Reaction turbines are seemingly innoculous pieces of equipment. A working fluid (
steam, exhaust gas or
water) causes the turbine rotor to spin, converting the
kinetic energy of the fluid into
mechanical energy. Simple enough. At first glance, all turbines would seem to operate due to direct
fluid pressure on the blades, a la
impulse turbine.
However,
things aren't quite that simple.
Enter Newton's Third Law of Motion.
Good 'ol
Isaac figured out that
for every action, there is an equal and opposite reaction. This principle is what drives a
reaction turbine.
As the working fluid flows through the
turbine blades, it is
deflected off the blades at a different angle than which it first hit the blade. This change in direction of the working fluid causes a
force to be exerted on the turbine in the
tangent direction, causing it to spin. Some
reaction turbines have their nozzles attached to the rotor. One of the earliest was built by
Hero of
Alexandria waaay back in 75 AD.
The
(minute) difference between the
impulse turbine and
reaction turbine is much more easily shown with the following example. Imagine you are sitting in a shopping cart and holding onto a firehose nozzle. When the pump truck
turns the pump up to eleven, you'll get pushed in the opposite direction as the nozzle is pointed. Hence, you are being driven by reactive forces. To get driven by
impulsive forces, you would have to
get sprayed with the firehose.
In
hydroelectric power generation, reaction turbines are most suited for medium to low
head.
Examples of reaction turbines are
Francis,
Parsons and propeller turbines.
Most turbines operate as a combination of
impulse and
reaction modes. The distinction between the two is used to show how it primarily receives power from the working fluid.
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