MECHANICAL ENGINEERING

New tool keeps computers cool

Adam Pautsch, Tim Shedd, Andrea Ashwood, and Curtis Lane

Tim Shedd (second from left) with his research group (from left) graduate students Adam Pautsch, Andrea Ashwood and Curtis Lane (23K JPG)

THE DAYS of the constantly humming computer fan are numbered: The chips inside today's ultra-powerful computers generate too much heat for air cooling technology to handle. To keep the next generation of computers cool, Assistant Professor Tim Shedd and graduate student Adam Pautsch have devised a new spray-cooling technique that drenches chips with high-velocity lines of liquid, much like sheets of wind-driven rain. Early tests show the system removes heat at rates three times faster than other spray technologies, or up to four times the density of heat experienced by the space shuttle upon re-entry.

Shedd and Pautsch created the device after analyzing the limitations of existing spray cooling technology at the request of Cray, Inc., a supercomputer manufacturer in Chippewa Falls, Wisconsin. They discovered that the coneshaped sprays produced by the current method led to runaway boiling at the chip surface. When this occurs, dry spots develop that resist re-wetting by fresh coolant, causing chip temperatures to spike by hundreds of degrees in a matter of seconds.

The UW-Madison engineers' linear nozzle array instead of shoots droplets of coolant in lines at a 45-degree angle to the chip surface. The device performs so well, says Shedd, because when the coolant contacts the chip, it mimics a boiling liquid — one of the most efficient and widely used means to remove heat — while avoiding the problems true boiling can cause. Cray is now considering the technology for use in the cooling system of one of its new supercomputers.

Studies of bone strength made stronger

A UNIQUE SYSTEM for measuring how mechanical loads affect bone growth is getting an upgrade in accuracy, thanks to Assistant Professor Heidi Ploeg and graduate student Sylvana Garc´e;a. Developed by Population Health Sciences Professor Everett Smith, the system, called Zetos, can keep small, cylindrical pieces of bone alive in culture for a recordsetting 49 days. To mimic the force bone experiences during exercise such as running, jumping and walking, Zetos compresses the bone samples inside a sterile plastic chamber using a computer-controlled piezoelectric actuator. It's already known that bone gets stiffer and stronger in response to loading. But exactly how this occurs remains unclear.

Once Zetos is standardized and validated, it should allow scientists to directly relate specific levels and types of mechanical stress to changes in bone stiffness. It should also reveal the physiological mechanisms underlying bone growth. Ploeg and Garc´e;a are currently conducting meticulous calibration studies using plastic cylinders and metallic diaphragms as stand-ins for bone specimens. Although they sometimes grow impatient to make measurements on actual bone, their careful quantification of system parameters like force and displacement will ensure even tiny changes in bone stiffness can one day be measured with confidence. Ploeg hopes the system will eventually help improve the design of surgical implants for strengthening bone. And Smith plans to employ Zetos in his research on the prevention and treatment of osteoporosis — a disease that is virtually universal in women over age 70.

Promoting partnerships in plastics

RANKED 10th in the nation in size, Wisconsin's plastics industry is as vital to the state's economy as milk and cheese production. But in the face of growing competition from foreign manufacturers, companies must innovate and cooperate in order to stay strong, say Professors Tim Osswald and Lih-Sheng (Tom) Turng, and Industrial and Systems Engineering Professor Raj Veeramani. With Dean Paul Peercy and Assistant Dean Larry Casper, the trio is now working to bolster the industry by enhancing existing partnerships and fostering new ones among UW-Madison, other state educational institutions, and several Wisconsin plastics manufacturers.

For their part, Osswald, Turng, and the Polymer Engineering Center they lead are helping Wisconsin companies develop emerging processes and materials — such as liquid silicone molding, nanocomposites, microcellular plastics, and bio-based polymers made from renewable resources — that will confer an advantage in the global marketplace. They are also encouraging new relationships among companies situated at various points in the supply chain. For example, they have helped connect a firm that retrieves plastics from old computers, one that makes new resins from recycled plastics, and a manufacturer that wants to use the resins in its products. Equally important is their collaboration with UW-Stout, UW-Platteville and the Madison and Milwaukee Area Technical Colleges to begin training a more diverse and highly skilled workforce for the plastics industry.

The plastics initiative has been jump-started by a $600,000 grant from the National Science Foundation. But the entire team is striving to create a statewide process and infrastructure for research and innovation, education, and partnership that will persist long after the NSF program ends.

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