Gas Absorption, Aeration, by Fluidic Oscillator Operated by Gas-Liquid Two-Phase Flow

Abstract

It is known that a conventional feedback type and other type of fluidic oscillators can be operated not only by gas or liquid single phase flow but also by gas(air)-liquid(water) two-phase flow (Shakouchi, 1989, 2001). The two-phase jet flow oscillates periodically of the oscillator under some conditions, and then the gas, air bubble, and liquid flows are mixed and stirred forcibly. The contact area and time between gas and liquid flows increase considerably and then the much increasing of mass transfer, the diffusion or absorption of gas into liquid, will be expected. It may be able to construct an entirely new compact type gas-absorber, aerator, with a simple construction. In this paper, first the performance of fluidic oscillator operated by gas-liquid two-phase flow is made clear experimentally. Next, the aeration performance of the oscillator, namely the diffusion or absorption rate of air, dissolved oxygen, into water under various kind of operation conditions are examined experimentally. The following major results will be shown. (1) The oscillatory frequency f increases linearly with increasing the Re number (= udf/ν, u: mean velocity of water flow at the nozzle exit, df: nozzle width, ν: kinematic viscosity) and the void fraction α. (2) The pressure loss, flow resistance, Δp of the oscillator or increases rapidly with increasing Ref and linearly increasing α. (3) Dissolved oxygen in water can be increased considerably by fluidic oscillator operated by air-water two-phase flow, and it was well known that a new compact type aerator can be constructed by fluidic oscillator.