Non-Newtonian Fluid

By Mohit Uniyal|Updated : August 26th, 2022

Non-Newtonian fluid is that fluid in which the rate of strain is not proportional to the stress, as well as its higher powers and derivatives. Before we get into the details of non-Newtonian fluid, it's important to understand what fluid is. A fluid is a substance that flows under the influence of shear forces. Liquids, gases, and plasmas are all examples of fluids. Plastic solids are considered fluids to some extent. Fluids can be classified as one of the following based on the relationship between shear stress and the rate of strain and its derivatives:

  • Newtonian fluid
  • Non-Newtonian fluid

Most Non-Newtonian fluids' viscosity (the progressive deformation caused by shear or tensile stresses) is determined by shear rate or shear rate history. However, some non-Newtonian fluids with shear-independent viscosity show normal stress differences or other non-Newtonian characteristics. The viscosity of the fluid might potentially change over time. As a result, a constant viscosity coefficient cannot be determined. Let's take a closer look at Non-Newtonian fluid.

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Non-Newtonian Fluid

Non-Newtonian fluid’s viscosity is usually dependent on shear rate or shear rate history, or their viscosity is independent of shear rate but nevertheless exhibits normal stress differences or other Non-Newtonian behavior. The relationship between shear stress and shear rate in a non-Newtonian fluid is different from the Newtonian fluid.

Many salt solutions and molten polymers, as well as many everyday items including custard, toothpaste, starch suspensions, corn starch, paint, blood, melted butter, and shampoo, are Non-Newtonian fluids.

Non-Newtonian Fluid Definition

Non-Newtonian fluid is one that does not obey Newton's viscosity law, which states that viscosity should remain constant regardless of stress. Unlike Newtonian fluid, when forced, the viscosity and fluid flow of non-Newtonian fluids can change from liquid to solid. Ketchup, for example, is a non-Newtonian fluid because it becomes runnier when shaken.

Types of Non-Newtonian Fluid

A non-Newtonian fluid has flow (viscosity) qualities that are different from Newtonian fluids. Non-Newtonian fluids are classified into four categories, as shown in the table below.

Types of Non-Newtonian Fluid

Behavior

Examples of Non-Newtonian Fluid

Dilatant (Shear Thickening)

Viscosity increases with increased stress.

Suspensions of cornstarch in water.

Pseudoplastic (Shear Thinning)

Viscosity decreases with increased stress.

ketchup, whipped cream, and nail polish.

Thixotropic

Viscosity reduces with time as a result of stress.

Peanut butter, yogurt, and hydrogenated castor oil.

Rheopectic

Viscosity rises over time as a result of stress.

gypsum paste, synovial fluid, and printer ink.

Shear Thickening Fluid (Dilatant)

When the shear rate is increased, the viscosity of a shear thickening fluid, or dilatant fluid, appears to increase. Corn starch suspended in water is a good example: it looks milky when agitated slowly, but it feels like an extremely viscous liquid when stirred violently.

Shear Thinning Fluid (Pseudoplastic)

Wall paint is an example of a shear-thinning fluid or pseudoplastic fluid: When applying paint to a surface, it should flow easily off the brush but not drip excessively. All thixotropic fluids are extremely shear thinning, however, they are time-dependent, whereas colloidal "shear thinning" fluids react instantly to changes in shear rate.

Thixotropic

When exposed to a steep change in shear rate, a thixotropic fluid needs a finite amount of time to reach equilibrium viscosity. Pseudoplastic fluids are thixotropic fluids that revert to a gel form nearly rapidly, such as ketchup.

Rheopectic

The strain rate of some fluids is a function of time. Rheopectic fluids are those that require a gradually increasing shear stress to maintain a constant strain rate.

Non-Newtonian Fluid Example

Understanding the behavior of non-Newtonian fluids is crucial for a number of reasons: such as disaster prevention and safety. Non-Newtonian flows can be found in many common substances.The example of non newtonian fluid is given below:

  • Cosmetics, toothpaste, and soap solutions
  • Butter, cheese, jam, mayonnaise, soup, taffy, and yogurt are some examples of foods.
  • Magma, lava, gums, honey, and extracts like vanilla extract are all examples of natural substances.
  • Blood, saliva, sperm, mucus, and synovial fluid are examples of biological fluids.
  • Slurries, such as cement slurry and paper pulp, emulsions, such as mayonnaise, and various dispersions are all examples of slurries.
Important Topics for Gate Exam
Induction MotorInductors in Parallel
Kinematic PairKirchhoff's Law
Laplace TransformMaximum Shear Stress Theory
Modulus of ElasticityNeutral Axis
Newtonian FluidsNewtonian Mechanics

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FAQs on Non-Newtonian Fluid

  • A Non-Newtonian fluid does not follow Newton's law of viscosity. They do not contain constant viscosity. The viscosity of the non-Newtonian fluid is variable. For example: Butter, cheese, jam, mayonnaise, etc are Non-Newtonian fluids.

  • Non-Newtonian fluids have a wide range of applications. Non-Newtonian fluid friction reduction, oil-pipeline friction reduction, surfactant applications in large-scale heating and cooling systems, scale-up, and flow tracers are just a small handful of them.

  • The types of non-newtonian fluids are as follows:

    • Dilatant Fluid
    • Pseudoplastic Fluid
    • Thixotropic Fluid
  • There are numerous non-Newtonian fluid examples.

    • starch, sugar in water 
    • blood, milk, colloidal solution
    • toothpaste, gel
    • paint, lipstick
    • Bentinitic solution.
  • A Newtonian fluid is one whose viscosity is unaffected by shear rate: when all other factors are equal, flow speeds and shear rates have no effect on viscosity. Newtonian fluids include air and water. As a result, water isn't a non-Newtonian fluid.

  • Newtonian fluids follow Newton's viscosity law. The shear rate has no effect on the viscosity. Although non-Newtonian fluids do not obey Newton's law, their viscosity (the ratio of shear stress to shear rate) is variable and depends on the shear rate.

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