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FRICTION LOSSES LAB SESSION (Experimental set-up (CALCULATION (NPSHA…
FRICTION LOSSES
LAB SESSION
AIM
: calculation of the pressure drop :!?:
pump
pipes (diameter)
THEORY (APPENDIX 2)
friction loss in a straight cylindrical pipe
∆Hf (
Pa
) =
4f
.(L/D).v^2/2 :red_flag:
f = Fanning friction factor
= a function of Reynolds number and relative surface roughness (only in turbulent region).
ε/D: Relative wall roughness
ε = surface roughness (mm)
D = pipe diameter (m)
L = pipe length (m)
Figure 1: Moody diagram = f factor over Renold's number
OR ∆Hf =
λ
.(L/D).v^2/2 :red_flag:
λ= Darcy factor = 4.f (-)
If there are
different pipe sections
with
different velocities
, the friction factor and friction losses need to be calculated separately for each section. :red_flag:
Friction loss in fittings and valves:
∆Hf = K.v^2/2
K: friction factor of the fitting (charts and figures)
Table 1: K-values for various fittings and valves
1 ball valve = gate valve (K) for this lab session's calculation :question:
inlets & outlets :!:
Minor friction losses :question:
associated with K
Major friction losses :question:
associated with lambda
Experimental set-up
use the right frequency-controlled pump at maximum power :!:
the valve in the joint press pipe is fully open :warning:
Measure up the complete set-up, lengths and diameters
(appendix 2)
Mark the distance the water travels in the pipes
measure length and diameter of the
different parts of the sections
pressure drop over the rota meter
(flow rate meter):
independent of the flow rate ( ∆p = 0,1 bar)
divide by 18 = m3/h so in this lab session: Q = 10 m3/h (max. flow rate).
Total pipe resistance:
P w,l = sum (1/2 rho. v^2 (λ x (L/D) + K)
Pipe characteristics
= graph of Pman versus flow rate
P_man=P_2-P_1+pg(h_2-h_1 )+1/2 ρ(〖v_2〗^2-〖v_1〗^2 )+∑▒〖1/2 ρv^2 (λL/D〗+∑▒〖k)〗 (1)
P man (pump) = static pressure difference + resistance of pipes :!:
in this lab session: h1 = h2 and v1 = v2:question:
CALCULATION
resistance of the pipe network for the maximum flow rate at 10 m^3/h
manometric pressure (pump)
engine power with pump efficiency = 20% and engine efficiency = 85%
Draw the system’s characteristic (pressure vs. flow rate) with FR = 0 to 10 m³/h
NPSHA
problems with the water sucking, so P decreas ans so T increase for water, then P increase that changes the state into vapor-liquid mixture = cause the damages to the blades of the pump (as explosion).
question NPSH- check appendix 3
http://www.pumpschool.com/applications/NPSH.pdf
We have
flow rate = 10 m3/h
density of water at room temp (assumption)
3 different diameters for 3 different surface areas A = π_r_2
3 different velocities: Q=v.A
v: velocity
A: surface area (of the circle)
define friction factor lambda (Fig. 1)
with old pipes for epsilon e = 1 mm
first: e/D
then: viscosity (from the book's table -
why does it has only the c p values
:question:) for Reynold's numbers
Re= (density x velocity x diameter) / viscosity
then use chart for lambda [meaning of the chart]
then, determine sum of K (for different velocities)
sudden
(from small to larger diameter): calculation (picture) :!:
NPSHR: manufature's values
MEASUREMENT
length of pipes
nominal diameter (inside) of pipes (written on the valve)
total length (ignore the corners, valves)
different d = different velocities
32 mm
40
50
with maximum flow rate 10 m^3/h
