As viscosity increases, pump performance diminishes due to friction loss. ![]() Reference: “Viscosity-enhanced droplet motion in sealed superhydrophobic capillaries” by Maja Vuckovac, Matilda Backholm, Jaakko V. Generally speaking, centrifugal pumps are most suitable for low viscosity fluids, since the pumping action generates high liquid shear. By being able to predict how the coatings can be used to modify fluid flow, the coatings may be helpful for engineers developing new microfluidics systems. They hope that further work on these systems could have significant applications for microfluidics, a type of chemical engineering technique that is used to precisely control liquids in small quantities and in manufacturing complex chemicals like medicines. The team developed a fluid dynamics model that can be used to predict how droplets would move in tubes coated with different superhydrophobic coatings. Matilda Backholm, one of the researchers on the project. With less air managing to squeeze past the low-viscosity droplets, these were forced to move down the tube with a slower speed than their more viscous counterparts,” explains Dr. This means that the air beneath a low-viscosity droplet in the tube couldn’t move out of the way as fast as for a more viscous droplet with a thicker air gap. “The crucial discovery is that the less-viscous liquids also managed to penetrate a bit into the air cushion surrounding the droplets, rendering a thinner air gap around these. For viscous liquids, the liquid inside the droplet hardly moved around at all, whereas a fast mixing motion was detected in the lower viscosity droplets. The researchers filmed the droplets as they moved through the tube, tracking not only how fast the liquid moved through the tube, but also how the liquid flowed inside the droplet. Droplets of glycerol a thousand times more viscous than water flow through the tube more than ten times faster than water droplets. The size of the effect is quite substantial. Maja Vuckovac, the first author of the paper. This larger air gap is what allowed for the viscous fluids to move through the tube faster than the less viscous ones when flowing due to gravity,” says Dr. “What we found was that when a droplet is confined to a sealed superhydrophobic capillary, the air gap around the droplet is larger for more viscous liquids. In this system, the superhydrophobic coating on the walls of the tube creates a small air gap between the inside wall of the tube and the outside of the droplet. Credit: Aalto Universityīut when a droplet is confined to one of the very narrow tubes used in microfluidics, things change drastically. ![]() This is especially true for thin and narrow pipes, like the ones used in microfluidics for producing medicine and other complex chemicals, so researchers are investigating if they can increase the speed at which liquids flow through narrow tubes without having to increase the pressure.Ī droplet of honey in a superhydrophobic coated tube. This technique, however, has its limits there is only so much pressure you can put into a pipe before you run the risk of bursting it. Traditionally, if you need to make a fluid flow faster through a pipe, you increase the pressure on it. The speed at which different fluids flow through pipes is important for a large range of applications: from industrial processes such as oil refineries to biological systems like the human heart. In fact, through these specially coated tubes, liquids a thousand times more viscous flow ten times faster. Researchers were surprised to find this behavior flipped on its head when the liquids flow through chemically coated capillaries. It’s widely known that thick, viscous liquids - like honey - flow more slowly than low-viscosity liquids, like water. In specially coated tubes, the more viscous a liquid is, the faster it flows. Low viscosity inks are generally found in rollerball or gel pens, where as a high viscosity oil-based ink is generally found in ballpoint style pens where dry time is more critical than smoothness.Drops of honey on a hydrophobic surface. Generally run out of ink more quickly as more ink is flowing through the nib. ![]() ![]()
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