Thursday 6 June 2019

Fluid Characteristics
June 06, 2019

Fluid Characteristics

 Fluid Characteristics
We discussed that there are different types of fluids, we classify them based on different  characteristics of fluids. In the article, we will discuss the different properties of fluids.
Some of these properties are
  • Density
  • Viscosity
  • Specific Gravity
  • Surface Tension
  • Vapor Pressure
  • Capillarity
  • Cohesion
  • Adhesion
  • Compressibility
Now let take a quick review of all these properties:

1. Density:
The density of the body is defined as the mass per unit volume of liquid. Or it is the ratio between the mass (m)  and volume (V)
Numerically, we can write it as
Its SI units are kg/m3.

2. Viscosity:
Viscosity is an important factor to describe the nature of fluid. It can be defined as the amount of resistance offered by the layers of fluid when shear stress is applied to it.
There are four types of viscosities:
  • Dynamic Viscosity.
  • Kinematic Viscosity.
  • Relative Viscosity.
  • Apparent Viscosity.
Before discussing them, I want to clear you the difference between the following terms:
Dynamic and kinematic, Dynamics is the branch of physics which deals with the study of motion and discussing that how the body moves while on the other hand kinematics is the branch of physics deal with the study of motion without discussing the cause of motion.
>Dynamic Viscosity:
Dynamic or absolute viscosity can be stated as the force required to overcome the internal friction in a fluid. Or the force required to move a fluid with a velocity of 1 m/s.
SI unit of dynamic viscosity is 
>Kinematic Viscosity:
Kinematic Viscosity is the ratio of dynamic viscosity to the density of the fluid. It tells us the effect of the gravitational force on a substance’s flow.
SI unit of kinematic viscosity is  
>Relative Viscosity:
The viscosity of a fluid with respect to another fluid is known as relative viscosity.
It is a dimensionless quantity.
>Apparent Viscosity:
For non-Newtonian fluids the viscosity of fluid changes with the change in shear stress. So, we need to specify a single point from whom reference we are measuring the change in the viscosity. The deviation of viscosity from that point is known as apparent viscosity.
3. Specific Gravity:
Specific gravity is the density of a fluid with respect to a reference fluid.
For liquids the reference fluid is water.
For gases the reference fluid is air.
It is also a Dimensionless quantity.
4. Surface Tension:
Surface tension is also an interesting property of the fluid. A fluid consists of different layers of molecules. The free layer or the layer at the interface or the top layer does not have its neighbor molecules. (In the case of top layer molecules above it are absent). This free surface of a liquid behaves like a stretched elastic membrane under tension. This gives rise to the phenomenon of Surface Tension.
5. Vapor Pressure:
In liquid, there is the distribution of energy among molecules. This energy distribution is not equal some molecules have more energy while some has less. The molecules with more energy will break the inter molecular force and will leave the liquid by forming vapors. In a close container, after some time these vapors attain equilibrium. At that time the pressure exerted by the vapors on the surface of the container is known as vapor pressure.
6. Capillarity:
The tendency of a liquid in a capillary tube to rise or fall due to its surface tension is referred to capillarity.
7. Cohesion:
The force of attraction between two molecules of the same substance is called cohesive force.
8. Adhesion:
The force of attraction between two molecules of the different substance is called adhesive force.
9. Compressibility:
The ability of a material to reduce its size or more specifically its volume by the application of pressure on it is termed as compressibility.
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Sunday 2 June 2019

Different Flow Types
June 02, 2019

Different Flow Types


Different Flow Types of Fluid
The Fluid is a substance which flows under the action of shear force. This flowing of fluid is categorized into different types on the following basis:
      1.       Viscous and Inviscid.
      2.       Internal, External, and Open Channel Flow.
      3.       Compressible and Incompressible.
      4.       Laminar, Turbulent and Transitional.
      5.       Natural and Forced.
      6.       Steady and Unsteady.
      7.       Uniform and Non-Uniform.
      8.       Rotational and Irrotational.  
      9.       One, Two and Three Dimensional.
      10.   Potential Flow.
Viscous and Inviscid Flow:
Viscous Flow
The Type of flow in which the resistance provided by the viscosity is considered
Inviscid Flow
The type of flow in which the resistance provided by the viscosity (to flow) is negligible.
Note: In real life, every fluid has some viscosity.

Internal, External, and Open Channel Flow:
Internal Flow
When the fluid is moving in some pipes or tubes then it is considered as internal flow.
External Flow
When the fluid is moving outside the pipe or on the surface of a body.
Open Channel Flow
In this type of fluid flow with a free surface and has constant pressure on the surface.

Compressible and Incompressible Flow:
Compressible Flow
The Type of flow in which the density of the fluid varies with the flow.
Incompressible Flow
The type of flow in which the density does not change with the flow.

Laminar, Turbulent and Transitional Flow:
Laminar Flow
The type of flow in which the layers of fluid are parallel to each other and do not mix with each other.
Turbulent Flow
The type of flow in which the layers of particles are not parallel to each other and mix randomly.
Transitional Flow
It is an intermediary state in which the particles move in a mixed pattern. (Laminar and turbulent) In the stage the fluid in changing from laminar to turbulent flow.

Natural and Forced Flow:
Natural Flow
The Flow of a fluid due to some natural source or means.
e.g.: gravity, buoyancy, etc.
Forced Flow
The flow of fluid with the help of some external power is known as forced flow.
e.g.: pumps or fan etc.

Steady and Unsteady Flow:
Steady Flow
The flow in which characteristics of fluid (velocity, temperature, pressure, and density, etc.) do not change at a point with time.
Unsteady Flow
The flow in which the characteristics of fluid changes at a point with time is known as unsteady flow.

Uniform and Non-Uniform Flow:
Uniform Flow
The flow in which the fluid characteristics changes with respect of time but does not change with respect to position is known as uniform flow.
Non-Uniform Flow
The flow in which fluid characteristics changes with respect to time as well as with respect to position is known as non-uniform flow.

Rotational and Irrotational Flow:
Rotational Flow
In this flow, the fluid particles while flowing along streamlines also rotate about their own axis.
Irrotational Flow
The flow in which particle while flowing along the streamline do not rotate about their own axis.

1D, 2D, and 3D Flow:
1D Flow
In one dimensional flow, velocity is a function of time and one space co-ordinate only.
2D Flow
In two-dimensional flow, velocity is a function of time and two rectangular space coordinates.
3D Flow
In three-dimensional flow, velocity is a function of time and three mutually perpendicular directions.

Potential Flow:
Potential Flow
The flow of ideal fluid is called potential flow. The ideal fluids have zero viscosity and negligible shear stress. In potential flow, neither circulation nor eddies can form within the stream. Friction cannot be developed in the potential flow so that there is no dissipation of mechanical energy into heat.

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Thursday 30 May 2019

Different Types of Fluids
May 30, 2019

Different Types of Fluids

Fluid:
Fluid is one which cannot remain at rest under the action of shear force or fluid is the one which can flow and deforms under the action of shear stress or external force.
Fluid can be categorized based on following properties:
  • Viscosity
  • Conductivity
  • Density
  • Compressibility
  • Temperature
  • Pressure etc.
Types of Fluid:
Fluid can be classified as:
  • Ideal Fluid
  • Real Fluid
  • Compressible Fluid
  • Non-Compressible Fluid
  • Newtonian Fluid
  • Non-Newtonian Fluid

Ideal Fluid:
An imaginary fluid which is incompressible and having no viscosity.
e.g.: This fluid does not exist.
Real Fluid:
An actual fluid which possesses viscosity is known as real fluid. (All the fluids, in actual practice, are real fluids).
e.g.: Water, Air etc.
Compressible Fluid:
A fluid in which the density of fluid changes with the change in external force or by applying some pressure.
e.g.: All the gases.
Non-Compressible Fluid:
A fluid in which the density of fluid does not change with the change in external force or by applying some pressure.
e.g.: All the liquids.
Newtonian Fluid:
A real fluid in which shear stress is directly proportional to the rate of shear strain or velocity gradient.
e.g.: Water, Benzene etc.
Non-Newtonian Fluid:
A real fluid in which shear stress is not directly proportional to the rate of shear strain or velocity gradient.
e.g.: Plaster, Honey, Ketchup etc.
There are three categories of Non-Newtonian Fluid:
·         Time Dependent Fluid.
·         Time Independent Fluid.
·         Visco-Plastic Fluid.
1. Time Dependent Fluid:
The fluids whose apparent viscosity changes with time as the fluid is continuously sheared are time dependent fluids.
      a) Thixotropic Fluids
·         b) Rheopectic Fluids
Thixotropic Fluids:
The fluids whose apparent viscosity decreases with time when sheared continuously.
These fluids are thick under normal condition but when shaken, agitated, sheared or stressed they will start to flow. It will take some time to become viscous again.
e.g.: The best example of thixotropic fluids is tomato ketchup.
Rheopectic Fluids:
 The fluids whose apparent viscosity increases with time when continuously stress is applied.
e.g.: The examples of such fluids are gypsum paste and printer ink.
2. Time Independent Fluid:
The fluids whose apparent viscosity does not change with time as the fluid is continuously sheared are time dependent fluids.
·         a) Dilatant Fluid.
·         b) Pseudo plastic Fluid.
Dilatant Fluid.
The type of fluid whose viscosity increases when shear stress is applied on it independent of time which mean that in no time the fluid will become viscous when stress is applied and in no time, it will return to its non-viscous condition when stress is removed.
e.g.: The best example of dilatant fluids is Corn Flour-Water Solution.
Pseudo Plastic Fluids:
The type of fluid whose viscosity decreases when stress is applied irrespective to time are known as pseudo plastic fluids.
e.g.: The best example of pseudo plastic fluids is Paint.
3. Visco-Plastic Fluid:
a) Bingham Plastic Fluid.

Bingham Plastic Fluid.
For some fluid, when the stress is moderate or low it acts as solid but on applying stress more than its yield stress the viscosity decreases and the fluid started to flow.
e.g.: The best example of Bingham Plastic Fluid is Toothpaste.

Diagrams



Graphical Representation for the understanding of different types of fluids



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