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Understanding Fluid Properties: Pressure Stress, Shear Stress & Surface Tension

Explore qualitative and quantitative responses of fluids to pressure and shear stress. Learn about surface tension, vapor pressure, and how they influence fluid behavior. Discover the impact of materials at interfaces and the dependence of properties on pressure and temperature.

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Understanding Fluid Properties: Pressure Stress, Shear Stress & Surface Tension

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  1. Fluid properties – Day 2

  2. Quick review from last time • Fluid properties (qualitative) • Quantitative response to pressure (stress) • A few extra comments • Quantitative response to shear (stress) • A few extra comments

  3. Summary from last time

  4. Response of fluids to pressure stress

  5. Response of fluid to shear stress

  6. Surface Tension • Beading, formation of liquid drops, and suspension of objects heavier than the liquid Images from wikipedia.org

  7. Surface tension – a liquid property Mercury Water • The surface tension depends on the materials at the interface • Surface tension depends on fluid and gas; force, F = σL • The contact force between the droplet and a (wetted) solid surface depends on how “fluid-phobic” the surface is (to that particular fluid) example

  8. Surface tension for liquid/fluid interface • When two surfaces contact, they meet at a line – the length of that line is key for surface tension Parallel to the solid surface is

  9. Note dependence on R Recall rg is g specific weight

  10. Why 2

  11. Vapor Pressure • Analogy: boiling temperature • Boiling temperature = temperature at which a liquid boils • Below maintains a liquid • Dependent on pressure • Vapor pressure • Vapor pressure = pressure at which a liquid vaporizes • Above, maintains a liquid • Dependent on temperature (Need gas/liquid interface)

  12. In Denver the atmospheric pressure is only 95% (see page 40) On Everest only 75%--the boiling points are reduced accordingly Boiling will occur

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