Fluid mechanics

• Fluid is a substance which can flow and deformed under a small amount of force exerted on it is called fluid. Example of fluid - Liquid and Gas
• Fluids • A fluid is anything that flows: liquids and gases • One common characteristic is that fluids have no fixed shape and are easily deformed: take the shape of their containers.
• Density • The density of a substance is the quantity of matter contained in a unit volume of the substance.

  
• Temperature • It is the property that determines the degree of hotness or coldness or the level of heat intensity of a fluid. Temperature is measured by using temperature scales.

   There are 3 commonly used temperature scales. 1. Celsius (or centigrade) scale 2. Fahrenheit scale 3. Kelvin scale (or absolute temperature scale)
• Increasing the shear rate, or the measure of how fast a  liquid is being deformed, tends to decrease viscosity.
• Temperature


  The viscosity of liquids generally decreases as temperature increases
• Pressure

  High pressure can increase viscosity, while low pressure can decrease it
• Shear rate

  Increasing the shear rate tends to decrease viscosity
• Shear stress


  Caused by the top layer on the adjacent lower layer and vice versa
• Viscosity

  Defined as the shear stress required to produce unit rate of shear strain
• Types of Fluid

  • Ideal fluid
  • Real fluid
  • Ideal plastic fluid
  • Newtonian fluid
  • Non-Newtonian fluid
• Kinematic Viscosity

  Ratio between dynamic viscosity and density of fluid
• Newton’s Law Of Viscosity states that the shear stress on a fluid element layer is directly proportional to the rate of shear strain
• Time Independent Fluid

  • Bingham fluid
  • Pseudo plastic
  • Dilatant
• Time Dependent Fluid

  • Thixotropic fluid
  • Rheopectic fluid
• Definition of viscosity

  Property of a given liquid that describes its resistance to flow
• Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with a gas, acts as a thin elastic sheet
• Surface tension

  A cohesive force at the surface of a liquid that arises due to the attraction between molecules
• If the surface is between two liquids (such as water and oil), it is called "interface tension"
• Capillarity (Capillary action)

  The phenomenon of rise or fall of a liquid in a capillary tube due to surface tension
• Capillarity

  Phenomenon of rise or fall of a liquid in a capillary tube due to surface tension
• Amontons’s law or Gay-Lussac’s law: 'The pressure of a given amount of gas is directly proportional to its temperature on the Kelvin scale when the volume is held constant'
• Ideal fluid: A fluid which is

  compressible and is having no

  viscosity is known as ideal

  fluid. It is only an imaginary

  fluid as all fluids have some

  viscosity
• Real fluid: A fluid possessing a viscosity is known as real fluid. All fluids in actual practice are real fluids.
• Ideal plastic fluid: A fluid, in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain is known as ideal plastic fluid.
• Newtonian fluid: A real fluid, in which the stress is directly proportional to the rate of shear strain, is known as

  Newtonian fluid.
• Non-Newtonian fluid: A real fluid in which shear stress is not proportional to the rate of shear strain is known as NonNewtonian fluid.
• Bingham fluid: do not flow at all until threshold shear stress (τ) is attained, and then flow linearly. Ex: Tooth paste, jellies etc
• Pseudo plastic: viscosity of fluid decrease with increase in velocity gradient. Ex: Rubberlatex etc.
• Dilatant: viscosity of fluid increases with  increase in velocity gradient. Ex: Starch in  water, pulp in water.
• Thixotropic fluid: Viscosity decreases with time. Ex: Gelatin, paint, yogurt, cream, etc.
• Rheopectic fluid: Viscosity increases with time. Ex: highly concentrated starch solutions.