Crossflow turbine

Figure 1. A crossflow turbine.[1]

Crossflow turbines, sometimes known as Mitchell-Banki or Ossberger turbines are a type of turbine that tends to be used in smaller hydroelectric sites with power outputs between 5-100 kW. These turbines are useful for a large range of hydraulic heads, from only 1.75 meters to 200 meters, although usually crossflow turbines are chosen for heads below 40 meters.[2]

In addition to being used in smaller hydroelectric facilities, one benefit of these turbines is they require comparatively less complex maintenance to keep them working. Because of this, they are more suitable for use in remote communities.[3] Although useful for a wide range of hydraulic heads and power outputs, generally these turbines are most efficient for low heads and low power outputs. Other turbines are likely more efficient and useful for large-scale applications.

Design

A crossflow turbine is designed using a large cylindrical mechanism composed of a central rotor surrounded by a "cage" of blades arranged into a water wheel shape. These blades are generally sharpened to increase the efficiency of the turbine by reducing the resistance to water flow. Water is directed onto the turbine through a nozzle that creates a flat sheet of water, and then is directed onto the blades using a guide vane. Water first hits the blades and moves to the inside of the turbine, with the water hitting the blades one more time as the water exits the center of the turbine.[2]

Operation

In this type of turbine, water enters as a flat sheet instead of a round jet - as is the case in Pelton turbines. The sheet of water is guided onto the blades of the turbine by an inlet guide vane, ensuring that the water hits the blades at the proper angle to maximize efficiency.[2] The water flows over the blades creating a torque on these blades. After hitting the blades, the sheet of water moves through the turbine and hits the blades once more as it leaves, producing more torque.[3] The first impact the water has with the blades produces more power than the second hit.

Since this type of turbine uses water jets that create an impulse on the turbine, the crossflow turbine is a type of impulse turbine, similar to the Pelton turbine.

References

  1. Wikimedia Commons. (August 25, 2015). Ossberger Turbine [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/8/8e/Ossberger_turbine_runner.jpg
  2. 2.0 2.1 2.2 Renewables First. (August 26, 2015). Crossflow Turbines [Online]. Available: https://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/crossflow-turbines/
  3. 3.0 3.1 G. Boyle. ``Renewable Energy: Power for a Sustainable Future``, 2nd ed. Oxford, UK: Oxford University Press, 2004.

Authors and Editors

Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: September 3, 2015
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