# Properties of fluids

8. Apr 2021
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### Properties of fluids

• 1. Subject: Fluid Mechanics and Machinery (FMM) FLUID, FLUID PROPERTIES AND TYPES OF FLUIDS BY Prof. Pranit Mehata ST. JOHN POLYTECHNIC, PALGHAR
• 2. FLUID??????  A fluid is a substance which is capable of flowing.  A fluid is substance which deforms continuously when subjected to external shearing force.  A fluid has following characteristics: 1. It has no definite shape of its own but conforms to the shape of the containing vessels. 2. Even a small amount of shear force exerted on fluid will cause it to undergo deformation which continuous as long as the force continues to applied.  A fluid may be classified as: liquid, gas and vapor
• 3. FLUID MECHANICS???  It is branch of engineering science which deals with the behavior of fluid under the conditions of rest and motion.  Three parts: Static, kinematics and dynamics  Fluid static: study of fluid under static conditions or fluid at rest  Fluid kinematics: study of fluids which are in motion, where pressure forces are nor considered.  Fluid dynamics: study of fluids which are in motion and pressure forces are considered.
• 4. PROPERTIES OF FLUIDS  Density or mass density  Specific weight or weight density  Specific gravity  Specific volume  Viscosity  Surface tension  Capillarity  Adhesion  Cohesion  Compressibility  Vapour pressure
• 5. DENSITY OR MASS DENSITY  It is defined as the ratio of the mass of fluid to its volume.  It is denoted by letter 𝜌 (rho)  Mathematically it is given by ,𝝆 = 𝒎 𝑽  The SI unit of density is 𝑘𝑔/𝑚3  For water the density is 1000 𝑘𝑔/𝑚3
• 6. SPECIFIC WEIGHT OR WEIGHT DENSITY  It is defined as the ratio of the weight of fluid to its volume.  It is weight per unit volume at standard temperature and pressure.  It is denoted by 𝑤.  Mathematically,𝑤 = 𝜌𝑔  The SI unit of specific weight is 𝑁/𝑚3  The value for water is 9.81×1000 𝑁/𝑚3
• 7. SPECIFIC GRAVITY  It is the ratio of the specific weight of the liquid to the specific weight of a standard fluid.  It is also called as relative density  It is dimensionless and has no units.  It is represented by S.  For liquid we take water as standard fluid while for gases we take air.
• 8. SPECIFIC VOLUME  It is defined as volume per unit mass of fluid.  It is denoted by 𝑣𝑠  Mathematically, 𝑣𝑠= 𝑉 𝑚  The SI unit of specific volume is 𝑚3/𝑘𝑔  𝑣𝑠= 𝑉 𝑚 = 1 𝑚 𝑉 = 1 𝜌  Thus it is reciprocal of density.  It is commonly applied to the gases.
• 9. VISCOSITY  It is the property of fluid which offers resistance to the movement of one layer over another adjacent layer of the fluid.  The two layers causes shear stress on each other.  This shear stress is directly proportional to the rate of change of velocity with respect to y.  It is denoted by 𝜏 (called Tau).  Mathematically, 𝜏 ∝ 𝑑𝑢 𝑑𝑦
• 10. VISCOSITY 𝜏 ∝ 𝑑𝑢 𝑑𝑦 𝜏 = 𝜇 𝑑𝑢 𝑑𝑦  Where, 𝜇 is Constant of proportionality and is known as dynamic viscosity 𝝁 = 𝝉 𝒅𝒖 𝒅𝒚  Thus viscosity may also be defined as the shear stress required to produce unit rate of shear strain.  The SI unit of viscosity or dynamic viscosity is 𝑁.𝑠 𝑚2  The CGS unit is Poise 1 Poise= 𝟏 𝟏𝟎 𝑵.𝒔 𝒎𝟐
• 11. KINEMATIC VISCOSITY  It is defined as the ratio of the dynamic viscosity to the density of fluid.  It is denoted by letter 𝜈 (Nu)  Mathematically, 𝜈= 𝜇 𝜌  The SI unit of kinematic viscosity is 𝑚2/𝑠  The CGS unit is stokes (= 𝑐𝑚2/𝑠) 1 Stokes= 𝟏𝟎−𝟒𝒎𝟐/𝒔
• 12. NEWTON’S LAW OF VISCOSITY  This law states that the shear stress (τ) on a fluid element layer is directly proportional to the rate of shear strain. Mathematically, 𝝉 = 𝝁 𝒅𝒖 𝒅𝒚  The fluids which obeys this law are called as Newtonian Fluids  The fluids which do not obey this law are called as Non-Newtonian fluids.
• 13. SURFACE TENSION  It is defined as the tensile force acting on a surface of liquid in a contact with gas or on the surface between two immiscible liquids.  It is due to cohesion between particles at the surface.  It is denoted by letter 𝜎 (Sigma)  The SI unit of surface tension is N/m.  The CGS unit is kgf/m.
• 14. SURFACE TENSION  Rain drops (A falling rain drop becomes spherical due to cohesion and surface tension).  Rise of sap in a tree.  Bird can drink water from ponds.  Capillary rise and capillary siphoning.  Collection of dust particles on water surface.  Break up of liquid jets. For liquid droplet For soap bubble For liquid jet 𝒑= 𝟒𝝈 𝒅 𝒑= 𝟖𝝈 𝒅 𝒑= 𝟐𝝈 𝒅
• 15. CAPILLARITY  It is a phenomenon by which a liquid (depending upon its specific gravity) rises into a thin glass tube above or below its general level.  This phenomenon is due to the combined effect of cohesion and adhesion of liquid particles.  It is expressed in cm or mm of liquid  Its value is depend upon the specific weight of liquid, diameter of the tube and surface tension of fluid. Capillary Action Capillary Rise Capillary Fall
• 16. CAPILLARI RISE  The rise of liquid surface is called as Capillary rise.  The rise of water is given by 𝒉 = 𝟒𝝈 × 𝒄𝒐𝒔𝜽 𝝆 × 𝒈 × 𝒅  The value of 𝜃 for water is zero.
• 17. CAPILLARI FALL  The fall of liquid surface is called as Capillary rise.  The fall of water is given by 𝒉 = 𝟒𝝈 × 𝒄𝒐𝒔𝜽 𝝆 × 𝒈 × 𝒅  The value of 𝜃 for mercury is 128°.
• 18. COMPRESSIBILITY  The property by virtue of which fluids undergo a change in volume under the action of external pressure is called as compressibility.  It decreases with increase in pressure.  It is also defined as reciprocal of bulk modulus (K).  Compressibility= 1 𝐾
• 19. TYPES OF FLUIDS  Newtonian fluids. The fluid which obey Newtons law is called Newtonian Fluids For such fluids μ does not change with rate of deformation. Examples. Water, kerosene, air etc.  Non-Newtonian Fluids: The fluid which do not obey Newton’s law is called Non-Newtonian Fluids. Examples: blood, solutions, mud flows etc.  Ideal Fluids: A fluid which is incompressible and having no viscosity is called as ideal fluid.  Real Fluid: A fluid possess viscosity is called as real fluid.