[Previous Months][Date Index][Thread Index][Join - Register][Login]
[Message Prev][Message Next][Thread Prev][Thread Next]

[IP] Pumping with a Tiny Bubble Johns Hopkins Engineers Use Pockets ofVapor to Push

HREF="http://www.jhu.edu/news_info/news/home99/jun99/bubble.html">email @ redacted
pkins: Johns Hopkins University N...

News Release

Office of News and Information
Johns Hopkins University
3003 N. Charles Street, Suite 100
Baltimore, Maryland 21218-3843
Phone: (410) 516-7160 / Fax (410) 516-5251
June 22, 1999
Phil Sneiderman, email @ redacted
Pumping with a Tiny Bubble
Johns Hopkins Engineers Use Pockets of Vapor to
Push Liquids through Micro Devices 

Many researchers are racing to develop miniature high-tech devices each 
smaller than a postage stamp to treat medical conditions, test new drugs 
and monitor pollutants. All of these require a tiny pump that can 
repeatedly and reliably push small amounts of liquid through narrow 
channels for rapid analysis.

To accomplish this, engineers at The Johns Hopkins University have 
invented a micropump powered by the repeated growth and collapse of a 
single bubble. Because the bubble is generated by heat, it is easy to 
control, the inventors say. And because the bubble-powered pump has no 
moving mechanical parts, it is unlikely to wear out too quickly. "It's 
very different from having a pump with a valve that has to open and 
close any number of times," says Andrea Prosperetti (pictured at right), 
the university's Charles A. Miller Jr. Distinguished Professor of 
Mechanical Engineering. "With no moving parts, the bubble-powered pump's 
prospects of failure are minimal."

Prosperetti, an internationally respected expert on the physics of 
bubbles, worked with two other Johns Hopkins mechanical engineering 
researchers Hasan Oguz and He Yuan to design, build and test a prototype 
bubble-based pump. They have presented their results at recent 
conferences sponsored by the Acoustical Society of America and the 
Defense Advanced Research Projects Agency 

The team's prototype utilizes two main tubes. One is 1.6 millimeters 
wide, about the width of the wire used to make a large paperclip. The 
other tube is half that diameter, but the inventors say the same 
principles would apply to smaller tubes as well. The prototype's main 
tubes are connected by an even narrower passage or "throat," measuring 
0.5 millimeters in diameter. The engineers inserted steel needles into 
each of the larger tubes, connected the needles to a power source and 
filled the tubes with a salt solution to complete the circuit. The 
current was "squeezed" as it passed through the narrow throat, causing 
the water to boil or vaporize at that location. This led to the 
formation of a bubble in the throat. As it expanded like a balloon into 
the wider channel, the bubble pushed fluid ahead of it.

This is the experimental setup of the Johns Hopkins bubble-based 
micropump, for use with an electrically conductive liquid.

This closeup shows the micropump's main tubes, electrodes within each. 
The bubble forms in the narrow connecting throat and expands into the 
wider tube, pushing liquid ahead of it.

When the electrical current is stopped, the bubble shrinks. Its final 
collapse, however, takes place not in the throat but in the wider 
channel. As a result, bubbles created in this system pump fluid through 
the tubes as they repeatedly expand and collapse. "You pump in the 
direction of the bubble's expansion," Prosperetti says. The prototype is 
capable of generating about five bubbles per second, but the inventors 
say it will be easy to move to much higher rates.

The bubble-powered pump could play a crucial role, for instance, in 
cutting-edge technology called micro total analysis systems. Engineers 
in this field are creating tiny devices on silicon chips, capable of 
detecting and analyzing small samples of fluid, then directing that some 
action take place. Their tiny size makes them ideal for a range of 
specialized tasks. For example, a small chip implanted in the body of a 
person with diabetes might regularly check the person's blood sugar 
level and order the release of the appropriate amount of insulin.

Also, pharmaceutical companies sometimes make minute quantities of 
thousands of potential drug compounds, looking for one variation that 
produces a beneficial chemical reaction. Each compound is costly to 
produce, but a micro-device would require less than a drop to analyze. 
Similarly, micro-devices could provide a low-cost method of 
simultaneously monitoring liquid pollutants produced by a factory at a 
large number of locations inside and outside of the plant.

"Every time you test something in these systems, you have to move fluids 
around in very tiny channels," says Prosperetti. "So there's been a 
search on for a means of actuation pumping without moving mechanical 
parts. We think bubbles are a good candidate for achieving this." Other 
researchers are developing different types of micropumps, including some 
that use miniaturized versions of traditional valves and other 
mechanical parts. But Prosperetti believes his bubble-powered pump is 
superior because it has no moving parts to wear out.

Although the test device built by the Johns Hopkins engineers creates 
bubbles with electrical current and a salt solution, Prosperetti says 
the system could also work with fluids that do not conduct electricity. 
For such liquids, tiny heaters embedded in the walls of the tubing could 
be used to form the bubbles.

Prosperetti and his colleagues have applied for a U.S. patent covering 
the bubble-based micropump technology. Their research was sponsored by 
the U.S. Air Force Office of Scientific Research and DARPA.

Color diagram of the bubble-powered micropump available; Contact Phil 

Note: Follow this link for images of the bubble forming.

Related Web Sites
Andrea Prosperetti's Home Page
Prosperetti's Research Group

Johns Hopkins Department of Mechanical Engineering
Insulin Pumpers website http://www.insulin-pumpers.org/
for mail subscription assistance, contact: HELP@insulin-pumpers.org