fluid flow friction factors

CHEMICAL ENGINEERING PRACTICAL MANUAL 2012 ____________________________________________________________________________________________________

1

FLUID FLOW MEASUREMENTS

AIM

The practical has a dual purpose. Firstly the practical serves to introduce the student to different

techniques of measuring the flow rate of fluids, and secondly to determine friction and shock losses in

various fittings.

THEORY

1. Friction losses

Friction losses in a pipe system can be determined by the following equation:

gd

vLfh F

f

2

4 2

1 6.

The fanning friction factor, fF, is determined from the Moody Chart, Figure 5. The Reynolds number

together with the pipe roughness, , the friction factor can be determined.

2. Shock losses

As mentioned earlier, shock losses occur in fittings. The type of fitting used determines the magnitude of

the pressure loss. This magnitude is characterised by a constant, the K-factor. The pressure drop in terms

of pressure head can be calculated by the following equation:

g

vKh

2

2

8.

The total head loss due to friction and shock are the sum of all the friction losses and shock losses in

the different fittings and pipes in the system.

The total head loss due to friction and shock are the sum of all the friction losses and shock losses in

the different fittings and pipes in the system.

3. Determination of k values

As mentioned earlier the shock losses in a pipe system can be attributed to fittings and valves. Other

sources for shock losses are sudden enlargements, sudden contractions, sharp point entry and sharp point

exit.

3.1 Sharp point entry and exit

The sharp point entry is located at the exit from a large tank into a pipe. This should not be confused with

a sudden expansion. A sharp point exit is located at the exit of a pipe into a large tank. The respective k

values are as follows:

1 NOTE: How to convert head to pressure: hgP


2

kentry = 0.5

kexit = 1.0

When you incorporate exit losses in your total head loss, you do not incorporate the kinetic head also, i.e.

the value of v1 and v2 are assumed the same.

3.2 Sudden Contraction

A sudden contraction can be represented by two pipes. At the connection between the two pipes, the

larger pipe changes immediately into a smaller pipe. This sudden change in diameter causes shock losses.

The extent of shock loss is determined by the ratio of di2 / di1.

1 for di22 / di1

2 < 0.715

2. for di22 / di1

2 > 0.715

The shock loss is then determined by using the velocity in the smaller pipe.

3.3 Sudden Expansion

In the case of a sudden expansion, the smaller pipe changes into a larger pipe. The fluid flows as a jet and

gradually expands to fill the larger pipe, there being a large recirculating flow outside the jet. Owing to

the low velocity gradients in the recirculating flow, there is very little frictional loss here: most of the

losses occur where the expanding jet reattaches to the wall.

The k value can be estimated by the following equation:

The velocity in the smaller pipe is used to determine the shock losses.

2

1

225.14.0i

i

d

dk

2

1

20.175.0i

i

d

dk

22

2

10.1i

i

d

dk


3

EXPERIMENTAL PROCEDURE

FRICTION AND SHOCK DETERMINATIONS

The effect of flow rate on pressure drop for the different fittings is investigated by adjusting the supply

valve accordingly. Use a low, medium and high flow rate. Measure the pressure drop across the

appropriate fitting at the set flow rate using the manometer.

1. Open valve 12 completely, and switch on the pump.

2. Select the fitting to be investigated and open the appropriate Flow regulating Gate valve

(FRGV) (11, 12 or 13). The flow through the fitting is regulated by the degree to

which the FRGV is opened. 3. Close the valves attached to the pressure measuring hoses and insert into pressure measuring

points. Open these valves SIMULTANEOUSLY.

4. Open the dump valve (14) to discard the water in the

RESULTS

1. Determine the fanning friction factor for the following smooth pipes:

(i) 15 mm

(ii) 20 mm

2. Calculate the shock constant for the following fittings:

(i) gate valve

(ii) globe valve

(iii) ball valve

(iv) sudden enlargemnet

Compare all answers to literature values.

CHEMICAL ENGINEERING PRACTICAL MANUAL 2012

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4

1

2

3

4 5

1

6

1 7

1

8 8

9

1

9

1

10

11

12

13

CHEMICAL ENGINEERING PRACTICAL MANUAL 2012

____________________________________________________________________________________________________

5

Label

1 10 mm smooth PVC pipe



4 Strainer

5 Gate valve

6 Globe valve

7 Ball valve

8 Pressure measuring points with connecting hoses

9 Water manometer

10 Mercury Manometer

11, 12, 13 Flow regulating Gate valves

NOMENCLATURE

Units

z Potential head m

P Pressure Pa

v Fluid velocity in tube m.s-1

Density of a fluid kg.m-3

hf Total frictional and shock losses m

fF Fanning friction factor -

L Tube length m

D Tube diameter m

Tube roughness m

Leq Equivalent pipe length for a pipe fitting m

So cross sectional flow area of the orifice m2

Cd dimensionless discharge coefficient -

m density of liquid in manometer kg.m-3

zm difference in height between the two arms of the manometer m

h head loss m

REFERENCES

1. Coulson, J.M. and Richardson, J.F., (1993) 'Chemical Engineering', Vol. I, 4th

Edition, Percamon Press, London .

2. Perry, R.H., (1997) “Perry’s Chemical Engineers’ Handbook”, Seventh edition.

3. Holland, F.A., (1999) “Fluid flow for Chemical Engineers”,2nd

Edition. Edward

Arnold, London.

fluid flow friction factors

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