Determination of Friction Factor for a Given Pipe Line

DETERMINATION OF FRICTION FACTOR FOR A GIVEN PIPE LINE

OBJECTIVE: To determine the friction factor for pipes of different sizes.

EXPERIMENTAL SET UP:

1. Pipe line of three different diameters of G.I.
2. Digital Pressure indicator to measure the pressure difference across the tapping, one at either end of the pipe line fitted with a Ball Valve.
3. A constant steady supply of water with a means of varying the flow rate using Centrifugal Pump.
4. Measuring tank to measure the flow rate.
5. Each pipe line is provided with separate control value to conduct experiment separately.

THEORY:

A closed circuit of any cross – section used for flow of liquid is known as a pipe. In hydraulics, generally, pipes are assumed to be running full and of circular cross section. Liquids flowing through pipes are encountered with frictional resistance resulting in loss of head or energy of liquids. This resistance is of two types depending upon the velocity of flow.

1. Viscous resistance and
2. Frictional resistance, due to Surface roughness.

The viscous resistance is due to the molecular attraction between the molecules of the fluid. At low velocities, the fluid appears to move in layer or lamina, and hence the nature of this flow or stream line and such flow is called Laminar flow. If the velocity of the liquid is steadily increased, at certain velocity termed as the lower critical velocity the parallel bands of liquid will become wavy. On further increase in the velocity, these instabilities will increase in intensity until a velocity corresponding to the upper critical velocity is attained. The region of flow bounded by the lower and upper critical velocities is termed as the transition zone. For all further increase in velocity of flow the streamline remains in a diffused state and the nature of this type of flow in termed as turbulent. In this case the flow is restricted by the friction between the liquid and the pipe surface which is known as frictional resistance.

Darcy – weisbach friction factor:

Darcy weisbach equation is commonly used for computing the loss of head to friction in pipes. It is given by,

where

f= Darcy friction factor

fl =Fanning friction factor

f= 4fl

The above equation indicates that the loss of energy head varies directly with the velocity head (V2/2g), the pipe length (L) and inversely varies with the pipe diameter (d). The constant of proportionality used in Darcy Weisbach equation, in the above form, f, is called Darcy’s friction factor (used mostly in Mechanical and Civil engineering applications). The Fanning friction factor (fl = f/4) is videly used in Chemical engineering applications.

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, 10Amps with earth connection.
4. Switch – on the pump & open the delivery valve.
5. Adjust the flow through the control valves of the pipe line.
6. Open the corresponding ball valves of the pipe line.
7. Note down the differential head reading in the manometer (expel if any air by opening the drain cocks provided with the manometer).
8. 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.
9. Change the flow rate & repeat the experiment for different diameter of pipes.

PRECAUTIONS:

1. Do not start the pump if the voltage is less than 180 V.
2. Do not forget to give electrical neutral & earth connections correctly.
3. Frequently (at least once in three months) Grease / Oil the rotating parts.
4. Initially, put clean water free from foreign material, and change once in three months.

TABULAR COLUMN:

FORMULAE:

Hf = Loss of head due to friction

Re = Reynolds number

Q = Discharge in m3/sec

V = Velocity in m/Sec

f = Friction factor

Area of Measuring Tank (A) = 0.075 m2

Length of pipe (L) = 1.3 m

Kinematic viscosity (ν) = 1.00X 10-6 m2/s

Acceleration due to gravity (g) = 9.81 m/s2

Diameter of pipe (d) =25, 12.5 mm (G.I)

1. DISCHARGE(Q):

where, A = Area of measuring tank in m2

R = rise of water level in cm.

t = Time taken in seconds for R cm rise of water.

1. Loss Of Head Due To Friction (HF):

hf = (P1- P 2)/ ρg m of water

p1, p2 in N/m2

Since p1, p2 are in bar

hf = (P1-p2) x 10.19 m of water

3. Velocity Head (V):

Discharge Q

V = ------= ------in m/s

Area of inlet section a

a = area of pipe (∏d2/4) in m2

4 .Friction factor (f):

2gdhf

fl = ------

4lv2

fl = Fanning friction factor

f = 4fl =Darcy friction factor

5. Reynolds Number (Re):

Inertia force V d

Re = ------or Re = ------(for circular pipe)

Viscous force v

Where, V = average velocity of flow

d = diameter of pipe

v = Kinematic viscosity coefficient of the fluid (water)

1X10-6 m2/s

RESULT: 1.Friction factor of pipe of dia 25mm___

2. Friction factor of pipe of dia 12.5mm___