oncoming wind speed. Now, it may seem strange, but in modern wind turbines, the tip of the blades is actually rotating faster than the speed of the oncoming wind. The optimum ratio is 6. In other words, if the wind speed is 8 metres per second, the tips of the blades are rotating at … have you worked it out? Yes, 48 metres per second. In case that doesn’t mean much to you, that is the same as 172 kilometres per hour. The best way to get this high tip speed is with three blades, pointing into the wind. This gets the maximum lift, which is the same force that enables a plane to take off and fly.
As an aside, some people say that wind turbines
can be used in every kind of environment, including urban locations. However, in my view, these turbines are usually very poor. The data shows that, in these locations, the wind is very gusty, or completely blocked by other buildings.
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