The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. A casement is needed to contain the water flow. The turbine is located between the high pressure water source and the low pressure water exit, usually at the base of a dam.
The inlet is spiral shaped. Guide vanes direct the water tangentially to the runner. This radial flow acts on the runner vanes, causing the runner to spin. The guide vanes (or wicket gate) may be adjustable to allow efficient turbine operation for a range of water flow conditions.
As the water moves through the runner its spinning radius decreases, further acting on the runner. Imagine swinging a ball on a string around in a circle. If the string is pulled short, the ball spins faster. This property, in addition to the water’s pressure, helps inward flow turbines harness water energy.
COMPARED TO INVOLUTE TURBINE:
- Requires much higher head (at least 5 times), pipe delivery at high speed
- water delivered and redirected in complex compressing channels
- gravity not utilized
- water pushes only to inside of vanes, not all the way through
- flow is reversed only 140? degrees compared to 480 degrees of involute canal turbine
- surface area of vanes much smaller
- flow not as streamlined and turbulence-free
- WE SHOULD BE ABLE TO GET 90% EFFICIENCY TOO
From Wikipedia, the free encyclopedia
Banki turbine. Image credit; European Communities, Layman’s Guidebook (on how to develop a small hydro site)
A Crossflow turbine, Banki-Michell turbine, or Ossberger turbine is a water turbine developed by the Australian Anthony Michell, the Hungarian DonÃ¡t BÃ¡nki and the German Fritz Ossberger.
BANKI TURBINE COMPARED TO INVOLUTE TURBINE:
- all of the advantages of the Banki Turbine are present in the involute turbine
- surface area of vanes much less than involute
- gravity not utilized with captured mass of water
- water pushes on upper vanes, then falls through center, creating turbulence
- with water falling on inside of lower blades, debris could collect easier than involute, where water stays in vane to bottom
- flow is not reversed, extracting less power from water
- double-pass flow through narrow vanes not as streamlined and turbulence-free as involute
- WE SHOULD BE ABLE TO GET MUCH HIGHER EFFICIENCIES WITH VARYING STREAM FLOW!
Read the full article here: https://web.archive.org/web/20190621111020/http://www.fundamentalform.com/html/other_turbines.html