Introduction to Hydraulics Hydraulics • The word hydraulics has been derived from the Greek word Hudour, which means "water." • Hydraulics may be defined as the science that deals with the mechanical behavior of water at rest or in motion. The science of fluids at rest is called hydrostatics, and the science of moving fluids is called hydrodynamics; they both are embedded in hydraulics. Hydraulics • Hydraulics is an applied science of fluid mechanics and studies, for the most part, the flow of incompressible fluids, which do not exhibit any changes in density as the pressure exerted on them is varied. Deals with the application of fluid mechanics to engineering devices involving liquids, usually water or oil Hydraulics Hydraulics Hydraulics Units Metric System - The metric system is an internationally agreed decimal system of measurement created in France in 1799. The International System of Units (SI)abbreviated SI after the French “Système International d’Unités,”, the official system of measurement in almost every country in the world, is based upon the metric system. Units US Customary Units - The US English System of measurement grew out of the manner in which people secured measurements using body parts and familiar objects. Units Fluid Mechanics A physical science dealing with the action of fluids at rest or in motion and with applications and devices in engineering using fluids. Divided into two portions: 1. Fluid Statics- Deals with fluid at rest 2. Fluid Dynamics – deals with fluid in motion What is a Fluid? A substance that deforms continuously when acted upon by a shearing stress of any magnitude What is a Fluid? A substance that deforms continuously when acted upon by a shearing stress of any magnitude Types of Fluids Ideal Fluids -Assumed to have viscosity -Incompressible - Have uniform velocity when flowing - No friction between moving layers of fluid -No eddy currents or turbulence Types of Fluids Real Fluids -Exhibit infinite viscosity - Non uniform velocity distribution when flowing - Compressible - Experience friction and turbulence in flow Properties of Fluids Mass density or Specific Mass, -ratio of its mass per unit volume For water: Ideal gas density, -found from the specific gas constant and ideal gas law For air: Ideal gas density, For air: Specific Volume, -Volume occupied by a unit mass of a fluid Unit Weight or Specific Weight, - ratio of its weight per unit volume For water: Specific Gravity, s - dimensionless ratio of a fluid’s density to some standard reference density. For liquids and solids, the reference density is water at For gases, ; air density= Viscosity, - Determines the amount of resistance to shearing forces Viscosity, - Determines the amount of resistance to shearing forces Note: 1 poise = 0.1 Pa-s Kinematic Viscosity, - ratio of dynamic viscosity of the fluid to its mass density Note: 1 stoke = 0.0001 Example : If the viscosity of water at 80 degrees Celsius is 0.00302 poise and its specific gravity is 0.95. a. Determine its absolute viscosity in Pa – s b. c. Determine its kinematic viscosity in Determine its kinematic viscosity in stokes. Answer: a) b) Surface tension, Pressure inside a Droplet of Liquid P 4 d Surface Tension of water at room temperature: 𝜎 = 0.073 𝑁/𝑚 Capillary rise/fall, F=W Example: Find the capillary rise in the tube of a mercury-air-glass interface with if the surface tension on the walls of the tube (diameter= 2mm) is 0.514 N/m. (Hg)=13,570 kg/ . Answer: - Bulk Modulus of Elasticity, - ratio of change in unit pressure to the corresponding volume change per unit of volume i Bulk Modulus of Elasticity, - ratio of change in unit pressure to the corresponding volume change per unit of volume i Example : Water having a volume of 1000 pressure of 2 x Use Answer: a) is subjected to a . Find the volume after the pressure is applied. Pa. Compressibility, - fractional change in the volume of a liquid per unit change in pressure in a constant temperature process Celerity, - the velocity of pressure waves Absolute Pressure, - the datum reference of zero pressure Gage Pressure, - referred from the local atmospheric pressure (can be positive or negative -vacuum) Standard Pressure Values: Sea level Absolute Pressure, - the datum reference of zero pressure Gage Pressure, - referred from the local atmospheric pressure (can be positive or negative -vacuum) Standard Pressure Values: Sea level Example: What are the values of absolute pressures of Point A and B? Point A reads a 180 kPa while Point B reads a 60 kPa vacuum. Answer: Example 1: A reservoir of glycerin has a mass of 1200 kg and a volume of 0.952 . Find its (a) Weight , (b) Unit Weight, (c) Mass Density, (d) Specific gravity. Answer: a) b) c) d) s.g.= 1.261 Example 2: If 200 of oil weighs 10520 lb, calculate its specific weight, density, and specific gravity. Hint: 1 slug = 32.2 lb 1 lb = 1 slug-ft/ Answer: c) s.g.= Example 3: One kilogram of hydrogen is confined in a volume of 200 L at -45 . What is the absolute pressure if R is 4115 Answer: ° Example 4: A gas at 40 under a pressure of 21.868 bar (abs) has a density of 36.9 kg/ What is the value of gas constant, R for this gas? Hint: 1 bar = 100 000 Pa Answer: Example 5: An oil (density= 888 kg/ ) of 7 mm thick has a viscosity of 0.44 Pa-s at 20 What shear stress (Pa) is required to move the plate at 3.5 m/s? Answer: