PRODUCT SELECTION
A. HOW TO SELECT A SUITABLE COOLING FAN
- THE NEED FOR FORCED-AIR COOLING SHOULD BE DETERMINED AT AN EARLY STAGE IN SYSTEM DESIGN. IT IS IMPORTANT THAT THE DESIGN PLANS FOR GOOD AIRYLOW TO HEAT-GENERATING COMPONENTS AND ALSO ALLOWS ADEQUATE SPACE AND POWER FOR COOLING FAN. FACTORS TO BE CONSIDERED IN FAN SELECTION INCLUDE REQUIRED AIRFLOW. AC OR DC POWER. VOLTAGE, SPEED, LIFE EXPECTANCY, BEAT DISSIPATION, IMPEDANCE PROTECTED AND AUDIBLE NOISE.
- THE AIRFLOW REQUIRED CAN BE OBTAINED USING AN EQUATION FOR CALCULATION WHERE: Q= 1.76W/Tc
- Q=AIRFLOW REQUIRED IN CFM(FT3/N41N)
- W=HEAT DISSIPATED IN WATTS
- TC=ALLOWABLE TENIPERATURE RISE IN °C(TC=TI-T2)
- FOR EXANDLE, 32CFM OF AIRFLOW IS REQUIRED
B. MEASURING ARIFLOW AND STATIC PRESSURE
- AN AMCA STANDARD 210 DOUBLE CHAMBER IS USED TO ACCURATELY MEASURE AIR VOLUME AND STATIC PRESSURE.
LIST OF EQUATIONS AND VARIABLE
- Q: AIR VOLUME = 60 C/4 D2=M2G/R PN (M3/MIN)
- C: COEFFICIENT OF NOZZLE AIR VOLUME
- D: DIAMETER OF NOZZLE (M)
- R: AIR DENSITY=1.293
- T: TEMPERATURE °C
- P: AIR PRESSURE (MM H2O)
- PN: DIFFERENTIAL PRESSURE OF AIR VOLUME (MM H2O)
- PS: STATIC PRESSURE (MM H2O)
- G: 9.8M/SEC2
- MAXIMUM STATIC PRESSURE AND MAXIMUM AIR VOLUME MEASUREMENTS MUST BE TAKEN SEPARATELY.
- MAXIMUM STATIC PRESSURE MEASUREMENT: WHEN THE NOZZLE IS CLOSED, THE PRESSURE IN CHAMBER A WILL REACH A MAXIMUM. THE PRESSURE DIFFERENCE PS REPRESENTS THE MAXIMUM STATIC PRESSURE ACHIEVABLE BY THE FAN.
- MAXIMUM AIR VOLUME MEASUREMENT THE NOZZLE IS OPENED AND THE AUXILIARY BLOWERS IS USED TO LOWER THE PRESSURE IN CHAMBER A TO PS=O. THE MAXIMUM AIR VOLUME CAN THEN BE CALCULATED USING PN. D AND THE AIR VOLUME EQUATION ABOVE. Q REPRESENTS THE MAXIMUM ACHIEVABLE AIRFLOW WITH THE FAN IN FREE AIR
C. SYSTEM IMPEDANCE & SYSTEM OPERATING POINT
- THE PERFORMANCE OF A FAN IN A SPECIFIC APPLICATION IS DETERMINED BY THE INTERSECTION OF THE DEVICE CHARACTERISTIC CURVE AND THE FAN CHARACTERISTIC CURVE THE FAN CHARACTERISTIC CURVE. THE FAN CHARACTERISTIC CURVE IS EXPLAINED IN THE MEASURING AIRFLOW AND STATIC PRESSURE SECTION. THE DEVICE CHARACTERISTIC CURVE IS A PROPERTY INHERENT TO AN INDIVIDUAL ELECTRONICS ENCLOSURE. IT DESCRIBES HOW AIR WILL FLOW THROUGH THE ENCLOSURE GIVEN ITS PARTICULAR OBSTACLES AND INTERNAL RESISTANCE. RESISTANCE CAN BE TURNS IN THE AIRFLOW OR CHAMBERS THAT THE AIR MUST FLOW THROUGH. THE FLOW RESISTANCE IS ROUGHLY PROPORTIONAL TO THE SQUARE OF THE VOLUMETRIC FLOW RATE. AS A RESULT, THE GRAPH OF STATIC PRESSURE VS. AIRFLOW IS PARABOLIC FOR THE ENCLOSURE. THIS CURVE CAN EASILY BE GENERATED EXPERIMENTALLY. BY TESTING THE ENCLOSURE PRESSURE AT VARIOUS AIRFLOW RATES.
- THE INTERSECTION OF COOLING FAN PERFORMANCE CURVE AND SYSTEM RESISTANCE CURVE IS THE SYSTEM OPERATING POINT. THIS IS THE DETERMINING FACTOR IN YOUR SELECT10N OF COOLING FAN.
- THE HIGHER THE SYSTEM OPERATING POINT MEANS THE HIGHER OF TOTAL HEAT DISSIPATION EFFICIENCY OF THE COOLING FAN YOU HAVE SELECTED AND YOUR DEVICE. IT IS ALSO TRUE FOR THE OTHER WAY ROUND.
D. ACOUSTIC NOISE LEVEL
- NOISE IS TESTED IN ACCORDANCE WITH ISO-3745 AND ANS112.35 IN AN ECHO-FREE ROOM WITH BACKGROUND NOISE LOWER THAN 15DBA. THE TESTING COOLING FAN RUNS IN FREE AIRFLOW AND A NOISE METER IS SET TO 1 METER AWAY FROM AIR ENTRANCE AND AT 90DEGREE TO THE FAN. THE TEST RESULT IS DEPICTED WITH SOUND PRESSURE LEVEL FREQUENCY BAND. IN DBAS.
FAN BEARING SYSTEM
COMPARISON OF BEARING RELATING CHARACTERISTICS
| CHARACTERISTICS | SB TYPE | BB TYPE | BS TYPE |
|---|---|---|---|
| (1)Material | Alloy copper, self lubricant type of powder metallurgical | Ball bearing | Alloy copper, ball bearing |
| Lower precision | Higher precision | One of each type | |
| (2)STRUCTURE DESIGN | COPPER ALLOY (SLEEVE TYPE) | BALL*2 | SLEEVE* (HEMPSHIRE TYPE) BALL*1 |
| (3)Manner of use | The relative movement between bearing and shaft is of line contact | SLEEVE* (HEMPSHIRE TYPE) BALL*1 | Both point and line contact |
| Larger running friction | Lower running friction | Running friction is between the two at left | |
| Oil is deposited at the inner side of ID of bear ing by vacuum impregnating and oil film formed with the heat generated through running friction | Ball inside the bearing is positioned by holder and rotates under assistance of lubricating grease | It has both WP/BP types features in use and operation load falls at the front end of ball, and copper alloy at the rear end is basically a supprot and adjust concentrically after positing of ball. | |
| Cooling fan is fixed vertically and is better to use | Cooling fan can be fixed in any position | Cooling fan is fixed vertically and is better | |
| (4)NOISE | UNDER LOW SPEED, QUIETER IN THE EARLY STAGE OF OPERATION | NOISE IS LOWER UNDER HIGH SPEED OF OPERATION | NOISE IS LOWER UNDER HIGH SPEED OF OPERATION |
| (5)Temperature resistance | Working temp: 10°C +70°C | Working temp: 30°C +75°C | Working temp: 10°C +70°C |
| Better heat shock capacity | Heat shock capacity in between | ||
| (6)LUBRICATION | LUBRICANT TENDS TO BECOME LESS EFFICIENT AT HIGH TEMP. | LUBRICATING GREASE IS NOT LIKELY TO BECOME LESS EFFICIENT | A COMPROMISE BETWEEN COST & EFFICIENCY |
| (7)Service life | Shorter (averaged appx. 20000-30000 HRS/40°C) | Longer (averaged appx. 35000-50000 HRS/40°C) | Aaveraged appx. 25000-40000 HRS/40°C) |
| (8)COST | LOWER | HIGHER | A COMPROMISE BETWEEN COST & EFFICIENCY |