Project Title: Modification of CPU Air-Cooled Fan

Project Proposal
Aim
Modification and Improvement CPU Axial Fan
Introduction

As processors, graphics cards, RAM and other components in computers have

increased in speed and power consumption, the amount of heat produced by
these components as a side-effect of normal operation has also increased. These
components need to be kept within a lower temperature range to prevent
overheating, instability, malfunction and damage leading to a shortened
component lifespan.

To cool these components, exhaust fan is the only way to flow the hot air outside
from the components and cool down the temperature in case. Fans attached to
components are usually used in combination with a heat sink to increase the
area of heated surface in contact with the air, thereby improving the efficiency of
cooling. For CPU cooling fan , axial fan is used. An axial fan is a type of a
compressor that increases the pressure of the air flowing through it. The blades
of the axial-flow fans force air to move parallel to the shaft about which the
blades rotate.
All of the designing in an axial fan revolves around the design of the propeller
that creates the pressure difference and hence the suction force that retains the
flow across the fan

As the above, a huge number of different sizes and shape of fans has been
developed by many developers to improve the cooling capacity from re-
designing hub size, pitch, blades angle and width, number of blades, etc.

Objective
1. Understand the principle of axial fan

2. Modifying a traditional CPU air-cooled fan so that it allows the CPU operates in
high performance by finding out the critical factors for improving the cooling
efficiency through analyzing using different measurement equipment and
 software packages and also compare different dimension of exhaust fan to take
the benefit and balance of fan

3. Selecting the most suitable material to make a CPU cooling fan by comparing
the traditional material and new material

4. Improve skills to integrate engineering sciences, design and manufacturing

technologies and to apply CAD/CAE/CAM systems to solve engineering design
problems academically

Determine
the
dimension[1]
of exhaust fan

Modify and
Test[2] the
assemble
exhaust fan
exhaust fan

Evaluate the
pons and cons
of exhaust fan

Methodology of Fan Modification

-Experimental details
*Approach
Activity: Measuring Wind Speed

Objectives:
will use an anemometer to measure wind speed at various distances and graph
the results.

Time Required: 45 minutes

*Equipment
Materials Required:
• Anemometer – (essential to activity and may be purchased for nominal cost)
• Pilot Tube
Sound Level Meter
Tahcometer
• Electric fan
• Tape measure
• Pencil
• Colored Pencils or Markers
• Masking Tape
• Wind Speed Data Sheet
• Graph Paper

Activity Procedures:

1. Locate an open area in the classroom to perform the Measuring Wind Speed
activity.

2. Plug the fan into an electrical outlet. There are safety precautions you should
follow when completing this activity.

3. NOTE: Please keep your hands and fingers at a safe distance when operating
the fan. DO NOT reach inside the fan cage or grab the blades when they are
moving.

4. Use the tape measure to measure a distance of 18” from the base of the fan.
Place a piece of masking tape on the work surface to identify the distance.

5. Turn on the fan to low speed setting.

6. Position the anemometer directly above the masking tape that marks one
distance from the base of the fan. Hold the anemometer so you can easily read
the scaled increments indicating wind speed and so you get the highest wind
speed possible.

7. Read the anemometer scale to determine the wind speed at a same distance.

8. Turn off the fan and record the wind speed of the first distance in the
corresponding cell of the Wind Speed Data Sheet.

9. Repeat this procedure to obtain wind speed recordings for medium and high
fan settings. Be certain to position the anemometer at the same location marked
distance and record the speeds into the corresponding cells on the Wind Speed
Data Sheet.
10. Use the tape measure to measure another distance from the base of the fan.
Place a piece of masking tape on the work surface to identify this distance.

11. Turn on the fan

Fan 1:

Fan 2:

Fan3:
Fan4:

Results & Analysis

A Experiment on existing fan
Room Temperature (°C) 22.5°C
Measuring Item Fan 1 Fan 2 Fan 3 Fan 4
Voltage (V) 12.0 12.0 12.0 12.0
Ampere (A) 0.70 0.46 0.78 0.24
Flow Temperature (°C) 22.8 22.6 22.5 22.7
Flow Velocity
15cm 0.9 3.1 5.1 1.7
13cm 0.9 3.3 6.2 1.8
11cm 0.9 3.6 7.2 1.9
9cm (m/s) 1.0 4.1 8 2
7cm 1.3 4.8 9.3 2.1
5cm 1.5 5.2 9.4 2.4
3cm 1.7 6.0 10.1 2.8
1cm 2.3 7.5 10.4 3.6
1598 8631 5194 3640
Revolution (rpm) 1604 8623 5177 3636
1601 8634 5169 3628
Average Revolution (rpm) 1601.0 8629.3 5180.0 3634.7
Temperature of heat sink (Before) (°C) 22.3 22.3 22.3 22.3
Temperature of heat sink (After) (°C) 22.1 21.3 21.3 21
Temperature Drop (°C) 0.2 1.0 1.0 1.3
(cmH2
Initial Pilot Tube Reading 0 0 0 0
O)
(cmH2
Final Pilot Tube Reading 1.3 8.0 19.6 6.0
O)

From further calculation:

Volume Flow rate (m3/s)
Fan 1 Fan 2 Fan 3 Fan 4
15cm 0.0181 0.0623 0.1025 0.0342
13cm 0.0181 0.0664 0.1247 0.0362
11cm 0.0181 0.0724 0.1448 0.0382
9cm 0.0201 0.0824 0.1608 0.0402
7cm 0.0261 0.0965 0.1870 0.0422
5cm 0.0302 0.1046 0.1890 0.0483
3cm 0.0342 0.1206 0.2031 0.0563
1cm 0.0462 0.1508 0.2091 0.0724
 Volume Flow rate vs Displacement
Volume Flow rate (m3/s) 0.2500

0.2000

0.1500
Fan1
Fan2
0.1000
Fan3
0.0500 Fan4

0.0000
0 2 4 6 8 10 12 14 16
Displacment(cm)

B Experiment on modified fan

Volume Flow rate (m3/s) @ 1cm %

Incre
Modification Fan Before After ase
Fan
Converging Nozzle 2 0.150796 0.180956 20%
Blades' trailing Fan 0.1105 52.70
edges 4 0.072382 84 %
Converging Nozzle +Blades' trailing Fan 0.1367 88.90
edges 4 0.072382 22 %

Analysis:
From the graph, we can see the trend that the volume flow rate decrease when
the distance increases is the same for all fans . It is because when further away,
the airflow would be less concentrated, thus drop in flow rate.
Comparing the fan 1 and fan 2 , they both have 7 blades but fan1 is made of
plastics while fan2 is made of aluminum.
For fan 2 and fan 4 , they are both made of aluminum but fan2 has 7 blades while
fan4 have 9 blades. Regardless of their revolution per minute, less blades has
higher volume flow rate. The turbulence and noise are mostly produced by the
leading and trailing edges of the blades and not their surface. Therefore,
less and wider blades will have better performance on efficiency and a lower
noise level.
For fan 2 and fan 3, both have 7 aluminum blades but fan 3 has inlet guide vanes.
With inlet guide vanes. the inlet airflow is directed at the most efficient angle to
enter the fan. From the result which matched our anticipation as the volume
flow rate of fan 3 is better than fan 2.

Pitot tube measures the increase in total pressure. Since the power of a fan is
defined as the function of pressure and flow rate. If a fan has higher final Pilot
Tube Reading, the output power is larger.

Modification
Certain modification is applied on the fan based on the working principle of axial
fan and the experiment with the existing fan.

1 Using Motor oil

Fan power output is the power delivered to the air by the fan. It is a function of the
fan air volume flow rate and the fan total pressure. If we want to modify our fan to
have better performance , we must increase the flow rate and total pressure.

From fan laws , fan air flow rate varies directly with fan speed
Q2 =Q1 ( )
Also fan pressure varies directly with the square of fan speed, P2 =P1 ( )2
Since power is a function of air flow rate and total pressure, increase RPM would
definitely raise the air flow rate and hence increase the output power as
Power= Q2 P2= Q1 ( )x P1 ( )2= Q1 P1( )3
Thus power would be greatly increase as it is related to the cubic of the RPM ratio. So
changing the rotational speed is one of the most efficient methods.
To increase the rotational speed, one approach is to add motor oil.
It is an oil used for lubrication of various internal combustion engines. The main
function is to reduce wear on moving parts; it also cleans, inhibits corrosion,
improves sealing, and cools the engine by carrying heat away from moving parts.

It creates a separating film between surfaces of adjacent moving parts to

minimize direct contact between them, decreasing heat caused by friction and
reducing wear, thus protecting the engine. When friction is reduced, the
rotational speed of motor would thus be promoted. Motor oil is also applied to
the surface of the blade and reduces the air friction on the blade, further increase
the flow rate. By this method, the power of the fan can increase significantly.

2 Reduce Fan outlet size

By using the Mass Conservation Law on a steady flow process - flow where the
flow rate do not change over time - through a control volume where the stored
mass in the control volume do not change - implements that inflow equals
outflow which this statement is called the Equation of Continuity.
The Equation of Continuity can be expressed
as:

m = ρ1V1A1 = ρ2V2A2
(In) (Out)
Where
m = mass flow rate (kg/s)
ρ = density (kg/m3)
v = speed (m/s)
A = area (m2)

The Mach number of this system

V
M =
vsound
where
M is the Mach number,
v is the velocity of the source relative to the medium, and
vsound is the speed of sound in the medium.
The Mach number of this system is as followings:
M = 7.5 / 334
= 0.02246 < 0.2
The result shows that we can regard the flow as an incompressible, steady and
isothermal.
Through this theory, we can modify the fan design by increasing flowrate of the
fan outlet using converging nozzle.

Inlet

The diameter of axial fan = 8cm = 0.08m

The area of axial fan = πr2 = π(0.08)2 = 0.02011m2
The flow velocity of axial fan = 7.5m/s
The volumetric flowrate = Av = (0.02011m2)(7.5m/s) = 0.15m3/s

Outlet

The diameter of outlet = 6cm = 0.06m

The area of axial fan =πr2 = π(0.06)2 = 0.01131m2
By using m = ρ1V1A1 = ρ2V2A2

As the Mach number < 0.2, the flow is incompressible so that we can assume that
the density both inlet and outlet are same.

The velocity of outlet (V2) = V1A1 / A2

V2 = 0.15 / 0.01131
= 13.26 m/s (Theoretic Result)

The performance increase from 7.5 m/s to 9.0 m/s.

Conclusion
1. A fan with blades made of aluminum is better than using plastics as material.
2. For our fan size, nine blades produce less power than seven blades.
3. Inlet guide vanes can help to enhance performance by adjusting the inlet airflow
angle.
4. Using motor oil, the friction between the fan and motor is reduced, increasing
the rpm which largely influence the power of the fan.
5. Diminish outlet area end up with higher exit velocity stated by the continuity
equation.
References
http://www.noctua.at/main.php?show=nine_blade_design&lng=en
http://www.spinifexfans.com.au/resources/noise-air-turbulence/
http://www.noctua.at/main.php?show=nf_b9_blade_design&lng=en
http://en.wikipedia.org/wiki/Motor_oil
http://www.engineeringtoolbox.com/equation-continuity-d_180.html