A small company solves global problems
Ultrasound technology is able to produce stronger paper, reduce costs, and provide a global solution to the problem of wastewater. This has all been possible since a growing company, Ultra Sonus, developed a fifty year-old technology that was previously only used at the lab-scale. The development occurred to a large part through the use of COMSOL.
Introduction
General manager Måns Virding (left) and R&D manager Johan Söderberg
Ultrasound is the area of science involving sound waves in the range from 20 kHz to 10 MHz. Ultra Sonus has developed an ultrasound technology that involves "loud speakers" transmitting sound waves through liquids, which contain gas bubbles. The waves make the bubbles grow and then collapse releasing energy equivalent to 10.000°C and a pressure of 500 bar. The phenomenon is known as cavitation and is currently used in two application areas: medical examinations and echo sonar where cavities (gas bubbles) are detrimental, as well as purification and other situations where cavities must be removed. The technology can also be used in the cleaning of tools.
Ultra Sonus - which is Latin for ultrasound - currently concentrates on ultrasound cavitation. For the last fifty years, it is a technology that has been thought of as applicable for use within fibre-separation, emulsion, disinfecting etc. The problem with existing oscillators (ultrasound transmitters) is that they are not able to provide the cavitation that is required for today's industrial applications.
"Yet through, the work of Johan Söderberg and others, we have developed and patented an ultrasound system that has a far greater effect than those used in industrial washing processes and in laboratories," said Ultra Sonus' general manager, Måns Virding.
Johan completed his Master of Science thesis at The Technical University of Linköping in the subject of "Dynamic Analysis of Ultrasound oscillators". He now works as the R & D manager at Ultra Sonus where he develops and designs the devices - work that is based on Finite Element Method (FEM) analysis.
Areas of applicability
"This technology is in principle appropriate for a hundred interesting applications; each with their own large markets. Naturally, we cannot concentrate on all of them, and we have chosen the application areas of paper manufacture and waste stream treatment", says Måns Virding.
Paper manufacturing is an interesting area because the principle is similar throughout the world, and because there a number of large paper companies that can assist Ultra Sonus being launched into several markets. There is always the risk of building fibre clumps at the wire section of a paper machine, and it has been observed that ultrasound waves can assist in separating these fibres. This in turn reduces the amount of raw material that goes towards making the paper. One of the world's largest manufacturers of paper machines, Voith Paper, is cooperating with Ultra Sonus in applying this technology.
Johan Söderberg tests and develops the new technology using COMSOL Multiphysics
Another key area where ultrasound technology is useful is in its application to waste stream treatment plants. Once again, the principles are worldwide, where the final product of pure water and sludge (20% - 30% dry) are often required. Waste water are a big problem throughout the world and 10 tons/year of sludge, costing 50 billion Swedish crowns a year, are treated just in Germany. Re-using this sludge in agricultural applications would be a possibility but for the often high levels of heavy metals and other poisonous substances present in a sludge. This is why a large amount of this waste is dumped into fills, an act that will be made illegal within the European Union by 2005. Ultrasound technology is able to help with the treatment and significantly reduce the amount of unusable sludge from treatment plants.
FEM - analysis - a prerequisite
A prerequisite for achieving adequate cavitation with ultrasound technology, which has never previously been done before, is to have complete control over the sound waves' propagation, shape, amplitude and frequency. This requires quite an advanced computing program and Ultra Sonus, after an extensive survey of the available software on the market, decided to use COMSOL Multiphysics.
The new ultrasound system that Johan developed consists of three parts: the electric system, cooling system and oscillation system. The electric system has the job of sending the alternating current, with correct frequency and amplitude, to the oscillator. The cooling system controls coolant temperature and flow rate, while the oscillation system transforms the electrical energy to sound waves with the highest efficiency as possible.
Johan conceptually designed his prototypes by directly sketching interesting geometries in COMSOL Multiphysics and running series of analyses. He could, at this stage, already decide appropriate geometries and save them as CAD drawings (in a DXF format) to then be used by the designers. This way of working has been seen to considerably accelerate production since it is the calculation and analysis that pinpoints appropriate geometry.
Visualizing the flow-field profile in a channel
Basically, the production depends upon the following analysis:
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| Structural Mechanics | Calculation of the eigenfrequency. |
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| Flow field | Calculation of the fluid flow. |
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| Wave propagation | Analysis of how the waves propagate and interact with the surrounding fluid. |
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| Heat expansion | Calculation of the distributions of temperature, potential and expansion. |
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"I obviously could have done these calculations in other programs," said Johan Söderberg, "but in that case, I would have had to acquire several programs for a total cost of 200 000-300.000 Swedish crowns (around 20 000-30 000 USD), which does not compare with COMSOL's low price. In this way, it is even better with the one type of software as I am only required to teach myself one user-interface. Geometry changes can also be done directly in the analysing software, so that I avoid swapping from one program to the next all the time."
Continuing development
The oscillator/transmitter in Ultra Sonus' product is made of a piezoelectric device with good efficiency and functionality throughout the ultra sound frequency range. Ultra sound is generated by a ceramic that oscillates when an electrical potential is applied to it. This process needs to be cooled when decent performance is required. When these parameters are satisfied, sufficient ultrasound waves can be generated that create powerful cavitation fields, which bring about the desired implosions.
The heart of the oscillator consists of a disc made from piezoelectric ceramic.
"In retrospect, I can say that it was the computational program that enabled us to move from a 'garage' company to one that is expert in its field," said Måns Virding. "Previously, we developed prototypes to see what would happen. Now we can simulate the oscillator and evaluate its functionality. In other words, we have skipped 3 - 4 steps in the development process and require far fewer prototypes than before."
A further advantage is that COMSOL is written in the MATLAB programming language, which was previously used in own developed applications. Yet, Johan does see an important disadvantage with the software, the fact that the calculations are in two dimensions, whereas the world works in three dimensions. "In this case", he said, "vital information could well be lost."
But the future looks good since the latest version of COMSOL Multiphysics supports 3D modeling. "I must say that three-dimensional calculations are something that I really need to be able to do, and this development will hopefully lead to making our work even more safe and effective in the future." said Johan.
The development work has also received larger prominence in the company, which comprises of a board filled with 'heavy weights'. An agreement of cooperation has been written with Voith Paper, one of the world's largest manufacturers of paper machinery, and with Stora Enso, which also contribute financially to the development.