Choice
Depending on the application, various types of working fluids are used. In a thermodynamic cycle it may be the case that the working fluid changes state from gas to liquid or vice versa. Certain gases such as Helium can be treated as ideal gases. This is not generally the case for superheated steam and the ideal gas equation does not really hold. At much higher temperatures however it still yields relatively accurate results. The physical and chemical properties of the working fluid are extremely important when designing thermodynamic systems. For instance, in a refrigeration unit, the working fluid is called the refrigerant. Ammonia is a typical refrigerant and may be used as the primary working fluid. Compared with water (which can also be used as a refrigerant), ammonia makes use of relatively high pressures requiring more robust and expensive equipment.
In air standard cycles as in gas turbine cycles, the working fluid is air. In the open cycle gas turbine, air enters a compressor where its pressure is increased. The compressor therefore inputs work to the working fluid (positive work). The fluid is then transferred to a combustion chamber where this time heat energy is input by means of the burning of a fuel. The air then expands in a turbine thus doing work against the surroundings (negative work).
Different working fluids have different properties and in choosing one in particular the designer must identify the major requirements. In refrigeration units, high latent heats are required to provide large refrigeration capacities.
Read more about this topic: Working Fluid
Famous quotes containing the word choice:
“...there are important considerations in the world beyond plain sewing and teaching dull little boys the alphabet. Any woman who has brains and willing hands finds twenty remunerative occupations open to her where formerly she would have found merely the inevitable two—plain sewing, or the dull little boys. All she had to do is to make her choice and then buckle on her armor of perseverance, while the world applauds.”
—Clara (Marquise)
“If we pretend to respect the artist at all, we must allow him his freedom of choice, in the face, in particular cases, of innumerable presumptions that the choice will not fructify. Art derives a considerable part of its beneficial exercise from flying in the face of presumptions.”
—Henry James (1843–1916)
“The question of place and climate is most closely related to the question of nutrition. Nobody is free to live everywhere; and whoever has to solve great problems that challenge all his strength actually has a very restricted choice in this matter. The influence of climate on our metabolism, its retardation, its acceleration, goes so far that a mistaken choice of place and climate can not only estrange a man from his task but can actually keep it from him: he never gets to see it.”
—Friedrich Nietzsche (1844–1900)