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 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.
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.
- Batch and Inline
- Low and High Viscosities
- Small and Large Volumes
- Cold and Hot Temperatures
- Versatile Installations
- 24/7 Operation under Full Load
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)
Ultrasonic Degassing of Molten Aluminium Alloys
The generation of cavitation in liquid metals is a highly demanding application and there are only very few techniques to produce sufficient and reliable cavitation in metal melts. However, the rate and intensity of cavitation are a crucial factors shaping the degasification results. Effective degasification requires reliable cavitation in order to obtain maximum structural refinement of the metal melt. Intense cavitation by high-performace ultrasound can improve the degassing by 30 to 60%.
Ultrasonic probe-type degassers are considered to be one of the most reliable outgassing methods, which have been proven scientifically viable on small and large scale. The generation of intense acoustic cavitation depends on various factors including ultrasonic process parameters, metal composition, surface tension, melt temperature, viscosity, as well as volume and dissolution level of gas inclusions in the metal melt. Ultrasonic process parameters can be precisely tuned to the metal melt composition and the influencing factors so that the right intensity of cavitation is obtained. The exact adjustment of the ultrasonic parameters are the fundamental for the advantages of ultrasonic degasification of metal melts. The main advantages of ultrasonic degassing include high degassing rates and the reduced environmental impact of the process. Since ultrasonic degasification results only in very little dross, ultrasonic metal melt degassing is a green, environmental-friendly technique.
Degassing aluminium melts: Ultrasonic degassing is a proven method to increase aluminium alloys density and decrease hydrogen contents in aluminium alloys. In comparison to alternative degassing procedures such as outgassing by using a rotary impeller, ultrasonic degassing excels by speed and efficiency. Studies have shown that an ultrasonic probe degassing system was about 3 times faster than impeller-driven gas removal.
As ultrasonic degasification does not involve conventional metal stirring, the protective aluminium oxide on the surface of the melt is not disrupted. Keeping the aluminium oxide layer intact prevents the introduction of aluminium oxide into the aluminium melt so that it maintains it protective effect against atmospheric contaminants. Ultrasonic degassing improves the grain refinement and structure of aluminium alloys. This in addition to the ultrasonically promoted removal of non-metallic gas inclusions from the liquid aluminium, makes ultrasound-driven metal melt treatments a superior technique for the production of high-quality metal castings.
The degasification of metal melts such as aluminium alloys requires high-performance, high-power ultrasonic equipment. The ultrasonic probe must be specified for use with high temperatures and high viscosities. The ultrasonicator must be able to deliver and maintain constant amplitudes over long time periods. Hielscher Ultrasonics is specialised in the development, manufacturing and distribution of high-power ultrasound equipment for demanding applications such as the degasification of metal melts. Supplying high-performance ultrasonicators at any scale and ultrasonic probes developed specifically for the treatment of liquid metals, Hielscher Ultrasonics is your partner for reliable and efficient metal melt applications.
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 br 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.
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Literature / References
- Mahmood Amani, Salem Al-Juhani, Mohammed Al-Jubouri, Rommel Yrac, Abdullah Taha (2016): Application of Ultrasonic Waves for Degassing of Drilling Fluids and Crude Oils. Advances in Petroleum Exploration and Development Vol. 11, No. 2, 2016. 21-30.
- Haghayeghi R.; Kapranos P. (2014): The effect of processing parameters on ultrasonic degassing efficiency. Materials Letter Volume 116, 1 February 2014. 399-401.
- Servant G.; Caltagirone J.P.; Gérard A.; Laborde J.L.; Hita A. (2000): Numerical simulation of cavitation bubble dynamics induced by ultrasound waves in a high frequency reactor. Ultrasonics Sonochemistry Volume 7, Issue 4, October 2000. 217-227.