Modern Engineering Thermodynamics

474 CHAPTER 13: Vapor and Gas Power Cycles
Note that the effect of a single regeneration unit in the previous example was to increase the thermal efficiency
by only 1.1%. The extra expense of the regenerators and the additional pumps cannot be economically justified
unless the system is large enough to make such a small thermal efficiency increment produces a significant savings
in fuel costs.
This type of Rankine cycle regeneration was first seriously proposed in 1890 and first implemented in 1898 with
a four-stage, quadruple-expansion (quadruplex), reciprocating piston-cylinder steam engine. This system
achieved an actual thermal efficiency of 22.8%, which was remarkably high for its day. After about 1910, the
production of large reciprocating piston-cylinder steam engines decreased rapidly. They were being replaced by a
new prime mover technology, the steam turbine. Consequently, regeneration was temporarily discontinued until
about 1920, at which point the steam turbine had been established as the preferred prime mover for large stationary
power plants. After 1920, regeneration became standard practice in the design of large, vapor cycle, turbine,
prime mover power plants.
WHAT IS THE WORLD’S SMALLEST STEAM ENGINE?
The world’s smallest steam engine was built using nanotechnology (the ability to create objects at the atomic scale). It is
about 5 microns wide (approximately the size of a red blood cell), and was developed by Dr. Jeff Sniegowski at Sandia
National Laboratories in Albuquerque, New Mexico. Steam is produced by a small electrical current that boils the water in
a tiny boiler. The engine was built using computer chip technology by photographing and reducing an image to a very
small size, then etching it on a silicon wafer. The etchings are done in layers to build up the three-dimensional working
engine. However, you need an electron microscope to see it.
13.8 THE DEVELOPMENT OF THE STEAM TURBINE
By the end of the 19th century, the large, slow-speed reciprocating piston-cylinder steam engine had reached its
upper limit in size and complexity. When the maximum practical piston speed had been reached in reciprocating
steam engine design, the only way to increase the work output further was to increase the physical size of
the engine. The largest reciprocating steam engine ever built in the United States was constructed in 1891 by the
E. P. Allis Company (renamed the Allis Chalmers Company in 1901) of Milwaukee, Wisconsin. It was installed
as a pumping engine at the Chapin mine in Iron Mountain, Michigan, in 1892. It was a duplex steeple
compound condensing engine with high-pressure cylinders 50. inches in diameter and low-pressure cylinders
100. inches in diameter, both with strokes of 10 ft. It was 54 ft high, 75 ft long, weighed 725 tons, and had a
flywheel 40. ft in diameter. At its maximum speed of 10. rpm it could produce over 1200 hp.
Meanwhile, a new heat engine prime mover technology was quickly being developed: the steam turbine. The
word turbine was coined in 1822 from the Latin root word turbo, for“that which spins.” When it was coined it
was applied only to water wheels (as in hydraulic or water turbines).
A turbine is a prime mover in which mechanical rotating shaft work is produced by a steady flow of fluid
through the system. The output work is produced by changing the momentum of the working fluid as it passes
through the system (the turbine). Reciprocating prime mover output work, on the other hand, is produced by
changing the pressure of a fixed mass of working fluid within the system (the piston-cylinder apparatus).
There are two basic types of turbine designs: impulse and reaction. Both the impulse and reaction turbine concepts
date from antiquity. The paddle-type water wheels developed in Italy in about 70 BC (and used throughout
the world, well into the 20th century AD) were of the impulse type (Figure 13.24, left). Also, in the first century AD,
a Greek known today only as Heron (or, in Latin, Hero) of Alexandria (Egypt) devised a simple reaction
steam turbine (called an aeolipile) in which a hollow copper sphere was made to rotate by steam jetting out of
four nozzles mounted perpendicular to the axis of rotation (see Figure 13.24, right). No practical use was then
made of this device. However, it was known to James Watt and his contemporaries because they experimented
with steam-driven reaction turbines of the Heron type and still found them impractical due to the extremely
high rotational speeds required to make them efficient enough to be competitive with existing reciprocating
steam engine technology.
In the impulse turbine, high-velocity fluid jets from stationary nozzles impinge on a set of blades on a rotor.
The impulse force generated by the momentum change of the fluid passing through these blades causes the