Our database now includes one hundred fans—75 in the 120 mm format and 25 models with a physical size of 140 mm. In this article, we have compiled all data into unified charts. What was once separated for clarity is now brought together again, and the commentary will also include a… look ahead regarding fan testing. But we can already reveal that there is still a lot more to come.
… and of airflow
With airflow measurements, we can well explain why the test tunnel is shaped the way it is. It doesn’t consist of two parts just so that the “exhaust” can be conveniently clogged for pressure measurements. The anemometer (i.e. the wind speed measuring instrument) is held together by two parts, two formations, through the flanges.
The front part, at the beginning of which the fan is mounted, becomes steadily narrower and from about two thirds of the way through the cross-section is smaller than that of a 120 mm fan. The reason for this is that the cross-section of the anemometer is always smaller than that of the fans tested. The taper towards the anemometer fan is as smooth as could be chosen and the tunnel walls are smooth. This has minimized the occurrence of unnatural turbulence.
The difference between the cross section at the intake (fan under test) and at the constriction point (anemometer) also means a difference in dynamic pressure, the principles of the Venturi effect apply here. In order to avoid distortion at this level and to ensure that the fan airflow is not different from what it actually is, the Bernoulli equation must be applied to the measured values (for maximum accuracy, the calculation also takes into account the internal cross-sectional area of the anemometer, i.e. its inactive part ). After all this, it is again possible to confront our results with the paper parameters.
We use an Extech AN300 anemometer with a large 100 mm fan for the measurements. Its big advantage over other anemometers is that it is made for bidirectional sensing. This allows tests at different fan orientations. However, the “pull” position is more suitable or accurate for measurements, even though it may not seem so at first glance, but we’ll explain.
Here, we get to the second part of the tunnel, the part behind the anemometer. It is part of the whole device, mainly to allow a laminar flow of air to arrive at the impeller of the anemometer. Otherwise, uncontrolled side whirls would be reflected in the results, which are inconsistent with accurate measurements. Therefore, we will test the flow in the pull position. If anyone would like us to elaborate more on this topic, we can elaborate further at any time in the discussion below the article. Ask away. 🙂
In regard to the anemometer, we shall return for a bit to noise measurements and to setting modes according to fixed noise levels. It may have occurred to you as you were reading that the anemometer fan is also a source of sound that needs to be filtered out when measuring fans. For this reason, we insert a securing pad between the frame and the anemometer fan before each measurement and mode setting according to the fixed noise level. This, by the way, also holds the anemometer fan during static pressure measurements.
Thank you for all the hard work in reviewing and compiling this information!
If it’s not too much effort, would it be possible to maintain a page like this going forward with each new reviewed fan added on? It’ll make a convenient location to be able to reference back to (a one-stop-shop if you would).
Thank you for the comment! 🙂
What exactly do you mean by keeping it the same as in this article?
We separated the 140 mm fans from the 120 mm ones to prevent the charts from becoming too long. Even as they are now—especially in the 120 mm category, where we have more models—the graphs already take up quite a lot of vertical pixels. If combined, navigating them would be rather inconvenient, even on high-resolution monitors
Great job, guys.
Thank you! 🙂