What are the advantages of the steam engine invented by Watt?

The steam engine is a reciprocating power machine, which converts the energy of steam into mechanical work. The appearance of the steam engine caused the industrial revolution in the18th century. Until the beginning of the 20th century, it was still the most important prime mover in the world, and then it gradually gave way to internal combustion engines and steam turbines.

From the end of 16 to the end of 17, the British mining industry, especially coal mines, has developed to a considerable scale, and it is difficult to meet the requirements of pumping groundwater only by manpower and animal power, and there are abundant and cheap coal as fuel on site. The needs of reality have prompted many people in Britain, such as Papan, savery and newcomen, to devote themselves to the exploration and experiment of "lifting water by firepower".

The world's first practical steam pump made in savery won the British patent named "Friends of Miners" on 1698. He first filled an egg-shaped container with steam, then closed the steam inlet valve and sprayed cold water outside the container to condense the steam in the container to form a vacuum. Open the water inlet valve, and the water at the bottom of the mine is sucked into the container through the water inlet pipe under the action of atmospheric pressure; Close the water inlet valve, reopen the steam inlet valve, and use steam pressure to press the water in the container out through the drain valve. When the water in the container is drained and filled with steam, close the steam inlet valve and drain valve, and spray water again to condense the steam. In this way, the two egg-shaped containers work alternately and can continuously drain water.

The pumps in savery rely on vacuum suction to pump water, and the pumping depth cannot exceed six meters. In order to pump water from a mine tens of meters deep, it is necessary to install a water pump in the depth of the mine and use high steam pressure to pump water to the ground, which is undoubtedly difficult and dangerous at that time.

Newcomen and his assistant Cali invented the atmospheric steam engine in 1705 to drive the independent water pump, which is called the newcomen atmospheric steam engine. This kind of steam engine was first popularized in Britain, then in continental Europe, and its modified products were still being manufactured until the beginning of19th century. The thermal efficiency of newcomen atmospheric steam engine is very low, which is mainly due to the fact that after steam enters the cylinder, it condenses on the cylinder wall that has just been cooled by water and loses a lot of heat. It is only promoted in coal-producing areas with low coal prices.

1764, British instrument repairman Watt noticed this shortcoming when repairing the newcomen steam engine model for Glasgow University, and invented the steam engine with the condenser separated from the cylinder wall in 1765, and obtained the British patent in 1769. In the early days, Watt's steam engine still used the balance bar and pull rod mechanism to drive the water pump. In order to remove the condensate and air from the condenser, Watt installed an air pump. He also installed an interlayer on the outer wall of the cylinder and heated the cylinder wall with steam to reduce condensation loss.

1782 or so, Watt further improved the machine and completed two important inventions: in the middle of the active cold working stroke, the steam inlet valve was closed to make the steam expand to do work and improve the thermal efficiency; Make the steam do work on both sides of the piston (double-acting) to improve the output power. At this time, the piston has to pull down the lever and push up the lever, and the fan-shaped balance bar and zipper are no longer applicable, so Watt invented the parallelogram mechanism. Watt also applied crank-connecting rod mechanism to steam engine at the end of 18.

Watt's creative work made the steam engine develop rapidly. He turned the machine that can only carry water into a widely used steam engine, which doubled the thermal efficiency and greatly reduced the coal consumption. So Watt was the main inventor of the steam engine.

/kloc-Since the late 8th century, steam engines have been widely used not only in mining, but also in smelting, textile, machinery manufacturing and other industries. It has increased the textile output in Britain by five times (from 1766 to 1789) in more than 20 years, provided a large number of consumer goods for the market, accelerated the accumulation of funds and put forward urgent requirements for the transportation industry.

The experiment of using steam engine as propulsion power on ships began in 1776. After continuous improvement, Fulton, USA made the first practical open-wheel propulsion steam engine ship "clermont". Since then, steam engines have been used as propulsion power on ships for more than one hundred years.

180 1 year, Trevithick of England put forward the concept of movable steam engine. 1803, this kind of movable steam engine using railway tracks first appeared in coal mining area, which is the prototype of locomotive. Stephenson of Britain improved the locomotive continuously, and created the "rocket" steam locomotive in 1829. The locomotive is towing a carriage with 30 passengers at a speed of 46 km/h, which has attracted the attention of all countries and created the railway era.

At the end of 19, with the rise of electric power application, steam engines were once used as the main power machinery of power stations. /kloc-in 0/900, there was a steam engine power station with a single unit power of 5 MW in new york, USA.

The development of steam engines reached its peak in the early 20th century. It has the advantages of constant torque, variable speed, reversibility, reliable operation and convenient manufacture and maintenance, so it was widely used in power stations, factories, locomotives, ships and other fields, especially in warships, and became the only prime Mover at that time.

Steam engines can be divided into single-acting and double-acting types according to the fact that steam works on one or both sides of the piston; According to the arrangement of cylinders, it can be divided into vertical and horizontal; According to whether steam expands in one cylinder or continuously in multiple cylinders, it can be divided into single expansion type and multiple expansion type; According to the flow direction of steam in the cylinder, it can be divided into reflux type and single flow type; According to the exhaust mode and exhaust pressure, it can be divided into condensation type, atmospheric type and back pressure type.

The simple steam engine is mainly composed of cylinder, base, piston, crank-connecting rod mechanism, slide valve steam distribution mechanism, speed regulating mechanism and flywheel. The cylinder and base are static parts. The new steam from the boiler enters the slide valve chamber through the main steam valve and throttle valve, and is controlled by the slide valve to alternately enter the left or right side of the cylinder to push the piston to move.

The development of steam engine is first reflected in the improvement of power and efficiency, which mainly depends on the improvement of steam parameters. At the beginning of the steam engine, the steam pressure was only 0.11~ 0.13mpa, and1reached 0.35 ~ 0.7 MPa at the beginning of the 9th century. 10 MPa in the 1920s. In terms of steam temperature, 19 did not exceed 250℃ at the end of the year, but it was used at 450 ~ 480℃ in the 1930s.

As for the efficiency, the total efficiency of the steam engine running continuously in the initial stage of Watt is less than 3% according to the calorific value of fuel; By 1840, the total efficiency of the best condensing steam engine can reach 8%; By the 20th century, the highest efficiency of steam engines can reach more than 20%.

In terms of rotational speed, at the end of 18, Watt steam engine only had 40 ~ 50 revolutions; At the beginning of the 20th century, the speed reached 100 ~ 300 rpm, and some steam engines once reached 2500 rpm. In terms of power, the power of a single machine was only a few horsepower at first, and the power of a marine steam engine at the beginning of the 20th century could reach 25,000 horsepower.

With the improvement of steam parameters and power, steam can not continue to expand in one cylinder, but must continue to expand in the connected cylinder, so there is a multi-stage expansion steam engine. Due to the limitation of the flash point of lubricating oil, the maximum temperature of steam used in steam engines is generally lower than 400℃, and mobile steam engines such as locomotives and ships are slightly lower, most of which are not higher than 350℃. Considering the possibility of expansion and the economy of the structure, the common pressure is below 2.5 MPa. The limited steam parameters also limit the further improvement of steam engine power.

The appearance and improvement of the steam engine promoted the social and economic development, but at the same time, the economic development in turn put forward higher requirements for the steam engine, such as high power, high efficiency, light weight and small size. Although people have made many improvements to the steam engine, expanding the scope of use and improving the performance, with the development of steam turbines and internal combustion engines, the steam engine has gradually declined because of its insurmountable weaknesses.

The weaknesses of the steam engine are: the boiler is indispensable, and the whole device is bulky; The pressure and temperature of fresh steam should not be too high, and the exhaust pressure should not be too low, so it is difficult to improve the thermal efficiency; It is a reciprocating machine, and the inertia force limits the increase of rotation speed; The working process is discontinuous and the steam flow is limited, which limits the promotion of power.

Therefore, the internal combustion engine, which abandoned the heavy boiler, gradually replaced the steam engine on ships and locomotives with its advantages of light weight, small volume, high thermal efficiency and flexible operation. The steam turbine has the advantages of high thermal efficiency, high single machine power, high rotating speed, light weight per unit power and stable operation, so the steam engine is pushed out of the power station.

Then the motor replaced the application of steam engine in industrial equipment because of its convenient use. The thermal efficiency of low-power steam engines is higher than that of steam turbines, so there is still room for steam engines to play a role in coal-producing areas or areas with only inferior fuels, or in some special occasions.

The steam engine has a great historical role, which has promoted the development of machinery industry and even society. The thermodynamics and mechanism established with its development laid the foundation for the development of steam turbines and internal combustion engines. Steam turbine inherits the characteristics of steam engine using steam as working medium, adopts condenser to reduce exhaust pressure, and abandons the shortcomings of reciprocating motion and intermittent steam intake; The internal combustion engine inherits the basic structure and transmission form of the steam engine, and forms a thermal cycle with much higher thermal efficiency by directly inputting fuel into the cylinder for combustion. At the same time, cylinders, pistons, flywheels, flying hammer governors, valves and seals used in steam engines are the basic components of many modern machines.