School Papers

Tears Ivan10/3Abstract:This article is about the Marangoni effect.

Tears of wine phenomenon and the Marangoni effect.Mitev, Ivan10/3Abstract:This article is about the Marangoni effect. It will include the following things. Firstly, a brief history of the effect(when and by who it was first discovered and observed) and definitions of all the terms needed to understand its explanation. Then, parametric equations describing the technicalities of the effect. Finally, photos and an experiment, demonstrating the effect in real life and its industrial and scientific uses. The aim of this article is to help my classmates better understand the effect and its uses.Introduction:    The Marangoni effect is a very important and completely overlooked effect in physics. It was discovered by James Thomson in 1855 when he was observed the “tears of wine” phenomenon. This is a phenomenon in which when observing a glass of wine, a ring of liquid forms above the near the top of the glass, way above the wine itself. Water droplets continuously fall from the top of the glass and back into the wine. I also observed the “tears of wine” phenomena and want to answer the following questions. How do “tears of wine” occur? Can “tears of wine occur with any other substances? Do “tears of wine” have any practical applications?Methodology:    In order to understand the Marangoni effect the following concepts need to be explained:derivative – the change of a scalar function’s output in respect to its input. It represents  the slope of the tangent of the graph of the functiongradient – a gradient is a vector form of a derivative and it points in the direction in which the function’s value will increase at a highest rateSurface tension – the tendency of a fluid to always try to acquire the least surface area possible. This is caused by the equal pull of the neighbouring liquid moleculesViscous forces – forces which measure a fluid’s resistance to flowHow does the Marangoni effect work:    The Marangoni effect occurs when there is a gradient of surface tension between two fluids. This means that the effect will occur at the point where the surface tension is growing at the fastest rate. This growth can be achieved by dissolving the fluids with different solutions(like in the “tears of wine” phenomenon) or by a change in their temperature. The Marangoni effect causes heat and mass to travel to the places with higher surface tension which leads to a change in the surface area. In some cases, it can be confused with the capillary effect which causes liquids to flow in an unnatural direction when put into tight spaces. The equation connected with the Marangoni number is the following: . The Marangoni number is used to express the proportion between the surface tension and the viscous forces of a fluid. This being said, the Marangoni number is useful for determining the flow of a fluid, generated by surface tension. To further explain the formula, ? stands for surface tension, L for length, for thermal diffusivity, is for viscosity, and ?T is for the change in temperature.Tears of wine:    As explained earlier, the “tears of wine” phenomenon is caused by the Marangoni effect. But how does it work? It occurs because alcohol has a lower surface tension than water and because in a glass of wine the concentration of alcohol is not evenly distributed, the parts with a lower alcohol concentration will pull the surrounding wine harder than parts with a higher concentration. This means that the water will move out of the high alcohol areas(the  centre of the glass) and move up the edges of the glass. However, due to the strong pull of gravity, the droplets will fall back into the fluid. This phenomenon occurs with other alcoholic drinks such as rum.Uses:A familiar example of the Marangoni effect is in soap films. When two soap bubbles meet, they merge and create a thin film between themselves which colours them in yellow, green and purple. An industrial use of the effect is when drying cut pieces of silicon. Normally, any liquid left on the pieces might damage them. However, alcohol vapour is sprayed on the silicon. This lets the Marangoni effect move the water using surface tension faster and more efficiently.Conclusion:This article explained the causes of the tears of wine phenomenon and how the Marangoni effect works. It also explained important mathematical and physics concepts and demonstrated the material with images. The article also provided formulas connected with the Marangoni effect It gave examples for uses of the effect.References:Multiphysics Cyclopedia.” COMSOL, www.comsol.com/multiphysics/marangoni-effect.Dunbar, Brian. “The Marangoni Effect: A Fluid Phenom.” NASA, NASA, www.nasa.gov/mission_pages/station/research/news/marangoni.html.”Marangoni Effect.” THERMOPEDIA™, THERMOPEDIA, www.thermopedia.com/content/29/.D’Aubeterre, A. “Experimental Study on Marangoni Effect Induced by Heat and Mass Transfer.” International Communications in Heat and Mass Transfer, Pergamon, 17 Mar. 2005, www.sciencedirect.com/science/article/pii/S0735193305000370.Meggs, Lori. “The Marangoni Effect: A Fluid Phenom (w/ Video).” Phys.org – News and Articles on Science and Technology, 11 Mar. 2011, phys.org/news/2011-03-marangoni-effect-fluid-phenom-video.html”Viscous Force.” Schlumberger, www.glossary.oilfield.slb.com/Terms/v/viscous_force.aspx.”Marangoni Number.” Wikiwand, www.wikiwand.com/en/Marangoni_number.