In this article we will learn about various types of fluids such as Ideal, Real , Newtonian And Non-Newtonian Fluid. We will discuss in detail about these types of fluids.
First, let’s know little about what is fluid.
Table of Contents
Fluid Definition:
The fluid is a substance that has no fixed shape, can flow, and is deformed under a small amount of force exerted on it.
Example of fluid – Liquid and Gas
Properties Of Fluids
1. Viscosity:
This refers to the resistance of a fluid to flow, and is dependent on factors such as temperature and pressure. High viscosity fluids are thicker and flow more slowly, while low viscosity fluids are thinner and flow more easily.
2. Density:
This refers to the mass per unit volume of a fluid, and is often measured in terms of specific gravity. Density is affected by factors such as temperature, pressure, and the composition of the fluid.
3. Compressibility:
This refers to the ability of a fluid to be compressed or squeezed, and is influenced by factors such as temperature and pressure.
4. Fluidity:
This refers to the ability of a fluid to flow and change shape in response to external forces, such as pressure or shear stress.
5. Surface tension:
This is a property of liquids that arises from the cohesive forces between the molecules at the surface of the liquid. It is the force that causes liquids to form droplets or a meniscus when in contact with a solid surface.
5. Buoyancy:
This refers to the upward force exerted on an object immersed in a fluid, which is equal to the weight of the displaced fluid.
6. Incompressibility:
This refers to the property of fluids that do not change volume under pressure, as opposed to gases which can be compressed.
7. Flow rate:
This refers to the volume of fluid that passes through a given area per unit time, and is influenced by factors such as the viscosity and density of the fluid, as well as the pressure gradient.
8. Shear stress:
This refers to the force exerted by a fluid parallel to a surface, and is responsible for the deformation or movement of the surface.
8. Turbulence:
This refers to the chaotic and irregular motion of fluids, which can occur at high speeds or when there is a large difference in velocity between adjacent layers of fluid. Turbulence can lead to mixing and dispersion of the fluid, and can have important effects on the dynamics of fluid flow.
Types Of Fluid:
- Ideal Fluid
- Real Fluid
- Newtonian Fluid
- Non-Newtonian Fluid
The description Of these fluids is as follows.
1. Ideal Fluid:
The Fluid which is non-viscous or friction-less and in-compressible is known as an ideal fluid.
Ideal fluid is perfect fluid but fluid without viscosity is not possible or does not exist in the real world, so ideal fluid is only an imaginary fluid.
2. Real Fluid:
All fluid that exists in the world comes under the category of real fluid because all the fluid that exists in the world has viscosity, compression, and surface tension.
Examples of real fluid: water, diesel, air, etc.
Before we start describing Newtonian and non-Newtonian fluid let’s discuss Newton’s law of viscosity
Newton’s Law of Viscosity:
Newton’s law of viscosity states that the time rate of deformation of fluid is directly proportional to the shear stress applied to it.
Shear stress ∝ time rate of deformation
F/A ∝ de/dt
F/A ∝ du/dy {time rate deformation is velocity gradient for fluid}
F/A = µ (du/dy)
where F/A = Shear stress
µ = Dynamic viscosity of fluid
du/dy = velocity gradient
3. Newtonian Fluid:
The fluid which follows Newton’s law of viscosity is known as a Newtonian fluid.
The Newtonian fluid has constant viscosity and it does not rely upon the shear stress applied to it.
Examples of Newtonian fluid: Air, water, Kerosene, etc.
4. Non-Newtonian Fluid
The fluid which does not follow Newton’s law of viscosity and relationship is based on all the three parameters i.e. shear stress, viscosity, and velocity gradient.
Example of non-Newtonian fluid: Blood, Paint, butter, ink, etc. types of fluid
The general equation of non-Newtonian fluid is given below.
τ = A (du/dy)^n + B
Types of Non-Newtonian fluid:
(a) Dilatant Fluid:
The non-Newtonian fluid has a value of B = 0 and the value of n is more than 1 in the general equation, thus the graph is gradually increased.
Example of Dilatant fluid: Butter and Quicksand etc.
(b) Pseudoplastic Fluid:
The non-Newtonian fluid has a value of B = 0 and the value of n is less than 1 in the general equation, thus the graph is gradually decreased.
Example of Pseudoplastic fluid: Blood, rubber, paints, etc.
Bingham Plastic:
The non-Newtonian fluid has a value of B = ty and n = 1 because it has a starting value of B that is greater than 0, thus its viscosity gradient is enhanced from that point.
An example of Bingham plastic is sewage slug, drilling mud
Thixotropic Fluid:
Thixotropic Fluid is a time-dependent fluid in which velocity is based upon shear stress and time duration of application.
The viscosity of the fluid is enhanced or reduced with time.
Example of Thixotropic Fluid: Let’s take an example of paint, it takes more time to brush to uneven smoothness.
Classification Of Fluids
Fluids are categorized into five types based on their flow properties:
- Steady
- Unsteady
- Compressible or incompressible
- Viscous or non-viscous
- Rotational or irrotational
1. Steady Fluid:
A steady fluid is a fluid whose density remains constant at each and every point while flowing.
2. Unsteady Fluid:
An unsteady fluid is a fluid whose velocity differs between any two points while flowing.
3. Compressible Fluid and Incompressible Fluid:
Fluids are classified into compressible and incompressible based on the Mach Number. An incompressible fluid has Mach Number less than 0.3, while a compressible fluid has Mach Number between 0.3 and 1.
4. Viscous or Non-Viscous:
Fluids with high viscosity are known as viscous fluids. They are generally thick and gooey, examples being shampoo and motor oil. Non-viscous fluids, on the other hand, have comparatively low viscosity, and they flow without any significant resistance to internal friction. Superfluid liquid helium is an example of a non-viscous fluid.
5. Rotational or Irrotational:
The flow of a fluid can be classified as rotational or irrotational based on the angle between the two intersecting lines of the boundary of the fluid element. If the angle changes while moving in the flow, the flow is a rotational flow. If the fluid rotates as a whole with no change in angles between the boundary lines, the flow of the fluid is classified as irrotational flow.
(a) Fluid Statics:
Fluid statics is the study of fluids at rest or non-motion and the pressure in fluids exerted by fluids on anybody.
(b) Fluid Dynamics:
Fluid dynamics involves the study of fluids in motion. Popular branches like aerodynamics and hydrodynamics are part of fluid dynamics.
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