1.0 SUMMARY
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.
2.0 OBJECTIVE;
To study the characteristics curves of a centrifugal compressor.
3.0 INTRODUCTION
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]
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]
4.0 THEORY
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 enter
In 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 γ-1
Tt1 Pt1 γ
Where, γ 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(γ-1)/γ -1) ηC
This 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, ηC. 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 = л d2 2(100) Δ p (3600)
4 ρ
Where;
Diameter, d = 0.044m
Ρ = 1.21 kg/m3
Both at 20°C and 1013 mbar and the pressure drop Δp at the nozzle in mbar.
η = Phyd 100%
Pel
Where Phyd can be calculated from the total pressure head and the flow rate. Phyd = 100(dp1 + dp2) Q
5.0 METHODOLOGY 5.1 Apparatus
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
5.2 Procedures
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 “η”
(f) Differential pressure 1st stage dp1 (g) Differential pressure 2nd stage dp2 (h) Compressor total pressure
(j) Outlet temperature Tout
5. 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.
6.0 RESULTS
Table 1: run 1 at speed 10000rpm
Table 2: run 2 at speed 11000rpm Flow in
m3/h Tin in deg°C Tout in deg°C dp1 in mbar dp2 in mbar Power in W Efficiency in % dptotal mbar Phyd W Pel W
0.0000 34.2773 39.6484 31.2988 19.6777 99.6094 0.0000 50.9766 0.0000 0.0000 0.0000 34.2773 39.6484 28.2227 19.1406 91.7969 0.0000 47.3633 0.0000 0.0000 14.2881 34.277 3 39.6484 24.365 2 18.212 9 93.7500 7.7104 42.5781 16.8989 219.1689 30.1219 34.277 3 39.7461 24.755 9 18.652 3 136.718 8 11.4153 43.4082 36.3205 318.1753 51.7361 34.277 3 40.3320 23.291 0 18.847 7 181.640 6 14.9120 42.1387 60.5581 406.1033 72.6994 34.375 0 40.6250 22.070 3 19.091 8 222.656 3 17.3157 41.1621 83.1239 480.0491 86.3875 34.375 0 40.7227 21.044 9 19.287 1 240.234 4 19.2655 40.3320 96.7829 502.3635 95.6105 34.3750 40.8203 19.7266 19.4336 246.0938 20.9728 39.1602 104.0034 495.8975 100.919 7 34.3750 40.8203 19.1895 19.5313 244.1406 22.4266 38.7207 108.5467 484.0088 105.426 8 34.375 0 40.8203 19.384 8 19.824 2 255.859 4 22.6905 39.2090 114.824 4 506.0469
Table 3: run 3 at speed 12000rpm Flow in m3/h Tin in deg°C Tout in deg°C dp1 in mbar dp2 in mbar Power in W Efficiency in % dptotal mbar Phyd W Pel W 0.0000 33.4961 36.5234 34.1309 19.5801 117.1875 0.0000 53.7110 0 0 0.0000 33.496 1 36.621 1 31.543 0 19.384 8 117.187 5 0.0000 50.9278 0 0 12.6009 33.496 1 36.718 8 30.078 1 18.945 3 138.671 9 4.7820 49.0234 17.1594 3 358.8311 31.5922 33.496 1 36.914 1 29.199 2 19.335 9 183.593 8 9.2424 48.5351 42.5924 5 460.8383 57.5479 33.496 1 37.695 3 28.222 7 19.775 4 263.671 9 11.9891 47.9981 76.7274 7 639.9747 82.6297 33.6914 38.0859 26.2695 20.5566 324.2188 14.5528 46.8261 107.4785 738.5399 94.7765 33.5938 38.2813 24.3652 20.2637 332.0313 16.0671 44.6289 117.4936 731.2687 103.032 9 33.593 8 38.281 3 23.095 7 20.507 8 332.031 3 17.6772 43.6035 124.794 3 705.9614 109.438 4 33.593 8 38.378 9 22.558 6 20.410 2 333.984 4 18.5775 42.9688 130.623 3 703.1258 113.007 5 33.593 8 38.378 9 22.363 3 20.410 2 335.937 5 19.0718 42.7735 134.270 1 704.0232 Flow in m3/h Tin in deg°C Tout in deg°C dp1 in mbar dp2 in mbar Power in W Efficiency in % dptotal mbar Phyd W Pel W 0.0000 33.7891 37.6953 38.4277 21.3379 162.1094 0.0000 59.7656 0.0000 0.0000 0.0000 33.7891 37.6953 36.4258 20.8984 166.0156 0.0000 57.3242 0.0000 0.0000 14.2881 33.6914 37.7930 36.1328 21.1914 199.2188 4.2218 57.3242 22.7515 538.9004 38.1016 33.8867 38.1836 36.5723 21.8750 300.7813 7.6973 58.4473 61.8592 803.6499 65.9939 33.8867 38.9648 33.6426 22.3145 367.1875 11.1404 55.9570 102.5783 920.7809 87.8198 33.8867 39.4531 30.6152 22.5098 410.1563 13.3879 53.1250 129.5952 968.0043 101.9262 33.9844 39.6484 29.1016 22.7539 437.5000 14.7252 51.8555 146.8175 997.0493 112.3027 29.8828 39.8438 27.2949 22.2656 439.4531 15.8056 49.5605 154.6051 978.1686 117.5335 33.8867 39.8438 26.5137 22.3633 439.4531 16.6143 48.8770 159.5744 960.4641
Table 4: run 4 at speed 13000rpm Flow in m3/h Tin in deg°C Tout in deg°C dp1 in mbar dp2 in mbar Power in W Efficiency in % dptotal mbar Phyd W Pel W 0.0000 33.9844 38.6719 47.2168 23.9258 222.6563 0.0000 71.1426 0.0000 0.0000 0.0000 33.9844 38.6719 44.6289 23.3887 226.5625 0.0000 68.0176 0.0000 0.0000 19.6371 33.9844 38.7695 40.1367 22.3633 248.0469 4.9179 62.5000 34.0922 693.2314 37.1978 33.9844 39.0625 41.9434 23.5352 347.6563 6.9949 65.4785 67.6572 967.2345 71.1222 34.0820 40.0391 42.3828 25.3418 521.4844 9.6006 67.7246 133.7979 1393.6394 91.8596 34.0820 40.4297 36.5234 24.7559 542.9688 11.6339 61.2793 156.3636 1344.0351 112.2017 34.1797 40.8203 33.4961 24.6582 566.4063 13.5685 58.1543 181.2503 1335.8214 121.5188 34.0820 40.9180 32.1777 24.7070 572.2656 14.5735 56.8848 192.0158 1317.5681 127.7966 34.1797 40.9180 30.9570 24.6582 568.3594 15.4012 55.6152 197.4288 1281.9036 130.1707 34.1797 41.0156 30.4688 24.8047 566.4063 15.8349 55.2734 199.8606 1262.1493
6.1 The pressure-flow rate characteristic curve, efficiency curve and temperature curve for different speeds
0.0000 5.0000 10.0000 15.0000 20.0000 25.0000 0.0000 20.0000 40.0000 60.0000 80.0000 100.0000 120.0000 140.0000 Efficiency (%) Flowrate (m3/hr) Efficiency vs. Flowrate 10000 rpm 11000 rpm 12000 rpm 13000 rpm
Figure 3; graph of Efficiency vs. Flowrate
dP Total vs. Flowrate 30.0000 35.0000 40.0000 45.0000 50.0000 55.0000 0.0000 20.0000 40.0000 60.0000 80.0000 100.0000 120.0000 140.0000 Flowrate (m3/hr) d P T o ta l (m b a r) 10000 rpm 11000 rpm 12000 rpm 13000 rpm
Temperature In vs. Flowrate 29.0000 30.0000 31.0000 32.0000 33.0000 34.0000 35.0000 0.0000 20.0000 40.0000 60.0000 80.0000 100.0000 120.0000 140.0000 Flowrate (m3/hr) T e m p e ra tu re ( C ) 10000 rpm 11000 rpm 12000 rpm 13000 rpm
Figure 5; graph of Temperature in vs. Flowrate
Temperature Out vs. Flowrate
36.0000 36.5000 37.0000 37.5000 38.0000 38.5000 39.0000 39.5000 40.0000 40.5000 41.0000 41.5000 0.0000 20.0000 40.0000 60.0000 80.0000 100.0000 120.0000 140.0000 Flowrate (m3/hr) T e m p e ra tu re O u t (C ) 10000 rpm 11000 rpm 12000 rpm 13000 rpm
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 : 105.4268 Speed 11,000 rpm: Maximum efficiency : 19.0718 Maximum Flowrate : 113.0075 Speed 12,000 rpm: Maximum efficiency : 17.6209 Maximum Flowrate : 121.4254 Speed 13,000 rpm: Maximum efficiency : 15.8349 Maximum Flowrate : 130.1707
6.3 Sample calculation;
For reading 10,000 rpm at 14.2881m3/h Flowrate.
Total dP, Δp = dP1 + dP2
= 24.3652 + 18.2129
= 42.5781 mbar
Volumetric flow rate, Q (theoretical) = л d2 2(100) Δ p (3600)
4 ρ = л (0.044m)2 2(100) (6.1523) (3600) 4 1.21 kg/m3 Q = 174.5576 m3 /hr Phyd (theoretically) = 100(dp1 + dp2) Q 3600 = 100(42.5781) (174.5576 m3 /hr) 3600 = 206.4536 W
Phyd (from exp) = 100(dp1 + dp2) Q
3600 = 100(42.5781) (14.2881m3 /hr) 3600 = 16.8989 W Pel = Phyd 100% η = (16.8989 m3 /hr) x 100% (7.7104m3/hr) = 219.1702 W
7.0 DISCUSSION
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
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.
8.0 RECOMMENDATION
During 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.
9.0 CONCLUSION
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.
10.0 REFERENCES
1. Miss Suhaini Mamat, the Experiment Manual Lab (Experiment 5: Centrifugal
Compressor).
2. http://www.fscconline.com/%22Passing%20Gas%22article/Centrifugal %20Compressor.gif
