Fluid Mechanics L#2

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Fluid Mechanics L#2

  1. 1. MET 306 Fluid Mechanics Lecture # 211/5/2012
  2. 2. Objective Determine the pressure at various locations in a fluid at rest. Explain the concept of manometers and apply appropriate equations to determine pressures. Calculate the hydrostatic pressure force on a plane or curved submerged surface. Calculate the buoyant force and discuss the stability of floating or submerged objects.11/5/2012
  3. 3. Pressure at PointFluid PressurePressure is used to indicate the normal force per unit area (P=F/A) at agiven point acting on a given plane within the fluid mass of interest. Py Ps Pz Ps Py Ps Pz That conclude the pressure at a point in a fluid at rest is independent of direction as long as there are no shearing stresses present. This important result is known as Pascal’s law 11/5/2012
  4. 4. Basic Equation For Pressure Filed dp dzThis equation indicate that the pressure gradient in vertical direction is negativethat is the pressure decrease as we move upward in the fluid at reset Incompressible Fluid  ( ρ ) constant  ( g )in most of fluid application is neglected Compressible flow P1 h p2 ( ρ ) is not constant  p R T g ( z2 z1 ) P2 p1 exp RT 0 11/5/2012
  5. 5. Basic Equation For Pressure Filed Open ExampleA tank has a gasoline and water as shown in theFigure. If the SG of gasoline is 0.68 determine thepressure at the gasoline water interface and at the 17 ftbottom of the tank Gasoline Water 3 ft 11/5/2012
  6. 6. Pressure Variation in Fluid at Rest p=po h A B γ = specific weightThe pressure is the same at tall points along the line AB even with irregular shape11/5/2012
  7. 7. Pressure MeasurementRepresentation of gage and absolute pressure11/5/2012
  8. 8. Pressure MeasurementManometer Manometer has three types: Piezometer Tube U-Tube Manometer Inclined-Tube Manometer11/5/2012
  9. 9. Piezometer Tube PA h 1 111/5/2012
  10. 10. U-Tube Manometer pA 2 h2 1 h111/5/2012
  11. 11. U-Tube ManometerExample 11/5/2012
  12. 12. Inclined-Tube ManometerExample 11/5/2012

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