Quote:
Originally Posted by TomO
Just a correction: the 50CFM seen in the VX motor is at 2200rpm, not idle. At idle (550 RPM) it's 12.32CFM.
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Woops, thanks!
Anyone care to check my math?
I did a similar calculation for someone claiming that they made a difference with a squirrel cage fan in a fog light hole in another thread, it came to less than 100 Watts produced at highway speed...
Tonight, I'll redo the formula with 100% VE at 6k RPM. We'll see the max theoretical figure that the 1.5 L engine could produce.
Or, I could do the same calculation for a 12 liter engine at 100% VE, if that would suit anyone's thoughts better.
Either way, the number is ridiculously low, and the engine still wouldn't be able to run properly with that much energy being extracted from the intake stream.
Remember, the Betz limit is there for a reason... the theoretical max extraction of energy from wind is 59%, because at 60%, equilibrium is reached (according to Betz, anyway.) If this weren't true, a brick wall would be 100% efficient at harnessing the wind's energy, since it would not allow any of the wind to pass.
With a fan, it's rotational speed is inversely proportional to the amount of air allowed to pass. The fan would provide more resistance to air passage at higher speeds, and less resistance at lower speeds, to the extent that (unlike I said earlier) full throttle would not be a stopped fan blade, but instead, a blade that spun only enough to allow an unrestricted passage for fluid (air).
Without actually doing the calculations, I can theorize that the fan in the intake would reach equilibrium, in a power generation sense, at almost all times. There wouldn't be enough energy to extract at high fan speeds, due to low intake volume, and the fan wouldn't extract enough of the available energy at low fan speeds, due to the low generator armature speed.