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CHE- 3115 Chemical Engineering Processes I - Laboratory Experiment 1

Pipe Flow Hydraulics

BACKGROUND

The conveyance of fluids through fixed conduits is the most common unit

operation in engineering practice. Applications range from delivery of microliter

volumes of medicines over millimeters of distance to delivery of cubic meter volumes of

oil over kilometers of distance. The relationship between flow rate, energy consumption

(pressure drop), pipe diameter, etc. may be expressed by a “semi-empirical” correlation,

such as Equation (3.20), whose mathematical form may be derived from basic fluid

mechanical theory but which relies on experimental data for calibration.

Equation 3.20 g

u

d

l

g

u

d

l

g

Ph

f

f2

8422

OBJECTIVE

To observe the relationship between pressure drop and flow rate and to examine

the accuracy of semi-empirical expressions used to correlate pipe flow data.

PROCEDURE

A. Pressure Drop in Straight Pipes

1. Close all manometer valves and open all flow regulator valves. Allow water to

flow through the apparatus until all trapped air bubbles are flushed from the

system and temperature equilibrium is achieved (approximately 10 minutes).

Measure and record the temperature. Values of density and viscosity of water at

this temperature may be found in one of the listed references.

2. Close the appropriate regulatory valves to allow flow through only through the

pipe segment whose inside diameter is given as 0.545 inches. Measure the length

of the pipe segment (1) between manometer valves 7 and 8.

3. Reduce water flow to a low rate. Open the two manometer valves. Increase

water flow rate until the water level in the upstream manometer tube is at

approximately 65 inches. Measure the volumetric flow rate (Q) and pressure drop

(∆P).

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4. Reduce the water flow rate until the pressure drop is 10 to 15% lower than the

value measured in part 3. Measure the volumetric flow rate. Repeat for a total of

at lest six flow rates between zero and the maximum.

5. Close manometer valves 7 and 8. Adjust the regulatory valves to allow flow

through only the pipe segment whose inside diameter is given as 0.430 inches.

Measure the length of the pipe segment between manometer valves 11 and 12.

Repeat steps 3-4.

6. Close manometer valves 11 and 12. Adjust regulatory valves to allow flow

through only the pipe segment whose inside diameter is given as 0.315 inches.

Measure the length of the pipe segment between manometer valves 15 and 16.

Repeat steps 3-4.

B. Fluid Metering

1. Close all manometer valves. Adjust regulatory valves to allow flow through only

the pipe segment containing the two flow meters. Reduce water flow to a low

rate. Open manometer valves 2-5. Increase water flow rate until the water level

in the upstream manometer tube is at approximately 65 inches.

2. Measure the volumetric flow rate and the pressure drop across each of the meters.

Reduce the flow until the pressure drop across the first meter is approximately 10-

15% lower. Measure values of volumetric flow rate and pressure drops. Repeat

for a total of at least six flow rates.

ANALYSIS

A. Pressure Drop in Straight Pipes

1. Calculate pressure values of Reynolds number for each flow rate in each pipe

size.

2. On a single graph, plot experimental values for pressure drop versus volumetric

flow rate for each of the three pipe sizes. Do the shapes of the curves agree with

that predicted by Equation (3.20)?

3. On a separate (log-log) graph, plot values for the friction factor φ, defined by

Equation (3.20), versus Reynolds Number. Compare the shape of the curve to

Figure 3.7. Over what range of values of Reynolds Number is the curve

reasonably linear? According to Equation (3.37) [φ = 8/Re], what should the

value of slope be for that portion of the curve? Compare the value of friction

factor corresponding to the highest value of Reynolds Number used to a value

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calculated using the Colburn analogy between heat transfer and fluid friction for

turbulent flow in smooth pipes [Equation (10.171), φ = 0.023 Re-0.2].

4. An empirical correlation for pressure drop as a function of volumetric flow rate

may be written as ∆P = kQn. Use the data for the largest diameter pipe to

calculate values of k and n. Under what conditions could this correlation be used?

B. Fluid Metering

1. Calculate the values of Reynolds number for each flow rate in the Venturi and

orifice meters. Present all values in one table.

2. Plot the volumetric flow rate versus pressure drop data for each meter as Q vs.

(∆P)1/2. Using the values of slope in each plot and Equation (6.19) [or (6-32)]

calculate the values of the coefficient of discharge, CD, for the venturi and orifice

meters. The pipe, venturi throat, and orifice diameters are given as Dp = 0.545 in.,

Dv = 0.312 in., and Do = 0.245 in., respectively.

Equation 6.19 2

22

1

2 ( )

1 ( )

DC A v PG Q

AvA

Equation 6.32 )(

2

2

2

2

1

21

AA

PvAAC

v

GQ D

3. Compare the derived CD values to those reported in the literature for various types

of orifices and Venturi meters, and discuss any differences.

REFERENCE

Coulson, J.M., and J.F. Richardson, Chemical Engineering, Vol. 1, 6th Ed., B-H Press

(1999).

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Pipe Flow Hydraulics ● Glossary of Terms

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Pipe Flow Hydraulics ● Glossary of Terms (continued)

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Pipe Flow Hydraulics ● Glossary of Terms (continued)

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Figure 1: Pipe Flow Hydraulics Unit

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Figure 2: Pipe Flow Hydraulics Unit – Top View