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CE 230-Engineering Fluid Mechanics

CE 230-Engineering Fluid Mechanics. Lecture # 2&3 Fluid properties (1). Units. Basic Units versus derived units SI versus Traditional units prefixes. What are the units of?. Mass Length Time Temperature Weight Pressure Energy Power. Intensive versus Extensive properties.

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CE 230-Engineering Fluid Mechanics

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  1. CE 230-Engineering Fluid Mechanics Lecture # 2&3 Fluid properties (1)

  2. Units • Basic Units versus derived units • SI versus Traditional units • prefixes

  3. What are the units of? • Mass • Length • Time • Temperature • Weight • Pressure • Energy • Power

  4. Intensive versus Extensive properties • Density • Specific weight • Specific gravity Tables A.2-A.4 at the end of the text Gases, air, water, and some liquids

  5. Example • What is the weight of a 1 cubic meter of water if the temperature is 5 C? • What if the temperature was 90 C? or 0 C?

  6. terminology • Incompressible fluid • Compressible fluid • Ideal fluid • Perfect gas?

  7. Perfect gas law • P=ρRT • R is the gas constant with units of m.N/kg K or ft lb/slug R See appendix

  8. Example 2.6 • What is the weight of a 10 cubic feet tank containing oxygen if it is pressurized to 385.3 psi and at a temperature of 70 F? answer 22.5 lb

  9. Elasticity & Bulk modulus • The needed pressure change needed to reduce the volume of a fluid Ev = -Δp/(ΔV/V) • What does it mean if Ev is very big? • For water Ev = 2.2 GN/m2

  10. Problem 2.46 • What pressure increase must be applied to water to reduce its volume by 1%?

  11. Surface tension • Due to unbalanced molecular forces at interface of two fluids. Force /length • For water-air surface σ=0.073 N/m • This accounts for capillary rise

  12. Estimate the capillary rise of water in a tube of diameter d.

  13. Applications of surface tension • Pressure in a droplet • Pressure in a soap bubble • Cylinder supported by surface tension • Ring being pulled out of liquid • Capillary rise between two plates

  14. Vapor pressure • The pressure at which a liquid boils • Function of T (direct proportion) • At what pressure does water boil? • Table A.5

  15. Example • Consider two cases of water boiling in a tea kettle one near the sea and the other on top of a very high mountain. a) compare the value of vapor pressure for both cases b) compare the temperature for both cases does this make sense?

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