Experiment Name: Pipe friction characteristics for different flow regimes for flow through pipes.
Figure:- Experiment set-up
Objective:
To determine experimentally the friction factor for flow through different pipes, and to compare it with theoretical value.
Apparatus Used:
a. Pipe friction apparatus consisting of G.I b. Pipes of different diameter,
c. Flow control valve at outlet of pipes,
d. U-tube differential manometer,
e. Volumetric tank,
f. Stop watch.
Theory:
When a fluid is flowing through the pipe, it is subjected to resistance to flow due to shear forces between the pipe wall and fluid particles and between the fluid particles also. This resistance is called frictional resistance. This resistance depends upon the velocity of flow and area of surface in contact. It also depends upon the type of flow, i.e. laminar or turbulent. This frictional resistance causes loss of pressure in the direction of flow.
Reynolds number (Re) is the non-dimensional number which determines whether the flow is laminar or turbulent. For pipe flow transition flow starts when Re exceed 2000 and turbulent when exceeds 4000. For both laminar and turbulent flow, the friction factor which is a measure of frictional resistance offered to fluid motion, depends on Reynolds Number (Re). Besides this, another important factor is the relative roughness (ε/d) for the pipe which determines the level of friction in case of turbulent flow. For constant diameter pipe the energy loss over the length L may be characterized by an equivalent head loss hf which can be expressed according to Darcy-Weisbach equation, as
hf =f× LU²/(D×2g)
where
f = Darcy’s friction factor
L= length of the pipe
D= diameter of the pipe
U = Average velocity of flow through the pipe
For fully developed laminar flow, theoretically it can be shown that f =64/Re i.e. f is Φ(Re) only.
For turbulent flow no such theoretical relationship exists. In turbulent flow region it has been seen f=Φ(Re, ε/d). However for smooth pipe (ε/d<10⁻⁶),range of Re (2000<Re<10⁵) with the following relation
f= 0.3164/Re¼
And this the variation of friction factor with Re with ε/d is usually shown in form of Moody’s diagram, which is the graphical representation of experimental data on friction of pipes with friction factor as a function of Reynolds Number and Relative roughness.
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Experimental procedure:
1. Start water flow by opening the inlet valve.
2. Check for leakages by closing two of outlet valves one by one for each pipe, and correct the leakage if any.
3. Open the outlet valves of the pipe to be tested.
4. Remove all the existing air bubbles from manometer and connecting pipes.
5. Reduce the flow. Adjust outlet valves then take readings of heads and flow rate.
6. Now, increase the flow and accordingly adjust the outlet valve, so that water will not overflow. Repeat above procedure for other pipes.
Observations:
Length of pipe between pressure tappings (L) = 1m,
Internal diameter of the G.I Pipes (D) = (i) Φ14 mm (ii) Φ19.5 mm,
Specific gravity of the manometric fluid= 13.57,
Cross sectional area of the volumetric tank (A) = 0.3m × 0.3m= 0.09 m²,
Temperature of the water= 20°C,
Kinematic Viscosity of the water from standard chart (ν)= 1.003 × 10⁻⁶ m²/Sec.
Note:- We only show three sample calculation of Φ14 mm diameter pipe, rest can be done in similar way. But in log-log graph we use all the data to plot the graph.
Required Graph to be plotted:
Draw f vs. Re in log-log graph paper
(2×3cycle). (Both Experimental & Theoretical)
[Draw f =64/Re for laminar flow and
f= 0.3164/Re¼ for turbulent flow.]
FAQ:
1. Draw the schematic diagram of the setup.
2. Provide sample calculation.
3. List out the sources of error.
1. There can be a fluctuation in Piezometric tube, so mean position must be taken.
2. The loss of head at valves and fittings can bring error.
3. Previously collected (Non-drained water) in Tank may cause error.
Written by:- SOUMIK.