The limited amount of liquids and gases that can be carried to space makes it imperative to recycle and reuse these fluids for extended human operations. During recycling processes gas and liquid phases are often intermixed. In the absence of gravity, separating gases from liquids is challenging due to the absence of buoyancy. This paper describes development of a passive phase separator that is capable of efficiently and reliably separating gas-liquid mixtures of both high and low void fractions in a wide range of flow rates that is applicable to for both space and earth applications.
The limited amount of liquids and gases that can be carried to space makes it imperative to recycle and reuse these fluids for extended human operations. During recycling processes gas and liquid phases are often intermixed. In the absence of gravity, separating gases from liquids is challenging due to the absence of buoyancy. This paper discusses a phase separator that is capable of efficiently and reliably separating gas-liquid mixtures of both high and low void fractions in a wide range of flow rates that is applicable to reduced and zero gravity environments. The phase separator consists of two concentric cylindrical chambers. The fluid introduced in the space between the two cylinders enters the inner cylinder through tangential slots and generates a high intensity swirling flow. The geometric configuration is selected to make the vortex swirl intense enough to lead to early cavitation which forms a cylindrical vaporous core at the axis even at low flow rates. Taking advantage of swirl and cavitation, the phase separator can force gas out of the liquid into the central core of the vortex even at low void fraction. Gas is extracted from one end of the cylinder axial region and liquid is extracted from the other end. The phase separator has successfully demonstrated its capability to reduce mixture void fractions down to 10−8 and to accommodate incoming mixture gas volume fractions as high as 35% in both earth and reduced gravity flight tests. The phase separator is on track to be tested by NASA on the International Space Station (ISS). Additionally, the phase separator design exhibits excellent scalability. Phase separators of different dimensions, with inlet liquid flow rates that range from a couple of GPMs to a few tens of GPMs, have been built and tested successfully in the presence and absence of the gravity. Extensive ground experiments have been conducted to study the effects of main design parameters on the performance of the phase separator, such as the length and diameter of the inner cylinder; the size, location, and layout of injection slots and exit orifices, etc., on the swirling flow behavior, and on the gas extraction performance. In parallel, numerical simulations, utilizing a two-phase Navier-Stokes flow solver coupled with bubble dynamics, have been conducted extensively to facilitate the development of the phase separator. These simulations have enabled us to better understand the physics behind the phase separation and provided guideline for system parts optimization. This paper describes our efforts in developing the passive phase separator for both space and ground applications.
Small neutrally buoyant oil droplets are difficult to remove from water under any condition, but this difficulty is compounded in oil spills in open water. While floating oil can be collected using several existing methods, there are currently few practical methods for recovering neutrally buoyant oil dispersed in the water column. In this work, a large number of cavitation generated microbubbles, small enough to attach to oil droplets and large enough to help the droplets rise to the surface in a timely manner were effectively used for oil recovery.Bubble generators using special nozzle designs induced cavitation in submerged water jets creating cavitation, bubble shearing and break up, and generated masses of poly-dispersed bubbles, ranging in size from a few microns to 300 microns. The generators used vortex cavitation initiated in swirl chambers. The bubble sizes and numbers produced were measured by means of image analysis of high speed videos. The effects of the various operating conditions on the bubble size distributions were investigated. The recovery of three types of crude oils from water under various salinities and bubble concentrations was measured.
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