CE 319 F Daene Mc Kinney Elementary Mechanics

CE 319 F Daene Mc. Kinney Elementary Mechanics of Fluids Pressure

Pressure • Fluid at rest – can not support shear stress • Normal stress on any plane is pressure (+ for compression)

Example (3. 4) • Prob. 3. 4: How many bolts are needed at B-B? 20 bolts, 2. 5 cm dia

Pressure, Absolute & Gage

Pressure Variation with Elevation • Static fluid – pressure varies only with elevation in the fluid.

Pressure Variation with Elevation • If g is a constant 1 2 z = z 1, p = p 1 z = z 2, p = p 2 Elevation head Pressure head Piezometric head z=0

Piezometric Head 2 1 z=0 Open Tank

Piezometric Head 1 2 3 z=0 Pressurized Tank

Example (3. 6) • Tank contins fluid with g. A > g. B • Which graph depicts the correct pressure distribution?

Leaking Storage Tank • • • Water has seeped in to the depth shown Find: Pressure at gas-water interface, pressure at bottom of tank Assume: Fluids are at rest 0 17 ft Gasoline SG=0. 68 1 water 2 3 ft

Example (3. 5) • Find l • Forces at surface inside tube d=0. 5 mm l water Fa Fw

Example (3. 8) • What is maximum force F 2 that can be supported?

Compressible Fluids • Density is nearly proportional to pressure • For perfect gasses • Need to know T = T(z) – Constant (Isothermal): – Linear:

Compressible Fluids • Assume constant and integrate • Assume linear and integrate Temperature variation with altitude for the U. S. standard atmosphere