1 June 2023

Within the liquid state of matter, we find different classes that we must take into account. Are They are distinguished by having specific properties. that make them different from each other. Therefore, it is very important to familiarize ourselves with the characteristics of each one. So stay with us and continue reading to learn what these fluids are!

Meaning and concept of a Newtonian fluid

Also called typical fluid, is one whose viscosity depends on changes in pressure or temperature. This means that its measurement represents its capacity in relation to the resistance of other flows and adapts to the shape of the container in which it is located.

When the temperature and pressure are constant, they determine the viscosity of the fluid. This relationship is due to shear stress experienced by the fluid in response to resistance. Compared to other fluids, where shear rate is applied to induce flow, the viscosity remains constant at different shear rates.

In the case of drilling fluids, they are not Newtonian, which means that their viscosity is not constant. These fluids represent a more complex class of fluids in terms of description. There is a curve that shows the relationship between effort and speed, since a linear deformation occurs. A clear example of a Newtonian fluid is water, as opposed to glue.

There are also other common fluids that behave Newtonian under specific conditions of pressure and temperature, such as gasoline, alcohol, benzene, or kerosene. Mathematically, for this type of fluid, the formula is used \tau_{xy}= \mu\frac{dv_{x}}{dy} to represent its behavior.

What are the properties of Newtonian fluids?

Between the most characteristic properties of fluids, We can highlight some physical properties. These are:

  • Change of form: Fluids do not have a force that restores them to their original shape when deformed, unlike solids. This means that they can easily change form without experiencing significant resistance.
  • Molecular dispersion: Fluids can change their state of molecular dispersion, thanks to their fluidity. This means that they can go from one state to another, such as solid to liquid or liquid to gas, when an external variable such as temperature is applied.
  • Density: It can be greater or less depending on the amount of matter contained in a given volume. It is usually represented in kilograms per cubic meter (kg/m3).
  • Goo: It is a very important property of fluids, since it determines their resistance to flow. A fluid with a high viscosity is more resistant to flow and tends to deform less, while a fluid with a low viscosity flows more easily.
  • Volume: It refers to the space it occupies. The shape and size of the container it is in will determine its volume. When it comes to liquids, they will take the shape of the container that contains them.
  • Pressure: It is the force exerted by the mass of the fluid on the bodies submerged in it. On the seabed, the pressure is higher compared to the atmospheric pressure on the earth’s surface.

These properties help us understand and describe the behavior of fluids in different situations and applications.

What are the types of Newtonian fluids?

Newtonian fluids fall into two main categories: ideal Newtonian fluids and non-ideal Newtonian fluids.

  • Ideal Newtonian fluids: These fluids have a constant viscosity independent of cutting speed or applied shear stress. In other words, the relationship between shear stress and cutting speed is linear and stable. Some examples of ideal Newtonian fluids include:

    1. Water: At normal temperatures and pressures, water behaves like an ideal Newtonian fluid.
    2. Gasoline: Gasoline also exhibits ideal Newtonian behavior under normal conditions.
  • Non-ideal Newtonian fluids: These fluids have a viscosity that can vary depending on the cutting speed or the applied shear stress. The relationship between shear stress and cutting speed may not be linear and may show more complex behaviors. Some examples of non-ideal Newtonian fluids are:

    1. Ketchup: Ketchup is a common example of a non-Newtonian fluid. Its viscosity varies depending on the cutting speed and can change when force is applied.
    2. Paint: Some paints can have non-Newtonian behaviors, showing different viscosities depending on the speed of application or the pressure exerted.

These are just representative examples, and there are many other fluids which can be classified as ideal or non-ideal Newtonians, depending on their viscous behavior.

Examples of Newtonian fluids

In the most common examples that we can find include:

  • Blood plasma: It is one of the best known fluids, its viscosity increases in response to applied shear stress, but does not vary with changes in velocity.
  • Mercury: It is the only metal that is liquid at room temperature. Some motor oils and transmission oils used in automobiles are also examples of Newtonian fluids.
  • Food and drinks: Water, milk, certain beverages and sugar solutions, corn syrups, and honey behave like Newtonian fluids.
  • Gasoline, glycerin, benzene: These liquids also exhibit Newtonian behavior, since their viscosity remains constant.
  • Hydrogen, air and oil-based liquids: These fluids can also be classified as Newtonian due to their constant viscous characteristics.

As we can see, many of the Newtonian fluids are present in our life daily. These examples demonstrate that Newtonian fluids are found in various elements and substances, and their characteristic properties allow us to classify them as such.

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