Some applications of gas and vapor bubbles

This thesis reports a few applications utilizing bubbles. It consists of two parts. The first part is focused on microbubbles and their applications to two particular microfluidic devices. The forced oscillations of gas bubbles in liquid filled tubes are explored experimentally first. The frequency dependence and damping of the forced oscillations of gas bubbles are in excellent agreement with a linear theory. This work is motivated by the possibility of using gas bubbles as actuators in fluid-handling microdevices.; Then a novel pumping device relying on surface tension is developed. The pump is driven by the growth and collapse of a single vapor bubble in a channel. The channel shape is such that it creates an asymmetry in the surface tension forces, which results in a pumping effect. This idea is implemented for an electrically conducting liquid. The channel diameters are of the order of 1 mm and repetition frequency is between 1 and 10 Hz. The device develops a head of a few centimeters of water, and typical flow rates in the range of 100 mul/min A simple modification of the design would render the same principle also applicable to the pumping of non-conducting liquids.; An application of vapor bubbles as actuators in a tactile display device is also studied. Tactile displays are used to provide spatially distributed force information or shape pattern to the user's fingertip in teleaction and virtual reality systems. The proposed tactile display device consists of a series of pins with a center to center spacing of 2 mm and pin diameter 1 mm. The advantage of this design is its low cost and small size. The single-pin performance suggests an excellent potential to use a pin array driven by vapor bubbles to simulate tactile sensations.; The second part of this thesis is devoted to the application of gas bubbles to the treatment of super-saturated water. An effective method to produce large numbers of small bubbles is necessary for this purpose. A novel microbubble generation method is investigated in a laboratory-scale system. The results show that the bubbles produced in this way are very effective at removing dissolved gases. A mathematical model is also developed which proves able to explain the data and to give useful information on the effect of the various parameters of the problem.