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[Fan Basics] 7th Period

Airflow resistance of the device

What is ventilation resistance?

"Ventilation resistance" refers to the difficulty of air flowing inside a device, and is also called "system impedance." Even if you change the fan installed, the ventilation resistance will hardly change unless the positions and number of components installed in the device change.
Generally, ventilation resistance can be approximated by a quadratic curve that is proportional to the square of the air volume. The tendency of a quadratic curve is that when ventilation resistance is low (air flows easily), the curve leans toward the X-axis, and when ventilation resistance is high (air flows less easily), the curve leans toward the Y-axis.

Figure 1: Relationship between ventilation resistance and mounting density inside the equipment

By knowing the point where the "ventilation resistance" of the equipment and the "airflow-static pressure characteristics" of the fan intersect, you can determine whether the fan is suitable for the equipment. This intersection point is called the fan's "operating point," and the airflow at the operating point is called the fan's "operating airflow."

Ventilation resistance and air volume-static pressure characteristics


How to measure ventilation resistance

Although it is possible to calculate the airflow resistance using a formula, in the latter case it is necessary to measure the operating airflow of the fan, so in either case a measuring instrument is required. In general, a multi-nozzle, double-chamber measuring instrument is used to evaluate the characteristics of a fan with high accuracy.
This measurement method converts the pressure difference between chambers A and B in the figure into the wind speed at the nozzle cross section, and calculates the air volume by multiplying this wind speed by the nozzle's cross-sectional area. By selecting nozzles with different openings to match the air volume range of the object being measured, highly accurate measurements can be made over a wide range of air volumes.

Figure 3: Structure of the multi-nozzle double-chamber measurement device

Generally, double-chamber measurement devices are large and often stationary, so the device to be measured must be transported to the location where the double-chamber measurement device is to be installed.

Achieve measurement of fan ventilation resistance with a compact and lightweight device!
"Airflow Tester"

However, there is also a portable measuring device called the "Airflow Tester" that we developed.
This uses the same multi-nozzle double chamber measurement method, so you can easily measure ventilation resistance and operating air volume with high accuracy.

By measuring the airflow resistance with this Airflow Tester, you can efficiently design a housing that takes heat countermeasures into consideration.

Double chamber measuring device Airflow Tester
mass Approximately 600kg Approx. 6kg
Size (mm) 1000×1000×6000 250×250×600
Air volume (m3 /min) 0.05-20 0.2-8.0
Static pressure (Pa) 0-2000 0-1000
Measurement method Double chamber system
Measurable items Operating air volume, ventilation resistance, air volume-static pressure characteristics
Air flow measurement accuracy ±2% ±7%


Supervised by: SANYO DENKI CO., LTD. Cooling System Design Department

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