Recent developments in current flow turbine design
Unlike wind turbine design, which is now a mature technology in which the axial flow propeller type turbine has emerged as the preferred design, water current turbine design is at an early stage of development. Incremental improvements to wind turbine technology since the early 1980s has reduced the cost of grid-connected wind energy by a factor of about 5, to the point where it is now economically competitive with conventional fossil fuels in some areas. This process has not yet happened with water current energy conversion, and subsidies will be needed for research for sometime to come.
The potential contribution of this form of energy is huge: it has been estimated that the UK could obtain 20% of its electricity from tidal currents. Several forms of turbine are being investigated around the world and none has yet emerged as a clear winner. Some of the various forms currently being evaluated are reviewed below.
Axial flow turbines
Marine Current Turbines Ltd in Britain are pioneering the use of axial flow turbines. In 1994 they demonstrated a 10 kW axial flow turbine in Loch Linnhe in Scotland, and they are currently developing a 300 kW turbine for the Severn Estuary off Devon, England. This turbine is expected to resemble one or two conventional wind turbines, mounted on a cantilever tower fixed to the ocean floor. Other small pontoon-mounted axial flow turbines have been built, for example by Teamwork Technology in the Netherlands and by Swenson at the Northern Territory University in Darwin, Australia.
Cross flow turbines
Turbines in which the direction of flow is across the axis of rotation are commonly referred to as “vertical axis” turbines, since their axis is usually vertical. However they are more accurately described as “cross flow” since their distinguishing feature is the fact that the direction of flow is across the axis of rotation, which may be horizontal. Davis conducted laboratory tests on a cross flow water turbine in 1981-2 and constructed a prototype which produced 20 kW electrical power and an estimated 45 kW shaft power in 1983. More recently a 6 m diameter vertical axis turbine has been installed in the Strait of Messina, between Sicily and the Italian mainland. It is expected to produce about 50 kW electrical in a 2.4 m/s current. Gorlov and co-workers in the United States have tested models of a cross-flow turbine with helical blades and claim that its performance is superior to a conventional Darrieus cross flow turbine. Gorlov has proposed large helical blade turbines to convert energy from the Gulf Stream
Open and ducted turbines
Like conventional hydropower turbines, installations such as the Rance River in France utilise the pressure difference created by a static head, i.e. the potential energy inherent in a difference in water surface elevation. In contrast, wind turbines and open water current turbines utilise the kinetic energy of a moving fluid directly. Between these extremes, Darrieus proposed placing turbines in ducts to augment the power extracted from a given sized turbine.
Blue Energy Canada has proposed two variants on this theme: a single turbine can be placed in aduct in open flow without obstructing the free flow of water around the installation, or alternatively their proposed “tidal fence” forces all of the flow to pass through the turbines. They have proposed an ambitious scheme to build a tidal fence across a strait and use a large number of vertical axis turbines to produce up to 2200 MW. Recently other organizations have also been investigating this concept.
2.Переведите на русский язык следующие английские сочетания:
1)pressure difference
2)intermittentflow
3)tidal basins
4)peak periods
5)wind turbine
6)disruption to ecosystems
7)negligible rise and fall
8)conventional fossil fuels
9)axialflowturbines
10)axis of rotation
3.Найдите в тексте английские эквиваленты следующих словосочетаний:
1)традиционные методы
2)статический напор
3)односторонний поток
4)кинетическая энергия
5)речные потоки
6)приливный подъем и падение
7)силы сопротивления
8)оффшорные нефтяные платформы
9)дно океана
10)турбины поперечного потока
4.Найдите в тексте слова, имеющие общий корень с данными словами. Определите, к какой части речи они относятся, и переведите их на русский язык:
1)creation
2)possible
3)nature
4)eligible
5)grow
6)unknown
7)underdeveloped
8)technique
9)competition
10)view
5.Задайте к выделенному в тексте предложению все типы вопросов (общий, альтернативный, разделительный, специальный: а) к подлежащему, б) к второстепенному члену предложения.
6.Выполните анализ данных предложений, обратив внимание на следующие грамматические явления:формы и функции причастия, независимый причастный оборот, формы и функции герундия, герундиальный оборот, инфинитивные конструкции (сложное дополнение, сложное подлежащее), существительное в роли определения, функции слов one (ones), that (those), условные предложения (сослагательное наклонение 1 и 2 типов):
1. A steady one-way flow could then be maintained through turbines in conduits connecting the estuaries.
2. Wind turbines and open water current turbines are known to utilise the kinetic energy of a moving fluid directly.
3. There is no need for a large tidal rise and fall – for example the Messina strait between Sicily and Italian mainland has 2.4 m/s currents with negligible rise and fall.
4. Unlike wind turbine design, which is now a mature technology in which the axial flow propeller type turbine has emerged as the preferred design, water current turbine design is at an early stage of development.
5. Everybody expected Gorlov and co-workers in the United States to have tested models of a cross-flow turbine with helical blades and claim that its performance was superior to a conventional Darrieus cross flow turbine.
7. Ответьте на вопросы по тексту:
1. How many methods of extracting energy from tidal flows are there?
2. More efficient turbines can be used for one-way flow, can’t they?
3. What is the less well-known method?
4. Innumerate some potential problems with tidal or marine current turbines.
5. Should these possible problems be insurmountable?
6. Who is pioneering the use of axial flow turbines?
7. How can you describe cross flow turbines?