experiment on loss of head( minor losses) in pipe fittings

7/22/2019 Experiment on Loss of Head( Minor Losses) in Pipe Fittings

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FM&HM LAB

EXPERIMENT ON LOSS OF HEAD

(MINOR LOSSES) IN PIPE FITTINGS

AIM:

To determine the head loss due to friction in Pipe Fittings and hence, to

determine the “ Head Loss Co-efficient ”.

APPARATUS:

Pipe fitting apparatus, stop watch

SPECIFICATIONS:

* Pump Capacity : 1 HP, 1 Ph.

* Collecting (Measuring) Tank Area : 0.0772 m2.

* Nominal Dia of Pipe : 1” NB (27mm ID).

* Fittings Used: 1) Bends & Elbows I Line.

2) Valves II Line.

3) Collar, Union, Contraction,

Expansion. III Line.

DESCRIPTION OF APPARATUS:

The apparatus consists of pipe lines in three different branches containing; (i)

Valves in one line, (ii) Bends & Elbows in second line, (iii) Collar, Union,

Contraction & Expansion in the third line.A U-Tube Manometer is connected

across each fittings with change-over valves. A constant steady supply of water

is provided using Centrifugal Pump with Valve for varying the flow rate.

A Measuring Tank with Stop Clock is provided for measurement of flow rate.A Sump Tank is mounted below the Collecting Tank.A Butterfly Valve is

provided for instantaneous dumping of collected water into the Sump tank and the

overflow pipe to facilitate to run the equipment on Closed circuit basis.

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FM&HM LAB

THEORY:

Like the straight pipes produce the friction to the flow of fluid due to

its inside roughness, the pipe fittings such as Valves, Bends, Elbows, Reducers /

Expanders, etc also offer Resistance / Friction to the flow of fluid. While the head

loss due to friction in straight pipes is expressed by the standard formulae:

f l V2

hf

= ------ .... (a)

2gd

the head loss due to friction in pipe fittings is expressed by

KV2

similar equation : ------- .... (b)

2g

By equating (a) and (b), we get the factor K = f l/d where K is the local head lossco-efficient of pipe fittings (non-dimensional) expressed in terms of the friction

factor (f), length (l) and diameter (d) of the pipe to which the particular type of

fitting is fitted.

In the equations where the branches of pipes are used for flow

analysis, all the resistances offered by the fittings are expressed in “equivalent

length” of pipe to which they are fitted, namely; L = Kd/f .This is to be added

to the length of the straight pipe of diameter ‘ d ’ with the friction factor ‘ f ’ (

0.025 generally assumed ), and the analysis is done further. Note that the valve of ‘K’ is to be evaluated from the formulae h

f ( pipe fitting ) =KV

2/ 2g where

V is the velocity of fluid flowing in the pipe line of diameter d to which the pipe

fitting is fitted.

Further, it is also be noted that, if in a branch of pipe lines, where the

various diameter pipes are involved, the similar kind of method is used for

converting all the other pipe of different diameters to the equivalent length of one

particular diameter. This way the analysis becomes simpler. In such cases, the

equivalent length is calculated from the formulae; L L1

L2

L3

--- = ----- + ----- + ----- + -----------

d5 d15 d

25 d

35

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FM&HM LAB

PROCEDURE:

1. Fill-in the sump tank with clean water.

2. Keep the delivery valve closed.

3. Connect the power cable to 1 Ph, 220V, 10 Amps

with earth connection.

4. Switch-ON the Pump & open the delivery valve.

5. Open the corresponding ball valve of the pipe line.

6. Adjust the flow through the control valve of the pump.

7. Open the corresponding ball valves.

8. Note down the differential head reading in the Mano-meter. (Expel if any air

is there by opening the drain cocks provided with the Manometer)

9. Operate the Butterfly Valve to note down the collecting tank reading

against the known time and keep it open when the readings are not

taken.10. Change the flow rate & repeat the experiment for different diameter

of pipe fittings.

OBSERVATIONS:-

SL. NO.

TYPE OF

PIPEFITTING

MANOMETER

READING mm of HgTIME TAKEN

FOR 10cm RISEOF WATER,

t ‘s’

VALVE POSITION

H1 h2

1.SUDDEN

CONTRACTION

25 - 10mm

2.SUDDEN

EXPANSION

10 - 25mm

3.90° LONG

BEND

4.90°

SHORT

BEND

5.45° LONG

BEND

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FM&HM LAB

CALCULATIONS:

∗ Area of Measuring Tank ‘A‘ = 0.0772 m2

∗ Acceleration due to Gravity ‘g‘ = 9.81 m/sec2

∗ Diameter of Bigger pipe ‘D‘ = 27 mm

∗ Diameter of Smaller pipe ‘d‘ = 10 mm

1. Actual Discharge (Q):

A × R where,

Q = ------------- m3/Sec 1000 is the conversion factor

1000 × t from mm to m.

A = Area of Measuring Tank

= 0.0772 m2

R = Rise of water level in mm

(Collecting Tank)

= 100mm

t = Time for R mm of rise in water in Secs.

=

2. Loss of Head due to Fitting (hf ) :

12.6 H

hf = ----------- mtrs

1000

Where,

H = Difference in Mercury column in mm of Hg in double column Manometer.

12.6 & 1000 are conversion factors.

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FM&HM LAB

3. Velocity Head (V):

Discharge Q Where,

V = ----------------------------- = ------- m/sec a1 = Area of pipe to which the

Area of Inlet Section a1 fitting is fitted= π D

2/4 m

2

= 5.72 x 10-4

m2

4. Additional Friction Loss (K):

Loss of Head

K = --------------------

Velocity Head

hf

= --------------

(V2/2g)

Note : Additional frictional loss (K) for sudden contraction and sudden expansion is

calculated from the formula as given below:

5. Additional Frictional Loss for sudden expansion (K) :

hf

K = --------------

(V1 – V2)2

2g

Q

V2 = -----

a2

Where,

a2 = area of the smaller diameter = π

d

2

/4 = 7.85x10

-5

m

2

.d = 10mm

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FM&HM LAB

6. Additional Frictional Loss for sudden contraction (K):

hf

K = ------------------

V2

0.5 x --------

2g

TABLE OF CALCULATIONS:

SL.

NO.

TYPE OF

PIPEFITTING

HEAD

LOSSCOEFFICI

ENT

1.

SUDDEN

CONTRACTION25 - 10mm

2.SUDDEN

EXPANSION

10 - 25mm

3.90° LONG

BEND

4.

90°

SHORTBEND

5.

45° LONG

BEND

RESULTS AND CONCLUSIONS:

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experiment on loss of head( minor losses) in pipe fittings

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