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Steam Engines<br />A series of lessons <br />by David C<br />Dec 2010<br />
Part 10<br />The little engine<br />
Now perhaps I’ve given you the impression that Newcomen’s steam pumps created a revolution in the way things were done in ...
It costs a lot of money to build a steam pump, and if you’ve been successfully running a business that draws power from a ...
Newcomen’s pumps were more like hammers than engines. They’re good for hitting things, or pulling water out of the ground,...
Joseph Cugnot in France no doubt experienced this problem when trying to drive his steam tractor in 1769. <br />The tracto...
The strictly up-and-down motion of the pump <br />was a major limitation to what it could do. <br />Compare that with wate...
Well, as you’ve seen in the last lesson, there were a number of people who saw possibilities for the steam pump if only it...
It would have been good for example to have a small steam pump in a boat to operate a set of paddles. <br />
Still others saw the possibility of driving a carriage across the ground, as long as the pump was small enough to sit on t...
But Newcomen’s steam pumps were big for a reason.<br />First, they had to be strong enough to lift water out of the ground...
Let’s suppose you had a small steam pump, <br />consisting of a small boiler and a small cylinder and a small piston. <br ...
Compare that with a cylinder that is a metre in diameter. <br />Now only 2 percent of the steam is in contact with the cyl...
That’s just the beginning. Now consider what happens when you inject a spray of cold water into the cylinder. <br />
Of course, you want to cool the steam down so that it will condense, but you don’t want to cool the cylinder wall down. If...
But if the cylinder is just 10cm across, only 80 percent of the steam can do that. The rest is either trickling down the c...
But if the cylinder is just 10cm across, only 80 percent of the steam can do that. The rest is either trickling down the c...
Consequently there was a drive to make steam pumps ever bigger, not smaller, and this was becoming increasingly easy to do...
This fact would have been well known <br />to the university students in Glasgow in the 1760s.<br />By this stage, 50 year...
The University of Glasgow had a scale model of a Newcomen pump that they would show to the students, and anyone observing ...
It was a nuisance to the lecturing staff, however, because they wanted this little model to demonstrate how a steam engine...
Rather than build a bigger model, they asked the university’s lab technician if he could tinker with it and make the thing...
The lab technician was a young fellow named James Watt, and by the time he’d fixed that damned thing, he had an idea that ...
Young James’s solution was to fit a second tank into the design; one kept perpetually cold so that any steam directed into...
But when you want to condense the steam to bring the piston down again, you no longer spray water into the piston. <br />N...
If the piston is to be kept hot at all times, <br />it makes sense now to put a blanket around it so that no heat can radi...
He couldn’t see it at the time <br />– nobody could – <br />but young James’s modifications made all steam engines efficie...
There would have to be a few more modifications, however, before ‘locomotion’ was truly possible.<br />Interestingly, Mr W...
End<br />dtcoulson@gmail.com<br />
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Dave steam 10 (the little engine)(29)

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Dave steam 10 (the little engine)(29)

  1. 1. Steam Engines<br />A series of lessons <br />by David C<br />Dec 2010<br />
  2. 2. Part 10<br />The little engine<br />
  3. 3. Now perhaps I’ve given you the impression that Newcomen’s steam pumps created a revolution in the way things were done in England in the 1700s. <br />If that’s the case, I’d better make it very clear that the steam pump <br />was very limited in what it could do, and was adopted only very slowly <br />by the businessmen of the time.<br />
  4. 4. It costs a lot of money to build a steam pump, and if you’ve been successfully running a business that draws power from a water wheel for all of your working life, why should you want to change to steam? <br />It was generally the new startup companies that bought Newcomen’s pump, and these generally were textile factories that made easy use of the pumps’ up-and-down thumping action. <br />
  5. 5. Newcomen’s pumps were more like hammers than engines. They’re good for hitting things, or pulling water out of the ground, but they’re not very good for turning things. <br />There were some attempts to get the rising and falling piston to operate a crank that would turn a wheel, but these were always unsatisfactory because of the pump’s jerky action. <br />
  6. 6. Joseph Cugnot in France no doubt experienced this problem when trying to drive his steam tractor in 1769. <br />The tractor would have lurched forwards staccato fashion with each pulse from the two pistons; turning the vehicle would have required disengaging one of the pistons while the other continued to thump away on the other side of the vehicle. <br />No wonder he crashed the tractor into a wall. <br />
  7. 7. The strictly up-and-down motion of the pump <br />was a major limitation to what it could do. <br />Compare that with water wheels, <br />which had been in operation for centuries. Whole industries had evolved around the smooth, circular motion that these wheels created. <br />So who really needed a steam pump, <br />other than the mine owners for whom the machine had been invented?<br />
  8. 8. Well, as you’ve seen in the last lesson, there were a number of people who saw possibilities for the steam pump if only it could be made a good deal smaller than it presently was. <br />
  9. 9. It would have been good for example to have a small steam pump in a boat to operate a set of paddles. <br />
  10. 10. Still others saw the possibility of driving a carriage across the ground, as long as the pump was small enough to sit on the wheels.<br />
  11. 11. But Newcomen’s steam pumps were big for a reason.<br />First, they had to be strong enough to lift water out of the ground.<br />But just as important was their efficiency. <br />Large piston chambers don’t lose heat <br />to the outside world as quickly <br />as small chambers do. <br />
  12. 12. Let’s suppose you had a small steam pump, <br />consisting of a small boiler and a small cylinder and a small piston. <br />Let’s suppose the cylinder is only 10cm in diameter. <br />That means the steam in the cylinder can never be <br />more than 5cm from the wall of the cylinder. <br />Now steam is a pretty good insulator, <br />but it still means that about 20 percent of the steam <br />is within a centimeter of the cylinder wall <br />and can be affected by the outside temperature. <br />
  13. 13. Compare that with a cylinder that is a metre in diameter. <br />Now only 2 percent of the steam is in contact with the cylinder wall, <br />and that means only 2 percent of the steam is going to be affected. <br />
  14. 14. That’s just the beginning. Now consider what happens when you inject a spray of cold water into the cylinder. <br />
  15. 15. Of course, you want to cool the steam down so that it will condense, but you don’t want to cool the cylinder wall down. If the cylinder is a metre across, you have 98 percent of the steam condensing without touching the cylinder wall. <br />
  16. 16. But if the cylinder is just 10cm across, only 80 percent of the steam can do that. The rest is either trickling down the cylinder wall or picking up heat from the cylinder wall and not condensing. <br />
  17. 17. But if the cylinder is just 10cm across, only 80 percent of the steam can do that. The rest is either trickling down the cylinder wall or picking up heat from the cylinder wall and not condensing. <br />Whichever is the case, you have a machine that is going to start off well but within a few beats of the piston is going to reduce to a pathetic little wobble that has no power in it at all. <br />
  18. 18. Consequently there was a drive to make steam pumps ever bigger, not smaller, and this was becoming increasingly easy to do with each passing decade as iron-casting and iron-cutting techniques improved. <br />To make steam pumps smaller didn’t make an awful lot of economic sense. <br />
  19. 19. This fact would have been well known <br />to the university students in Glasgow in the 1760s.<br />By this stage, 50 years after <br />the invention of the steam pump <br />it was possible to go to university <br />and learn how to build one. <br />
  20. 20. The University of Glasgow had a scale model of a Newcomen pump that they would show to the students, and anyone observing this little thing in action got a very clear lesson that little steam engines simply didn’t work because … well ... it didn’t work.<br />
  21. 21. It was a nuisance to the lecturing staff, however, because they wanted this little model to demonstrate how a steam engine ‘should’ work. <br />
  22. 22. Rather than build a bigger model, they asked the university’s lab technician if he could tinker with it and make the thing work a little better. <br />
  23. 23. The lab technician was a young fellow named James Watt, and by the time he’d fixed that damned thing, he had an idea that was going to make him fabulously rich and make him perhaps the best known engineer who ever lived. <br />
  24. 24. Young James’s solution was to fit a second tank into the design; one kept perpetually cold so that any steam directed into it would condense very quickly. <br />Naturally, this tank was to be called the condenser. <br />Well, when you introduce steam to the piston chamber, it of course pushes the piston up as you’d want it to do. <br />
  25. 25. But when you want to condense the steam to bring the piston down again, you no longer spray water into the piston. <br />Now you open a valve that lets the steam escape to the condenser, where of course it condenses. <br />The advantage of this design is that the piston chamber can be kept hot at all times; you no longer lose heat by spraying water into it. <br />
  26. 26. If the piston is to be kept hot at all times, <br />it makes sense now to put a blanket around it so that no heat can radiate off into the open air. <br />These and other minor modifications <br />made the steam pump some 5 times more fuel-efficient than it had ever been, <br />which inspired Watt very quickly to visit a lawyer and slap a patent on his modifications before anyone else discovered them. <br />
  27. 27. He couldn’t see it at the time <br />– nobody could – <br />but young James’s modifications made all steam engines efficient, no matter what size they were. That meant (in theory) it was possible to build a steam engine small enough to fit onto a set of wheels and drive it down a road. <br />
  28. 28. There would have to be a few more modifications, however, before ‘locomotion’ was truly possible.<br />Interestingly, Mr Watt would be responsible for all of those essential modifications.<br />And most interesting of all, he wouldn’t even know what those modifications were leading to.<br />
  29. 29. End<br />dtcoulson@gmail.com<br />

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