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Fluid properties – Day 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. Summary from last time. Response of fluids to pressure stress.
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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
Surface Tension • Beading, formation of liquid drops, and suspension of objects heavier than the liquid Images from wikipedia.org
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
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
Note dependence on R Recall rg is g specific weight
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)
In Denver the atmospheric pressure is only 95% (see page 40) On Everest only 75%--the boiling points are reduced accordingly Boiling will occur