advertisement

Hydraulics & Hydrology Review Lecture3 Dr. Jawad Al-rifai 1 WATER PRESSURE Mass per unit volume is referred to as the density of a fluid. The density of water at temp. 15C & pressure of 1 atmosphere is 999kg/m3 The force exerted by gravity on 1.0 cu ft (1.0 m3) of water is 62.4 lb (9.80 kN); eq density X gravity (32.2ft/s2; 9.81m/s2 ) Pressure is the force exerted per unit area Water pressure is exerted equally in all directions, and increases linearly with depth ◦ Pressure in psi is equal to 0.433 times the depth in feet ◦ Pressure in KPa is equal to 9.8 times the depth in meter 2 3 A piezometer consists of a small tube rising from a container of water under pressure The height of the water in the tube denotes the pressure of the confined water Water pressure is commonly measured by a Bourdon gauge A mercury column can be used to measure relatively high pressure values 4 If the pressure measured is greater than atmospheric, this value is sometimes called gauge pressure If the pressure measured is less than atmospheric, it is referred to as a vacuum Absolute pressure is the term used for a pressure reading that includes atmospheric pressure ◦ The pressure relative to absolute zero 5 6 4–2 PRESSURE-VELOCITY-HEAD RELATIONSHIPS The association between quantity of water flow, average velocity, and cross-sectional area of flow is given by the equation This formula is known as the continuity equation 7 For an incompressible fluid such as water: If cross-sectional area decreases, velocity of flow must increase If the area increases, the velocity decreases 8 Total energy in a hydraulics system is equal to the sum of elevation head + pressure head + velocity head 9 10 11 Valves, fittings, and other appurtenances disturb the flow of water, causing losses of head ◦ In addition to the friction loss in the pipe Distribution system losses due to appurtenances are relatively insignificant compared to pipe friction losses In pumping stations & treatment plants, minor losses in valves & fittings are a major part of the total losses 12 4–2 PRESSURE-VELOCITY-HEAD RELATIONSHIPS Unit head losses may be expressed as being equivalent to the loss through a certain length of pipe or by the formula 13