"In conventional FFHS devices, the difference in temperature between the base of the finned heat sink and ambient air is almost entirely accounted for by the temperature drop across the boundary layer. The exception to this rule is lap top computers, where available electrical power is extremely limited. In this special case, CPU clock speeds and fan rotor speeds are reduced to conserve power, albeit at the expense of CPU performance. At these low fan speeds the residence time of air in the heat exchanger is greatly extended, resulting in much higher exhaust air temperatures."
Already they are getting mixed up with temperature and heat. Who cares the temperature of the air? If it is moving very slow it removes less heat. If the air (or water) is moving fast but only rises by 1c or less it is still removing alot of heat.
"The high level of audible noise generated by the larger, more powerful fans used in high-capacity CPU coolers has also proved a deterrent to further scaling up of such devices."
Just isn't true when pertaining to CPU coolers
"commercially available CPU cooler typical of those used in many desktop computers. For example, the calculation below is for a Bitspower model NP15S CPU cooler with thermal resistance rating of 0.92 K W-1, fan diameter of 60 mm, and fan speed: 4800 rpm."
Again, just isn't true. This HSF was on sale in 2001. It's only 26mm high (fan plus heatsink). Most desktop fans are 25mm high on their own. 4800rpm? lol. 60mm? not these days. 0.92 K/w? very poor compared to average nowadays.
Nexus low-7000 acheives: 0.29 c/w at 7v 1200rpm 18dba
0.23 c/w at 12v 1900rpm 31dba
"Accordingly, the temperature of the air discharged by such a CPU cooler is only slightly greater than the temperature of the surrounding ambient air, even if the CPU is running very hot."
Again mixing up heat and temperature.
"figure 5: the pressure-flow curve for a 4800rpm 60mm axial fan typical of those used in cpu cooling applications"
These havent been typical for over a decade.
"Our version 1 prototype device on the other hand has a measured thermal resistance of 0.2 C/W
For example, state-of-the-art CPU coolers providing thermal resistances as low as 0.2 C/W are not only very large devices unsuitable for mass market applications, but in addition are prohibitively expensive."
yet the low-7000 acheives 0.23 c/w at a cost of around £40 in shops, so much less at trade prices.
"As a final example, we note that the much lower noise levels generated by this new air cooling architecture has significant implications for scaling up air flow (and therefore cooling), as discussed in Section 1. While we have yet to record comparative laboratory data pertaining to sound levels, consistent with the discussion of fan noise in Section 1, it is clear that low noise operation will ultimately be another important advantage in real-world applications."
All HSFs mentioned in the white paper were manufactured 2002 or earlier.
At "several thousand rpm" their cooler uses 3-4 watts, I think most of ours work at 1.5 ish.
"No quantitative acoustic measurements were conducted due to limited resources, either. Nonetheless, it was obvious during initial testing that the broadband acoustic spectrum generated by conventional small high-speed fans was largely absent in the version 1 prototype device."
ie they can hear it in their lab, plus small high-speed fans are no longer conventional. The version 1 prototype was a 100mm diameter item, so should be compared with 92mm and 120mm fans. A quick look at a nexus fan of that size would show 18-21 db (from memory, probably innaccurate). I doubt their lab has an ambient noise level of that or less.
"With regard to the effect of PWM frequency, the Motortron ESC has only two settings, 8 KHz and 16 kHz. Nonetheless, recording of data at both PWM frequencies was important in that it showed that operation 16 KHz provided an improvement in motor efficiency, significant reduction in audible electro-acoustic noise associated with magnetostriction of the brushless motor stator poles."
ie, they can hear the change in noise in their lab.
"The FY09 Tier 1 LDRD and Sandia
Royalty funds invested in this proof-of-concept study have resulted in a major breakthrough in air-cooling technology. The arguments put forth in the original proposal in support of the boundary layer thinning effect, negligible air gap thermal resistance, low electrical power consumption, low-noise operation, and immunity to fouling have all been shown to be correct."
havent shown lower noise, consumes more power, might be cheaper to make but will it be cheaper to buy?, immunity to fouling has advantages with certain markets, but not the overclocking crowd who are the target for >3ghz clock speeds. The rest of the world has happily moved on to parallel cpus at lower clock speeds. They haven't shown much lower thermal resistance than what is already available to the consumer at reasonable prices.
Just my 2 cents