CE 3620: Water Resources Engineering
Fall 2015
Lab 4: Headloss along a Pipe and at Fittings
BACKGROUND
As water flows through a pipeline, energy is lost due to friction along pipe walls and flow
separation at fittings. This energy loss is termed headloss. The headloss due to pipe friction is
commonly estimated using the Darcy-Weisbach equation: HL = f LV2/2gD. The required friction
factor (f) is obtained from the Moody Diagram as a function of Reynolds number (Re = VD/ν)
and the roughness of the pipe (or pipe material). The headloss at bends and fittings, also termed
minor losses, are computed as: HM = K V2/2g. Values of the minor loss coefficient (K) are
tabulated for a number of fittings and transitions in text books.
LAB OBJECTIVES
 To investigate the effect of Reynolds number on headloss.

To verify minor loss coefficients for fittings.
EXPERIMENTAL PROCEDURE
1. Record the temperature of the water in the hydraulic bench on the attached data sheet.
NOTE: The apparatus for this experiment includes a number of fittings and four
horizontal pipes for which the internal diameters are D = 4.572 mm, 7.780 mm, 10.872
mm, and 17.348 mm. All pipes are a ‘smooth’ roughness. You will isolate various
pipes/fittings by connecting the plastic tubes from the Rosemount Differential Pressure
Transmitter (RDPT) accordingly and opening/closing valves to force water through the
pipe/fitting of interest. Also, the RDPT accounts for the difference in elevation between
ports, so even if the ports are not at the same elevation, when no flow moves through the
system, the RDPT will record a zero pressure difference. Therefore, you do not need to
add the height difference in your calculations.
2. Connect the RDPT to each end of the horizontal pipe with D = 10.872 mm). Open the
appropriate valve(s) to allow water through this section of the apparatus, and close the
remaining valves in order to ensure all water is flowing through the section to be tested.
3. Turn on the pump in the hydraulic bench and open the valve all the way. To adjust the
flow to the experimental apparatus, use the supply valve located near the water outlet.
4. Open the supply valve to allow water to enter the apparatus. Allow water to flow through
the apparatus for about 1 minute to purge air from the system, and then close the supply
valve. The differential head should be zero.
5. To ensure that all air is out of the system, open the two vales at the RDPT. Close the
valves once all air has been purged from the pipes and tubing.
6. On the PC, start the program to obtain digital readouts for differential pressure and flow
rate. (Ask your TA for instructions.)
1
7. Open the supply valve fully. Record the headloss (cm) from the PC screen in the
appropriate columns of the attached data sheet.
8. Record the flow rate reported by the Mag Meter.
9. Repeat the above steps for five different discharges for a total of six trials. The
successive flow rates should be reduced in roughly equal increments down to a very low
flow rate. (Remember: Use the supply valve to adjust the flow).
10. Repeat for each of the following fittings:
a. Sharp bend
b. Gradual bend
c. Tee (Note: Water must flow in both pipes downstream of Tee)
d. Gate valve fully open
Be sure to remove air in the plastic tubes each time you move them to a different
port by opening the values near the RDPT! Also, in order to appropriately isolate the
minor loss, remember to include the headloss for the pipe upstream/downstream of
the fitting as the ports to measure pressure are not immediately adjacent to each fitting.
RESULTS
Compare values of the friction factor obtained experimentally with theoretical values obtained
using computed Re and the Moody diagram. In addition, compare calculated minor loss
coefficients with published values (see Section 4.1.3.2 of Water Resources Engineering by
Wurbs & James). Record measurements taken during lab in the tables on the attached data sheet.
Type these results up in a spreadsheet and include them in the report.
CALCULATIONS
Show sample calculations for one trial (i.e., for one flow rate) as outlined below. Label variables
and use units in your calculations. Make sure to show all equations used, as well as any unit
conversions.
 Calculate theoretical values of headloss as a function of Re using the Moody Diagram. Note:
The kinematic viscosity (ν) is a function of temperature and can be found in Section 3.2 of
Water Resources Engineering by Wurbs & James.
 Calculate the experimental friction factors using measured values of headloss and flow rate.
 Calculate the experimental minor loss coefficients for each fitting and compare with
theoretical minor loss coefficients from Section 4.1 of Water Resources Engineering by
Wurbs & James.
 Calculate the percentage difference (theoretical versus experimental) for the friction factors
and minor loss coefficients.
DISCUSSION
1. What are possible reasons for discrepancies in experimental and theoretical values?
2. How could you save pumping costs in a piping system?
2
DATA SHEET
Water Temperature: _________________
Table 1. Straight Pipe Data (D = 10.842 mm)
Trial
Flow
(L/min)
Friction Factor (f)
Headloss
(cm)
% Difference
Re
Experimental
Theoretical
1
2
3
4
5
6
Length of Pipe (L):
100 cm__
Absolute Roughness (ε): ___________
**Stainless Steel (look online for reference)
Relative Roughness Coefficient (ε/D): ____________
Experimental Friction Factor: f 
2DgH L 2DgH L

2
LV 2
Q
L 
A
Theoretical Friction Factor (using Moody diagram):
Q
D
VD  A 
Re 



3
Table 2. Sharp Bend Data (D = 17.348 mm)
Trial
Flow
(L/min)
Headloss (cm)
Total
Pipe
Loss Coefficient (K)
Bend
Experimental
Theoretical
1
2
3
4
5
6
Length of Straight Pipe (L):
_________
Relative Roughness Coefficient (ε/D): ____________
Total Headloss: Read from computer
Pipe Headloss: H L(pipe)
Q
fL  
A
  
2gD
2
where f is obtained from the Moody Diagram
Bend Headloss (HL(bend)) = Total Headloss – Pipe Headloss
Experimental Loss Coefficient: K m 
H L(bend ) 2g
V2
Theoretical Loss Coefficient: See book/go online
4
%
Difference
Table 3. Gradual Bend Data (D = 17.348 mm)
Trial
Flow
(L/min)
Headloss (cm)
Total
Pipe
Loss Coefficient (K)
Bend
Experimental
Theoretical
1
2
3
4
5
6
Radius of Bend (R): 10.16 cm__
Length of Straight Pipe (L): _________
Relative Roughness Coefficient (ε/D): ____________
Total Headloss: Read from computer
Pipe Headloss: H L(pipe)
Q
fL  
A
  
2gD
2
where f is obtained from the Moody Diagram
Bend Headloss (HL(bend)) = Total Headloss – Pipe Headloss
Experimental Loss Coefficient: K m 
H L(bend ) 2g
V2
Theoretical Loss Coefficient: See book/go online
5
%
Difference
Table 4. Tee Data (D = 17.348 mm)
Trial
Flow
(L/min)
Headloss (cm)
Total
Pipe
Bend
Loss Coefficient (K)
Tee
Experimental
Theoretical
1
2
3
4
5
6
Radius of Bend (R):
10.16 cm__
Length of Straight Pipe (L): _________
Relative Roughness Coefficient (ε/D): ____________
Total Headloss: Read from computer
Pipe Headloss: H L(pipe)
Q
fL  
A
  
2gD
Bend Headloss: H L( bend )  K m
2
where f is obtained from the Moody Diagram
V2
using Km from book/online
2g
Tee Headloss (HL(tee)) = Total Headloss – Pipe Headloss – Bend Headloss
Experimental Loss Coefficient: K m 
H L(tee ) 2g
V2
Theoretical Loss Coefficient: See book/go online
6
%
Difference
Table 5. Gate Valve (Fully Open) Data (D = 17.348 mm)
Trial
Flow
(L/min)
Headloss (cm)
Total
Pipe
Loss Coefficient (K)
Valve
Experimental
Theoretical
1
2
3
4
5
6
Length of Straight Pipe (L): _________
Relative Roughness Coefficient (ε/D): ____________
Total Headloss: Read from computer
Pipe Headloss: H L(pipe)
Q
fL  
A
  
2gD
2
where f is obtained from the Moody Diagram
Gate Valve Headloss (HL(gate)) = Total Headloss – Pipe Headloss
Experimental Loss Coefficient: K m 
H L(gate) 2g
V2
Theoretical Loss Coefficient: See book/go online
7
%
Difference