Fluid Mechanics Overview for Dredging
Important concepts water, sediment flow through pipes, losses due to friction in pipe systems.
Definitions of Fluid Mechanics Properties
- ρ = mass/volume = fluid density
- ρwater = 1.94 slugs/ft3 = 999 kg/3
- ρseawater = 1.99 slugs/ft3 = 1030 kg/m3
- g = length/time2 = acceleration due to gravity
- g = 32.2 ft/s2; 9.81 m/22
- y = weight/volume = ρg = specific weight
- y water = 62.4 lb/ft3; 9.8 kN/m3
- y seawater = 64.0 lb/ft3; 10.1 kN/m3
- SG = specific gravity = ρsubstance /ρwater @ 4° Celcius
- SG SAE 30 = 0.91
- SG water = 1.00
- SG seawater = 1.03
- SG HG = 13.61
- SG slurry = 1.1 – 1.5
- SG (solid) sand = 2.65
- SG (loose) sand = 1.9 – 2.1
- μ – dynamic viscosity
- t = μ du/dy
- ⋎ – kinematic viscosity
- ⋎ = μ/ρ
- Re – Reynolds Number inertia force / viscous force
- Re = ρ D U/μ = U D/v (pipe flow)
- U – average velocity in pipe
- D – pipe inside diameter
Reynolds Number (Re) for Pipe Flow
To determine if slurry flow is laminar or turbulent
- Re < 2000 Laminar Flow
- Re > 4000 Turbulent Flow
Slurry (1.2 Specific Gravity) flows at 15 ft/2 through a 24 inch inside diameter pipe.
Is the flow laminar or turbulent?
Re = (1.94 slugs/ft3(1.25)(15 ft/s)(24 in/12 ft)2.34E-5 lb s/ft2)
Re = 3,110,000
Flow is TURBULENT
Pressure & Buoyancy
How pressure is quantified and buoyancy in individual sediment grains that are floating through your slurry. Buoyant force is equal to weight of the displaced fluid x by the specific weight of the displaced fluid.
Compare different contributions to energy flow in pipe systems. Calculate flow rates, velocities, losses.
Calculate Losses in Pipe Systems