17. Pipe flow V (11.5-11.7) › fileadmin › tvrl › files › vvrf10_oldvvr120_ › 17_16.pdf · VVR 120 Fluid Mechanics 17. Pipe flow V (11.5-11.7) • Pump types • Pump systems

VVR 120 Fluid Mechanics

17. Pipe flow V (11.5-11.7)

• Pump types

• Pump systems

• Pumps in series and in parallel

Exercises: D35-36, and D38


Pump types – centrifugal pump


Pump types – axial flow pumps


Rotating movement by centrifugal impeller or propeller

Pressure increases over the pump

Pressure increases over pump:

(pout – pin) / g = Hp = pump head

Specific energy consumption pump =

(w Q Hp)/(3600 Q η) kWh/m3

Efficiency η = power output/power input


Energy line

Energy line

Hvalve

Hp = function(Qp)


A pump is characterized by a so-called pump curve

η = power output/power input


Calculation of flowrate and pressure in a

pump system

Water is pumped from reservoir A to

reservoir B

What will the flowrate, Qp, be if the pipe

characteristics, L, D, ks are known as well

as static head, z, and pump curve?

The pressure increase over pump (energy

supply from pump to water) should

achieve two things with respect to lifting

water from reservoir A to B:

1) overcome geometric height, z

2) overcome head losses hf1 + hf2


The hydraulic characteristics for the

pipe system, Hsyst, is obtained from

the energy equation

(local losses neglected in this case)

Hsyst states how much energy that is

needed to transport 1 kg of water

from A to B

Hp states how much energy the

pump can provide to the water

When the pump is introduced in the

pipe system the flowrate and pump

head will adjust so that Hsyst = Hp

22

2

gA

Q

D

Lfz

losseshzsystH

Qp in pipe

Pressure

increase

over pump


D36 Water is pumped between two

reservoirs with the same water surface

elevation zo. Total pipe length is L =

2500 m, diameter D = 0.1 m and

equivalent sand roughness k = 0.0001

m. The pump characteristics is given

by the figure. What is the maximum

permissible distance x from the

upstream reservoir to the suction side

of the pump, if the pressure must not

be less than atmospheric. The local

losses may be neglected. The

temperature is 20C.

12

3



PARALLEL PUMPING

Pumps operating in parallel are replaced by a fictive equivalent pump

with a pump curve obtained by horizontal addition of the single pumps´

pump curves

2 pumps in parallel

Equivalent pump


PUMPS IN SERIES

Pumps operating in series are replaced by a fictive equivalent pump

with a pump curve obtained by vertical addition of the single pumps´

pump curves

2 pumps

1 pump


EXAMPLES OF SYSTEM CURVES

1) Two pumps operating in parallel

If one pump runs If two pumps run

System curve (independent of number of

pumps)


2) Heat pump systems

Heat pump system


3) Increase of natural flow rate

Without pump: 022 2

2

2

2

gA

Q

D

LfzH

gA

Q

D

Lfz syst

Hsyst

Hpump

Qwithout

Qwith


4) Flow control using a valve

2

2

2)(

gA

Q

D

LfKzH valvesyst

hvalve

Valve

Increasing

Kvalve

(choking)


5) Time-varying reservoir surface

)variesΔz(2 2

2

gA

Q

D

LfzH syst


6) Flow regulation using speed-adjustable pumps

Speed-

adjustable

pump

Pump

curves

(rotation

per min)


D35 Water is to be pumped by two centrifugal pumps through a

pipeline connecting two reservoirs. The pumps can be operated in

parallel or one at a time. The pipeline is 2000 m long, diameter 250

mm and equivalent sand roughness is 0.2 mm. The static lift is 25.0

m. Calculate the specific energy consumption (kWh/m3) both for

single pump operation and when both pumps operate.

The pump characteristics are

Discharge Q (m3/s) 0.020 0.030 0.040 0.050

Head (m) 55 47 35 20

Total efficiency (%) 78 80 72 60



D38 Water (20C) is pumped between two reservoirs through two

identical, parallel pipes each with a diameter of 0.2 m, length 1000 m,

and equivalent sand roughness of 410-4 m.

a) What flow is expected through the pump?

b) How much energy (kWh) is needed to pump 1 m3 of water? The

efficiency of the pump h = 0.75


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17. Pipe flow V (11.5-11.7) › fileadmin › tvrl › files › vvrf10_oldvvr120_ › 17_16.pdf · VVR 120 Fluid Mechanics 17. Pipe flow V (11.5-11.7) • Pump types • Pump systems