Water, oil, alcohol, glycerin and gasoline are common examples of Newtonion fluids. The viscosity of a Newtonion fluid is only dependent on the temperature of the fluid (consequently, the requirements for pumping water through a pipe is an easily predictable evolution). If you stir a glass of water with a spoon, the viscosity does not change no matter how vigorously or how long you stir. Water is considered a Newtonion fluid because it behaves in a classical way. If a material has a viscosity that is independent of the applied shear stress, then it is referred to as an ideal or Newtonion fluid. Consequently, this newer class of liquids/fluids is referred to as non-Newtonion. In the modern era and the advent of polymers and other modern liquids, we now have fluids where this is no longer true. For the simple and perhaps more natural fluids that existed during Newton’s lifetime (1642-1726), he figured out that the viscosity of most fluids changed only with temperature. These classic fluid properties are named for scientist Sir Isaac Newton. We call these fluids Newtonion because they act in a predictable (classic physics) sort of way. If the moving plate reaction is constant (linear), then the resulting action of the moving pieces represents approximately the same way a Newtonion fluid would react. Note that in this imaginary stack of plates, the second, third and fourth plates in the stack will also move, but with lesser amounts of distance and speed. In the example, you exert a fixed amount of force to the top plate and it consequently moves at a certain speed (velocity) over a specific distance in a measured amount of time. First, imagine you are pushing two or more flat plates or boards stacked on top of one another. TermsĪ set of terms we need to explain to understand viscosity are stress and strain and how they will affect the fluid properties. Note that the opposite or inverse of viscosity is fluidity. Lastly, an alternate method to visualize viscosity is the internal fluid friction resulting when one layer of fluid is forced to move in relation to another layer. Pouring slow means a thicker fluid, which also means a higher viscosity, or you can think of it as possessing a higher resistance to the applied force. Simply put, it pours either fast or slow. To take the viscosity concept another step, it is also that property of a fluid that resists a shearing force. The faster the ball falls, the lower the viscosity of the fluid. One way to visualize viscosity is by watching a metal ball fall through a glass container of the liquid at different speeds for various viscosities. With rare exceptions, the viscosity for every fluid will change indirectly with the temperature if the temperature of the fluid goes up, the viscosity will decrease and vice versa. Viscosity is a fluid’s resistance to flow or pour, but not all fluids resist or react in the same way or even in the same time reference. For a more in-depth, technical article, see my co-contributor’s article from Pumps & Systems, December 2011, by Dr. I was thinking I might take a simpler approach for the purpose of this column.Ī major portion of any discussion regarding the subject concerns viscosity, and I suggest you read my article on the subject ( Pumps & Systems, November 2017). I call non-Newtonian fluids rascals because they do not follow the rules. Every time I review the characteristics of both fluids, I get caught up in the overwhelming array of nomenclature and technical terms. Fluids fall into two classifications-Newtonion or non-Newtonion. Before you select a pump for any service, you need to know and understand the characteristic properties of the fluid you wish to pump.
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