Noctua NF-A14x25r G2 PWM
Close up of the new Noctua NF-A14x25r G2 PWM fan and its first tests. However, consider these as material for a “rough idea”, since as you already know, the pilot 140 mm LCP fans have atypical mounting holes for their format, so their mounting to the wind tunnel was necessarily non-standard. However, a few things can be concluded from these partial measurements as well.
The new 140-millimeter Noctua NF-A14x25r G2 PWM fan is aimed mainly at CPU coolers, primarily for cooling the new Noctua NH-D15 G2 (LBC/HBC) CPU coolers. It can also be suitable as a replacement for older, less efficient fans, for example on the NH-D15 G1’s heatsink (instead of NF-A15 PWM fans), but also other non-Noctua fans whose clips support 105 × 105 mm spacing for 140 mm fans (that is the standard spacing for 120 mm fans). This is the main reason why they are virtually incompatible with liquid cooler radiators and also with many cases.
Those cases that support 140 mm fans may not have the required mounting hole spacing for the Noctua NF-A14x25r G2 PWM and again for models that do, the impeller of these fans will be too large and even if it did fit, some part of the case bracket structure may interfere with it, which can be expected to have a negative effect on the acoustic properties. On the contrary, Noctua NF-A14x25r G2 PWM fans are suitable for the heatsinks of tower coolers, including the older Noctua NH-D15 (G1) cooler. These fans are compatible with the latter in terms of mounting. However, the sound profile may not be as pleasant as on the new heatsink, as psychoacoustic optimizations of the new fans on the old heatsink were naturally not Noctua’s focus.
And now on to the design details, which are in many ways the same as they will be later for the square-framed fans (Noctua NF-A14x25 G2 PWM).
Models with a circular frame (Noctua NF-A14x25r G2 PWM), which have already been released, are also not suitable for radiators due to leaky corners. Even if you manage to install them in a makeshift way, due to the leaks between the fan frame and the radiator frame, the air pressure/flow will drop and thus naturally the cooling performance will also drop. The latter probably won’t be downright bad, but expectations of peak performance may quickly dissipate. We saw what the difference between tight and leaky corners in a radiator application can be with the BeQuiet Silent Wings Pro 4 fans, which come with different types of corners. And a similar design to the one on the Noctua NF-A14x25r G2 PWM, with the highest leakage rate, delivers the worst results on radiators, naturally.
The NF-A14x25r G2 PWM fans, like all “second generation” LCP models, have humped blades (Progressive-Bend impeller) to achieve a higher pressure differential at points close to the impeller hub.
To achieve the best possible results, it is then articulated, with protrusions up to 0.5 mm in height. These are to bring the air streams in front of the impeller blades to achieve higher airflow. Only cosmetically, of course. Centrifugal Turbulator, as Noctua calls this innovation, is one of the new micro-optimisations.
The “old” micro-optimisations remain, although for example ISM (Inner Surface Microstructures) have a slightly different shape and depth again. The shape of this structure on the inside of the fan frame is based on the size of the gap that is between the blades and the tunnel. The smaller it is, the shallower the ISM is as well, since such a large microturbulent layer is not required to achieve optimum results.
In the previous generation NF-A14 PWM fans, the ISM is quite deep due to the several times larger gap between the frame and the blade tips. In the case of the NF-A14x25r G2 PWM, this gap is only around 0.7 mm.
While making this gap very small is beneficial for achieving the highest possible static pressure (and therefore airflow through an obstacle), it has also caused the most recent delay in the release of these fans. We also have a separate article on this topic – Noctua on NF-A14x25 G2 frame deformations (interview).
The “old” aerodynamic micro-optimisations (Stepped Inlet Design or Flow Acceleration Channels) have been joined by
winglets to reduce unwanted microturbulence at the blade tips.
In regards to the winglets, Noctua talks about a very good synergy with its AAO (Advanced Acoustic Optimization) frames and the overall design of the Progressive-Bend impeller. The latter, by the way, in this case has 9 blades.
The gaps between the individual blades appear to be quite large, but for high flow even through obstacles, there must be a combination of several elements. This will be dealt with, however, in the detailed analysis of the square-framed fans. For now, just the basics, which include information on the amount of static pressure (up to 2,56 mm H2O) and airflow (up to 155,6 m3/h). The values given in brackets refer to the maximum speed, which is specified and achieved at 100% PWM duty cycle or at linear (DC) 12 V, which is about 1500 rpm. With the slowing adapter to approx. 1250 rpm, the static pressure is supposed to be 1,3 mm H2O and the airflow then 127,1 m3/h.
And a short test at the end
Although the NF-A14x25r G2 PWM fan is incompatible with our wind tunnel mounts, we still tried a “makeshift” solution with atypical mounting. Namely, using a hot glue gun.
The above mounting procedure is of course completely outside of our strict criteria, which includes constant mounting pressure, but it’s at least “something” until it’s time to fully test the square frame models (NF-A14x25 G2 PWM) with the standard spacing for 140mm fans in September. In addition, the measurements of the NF-A14x25r G2 PWM in the tests below are based on only one sample (instead of three samples, as is standard), so take them with a grain of salt.
For our demonstration, we selected the “36 dBA” mode without an obstacle, which corresponds to a speed of about 810 rpm at zero static pressure. This is the third quietest and also the fourth noisiest setting in which we test fans based on standardized noise levels. Downwards, but also upwards, the relative ranking may be different, or the ratios between the compared fans may be greater. The ranking of the NF-A14x25r G2 PWM fan at the very top may still mean nothing for your particular situation. Especially in a mode where the fan faces no obstacle.
The NF-A14x25r G2 PWM’s relatively lower static pressure also doesn’t indicate that the airflow through obstacles, such as radiators, needs to be lower compared to competing fans with higher static pressures (think Thermaltake Toughfan 14 Pro…). The important thing to remember here is that the static pressure is measured at zero airflow, i.e. at a significantly higher resistance than in practice on a radiator. And then the acoustic response also plays a role on obstacles. So no jumping to conclusions yet, we have to wait for a complete all-round analysis of the square-framed model, the NF-A14x25 G2 PWM.
What the quantity “static pressure” means and how to understand it is discussed in this article.
English translation and edit by Jozef Dudáš
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