Reaction turbines and water wheels, a type of turbine, are very efficient machines. Because of their unique design, maximum energy is extracted from the flowing stream. This leads to offshoot advantages, such as improved power transfer to pulleys or grinding stones. In 2011, all turbines are reaction, since other types of turbines are inefficient and antiquated technology.
Because the blades of a reaction turbine direct nozzle flow opposite the spin, an action / reaction physics process takes place. This is very much akin to filling a balloon with air and letting it go. The escaping air forces the balloon in the opposite direction. Engineer J. B. Calvert of the University of Denver describes an S-shaped lawn sprinkler as a reaction device. In terms of energy input versus energy output, a reaction turbine is far more efficient than the old-style impulse turbine, which just had the force of the liquid from the nozzle hitting paddle blades.
Energy Input Advantage
In comparing an impulse turbine to a reaction turbine, you find the energy inputs are different. To extract the same amount of power output from an impulse turbine, you need a lot more energy input. For a gravity-fed water system, this means the water has to fall a greater distance for an impulse turbine. For a steam turbine system, more steam is required for an impulse turbine.
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Materials Usage Advantage
Because the efficiency is greater for a reaction turbine over an impulse turbine, not as many materials are needed to build a reaction turbine that produces the same energy output. An impulse turbine would require a bigger housing, more paddles and a larger diameter. All this translates into more materials, and more materials cost to build an impulse turbine.
Power Output Advantage
For the same size of turbines, a reaction turbine puts forth more power than an impulse turbine. Impulse turbines are simply not efficient in terms of energy output. For this reason, impulse turbines are antiquated technology and no longer used in modern turbine systems, such as a steam-powered electrical generating facility.