The pumping effect of growing and collapsing bubbles in a tube

The flow induced by the suitably timed growth and collapse of one or severa l bubbles in a finite tube joining two liquid reservoirs is simulated by a simple quasi-one-dimensional model. Viscous and surface tension effects are accounted for in an approximate manner. It is shown that, in certain param eter ranges, the system is capable of a net pumping action that moves the l iquid from one reservoir ro the other even in the presence of an adverse pr essure difference. The fact that this net pumping effect is also encountere d in the case of a single bubble, provided ii is not located at the midpoin t of the tube, is particularly remarkable. The mechanism responsible for th is result is discussed. In practice the effect can be exploited to build a micropump by embedding electrical heaters in the wall of a small channel.