Inkjet printing as one of the directions of applied fluid dynamics

"Golden Age" hydrodynamics

The year of the appearance of hydrodynamics as a science can be considered the year 1628, when Benedetto Castelli's little work was published. In it, despite the initial erroneous assumptions, he quite accurately explained for his time several phenomena when fluid flows in rivers and canals. However, even before this, there were attempts to study the resistance of the environment to the movement of the body by such famous scientists as Leonardo da Vinci and Galileo Galilei. Subsequently, a great contribution to the development of hydrodynamics was made by Newton, Euler, Torricelli, Bernoulli, D'Alembert, and many others.

Modern science is developing exponentially. This is because advances in one area provide material for creating new tools used for research in other areas. Therefore, it would be fair to say that a real “golden age” has arrived for hydrodynamics. At the same time, the approach to research has changed. Now significantly improved ways to obtain experimental data. If earlier a theory was built and then confirmed or refuted by an experiment, today the theory is based on a complex of high-precision measurements.



To study laminar and turbulent fluid flows at the Max-Planck Institute, a camera is now used that makes up to 1 million frames per second. The previous camera was 500 times slower and took 2,000 frames per second. Thousands of particles can be traced when studying turbulent flow with cameras. Their trajectories and speed of movement are converted into data arrays, which are then processed by powerful computing equipment. This allows you to build numerical models of the processes taking place and to better understand the nature of such phenomena as, for example, turbulence.

The study of the formation of droplets in the clouds can significantly improve the accuracy of weather forecasting. Especially for this, a laboratory of an environmental research station in Germany was set up on the Zugspitze mountain (2,962 m / 9,718 ft). 4 high-speed cameras are installed along the 7-meter rail track. When clouds pass through them, the cameras provide an opportunity to study in the smallest detail the processes occurring in the volume of several cubic centimeters. Researchers observe how the fine mist from turbulence coalesces into larger droplets.

In other words, they study the birth of rain. But scientists do not intend to dwell on existing opportunities and are already designing the delivery of high-speed cameras to the clouds with the help of a kite and balloon hybrid.

How diverse the scope of hydrodynamics, can be judged by its main sections:

• Ideal environment - this section examines the behavior of an ideal fluid, in which the description can neglect internal friction, thermal conductivity and tangential stresses.
• Hydrodynamics of laminar flows - studies the movement of uniform flows without pulsations and mixing of layers.
• Turbulence is a very complex modeling process. Turbulence occurs with a sharp deviation of pressure, speed, temperature, density from some average values. For example, in the surf zone, the incident wave mixes with the air to form foam. Often, the passengers of the aircraft feel the vibration when the aircraft enters the zone of turbulence. We can also observe the phenomenon of turbulence in boiling water. This is a very important section, without which no pipeline is built.
• Supersonic hydrodynamics is a specific section that studies the behavior of currents at speeds approaching or exceeding the speed of sound. The main feature of the behavior of such flows is the occurrence of shock waves.
• Heat and mass transfer - studies the complex behavior of liquids with uneven temperature distribution. This can locally change the properties of the medium, such as density, viscosity, thermal conductivity.
• Geophysical hydrodynamics - studies the natural phenomena of a planetary scale. This includes air flow, sea and ocean currents, circulation in the liquid core and much more.
• Magnetic Fluid Dynamics - describes the movement of an electrically conductive fluid in a magnetic field. In addition, this section studies the phenomena of space physics: chromospheric flares in the sun, the origin of the magnetic fields of galaxies, sunspots.
• Rheology - studies the movement of nonlinear fluids, which include gels, pastes, pseudoplastic, viscoelastic. Rheology is widely used in materials science and in the study of geophysical processes.
• Applied fluid dynamics - works with specific scientific and technical problems.

Inkjet development

One of the directions of applied fluid dynamics is inkjet printing. For more than 15 years, Océ has been working in this area with the Max-Planck Institute. A group of scientists led by Professor Detlef Lohse studies the processes associated with inkjet printing to determine the maximum printing speed. That is, determining the limit when the injection of ink from the nozzles of the print head and the fixation of the droplets on the carrier will become unstable.

At the same time, ways are being developed to maximize support for the stability regime.
Modern inkjet printing uses two ink injection technologies. In one case, the role of the piston, which pushes a drop of ink from the nozzle of the print head, is performed by a piezoplate, and in the other, by a vapor bubble. Canon is the only manufacturer in the world that produces jet equipment using both technologies. In addition, Océ specializes in the production of printers with piezo-acoustic print heads.

The first steps in the development of its own inkjet technology Océ took in the early 90s of the last century. The company appreciated the enormous potential of inkjet technology. Unlike other types of printing, there are fewer rotating parts. This means that as parts are reduced, the initial cost of equipment decreases and downtime for maintenance is reduced. Therefore, to create its own unique inkjet technology, it was necessary to understand hydrogasdynamic processes. It was then that partnerships began to emerge with the Max-Planck Institute in Göttingen (Germany) and the University of Twente (the Netherlands).

The researchers were faced with a mass of interesting problems that required a comprehensive solution. It was necessary to take into account the physicochemical and optical properties of the ink, the mode of injection of droplets, the delivery of ink to the head, and the feed rate of the printed carrier. The change of only one characteristic entailed an adjustment of the others.



With the external similarity of the piezoacoustic and bubble jet technologies, they have serious differences, both in the processes themselves and in the possibilities. Bubble technology uses solvent inks or water-based inks. The principle of operation of such printing is that there is a microheating element in each printing cell. When an electrical impulse is applied, the element heats up, and the ink layers adjacent to it boil. At the same time a vapor bubble is formed sharply. He, in turn, performs the function of a kind of "piston", pushing a portion of ink from the nozzle. Here all phenomena of fluid dynamics are fully manifested.

In the piezoacoustic technology, the role of a “pusher” is played by a piezoplate. It changes its geometry under the influence of electrical impulses. Due to this, a drop of ink is injected from the nozzle. By modulating the signal applied to the piezoplate, it is possible to set the drop volume with high accuracy. This gives a lot of advantages of piezo-acoustic printing technology:

• Accurate dosing optimizes ink consumption;
• Provides accurate color on all prints;
• The ability to use solvent-free ink (UV-ink, solid), which instantly crystallizes on the carrier and does not require drying;
• As a consequence of the previous paragraph, the reduction of energy consumption and the ability to print on media that are critical to heating;
• High speed printing indelible and wear-resistant prints;
• Due to instantaneous crystallization of the ink, inexpensive grades of paper can be used as a carrier, since a drop is fixed on the surface of the carrier without being absorbed into it.

Research in the field of fluid dynamics inkjet technology is not limited to the printing industry. Modern technologies allow you to print on various media and use a variety of printing compositions. So already mastered printing on glass, wood, metal, plastic. Relatively recently, volume printing began to be practiced, allowing to transfer not only colors, but also the volume texture of the surface. Thus, it becomes possible to print not only on the material, but also by the material itself. This may be used in printing chips or touch screen coatings.

On the border of fundamental and applied research, new perspectives appear that no longer seem so fantastic. There are significant similarities in the physical characteristics of blood and ink. They have similar viscosity and fluidity. It would seem, what does this have to do with inkjet printing? But perhaps this is the first steps to print living tissues or even entire organs.