Steam Engine The operation of machines to grind corn and to lift stones requires power, which

2.2.2 Steam Engine The operation of machines to grind corn and to lift stones requires power, which

was initially provided by human muscle, and later by animals such as horses and oxen. The water mill, that creates power from moving streams, was introduced in China and Greece around 100 BCE to grind wheat into flour. It has a horizontal millstone that is connected by a vertical shaft to a second horizontal wheel of pad- dles at the bottom driven by a stream of water. The Roman engineer Vitruvius intro- duced a far more efficient water mill with a vertical wheel mounted on a horizontal

61 axis, which can be efficiently moved by either a rapidly moving stream at the bot-

2.2 ENERGY AND POWER

tom of the wheel, or falling water on top of the wheel. This rotation of the vertical wheel must be transferred by a gear to rotate the horizontal millstone.

Wind power makes sense in windy places that are without rapidly flowing water, and apparently began in Islamic Persia and spread to Europe around 1200. It used a horizontal wheel around a vertical shaft, with vertical funnels on arms that are operated by winds from any direction. However, on one side the arm collects wind and retreats to generate power, but on the opposite side the arm spills wind and advances to consume some of the power generated. The classic modern windmills of Greece and Holland have vertical wheels with arms cov- ered with sails, and must be turned to face the wind.

Water mills and windmills must be located near sources of running water or wind. On the other hand, heat engines that depend on hot gases generated in com- bustion can be located anywhere. The simple steam engines built by Hero of Alexandria (62 AD) had a metal sphere on an axis, with two jets on opposite sides. When steam filled the metal sphere, it escaped from the two jets and caused the sphere to spin. It was used more as a fanciful toy than practical machinery. For steam engines to be useful, the inventors had to find an economical way to translate steam power into mechanical energy, and harness it for a practical problem.

Sixteen centuries after Hero, Thomas Savery of Scotland built a working steam engine to pump water out of flooded mines. In his engine and the subsequent improvements created by Thomas Newcomen in 1712, the reciprocal or back- and-forth motion created in a steam-filled piston was transferred through a lever to produce a lifting action on the other end. The first industrial steam engines operated by a lever built as a long rocking beam with a pivot in the middle. Newcomen placed on one arm a vertical steam cylinder with a piston, while the other arm was connected to a hoist in a pool of mine water. The cylinder was first filled with steam to make the piston rise, so the other arm of the beam would dip into the mine water. He then introduced a spray of cold water into the steam cylinder, where the sudden change in temperature condensed the steam and created a vacuum that sucked the piston down. The force of the downward motion caused the other arm to rise and pump water out of the mine. It was a great improvement over human and animal strength, but New- comen’s engine was slow and inefficient. Only the down stroke was a power stroke, so half of the time and motion was not productive; moreover, the repeated heating and cooling of the cylinder consumed a lot of fuel. Finally, it was a low-pressure system that needed a very large engine to do a modest amount of work—the cylinder was pushed down by no more than one atmospheric pressure, or only 760 mm of mercury.

BIOGRAPHY: JAMES WATT James Watt was born in 1736 in Scotland. His father was a ship builder and owner, and his

mother was well educated. He was home schooled by his mother, he had good manual dexterity, and enjoyed mathematics and Scottish legends, but he disliked studying Greek and Latin. When he was 18, his mother died and his father’s health began to fail. He traveled to London to study instrument-making, but returned to Glasgow after a year without serving the full 7-year apprenticeship, and was thus not accepted by the Guild.

62 CHAPTER 2 INVENTIONS FOR WORK

FIGURE 2.8 James Watt.

Instead, he went to work at the University of Glasgow with the physicist Joseph Black, who became his friend.

Watt was a very skilled mechanic and ingenious inventor, and always looked for more refinement in his engines. He was not a good businessman, and disliked bargaining and negotiating. Despite his lack of formal education, he was good at society and conversa- tions in scientific societies. He retired in 1800 when his patent and partnership expired. He continued to invent, became a fellow of the Royal Society and a foreign associate of the French Academy of Science. He died in 1819 at his home in Birmingham at the age of

83. A colossal statue was placed in the Westminster Abbey, which was later moved to Scotland Fig. 2.8 shows an engraving of Watt as a prosperous gentleman.

James Watt had a machine shop in Scotland. Professor John Robison of the University of Glasgow called the attention of Watt to the Newcomen steam engine, and

he began to experiment with it. The University owned a model Newcomen engine that was in London for repairs, and Watt had it returned and repaired in 1763. He demon- strated that 80% of the steam heat was wasted from the repeated heating and cooling of the cylinder. In 1765, he invented a second condensation chamber that could be kept cool (20 C), which made it possible to keep the first power cylinder hot (100 C).

63 The next stage of making a full-scale steam engine required much more capi-

2.2 ENERGY AND POWER

tal, and Watt also needed precision machining of the piston and the cylinder. It was not enough to come up with a great invention, as he required sources of finance for the long and expensive path of development, manufacturing, and marketing. In addi- tion, the system of patent protection for inventors was in the early days, and required an Act of Parliament. His early backer, John Roebuck, went bankrupt forcing Watt to find other employments to pay his bills. He finally found another partner in Matthew Boulton, and they formed the partnership of Boulton & Watt that lasted 25 years.

In the year 1776, his first commercial engines were installed and worked for pumps, mostly in Cornwall for pumping water out of mines. The market for his engines was greatly increased when Watt converted the reciprocating motion of the piston by a system of mechanical linkages, to produce rotation power for grinding, weaving, and transportation. He also introduced a double acting engine, shown in Figure 2.9, in which the steam entered from the left in the upper frame to push the cylinder to the right, and later from the right in the lower frame to push the cylinder

FIGURE 2.9 Watt’s double- acting steam engine.

64 CHAPTER 2 INVENTIONS FOR WORK

to the left. Note that there are three key advantages of this design: each stroke is a power stroke, which doubles the horsepower; the steam is the source of power and can be much higher than one atmospheric pressure; and the back-and-forth motion has been converted to a rotary motion suitable for many more applications.

Hotter steam provides higher power. If we substitute a 1 horsepower single- acting piston with steam at 100

C and 1.0 atmosphere pressure, with a double- acting piston with the same volume and steam at 150

C and a pressure of 5.4 atmospheres, it becomes a 10 horsepower engine. If we were to increase the steam temperature to 200 or 300

C, the steam pressure becomes 15.3 and 86.8 atmo- spheres, and the engine with the same volume becomes 30 and 173 horsepower! Of course, higher temperature and pressure also bring with them a higher danger of explosion, especially in an era before the development of high-strength steel, tight valves, and cylinders. The early Industrial Revolution witnessed a number of explo- sions that created a great deal of public fear of this dangerous venture into high- powered machinery.

Watt also invented a way to control his engine from running too fast by a throttle valve and a centrifugal governor. Many other improvements were made through the years, and he was most proud of the parallel motion/three-bar linkage patented in 1784. The sum of all these improvements produced an engine that was up to five times as efficient in its use of fuel and many times more powerful than the Newcomen engine.

SCIENCE AND TECHNOLOGY: CARNOT EFFICIENCY Let the amount of heat going into a heat engine be called Q H , and the work produced be

called W. In general, W is less than hot energy Q H , so the remaining colder energy is dis- charged and called Q C . The First Law of Thermodynamics specifies that Q H ¼WþQ C , or that the energy is conserved. Later people would say that this law shows that “There is no free lunch.”

In a heat engine, Q H is delivered at a steam temperature of T H , and the Q C is discharged at a cooling water temperature of T C . The famous Carnot rule is based on the absolute tem- perature on the Kelvin scale, where degrees Kelvin equal degrees Centigrade plus 273.1. The Carnot rule states that W =Q H ðT C =T H Þ which is to say that “You cannot break even.” So if the steam has a temperature of 150

C, and the cooling water has a temperature of 20

C, then the maximum efficiency is 1 (20 þ 273)/(150 þ 273) ¼ 0.307 or 30.7%. This is the maximum efficiency, and you usually do worse since you have leaks, heat losses, and frictions. You can increase the efficiency by making T C lower by finding a source of colder cooling water; or you can make the steam hotter by making T H higher, which also means a higher pressure.

In retrospect, James Watt was not the inventor of the steam engine. By a series of critical improvements, he made the steam engine more than five times as efficient as the previous versions, and made it popular with many mine operators and industrial manufacturers. He has been justly credited with starting the Industrial Revolution.

The steam engine had an enormous impact on modern life—perhaps the most profound impact since the invention of agriculture. The successful thermal engine converted heat energy from combustion into mechanical energy and gave us nearly

65 unlimited power. The textile mills in England made tremendous improvements in

2.2 ENERGY AND POWER

manufacturing speed and efficiency, and their productivity made European and Asian handlooms obsolete. The industrialized nations became more rich and power- ful being the workshop of manufactured goods for the world; the rest of the world were given the roles of customers of manufactured goods and providers of raw material, and became intimidated and dominated.

Within the island of Britain, manufacturing became a much more productive source of employment than traditional agriculture and animal stock keeping, which led to a mass migration of underemployed farm workers to the cities looking for better-paying jobs. The population of London grew rapidly, from 1.3 million in 1825 to 6.5 million by 1900. The steam engine also led to a revolution in transportation, including the navigation of rivers by steamboat and the connection of continents by railroads. A trip from New York to Philadelphia used to take 2 days by horse-drawn coach; on a train, it took only 2 h. Oceangoing steam ships cut the trip from London to New York from a month to 3 days. Rapid transit could now deliver heavy freight at

a fraction of the cost of animal power, which lowered the regional differences in the cost and availability of goods, and diminished barriers in languages and cultures. The Trans-Siberian Railroad played a major role in the Russian conquest of Asia, and made possible the rapid movement of troops from Moscow to Alaska.

The following decades saw many advances in the heat engine that produced power with a much smaller volume and weight, which was critical in transportation. Instead of a boiler to generate steam, and a separate cylinder and piston to generate thrust, the internal combustion engines combined the two volumes into one, such as the gasoline and diesel engines. The invention of turbines replaced the back- and-forth motion of the cylinders with the smooth rotation of wheels with blades. Since higher temperatures are needed for higher Carnot efficiency, modern turbines use very high temperature alloys and ceramic parts to withstand up to 1400

C. The coming of nuclear power created its own bright advantages and dark menaces. For all of its virtues, it must be said that the Industrial Revolution also devas- tated the lives of millions. As Charles Dickens made famous, the housing in London and Manchester was crowded and dangerous, the air was polluted by dark smoke, and the sun was seldom seen. William Blake called them the “Dark Satanic Mills.” In the countryside, the demands of fuel created Welsh coal mines with appallingly low standards of safety and sanitation. Today we have a deep concern with global warming, which has been linked to the effects of burning fossil fuels and releasing carbon dioxide into our environment. The steam engine and the Industrial Revolu- tion started a path that changed our lives and our world.