Fluid:
A fluid is a substance which is capable to flow and take the shape of its container. It includes liquids and gases. Fluids have the ability to deform continuously under an applied shear stress. Examples of fluid are water, oil, air, gases and vapours etc.
Fluids may be classified into two categories:
- Liquids: These are fluids that have a definite volume but no fixed shape. Liquids can flow and take the shape of their container. Examples include water, oil, and milk.
- Gases: Gases are fluids that have neither a definite volume nor a fixed shape. They expand to fill the available space. Examples include air, oxygen, and carbon dioxide.
Types of Fluid:
The fluids may be classified into the following types:
- Ideal Fluid
- Real Fluid
- Newtonian Fluid
- No Newtonian Fluid
- Ideal plastic Fluid
- Thyxotropic substance
1. Ideal Fluid: Ideal fluid is a fluid which is incompressible, has no viscosity and no searing resistance is known as ideal fluid or perfect fluid. In nature there is no fluid having such properties. Ideal fluid is only an imaginary fluid, as all the fluids which exist, have some viscosity. However, fluids which have low viscosity such as water and air can be treated as idle fluid under certain conditions.
2. Real Fluid: A real fluid is any fluid that exists in the real world, including both liquids and gases. Real fluids have properties such as viscosity, compressibility, and thermal expansion.
3. Newtonian Fluid: A Newtonian fluid is a type of real fluid, in which the shear stress is directly proportional to the rate of shear strain. In simpler terms, its viscosity remains constant regardless of the applied force or deformation rate. Water and most common liquids are examples of Newtonian fluids.
4. Non-Newtonian Fluid: A non-Newtonian fluid is a type of real fluid that does not follow the linear relationship between shear stress and shear rate observed in Newtonian fluids. These fluids can have variable viscosity depending on factors like shear rate, temperature, or pressure. Examples include shear-thinning fluids (like ketchup), shear-thickening fluids (like cornstarch and water mixtures), and viscoelastic fluids (like certain types of polymers).
5. Ideal plastic Fluid: An ideal plastic fluid is a hypothetical substance that acts like a solid until enough force is applied to make it flow like a liquid. It’s as if it can switch between being solid and liquid depending on the amount of pressure or stress it experiences.
6. Thyxotropic substance: A thyxotropic substance is a material that becomes less viscous (thins out) over time when subjected to continuous stress or agitation. This means that as you apply force to the substance, it becomes easier to flow. However, once the stress or agitation is removed, the substance returns to its original, more viscous state.
Thyxotropic substances are commonly encountered in various applications such as paints, gels, drilling fluids, and certain types of food products.
Properties of Fluid:
- Density
- Weight Density
- Specific Volume
- Specific Gravity
- Viscosity
- Compressibility
- Surface Tension
- Kinematic Viscosity
1. Density: Density or mass density of a fluid is defined as the ratio of the mass of fluid to its volume. Thus, mass per unit volume of a fluid is called density. It determines how heavy or light a fluid is.
- Density = Mass of Fluid/Volume of Fluid
- Units = kg/m^3 in SI.
2. Weight Density: Weight density or specific weight of a fluid is defined as the ratio of weight of fluid to the volume of fluid as standard temperature and pressure.
- Weight Density = Weight of Fluid/Volume of Fluid.
- Units = N/m^3 in SI.
3. Specific Volume: Specific volume of fluid is defined as the ratio of a volume of fluid to the mass of fluid. Specific volume is reciprocal of density.
- Specific volume = Volume of Fluid/ Mass of Fluid.
- Units = m^3/Kg in SI.
4. Specific Gravity: Specific gravity is defined as the ratio of a specific weight of the liquid to the specific weight of the standard fluid. For liquid, water is taken as the standard fluid and for gases air is taken as the standard fluid. Specific gravity is also called relative density and it is dimensionless and has no units.
5. Viscosity: Viscosity is the define as the property of flute which resistance of a fluid to flow. It measures how easily a fluid can deform or move. Fluids with high viscosity, like honey or molasses, flow slowly, while fluids with low viscosity, like water or air, flow more easily.
- Units = Newton-Second/meter square = Ns/m^2 in SI.
- poise (in CGS)
6. Compressibility: Compressibility refers to the ability of a fluid to be compressed or reduced in volume under pressure. Gases are highly compressible compared to liquids, which are relatively incompressible.
7. Surface Tension: Surface tension is the property of a liquid that causes its surface to behave like a thin, elastic membrane. It is caused by the cohesive forces between the molecules of the liquid, which pull the molecules on the surface inward, creating a tension that minimizes the surface area of the liquid. This results in the formation of droplets and allows small objects to float on the surface of the liquid without sinking.
8. Kinematic Viscosity: Kinematic viscosity is defined as the ratio between dynamic viscosity and density of fluid.
- Kinematic Viscosity = Viscosity/Density
- Units = (Length X length)/Time = m^2/s in SI.
“MechView: Unveiling Mechanical Engineering, Simply Explained!”