2 x 45 deg. elbow vs. 90 deg. elbow air resistance

I always used these cheap house air duct parts for dust collection piping. But for dust collection, 90° elbows would ideally be with a much larger radius. I could configure two of these elbows to make a larger radius 90° elbow, but would such a crude approximation result in less air resistance? so I did a quick test with my dust collector.

For a dust collector like this with a centrifugal blower, the more air that flows through it, the more power it consumes. This is because any air going through it must be accelerated in the fan, whereas if air flow is blocked off, it's the same air that just keeps going around and around in the blower without the need to re-accelerate it.

So I measured motor power consumption to gauge air flow. Results were:

90°		850 watt —> 764 watt	(down 85 watt)
2 x 45°		850 watt —> 793 watt	(down 57 watt)

So 2x45° has 2/3 effect on air flow as 1x 90°

This even though the two elbows together make for a longer duct, and with twice as many ridges in the elbows.

More interesting stuff relating to fluid dynamics:

Effect of hoses on shopvacs and dust collector air flow

Dust collector analysis via Computational fluid dynamics

Analyzing the cyclone

Mini tornado experiment

Blower impeller design experiments

Fun with the
Venturi effect

Sucking down on this cone makes it rise, and feynman sprinkler