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    Energy conversion

    Developments of the Industrial Revolution

    Steam engines

    The rapid growth of industry in Britain from about the mid-18th century (and somewhat later in various other countries) created a need for new sources of motive power, particularly those independent of geographic location and weather conditions. This situation, together with certain other factors, set the stage for the development and widespread use of the steam engine, the first practical device for converting thermal energy to mechanical energy.

    The foundations for the use of steam power are often traced to the experimental work of the French physicist Denis Papin. In 1679 Papin invented a type of pressure cooker, a closed vessel with a tightly fitting lid that confined steam until high pressure was generated. Observing that the steam in the vessel raised the lid, he conceived the idea of using steam to power a piston and cylinder engine.

    Thomas Savery, an English inventor and military engineer, studied Papin’s work and built a steam-driven suction machine for removing water from coal mines. Savery’s machine (patented in 1698) consisted of a boiler, a closed, water-filled reservoir, and a series of valves. Steam was introduced into the reservoir, and the pressure of the steam forced the water out through a one-way outlet valve until the vessel was empty. Water was then sprayed over the surface of the vessel to condense the steam and create a vacuum capable of drawing up more water through a valve below. Unfortunately the vacuum created was not perfect, and so water could only be lifted to a limited height.

    Newcomen engine

    Some years later another English engineer, Thomas Newcomen, developed a more efficient steam pump consisting of a cylinder fitted with a piston—a design inspired by Papin’s aforementioned idea. When the cylinder was filled with steam, a counterweighted pump plunger moved the piston to the extreme upper end of the stroke. With the admission of cooling water, the steam condensed, creating a vacuum. The atmospheric pressure in the mine acted on the piston and caused it to move down in the cylinder, and the pump plunger was lifted by the resulting force.

    Because Savery had obtained a broad patent for his steam device, Newcomen could not patent his engine. He thus entered into a partnership with Savery, and together they built, in 1712, the first piston-operated steam pump. Several years later Smeaton improved the Newcomen engine, almost doubling its efficiency. Although engines of this kind converted only about 1 percent of the thermal energy in the steam to mechanical energy, they remained unrivaled for more than 50 years.

    Watt’s engine

    In 1765 James Watt, a Scottish instrument maker and inventor, modified a Newcomen engine by adding a separate condenser to make it unnecessary to heat and cool the cylinder with each stroke. Because the cylinder and piston remained at steam temperature while the engine was operating, fuel costs dropped by about 75 percent.

    Watt entered into a partnership with Matthew Boulton, who owned a factory in Soho, near Birmingham, England. At Boulton’s insistence he set out to develop a new kind of engine that rotated a shaft instead of providing simple up-and-down motion. He found a way to obtain an inflexible connection between piston and rod (beam) and invented special gear arrangements to convert the up-and-down movement of the beam into circular motion. A heavy flywheel was added to smooth out the variations in the force delivered to the engine shaft by the action of the piston in the cylinder. The flow of steam to the engine was regulated by a governor connected to the flywheel. In addition, Watt applied steam to both sides of the piston to produce greater uniformity of effort and increased power.

    Although far more difficult to build, Watt’s rotative engine opened up an entirely new field of application: it enabled the steam engine to be used to operate rotary machines in factories and cotton mills. The rotative engine was widely adopted; it is estimated that by 1800 Watt and Boulton had built 500 engines, of which less than 40 percent were pumps and the rest were of the rotative type.

    High-pressure steam engines

    Although Watt understood the advantages of utilizing the expansive power of steam within a cylinder, he refused to use steam under high pressure for reasons of safety. This limited the application of steam engines. By the early years of the 19th century, however, the American inventor Oliver Evans had built a stationary high-pressure steam engine for driving a rotary crusher to produce pulverized limestone for agricultural use. Within a few years Evans had designed lighter-weight high-pressure steam engines that could do various other tasks, such as drive sawmills, sow grain, and power a dredge. From 1806 to about 1816 he produced more than 100 steam engines that were employed with screw presses for processing paper, cotton, and tobacco.

    Other major advances in the use of high-pressure steam were achieved by Richard Trevithick in England during the early years of the 19th century. Trevithick built the world’s first steam-powered railway locomotive in 1803. Two years later he adapted his high-pressure steam engine to drive an iron-rolling mill and to propel a barge with the help of paddle wheels.

    Watt’s engine was able to convert only a little more than 2 percent of the thermal energy in steam to work. The improvements introduced by Evans, Trevithick, and others (e.g., three separate expansion cycles and higher steam temperatures) increased the efficiency of the steam engine to roughly 17 percent by 1900. Yet, within the next decade the steam engine was supplanted for various important applications by the more efficient steam turbine. Owing to technological advances and the use of high-temperature steam, steam turbines have attained an efficiency of thermal energy conversion of approximately 40 percent.

    Everett B. Woodruff The Editors of Encyclopaedia Britannica

    Stirling engine

    Many of the early high-pressure steam boilers exploded because of poor materials and faulty methods of construction. The resultant casualties and property losses motivated Robert Stirling of Scotland to invent a power cycle that operated without a high-pressure boiler. In his engine (patented in 1816), air was heated by external combustion through a heat exchanger and then was displaced, compressed, and expanded by two pistons. Stirling also conceived the idea of a regenerator to store thermal energy during part of the cycle and then return this energy to the working fluid. A successful Stirling engine was built for factory use in 1843, but general use was restricted by the high cost of the device. Nevertheless, until about 1920, small engines of this type were used to pump water on farms and to generate electricity for small communities.

    Since the Stirling engine is efficient, produces less pollution than most other kinds of engines, and operates on virtually any kind of fuel, efforts have been made intermittently since the late 1930s to reduce its manufacturing costs. Modern versions of the Stirling engine employ pressurized hydrogen or helium instead of air. Since the 1970s the engine has been adapted for many uses, including cryogenic refrigeration, submarine propulsion, and electrical production.

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