1. Fluid Mechanics - Introduction + Fluid Properties-1.pdf
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This document provides an introduction to fluid mechanics, defining fluid properties and differentiating between solids, liquids, and gases. It covers important concepts such as density, specific weight, specific gravity, and viscosity, as well as the SI and English systems of units. The lecture aims to facilitate understanding of fluid behavior under various conditions and its engineering significance.
1. Fluid Mechanics - Introduction + Fluid Properties-1.pdf
- 1. Department of Pet. Eng., HU Fluid Mechanics Lecture 1 Introduction to Fluid Mechanics Fluid Properties Dr. Ali Al-Shatri Prof. Dr. Mazen Ahmed Muherei Semester I 2024-2025
- 2. Lecture Objectives • Define fluid and discriminate between liquids, gases and solids. • Define the basic fluid properties. • Identify the density of water in different units • Identify the relationships between specific weight, specific gravity, API and density, and solve problems using their relationships • Ensure consistency of units • Identify the units for the basic quantities of time, length, force and mass (S.I and English systems).
- 3. What do you know about Fluid Mechanics? Is the science that deals with the action of forces on fluids. What is a Fluid? a fluid is a substance that deforms continuously (i.e. flow) when acted on by a shearing stress of any magnitude
- 4. Fluid Definitions • in contrast to a solid, a fluid is a substance the particles of which easily moves and change their relative position. • a fluid is a substance that deforms continuously – that is, flow under the action of a shear stress. (Force/Area). • a solid can resist a shear stress if not exceed the elastic limit of a material. • the rate of deformation of the fluid is related to applied shear stress by viscosity. – Thus very viscous fluids such as honey and cold oil, drilling fluids, cement slurries flow very slowly for a given shear stress but water flow rapidly (because of its low viscosity). • Viscosity is a measure of the resistance of a fluid to flow
- 5. Distinction Between Solids, Liquids and Gases • a fluid can be either a gas or a liquid. • in a liquid, the spacing between molecules is constant. It changes slightly with changes in temp and press. • a given mass of liquid occupies a definite volume of space and assumes the shape of the container. • liquid molecules can move with respect to each other when shearing force is applied.
- 6. Distinction Between Solids, Liquids and Gases - continued • in a solid, the spacing between molecules is constant and the molecules are arranged in a specific lattice formation and their movement is restricted. • in a gas, the spacing between molecules is much wider than either solids or liquids and is also variable. • gas completely fills the container in which it is placed. • the gas molecules travel in straight lines through space until they either bounce off the walls of the container or are deflected by interaction with other gas molecules.
- 7. Fluid Properties • Extensive Properties: properties related to the total mass of the fluid and are usually represented by upper-case letters, for example mass (M) and Weight (W). • Intensive Properties: properties independent of the amount of the fluid and are often designated by lower-case letters, such as pressure (p) and density (ρ).
- 8. • Density (ρ - rho): mass per unit volume • Liquids are incompressible: density varies slightly with Temperature and Pressure. • Gases are compressible: density varies widely with Temperature and Pressure. • ρ = M/V; Density of Air = 1.23 kg/m3 • Density of water = 1000kg/m3; 1g/cm3; 1kg/L; 62.34 lbm/ft3; 8.33 lbm/gal; 350 lbm/bbl; 0.433 psi/ft Fluid Properties-continued
- 9. Fluid Properties-continued • Density of gases: the fundamental equation of state for an ideal gas (Z=1) is: • P.V = n.R.T; but n = M/(M.wt) • P.V =R.T.M/(M.wt) • P.(M.wt) = R.T.(M/V); but M/V = ρ • P.(M.wt) = R.T.ρ ----- ρ = P.(M.wt)/(R.T) P: absolute pressure; T: absolute temperature; V: volume; M: mass of the gas; M.wt: Molecular weight; ρ: density of the gas.
- 10. Fluid Properties-continued • Specific Weight (γ - gamma): the ratio of weight of a given fluid to its volume . The weight of fluid per unit volume. • γ = W / V = Mg/V = ρg • Water specific weight = 9814 (N/m3) • Air specific weight = 12.07 (N/m3)
- 11. Fluid Properties-continued • Specific Gravity (S.G): the ratio of density of a given liquid to the density of water at a standard reference temperature. The standard reference temp is often a 4 ºC. • or: the ratio of specific weight of a given liquid to the specific weight of water at a standard reference temperature. • γ = γliquid / γwater =(ρg)liquid/(ρg)water =(ρ)liquid/(ρ)water • water s.g = 1 (unitless) • API =(141.5/S.G.) -131.5; S.G. = 141.5/(API + 131.5)
- 12. Fluid Properties-continued • Vapor Pressure (V.P): a liquid in a closed container is subjected to a partial vapor pressure in the space above the liquid due to the escaping molecules from the surface; • it reaches a stage of equilibrium when this pressure reaches saturated vapor pressure.. • Since this depends upon molecular activity, which is a function of temperature, the vapor pressure of a fluid also depends on its temperature and increases with it.
- 13. Fluid Properties-continued Engineering Significance of Vapor Pressure (V.P): • in a closed hydraulic system, pipelines or pumps, water vaporizes rapidly in regions where the pressure drops below the vapor pressure. There will be local boiling and a cloud of vapor bubbles will form; • this phenomenon is known as cavitations and can cause serious problems, since the flow of fluid can sweep this cloud of bubbles into an area of higher pressure where the bubbles will collapse suddenly.
- 14. Fluid Properties-continued • Specific Volume (S.V): the ratio of volume of a given liquid to its mass. Specific Volume equal to the reciprocal of density. • Specific Heat (C): is the property that describes the capacity of a substance to store thermal energy (for water 4184 J/Kg/ºK@20ºC). • Cp: specific heat at constant pressure. • Cv specific heat at constant volume.
- 15. Fluid Properties-continued • Specific Internal Energy (u): is the energy that the substance possesses because of the state of the molecular activity in the substance, usually expressed per unit mass. The internal energy is generally a function of temp and press. However, for ideal gases, it is a function of temp alone. • Specific Enthalpy (h): is the enthalpy of a fluid per unit mass. The specific enthalpy is equal to the specific internal energy of the fluid plus the product of pressure and specific volume …. h = u + P/ρ.
- 16. SI system of units • Temperature: the basic unit is Kelvin (ºK) or Celsius (ºC) ; absolute temp ºK= ºC+273.15 • Mass: the basic unit is kilogram (kg). • Length: the basic unit is meter (m). • Time: the basic unit is second (s). • Force: the force required to accelerate a (kg-mass) at one meter (m) per square second (s2) is defined as the Newton (N) or (kg.m/s2) • Weight: the weight of a (kg-mass) at the earth’s surface is W = M.g = kg *9.8 m/s2 = 9.8 N
- 17. SI system of units • Work & Energy: the basic unit is Joule (J) or (N.m) ; • Power: the basic unit is Watt (w). • Prefixes used in SI system: K (kilo) = 103: c (centi) = 10-2 M (mega) = 106: m (milli) = 10-3 G (giga) = 109: µ (micro) = 10-6
- 18. English system of units • Temperature: the basic unit is Rankine (ºR) or Fahrenheit (ºF) ; absolute temp ºR= ºF+460; ºF=1.8ºC+32º • Mass: the basic unit is slug (14.59 kg; 32.2 lbm). • Length: the basic unit is foot (ft) (ft = 30.48cm). • Time: the basic unit is second (s). • Force: the force required to accelerate a one (slug-mass) at one foot (ft) per square second (s2) is defined as the pound force (lbf) or (slug.ft/s2) or (32.2 lbm ft/s2) • Weight: the weight of a (lb-mass) at the earth’s surface is W = M.g = lbm *32.2 ft/s2 = 1 lbf