Performance Evaluation

►Thermal Module

FCN establishes the thermal parts CFD simulation capability. Below are four different types heat sink design with or without heat pipe.

 
The simulation results show that the Type 3 has the lower junction temperature.



FCN also has established the system level simulation capability.

 

The system layout
 
 Temperature Distribution AnalysisVelocity Distribution Analysis

The simulation results as below table:

 


►Axial Fan


The resistance of P-Q curve & SRC system

 
Radial-fan and Axial-fan are the two main types in fan categories.
The difference between Radial-fan and Axial-fan is that Radial-fan can generate higher pressure, but Axial-fan has more air flow ratio.
No matter what the fan types are, the fan performances should be followed the two rules
1. Air Movement and Control Association (AMCA) 210-85
2. Laboratory Method of Testing Fans for Rating
The test result followed the two rules is called P-Q curve which is shown in Fig.1.
Three main points are distributed in P-Q curve, that are
Pmax : At the point, the fan has the maximum pressure and the corresponding flow ratio is zero.
Qmax : At the point, the fan has the maximum flow ratio and the corresponding pressure is zero.
OP: OP is the abbreviation of operation point or optimum point, it means that the fan usually be operated at this point, and the fan should have the best efficiency at this point.


Fig.1 P-Q Curve
 
 
When the fan geometry size and fan voltage (or RPM) are been defined, the P-Q curve will be drawn by recording the difference Q points and the corresponding P points. The P-Q curve can be used to distribute the characteristic of fan, so the P-Q curve also be called the fan characteristic curve.
 

What is the resistance of fan

When the air flow thought the system, it will pass some components of the system, these components will hinder the air and the pressure of the air will also decrease. The potential capacity of hindering is called as resistance. If the pressure loss at difference flow ratio are recorded, the system resistance curve can be drawn ( shown as Fig.2)
The intersection of P-Q and System resistance curve is called OP (operator point) (shown as Fig.2).
The different system resistances will get different OP at the same fan.

 

Fig.2 the system resistance curve
 

How to determine the fan preference from P-Q and System resistance curve

A What is P-Q (fan characteristic) and System resistance curve?
1. Solid line (FPC) in below figure is the P-Q (fan characteristic) curve, it can be measured by wind tunnel.
2. Dotted line (SRC) in below figure is the System resistance curve, it also can be measured by wind tunnel if the system can be available or provided from custom. 
3. The intersection of FPC and SRC is the OP(operator point), the best way to choose the suitable fan is to consider the OP, not the Pmax or Qmax.
*It is suggested to find the suitable fan with the SRC data.
B. How to choose the suitable fan by FPC and SRC ?
1. In Fig3(a), two system resistance curves and one fan P-Q curve are shown. As indicated in previous statements, OP#A is the operator point, but OP#B is the operator point and the optimum point for fan. The fan is more suitable for system B than system A.
2. In Fig.3(b), two fan P-Q curve and one system resistance lines are shown. If the requirement of flow ratio in system is about 88 CFM, it means the system will need about 5 mmAq static pressure to overcome the system resistance. For system, the Fan A will be the better choice than Fan B.


Fig.3(a)

Fig.3(b)
 

Coustical Engineering

 
General design requirements for the fixture are:
  • The distance from the fan to the fixture must be at least one fan diameter. The fixture’s thickness must be less than or equal to 1 cm. No part of the fixture must be in the path between the fan and the microphone. The fixture must remain stationary during the course of testing. The fixture must not contribute to the noise when the fan operates: no rattles, fixture resonances, or squeaks. The fixture should occupy minimal volume.
  • The fixture should minimize reflections. To minimize reflections, cross-sections of the fixture must be circular.
  • The points at which the suspension attaches to the fixture must be located symmetrically about the fixture.
  • The fixture’s stand must occupy minimal volume as with the fixture itself. Care should be taken to minimize the number and size of legs. A single post with heavy base is recommended. The diameter of post must be less than or equal to 5 cm.

 
Figure 1  Example fixture and suspended fan. Dfan is equal to the fan diameter.
 

 

Instrumentation

  • Free-field microphone and preamp meeting Type I sound level measuring system.
  • Microphone calibrator.
 
  • Vibration transducers, for example, piezoelectric accelerometers. The following performance characteristics are required.
    • Low mass:  less than 2 grams for square form factor axial fans greater than 60mm in size; less than 1 gram for smaller fans and for small blowers such as for notebooks.
    • 5 to 5000Hz frequency range.
  • Vibration calibrator.
 
  • Noise and vibration data acquisition and analysis system with the following capabilities.
    • Two or more channels of parallel data acquisition.
    • Sampling rate of 44100Hz or greater.
    • Frequency range DC to 20000Hz or greater.
    • Spectrum analyses: octave, third octave, and FFT.
    • Sound quality analyses: loudness (ISO 532B), prominence ratio, and tonality.
    • Modulation analysis.
    • Level versus time analyses.
    • Order tracking and order level versus speed analyses.
 
  • Sensor for measuring fan rotation speed, for example, photo tachometer.
  • DC power supply with sufficient voltage and current to power the fan(s) to test.
  • Function generator to produce PWM signal for PWM speed controlled fans.
  • Multi-meter.
  • Temperature and humidity monitor.
 
The fixture and suspension should be checked to insure they do not generate noise when the fan is operated throughout the speed range of the test. The best means to accomplish this check is to run the fan through the entire speed range and observe (listen) if the fixture and suspension generate noise. Noise can be generated if the elastic suspension vibrates or resonates, if the fixture vibrates or rattles, or if transducer cables vibrate or rattle.
 
The following table lists some guidelines to minimize noise generated by the suspension and fixture.

 
DO DO NOT
Do attach the elastic directly to the fan and fixture. Do not use metal hooks (such as paper clips) to attach elastic to the fan or fixture.
Do use single stranded elastic such as small diameter bungee cord. Do not use double stranded elastic such as looped rubber bands. Closely spaced elastic strands may create slapping noise if they vibrate and come into contact.
Use small diameter (1.5mm) bungee cord instead of rubber band elastic. Do not allow transducer cables to vibrate or rattle against the suspension or fixture.
Table 1    Guidelines to minimize noise generated by the suspension and fixture.
 

Fan Orientation

Axial fans are mounted in the fixture such that the direction of air flow is away from the microphone. The axis of rotation of the fan is horizontal. In hemi-anechoic chambers, the height of the bottom edge of the fan above the floor must be at least 100 cm.
 
Blowers are mounted in the fixture with the axis of rotation horizontal, and the air inlet facing the microphone. The air exhaust is to point vertically upwards.
 
For the case of dual air inlet blowers, the motor struts must be on the side away from the microphone. The air exhaust is to point vertically upwards.

 

Fan Speed Control

The rotation speed of the fan or blower must be controlled using the same control strategy for which the fan is designed.
  • Speed of linear DC voltage fans is controlled by varying a DC voltage. Speed of PWM fans is controlled by varying the duty cycle of a PWM signal. PWM parameters must be reported.   
  • Speed of thermistor controlled fans is controlled by varying the electrical resistance of a signal simulating the thermistor output.
 

Fan Speed Sensor

All acoustic and vibration measurements defined in this procedure require simultaneous monitoring or measuring of the fan speed.
 
When a photo tachometer is used as the fan speed sensor, the preferred position for the sensor is downstream of the fan exhaust so that it is not between the fan and microphone, as illustrated in Figure 2. If the photo tachometer is positioned upstream of the fan, then position it off to the side so it is not in the direct path between the fan and microphone. The minimum allowable distance of the speed sensor from the fan is two fan diameters, and further distances are recommended. The mounting fixture for the speed sensor must minimize reflecting surfaces; use a thin support stand.
 
For the case of dual-rotor fans, two photo tachometers are required, one downstream and one upstream. The upstream photo tachometer must not be in the direct path between the fan and microphone. Position the upstream photo tachometer off to the side.
 
If the photo tachometer requires a reflective spot on the fan, create the reflective spot in a manner that minimizes the unbalance to the fan. Use a minimal amount of reflective tape or paint and position the spot as close to the axis of rotation as possible, at the root of the blades, rather than the tips.
 
For fans that output a tachometer signal, that signal may be used to monitor fan speed.

 

Microphone and Fan Locations

Figure 2 shows the microphone positioning as well as the general testing layout.
 
Requirements for the location of the microphone and fan are:
  • The microphone must be located on the axis of rotation of the fan at a distance of 50 cm from the intake of the fan.
  • The microphone must be at least 100 cm from any chamber wall or floor. For chambers with acoustical wedges, the distance is measured to the tip of the wedges.
  • Any surface of the fan must be at least 100 cm from any chamber wall or floor. For chambers with acoustical wedges, the distance is measured to the tip of the wedges.
 
 

 
Figure 2                Requirements and relative location of the microphone, fan, and tachometer.
 

Vibration Transducer Locations

For axial fans having square form factor, measure vibration in the vertical direction as close as possible to the top two corners of the fan, at the top of the edge of the downstream face. Reference Figure 3.  It is required to record the distance, ΔL, between these two measurement points.
 
 

 
Figure 3      Position of accelerometers on axial fan with square form factor.
 
Accelerometers must be mounted on a flat surface on the fan. Wax or glue may be used to attach the accelerometer. If using wax, it must be an appropriate wax supplied by an accelerometer manufacturer for the purpose of mounting accelerometers. When using wax, proper mounting techniques must be followed:
  • Use minimal amounts of wax.
  • Fan surface must be clean and smooth.
  • Smear a thin layer between the accelerometer and fan surface.
  • Be sure the thin wax layer covers the entire area of the accelerometer base.
  • Accelerometer must seat firmly on the mounting surface. No rocking or looseness.
 
If using glue to mount accelerometers, proper mounting techniques must be followed: Fan surface must be clean and smooth.
  • Avoid glue build-up on the accelerometer base.
  • Accelerometer must seat firmly on the mounting surface. No rocking or looseness.
Measurement Procedure

General

Other test system operating noises

The only noise source in the acoustic chamber during the test is the fan under test. The equipment used to power and control the fan must be located outside the acoustic chamber or otherwise acoustically isolated.
 

Corrections for background noise

No correction for background noise is to be applied. Frequency intervals influenced by background noise may be identified.
 

Measurement System Input voltage range

Optimize the data acquisition system’s voltage input range to the transducer signal levels. Adjust the input voltage range as low as possible without producing a voltage overload condition. For example, use the auto-range feature of your data acquisition system prior to recording data.
 

Fan Operating Conditions

Fan is operated in free-air delivery conditions, that is, without any load or pressure conditions. Fan operating speeds are specified in succeeding sections.
 

Signals to Measure

Record signals from microphone and vibration transducers simultaneously at each operating condition.
 

Digital Sampling Rates

Acoustic signals require analysis up to 20 kHz. For acoustic signals, use a digital sampling rate of 44.1 kHz or greater.
 
Vibration signals require analysis up to 5 kHz. For vibration signals, use a digital sampling rate of 11025 Hz or greater.

 

Constant Speed Operating Condition

Recording time
Recording duration shall be at least 10 seconds.

Speed Sweep Operating Condition
In a speed sweep operating condition, the fan speed increases from a start speed up to an end speed. The fan speed must change smoothly and continuously.
 

Fan speeds and sweep rate

  • Start speed ≤ RPMmin
  • End speed ≥ RPMmax
  • At least 30 seconds per doubling of speed.
 

Recording time

Recording time must be sufficient to record the entire fan speed sweep.

Data Analyses

Signal Processing for Vibration

Linear Vibration Acceleration

For square form factor, axial fans (Figure 3), the linear (or translational) vibration time waveform is calculated from the average of the two accelerometer signals as follows:
 

                                              
 
For fans having other form factors (for example, centrifugal blowers) Dell Acoustical Engineering must specify the accelerometer location at which to measure translational vibration.
 

Angular Vibration Acceleration

For square form factor, axial fans (Figure 3), the angular (or rotational) vibration time waveform is calculated from the difference of the two accelerometer signals as follows:
 

                                              
 
where ΔL is the distance (in meters) between the sensing axes of the two accelerometers.
 
For fans having other form factors (for example, centrifugal blowers) Dell Acoustical Engineering must specify the accelerometer locations and method for calculating angular acceleration. Angular vibration may not apply to some form factors.

 

Analyses for Constant Speed Operating Conditions

The following analyses may be conduct at each fan speed. All acoustic decibel levels use a reference of 20 x 10-6 Pascals.

A-weighted sound pressure level  

  • In decibels, dBA.
  • Averaging time of at least 10 seconds.
 

Loudness

  • According to ISO 532B.
  • In sones.
  • Averaging time of at least 10 seconds.
 

Tonality

  • Aures method.
  • In units of tu.
  • Averaging time of at least 10 seconds.
 

Prominence Ratio

  • According to ISO 7779 and ECMA-74.
  • In decibels.
  • Averaging time of at least 10 seconds.
 

Modulation

  • In percent.
  • Percent modulation versus modulation frequency and carrier frequency.
  • Averaging time of at least 10 seconds.
 

One third octave A-weighted sound pressure level spectrum 1/3rd octave band center frequencies, 100 to 20000Hz.

  • A-weighted band levels in decibels, dBA.
  • Averaging time of at least 10 seconds.
 

Linear Vibration Acceleration

From the linear vibration acceleration time waveform, analyze the following in units of m/sec^2.
  • Overall, 20 – 5000 Hz
  • Amplitude of the fundamental frequency of rotation and harmonics.
  • Amplitude of the fan motor pole pass frequency and harmonics.
  • Third octave band spectrum.
 

Angular Vibration Acceleration

From the angular acceleration time waveform, analyze the following in units of rad/sec2.
  • Overall, 20 – 5000 Hz
  • Amplitude of the fundamental frequency of rotation and harmonics.
  • Amplitude of the fan motor pole pass frequency and harmonics.
 

Analyses for Speed Sweep Operating Conditions The following analyses may be conducted for fan speed sweeps.

A-weighted sound pressure level versus fan speed.  Averaging time equal to 0.05 seconds.
  • Speed step of 20 rpm.
 

Vibration Order Tracks

Linear vibration in m/sec2 and angular acceleration in rad/sec2.
  • Averaging time equal to 0.05 seconds.
  • Speed step of 20rpm.
 

Reporting for Constant Speed Operating Conditions Report the following results at each operating speed. All acoustic decibel levels use a reference of 20 x 10-6 Pascals.

 

A-weighted sound pressure level       

Report the A-weighted sound pressure level, dBA.
 

Loudness

Report the loudness in sones.
 

Tonality

Report the tonality in tu.
 

Prominence Ratio

Report the prominence ratio for the following frequencies if there is a corresponding discrete peak in the FFT spectrum and the prominence ratio is greater than 5 dB.
  • fundamental frequency of rotation
  • fan motor pole pass frequency and harmonics
  • fan blade pass frequency and harmonics
  • other discrete peaks
 

Modulation

Report the maximum percent modulation and corresponding carrier and modulation frequencies.
 
Report the maximum percent modulation and corresponding carrier frequency for modulating frequency equal to the fundamental frequency of rotation and 2nd, 3rd, and 4th harmonics (F1, F2, F3, F4).

 

One third octave band A-weighted sound pressure spectrum Report the one third octave band sound pressure levels, 100 to 20kHz.

 

Linear Vibration

Report the linear vibration acceleration in units of m/sec2 of:
  • Overall, 20 – 5000 Hz
  • Amplitude of the fundamental frequency of rotation and harmonics.
  • Amplitude of the fan motor pole pass frequency and harmonics.
  • Third octave band spectrum, 25 to 5kHz.
 

Angular Vibration

Report the angular vibration acceleration in units of rad/sec2 of:
  • Overall, 20 – 5000 Hz
  • Amplitude of the fundamental frequency of rotation and harmonics.
  • Amplitude of the fan motor pole pass frequency and harmonics.
Reporting for Speed Sweep Operating Conditions Report the following results for each fan speed sweep.

A-weighted sound pressure level versus fan speed in decibels.

Vibration acceleration versus fan speed
Report the vibration acceleration in m/sec2 for the following orders: fundamental frequency of rotation (1st order).

  • fan motor pole pass frequency (typically 4th or 8th order).

 

Prominence ratio versus fan speed

Provide an X-Y-Z plot (3-dimensional plot) of prominence ratio vs. frequency vs. fan speed where:
X-axis is fan speed (rpm);
Y-axis is frequency (Hz); and
Z-axis is prominence ratio (dB) and can be represented using color intensity.


►Centrifugal Fan

We can perform the fluid dynamic performance test which includes flow-rate and static –pressure by wind tunnel. And we can also evaluate the sound pressure and quality performance for fan alone or system configuration in our acoustic lab.