Met 212 _2


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Met 212 _2

  1. 1. MET 212 Fluid Mechanics Lecture # 21/15/2013
  2. 2. Objective Measures of Fluid Mass and Weight Density Specific Wight Specific Gravity Ideal Gas Law Viscosity Dynamic Viscosity Kinematic Viscosity Surface Tension1/15/2013
  3. 3. Measures of Fluid Mass and Weight Density  The density of the fluid designated by Greek symbol (ρ)  Defined as a mass per unit volume  Used to characterize the mass of fluid  BG= slugs/ ft3 and SI= kg/m3 Specific Weight  The specific weight of the fluid designated by Greek symbol (γ)  Defined as weight per unit volume  Used to characterize the weight of the system  BG= lb/ ft3 and SI= N/m3 Specific Gravity  The specific gravity of the fluid designated by SG  Defined as a ratio of the density of the fluid to the density of the water  The density of the water @ 4oC is BG=1.94 slugs/ft3 and SI=1000 kg/m3 1/15/2013
  4. 4. Measures of Fluid Mass and WeightSpecific Gravity (Example) Calculate the density of the mercury in two system BG and SI by knowing the SGmercury @ 20oC is 13.551/15/2013
  5. 5. Ideal Gas Law Gas are highly compressible in comparison to liquid, So from the Ideal gas law change in the temperature or the pressure of the gases can directly change the density. p   RT Where p is the absolute pressure, ρ is the density, T is the absolute temperature and R is gas constant  R=R/m  R is universal gas constant 8314.3J/kg mole K  m is the molar mass1/15/2013
  6. 6. Ideal Gas LawExample The absolute pressure and temperature of a gas in large chamber are found to be 500 kPa and 60oC respectively. Find the density if the air has m =28.971/15/2013s
  7. 7. Viscosity Dynamic viscosity BG and SI du   Slug/ft s Kg/ms dy See Figure 1.1 Kinematic Viscosity  SI v  m2/s1/15/2013
  8. 8. Viscosity Example Determine the value of the Reynolds number using SI system for fluid with viscosity of 0.38 N.s/m2 and specific gravity of 0.91 flow into pipe with diameter of 25 mm with velocity of 2.6 m/s.1/15/2013
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  11. 11. Surface Tension At interface between a liquid and the gas forces develop in the liquid surface which case the surface to behave as “skin” or “membrane”1/15/2013
  12. 12. Surface Tension(σ) The pressure inside the drop can be calculated using free body diagram . The force developed around the edge due to the surface tension is 2πRσ this force must be balance by the pressure difference 2R  pR 21/15/2013
  13. 13. Surface Tension(σ) 2R ϴ R h  2R cos 2 R 2 h h1/15/2013
  14. 14. Surface Tension(σ)Example What diameter of clean glass tubing is required to rise water at 20oC in tube to 1mm. Where σ of water is 0.0728 N/m and the θ =0.1/15/2013