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Experiment
Objective:
To fine the characteristic curve for an axial fine operating at constant speed.
Apparatus:
๏ท The FM41 Axial Fan demonstration unit ๏ท The IFD7 Armfield interface device ๏ท Compatible PC with Arm field FM50-304 software installed
Chemical / Fluid:
๏ท Air
Terms and their forms:
Column Heading Abbreviation Units Description Pump Setting S % Measured Pump speed (rotational) N Rpm Measured Inlet Pressure Pin kPa Measured Outlet Pressure Pout kPa Measured Motor Torque T Nm Measured Volumetric Flowrate Q dm^3 /s Measured Inlet diameter Din M Diameter of inlet pipe din=0.0235m
Outlet diameter Dout M Diameter of outlet pipe dout=0.0175m Inlet Area Ain (^) m 2 Cross-sectional area of inlet pipe ๐๐๐^2 ๐ด๐๐ = ๐ ( 2 ) Outlet Area Aout (^) m^2 Cross-sectional area of outlet pipe ๐๐๐ข๐ก^2 ๐ด๐๐ข๐ก = ๐ ( 2 ) Inlet Velocity Vin m/s ๐ ๐๐๐ = ๐ด ๐๐ Outlet Velocity Vout m/s (^) ๐ ๐ ๐๐ข๐ก =^ ๐ด (^) ๐๐ข๐ก Change in Static Head Hs M ๐ป = ( ๐๐๐ข๐ก โ ๐๐๐ ) ๐ ๐๐ ๐ ๐๐ ๐๐๐๐ ๐๐ก๐ฆ ๐๐ ๐ค๐๐ก๐๐ ๐๐ ๐๐ / ๐^3 Change in Velocity Head Hv M ( ๐๐๐ข๐ก โ ๐๐๐ )^2 ๐ป๐ฃ = 2 ๐ Change in Elevation Head He M Vertical distance between inlet and outlet Change in Total Head Ht M Ht = Hs + Hv + He Hydraulic Power Ph W (^) ๐โ = ๐ป๐ก๐๐๐ (Where Q is in m^3 /s) Mechanical Power Pm W^2 ๐๐๐ก ๐๐ = 60 Pump Efficiency E % ๐โ / x 100 = E ๐๐
๏ท If time permits, addition rotation speed settings may be investigated to give a full series of the performance data. Remember to create a new result sheet for each set of data. Alternatively, each student or set of the students may take a data for different rotational speed and the result and then be combined. Theory: Fluid machines are usually characterized in two distinct classes: rotodynamic and positive displacement. In a rotodynamic machine, relative motion is required between the rotating element of the machine (the rotor or impeller) and the fluid stream. In a positive displacement machine, the machine components mechanically displace a set volume of fluid. In a rotodynamic machine, the changes in fluid velocity and pressure between inlet and outlet are of considerably greater significance in determining performance than for a positive displacement machine, where machine speed is the key parameter. Centrifugal fans (such as air-bed inflators), and axial fans (such as desk fans and computer power supply coolers), are both types of rotodynamic machines. A bicycle pump is an example of a positive-displacement machine. The axial fan is an axial flow rotodynamic machine. Air is drawn along by fan blades rotating about an axis parallel to the direction of air flow (hence the name axial fan), as in an aircraft propeller. The air stream does not undergo a significant change of mean flow direction (as is seen in the centrifugal fan), but turbulence and swirling within the air stream is introduced by the action of the fan blades.
Figure 1. Pump manufacturing and fan system designer require a method for indicating fan requirement performance to allow the correct fan to be selected for any given system and performance requirement. Designer will wish to select a fan that will be able to produce the required flow rate and pressure difference under the typical system conditions, and also to select a fan that will operate efficiently under the normal use. The general relationship between various form of energy, based on the first experiment thermodynamics applied for a unit mass of fluid flowing through the control volume (such as a fan itself) is expressed as: Ws =
( V 2
2 โ V 1 2
P 2 โ P 1
ฯ
+F............ (1)
When lines the constant efficiency are superimposed on such graph for the
range of fan rotation speed, a comprehensive illustration of pump
performance is obtained:
Observations: Serial No. Atm.pressure (KPa) Fan Setting S(%) Air Flow Rate Q(L/s) Total Pressure(P a) Efficiency(%) Power(W) 1 101 100 28.4 66 27.6 1. 2 101 100 28.2 65 27.0 1. 3 101 100 27.3 66 26.4 1. 4 101 100 27.2 67 26.8 1. 5 101 100 27.1 66 26.2 1. 6 101 100 26.9 65 25.6 1. 7 101 100 26.5 66 25.9 1. 8 101 100 26.0 67 25.7 1. 9 101 100 25.6 68 25.2 1. 10 101 100 25.4 69 24.8 1. 11 101 100 25.4 68 24.6 1.
Graph Analysis: 25 25.5 26 26.5 27 27.5 28 28.5 29
65
66
67
68
69
25
26
27
28 f(x) = 0.85 x + 3. Rยฒ = 0. f(x) = โ 0.98 x + 92. Rยฒ = 0.
Chart Title
Total Fan Pressure(Pa) Linear (Total Fan Pressure(Pa)) Efficiency(%) Linear (Efficiency(%)) Air Flow Rate(L/s) Total Pressure(Pa) Efficiency(%) 25 25.5 26 26.5 27 27.5 28 28.5 29
Power(W) Air Flow Rate(L/s) Fan Power(W) Results and Discussions: The software logs the following variable: ๏ท Inlet temperature T (C) ๏ท Orifice pressure P 1 (Pa)
