Chapter 1: Fundamental Properties of Water
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