Steam Revolution: The Industrial Revolution
According to legend, James Watt came up with a steam engine, looking at the steam coming out of the spout of a boiling kettle. Of course, this is just a myth. In fact, the history of steam engines dates back many centuries, dozens of names and countless designs, some of which remained on paper. And yet not one grave in Westminster Abbey has such a respectful epitaph as on the grave of Watt. His name is the familiar unit of power, watt, equal to 1/746 hp. What did this famous Scot do, and what helped him to make such a significant contribution to technological progress?
Toys of the Ancients
The first mention of the use of steam power to perform mechanical work is found in the writings of scientists who worked in the famous Alexandrian museion 150 years before our era. From the book of Heron of Alexandria that has come down to us, we learn about the amazing mechanisms invented by himself and his predecessors Ktesiby and Filon. These witty devices were more like toys made for the amusement of the public, but in fact were the result of real physical experiments, from which conclusions were drawn about the properties of substances.
Here we find the first descriptions of a siphon, thermoscope and a distant ancestor of a steam turbine.
From the book of Heron it is clear that the Greeks at the beginning of our era possessed sufficient technical knowledge to anticipate machines that appeared only in the XVIII century. They knew gears, hydrostatics, siphon applications, air compressibility, and the driving force of steam. But things didn’t go beyond toys for entertaining the public, “magical” effects in temples and weapons devices like catapults.
In the records of Heron, which, fortunately, have not been lost for centuries, you can find a detailed description of about a hundred such structures. At number 11, here is the first mention of the use of heat to propel liquids: after a fire was made on the altar, liquid began to pour from the vessel that the figure held in the hands of the pedestal, symbolizing the fulfillment of the libation. Most often, they cite as an example the largest building in the literal sense of the word, described by Heron at number 37 - a device for automatically opening the doors of a temple. It was more complicated and spectacular than the previous one. The priest made a fire in the altar located in front of the temple, and when the fire flared up enough, the doors of the temple opened wide for the delight of believing spectators.
With the beginning of the Roman era, science gradually began to decline, the Alexandrian museon was closed, and as much as 1.5 thousand years were forgotten about the properties of water vapor.
Well forgotten old
Mention of the first attempts of Europeans to reproduce Greek steam engines are found closer to the XVI century. (Although one case in Reims is known that dates back to 1120, when a local school professor Herbert built an organ where air was pumped, previously “compressed by heating water.”)
Then, more than 400 years ago, the first mention of atmospheric pressure had just appeared, and there was a debate in the European scientific community about the nature of heat. It was the time of creating thermometers and temperature scales, studying the properties of gases and trying to master the force of expansion of water vapor. It was experimentally established that when the steam is cooled in a closed container, a noticeable rarefaction (pressure decrease) occurs, which can also be used to perform mechanical work. When finally it was possible to more or less deal with atmospheric pressure, temperature, some properties of gases and obtaining a "vacuum", it was time to move from science to practice.
The greatest success in applying this knowledge was made by the British. Engineer Severy and self-taught Newcomen designed a heat engine to lift water from coal mines. In their machine, the steam produced in the boiler flowed through the valve into the cylinder, raising the piston. Then the valve was closed and the cylinder was watered with cold water, while the steam condensed, a vacuum arose and the piston dropped under the influence of atmospheric pressure. Although these devices consumed a huge amount of heat and had an efficiency of approximately 0.5%, they served almost half a century in the coal mines of Cornwall and Northern England and were even sold on the continent.
The mystery of "hidden warmth"
Watt worked at the University of Glasgow, where he was engaged in the manufacture of mechanical instruments, chemistry, physics and was an assistant to Professor Joseph Black, who not only taught, but also conducted experiments and studied thermal processes. Being a very advanced educational institution at that time, the university for the study of natural sciences acquired the most modern and expensive device - the Newcomer engine. Having received an offer to repair it, Watt seriously engaged in research on steam engines. To begin with, he studied in detail the works of his predecessors, and when he tried to understand the operation of the engine, he discovered that he consumes an excessively large amount of fuel. Why? There was no answer, and Watt decided to make his own experimental setup.
He built a new boiler to measure the amount of evaporated water and condensed steam in each engine cycle. The first experimental conclusion was this: very little steam is enough to heat a large amount of water. After discussing the results of experiments with Black, Watt received detailed explanations from the professor about this phenomenon - it turned out that Watt's experiments confirmed the guesses of Black himself
about the existence of "latent heat."
The professor told his assistant about the following. Consider the process of converting water to steam. We supply heat and the water gradually heats up to a boiling point of 100 ° C. To turn it all into steam, you need to continue heating. We continue to heat up, but the temperature does not increase and remains at 100 ° C until all the water has boiled away. Only after this does the temperature of steam begin to increase with further heating. This means that all the heat transferred to the substance during the evaporation process is stored or “hidden” inside the steam. Moreover, the amount of this thermal energy is very significant: steam can heat five times more water from the freezing point to boiling than it weighs: if we combine 5 kg of water at 0 ° C and 1 kg of steam at 100 ° C, we get 6 kg of boiling water. And if instead of steam you take water at the same 100 ° C, you get 6 kg of water with a temperature of just a little over 16 ° C.
About the benefits of walking
The first experiments were followed by careful quantitative measurements. Having determined that steam is by weight a much larger heat accumulator than water, Watt realized that to reduce losses, you need to find a way to keep the cylinder as hot as the steam entering it during the entire cycle of the engine. At first he tried to make a more economical cylinder by using wooden materials with greater thermal insulation and heat-conducting tubes, but no significant changes occurred. A fundamentally different solution was needed.
One evening, Watt went out for a walk, as always, without ceasing to reflect on the steam engine. Passed by the old laundry room and the shepherd’s house, when a wonderful idea occurred to him: if the steam has the property of elasticity, it will move into a vacuum, and if the cylinder is connected to the evacuated tank, the steam rushes there and can be condensed without cooling the cylinder. When Watt returned home, a new design was already ready in his head. So the missing element of the steam engine was invented - a separate container for condensation of steam, which in modern devices is called a condenser.
To test his invention, Watt used a large brass surgical syringe 35 cm in diameter and 25 cm long as a steam cylinder and piston. The syringe was turned upside down and the piston rod hung down for convenience, and above and below there were tubes for introducing steam from the boiler, equipped with taps that acted as steam valves. The tube also led from a cylinder to a condenser made of two tin tubes connected together, and another tube connected to the condenser, where Watt inserted a small piston, was used to pump out air. All three tubes were lowered into a container of cold water. This small model turned out to be workable, and the quality of the vacuum was such that the piston lifted a weight of 7 kg!
The condenser made it possible to reduce fuel consumption by almost five times compared to the Newcomen machine and increase the efficiency to 2.5%. But Watt did not stop there. He found that the valve can be closed before the cylinder is completely filled with steam, because the steam, expanding, will still raise the piston. As a result of such additional savings, efficiency increased to 4.5%. Further, Watt connected a rotary-translational mechanism to his design, made a two-way steam inlet, a steam jacket around the cylinder - that is, he introduced practically all the elements of modern steam engines that people used for almost 200 years, until in the 20th century they were replaced by more efficient engines internal combustion.
In our time, steam locomotives have already become a rarity, but without the use of the driving force of steam, modern life is still impossible to imagine. After all, the main element of all current power plants is a steam turbine, the next step in the history of steam engines. Here the steam does not lift the piston, but turns the blades, which turned out to be much more profitable from the point of view of energy consumption.
However, the first working prototype of a steam turbine - "eolipil" - is described in the book of Heron of Alexandria at number 50. Two thousand years ago, the use of this jet steam engine was fully consistent with the needs of the time - using it they created moving images around the altar.
With Greek eolipil, modern steam turbines are related, perhaps, only to steam and the idea of using its driving force. Although hundreds of technical inventions and improvements have already been incorporated into them, they have an efficiency of over 40% and a capacity of hundreds of megawatts, their most important element, in addition to the wheel with vanes, is the condenser, the same pumped-out tank invented by Watt, where steam rushes from the steam boiler, causing turbine blades to spin wildly and giving us all the gigantic reserves of its “latent heat”.The article was published in the journal Popular Mechanics (No. 5, May 2005).