Experiment No. (5)
Losses in Pipe Systems and Fittings
5.1 Introduction
When water flows through a pipe system there are resistances as a result of changes
in direction, valves and fittings and pipe friction. The flow resistances are
directly
dependent on the geometry of the pipe elements and the number and type of fittings. In
addition, the flow velocity plays a key role in the occurrence of pressure losses.
One of the most common problems in fluid mechanics is the estimation of pressure
loss. This apparatus enables pressure loss measurements to be made on several small-bore
pipe circuit components, typical of those found in central heating installations.
5.2 Objectives
The following specific topics can be investigated on this experimental:
1. Influence of pipe diameter, flow velocity, flow rate change.
2. Losses from pipe components such as angles, bends and T-pieces.
3. Losses due to changes of cross section and shut-off fittings of various types.
4. Determination of pump characteristics, system characteristics and the operating
point.
5.3 Description of Measuring Points and Measuring Bodies
The components in each of the circuits are as shown in Figs. (5.1), (5.2) and (5.3):
Fig. (5.1): Rotameter
Fig. (5.2): Description of measuring points and measuring bodies
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Fig. (5.3): Pipe system
2.5 Results and Calculations
The head loss in pipe is:
𝑓 𝐿𝑉 2
=
𝑙
2𝑔𝑑
(5.1)
Where, 𝛾 = 𝜌𝑔, substituting in Eq. (2.1),
𝑓 𝐿𝑉 2𝜌
𝑃𝑣 = 𝛾
=
𝑙
2𝑑
(5.2)
Where: 𝑃𝑣
= the specific weight of the flow.
𝛾
𝑙
𝑓
= the pressure losses in pipe.
= head loss in the pipe.
= the coefficient of friction.
L
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= the length of the piper.
V = the flow velocity in the pipe.
𝜌
= the density of the flow.
D = the diameter of the pipe.
In view of the small different in flow velocity between V and V , a
1
2
constant
pipe coefficient of friction can be assumed 𝑓 = 0.037. The flow velocity V
is
calculated from the volumetric flow 𝑉̇ and the pipe cross-section
4 𝑉̇
𝑉 = π𝑑2
(5.3)
The displays on the manometer and the rotameter are noted in tables.
Table (5.1): Circuit
Open
V2
V7
V8
x
x
x
V11
Close
2.5.1 Influence of Different Pipe Diameters and Flow Velocities on Pipe Losses
Table (5.2): Measured results for pipe section 10 and pipe section 4
Pipe section 10: Copper pipe 18 Ч 1, 𝑑𝑖 = 16 𝑚𝑚, 𝐿 = 1000 𝑚𝑚
Volumetric flow 𝑉̇ in 𝑚3/
4 𝑛 𝑚𝑚
5 𝑛 𝑚𝑚
Head Loss
𝐿
𝑛 𝑚𝑚
Head Loss
𝐿
𝑛 𝑚𝑚
Pipe section 4: Copper pipe 28 Ч 1, 𝑑𝑖 = 26 𝑚𝑚, 𝐿 = 1000 𝑚𝑚
Volumetric flow 𝑉̇ in 𝑚3/
10
𝑛 𝑚𝑚
11
𝑛 𝑚𝑚
The measured head loss can be plotted against the flow rate. This illustrates
the
quadratic dependency of the flow and thus of the flow velocity.
2.5.2 Calculation of Coefficients of Friction for Pipe Elbows
The displays on the manometer and the rotameter are noted in tables.
Table (5.3): Measured results for pipe section 1 and pipe section 5
Pipe section 1: Cu angle 900, 𝑑𝑖 = 26 𝑚𝑚
Volumetric flow 𝑉̇ in
1 𝑛 𝑚𝑚
𝑚3/
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2
𝑛 𝑚�
Head Loss
𝐿
𝑛 𝑚𝑚
Pipe section 5: Gunmetal T bend, 𝑑𝑖 = 16 𝑚𝑚
Volumetric flow 𝑉̇ in
5 𝑛 𝑚𝑚
𝑚3 /
6
𝑛 𝑚𝑚
Head Loss
𝐿
𝑛 𝑚𝑚
2.5.3 Regulation and Shut-off Fitting
The displays on the manometer and the rotameter are noted in tables.
Table (5.4): Measured results for pipe section 7 and pipe section 8
Pipe section 7: Thermostatic valve 1/2′′
Volumetric flow 𝑉̇ in
𝑚3/
7
𝑛 𝑚𝑚
Pipe section 8: Shut-off gate valve 1/2′′
Volumetric flow 𝑉̇ in
8 𝑛 𝑚𝑚
𝑚3/
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8
9
𝑛 𝑚𝑚
Head Loss
𝐿
𝑛 𝑚𝑚
𝑛 𝑚𝑚
Head Loss
𝐿
𝑛 𝑚𝑚