Ultrasound-assisted degassing

Ultrasound-based degassing Involves removing gases from solutions without the need for heat or vacuum. The cavitational effects underlying sonochemical action are also the basis of the extremely effeotlve use of US to degas liquids. Onoe cavitation bubbles have 

A distinction should be made between the bubbles which are formed by cavitation and those which occur naturally in the parent liquid or are induced by ultrasonic action (sparging). Cavitation bubbles, which range in size from infinitesimal to visible (40 pm and above) appear only when the radiating surface is activated and vanish apparently instantaneously when the power is turned off (in fact, they vanish within a half-cycle or 25 X 10 s at 20 kHz). Naturally occurring bubbles of entrapped air or other gases are most evident in freshly poured hot tap water as cloudiness or in still water as small bubbles adhering to the undersurface and the vessel walls. Sparged bubbles, which are those induced mechanically by external means such as ultrasonic action at or near the gas-liquid interface (the surface), tend to float in the liquid and even produce foam. 

One salient example of the need for degassing in the clinical field and of the effectiveness of ultrasound for this purpose is a prototype of ultrasonic micro-degassing device for portable dialysis systems. The bubbles inside these systems reduce the effective exchange surface area, which is extremely important here [104]. 

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The removal of unwanted air or gas is important in many food processes and it can be extremely difficult especially in very viscous liquids such as chocolate. Ultrasonically assisted degassing is particularly rapid in aqueous systems and can be used to remove any dissolved gas down to a very low level, thus is of great benefit in situations requiring the rapid and controlled removal of a gas or gases from a system. However ultrasound has also been employed to degas liquids as viscous as molten glass [73] and as dense as molten metals [74] during their solidification process. 

Although the use of ultrasound to assist sample preparation has so far been limited in relation to its potential [39,40], few analytical chemists are unaware that US can help, improve, aoeelerate or automate the preliminary steps of the analytical process — particularly those preoeding sampling (e.gf. cleaning the lab material or degassing solvents). Ultrasound has also found a variety of uses in the detection step ranging from... 

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