1 / 37

Hydraulics Chapter - 1- ppt

Introduction to hydraulics and the properties of fluids for civil engineers

Mekash
Download Presentation

Hydraulics Chapter - 1- ppt

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Debre Tabor University Department of Civil Engineering Course: Hydraulics Course code: Ceng-2161 Prerequisites: App. Maths - I and Eng. Mech. (Statics) Target group: G2Civil Eng’g students Instructor: Mek. Sh. Hydraulics

  2. Course contents • CHAPTER ONE: INTRODUCTION TO HYDRAULICS AND PROPERTIES OF FLUID • General description • Properties of fluids • Pressure, compressibility & Elasticity • Surface tension & capillarity • CHAPTER TWO: HYDROSTATICS OF FLUIDS • Hydrostatics pressure and measurement of pressure • Hydrostatic pressure on plane & curved Surfaces • Buoyancy, Stability of Floating & Submerged bodies Hydraulics

  3. Cont… • CHAPTER THREE: KINEMATICS OF FLUID FLOW • Types of flow • Continuity equation • Stream function & Velocity potential • Flow Nets • CHAPTER FOUR: BASICS OF FLUID DYNAMICS • Equation of Motion • Hydraulics grade line & Energy grade line • Impulse – momentum equation • CHAPTER FIVE: DIMENSIONAL ANALYSIS AND SIMILITUDE • Dimensional homogeneity • The Buckingham p theorem • Similitude; Model Studies Hydraulics

  4. CHAPTER ONE INTRODUCTION TO HYDRAULICS AND PROPERTIES OF FLUID Hydraulics

  5. 1. Introduction • What is hydraulics? • Hydraulics is derived from a Greek Word " Hydraulikos" which means ‘water’. • It is the study of waterand other engineering fluids. • Engineering fluid includes water, wastewaterin waste disposal and oils in hydraulic control gear. Hydraulics

  6. Difference b/n Fluid Mechanics and hydraulics Hydraulics

  7. Why do we study hydraulics? • To provide adequate water for society (water supplies) • To dispose excess or waste water (Drainage/sewerage ) • protection of society from uncontrolled water (flood protection) • Applications of hydraulics includes; • Design of a wide range of hydraulic structures (dams, canals, weirs etc.) and machinery (pumps, turbines …) • Coastal engineering and Lakeshore engineering • Design of a pipelinesfor transporting liquids. • Power generation • Irrigation • Flood protection (sea or river defenses) • Surface and ground water studies • Flow metering like orifice meter • Pressure measurement Hydraulics

  8. Hydraulics

  9. 1.2. Properties of fluid • Maters can be three states/phases: liquid, solid, andgases Example: water appears in liquid, solid (Snow and ice), or gaseous (moisture or water vapor). • Liquids and gases called fluids because of their ability to flows, to deform when a force is applied. • Fluids: Fluids are substances, which deform continuously under the application of a shear force, no matter how small the force might be. • They are characterized by their ability to flow. Hydraulics

  10. General properties of fluid Properties: intensive, extensive, physical, and chemical. 1. Extensive properties • The properties of fluids that depend on the size of a sample of matter. Example: mass(M), volume(V) • As amount of substance increases, M, V will increase. Example: 1L and 100L have different masses. 2. Intensive properties • The properties of fluids that is independent of the size of a sample of matter. Example: Density(), Pressure(P) and Temperature(T) Example:density of 1L and 100L water is the same. Hydraulics

  11. 3. Physical properties of fluid • A physical property can be specified without reference to any other fluid. Density, specific volume, Viscosity, Surface tension, the bulk modulus of elasticity or Compressibility, Vapor pressure, color, etc. are all examples of physical properties. • Density(), There are 3 forms of density; mass density, unit/specific weight & specific gravity • Mass density or density, denoted by  (rho) • It is defined as the mass per unit volume SI unit, Kg/ m3, Dimensionally, ML-3, Hydraulics

  12. Cont.… ii. Specific weight / unit weight / unit gravity force /, designated by  (gamma) • It is defined as the weight per unit volume. • SI unit N/m3 (usually KN/ m3) • Dimensionally (ML –2 T-2) • At 40c ‘’ for water is 9.806 / 9.81 KN /m3/ • It changes with location on the earth’s surface depending upon g. Hydraulics

  13. Cont.… iii. Specific gravity (S) or relative density (r.d.) Defined as a ratio of mass of a body to an equal volume of a substance taken as standard (mainly water for liquids). • It is dimensionless • E.g. 2. Specific volume () • It is the volume of fluid occupied by a unit mass of fluid or simply the reciprocal of density. • Commonly applied to gases Hydraulics

  14. Examples 1.Calculate the specific weight, density and specific gravity of one liter of a liquid which weights 7N. 2. The density of a substance is 2.94 g/cm3. What is it’s a) Specific gravity b) Specific volume c) Specific weight Hydraulics

  15. Solutions • Given: V = 1L = 0.001m3 Weight(W) = 7N • Specific weight () = W/V = N/m3 W = mg = kg[m/S2]= N  = 7N/0.001m3 = …………. • Density () =  =g,= /g = ………. • specific gravity (S) = density of fluid/density of water = ( = / g ) / 1000kg/m3= ………… 2.Given: Density of sub.= 2.94g/cm3= 2940kg/m3 • Specific grav.= 2940/1000kg/m3= 2.94kg/m3 • Specific vol. = 1/2.94kg/m3 • Specific weight () = g  = 2940kg/m3 * 9.81m/S2 = ………. Hydraulics

  16. 3. The bulk modulus of elasticity or Compressibility, K (kappa) • The bulk modulus or elasticity is a measure of the resistance to compression of a substance. • For most practical purposes liquids may be regarded as incompressible. However, there are certain cases, such as water hammer, where compressibility should be taken into account. • The bulk modulus for a liquid is defined as the ratio of a change in pressure to the relative change in volume. Hydraulics

  17. Cont.… • The compressibility of a fluid is expressed by defining a modulus of elasticity on the basis of volume. • If the pressure of a volume of fluid is increased by dp, it will cause a volume decrease dv, then the bulk modulus of elasticity is defined as • Bulk modulus (K) = • Volumetric strain = • is original fluid volume • The (-ve) sign indicates a decrease in volume with increase in pressure. Hydraulics

  18. Cont.. • Mass of certain volume is constant, differentiating • = = = • From K= , ……………………… (2) • From equation (1) and (2) • and • A high value of K means that fluids are not easy to be compressed. • Example: and (water 100 times more compressible than steel). Hydraulics

  19. Cont.… 4. Viscosity • Viscosity is the measure of fluid resistance to flow or resistance to shear because of internal friction. • ‘Think of a fluid as a composed of layers like the individual sheet of paper. When one layer moves relative to another there is resistance force. This frictional resistance to a shear force and to flow is called viscosity’. • Viscometer-It is an instrument to measure viscosity. Hydraulics

  20. Cont.… • There are two ways of expressing viscosity; • Dynamic/absolute viscosity, • defined as the shear stress required to produce unit rate of angular deformation. [fluid flow due to external forces] • The SI unit ofis N.s /m2 or Pa.s (kg/ m.s), • Dimensionally = (ML-1 T-1) (FL-2 T) • The smallest unit is called the poise. • One poise = 0.1 Ns/m2 = 0.1 kg m-1 s-1 = 0.1 Pa.s • Heavy oils have greater viscosity than water and water is more viscous than air. • Kinematic viscosity, , termed as ‘nu’ • Is ratio of absolute viscosity to mass density. [Fluid flow due to it own weight] • SI unit of is m2/s. • The smallest unit of is called the stoke. • 1 stoke = 1 cm2/s =1 x 10-4m2/s, For water,  = 1.14 mm2/s at 150c Hydraulics

  21. The viscosity of a fluid is a measure of its resistance to deformation at a given rate. • The bulk modulus of a substance is a measure of how resistant to compression that substance is. • Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible Hydraulics-II

  22. Cont.… Types of fluids • Newtonian fluids • A fluid, which obeys Newton’s law of viscosity, is known as a Newtonian fluid and they will have a certain constant viscosity. (linear r/n ship b/n vs dv/dy) • For this fluid the plotting of shear stress () against velocity gradient () is a straight line passing through the origin. • The slope of this line gives viscosity. • E.g. water, gasoline and light oils. Hydraulics

  23. Cont.. 2. Non-Newtonian fluids • A fluid having non-linear relationship b/n applied shear stress and the rate deformation/velocity gradient. • Their graph is a curve, not straight line. • E.gslurries, suspensions, gels and colloids. Hydraulics

  24. Cont.. 3. Real fluids • A fluid which posses viscosity. • E.g. Newtonian and non Newtonian fluids 4. Ideal fluids • Is a fluid which is incompressible and non-viscous/inviscid. (zero viscosity). • Always have zero shear stress hence plotting coincides with X-axis. 5. Ideal solid • No deformation will occur under any loading conditions hence plotting coincides with Y-axis. Hydraulics

  25. Cont.. Hydraulics

  26. 5. Surface tension () and capillarity • Surface tension is a tensile force, which exists on the surface of a liquid when it is in contact with another fluid, a solid boundary or gases. • Consider the figure above, molecules inside are under attractive forces in all directions and the vector sum of these forces is zero. • But, at the surface molecules are under unbalanced upward and downward attraction(acted on by a net in ward cohesive force that is perpendicular to the surface) which causes the surface to behave as if it were a ‘skin’ or elastic membrane stretched over the fluid mass giving rise to the phenomenon of surface tension. Hydraulics

  27. Cont.. • Surface tension effect enables: • An isolated drop of liquid to take nearly a spherical shape. • A drop of water to be held in suspension at a tap. • A vessel to be filled slightly above the brim. • Dust particles and needle to float on the surface of liquids. • Capillary rise and depression in thin-bored tubes. Hydraulics

  28. Cont.… Capillarity or meniscus effect • When a tube of small diameter called capillary tube is inserted in to a container of liquid, the level will rise or fall within the tube depending up on the relative magnitudes of the cohesion of the liquid and the adhesion of the liquid to the wall of the containing vessel. • Liquids rise in tubes if they wet (adhesion > cohesion) and fall in tubes if they do not wet (cohesion > adhesion) • The phenomenon of rise and fall of liquid in a capillary tube is known as capillarity. Hydraulics

  29. Cont.. • The curved free surface of a liquid in a capillary tube is known as meniscus. • Water in glass curves up slightly at the edge where it touches the glass surface and curves down at the edge for mercury in glass. Hydraulics

  30. Cont.. • The magnitude of the capillary rise (or depression), h, is determined by the balance of surface tension force between the liquid and solid surface and the weight of the liquid column above (or below) the liquid free surface. • Surface tension force, ..... (1) • Weight of liquid column above or below free surface, W=mg == = … (2) Equating equation (1) and (2) = Hydraulics

  31. Cont.. • It is to be noted that for <<, h is positive (concave meniscus and capillary rise) and that for << h is negative (convex meniscus and capillary depression). • For pure water and clean glass  = 0o • for water, = 0.0735 N/m Hydraulics

  32. 6. Vapor pressure • A change from the liquid state to the gaseous state is known as vaporization. • When evaporation takes place in the closed vessel the molecules escape from liquid surface and accumulates b/n free liquid surface and top of the vesselthese accumulated vapor molecules exerts a pressure on liquid surface this pressure is called vapor pressure. • Also vapor pressure of a liquid is the pressure at which the liquid vaporizes or boils as it changes from the liquid to the gaseous or vapor state. • The vapor pressure is strongly dependent on temperature (as T increase vapor pressure increase). Hydraulics

  33. Cont.. • Boiling occurs when vapor pressure equals or greater than atmospheric pressure. • Water boils at atmospheric pressure when the temperature is 1000c and at higher elevations the atmospheric pressure is less; hence, water evaporates at temperatures lower than 1000C. Hydraulics

  34. 4. Chemical properties of water Acid-base reactions • Water undergoes various types of chemical reactions. • One of the most important chemical properties of water is its ability to behave as both an acid(a proton donor) and a base(a proton acceptor), the characteristic property of amphoteric substances. Oxidation-reduction reactions When an active metal such as sodium is placed in contact with liquid water, a violent exothermic (heat-producing) reaction occurs that releases flaming hydrogen gas. Hydraulics

  35. Examples • Determine the bulk modulus of elasticity of a liquid, if the pressure of the liquid is increased from 70N/cm2 to 130N/cm2. The volume of the liquid decreases by 0.15 percent. And determine its compressibility. • What is the bulk modulus of elasticity of a liquid which is compressed in a cylinder from a volume of 0.0125m3 at 80N/cm2 pressur to a volume of 0.0124m3 at 150N/cm2 pressure Hydraulics

  36. Examples1.A plate 0.025 mm distance from a fixed plate, moves at 60cm/s and requires a force of 2N per unit area to maintain this speed. Determine the fluid viscosity and kinematic viscosity between the plates.2.If the velocity distribution over a plate is given by in which u is the velocity in meter per second at a distance Y meter above the plate, determine the shear stress at Y=0 and Y=0.15m. Take dynamic viscosity of fluid as 8.63 poises. Hydraulics

  37. CHAPTER TWO HYDROSTATICS OF FLUIDS Hydraulics-II

More Related