There is a long history of harnessing the power of the tides to do work. There were tidal mills on the coasts of England and France in the Middle Ages. Electricité de France today operates a 240 MW power station that uses the considerable tides of the Rance estuary. There are a few smaller plants around the world and several proposals for producing electricity from tidal activity.

Perhaps the newest development in tide-to-electricity technology is a device developed by researchers at the University of Southampton in England. It is a self-contained bidirectional turbine and generator.

A bidirectional hydroelectric generator is derived from a thruster for submersibles.

The developers, Stephen Turnock and Suleiman Abu-Sharkh, didn't start out with an electric generator in mind. They originally designed a bidirectional thruster for remotely operated submersibles. It is a direct-drive electric motor with a propeller that can reverse direction so an operator can move a craft forward and back. It's manufactured by a British company.

The reversal of the system—that is, letting the force of running water turn the blades—generates electricity. According to Abu-Sharkh, when he and Turnock tried that, the system became a generator with an efficiency of 35 percent.

Their intention is to optimize the design for electrical output. Part of the funding for the thruster's development came from the Engineering and Physical Sciences Research Council, a British government agency, so Abu-Sharkh and Turnock, both senior lecturers in the university's School of Engineering Sciences, are seeking backing from the council, among other sources, to pursue their current project.

They have tested a 25 cm diameter prototype that produces about 70 watts in a flow of 2 meters per second. Power is proportional to the square of the diameter and the cube of the speed flow. If the diameter is increased to 5 m and the flow is 4 m/s, then the output power is estimated to be 224 kW.

The hydroelectric generator is suitable for use in tidal currents because its basic design is to be bidirectional, so it will work with the rising and falling tides. According to Abu-Sharkh, "The housing and blade sections of the turbine are rotationally symmetrical. The blade sections are a new design whose shape has been optimized for the operational Reynolds number."

Other projects in Britain are also looking at ways to generate electricity from tidal currents. A unit of Rolls-Royce, for example, in partnership with a Norwegian company, Hammerfest Strøm AS, is running a test of a tidal turbine in northern Norway. Another British company, Marine Current Turbines Ltd., said it expects to have a commercial-scale tidal turbine in operation in a few years.

Turnock and Abu-Sharkh say the permanent magnet rotor of the electric motor forms a ring around the tips of the propeller blades. The stator of the machine is in the housing, thus resulting in a compact unit. They said the design can create a self-contained package that can be prefabricated so there will be few on-site construction costs. "Just drop it into flowing water and it will start generating electricity. It will work best in fast-flowing, shallow water," Turnock said. He foresees rows of these devices secured to sea floors and riverbeds.

There is still a bit of work to do. According to Abu-Sharkh, "Given the unconventional proportions of the machine, having a large gap and a short axial length, and the need to match the machine and propeller/turbine characteristics, the design of a device that has good performance needs careful analysis and modeling."

The time is at hand to address the devastating effects of increasing water scarcity and declining water quality around the world, according to a national laboratory and a Washington think tank.

A recently released white paper, Addressing Our Global Water Future, written jointly by Sandia National Laboratories of Albuquerque, N.M., and the Center for Strategic and International Studies, is the result of two conferences held last year in Washington.

At those conferences, representatives of major multinational companies, government officials, and technical experts discussed U.S. policy and the role of emerging water technologies in regions of the world where the United States has strategic interests. Discussions centered on countries with dwindling fresh water supplies and the range of technology innovation needed to help resolve water problems. Sandia provided information on emerging water technologies with potential to address water scarcity and quality issues.

The primary authors are Laura Keating of CSIS and Howard Passell of Sandia, although numerous others from both organizations contributed to the document.

According to Ray Finley, manager of Sandia's Geohydrology Department, Sandia, as a national security laboratory, has the responsibility to help provide for the security of the U.S. That includes regions of the world that are of strategic importance to the United States and can affect national security.

"The lack of clean water can create conditions that lead to destabilization in regions of the world that are already poor and having problems," he said. "Lack of potable water can result in famine, conflict over resources, and poor governance. Failed and failing states threaten U.S. security because of their potential to harbor terrorist groups."

Examples are instability in the Middle East and Africa—both places where fresh water for consumption and sanitation is in short supply.

The report expands this theme, saying that "global trends of increasing population, increasing resource consumption, and decreasing natural resource availability—including fresh water—have pushed many human social, economic, and political systems to an important tipping point. We face large-scale future dislocations and crises unless significant action is taken now by leaders in both developed and developing countries."

A distributor in Pennsylvania decided it wanted to offer a compact, portable system to filter hydraulic fluids. The company, Fluid Power Inc. based in Blue Bell, Pa., came up with something small and light enough to fit the kind of hand truck that delivers cases of beer.

Fluid Power, which sells hydraulic, pneumatic, and lubrication systems and parts, said that its portable filtration and transfer unit is able to reduce operational downtime because maintenance can be scheduled and oil can be cleaned while a machine is in use.

Cleans and rolls: A compact system designed to filter hydraulic fluids is built to fit a hand truck.

The company builds the units to order. The drums, gauges, hoses, and so forth are off the shelf, and the system is powered by a half-horsepower Baldor electric motor that can plug into a 115 V wall socket. Flow rate is advertised at 420 gallons per hour with a maximum pressure of 65 psi. The system weighs 130 pounds.

The company recommends periodic cycling of oil through the unit and says that cleaning the fluid can increase the life of a system's parts. It also suggests passing new oil to the machine reservoir by way of the filter unit to assure that the hydraulic fluid is clean.

A supplier of specialty gases and gas-handling equipment is offering an updated edition of a handbook on the design of gas delivery systems. The company, Scott Specialty Gases, is offering the short book, Design & Safety Handbook for Specialty Gas Delivery Systems, in portable document format (pdf) and in print.

Both forms are available through the Scott Web site, www.scottgas.com.

The downloadable version can be found in the Web site's "Technical Data" section, under "product literature." The text is 42 pages long and addresses a range of issues involving specialty gases and the systems that deliver them.

The U.S. Chemical Safety and Hazard Investigation Board has issued a case study of a pressure-vessel failure in Houston and has recommended that the city adopt stricter codes, including the ASME Boiler and Pressure Vessel Code Section VIII.

Some portions of ASME codes are legal standards in all 50 states, but 11, including Texas, have not adopted Section VIII, which sets safety guidelines for pressure vessels. A city spokesman said Houston is considering the recommendations.

On Dec. 3, 2004, an explosion and burning wax at the Marcus Oil and Chemical facility in Houston caused property damage as far as a quarter-mile away. The Chemical Safety Board found that an inadequate repair weld had weakened the vessel, which held polyethylene wax, and the presence of oxygen had permitted a fire to flash back into the tank.

The full case study report is available on the board's Web site, www.csb.gov.

home | features | breaking news | marketplace | departments | about ME back issues | ASME | site search

© 2006 by The American Society of Mechanical Engineers