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Unformatted text preview: • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Course material can be found on web http://lmes2.ust.hk • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Chap 1 Fluid Properties Fluid Density Viscosity Surface tension effect Vapor pressure Units • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit 1.1 Continuum Model 1.1.1 Some Scales ? Mean distance between molecules (or Mean free path) l In normal temperature, air molecules, l ∼ 10 8 m, 1 nm= 10 9 m ? Size of considered parcels ( Characteristic length) L Pipe flow, airfoil L ∼ 1 m ? Sample box size (a patch of fluid parcels ¤ s • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit 1.1.2 Fluid Parcels Volume of fluid parcel δV = s 3 must δV L 3 1 Fluid parcel is infinitely small compared to macroscopic scale Volume of fluid parcel δV = s 3 must δV l 3 1 Fluid parcel is infinitely large compared to microscopic scale So l 3 δV L 3 Fluid parcel is infinitely large (in microscopic scale) and infinitely small (in macroscopic scale) • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Assume mass distribution in 2Dimensional (mass can be molecule, atom, particle) To measure mass density by using boxes with different sizes • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Count number of masses in each box ( count 1/2 if mass is on the edge, count 1/4 if mass is on the corner) • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Mass density of different sized boxes • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Extend above example to 3D, and include much more masses • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Fluid Parcel Volume of fluid parcel δV = s 3 must δV L 3 1 Fluid parcel is infinitely small compared to macroscopic scale. Fluid parcel can be considered as mass point, which has no volume (fluid particle ). Fluid is continuum macroscopically. • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit Volume of fluid parcel δV = s 3 must δV l 3 1 Fluid parcel is infinitely large compared to microscopic scale, including enough molecules. One individual has no effect in measurement of density. s = 1 μ m ,l = 10 nm , δV l 3 = 10 6 Therefore, l 3 δV L 3 Fluid parcel is infinitely large (in microscopic scale) and infinitely small (in macroscopic scale) • First • Prev • Next • Last • Go Back • Full Screen • Close • Quit 1.1.3 Property of Continuum Model for Fluid ? Fluid is continuously distributed, and can be divided infinitely into macroscopic small element, which has uniformly distributed mass; ? Fluid state inside the small element obey thermodynamic relations if there is no chemical reaction and dissociation; ? Mechanical and thermodynamic states of fluid are continuously dis...
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This note was uploaded on 04/18/2009 for the course CE 309 taught by Professor Lee during the Spring '07 term at USC.
 Spring '07
 Lee

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