Closed Loop AIO Liquid Coolers: 14-way Mega Roundup Reviewby E. Fylladitakis on February 12, 2014 7:00 AM EST
Although the testing of a cooler appears to be a simple task, that could not be much further from the truth. Proper thermal testing cannot be performed with a cooler mounted on a single chip, for multiple reasons. Some of these reasons include the instability of the thermal load and the inability to fully control and/or monitor it, as well as the inaccuracy of the chip-integrated sensors. It is also impossible to compare results taken on different chips, let alone entirely different systems, which is a great problem when testing computer coolers, as the hardware changes every several months. Finally, testing a cooler on a typical system prevents the tester from assessing the most vital characteristic of a cooler, its absolute thermal resistance.
The absolute thermal resistance defines the absolute performance of a heatsink by indicating the temperature rise per unit of power, in our case in degrees Celsius per Watt (°C/W). In layman's terms, if the thermal resistance of a heatsink is known, the user can assess the highest possible temperature rise of a chip over ambient by simply multiplying the maximum thermal design power (TDP) rating of the chip with it. Extracting the absolute thermal resistance of a cooler however is no simple task, as the load has to be perfectly even, with the ability to vary the load, as the thermal resistance also varies depending on the magnitude of the thermal load. Therefore, even if it were possible to assess the thermal resistance of a cooler while it is mounted on a working chip, it would not suffice, as a large change of the thermal load can yield very different results.
Appropriate thermal testing requires the creation of a proper testing station and the use of laboratory-grade equipment. Therefore, we created a thermal testing platform with a fully controllable thermal energy source that may be used to test any kind of cooler, regardless of its design or compatibility. The thermal cartridge inside the core of our testing station can have its power adjusted between 60W and 340W, in 2W increments (and it never throttles). Furthermore, monitoring and logging of the testing process via software minimizes the possibility of human errors during testing. A multifunction data acquisition module (DAQ) is responsible for the automatic or the manual control of the testing equipment, the acquisition of the ambient and in-core temperatures via PT100 sensors, the logging of the test results, and the mathematical extraction of performance figures.
Finally, as noise measurements are a bit tricky, we're measuring these manually. Fans can have significant variations in speed from their rated values, thus their actual speed during the thermal testing is acquired via a laser tachometer. The fans (and pumps, when applicable) are powered via an adjustable, fanless desktop DC power supply and noise measurements are being taken 1m away from the cooler, in a straight line ahead from its fan engine. At this point we should also note that the decibel scale is logarithmic, which means that roughly every 3 dB(A) the sound pressure doubles. Therefore, the difference of sound pressure between 30 dB(A) and 60 dB(A) is not "twice as much" but nearly a thousand times greater. The table below should help you cross-reference our test results with real-life situations.
|Noise Level Reference Values|
|35-38dB(A)||Very quiet (whisper)|
|38-40dB(A)||Quiet (slight humming)|
|40-44dB(A)||Normal (humming noise, comfortable level)|
|44-47dB(A)||Loud* (strong aerodynamic noise)|
|47-50dB(A)||Very loud (strong whining noise)|
|50-54dB(A)||Extremely loud (level equivalent to a ≈1500W vacuum cleaner)|
|>54dB(A) *||Intolerable for home/office use; special applications only.|
* Noise levels above this are not suggested for daily use