Lecture 5 and 6 Flashcards
reynolds number is the ratio of
the inertial to viscous forces
low reynolds number
viscosity dominates
high reynold number
inertia dominates
relative roughness is
roughness/diameter both in mm as relative roughness is dimensionless
transition zone
zone between laminar and turbulent - neither laminar or turbulent somewhere inbetween the two
if velocity isnt given
estimate a value for reynolds number of 10^5 use this to find friction factor and pressure loss from which we can calculate another speed and therefore another reynolds number
pressure head pressure =
density of fluid * g * height of pressure head in m
ie 100mm H20 pressure head
1000 * g * 100/1000
iterative approach to friction factor (no veloctiy given)
Guess reynolds number of 10^5 -> work out friction factor -> use friction factor equation to find C -> work out new reynolds number
compare to see difference if less than 10% this is acceptable if not repeat
minor losses due to
expansions
contractions
bends
minor losses drop in pressure do
creation of eddies and turbulence
pressure minor losses =
pressure loss coefficient * 0.5 * density * C^2
minor losses are losses that are
not due to the pipe itself
sudden expansion into reservoir k=
(1-A1/A2)^2 = 1^2 = 1
sudden contraction from reservoir k=
d2/d1 = 0 -> k=0.5
where is a diffuser with an expansion of 90 degrees between the two sides of the pipe worse than sudden expansion
see LBot at 90 = 2( phi) k is greater than 1 which is above sudden expansion therefore greater losses
