1.1, 1.2

Monday, August 18, 2008

8:54 PM

Chapter 1: Fundamental Properties of Water

(this is review material, it will be covered rapidly and you are responsible for knowing all of it)

Hydraulic Engineering: application of engineering principles and methods to the planning, control, transportation, conservation, and utilization of water.

1.1 atmospheric pressure at sea level is 101.3 kPa = 14.7 psi = 760 mmHg = 10.33 m H2O

Pascal is the same as:

Problem: use information above to estimate the density of mercury

P = rho g h

is the governing equation

this is how high each liquid rises in an evacuated tube (draw the two tubes) so P = 101.3 kPa

strategy: set P = for both tubes = 1 atmosphere, solve for rho (density)

the partial pressure of water in the atmosphere is the vapor pressure, each separate gas in the atmosphere exerts a partial pressure and together they add to the total pressure

pure water vapor pressure depends highly on temperature

(show how condensation occurs on a soda can on the graph)

boiling point is when the vapor pressure equals the total pressure

in closed systems (pipes) cavitation occurs when the vapor pressure exceeds the local total pressure

1.3

Monday, August 18, 2008

9:17 PM

density = mass/volume (kg/m3)

specific weight = weight/volume = mass*gravity/volume = N/m3 by definition

prove it:

density and specific volume of air

1.4 Viscosity

Monday, August 18, 2008

9:28 PM

tau = mu dv/dt

shear stress (tau, N/m2) equals a proportionality constant (mu, the absolute or dynamic viscosity, N s/m2) times the change in velocity with distance

kinematic viscosity = absolute viscosity/density

Note: Table 1.3 will be useful in solving problems

1.5 Surface Tension

Monday, August 18, 2008

9:40 PM

molecules in fluids attract each other leading to surface tension

surface tension depends upon the properties of the two fluids in contact

liquids may be attracted to or repelled by a solid surface

attraction = wetted surface = capillary rise

repulsion = non wetted surface = capillary drop

Example:

thickness of capillary fringe depends upon pore sizes in the soil

clay = small pores, high capillary rise

sand = large pore sizes, low capillary rise

With notes on the dimension in SI units, the height h of a liquid column (m) is given by:[1]

where:

  • is the liquid-air surface tension (J/m² or N/m)
  • θ is the contact angle
  • ρ is the density of liquid (kg/m3)
  • g is acceleration due to gravity (m/s²)
  • r is radius of tube (m).

For a water-filled glass tube in air at sea level,

is 0.0728 J/m² at 20 °C

θ is 20° (0.35 rad)

ρ is 1000 kg/m3

g is 9.8 m/s²

therefore, the height of the water column is given by:

.

Thus for a 2 m wide (1 m radius) tube, the water would rise an unnoticeable 0.014 mm. However, for a 2 cm wide (0.01 m radius) tube, the water would rise 1.4 mm, and for a 0.2 mm wide (0.0001 m radius) tube, the water would rise 140 mm (about 5.5 inches).

Pasted from <

gap between the plates is changed; where is it larger or smaller?

hydrophilic and hydrophobic examples

hydrophilic drop spreads

hydrophobic drop bounces off

link will show videos of this if it works

Monday, August 18, 2008

10:04 PM

Elasticity of Water

Monday, August 18, 2008

10:04 PM

water is about 100X as compressible as steel,

usually we treat it as incompressible (remember engineering is all about useful approximations)

sometimes the compressibility of water is important:

water hammer = sounds in pipes when water is forced to stop suddenly with a bang

confined aquifers = water is under pressure and compresses

1.7 Forces in Fluids

Monday, August 18, 2008

10:06 PM

body forces (e.g., gravity forces on the water) units of N/m3

surface forces (e.g., the force of a pipe wall or dam on water) units of N/m2

line forces (surface tension) with units of N/m