To design more efficient chemical reactors, fuel cells, or μ-TAS, it is important to understand the behavior of oxygen, which has close relation with chemical reactions in devices. Conventional oxygen probes such as galvanic cell type cannot be applied to unsteady oxygen concentration measurements in small systems, because such probes have long response time and large probe head. In this study, we have focused on the pressure-sensitive paint (PSP) technique, which enables us to measure 2-dimensional oxygen concentration distribution with milliseconds time response. As an application of oxygen concentration measurement technique using PSP, we measured oxygen concentration in the mixing channel which is the same type as the first report. It is well known that the flow structure of the mixing channel changes from steady to unsteady (e.g. oscillation and chaotic motion) with increasing the Reynolds number. The flow fields are analyzed 2-dimensionaly in previous studies, thus we investigated the effect of 3-dimensional geometry of the channel on the flow structure and found that the critical Reynolds number for the transition from steady to unsteady flow depends not on the length but on the depth of the channel.

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The purpose of the present research is to study the effect of a pipe length immersed under water on the tone generated from a resonated pipe caused by the impact sound of water drops on the water surface. Experiments have been carried out through the simultaneous measurement of both the generated sound and the formation of air bubbles. A water jet spouted instantaneously from the nozzle changes into many water droplets within a distance of about 20cm from the nozzle exit. The dominated tone radiated from the exit of the resonated pipe is produced by the vibration of the air-bubbles and by the resonance of air-column in the pipe. If a pipe length is immersed deeper under water, the column of air-bubble is made longer and its vibration is generated later. Moreover, the pipe length immersed under water shifts the dominant frequency component of the sound source based on the bubble vibration to the lower frequency.

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