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Purpose
Purpose
To measure the energy loss due to friction in various pipes and valves
Prelab
Prelab
Print the Data Collection Sheet to assist with data collection.
Theory
Theory
PART 1: PIPES
As fluid flows through a pipe, it loses energy. The energy loss causes a decrease in pressure between two points in a flow system. The loss is represented by the general energy equation:
(P2 - P1) /γ + (v2 - v1 )/2g +(z2 - z1) + hs + hf =0
(P2 - P1) /γ + (v2 - v1 )/2g +(z2 - z1) + hs + hf =0
where:
P1, P2 are the pressures at point 1 and 2 respectively (kN/m2)
z1, z2 are the vertical displacements of point 1 and 2 (m)
v1, v2 are the fluid velocities at point 1 and 2 (m/s)
γ is the specific weight of the fluid (kN/m3)
g is the acceleration due to gravity (m/s2)
hs is the shaft work (+ for turbine, - for pump) head (m)
hf is the frictional head loss (m)
For pipe and tube flow, we have Darcy's equation for hf and Reynold's number :
hf = f • L/D • v²/2g
hf = f • L/D • v²/2g
where:
hf is the head loss due to friction (m)
L is the pipe length (m)
D is the pipe diameter (m)
v is the average velocity of flow in the pipe (m/s)
f is the friction factor (dimensionless)
ρ is the fluid density (kg/m3)
μ is the fluid viscosity (Pa s)
Steps for finding the friction factor f:
Calculate Reynold's number for the flow.
Calculate the roughness (ε/d) using the chart from your text.
Using a Moody chart, find the intersection of Reynold's number, and roughness you calculated to find "f".
PART 2: VALVES
Valves are found in most fluid flow systems. They are used to regulate the rate of flow. They can come in the form of globe valves, angle valves, gate valves, butterfly valves, and any type of check valve.
As fluid flows through a valve, energy is lost in the form of friction:
hm = K • v²/2g
hm = K • v²/2g
where:
hm is the minor energy loss due to friction in valves and fittings (m)
K is the resistance coefficient (dimensionless)
v is the average velocity of flow in the pipe (m/s)
g is the acceleration of gravity (m/s2)
Pipe & Valve Diagram Cross-Section
Procedure
Procedure
PART 1: PIPES
Connect the hose from the pump to the plywood stand.
Assure the exit hose empties into the plastic barrel.
(This has been probably been done for you.)
Connect the ends of the white tubing into the plugs along the pipe.
Start the water flowing.
Adjust the flow via:
the valve (at the end of the bench)
the valve (right of plywood panel)
for a reading 1/2 way up the flow meter (left of plywood panel)
Bleed any air bubbles from the white tubing.
(This has probably been done for you also.)
Check the zero.
With the ends of the white tubing connected to a pipe with no flow, check the pressure gauge reading
If the pressure is not zero, record the value on the Data Collection Sheet and subtract it from all other readings under this set-up.
Adjust the flow for 2 GPM.
For the 3 pipes, record the flow and the pressure drop on the Data Collection Sheet.
Repeat step 9 for 3, 4 and 5 GPM.
Measure the lengths of pipe between the pressure measurement points (on the 3 pipes) and record them on the Data Collection Sheet.
PART 2: VALVES
Adjust the flow for 2 GPM.
Direct the flow through the pipe section with the device under test.
Connect the short ends of the white tubing into the plugs on either side of the fixture under test.
Measure the pressure difference and record the flow and pressure drop on the Data Collection Sheet.
Repeat 2, 3 & 4 for the four valves on the board.
(For the Globe Valve, take the reading with the valve fully open.)
Adjust the flow valve on the table to change the flow rate to 3, 4 & 5 GPM
Repeat steps 2 to 5.
Measure the total length of pipe between the pressure measurement points on either side of the valves and record them on the Data Collection Sheet.
You will need to subtract the losses in the pipe from the measured losses for the gauges later.
For that, you need to know how much pipe was included in each pressure measurement.
Results
Results
PART 1: PIPES
On one figure, plot head loss per meter of pipe (y-axis) in inches of H2O against the flow (x-axis) in US Gal/min. (Three plots on one figure.)
Calculate hf from equation (1) and f from equation (2). Compare this f value with the value predicted using Moody's Diagram.
PART 2: VALVES
On one figure, plot head loss against flow for each valve or fixture (y-axis) in inches of H2O against the flow (x-axis) in US Gal/min. (Four plots on one figure.)
Be sure to subtract the losses from the pipe on either side of the fixture from the fixture losses as you only want to plot the losses due to the fixtures.
Use obtained values to calculate K for each fixture. Compare with published values you find.
Questions
Questions
How does the flow through two 1" diameter PVC pipe compare to the flow through one 2" diameter PVC?
Compare X-Sectional Area, Velocity, Mass Flow Rate, and Frictional Losses. You can use the lab data for properties of PVC pipe.
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