Interesting so, KnC is a 250/900 = 0.28 W/mm^2 chip and HashFast is a 350/324 = 1.08 W/mm^2 chip, requiring a cooling solution that can transfer 5.6x the heat per mm^2. I really hope your cooling solution holds up 24/7!
Out of comparison, an ATI 7970 is a 250/365 = 0.68 W/mm^2 chip and an nVidia GTX Titan is 250/561 = 0.45 W/mm^2 chip.
Out of comparison, an ATI 7970 is a 250/365 = 0.68 W/mm^2 chip and an nVidia GTX Titan is 250/561 = 0.45 W/mm^2 chip.
Hashfast's chip at nominal (400GH/s) is expected to consume about 250W of power, not 350W. i.e. 0.77W/mm^2. Overclocked Sandy Bridge E in shipping commercial products with the same cooling system runs 350W with a 425mm^2 die, 0.82W/mm^2.
OK, so two questions:
1) https://hashfast.com/shop/babyjet/ states 350W power draw (+/- 20%), but the chip only consumes 250W? 100W for cooling/misc?
2) An overclocked Sandy Bridge-E doesn't "run" at 350W, for example check this (pic below). The 349W here is System Peak Power, a very different metric (system vs CPU and peak vs sustained).
Subtracting the system idle power (85W@4.7GHz), even at peak usage it would run at 264W (and it would die from electromigration if run like this 24/7), so 264/425 = 0.621W/mm^2, still 20% below 0.77W/mm^2.
Edit: Let's not forget that a Sandy Bridge-E uses a high quality heatspreader (IHS) with fluxless solder, so the actual contact area with the cooler is much bigger than the die size, reducing the W/mm^2 requirements by a large amount.