Performance Test on Single Stage Axial Flow FanAkhil Jaiswal, Akhil Praveen, ASP Gautam, Amal Jyothis V, Amit Kamboj, Anand Kumar, Anurag Singh T

B. Tech. Aerospace Engineering, Indian Institute of Space Science and Technology

Abstract— A performance test was carried out on single stage axial flow fan test rig and the variables for performance evaluation were measured. By varying the fan motor rotational speed, input and output power calculations were done using the measured variables and variation of efficiency with fan rpm was studied. Maximum efficiency was obtained at 2000 rpm.

Keywords- Single Stage Axial Flow Fan, Efficiency.

I. INTRODUCTION

An axial fan is a type of a compressor that increases the pressure of the air flowing through it [1]. The blades of the axial-flow fans force air to move parallel to the shaft about which the blades rotate. In other words, the flow is axially in and axially out, linearly, hence the name.

By comparison, a centrifugal or radial flow fan moves air perpendicular to the axis of rotation. Axial flow fans are better suited for low-resistance, high-flow applications, whereas centrifugal flow fans apply to high-pressure resistance, low-flow conditions.

Axial flow fans, while incapable of developing high pressures, they are well suitable for handling large volumes of air at relatively low pressures. In general, they are low in cost and possess good efficiency, most have a large hub and can have blades of airfoil shape.

Depending on the operation range of the static pressure, medium to high, the hub diameter can vary from 30 to 80% of the blade outside diameter.

The hub/tip ratio is defined as

r=RH

RT

Figure 1. Fan Nomenclature[2]

Figure 2. Schematic of Single Stage Axial Flow Fan1. Fan Motor 2. Fan Blade3. Stator Vanes 4. Pitot Probe5. Air Flow Duct 6. Pressure Tappings

II. EXPERIMENT

The experiment was done on a typical centrifugal blower set up at L002 Thermal lab at IIST. The set up mainly of a pump, a motor and test rig. Test Rig consists of a single stage axial flow fan. At both upstream and downstream of the fan, holes are provided with suitable mounting attachments to enable probe to traverse in a radial direction. A straight probe is provided for this purpose. At the inlet duct, a standard Pitot-Static probe is provided to measure the flow rate through the fan.

A multi-limb manometer is provided to measure the following: static pressure at the hub and tip at the 4 stations, the static and dynamic pressure of the straight probe, and the Pitot-Static probe. An energy meter is used to measure the input power. A non-contact type tachometer is provided to measure the fan rpm directly.

Figure 3. Multi Limb Manometer

III. PROCEDURE

Connect the multi-limb manometer limbs to the various static pressure taps of the rig and the two probes. Then fill the manometer reservoir with water. Switch on the control panel with the motor speed control at minimum. Slowly increase the motor speed to a required test speed. Note the time taken for 10 pulses in energy meter. Start taking reading from the manometer (water column heights) with one of the limbs open to atmosphere. The open limb provides a reference atmosphere water column height. The pressure (positive of vacuum) at that station is noted down. For the limbs connected to the probe, the difference between the water column heights directly gives the velocity head. Repeat the above procedure for different speed conditions of the motor and note down the readings. Switch off the motor after decreasing its speed slowly. Tabulate the observations and calculate the required values.

IV. OBSERVATIONS

Table 1. Pressure Readings across Fan

S. No.

Fan SpeedTime 10 rev

Static Pressure Rise across Fan

P2T P2H P3T P3H

RPM s cm of water

1 1955 16.8 28.6 28.1 25.1 26.7

2 2048 14.5 28.8 28.2 25 26.7

3 2149 12.8 29 28.3 24.9 26.8

4 2250 11.1 29.2 28.5 24.8 26.9

5 2349 9.7 29.5 28.8 24.6 27

6 2457 8.1 29.9 29.3 24.4 27.1

Table 2. Pitot Probe Readings

S. No. Fan Speed Time 10 revPitot Tube Reading

h1 h2RPM s cm of water

1 1955 16.8 7.8 9.22 2048 14.5 7.7 9.23 2149 12.8 7.6 9.34 2250 11.1 7.6 9.45 2349 9.7 7.5 9.56 2457 8.1 7.4 9.5

V. EQUATIONS AND SAMPLE CALCULATION

For reading #2:

For Fan Input Power[3],Input power to motor = (3600*n)/(K*t) kWWhere,

K= Energy meter constant = 1600 imp/kWh.t =Time for ‘n’ impulses in seconds.n = 10t = 14.49 s.

Efficiency of VFD and Motor = 80% (assumed)Motor Output Power = (0.8*3600*n)/(K*t) kWFan input Power, Pi = Motor output

= 1.242 kW

For Fan Output Power,

Flow rate, Q = (A * V) m3/sWhere,

Inlet area, A = 0.135 m2

Velocity, V = √(2*g*Ha) m/s = √(2*g*(Hw/100)*(ρw/ρa)) m/s

Hw = Velocity head in cm of water.= 1.5 cm of water

Velocity, V = 15.091 m/sStatic pressure head across the fan,

h = (Delivery head – Suction head) m of waterh = 0.0265 m of water

Delivery head,hD = ((atm- P3T)+ (atm- P3H))/2 m of water = 0.0015 m of water

Suction head,hS = ((atm- P2T)+ (atm- P2H))/2 m of water = -0.025 m of water

Fan output power , Po = (ρ*g*h*Q)/1000 kWg = 9.81m/s2

Q = 2.037 m3/sPo = 0.529 kW

Efficiency of the axial flow fan,η = (Po/Pi)*100%η= 42.63 %

VI. GRAPHS

Graph 1 Input Power Vs Flow Rate

Graph 2 Fan speed Vs Flow Rate

Graph 3 Head Vs Flow Rate

Graph 4. Efficieny Vs Flow Rate

VII. RESULT

The air flow rate was varied from 1.96 to 2.41 m3/s. Correspondingly, the graph of total head, fan speed and input has been obtained. The total head varied from 24 cm to 38 cm while the power varied from 1071W to 2232 W. The efficiency varied from 40%- 44% and peak in efficiency is achieved at a flow rate of 1.968 m3/s at around 2000 rpm.

VIII. CONCLUSION

It can be inferred that as flow rate is increased then the fan speed increases linearly and input power increases with the cube of flow rate [4]. The efficiency has a maximum value of maximum to 44% in the range of fan speeds at which the tests are done. Unlike standard test results referred from the internet where efficiency increases and then decreases, in this experiment, it keeps on decreasing monotonically in contrast to standard results. One reason for such an occurrence may be that we might be doing the test beyond the point of maximum efficiency rpm. This is also supported by the increase in pressure head with flow rate in this experiment unlike standard performance test results where pressure head increases only in the region of surge where efficiency starts decreasing.

Further there can be sources of error due to which we obtained discrepancy in results. There could be several reasons for this such as error in reading of devices manually like manometer, tachometer, bubbles in the manometer, etc.

ACKNOWLEDGMENT

We would like to acknowledge with appreciation the numerous and valuable persons whose contribution has been important in this report. We would like to thank our instructors Dr. Deepu M and Dr. Rajesh S for their valuable help. We also thank our lab assistants for clearing our doubts.

REFERENCES

[1] http://en.wikipedia.org/wiki/Axial_fan_design

[2] http://eeref.engr.oregonstate.edu/@api/deki/files/841/=Axial_Fan.png

[3] Dr. Rajesh S, Dr. Deepu M, IIST Lab Hand Out

[4] http://www.nyb.com/Catalog/Letters/EL-03.pdf

APPENDIX I

Specifications Single Stage Axial Flow Fan Test Rig:Overall dimensions of Test Rig:

Length = 1.6 m Width = 1 m Height = 1.5 m Maximum Pressure developed by the fan = 80 mm of WG Maximum flow delivered = 2.3 m3/sec

Technical specifications of the fan: Fan Blades - 8 off air foil section Inlet guide vanes (IGV) - 8 off flat plate section Outlet guide vanes (OGV) - 8 off pelage section Load vanes - 8 off flat plate section

Motor: Power - 5 HP Speed range - 0 to 2800 rpm

APPENDIX II

Table 3. Calculated Values for all Readings

Sl no .

Fan Speed

Time for 10 Rev of Energy disc

Static Pressure

Head across fan

Flow Rate

Fan Input power

Fan output Power

Efficiency

N(rpm)

t(s)h(m of water)

Q(m3/s) Pi(kW) Po(kW) η(%)

1 1955 16.8 0.0245 1.968261.0714285

70.47306

144.1523971

8

2 2048 14.5 0.02652.03734

21.2422360

20.52963

842.6358369

7

3 2149 12.8 0.0282.16891

71.4084507

0.595758

42.29881977

4 2250 11.1 0.032.23179

71.6289592

80.65681

840.3213151

8

5 2349 9.7 0.0335 2.352521.8518518

50.77312

141.7485093

8

6 2457 8.1 0.03852.41061

62.2332506

20.91045

440.7680860

2