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Diagram of a Cross-flow turbine
1 — air-venting valve
2 — distributor
3 — turbine casing (all thick grey)
4 — runner
5 — removable rear casing
6 — blades
7 — water flow
8 — shaft

A cross-flow turbine, Bánki-Michell turbine, or Ossberger turbine[1] is a water turbine developed by the Australian Anthony Michell, the Hungarian Donát Bánki and the German Fritz Ossberger. Michell obtained patents for his turbine design in 1903, and the manufacturing company Weymouth made it for many years. Ossberger's first patent was granted in 1933 ("Free Jet Turbine" 1922, Imperial Patent No. 361593 and the "Cross Flow Turbine" 1933, Imperial Patent No. 615445), and he manufactured this turbine as a standard product. Today, the company founded by Ossberger is the leading manufacturer of this type of turbine.

Unlike most water turbines, which have axial or radial flows, in a cross-flow turbine the water passes through the turbine transversely, or across the turbine blades. As with a water wheel, the water is admitted at the turbine's edge. After passing the runner, it leaves on the opposite side. Going through the runner twice provides additional efficiency. When the water leaves the runner, it also helps clean the runner of small debris and pollution. The cross-flow turbine is a low-speed machine that is well suited for locations with a low head but high flow.

Although the illustration shows one nozzle for simplicity, most practical cross-flow turbines have two, arranged so that the water flows do not interfere.

Cross-flow turbines are often constructed as two turbines of different capacity that share the same shaft. The turbine wheels are the same diameter, but different lengths to handle different volumes at the same pressure. The subdivided wheels are usually built with volumes in ratios of 1:2. The subdivided regulating unit, the guide vane system in the turbine's upstream section, provides flexible operation, with 33, 66 or 100% output, depending on the flow. Low operating costs are obtained with the turbine's relatively simple construction.

Details of design[edit]

Ossberger turbine section

The turbine consists of a cylindrical water wheel or runner with a horizontal shaft, composed of numerous blades (up to 37), arranged radially and tangentially. The blade's edges are sharpened to reduce resistance to the flow of water. A blade is made in a part-circular cross-section (pipe cut over its whole length). The ends of the blades are welded to disks to form a cage like a hamster cage and are sometimes called "squirrel cage turbines"; instead of the bars, the turbine has trough-shaped steel blades.

The water flows first from the outside of the turbine to its inside. The regulating unit, shaped like a vane or tongue, varies the cross-section of the flow. The water jet is directed towards the cylindrical runner by nozzle. The water enters the runner at an angle of about 45/120 degrees,transmitting some of the water's kinetic energy to the active cylindrical blades.

Ossberger turbine runner

The regulating device controls the flow based on the power needed, and the available water. The ratio is that (0–100%) of the water is admitted to 0-100%×30/4 blades. Water admission to the two nozzles is throttled by two shaped guide vanes. These divide and direct the flow so that the water enters the runner smoothly for any width of opening. The guide vanes should seal to the edges of the turbine casing so that when the water is low, they can shut off the water supply. The guide vanes therefore act as the valves between the penstock and turbine. Both guide vanes can be set by control levers, to which an automatic or manual control may be connected.

The turbine geometry (nozzle-runner-shaft) assures that the water jet is effective. The water acts on the runner twice, but most of the power is transferred on the first pass, when the water enters the runner. Only ⅓ of the power is transferred to the runner when the water is leaving the turbine.

The water flows through the blade channels in two directions: outside to inside, and inside to outside. Most turbines are run with two jets, arranged so two water jets in the runner will not affect each other. It is, however, essential that the turbine, head and turbine speed are harmonised.

The cross-flow turbine is of the impulse type, so the pressure remains constant at the runner.

Advantages[edit]

The peak efficiency of a cross-flow turbine is somewhat less than a Kaplan, Francis or Pelton turbine. However, the cross-flow turbine has a flat efficiency curve under varying load. With a split runner and turbine chamber, the turbine maintains its efficiency while the flow and load vary from 1/6 to the maximum.

Since it has a low price, and good regulation, cross-flow turbines are mostly used in mini and micro hydropower units of less than two thousand kW and with heads less than 200 m.

Particularly with small run-of-the-river plants, the flat efficiency curve yields better annual performance than other turbine systems, as small rivers' water is usually lower in some months. The efficiency of a turbine determines whether electricity is produced during the periods when rivers have low flows. If the turbines used have high peak efficiencies, but behave poorly at partial load, less annual performance is obtained than with turbines that have a flat efficiency curve.

Due to its excellent behaviour with partial loads, the cross-flow turbine is well-suited to unattended electricity production. Its simple construction makes it easier to maintain than other turbine types; only two bearings must be maintained, and there are only three rotating elements. The mechanical system is simple, so repairs can be performed by local mechanics.

Another advantage is that it can often clean itself. As the water leaves the runner, leaves, grass etc. will not remain in the runner, preventing losses. Therefore, although the turbine's efficiency is somewhat lower, it is more reliable than other types. No runner cleaning is normally necessary, e.g. by flow inversion or variations of the speed. Other turbine types are clogged more easily, and consequently face power losses despite higher nominal efficiencies.

See also[edit]

References[edit]

  1. ^ E.F. Lindsley, Water power for your home, Popular Science, May 1977, Vol. 210, No. 5, 87-93.

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Cross-flow_turbine — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
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14 news items

The Guardian

The Guardian
Sun, 05 Oct 2014 21:30:05 -0700

Over at Cole, where the streams now wind through beautifully landscaped gardens beside welcoming buildings of honey-coloured stone, a sophisticated cross-flow turbine puts the Pitt to modern use, supplying the property with power, and passing any ...
 
International Water Power and Dam Construction
Fri, 19 Sep 2014 08:56:15 -0700

It is encouraging local turbine manufacturers to become involved and, after scouring the local market, discovered that cross-flow turbine production capacity is limited to 40KW. Therefore, NSP has decided to limit each turbine unit to 40KW: if a higher ...
 
HydroWorld
Tue, 15 Oct 2013 12:03:24 -0700

The powerhouse configurations included a simplex, cross-flow turbine and an asynchronous generator housed in a non-insulated cinder block powerhouse on an engineered concrete slab. The penstock configuration was assumed to include a buried PVC ...
 
Bangor Daily News
Sun, 18 Dec 2011 13:59:26 -0800

The core technology, Ferland said, of ORPC's proprietary “Tidgen” systems is a rectangular, cross-flow turbine that resembles a paddle wheel. In its current configuration, each unit is 98 feet wide and 17 feet deep. When submerged in a six-knot tidal ...
 
2merkato - Ethiopian Business Portal
Sat, 22 Dec 2012 12:48:45 -0800

... Agro stone mixer pedal driven pumps and rope and washer pump, cross flow turbine as mixers, Soil crushers, hydraform making machine, roof tile machine, Soil block machine, hollow block machine, different kinds of molds, wind pumps, ram pump, Boats, ...
 
New York Times (blog)
Wed, 23 Mar 2011 12:10:40 -0700

Interactive feature on how a cross-flow turbine creates energy from strong tidal currents. Carbon Emissions Across the United States Map of carbon emissions by state, generated mostly by electric power production and transportation. The Danger of ...
 
ESI Africa
Thu, 12 Jul 2012 08:07:37 -0700

It is a ±15 kW installation utilizing a cross flow turbine and a synchronous generator discharging through the roof into the reservoir. The plant which was commissioned in November 2011 has a maximum capacity is ±15 kW of renewable, zero-emissions, ...
 
High Performance Composites
Thu, 30 Sep 2010 07:23:51 -0700

The company's Turbine Generator Unit (TGU) comprises an all-composite cross-flow turbine system and a composite-and-steel support frame, the latter built by U.S. Windblade (Bath, Maine). The turbine incorporates a carbon fiber/E-glass fiber hybrid ...
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