Highly Efficient De-Aeration of Liquids using Ultrasonics

Whilst degassing or outgassing is often an extremely time-consuming process step, ultrasonication can accelerate the coalescence of gas bubbles and their rise significantly. Ultrasonic outgassing can be used in batch and inline setups and can be also combined with conventional degassing techniques such as sparging with inert gases, impeller degassers, heating or vacuum in order to enhance efficiency and speed of gas removal.

Removing Gas from Liquids

The terms deaeration, degassing and outgassing refer to the removal of free and dissolved gasses, particularly reactive gases such as oxygen or CO2, from a fluid. Eliminating oxygen is important to prevent detrimental end-product changes and improve downstream processing. Degassing is a necessary processing step for many applications and industries. In industrial manufacturing, degassing is a common process step to ensure product stability, quality and continuous product standards. Oxygen is a factor that influences the product quality and stability on various levels.
Therefore, deaeration is an established process step in the food & beverage, chemical, pharmaceutical and cosmetic industry. But also in laboratories, samples require often degassing before analysis (e.g., before HPLC, assays, particle measurements etc.).
Often mixing processes using e.g., high-shear blade or rotary impeller mixers often make subsequent degassing of the product necessary, since these mixing techniques commonly introduce high amounts of gases into the product. Such gas and air inclusions usually have negative effects on the product, as they can make fats and oils rancid, deteriorate products by oxidation, discolouring and unwanted alterations of smell and taste. As degassed products are chemically more stable and have a longer shelf life, degasification is an essential processing step requiring a reliable technique.
 

Ultrasonic degassing: Entrapped gas bubbles are removed from oil using the ultrasonicator UP400St

Ultrasonic Degasification and De-Aeration

Ultrasonic degasification and deaeration is a highly potent alternative to traditional degassing methods of liquids that include boiling, reducing pressure to vacuum, or sparging with inert gases. These traditional degassing methods often come with disadvantages such as thermal degradation (due to heating), time- and energy-consuming processing and/or insufficient gas removal. Ultrasonic degassing is based on the working principle of acoustic cavitation. When high-power ultrasound waves are coupled into a liquid, the liquid is compressed and expanded during high-pressure and low pressure cycles, respectively. During low-pressure cycles, minute vacuum bubbles (so-called cavitation bubbles) are created, which grow over several pressure cycles. During those cycles of bubble growth, the dissolved gases in the liquid enter the vacuum bubble, so that the vacuum bubble transform into growing gas bubbles. Furthermore, micro-turbulences and liquid jets cause intense agitation and mass transfer. These ultrasonically generated conditions cause gas bubble coalescence, which is the unification of small dissolved gas bubbles to larger gas bubbles, which quickly rise to the surface of the liquid, where there they leave the liquid.
The temperature changes caused by ultrasonic vibration and cavitation are confined to very small local spaces and the temperature rise in the total volume can be neglected as it does not interfere with the product quality.
 

Decrease of dissolved oxygen with time for ultrasonic frequency of 24 kHz using the sonicator UP400ST at amplitudes of 100 %, 80 %, 60 %, 40% and 20 %.
Study: ©Rognerud et al., 2020.

 
Depending on the volume, viscosity and gas inclusions of the liquid or slurry, ultrasonic de-aeration can be run as batch or inline process. An high-power ultrasonic probe emits acoustic cavitation into the liquid, so that the liquid is efficiently degassed.
Ultrasonic degasification can be also implemented to improve already existing degassing systems such as heating, vacuum or sparging.
Ultrasonic degassing and defoaming is used on industrial scale to remove dissolved gases from water, oils, foods and beverages, chemical solutions, hydraulic fluids, coolants, drilling fluids, crude oil, emulsions, paints, inks, adhesives, varnishes, coatings, epoxies, shampoos, detergents and many other products.
 

Ultrasonic degassing using a flow cell setup. This experiment was a prototype small-scale water loop with a volume of 0.8 gallon, inert gas flow of 0.2 sfcm/min, and intensity of 275 W/cm2. This shows a reduction in oxygen removal time by about 70%.
Study and picture: Rubio et al. 2016

Ultrasonic degassing in a inline setup using the ultrasonicator UIP1000hdT with flow cell.

Ultrasonically Enhanced Sparging

Sparging liquids with inert gas (also known as inert gas purging) is a common treatment to remove unwanted gases such as oxygen and carbon dioxide from the liquid. For sparging applications, nitrogen, argon, helium and other inert gases are commonly used. Bubbling a solution with a high-purity (typically inert) gas can pull out undesired, typically reactive dissolved gases such as oxygen and carbon dioxide. The sparging process relies on mass transfer and is itself a quite slow procedure. I order to intensify the sparging with inert gases, the liquid-gas solution is often agitated vigorously and bubbled for a long time. Ultrasonication is a degasification-intensifying technique, which improves mass transfer and thereby the sparging significantly. When high-power ultrasound waves are coupled into liquids or slurries, cavitation bubbles are generated. These cavitation bubbles break up larger purge gas bubbles into small bubbles and disperse the bubbles uniformly, which results in faster and cleaner degassing effects. The intense agitation and turbulences created by ultrasonication promotes gas-liquid mass transfer and thereby the quick removal of unwanted gases.
In order to accelerate and to make the sparging procedure more efficient, high-performance ultrasonics is used to sonomechanically improve the mass transfer performance between gas and liquid. The sonomechanical effects generated by acoustic cavitation include local pressure and temperature differentials, microturbulences and agitation. These forces improve degassing performance by contributing to an increase in the diffusive mass transfer due to bubble breakup, dispersion and the subsequent increase interfacial area, which finally result in a fast removal of entrapped gases from the liquid.
To achieve the desired outgassing effects, high-power ultrasonication is required. When a liquid is spared with an inert gas in a two-phase flow, rectified diffusion is desired to increase the mass transfer and removal rate of dissolved gasses. Applying rectified diffusion can be difficult because entrapped and dissolved gas bubbles tend to avoid entering the ultrasonic cavitation field at lower intensities. However, at elevated intensities (higher than 300 W/cm² at approx. 20 kHz) gas bubbles no longer avoid the cavitation zone and are broken up by sonomechanical forces. (cf. Jagannathan et al. 2011)

High-Power Ultrasonic Degassing Systems

Hielscher Ultrasonics is long-termed experiences manufacturer of high-performance ultrasonic equipment that is used worldwide in laboratories and industrial production. The degasification of liquids and slurries is a demanding application that requires high-power ultrasonic probes which can couple established amplitudes into liquids to remove entrapped gas bubble and air pockets. All Hielscher ultrasonic devices are designed and manufactured to be operated for 24/7 under full load. Ultrasonic processors are available from compact 50 watts laboratory ultrasonicators to 16,000watts powerful inline ultrasonic systems. A wide variety of booster horns, sonotrodes and flow cells allow for the individual setup of an ultrasonic degassing system in correspondence to the liquid, viscosity and gas inclusions.
For the deaeration and outgassing of liquid metals, precisely set and maintained amplitudes are required. Hielscher Ultrasonics manufactures high-performance ultrasonic probes that are specified for very process-optimized amplitudes and temperatures. If your degassing application requires unusual specifications, customized ultrasonic sonotrodes are available. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.

Batch and Inline

Hielscher ultrasonic probes for degasification can be used for batch and continuous inline degasification and deaeration. Depending on volume, viscosity and entrapped gases, we will recommend you the most suitable ultrasonic outgassing setup.

Ultrasonic Probes for Degassing Any Volume

Hielscher Ultrasonics product range covers the full spectrum of ultrasonic processors from compact lab ultrasonicators over bench-top and pilot systems to fully-industrial ultrasonic processors with the capacity to process truckloads per hour. The full product range allows us to offer you the most suitable ultrasonic degassing equipment for your liquid, process capacity and production targets.

Precisely Controllable Amplitudes for Optimum Results

All Hielscher ultrasonic degassing systems are precisely controllable and thereby reliable work horses. The amplitude is one of the crucial process parameters that influence the efficiency and effectiveness of sonomechanically induced degasification. All Hielscher Ultrasonics’ processors allow for the precise setting of the amplitude. Sonotrodes and booster horns are accessories that allow to modify the amplitude in an even wider range. Hielscher’s industrial ultrasonic processors can deliver very high amplitudes and deliver the required ultrasonic intensity for demanding applications. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation.
Precise amplitude settings and the permanent monitoring of the ultrasonic process parameters via smart software give you the possibility to adjust the ultrasonic process parameters for most effective ultrasonic degasification. Optimal sonication for highly efficient gas removal!
The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments. This makes Hielscher’s ultrasonic equipment a reliable work tool that fulfils your deaeration process requirements.

Highest Quality – Designed and Manufactured in Germany

As a family-owned and family-run business, Hielscher prioritizes highest quality standards for its ultrasonic processors. All ultrasonicators are designed, manufactured and thoroughly tested in our headquarter in Teltow near Berlin, Germany. Robustness and reliability of Hielscher’s ultrasonic equipment make it a work horse in your production. 24/7 operation under full load and in demanding environments is a natural characteristic of Hielscher’s high-performance degassers.