As given in question, we must select the pump which will fit into the situation given in the question, in the same time, I have to consider the reliability of the ranking cycle also. The temperature in this condition is around 30o. The pressure of the system is little high and corrosion resistance. We can consider the pump which can minimise the noise and its thermal conductivity is low. After evaluating the several pipes, we have chosen Polypropylene copolymer form Acu-tech polymer Company. The reason behind choosing this company pipe is it satisfies the entire above requirement. Polypropylene is readily cheaper, corrosion resistance flexible and easily fixed at required position. Its low coefficient of friction will also provide good effect on flow of liquid and ease on the efficiency of the pump.
The selection of internal diameter must be done according the requirement of the system. The flow rate flow the system is 0.233 m/sec (0.000233 m3/sec). The velocity of the pipe should be as high as to inhale air and low enough avoid noise. In this condition the rated capacity is 0.6 m/s to 1.3m/sec. In this condition the dia. can be calculate from the given formula. Taking velocity as 1m/sec
where, D = 17.228 mm
The available diameter of pipe with Acu-tech Company is as follows
Table 1 ID of pipe with flow specified flow rate (Acu-tech)
|
Internal Diameter |
Velocity of Fluid |
|
16.7 mm |
0.725 m/s |
|
21.1 mm |
0.812 m/s |
|
27.0 mm |
1.2 m/s |
From the table it is clear that, the selected diameter will be 21.2 mm.
Now we will have a look on the condenser, to avoid the fouling, we must keep up the velocity, but not too much to ensure that damage may not occur to the condenser. The average velocity for must keep for this kind of condenser is around 1 m/s to 10 m/s (Silowash, 2010). As given in the question the flow rate inside the condenser is 0.233 l/sec and the internal diameter of pipe is 14.23 mm. In this condition, the velocity of water inside the condenser pipe will be 1.447 m/sec. We can see that the velocity is within the specified range. The cross section area of the condenser and other parameter is as follows
Table 2 The condenser parameter
|
Fluid in the condenser |
|
|
Internal Diameter |
0.01423 m |
|
Cross-sectional Area |
0.000159 m^2 |
|
Velocity |
1.447 m/s |
The plotting of system characteristic can be done with the help of little calculation, and some assumption also. The dynamic velocity of water is taken at 20oC to be 1.002 x 10-3, and density of water is taken as 995.7 kg/m3 (David Reay, 2014). The calculation for another parameter is as given below
First, we must calculate Reynold no as given below
We can see that the Reynold number is greater than 2300, which means that there is turbulent flow inside the pipe. Now the next calculation will be finding the Darcy equation value. We have considered absolute roughness of calculation = 0.0015 mm, the relative roughness for the pipe as given below.
For Reynold no greater that 4000, we will use
From the figure, the pipe length is 18.5 m
The major head loss for pipe can be given by formula =
For Reynold no greater than, 4000, we will use
The major head loss for condenser can be given by formula =
The main component with their K value
|
Components |
K-Value |
No of parts |
Total |
|
90o bend |
0.9 |
5 |
4.5 |
|
Shower heads |
1 |
1 |
1 |
|
Globe Valve |
10 |
1 |
10 |
|
Cooling tower inlet |
0.5 |
1 |
0.5 |
|
Strainer |
3.6 |
1 |
3.6 |
|
Total |
19.6 |
||
|
180o bend |
0.2 |
6 |
1.2 |
Figure 1-System characteristic curve
As per given temperature and pressure which is calculated above, we can choose the pump UPA15-90N. This is due to the reason that pump is suitable for both flow which 0.26 l/s to 0.29 l/sec. is the point of intersection which is (0.3 flow rate and head loss 5, which means that the characteristic profile curve is at slight higher than calculated profile, it clearly means that the pump will run at slight lower efficiency.
Figure 2-System curve Total head vs Flow rate
This is due to the reason hat, it depends upon several other factor like, elevation, diameter of piping, length of piping, pressure drops across various bends and fitting, material used for piping, etc. In this condition best efficiency point is being chosen for given situation.
In general, the location of the pipe is kept at vertical side of pipe system and it should be away from strainer, such that efficiency of the strainer is retained.
To know the reason first we have to calculate the (NPSH) which is net positive suction head, The NPSH for availed pump and what is the required NPSH for the system.
The NPSH for available resources is as follows,
The given term hsp is calculated as follows
and hs = 2.5 m (This is required height of the pump below the cooling tower. Hf is denoted for head loss in pipe from intel side of the system
= 0.7936+1.3543+0.6586+0.1537 = 2.9602 m
And finally,
The NPSH available = = 10.3287+2.5-2.9602-0.2350 = 9.6334 m
But from the manual it clear that the minimum requirement for given pump is 850 mm, It means that, we can successfully implement the given pump in the system to avoid the cavitation.
As given in the question,
The find the K value for which the flow rate is to be halved. In this condition the velocity Reynolds no and fiction factor all should be calculated,
|
Pipe |
Condenser result |
|
|
Velocity |
0.3968137 |
0.880503145 |
|
Re |
8395.65911 |
12504.55065 |
|
Friction factor (f) |
0.03249957 |
0.029218623 |
Based on the above factor we must gain calculate the all losses by keeping the K value for strainer in the equation, which is as follows
We know that total head loss
, K = 117.1037 m3/h Ans
Figure 3- Flow rate Vs Total head constant graph
The performance of the pump system definitely varies with time, Most of the time its efficiency is getting reduced, the change in performance may occurs for several reasons, some of the them are as follows;
As per the figure and question given, we have selected PP-R pipe for economic factor as well as easy to handle. The system characteristic is calculated as (0.29, 4.46).
The constant value for f is taken as f = 0.0000015, the graph of flow rate Vs total head is presented for CPVC pipe. The efficiency of the pump which is considered for operation is around 62%.
The selection of pump was “UPA15-90N ” and selected rpm to obtain best efficiency point is 1450. The BEP point selected is 396 kg/min at total head around 70 m is calculated.
The explanation for difference in actual BEP and selected BEP is given as a fourth point. We have tried to find the reason that, why suction is always at high pressure, so that cavitation can be avoided.
The value of K was calculated based on affinity equation and BEP data. The graph for flow rate vs total head has shown which has constant line after initial fluctuation.
References
Anon, 2010, Material Selection using CES edupack, Granta Design, pp, 1-57,
Bachus, A, C, 2006, Know and Understand Centrifugal Pumps, 1st ed, Oxford: Elsevier,
Cengel, Y, 2017, Fluid Mechanics, 3rd ed, New York: Mc Graw Hill,
Chaurette, J, 2008, Pump system analysis and sizing, 6th ed, New York: Fluid Design Ink,
Crawford, J, 2016, Marine and Offshore Pumping and Piping Systems, 6th ed, London: Butterworth,
David Reay, R, M, P, K, 2014, Heat Pipes: Theory, Design and Applications, 6th ed, Amestradam: Elsevier,
Guha, H, a, 2009, The design of a test rig and study of the performance and efficiency of a Tesla disc turbine, Journal of Power and Energy, 1(1), pp, 451-455,
Gülich, J, F, 2014, Centrifugal Pumps, 3rd ed, New York: Springer,
Robert Jacobs, R, C, 2013, Operations and Supply Chain Management, 14th ed, New York: McGraw-Hill Higher Education,
Silowash, B, 2010, Piping Systems Manual, 2nd ed, New York: Mc Graw Hill,
Skousen, P, L, 2011, Valve Handbook 3rd Edition, 3rd ed, New York: Mc Graw Hill,
Spellman, F, R, 2017, Water and Wastewater Conveyance: Pumping, Hydraulics, Piping, and Valves, 2nd ed, Boca raton: CRC publisher,
Thomas, C, E, 2015, Process Technology Equipment and Systems, 4th ed, Stanford: Cengage Learning,
White, F, 2013, Fluid Mechanics, 7th ed, New York: Mc Graw Hill
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