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James Watt
Cải tiến máy hơi nước; Cách mạng công nghiệp
- 1736 – 1819
- Sảnh các Nhà phát minh và Kỹ sư · 5/12
Sảnh các Nhà phát minh và Kỹ sư
Cải tiến máy hơi nước; Cách mạng công nghiệp
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James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, engineer and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.
While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines. At the time engineers such as John Smeaton were aware of the inefficiencies of Newcomen's engine and aimed to improve it. Watt's insight was to realise that contemporary engine designs wasted a great deal of energy by repeatedly cooling and reheating the cylinder. Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines. Eventually, he adapted his engine to produce rotary motion, greatly broadening its use beyond pumping water.
Watt attempted to commercialise his invention, but experienced great financial difficulties until he entered a partnership with Matthew Boulton in 1775. The new firm of Boulton and Watt was eventually highly successful and Watt became a wealthy man. In his retirement, Watt continued to develop new inventions though none was as significant as his steam engine work.
As Watt developed the concept of horsepower, the SI unit of power, the watt, was named after him.
James Watt was born on 19 January 1736 in Greenock, Renfrewshire, the eldest of the five surviving children of Agnes Muirhead (1703–1755) and James Watt (1698–1782). Watt was baptised on 25 January 1736 at Old West Kirk, in Greenock. His mother came from a distinguished family, was well educated and said to be of forceful character, while his father was a shipwright, ship owner and contractor, and served as the Greenock's chief baillie in 1751. The Watt family's wealth came in part from Watt's father's trading in slaves and slave-produced goods. Watt's parents were Presbyterians and strong Covenanters, but despite his religious upbringing he later became a deist. Watt's grandfather, Thomas Watt (1642–1734), was a teacher of mathematics, surveying and navigation and baillie to the Baron of Cartsburn.
Initially, Watt was educated at home by his mother, later going on to attend Greenock Grammar School. There he exhibited an aptitude for mathematics, while Latin and Greek failed to interest him.
Watt is said to have suffered prolonged bouts of ill-health as a child and from frequent headaches all his life.
After leaving school, Watt worked in the workshops of his father's businesses, demonstrating considerable dexterity and skill in creating engineering models. After his father suffered unsuccessful business ventures, Watt left Greenock to seek employment in Glasgow as a mathematical instrument maker.
When he was 18, Watt's mother died and his father's health began to fail. Watt travelled to London and was able to obtain a period of training as an instrument maker for a year (1755–56), then returned to Scotland, settling in the major commercial city of Glasgow, intent on setting up his own instrument-making business. He was still very young and, having not had a full apprenticeship, did not have the usual connections via a former master to establish himself as a journeyman instrument maker.
Watt was saved from this impasse by the arrival from Jamaica of astronomical instruments bequeathed by Alexander MacFarlane to the University of Glasgow – instruments that required expert attention. Watt restored them to working order and was remunerated. These instruments were eventually installed in the Macfarlane Observatory. Subsequently, three professors offered him the opportunity to set up a small workshop within the university. It was initiated in 1757 and two of the professors, the physicist and chemist Joseph Black as well as the famed economist Adam Smith, became Watt's friends.
At first, he worked on maintaining and repairing scientific instruments used in the university, helping with demonstrations, and expanding the production of quadrants. He made and repaired brass reflecting quadrants, parallel rulers, scales, parts for telescopes, and barometers, among other things.
Biographers such as Samuel Smiles assert that Watt struggled to establish himself in Glasgow due to opposition from the Trades House, but this has been disputed by other historians, such as Harry Lumsden. The records from this period are fragmentary, but while it is clear that Watt encountered opposition, he was nevertheless able to work and trade as a skilled metal worker, suggesting that the Incorporation of Hammermen were satisfied that he met their requirements for membership, or that Watt managed to avoid their outright opposition.
In 1759, he formed a partnership with John Craig, an architect and businessman, to manufacture and sell a line of products including musical instruments and toys. This partnership lasted for the next six years, and employed up to 16 workers. Craig died in 1765. One employee, Alex Gardner, eventually took over the business, which lasted into the 20th century.
In 1764, Watt married his cousin Margaret (Peggy) Miller, with whom he had 5 children, 2 of whom lived to adulthood: James Jr. (1769–1848) and Margaret (1767–1796). His wife died in childbirth in 1773. In 1777, he married again, to Ann MacGregor, daughter of a Glasgow dye-maker, with whom he had 2 children: Gregory (1777–1804), who became a geologist and mineralogist, and Janet (1779–1794). Ann died in 1832. Between 1777 and 1790 he lived in Regent Place, Birmingham.
There is a popular story that Watt was inspired to invent the steam engine by seeing a kettle boiling, the steam forcing the lid to rise and thus showing Watt the power of steam. This story is told in many forms; in some Watt is a young lad, in others he is older, sometimes it's his mother's kettle, sometimes his aunt's, suggesting that it may be apocryphal. In any event, Watt did not invent the steam engine, but significantly improved the efficiency of the existing Newcomen engine by adding a separate condenser, consistent with the now-familiar principles of thermal efficiency. The story was possibly created by Watt's son, James Watt, Jr., who was determined to preserve and embellish his father's legacy. In this light, it can be seen as akin to the story of Isaac Newton and the falling apple and his discovery of gravity.
Although likely a myth, the story of Watt and the kettle has a basis in fact. In trying to understand the thermodynamics of heat and steam, James Watt carried out many laboratory experiments and his diaries record that in conducting these, he used a kettle as a boiler to generate steam.
In 1759 Watt's friend John Robison called his attention to the use of steam as a source of motive power. The design of the Newcomen engine, in use for almost 50 years for pumping water from mines, had hardly changed from its first implementation. Watt began to experiment with steam, though he had never seen an operating steam engine. He tried constructing a model; it failed to work satisfactorily, but he continued his experiments and began to read everything he could about the subject. He came to realise the importance of latent heat—the thermal energy released or absorbed during a constant-temperature process—in understanding the engine, which, unknown to Watt, his friend Joseph Black had previously discovered years before. Understanding of the steam engine was in a very primitive state, for the science of thermodynamics would not be formalised for nearly another 100 years.
In 1763, Watt was asked to repair a model Newcomen engine belonging to the university. Even after repair, the engine barely worked. After much experimentation, Watt demonstrated that about three-quarters of the thermal energy of the steam was being consumed in heating the engine cylinder on every cycle. This energy was wasted because, later in the cycle, cold water was injected into the cylinder to condense the steam to reduce its pressure. Thus, by repeatedly heating and cooling the cylinder, the engine wasted most of its thermal energy rather than converting it into mechanical energy.
Watt's critical insight, arrived at in May 1765 as he crossed Glasgow Green park, was to cause the steam to condense in a separate chamber apart from the piston, and to maintain the temperature of the cylinder at the same temperature as the injected steam by surrounding it with a "steam jacket". Thus, very little energy was absorbed by the cylinder on each cycle, making more available to perform useful work. Watt had a working model later that same year.
Despite a potentially workable design, there were still substantial difficulties in constructing a full-scale engine. This required more capital, some of which came from Black. More substantial backing came from John Roebuck, the founder of the celebrated Carron Iron Works near Falkirk, with whom he now formed a partnership. Roebuck lived at Kinneil House in Bo'ness, during which time Watt worked at perfecting his steam engine in a cottage adjacent to the house. The shell of the cottage, and a very large part of one of his projects, still exist to the rear.
The principal difficulty was in machining the piston and cylinder. The ironmasters at Coalbrookdale had cast and bored cylinders for Newcomen engines for decades, but a cylinder procured from them by William Small for the Kinneil engine proved unsatisfactory. Watt's engine needed a piston that was air tight, whereas Newcomen engines used a little water above the piston, so the seal only had to be water tight. Much capital was spent in pursuing a patent on Watt's invention. Strapped for resources, Watt was forced to take up employment—first as a surveyor, then as a civil engineer—for 8 years.
Roebuck went bankrupt, and Matthew Boulton, who owned the Soho Manufactory works near Birmingham, acquired his patent rights. An extension of the patent to 1800 was successfully obtained in 1775.
Through Boulton, Watt finally had access to some of the best iron workers in the world. The difficulty of the manufacture of a large cylinder with a tightly fitting piston was solved by John Wilkinson, who had developed precision boring techniques for cannon making at Bersham, near Wrexham, North Wales. Watt and Boulton formed a hugely successful partnership, Boulton and Watt, which lasted for the next 25 years.
In 1776, the first engines were installed and working in commercial enterprises. These first engines were used to power pumps and produced only reciprocating motion to move the pump rods at the bottom of the shaft. The design was commercially successful, and for the next five years, Watt was very busy installing more engines, mostly in Cornwall, for pumping water out of mines.
Boulton and Watt did not have their own foundry until Soho foundry opened in 1795, so the main castings and cylinders were made by others according to drawings made by Watt, who served in the role of consulting engineer. The erection of the engine and its shakedown was supervised by Watt, at first, and then by men in the firm's employ, with the actual work being accomplished by the purchaser of the engine. Supervising erectors included at various times William Murdoch, John Rennie, William Playfair, John Southern, Logan Henderson, James Lawson, William Brunton, Isaac Perrins, and others.
These were large machines. The first, for example, had a cylinder with a diameter of 50 inches and an overall height of about 24 feet, and required the construction of a dedicated building to house it. Boulton and Watt charged an annual payment, equal to one-third of the value of the coal saved in comparison to a Newcomen engine performing the same work.
The field of application for the invention was greatly widened when Boulton urged Watt to convert the reciprocating motion of the piston to produce rotational power for grinding, weaving and milling. Although a crank seemed the obvious solution to the conversion, Watt and Boulton were stymied by a patent for this, whose holder, James Pickard and his associates proposed to cross-license the external condenser. Watt adamantly opposed this and they circumvented the patent by their sun and planet gear in 1781.
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