Forever blowing bubbles
15 Jan 2000
Process engineers are very familiar with pumps and the various technologies they use. But it's unlikely that they've ever seen anything like the pumps currently being developed at Johns Hopkins University's mechanical engineering department. Unless they have very good eyesight, they wouldn't be able to.
The pumps are tiny - smaller than a postage stamp. Rather than relying on pushing a piston along a cylinder, spinning a rotor or squeezing a tube, they work by repeatedly blowing a bubble at the end of a narrow tube. The development team, led by Professor Andrea Prosperetti, believes the pump is likely to find uses in drug delivery systems and equipment for analysing very small volumes of fluids, such as environmental pollutants.
The mechanism currently relies on the process fluid conducting electricity. The pump consists of a pair of tubes, one slightly wider than the other, connected by a narrow conical `throat'. Each tube contains a steel electrode. When a current is passed through the needles, the liquid boils as it passes through the throat and generates a bubble of vapour. This expands into the larger tube and pushes liquid ahead of it. As it passes through the throat, it collapses. `It's very different from having a pump with a valve that has to open and close any number of times,' says Prosperetti. `With no moving parts, the bubble-powered pump's prospects of failure are minimal.'
The electrical `power' for the pump could easily be replaced by tiny heaters embedded in the tubes, which would allow non-conductive fluids to be pumped. Such systems could be mounted on silicon chips for micro-analysis systems, which could form part of an online monitoring system functioning at several locations around a chemical plant.
