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) 2) 3)

Bends & Elbows Valves Collar, Union, Contraction, Expansion.

I Line. II Line. 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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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 loss co-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 hf ( pipe fitting ) =KV2/ 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 --= ----- + ----- + ----- + ----------5 d35 d25 d d15

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PROCEDURE: 1. 2. 3. 4. 5. 6. 7. 8. 9.

10.

Fill-in the sump tank with clean water. Keep the delivery valve closed. Connect the power cable to 1 Ph, 220V, 10 Amps with earth connection. Switch-ON the Pump & open the delivery valve. Open the corresponding ball valve of the pipe line. Adjust the flow through the control valve of the pump. Open the corresponding ball valves. 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) 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. Change the flow rate & repeat the experiment for different diameter of pipe fittings.

OBSERVATIONS:-

SL. NO.

1. 2.

TYPE OF PIPE FITTING

MANOMETER READING mm of Hg H1

h2

TIME TAKEN FOR 10cm RISE OF WATER, t ‘s’

SUDDEN CONTRACTION

25 - 10mm SUDDEN EXPANSION

10 - 25mm

3.

90° LONG BEND

4.

90° SHORT BEND

5.

45° LONG BEND

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VALVE POSITION

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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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3. Velocity Head (V): Discharge Q V = ----------------------------- = ------- m/sec Area of Inlet Section a1

Where, a1 = Area of pipe to which the fitting is fitted = π D2/4 m2 = 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 d2/4 = 7.85x10-5 m2. 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: HEAD SL. NO.

1. 2.

TYPE OF PIPE FITTING

LOSS COEFFICI ENT

SUDDEN CONTRACTION

25 - 10mm SUDDEN EXPANSION

10 - 25mm

3.

90° LONG BEND

4.

90° SHORT BEND

5.

45° LONG BEND

RESULTS AND CONCLUSIONS:

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