Fluid Mechanics II Chapter 1: Introduction, Basic Principle and Properties of fluid Mr. MD Mukhawana IMF2111 Fluid Mechanics for Mechanical Engineering Second Semester 2015 MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY All matter can be divided into 2 major classes 1) Solid 2) Fluids (Liquids and Gas) The difference between a solid and fluid can be defined by 1) The stress-strain relationship 2) The elasticity MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Solid requires external forces to cause it to deform. Fluid will deform without the application of external forces. will take on the shape of the container in which they are held. -Ex. water, oil, gas etc. MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY FLUIDS Fluids can be classified into 2 forms of matter 1) Liquids 2) Gases viscosity Fluid compressibility Relative density Mass density Physical Properties Specific weight MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Specific volume Compressibility :to compress something into a small space. Liquids Liquids are considered to be incompressible. Liquids only change in volume when subjected to very high pressure. Gases Gases are very compressible. Their volume can increase/decrease when subjected to slight variation in pressure. MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Units (SI) MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Ideal Gases Where P= pressure V= volume R= gas constant T= Temperature in kelvin (273.15 + 0C) ρ= density MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Continuity : is the state of being continuous. Liquids When a liquid is held in a container, its entire mass will arrange itself so as to be in contact with the bottom and the sides of that container, and a well-defined surface of the liquid will form. Gases A gas held in a closed container will not form a well-defined surface and will tend to fill the entire container. MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Density () Density is the mass of the fluid per unit volume =M V M V = Density of fluid, kg/m3 = Mass of fluid, kg = Unit volume, m3 MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Specific Weight/Unit Weight () The specific weight is the weight of the fluid per unit volume weight ,W volume,V mg V g MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Specific volume, v The specific volume is the volume of the fluid per unit mass 1 volume, V mass, m MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Specific Gravity (SG) A ratio of the density of a liquid to the density of water at standard temperature and pressure (STP) (20C, 1 atm) MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Viscosity MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Dynamic Viscosity () Viscosity is the measure of a fluid’s resistance to internal shear stresses. 𝛕𝐿 µ= 𝑉 = Dynamic viscosity, N.s/m2 or Pa.s = Internal shear stress, N ( =F/A) v = Velocity, m/s L = fluids layer thinkness R = Radius ω = Angular ń = Revolution MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY velocity per minutes MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Kinematic Viscosity () The kinematic viscosity of a fluid is the ratio of its dynamic viscosity to its density. = = kinematic viscosity, m2/s = Dynamic viscosity, N.s/m2 or Pa.s = Density of fluid, kg/m3 MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY Surface Tension () The capacity of liquids to resist tensile stresses at their surface is called surface tensile. MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY MD MUKHAWANA : UNIVERSITY OF JOHANNESBURG, DEPARTMENT OF MECHANICAL AND INDUSRIAL TECHNOLOGY
