Pump Investigation - This is my group lab report PDF

Preview

Summary

This is my group lab report...

Description

Pump Investigation Abstract This experiment examined the efficiency and the pump characteristics of the centrifugal and gear pump. This was achieved by looking at the connection between the pressure and flow rate. Subsequently, the dimensional analysis and the effect of cavitation of a centrifugal pump were also examined. A turbine flow meter was used to measure the flow rate, whilst the inlet and outlet pressures were measured by pressure sensors. Armfield FM50-304 and Armfield FM52 were computer software used during this experiment. For both, centrifugal and gear pumps, the flow rate could vary by using the software. The software recorded the results , which they were then used to help support the hypothesis of this experiment. Furthermore, the data from the experiment proved the effect of cavitation and the effect of different pump speeds on the centrifugal pump but also different pump characteristics of the gear pump. Lastly, the final observation was that the gear pump was less sensitive to cavitation whilst the centrifugal’s pump efficiency increases as the volumetric rate decreases.

Introduction The aims of this experiment were to examine; the flow rate, head and efficiency of a centrifugal pump at different pump speeds, the use of dimensional analysis and effects of cavitation. Also, to examine the different pump characteristics of a gear pump. A centrifugal pump can be defined as a mechanical device used to move fluid with rotors, called impellers. A major problem of centrifugal pumps is cavitation. It reduces the efficiency of the pump and damages the impeller. Cavitation is the development of bubbles in a liquid at low pressures around an impeller.(Crane Site 2014). A gear pump is defined as a positive displacement pump with a very accurate speed control. (Extrusion (second edition) 2014). To achieve maximum efficiency and optimum pump size, it is important to understand the effects of pressure rise varying with flow rate for a given pump. This was investigated by dividing the experiment in two sections. First, the centrifugal pump and cavitation were examined followed by the gear pump.

Figure 1: This diagram shows the correlation between outlet pressure, flow rate, efficiency and power output. (Year 1 Lab Report Booklet 2019/2020)

Methodology The experiment was divided into two sections. The first part of this experiment was to investigate the centrifugal pump whilst the second part was to investigate the gear pump. Firstly, it was made sure that the inlet valve outlet valves were open. After, the FM50 pump was turned on using the ‘on’ button of the software. Subsequently, the pump speed was set at 100% using the pump settings of the software. Then, the maximum flow rate was noted down and after, the gate valve was closed to give a flow rate of 0. Following that, the ‘GO’ icon was pressed and the sensor readings were recorded. Then, the gate valve was slightly opened until the flow rate was approximately 0.10 of the maximum flow rate. After the sensor readings were stabilized the ‘GO’ icon was pressed to record the next result. Thereafter, the flow rate was increased by 0.10 of the maximum flow rate , and after the readings were stabilized the ‘GO’ icon was pressed. This was repeated until the gate valve was fully opened. Lastly, the pump speed was reduced to 0% using the button on the software. The file with the data tables was saved. To continue the investigation of the centrifugal pump, the experiment was repeated with a 75% and a 50% pump speed. The last part of the investigation of the pump was the Cavitation. Firstly, the speed of the pump was set at 80%, due to some safety reasons. Then, it was ensured that the inlet and outlet valves were opened. Afterward, the maximum flow rate was recorded. Subsequently, the inlet valve was slightly closed at approximately 0.10 of the maximum flow. The readings were taken in a similar way as before. This was repeated until the valve was fully closed. Lastly, to prevent the valve from breaking/ exploding, for the last reading it was left partially closed. For the second part of the experiment, the gear pump was investigated. After observing the apparatus, the needle valve was opened. Then, the pump was set at a speed of 80%. After checking if the pump was working, the sensor display was checked. After the pump started working, it was checked that the flow rate was increasing. Then, the ‘go’ icon was selected and all the readings from the sensor started appearing in the results data table. Afterwards, the needle valve was slightly closed which affected the outlet pressure, and the ‘go’ icon was pressed again. After that, the needle valve was again slightly closed until the flow rate was decreased by 1/10 from the previous reading. This was repeated until the valve was fully closed, and each time the readings were recorded. Following that, a similar set of readings and data were taken in an almost identical way, but this time the experiment started with the needle valve being fully open.

Results

Centrifugal Pump Figure 2: Static head Hs vs flow rate- 100% pump speed

Figure 3: Static head Hs against flow rate- 75% pump speed

Figure 4: Static head Hs against flow rate- 50% pump speed

Figure 5: pump characteristics against flow rate- cavitation

Comparing the figures 2,3 and 5 it can be observed that all graphs have a similar shape ( a negative correlation). Also, Figure 2, at 100% pump speed has the bigger maximum flow rate value compared to figures 3 and 4. Furthermore, on Figure 5 it can be seen how the pump behaved under the effect of cavitation. As the test could not be run at 100% pump speed,due to some safety reasons, the comparison between the total head at cavitation and the total head at 100% pump speed is not possible.Lastly, Cavitation can cause major problems to the pump thus it needs to be controlled.

Gear Pump

Figure 6: Gear pump characteristics at 80%

In Figure 6 it can be observed that as the outlet pressure is increasing the efficiency and the flow rate of the pump are decreasing but the input power is increasing. Also, by comparing Figure 1 and figure 6 it can be seen that the theoretical shape of the characteristic curve (figure 1) is very similar with the shape of the curve in figure 6.

Discussion The objectives of this experiment were to examine the pump characteristics of the gear pump, the mutual relationship between the pressure and the flowrate of the centrifugal pump as well as the effect of cavitation. This objective was then supported by the data.

Firstly, for the centrifugal pump, the graphs and curves for all three speeds (figures 2,3 and 4) have a negative correlation. The static head decreases once the flow rate increases, and this shows that the pump speed only has a minimum effect on the flow rate. However higher pump speed will give a higher static head thus the flow rate increases as well. Figure 7,8,9 in the appendix section illustrate the Head-flow coefficient graphs where CH is plotted against CQ. For all the pump speeds, the curves are similar and they show the same relationship. This concludes that the pump speed has no significant relationship with the characteristic curve therefore the curve collapses well onto a single curve when they are non-dimensional. Next, figure 10 shows the relationship between efficiency and flow rate for 100% speed. It shows a negative correlation therefore as the flow rate increases, efficiency decreases.This shows that the efficiency of the pump is affected by the flowrate. Furthermore, figure 6 is a comparison between cavitation and 100% speed. Cavitation is a process when air pockets are exposed to a higher pressure, they will explode and release the excess energy to the surrounding pipe.Therefore when cavitation was carried out, the speed was only set to 80% due to safety reasons. Thus the effect of cavitation could not be compared as maximum speed is not used. For gear pump experiment, figure 6 clearly shows the relation between the pump performance and the outlet pressure. The outlet pressure has a positive correlation with the input power while having a negative correlation with flow rate as well as overall efficiency.

Conclusion In conclusion, all the objectives of this experiment had been achieved. For a centrifugal pump, its efficiency increases as the volumetric flow rate decreases. Therefore to create a more efficient pump, slower flow rate is needed. Cavitation can also cause the efficiency of the pipe to decrease. As for the gear pump, the results obtained provide the same trend as figure 1.We can conclude that the gear pump is less sensitive to cavitation as it is bi-rotational thus fluid can be passed on easily. Thus, it is better to use a gear pump instead of a centrifugal pump.

Appendix

Figures: Figure 7: CHvsCQ for 3 head flow characteristics- 100% pump speed

Figure 8: CHvsCQ 3 head flow characteristics- 75% pump speed

Figure 10: Pump efficiency against flow rate- Centrifugal Pump Figure 9: CHvs CQ for 3 head flow characteristics- 50% pump speed

Tables: Table 1: Flow coefficient (CQ) and head coefficient (CH) for the three head flow characteristics- 100% pump speed

CQ

CH- Static Head Hs

CH- Velocity Head Hv

CH- Elevation Head He

0

0.001998756

0

2.2708E-05

8.75339E-05

0.001885501

9.50865E-06

2.2708E-05

0.000154472

0.001849593

2.96117E-05

2.2708E-05

0.000231707

0.001793335

6.66264E-05

2.2708E-05

0.000314092

0.001709741

0.000122428

2.2708E-05

0.000386179

0.00165278

0.000185073

2.2708E-05

0.000473713

0.001466865

0.000278482

2.2708E-05

0.00054065

0.00133644

0.000362744

2.2708E-05

0.000617886

0.001173166

0.000473788

2.2708E-05

0.000684824

0.001009957

0.000582002

2.2708E-05

Table 2: Flow coefficient (CQ) and head coefficient (CH) for the three head flow characteristics- 75% pump speed

CQ

CH- stati head Hs

CH- Velocity Head Hv

CH- Elevation Head He

0

0.001916399

0

4.03704E-05

6.8654E-05

0.001813594

5.84923E-06

4.03704E-05

0.000130443

0.001781675

2.11157E-05

4.03704E-05

0.000199097

0.001720674

4.9192E-05

4.03704E-05

0.000267751

0.001680439

8.89668E-05

4.03704E-05

0.000336405

0.001599795

0.00014044

4.03704E-05

0.000398193

0.001515084

0.000196768

4.03704E-05

0.000466847

0.001354025

0.000270468

4.03704E-05

0.000535501

0.001258231

0.000355867

4.03704E-05

0.000604155

0.001092941

0.000452964

4.03704E-05

0.000659078

0.000955512

0.000539065

4.03704E-05

Table 3: Flow coefficient (CQ) and head coefficient (CH) for the three head flow characteristics- 50% pump speed

CQ

CH- static head Hs

CH- velocity head Hv

CH- Elevation Head He

0

0.001784335

0

9.08333E-05

6.17886E-05

0.001690587

4.73788E-06

9.08333E-05

0.000123577

0.001637464

1.89515E-05

9.08333E-05

0.000185366

0.001649885

4.26409E-05

9.08333E-05

0.000247154

0.001602976

7.5806E-05

9.08333E-05

0.000308943

0.001515484

0.000118447

9.08333E-05

0.000370732

0.001359265

0.000170564

9.08333E-05

0.00043252

0.001315534

0.000232156

9.08333E-05

0.000494309

0.001181154

0.000303224

9.08333E-05

0.000556097

0.001062439

0.000383768

9.08333E-05

0.000617886

0.000934321

0.000473788

9.08333E-05

0.00064878

0.000903084

0.000522351

9.08333E-05

Table 4: Data gathered during Cavitation -Centrifugal Pump

Table 5: Data gathered during 100% pump speed- Centrifugal pump

Table 6: Data gathered during 75% pump speed- Centrifugal pump

Table 7: Data gathered from 50% pump speed- Centrifugal Pump

Table 8: Data gathered during the gear pump experiment

References Crane Site. (2014). What is pump cavitation . Available: https://blog.craneengineering.net/what-is-pump-cavitation. Last accessed 20/03/20. John R.WagnerJr., Eldridge M. Mount III, Harold F. Giles Jr.. (2014). Gear pump System . In: () Extrusion . 2nd ed. (): William Andrew . 417-424. Useful information on centrifugal pumps.  Available: https://www.michael-smith-engineers.co.uk/resources/useful-info/centrifugal-pumps. Last accessed 25/03/2020. Year 1 Lab Report Booklet 2019/2020 . Chemical and Process Engineering. University of Surrey. Page: 45...