Upload
others
View
7
Download
0
Embed Size (px)
Citation preview
Sep 27, 2017Dr./ Ahmed Nagib Elmekawy
REE 307
Fluid Dynamics II
Branched Pipe System
2
โข Pipe in Series
โข Pipe in Parallel
Branched Pipe System
3
โข Pipe in Series
โข Pipe in Parallel
Branched Pipe System
4
โข Electrical circuits
๐๐๐๐ก๐๐๐ = ๐ถ๐ข๐๐๐๐๐ก ร ๐ ๐๐ ๐๐ ๐ก๐๐๐๐
โข Fluid Flow
โ๐ =๐๐๐2
2๐๐=0.8 ๐๐๐2
๐๐5= ๐ ๐2
๐ : ๐๐๐๐ ๐๐๐ ๐๐ ๐ก๐๐๐๐ =0.8 ๐๐
๐๐5
Branched Pipe System
5
โข Pipe in Series
๐1 = ๐2 = ๐3
โ๐๐ดโ๐ต = โ๐1 + โ๐2 + โ๐3
Branched Pipe System
6
โข Pipe in Parallel
๐๐ก๐๐ก๐๐ = ๐1 + ๐2 + ๐3
โ๐๐ดโ๐ต = โ๐1 = โ๐2 = โ๐3
๐1๐1๐12
2๐๐1=๐2๐2๐2
2
2๐๐2
๐1๐2
=๐2๐2๐1๐1๐1๐2
0.5
Branched Pipe System
7
โข Loop
๐1 = ๐2 + ๐3๐๐ด๐พ+๐๐ด2
2๐+ ๐ง๐ด =
๐๐ต๐พ+๐๐ต2
2๐+ ๐ง๐ต + โ๐1 + โ๐2
๐๐ด๐พ+๐๐ด2
2๐+ ๐ง๐ด =
๐๐ต๐พ+๐๐ต2
2๐+ ๐ง๐ต + โ๐1 + โ๐3
โ๐2 = โ๐3
Branched Pipe System
8
Supply at several points
Branched Pipe System
9
โข Three Tank Problem
Branched Pipe System
10
โข Three Tank Problem
Branched Pipe System
11
โข Three Tank Problem
Branched Pipe System
12
โข Three Tank Problem
Solution of 3 Tanks Problem
13
1. Assume EJ less than Za, and greater than Zc
๐ธ๐ > ๐ธ๐ฝ > ๐ธ๐2. Applying Bernoulli's equation between A & J
๐ธ๐= ๐ธ๐ฝ+ โ๐
ฮ๐ธ๐โ๐ฝ = ๐ธ๐ฝ โ ๐๐ = โ๐= 0.8 ๐๐๐๐
2
๐๐5
โด ๐๐ =โ๐๐๐
5
0.8 ๐๐
๐๐๐+ ๐๐ +
๐๐2
2๐= ๐ธ๐ +
0.8 ๐๐๐๐2
๐๐5
Solution of 3 Tanks Problem
14
Similarly between B & J : Get ๐๐between C & J : Get ๐๐
3. Checking the assumption
If ๐๐+ ๐๐+ ๐๐ = 0.0 Right Assumption
If ๐๐+ ๐๐+ ๐๐ โ 0.0 ๐๐> (๐๐+ ๐๐)
Wrong Assumption
๐๐< (๐๐+ ๐๐)
Increase the Energy of
junction (EJ), and decrease
the losses
Increase the Energy of
junction (EJ), and decrease
the losses
Solution of 3 Tanks Problem
15
4. We repeat the last step, by increasing or decreasing the value
โ๐ = ๐๐+ ๐๐+ ๐๐ โ 0.0 < ๐๐๐๐๐๐๐๐๐
As it won't equal to zero
Branched Systems
Supply at Several Points
16
โข Pipe Flows
- For known nodal demands, the rates can be partially determined.
- Flow rates & directions in the pipe routes connecting the sources
depend on the piezometrie heads at the sources and the
distribution of nodal demands.
โข Velocities
- Also partially known.
โข Pressures
- Conditions are the same as in case of the single source, once the
flows and velocities have been determined.
โข Hydraulic calculation
- Single pipe calculation can only partially solve the system.
- Additional condition รฌs necessary.
Solution of Branched Pipe
Systems
17
โข Note
In case of rectangular duct or not circular cross section.
๐ =4๐ด
๐ค๐๐ก๐ก๐๐ ๐๐๐๐๐๐ก๐๐ (๐)
Example
18
โข Given :
โข Required :
Qa, Qb, Qc, Flow Direction
L1 = 3000 m D1 = 1 m f1 = 0.014 Za = 30 m
L2 = 6000 m D2 = 0.45 m f2 = 0.024 Zb = 18 m
L3 = 1000 m D3 = 0.6 m f3 = 0.02 Zc = 9 m
Solution
19
1. Assume EJ = 25 m
2. Applying Bernoulli's equation between A & J
๐ธ๐= ๐ธ๐ฝ+ โ๐
๐๐๐+ ๐๐ +
๐๐2
2๐= ๐ธ๐ +
0.8 ๐๐๐๐2
๐๐5
ฮ๐ธ๐โ๐ฝ = ๐ธ๐ฝ โ ๐๐ = โ๐= 0.8 ๐๐๐๐
2
๐๐5
โด ๐๐ =โ๐๐๐
5
0.8 ๐๐=
30โ25 ร9.8ร15
0.8 ร0.014ร3000
โด ๐๐ = 1.2 m3/s
Solution
20
3. Similarly between B & J and C & J
โด ๐๐ =25โ18 ร9.8ร0.455
0.8 ร0.024ร6000= 0.105 m3/s
โด ๐๐ =25โ9 ร9.8ร0.65
0.8 ร0.02ร1000= 0.873 m3/s
โ๐ = ๐๐+ ๐๐+ ๐๐ = 1.2 โ 0.105 โ 0.873 = 0.222 > 0.0
๐๐ = 1.2 m3/s ๐๐ = 0.105 m3/s ๐๐ = 0.873 m3/s
Solution
21
4. Increase energy of junction (EJ = 26.6 m)
โด ๐๐ =โ๐๐๐
5
0.8 ๐๐=
30โ26.6 ร9.8ร15
0.8 ร0.014ร3000= 0.996 m3/s
โด ๐๐ =26.6โ18 ร9.8ร0.455
0.8 ร0.024ร6000= 0.116 m3/s
โด ๐๐ =26.6โ9 ร9.8ร0.65
0.8 ร0.02ร1000= 0.916 m3/s
โ๐ = ๐๐+ ๐๐+ ๐๐ = 0.996 โ 0.116 โ 0.916 = โ0.036 โ 0.0
๐๐ = 0.996 m3/s ๐๐ = 0.116 m3/s ๐๐ = 0.916 m3/s
Solution
22
Solution
23
โข For more accuracy, use more assumptions, but the result can
be accepted, as โQ is very small w.r.t the smallest value, which
is Qb
โข For more accuracy and saving time, use programming
languages to solve the problem.
Network of pipes
24
Function of piping system:
1. Transmission ---- One single pipeline
2. Collection ---- Waste water system
3. Distribution ---- Distribution of drinking water
---- Distribution of natural gas
---- Distribution of cooling water
---- Air conditioning systems
---- Distribution of blood in veins and
arteries
Types of Network
25
1. Branched network
Properties
1. Lower reliability
2. High down time
3. Less expensive
4. Used in rural area
Types of Network
26
2. Looped network
Properties
1. Higher reliability
2. lower down time
3. More expensive
4. Used in urban area
Looped Networks
27
Looped Networks
28
โข Pipe Flows
โข Flow rates and directions are unknown.
โข Velocities
โข The velocities and their directions are known only after the
flows have been calculated.
โข Pressures
โข Conditions are the same as in case of branched networks
once the flows and hydraulic losses have been calculated
for each pipe.
โข Hydraulic calculation
โข The equations used for single pipe calculation are not
sufficient.
โข Additional conditions have to be introduced.
โข Iterative calculation process is needed.
Network Components
29
1.Pipes
2.Pipes fitting
3.Valves
4.Pumps / Compressors
5.Reservoir and tanks
Network Analysis โ Hardy Cross Method
30
โข Pipe/Element/Branch: 12, 23, 36, 16, 34, 65, 45
โข Hydraulic node (junction): 1, 2, 3, 4, 5, 6
โข Loop: 12361, 63456
Network Analysis โ Hardy Cross Method
31
โข It is not acceptable that the outlet of consumption
is a junction
Basic Equations
32
1. Continuity equation ฯ๐ at any node = 0.0
2. Energy equation ฯโ๐๐๐ ๐ around any closed loop = 0.0
For losses โ๐=0.8 ๐๐๐2
๐๐5
๐ = fn(Re, ๐
๐) from Moody Chart
Basic Equations
33
โข In case of using programming, we can't use moody chart
Hazen Williams equation Colebrook equation
โ๐๐ฟ=
๐ ๐๐
๐ท๐
๐ = 1.852
๐ = 4.8704
๐ =10.675
๐ถ๐,
๐ถ = 60 โท 140
๐ถ : is a constant depending on
the pipe age and roughness
(pipe condition)
1
๐= โ2 log
ฮคํ ๐ท
3.7+
2.51
๐ ๐ ๐
โ๐๐ฟ= ๐
๐2
2๐๐
โข Colebrook is a curve fitting
โข 1st equation is solved by
trial & error
โข Colebrook equation is the
most commonly used in the
industrial field
Rough Smooth
Hardy Cross Method
34
1. Assume flow rate at each pipe ๐0, so that:
โข The velocity range between 1 - 3 m/s
โข Satisfying the continuity equation
2. If โ๐ = 0.0 (stop) Impossible
If โ๐ โ 0.0
2. Adjust ๐: ๐ = ๐0 + โ๐
โ๐๐๐ ๐ = ๐๐๐ = ๐ ๐0 + โ๐ ๐
โ๐๐๐ ๐ = ๐ ๐0๐ + ๐โ๐๐0
๐โ1 + โฆ . .
Since ฯโ๐๐๐ ๐ = ฯ๐๐๐ = 0.0 โด โฯ๐ ๐0|๐0|๐โ1 = ฯ๐ ๐|๐0|
๐โ1โ๐
Hardy Cross Method
35
โด โ๐๐0|๐0|๐โ1 =๐๐|๐0|
๐โ1โ๐
โด โ๐ =โ๐ฯ๐0|๐0|
๐โ1
ฯ๐ ๐|๐0|๐โ1
โ๐๐๐ ๐ =0.8 ๐๐๐2
๐๐5= ๐๐๐
where
n=2
๐ =0.8 ๐๐
๐๐5โฆโฆpipe resistance
Hardy Cross Method
36
Note:
Since โ๐๐๐ ๐ won't reach 0.0
Then Hardy Cross Method is used till
ฯ |โ๐| <Small value (Tolerance)
Network Analysis โ Hardy Cross Method
37
โข Pipe/Element/Branch: 12, 23, 36, 16, 34, 65, 45
โข Hydraulic node (junction): 1, 2, 3, 4, 5, 6
โข Loop: 12361, 63456
Kirchhoff's Laws
38
Flow continuity at junction of pipes
The sum of all ingoing and outgoing flows in each node equals
zero (ฯ๐๐= 0).
Head loss continuity at loop of pipes
The sum of all head-losses along pipes that compose a complete
loop equals zero (ฯโ๐ป๐; = 0).
โข Hardy Cross Method
o Method of Balancing Heads
o Method of Balancing Flows
โข Linear Theory
โข Newton Raphson
โข Gradient Algorithm
Hardy CrossMethod of Balancing Heads
39
Step 1
Arbitrary flows are assigned to each pipe; (ฯ๐๐ = 0).
Step 2
Head-loss in each pipe is calculated.
Step 3
The sum of the head-losses along each loop is checked.
Step 4
lf ฯโ๐ป๐ differs from the required accuracy, a flow
correction ๐ฟ๐ is introduced in loop โiโ
Step 5
Correction ๐ฟ๐ is applied in each loop (clockwise or anti-
clockwise). The iteration continues with Step 2
Hardy CrossMethod of Balancing Heads
40
โด โ๐ =โฯ๐๐0|๐0|
๐โ1
ฯ๐ ๐|๐0|๐โ1
๐ฟ๐๐ =โฯ๐=1
๐ โ๐ป๐
2ฯ๐=1๐ |
โ๐ป๐๐๐
|
Dealing with network pressure heads
41
1. Using valves or fittings
โข Valves and fittings are source of energy loss
Dealing with reservoir
42
1. Draw a pipe connecting the tanks, and it's resistance = โ2. This pipe creates a new loop
3. The losses between the tanks = the difference between the
heads of the tanks, and it's sign depends on the direction of
the loop
Example:
โ๐ก๐๐๐(๐ด) = 100 ๐
โ๐ก๐๐๐(๐ต) = 70 ๐
โโ = 100 โ 70 = +30 ๐(+) the flow direction in the
pipe is the same direction
of loop III
Example
43
Example
44
Example
45
L ๐๐0|๐0|๐โ1 ๐๐|๐0|
๐โ1
3-4
4-1
1-3
5(-30)(30)
6(70)(70)
3(35)(35)
5(2)(30)
6(2)(70)
3(2)(35)
28575 1350
L ๐๐0|๐0|๐โ1 ๐๐|๐0|
๐โ1
1-2
2-3
3-1
1(15)(15)
2(-35)(35)
3(-35)(35)
1(2)(15)
2(2)(35)
3(2)(35)
-5900 380
โ๐1 =โ28575
1350= โ21.17 ๐3/๐ โ๐2 =
5900
380= 15.53 ๐3/๐
|โ๐| = 21.17 + 15.5 = 36.67 > Tolerance
Epanet Software
46
Why do we solve network problems ?
47
1. Replacement and renovation of networks
2. Network Design
Consumption of network elements
Flow rate of network
Select Velocity (1-3 m/s)
Diameter
3. Selecting pumps, valves and fittings