SUMMARY

CENTRIFUGAL COMPRESSOR

1.0SUMMARY

Compressor is used to take a definite quantity of fluid which is usually a gas or air and deliver it at a required pressure. In other words, the job of a compressor is to increase the pressure of the incoming fluid. Choice of centrifugal compressors is determined by their characteristics curves based on the pressure required and the amount of input of mechanical work that is power input. From the result that we obtain, the highest efficiency of compressor was running with the speed 10 000 rpm. The efficiency at speed 10000 rpm higher than others and it only produced lower flow rate than other. The lowest was at speed 10000 rpm curve that in unstable condition. For all the speeds measurement, the inlet temperature values were almost similar. The most important are the outlet temperature values. While doing the experiment, the butterfly valve is very difficult to handle. The computer that we used also have problem because the software that been used sometimes detect faster sometimes slower so the value that we need is not accurate. For the conclusion, the highest was at speed 10000 rpm but it produce lower flow rate than other speeds. 2.0OBJECTIVE;To study the characteristics curves of a centrifugal compressor.

3.0INTRODUCTION

Compressor is a part of a system that used conservation of energy to change the energy from one to another. It is used in many mechanical systems such as power plant, refrigerator and jet engines to increase the pressure of the fluid. Several types of compressor are used such as axial compressor and centrifugal compressor. A compressor is called axial compressor when the air is turned perpendicular to the axis of rotation from left to right, whereas it is called centrifugal compressor as the flow through the compressor is turned perpendicular to the axis of rotation spin around the shaft. In general, the compressor consists of two main parts; blades and shaft. The fluid can be air or gas flows through the moving and fixed blades. The work input to the shaft is transferred by the moving blades to the air. A centrifugal compressor is made up of an impeller with a series of curved radial vanes. Air is drawn in near the hub, called the impeller eye and is spin round at high speed by the vanes on the impeller as the impeller rotates at high rotational speed. The static pressure of the air increases from the eye to the tip of the impeller. Centrifugal compressors or blowers are used for a wide range in engineering and there is no basic difference in the design for any of the different applications. [1]

Figure 1; a centrifugal compressor [2]Centrifugal compressors are widely being used for many applications such as in pipeline transport of natural gas to move the gas from the production site to the consumer, in oil refineries, natural gas processing plants, petrochemical and chemical plants, in air separation plants to manufacture purified end product gases, in refrigeration and air conditioner equipment refrigerant cycles and also in industry and manufacturing to supply compressed air for all types of pneumatic tools. [3]4.0THEORY

The performance of the compressor is characterized by the pressure ratio across the compressor (CPR), the rotational speed of the shaft necessary to produce the pressure increase and an efficiency factor that indicates how much additional work is required relative to an ideal compressor. [1]

P2, T2 (exit)

Q out

Win

P1, T1 (enter)

Figure 2: schematic diagram of typical compressor

The increase of the pressure is measured by CPR. This is the ratio of the air total pressure, pt exiting the compressor to the air pressure flowing in the compressor. This CPR number must be always greater than 1.0. [1]

CPR = Pt2 / Pt1 or P exit / P enterIn order to produce the increase in pressure, the compressor must perform work on the flow. The shaft turns the blades at a high rate of speed. Several stages are usually employed to produce a high CPR, with each stage producing a small pressure increase. In the centrifugal compressor, additional pressure increase is obtained from turning the flow radically, radiating from or converging to a common center. Since no external heat is being added from the compressor during the pressure increase, the process is isentropic. The total temperature ratio across the compressor is related to the pressure ratio by the isentropic flow equations. [1]

Total temperature ratio=Tt2=Pt2-1Tt1

Pt1 Where, is the ratio of specific heats.

Work must be done to turn the shaft on which the compressor is mounted. From the conservation of energy, the compressor work per mass of airflow CW is equal to the change in specific enthalpy, ht of the flow from the entrance to the exit of the compressor.

CW=ht2-ht1

The term specific means per mass of airflow. The enthalpy at the entrance and exit is then can be related to the total temperature, Tt by the equation;

CW=Cp2Tt2-Cp1Tt1

Where Cpi is the specific heat at each particular point.

Performing rearrangement, the equation of compressor work per mass of airflow can be written;

CW=CpTt1 (CPR(-1)/ -1)

CThis equation relates the work required to turn the compressor to the compressor pressure ratio, the incoming total temperature, some properties of gas and an efficiency factor, C. The efficiency factor is included to account for the actual performance of the compressor as opposed to the ideal isentropic performance of the compressor. In an ideal performance, th value of the efficiency would be 1.0. However, in reality, the value is always less than 1.0. So, additional work is needed to overcome the inefficiency of the compressor to produce a preferred CPR. The work is provided by the power turbine which is connected to the compressor by the central shaft. It is worth to note that the CPR is related to the total temperature ratio across the compressor. Since the CPR is always greater than 1.0 and the value of the ratio of specific heats is about 1.4 for air, the total temperature ratio is also greater than 1.0. It means air heats up as it passes through the compressor. The efficiency of a compressor can also be improved by carrying out the compression in several stages. This is called multistage compression. [1]

Volumetric flow rate, Q= d2 2(100) p (3600)4

Where;

Diameter, d=0.044m

=1.21 kg/m3Both at 20C and 1013 mbar and the pressure drop p at the nozzle in mbar.

=Phyd 100%

PelWhere Phyd can be calculated from the total pressure head and the flow rate.

Phyd=100(dp1 + dp2) Q3600

5.0METHODOLOGY

5.1Apparatus

Two stage compressor

Transparent intake

Shaped inlet for good flow

A protective plate

Transparent outlet

Butterfly valve

Pressure measuring point

Electric motor in the housing

A speed adjuster

An optical sensor

Housings

5.2Procedures

1. The windows and the analysis software is being start.2. The actual measure values is being display by choosing the command system diagram on the menu 3. The measure data has been record in an ASCII file. 4. Every time the save measurement button is click is will be save into the previously into the ASCII file. The data that have been recorded consists of

(a) Time

(b) Volumetric flow rate

(c) Speed n of the compressor

(d) Electrical power

(e) Efficiency

(f) Differential pressure 1st stage dp1(g) Differential pressure 2nd stage dp2(h) Compressor total pressure

(i) Inlet temperature Tin (j) Outlet temperature Tout5. The compressor characteristic curves is being recorded(a) The interface module is being switch on

(b) The power meter at the switch on the rear is being switch on

(c) The butterfly valve is being close completely

(d) The speed of the compressor is being set by the speed adjuster

(e) The butterfly valve is being opened a little and the flow rate for the first measurement point is being set

(f) Whenever the flow rate is being dropped the speed need to be adjust(g) The measurement is being recorded when it is in steady state

(h) The process is being repeat until the butterfly valve is fully open

6. The pressure-flow rate characteristic curve was recorded for 4 different speeds which are 10000 rpm, 11000 rpm, 12000 rpm and 13000 rpm.

6.0RESULTS Table 1: run 1 at speed 10000rpmFlow in m3/hTin in degCTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %dptotal mbarPhyd WPel W

0.000034.277339.648431.298819.677799.60940.000050.97660.00000.0000

0.000034.277339.648428.222719.140691.79690.000047.36330.00000.0000

14.288134.277339.648424.365218.212993.75007.710442.578116.8989219.1689

30.121934.277339.746124.755918.6523136.718811.415343.408236.3205318.1753

51.736134.277340.332023.291018.8477181.640614.912042.138760.5581406.1033

72.699434.375040.625022.070319.0918222.656317.315741.162183.1239480.0491

86.387534.375040.722721.044919.2871240.234419.265540.332096.7829502.3635

95.610534.375040.820319.726619.4336246.093820.972839.1602104.0034495.8975

100.919734.375040.820319.189519.5313244.140622.426638.7207108.5467484.0088

105.426834.375040.820319.384819.8242255.859422.690539.2090114.8244506.0469

Table 2: run 2 at speed 11000rpmFlow in m3/hTin in degCTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %dptotal mbarPhyd WPel W

0.000033.496136.523434.130919.5801117.18750.000053.711000

0.000033.496136.621131.543019.3848117.18750.000050.927800

12.600933.496136.718830.078118.9453138.67194.782049.023417.15943358.8311

31.592233.496136.914129.199219.3359183.59389.242448.535142.59245460.8383

57.547933.496137.695328.222719.7754263.671911.989147.998176.72747639.9747

82.629733.691438.085926.269520.5566324.218814.552846.8261107.4785738.5399

94.776533.593838.281324.365220.2637332.031316.067144.6289117.4936731.2687

103.032933.593838.281323.095720.5078332.031317.677243.6035124.7943705.9614

109.438433.593838.378922.558620.4102333.984418.577542.9688130.6233703.1258

113.007533.593838.378922.363320.4102335.937519.071842.7735134.2701704.0232

Flow in m3/hTin in degCTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %dptotal mbarPhyd WPel W

0.000033.789137.695338.427721.3379162.10940.000059.76560.00000.0000

0.000033.789137.695336.425820.8984166.01560.000057.32420.00000.0000

14.288133.691437.793036.132821.1914199.21884.221857.324222.7515538.9004

38.101633.886738.183636.572321.8750300.78137.697358.447361.8592803.6499

65.993933.886738.964833.642622.3145367.187511.140455.9570102.5783920.7809

87.819833.886739.453130.615222.5098410.156313.387953.1250129.5952968.0043

101.926233.984439.648429.101622.7539437.500014.725251.8555146.8175997.0493

112.302729.882839.843827.294922.2656439.453115.805649.5605154.6051978.1686

117.533533.886739.843826.513722.3633439.453116.614348.8770159.5744960.4641

121.425433.886739.843826.171922.7539435.546917.620948.9258165.0231936.5193

Table 3: run 3 at speed 12000rpmTable 4: run 4 at speed 13000rpm

Flow in m3/hTin in degCTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %dptotal mbarPhyd WPel W

0.000033.984438.671947.216823.9258222.65630.000071.14260.00000.0000

0.000033.984438.671944.628923.3887226.56250.000068.01760.00000.0000

19.637133.984438.769540.136722.3633248.04694.917962.500034.0922693.2314

37.197833.984439.062541.943423.5352347.65636.994965.478567.6572967.2345

71.122234.082040.039142.382825.3418521.48449.600667.7246133.79791393.6394

91.859634.082040.429736.523424.7559542.968811.633961.2793156.36361344.0351

112.201734.179740.820333.496124.6582566.406313.568558.1543181.25031335.8214

121.518834.082040.918032.177724.7070572.265614.573556.8848192.01581317.5681

127.796634.179740.918030.957024.6582568.359415.401255.6152197.42881281.9036

130.170734.179741.015630.468824.8047566.406315.834955.2734199.86061262.1493

6.1 The pressure-flow rate characteristic curve, efficiency curve and temperature curve for different speeds

Figure 3; graph of Efficiency vs. Flowrate

Figure 4; graph of dP Total vs. Flowrate

Figure 5; graph of Temperature in vs. Flowrate

Figure 6; graph of Temperature out vs. Flowrate

6.2

The determination of maximum efficiency and the flow rate for each speed.

The maximum efficiency and the Flow rate for each speed are:

Speed 10,000 rpm: Maximum efficiency: 22.6905 Maximum Flowrate: 105.4268Speed 11,000 rpm: Maximum efficiency: 19.0718 Maximum Flowrate: 113.0075Speed 12,000 rpm: Maximum efficiency: 17.6209 Maximum Flowrate: 121.4254Speed 13,000 rpm: Maximum efficiency: 15.8349 Maximum Flowrate: 130.17076.3Sample calculation;For reading 10,000 rpm at 14.2881 m3/h Flowrate.Total dP, p=dP1+dP2

=24.3652+18.2129

=42.5781 mbar

Volumetric flow rate, Q (theoretical)= d2 2(100) p (3600)4

= (0.044m)2 2(100) (6.1523) (3600)

4 1.21 kg/m3

Q=174.5576 m3/hrPhyd (theoretically)=100(dp1 + dp2) Q3600

=100(42.5781) (174.5576 m3/hr)

3600

=206.4536 WPhyd (from exp)=100(dp1 + dp2) Q3600

=100(42.5781) (14.2881m3/hr)

3600

=16.8989 WPel =Phyd 100%

=(16.8989 m3/hr) x 100%

(7.7104 m3/hr)

=219.1702 W7.0DISCUSSION

This experiment is carried out to study the characteristics of a centrifugal compressor. The experiment was performed in varying speed at appoximately 10000rpm, 11000rpm, 12000rpm and 13000rpm.

During the experiment five parameters has been recorded. That are flow rate in unit m3/hr, temperature in unit C, pressure in unit mbar, power in unit Watt and also percentage of efficiency.

From the result that we obtain, we observe that the highest efficiency of compressor when running with the speed 10 000 rpm. Follow by the speed 11 000 rpm, 12 000rpm and lastly 13 000.This is because at this speed, the compressor running better than others speed condition. At his speed also give better performance than the others.

By referring the graphs efficiency vs. flow rate, we can see that the efficiency at speed 10000 rpm higher than others and it only produced lower flow rate than other. Meanwhile at speed 13000 rpm, the curve show that it is in stable condition. Even it efficiency lower but it can produce higher flow rate. For speed 11000 and 12000 rpm, both of them are in the medium condition.

By referring the graphs total pressure vs. flow rate, the speed 13000 rpm required more pressure than other. It also in the stable condition and produce more flow rate than other. The lowest was at speed 10000 rpm curve that in unstable condition.By referring the graphs temperature of inlet and outlet vs. flow rate; we also observe that the highest outlet temperature is at speed 13 000 rpm and the lowest at 10000 rpm speed. This is because of the compressor produce more energy at the high speed than the inlet temperature. For all the speeds measurement, the inlet temperature values were almost similar .The most important are the outlet temperature values. Our opinion is the speed 10000 rpm is the stable condition to running the compressor. To produce more flow rate and high temperature the more speed is much better. But, the compressor cannot be operates at high speed to avoid the compressor from damage.While doing the experiment we notice that many problems have occurred. The problem is mostly because of the equipment. We notice that the butterfly valve is very difficult to handle. Whenever we increase the angle of the butterfly valve the speed of the equipment will decrease most of the time so it is difficult to maintain the average speed. The butterfly valve itself have problem because the holder of the valve is loose so it is impossible to control.

The computer that we used also have problem because the software that been used sometimes detect faster sometimes slower so the value that we need is not accurate.

8.0RECOMMENDATIONDuring do the experiment, we face some problem while handling the equipment. The problem is when we handle the butterfly valve. When we increase the speed of the butterfly valve, it becomes hard to adjust. It was also not tight enough so we cannot set the valve accurately. So it needs to be tight so it will not move when we adjust it.

The computer needs to be upgrade into a newer model because the capacity of the ram is low so sometimes the computer will be lagging for a number of times. 9.0CONCLUSION

The objective of this experiment is to study the characteristics of a centrifugal compressor. By doing this experiments, now we know how to operate the centrifugal compressor properly at different speed. From the experiment that has been performed, it can be said that the experiment was successfully done at different speed to get the most efficient speed of the centrifugal compressor and we learn and study the characteristic curves of a centrifugal compressor for different speed which were at 10000, 11000, 12000, and 13000 rpm. And from our observation, we determined that the stable condition to operated the compressor at the speed 10000 rpm. This is because of its efficiency better than others.So, we know which speed give best efficiency. Of course at speed 10000 rpm but it produce lower flow rate than other speeds. At this speed, it also produces lowest outlet temperature than others. This condition suitable for operation and avoid the compressor from any damage.10.0REFERENCES

1. Miss Suhaini Mamat, the Experiment Manual Lab (Experiment 5: Centrifugal Compressor). 2. http://www.fscconline.com/%22Passing%20Gas%22article/Centrifugal%20Compressor.gif

3. http://en.wikipedia.org/wiki/Centrifugal_compressor

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_1295698666.xlsefficiency vs. frate

0000

0000

7.71044206624.78203535084.22183513644.9178652763

11.41525840769.24238491067.69728708276.9949140549

14.911995887811.989141464211.14036369329.6006116867

17.315710067714.552836418213.387870788611.633893013

19.265502929716.067087173514.72519493113.5684518814

20.972753524817.677209854115.805569648714.5734977722

22.42660713218.577510833716.614299774215.4012174606

22.690456390419.071832656917.620901107815.8349399567

10000 rpm

11000 rpm

12000 rpm

13000 rpm

Flowrate (m3/hr)

Efficiency (%)

Efficiency vs. Flowrate

dp total vs frate

50.976562550.976562550.976562550.9765625

47.3632812547.3632812547.3632812547.36328125

42.57812542.57812542.57812542.578125

43.40820312543.40820312543.40820312543.408203125

42.13867187542.13867187542.13867187542.138671875

41.16210937541.16210937541.16210937541.162109375

40.3320312540.3320312540.3320312540.33203125

39.1601562539.1601562539.1601562539.16015625

38.72070312538.72070312538.72070312538.720703125

39.20898437539.20898437539.20898437539.208984375

10000 rpm

11000 rpm

12000 rpm

13000 rpm

Flowrate (m3/hr)

dP Total (mbar)

dP Total vs. Flowrate

T in vs. Flowrate

34.2773437533.4960937533.789062533.984375

34.2773437533.4960937533.789062533.984375

34.2773437533.4960937533.6914062533.984375

34.2773437533.4960937533.8867187533.984375

34.2773437533.4960937533.8867187534.08203125

34.37533.6914062533.8867187534.08203125

34.37533.5937533.98437534.1796875

34.37533.5937529.882812534.08203125

34.37533.5937533.8867187534.1796875

34.37533.5937533.8867187534.1796875

10000 rpm

11000 rpm

12000 rpm

13000 rpm

Flowrate (m3/hr)

Temperature (C)

Temperature In vs. Flowrate

Chart4

39.648437536.523437537.695312538.671875

39.648437536.6210937537.695312538.671875

39.648437536.7187537.7929687538.76953125

39.7460937536.914062538.1835937539.0625

40.3320312537.695312538.9648437540.0390625

40.62538.085937539.45312540.4296875

40.7226562538.2812539.648437540.8203125

40.820312538.2812539.8437540.91796875

40.820312538.3789062539.8437540.91796875

40.820312538.3789062539.8437541.015625

10000 rpm

11000 rpm

12000 rpm

13000 rpm

Flowrate (m3/hr)

Temperature Out (C)

Temperature Out vs. Flowrate

10000 rpm

Flow in m3/hTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %

0.000034.277339.648431.298819.677799.60940.000050.97660.00000.0000

0.000034.277339.648428.222719.140691.79690.000047.36330.00000.0000

14.288134.277339.648424.365218.212993.75007.710442.578116.8989219.1689

30.121934.277339.746124.755918.6523136.718811.415343.408236.3205318.1753

51.736134.277340.332023.291018.8477181.640614.912042.138760.5581406.1033

72.699434.375040.625022.070319.0918222.656317.315741.162183.1239480.0491

86.387534.375040.722721.044919.2871240.234419.265540.332096.7829502.3635

95.610534.375040.820319.726619.4336246.093820.972839.1602104.0034495.8975

100.919734.375040.820319.189519.5313244.140622.426638.7207108.5467484.0088

105.426834.375040.820319.384819.8242255.859422.690539.2090114.8244506.0469

11000 rpm

Flow in m3/hTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %

0.000033.496136.523434.130919.5801117.18750.000053.711000

0.000033.496136.621131.543019.3848117.18750.000050.927800

12.600933.496136.718830.078118.9453138.67194.782049.023417.1594294569358.8310875635

31.592233.496136.914129.199219.3359183.59389.242448.535142.592453659460.8383449846

57.547933.496137.695328.222719.7754263.671911.989147.998176.7274671047639.9746581822

82.629733.691438.085926.269520.5566324.218814.552846.8261107.4785062277738.5399185387

94.776533.593838.281324.365220.2637332.031316.067144.6289117.4935860964731.2687410479

103.032933.593838.281323.095720.5078332.031317.677243.6035124.7942768812705.9613927256

109.438433.593838.378922.558620.4102333.984418.577542.9688130.6232790212703.1258395714

113.007533.593838.378922.363320.4102335.937519.071842.7735134.2701202828704.0231670369

12000 rpm

Flow in m3/hTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %

0.000033.789137.695338.427721.3379162.10940.000059.76560.00000.0000

0.000033.789137.695336.425820.8984166.01560.000057.32420.00000.0000

14.288133.691437.793036.132821.1914199.21884.221857.324222.7515538.9004

38.101633.886738.183636.572321.8750300.78137.697358.447361.8592803.6499

65.993933.886738.964833.642622.3145367.187511.140455.9570102.5783920.7809

87.819833.886739.453130.615222.5098410.156313.387953.1250129.5952968.0043

101.926233.984439.648429.101622.7539437.500014.725251.8555146.8175997.0493

112.302729.882839.843827.294922.2656439.453115.805649.5605154.6051978.1686

117.533533.886739.843826.513722.3633439.453116.614348.8770159.5744960.4641

121.425433.886739.843826.171922.7539435.546917.620948.9258165.0231936.5193

13000 rpm

Flow in m3/hTout in degCdp1 in mbardp2 in mbarPower in WEfficiency in %

0.000033.984438.671947.216823.9258222.65630.000071.14260.00000.0000

0.000033.984438.671944.628923.3887226.56250.000068.01760.00000.0000

19.637133.984438.769540.136722.3633248.04694.917962.500034.0922693.2314

37.197833.984439.062541.943423.5352347.65636.994965.478567.6572967.2345

71.122234.082040.039142.382825.3418521.48449.600667.7246133.79791393.6394

91.859634.082040.429736.523424.7559542.968811.633961.2793156.36361344.0351

112.201734.179740.820333.496124.6582566.406313.568558.1543181.25031335.8214

121.518834.082040.918032.177724.7070572.265614.573556.8848192.01581317.5681

127.796634.179740.918030.957024.6582568.359415.401255.6152197.42881281.9036

130.170734.179741.015630.468824.8047566.406315.834955.2734199.86061262.1493