A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

STEAM ENGINES

DOI: 10.1615/AtoZ.s.steam_engines

The potential of steam, the gaseous form of water, as an agent for the transfer of heat energy into mechanical work has been known for some two millenia. The eighteen hundred times expansion which occurs when water is boiled into steam had been recognized in classical times and the magic toys or perhaps temple devices of Hero of Alexandria utilized the properties of steam in a number of ways.

However, the restrictions of technology and a defective understanding of the nature of heat precluded further advances until after 1600 when the experiments of Torricelli on atmospheric pressure, Robert Boyle with gases and the demonstrations of von Guericke of the properties of a vacuum, coupled with early glimpses of an understanding of the nature of steam led to the conjectures of Samual Morland and others as to its possible use as a source of power.

In 1675, Papin devised an apparatus whereby a weight was lifted utilizing the condensation of steam. By 1698, further developments by Thomas Savery resulted in the first commercially successful steam engine "to raise Water by the force of Fire". However this, although utilizing both the expansive and condensing properties of steam, was restricted in its application to the lifting of water and pumping. The particular requirement for the draining of mines reflected the increasing demand for minerals especially coal.

The imperative for power, which hitherto had been met by the efforts of human and animal muscle, wind and water power, engendered by the burgeoning of the industrial revolution, led to further developments. While there may have been others, Thomas Newcomen, an ironmonger of Dartmouth, is credited with the building the first steam engine in which "a piston was moved in a cylinder by the agency of steam".

Usually described as the Newcomen atmospheric engine, the first full sized example, a mine pumping engine, appears to have been built in 1712 near Dudley Castle in Staffordshire. It was probably the outcome of a long struggle with models in which the many technical difficulties such as the matching of the piston to the cylinder were at least partially overcome. The Newcomen engine derived its effort from the condensation of steam, at very nearly atmospheric pressure, in the cylinder, the other end of which was open. The resulting partial vacuum led to the piston being forced down by atmospheric pressure. The piston was connected to a pivoted beam, which at its other end held a heavy set of pump rods. A valve was opened into the cylinder below the piston and steam (at a very low pressure) admitted. This permitted the piston to rise, drawn up by the weight of the pump rods. The. cycle was then repeated.

Immensely inefficient in that its action depended on the alternative heating and cooling of water and steam, the Newcomen engine nonetheless achieved widespread acceptance for pumping applications and by the middle of the eighteenth century several hundreds were in use.

In 1763, James Watt, a Glasgow instrument maker, developed and later patented his invention of the separate condenser, thus eliminating one of the major ineficiencies of the Newcomen engine. While still using steam at very low pressures, the increased efficiency of the Watt engines enabled them to be developed for rotative purposes. Aided by the manufacturing and business acumen of Watt's partner, Matthew Boulton of Birmingham, and his assistant, William Murdoch, their use became widespread. Almost contemporaneously Richard Trevithick used his experience with Cornish mining engines to employ the increased potential for work of the expansive properties of high pressure steam.

Technical advances such as the ironfounding innovations of the Darbys of Coalbrookdale, as well as the large cylinder boring techniques of Wilkinson soon resulted in the steam engine becoming the prime mover and facilitator of the rapid expansion of the industrial revolution, first in Britain then in Europe and the United States. As a translator of heat to mechanical energy, its potential for terrestrial and marine transport was being widely explored.

In Cornwall particularly the further applications of high pressure steam were investigated which lead to the development of Woolf ’s compound engines and the development of boiler design. At the same time, much effort and ingenuity was deployed in the development of valve gears, condenser design and packing and sealing materials.

The theoretical aspects of the steam engine remained empirical and erroneously understood. Concepts of the nature of heat were allied to current ideas of caloric and related power to steam pressure. The writings of Carnot, and the experiments of Count Rumford, and James Joule of Manchester culminated, in 1843 with the introduction of new concepts which led to the understanding that "Heat and energy are mutually convertible . . ." and that the heat in a steam engine is the vital driving force and the pressure only a secondary force.

The work of Rankine and William Thomson (Lord Kelvin) further clarified the theoretical understandings and demonstrated that the steam engine was extremely inefficient. Thomson derived the key formula for the efficiency of a perfect heat engine which showed that the greater the temperature drop, the greater the efficiency of the engine. Henceforth the emphases of development were directed to "improving the construction of the steam engine and in seeking to obtain from it a larger amount of useful work with a given expenditure of fuel". There followed many technical advances including the Corliss Valve, high speed engines and improved governors. Towards the end of the nineteenth century the demands of steam power to generate electricity, as well as the massive power demands of textile mills and metal industries, represented only a fraction of the fields of application for what had become a universal prime mover. Other developments involved the Uniflow concept, superheating and innovations in boiler design and fuel utilization.

The reciprocating engine utilizes the expansion of steam, but the Aelopile of Hero, a turbine like toy, demonstrated the kinetic energy of steam. In 1884, Charles Parsons pioneered its practical application in the Steam Turbine. In this, the steam acts by either impulse or reaction as a mass that is set in motion in consequence of its own power to expand. Much development, including the discovery of the major contribution of efficient condensers to cycle efficiency, demonstrated the particular advantages of steam turbines for high speed applications such as electricity generation and, with appropriate gearing, ship propulsion.

Despite the development of various modes of internal combustion engine and their primacy in terms of size, flexibility and relative efficiency, the steam engine in its turbine incarnation remains a widely used form of power generator, and is virtually the universal final stage of the various methods of the conversion of nuclear energy into power.

REFERENCES

Bourne, J. (1846) A Treatise on the Steam Engine, Longmans, London.

Dickinson, H. W. (1938) A Short History of the Steam Engine, Cambridge, U.P. DOI: 10.1016/S0016-0032(39)90848-3

Farey, J. A. (1971) A Treatise on the Steam Engine, Volste 1 and 2, David and Charles.

Hills, R. L. (1988) Power from Steam, Cambridge, U.P.

Rankine, W. J. M. (1861) A Manual of the Steam Engine and Other Prime Movers, Griffin, Bohn, London.

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