Lab 1 Series Parallel Pumps

SEGi University

Series & Parallel Pumps by Sasiskala Regal A/P Selvaraja (SCM 015 722) Lab Partners: 1) Melvin Tan 2) Balvinder Singh 3) Manimegalai 4) Wong Kai Jun 5) Mukundhan

ECE2332 Chemical Engineering Practices Submitted: 24th January 2013 Supervisor: Ms Chan Yi Shee

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1 Abstract Centrifugal pumps assembled in series or in parallel are used in a wide range of applications in the processing industry. Therefore, it is vital for students to know the performance characteristics of centrifugal pumps in series and parallel operation. This can be determined via several relationships such as Total Head versus Flowrate, Power Input versus Flowrate or Efficiency versus Flowrate. In this experiment, the technique used to determine the characteristics of the pump is by comparing the pressure difference with the flowrate. Hence, the main objective of this experiment is to develop pump characteristics curves for a single pump, two pumps in series, and two pumps in parallel by measuring pressure difference(P) and flowrate (Q) using the experimental apparatus. The assembly is constructed in a way that the valves can be adjusted accordingly to activate an individual single pump, series pump and parallel pump. Pumps in series produce twice the head for a given flow rate whereas pumps in parallel are expected to have twice the flow rate of single pump for a given head.

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2 Introductions

Pumps are machines that used to transfer liquid from a location of low elevation to a higher elevation. There are various types of pumps and they are classified in two major categories: (1) dynamic or kinetic and (2) positive displacement. Dynamic or kinetic are types of pumps in which energy is continuously added to the fluid to increase its velocity. Centrifugal pumps falls under this category. The principle used for centrifugal pump is the centrifugal force in the form of dynamic pressure which is generated by rotary motion of one or more rotating wheels called the impellers. Since the 1940's, the centrifugal pump has become the pump of choice for many applications. Many different industries employ centrifugal pumps for varied uses according to the industry. For example: cryogenics use centrifugal pumps in extreme cold applications; dairy farmers use centrifugal pumps to keep their product at the proper temperatures, hot and cold; electric utility companies use centrifugal pumps, or turbines, to produce energy; food service, construction, distillery, and automotive companies are a few more examples of industries that employee centrifugal pumps for their many applications.

A single pump often cannot deliver the flow rate or head necessary for a particular system. However, two pumps or more can be combined in series to increase the height to which the fluid can be pumped at a given flowrate, or combined in parallel to increase the flow rate associated with a given value of head. Applying parallel pumps in a system can be a costeffective solution when capacity requirements call for an unrealistically large pump and motor. Using parallel pumps can also reduce current surge during motor start up by staging two or more smaller pumps. This is a problem which may otherwise require expensive equipment such as electronic soft starters or part winding type motors. One of the most notable benefits of parallel pumps is the redundancy built into the system. If one pump were to fail in a two pump system, the second pump would not only continue to operate, but would also increase its output.

In theory, if two pumps are combined in series, the pumping system will produce twice the head for a given flow rate. Similarly, if two pumps are combined in parallel, the pumping system is expected to have twice the flow rate of single pump for a given head.

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Pressure is an Indication of Resistance to Flow The kinetic energy of a liquid coming out of an impeller is harnessed by creating a resistance to the flow. The first resistance is created by the pump volute (casing) which catches the liquid and slows it down. When the liquid slows down in the pump casing some of the kinetic energy is converted to pressure energy. It is the resistance to the pump's flow that is read on a pressure gauge attached to the discharge line. Head In newtonian fluids (non-viscous liquids like water or gasoline) we use the term head to measure the kinetic energy which a pump creates. Head is a measurement of the height of a liquid column which the pump could create resulting from the kinetic energy the pump gives to the liquid (imagine a pipe shooting a jet of water straight up into the air, the height the water goes up would be the head). The main reason for using head instead of pressure to measure a centrifugal pump's energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not change. So we can always describe a pump's performance on any newtonian fluid, whether it's heavy (sulfuric acid) or light (gasoline) by using the term head. If the discharge of a centrifugal pump is pointed straight up into the air the fluid will pumped to a certain height - or head - called the shut off head. Relationship of Head to Pressure Since the unit of head is a shortened version of the unit of flow energy (“ft” versus “ftlbf/lbm”), and since flow energy is equal to the fluid’s pressure multiplied by its specific volume (FE = Pν), the pressure equivalent to a particular head can be determined by dividing the head by the fluid specific volume. Since specific volume is the reciprocal of density, dividing the head by the specific volume is equivalent to multiplying the head by the density of the fluid: Pressure = head/specific volume = head(ft-lbf/lbm)× ρ(lbm/ft³) Unit conversion: lbf/in²=psi 1 kgf / cm² = 14.2233433 psi

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The "Performance Characteristics" of a pump at a fixed speed are represented by the following graphical relationship: Pressure Difference (ΔP) versus Discharge (Q) In this experiment pressure gauge is attached to the discharge line to measure the pressure. The difference in pressure is proportional to the total head. A rotameter is used to measure the flowrate. The rotameter reads flow rate directly in litre per minute for a fluid having a specific gravity of 1.0. If water is used, flow can be read directly from the rotameter. The rotameter reading is obtained from the position of the widest part of the float.

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3 Experimental methods and materials

Figure 3(a) Equipment Assembly Series Pumps

Parallel Pumps P1

P1

P2 P2

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3.1 Specifications of the unit a) Pumps 2 units of Horizontal Single Stage Centrifugal Pump(P1)and(P2) Flowrate: 20-90 LPM Head: 20.7-15m Max Head: 22m

b) Circulation Tank Transparent acrylic water tank is provided to supply water to P1 and P2.

c) Flowrate and pump head All gauges and meters are provided in a way for easy viewing and data collection.

d) Process piping The process piping is made of industrial PVC pipes. Valves used are nonferrous to minimize rust and corrosion.

3.2 Overall Dimensions Height: 700mm Width: 650mm Depth: 1100mm

3.3 General Requirements Electrical: 240 VAC, 1-phase, 50Hz Water: Clean tap water

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3.4 Experimental Methods The apparatus is set up as shown in figure 3(a) above. 1. The tank is filled with water until the end of the pipe output is submerged with water. 2. The main power supply is switched on. Experiment1: Single Pump Operation 1. Valve 1&4 are fully opened and valve 2&3 are fully closed to activate a single pump. 2. Valve 5 is opened until the flowrate reaches 20 LPM. 3. The pressure reading observed from the pressure gauge 1&2 is recorded using digital and analogue techniques. 4. Steps 1, 2 and 3 are repeated to obtain seven different flowrates and pressures.

Experiment2: Series Pump Operation 1. Valve 1&3 are fully opened and valve 2&4 are fully closed to activate a series pump. 2. Valve 5 is opened until the flowrate reaches 20 LPM. 3. The pressure reading observed from pressure gauge1, 3&4 is recorded using digital and analogue techniques. 4. Steps 1, 2 and 3 are repeated to obtain seven different flowrates and pressures.

Experiment3: Parallel Pump Operation 1. Valve 1, 2&4 are fully opened and valve 3 is fully closed to activate a series pump. 2. Valve 5 is opened until the flowrate reaches 20 LPM. 3. The pressure reading observed from the pressure gauge1, 2&4 is recorded using digital and analogue techniques. 4. Steps 1, 2 and 3 are repeated to obtain seven different flowrates and pressures.

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4 Results and analysis Table 4.1 Single Pump Operation Rotameter (LPM) 20 30 40 50 60 70 80 90

Pressure Gauge 1 (Pl1) bar kgf/cm² 1.04 0 1.04 0 1.03 0 1.03 0 1.02 0 1.01 0 1.01 0 0.99 0

Pressure Gauge 2 (Pl2) bar kgf/cm² 3.06 2.15 3.00 2.01 2.94 2.00 2.88 1.90 2.81 1.80 2.73 1.80 2.63 1.60 2.51 1.50

Pressure Difference, (P2-P1) bar kgf/cm² 2.02 2.15 1.96 2.01 1.91 2.00 1.85 1.90 1.79 1.80 1.72 1.80 1.62 1.60 1.52 1.50

Graph 4.1 Single Pump Operations

Graph of Pressure Difference(P2-P1) against Flowrate 2.5

ΔP(P2-P1)

2

P2-P1(bar)

1.5

1

P2-P1(kgf/cm²)

0.5

0 0

20

40

60

80

100

Flow rate,Q(LPM)

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Table 4.2 Series Pump Operation Rotameter (LPM)

20 30 40 50 60 70 80 90

Pressure Gauge 1 (Pl1) bar kgf/cm² 1.04 0 1.03 0 1.03 0 1.02 0 1.01 0 1.01 0 1.00 0 0.99 0





Pressure Gauge 4 (Pl4)

Pressure Difference, (P2-P1)

Pressure Difference, (P4-P1)

bar kgf/cm² 2.00 2.00 2.00 1.95 1.90 1.90 1.85 1.84 1.82 1.77 1.79 1.70 1.63 1.63 1.58 1.52

bar kgf/cm² 2.10 1.96 2.00 1.90 2.00 1.86 1.90 1.79 1.84 1.73 1.80 1.66 1.65 1.58 1.60 1.49

Table 4.3 Parallel Pump Operation Rotameter (LPM)

40 60 80 100 120 140 160 180

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Pressure Gauge 1 (Pl1) bar 1.03 1.03 1.02 1.02 1.01 1.00 0.99 0.98

kgf/cm² 0 0 0 0 0 0 0 0

Pressure Gauge 2 (Pl2) bar 3.03 2.98 2.92 2.86 2.78 2.70 2.62 2.50

kgf/cm² 2.00 2.00 1.90 1.85 1.82 1.79 1.63 1.58

bar 2.99 2.93 2.88 2.81 2.74 2.66 2.57 2.47

kgf/cm² 2.10 2.00 2.00 1.90 1.84 1.80 1.65 1.60

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Graph 4.2 (a) Series Pump Operation


ΔP(P3-P1)

2

P3-P1(bar)

1.5

1

P3-P1(kgf/cm²)

0.5

0 20

30

40

50

60

70

80

90

Flow rate,Q(LPM)

Graph 4.2 (b) Series Pump Operation

Graph of Pressure Difference(P4-P1) against Flowrate 4.5 4

ΔP(P4-P1)

3.5 3

P4-P1(bar)

2.5 2

P4-P1(kgf/cm²)

1.5 1 0.5 0 20

30

40

50

60

70

80

90

Flow rate,Q(LPM)

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Graph 4.3(a) Parallel Pump Operation


ΔP(P2-P1)

2

1.5

P2-P1(bar) 1

P2-P1(kgf/cm²) 0.5

0 40

60

80

100

120

140

160

180

Flow rate,Q(LPM)

Graph 4.3(b) Parallel Pump Operation


ΔP(P4-P1)

2

1.5

P4-P1(bar) 1

P4-P1(kgf/cm²) 0.5

0 40

60

80

100

120

140

160

180

Flow rate,Q(LPM)

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5 Discussion Based on the graphs obtained it can be clearly seen that pressure drop and flow rate are dependent on each other. The higher the flowrate through a restriction, such as a valve, the greater the pressure drop. Conversely, the lower the flow rate, the lower the pressure drops. In series arrangement, each pump handles the same flow rate, but the total pressure difference produced by the combination of pumps will be additive. Since each pump generates a pressure difference corresponding to a flow Q, when configured in series, the total pressure difference developed is PT = P1 + P2, where P1, P2 are the pressure difference developed by the pumps in series at the common flow rate Q. In this experiment, PT = (P3-P1) + (P4-P1) at corresponding Q Based on table 4.1 and 4.2, the pressure difference produced by the series pump operation is twice the pressure difference of the single pump at the same flowrate. For example, at flowrate of 20LPM, the total pressure difference of single pump is 2.02bar but the total pressure difference for series pump is 5.93bar which can be said twice of that single pump.In short, centrifugal pumps in series are used to overcome larger system head loss than one pump can handle alone.

For pumps configured in parallel, the flow rate Q is split between the pumps at the inlet into Q1 and Q2 and after passing through the pumps on the discharge side, the flows recombine back to the flow rate of Q. Each pump develops the same pressure difference at the corresponding capacity. In this experiment, Q= Q (pump1) + Q(pump2) Based on table 4.1 and 4.3, the flowrate of parallel pump is doubled compare to that of single pump provided the pressure difference is constant. For example, the flowrate of single pump operation is 90LPM when the pressure difference is 1.52bar. At the same pressure difference (1.52bar), the flowrate of parallel pump operation is 180LPM .In short, centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone.

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Accuracy of Reading When air enters a pump it sometimes gets trapped in the volute, this reduces the capacity, creates vibration and noise. Vibration causes difficulty in accurate reading of the gauge, due to pointer oscillation. Thus, the graphs obtained does not produce smooth lines/curves.Besides that, if the pump has been installed for some period of time, any pump wear, such as opening up of the impeller wearing ring clearance, change (decrease) the pump performance. The kinds of loss of centrifugal pumps can be differentiated in: Internal losses: -Wheel friction losses by friction at the external walls of the wheel. External or mechanical losses: -Sliding surface losses by bearing friction or seal friction. - Air friction at the clutches. The friction loss can be calculated using Bernoulli’s equation:

 p 2 V22   p1 V12     z 2      z1   H P  H L  g 2 g   g 2 g  H p is the pressure head produced by the pump H L is the energy loss due to friction and pipe fittings. V1 = V2 if the pipe diameters are equal at the inlet and outlet sections.

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6 Conclusion When two pumps are assembled in series the total pressure difference produced by the combination of pumps will be additive .In other words, pressure difference is doubled at a given flowrate. However, pumps combined in parallel doubles the flowrate that of a single pump for a given head. Therefore, entrifugal pumps in series can overcome larger system head loss than one pump can handle alone.However, centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone.

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7 References

http://www.slideshare.net/physics101/centrifugal-pumps-in-series-and-parallel-15147342 http://ebookbrowse.com/lab-3-pumps-in-series-and-parallel-pdf-d70839148 http://ptumech.loremate.com/fluid-machinery/node/16 http://www.thomasnet.com/about/centrifugal-pumps-64322407.html http://www.pricepump.com/pumpschool/psles.html http://www.ashraebistate.org/sites/all/files/events/Pump_Fundamentals_Tech_Session.pdf http://wea-inc.com/pdf/parrallel.pdf http://www.wcnoc.com/GFES/Study%20for%20test/FluidsCh3.pdf http://www.cheresources.com/invision/blog/4/entry-322-multiple-centrifugal-pumps-in-series-andparallel/

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Lab 1 Series Parallel Pumps

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