Turbulence and swirling air are connected with air travel problems, rough seas and even hurricanes and cyclones. Moreover, they also hinder the flow of fuel in pipes. Piping oil, gasoline, ethanol and even water from one place to another involves a turbulent environment, full of whirlpools that reduce the flow and that require powerful equipment to drive the liquid. This phenomenon, intrinsic to any type of liquid, has been studied for years. The solution, to make it easier to pump oil over long distances, was to dissolve small amounts of certain polymers in the fuel. The polymers function as reducers of hydrodynamic friction. The procedure is already used, for example, in Alaska, the US state, in oil pipelines 1,287 km long.
Still, a solution was required for ethanol, the fuel alcohol that is increasingly important in the Brazilian market, as well as for ethanol exporting, which increasingly involves piping it. “Adopting a friction reducer can increase the ethanol flow in a pipeline by 20% or more, implying proportional savings of the power required to drive the pumps that propel the liquid,” says professor Edvaldo Sabadini, from the Chemistry Institute at the State University of Campinas (Unicamp). He studied the phenomenon and found an effective polymer for the pumping of ethanol, so much so that he deposited a patent request with INPI, the National Institute of Industrial Property, through Inova, the university?s Innovation Agency.
“The attrition reducer lessens the turbulence and eliminates the very small vortices that form when the liquid picks up speed,” says Sabadini. Vortices are very fast whirling movements, with chaotic direction and formation, characterizing a turbulent system. “These microscopic whirlpools restrain the liquid in all directions. The polymers that are added to the ethanol interact with these vortices, absorbing their energy and keeping them from propagating.” Poliethylene oxide was the polymer used in the experiment, but the researchers are looking into other cheaper and more commercial alternatives, because the aforementioned polymer is used mainly in laboratories. “One only needs a very small amount of polymer, something of the order of 30 parts per million (ppm), which is equivalent to adding 30 grams of polymer to 1 ton of ethanol. A larger quantity does not yield additional benefits. The polymer must have super-macromolecules with extremely high molecular mass and the characteristics of being flexible and highly soluble in the liquid in which it will be used,” says Sabadini.
The researchers believe that the lessening of the vortices results from the stretching and shrinking movement of the polymer’s molecules. This, in any event, is the explanation that is accepted to date, although the studies on the nature of the turbulence have been inconclusive. “It is still one of the major challenges of physics,” says Sabadini. To exemplify this, he recalls that the German physicist and 1932 Nobel Prize laureate Werner Heisenberg allegedly said (this was not written down) that if he met God, he would ask two questions: Why is relativity so strange? And how can one explain turbulence? Apparently Heisenberg stated that God would know the answer to the first question, but not to the second.
To study and to attempt to broaden the understanding of the interaction between the polymer and turbulence and to choose a substance to act as a hydrodynamic friction reducer for ethanol, the researchers resorted to an experiment that relies on the effect of drops falling onto a liquid. After impact, a splash takes place, lasting about 0.1 second. At first, a sort of crown emerges and soon after a jet perpendicular to the liquid’s surface appears. The group observed that the splash has different structures depending on whether the water is pure or contains polymer. With the additive, the water forms a far larger jet. “The impact of the drop creates turbulence and the friction reducer allows the liquid to slide more easily and with less dissipation of energy, impelling the jet higher.” The experiment was conducted with an ultrafast camera, capable of capturing more than 18 thousand frames per second, acquired by means of a FAPESP regular research awards. “We measured the milliseconds of each image.” The experiment was conducted with water because ethanol’s superficial tension is low, which makes observation of the splash difficult.
The effect of the polymer in the ethanol was proven by the researchers by means of a rheometer, a device that comprises of a sort of cylindrical tumbler that holds the liquid to be studied, plus a cylinder of a smaller diameter in its interior. This cylinder can rotate at various speeds. The liquid fills the space between the two cylinders. In the case of ethanol, the effort was measured with the cylinder rotating at 1,200 rpm. Then the effort of the alcohol with polyethylene oxide dissolved in it was measured at the same rotation. This showed a 15% reduction in friction. In a way, the device simulates the turbulence found within alcohol pipelines. Thus, according to Sabadini, pumping large amounts of ethanol with additive along pipelines might generate substantial savings. Sabadini is also studying, along with the Unicamp Petroleum Study Center, the use of friction reducers for diesel and oil, as these are seldom used in Brazil.
The history of friction reducers in liquids began back in 1948, with chemist B. A. Toms from the University of Birmingham, in England. He showed that a diluted solution of polymethyl methacrylate mixed with monochlorobenzene offered less resistance to flow than the pure solvent. One of the striking images of these reducers is a late 1960’s photograph of a demonstration by New York firemen, in the US. They used the same pump to propel water in one hose and water with a little polyethylene oxide in another. The jet with additive went 80% further. Now it is ethanol’s turn.
Reduction of hydrodynamic friction based on images of the impact of drops (nº 05/00873-8); Modality Regular Research Awards; Coordinator Edvaldo Sabadini – Unicamp; Investment R$ 36,677.24 and US$ 60,372.00 (FAPESP)
ROCHA, N. O. et al. New experimental technique to measure the efficiency of drag reducer additives for oil samples. Energy & Fuels. v. 23, p. 4,529-32. 2009.
SABADINI, E.; ALKSCHBIRS M. I.; Drag reduction in aqueous poly (ethylene oxide) solutions based on drop impact images. Journal of Physical Chemistry B. v. 108, p. 1,183-88. 2004.