Understanding Surface Tension and Fluid Viscosity
Explore the concepts of surface tension, instability, energy per area, capillary action, contact angles, viscosity, and Reynolds number in fluids. Learn about the forces and phenomena governing the behavior of liquids at a molecular level.
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Presentation Transcript
Surface tension 9.8.1
Surface can be Unstable compared to the bulk liquid
Surface minimizes area It is tense Force per unit length = tension Unit = N/m
Energy per Area N/m = J/m2 Energy penalty per area of surface
Cavity in a liquid Surface area 4 r2 Energy 4 r2 Tension causes an inward force Pressure difference 2 /r
Wetted capillary Higher pressure on concave side 2 /r = gl 2 l = gr l
Contact angle Liquid in contact with a surface Serway & Vuille, Fig. 9.42 good adhesion poor adhesion
Capillary with contact angle Contact angle changes the curvature 2 cos /r = gl 2 cos l = gr l
Viscosity fluid resistance to flow 9.8.3
How Its Defined Force required to slide a fluid layer past another Fd Av = Serway & Vuille Fig 9.47 F = force v = speed A = area d = distance to motionless layer
Reynolds Number Dimensionless quantity indicating propensity to turbulence vd RN = ratio of inertial to viscous influences Laminar flow if RN < 2000 Turbulent flow if RN > 3000
Turbulent and Laminar Flow Irregularities cause turbulence at lower Reynolds numbers Image: AASHTO
