Dust collection flex tubing, what's good?

[Todd Fatheree]

And to make it even more confusing, it is sometimes better to induce a turbulent boundary layer to get better flow than something that is strictly laminar.

Four and a half years of engineering school say "yes". The question is, what equations govern this type of flow? It sure isn't Bernoulli and I'm not sure Boyle's strictly applies. Boyle's Law is more applicable to a pressure cooker or a engine cylinder. I'm not sure it can be extended to a flow such as what we're discussing. But then, my specialization was solid mechanics, not fluids.

If you define "Swiss" by living in Switzerland, then this one is correct. Most people, howeve, define "Swiss" to mean, "born in Switzerland". It's clear he was born in the Netherlands.

goes with Netherlands

todd

[Scott Lurndal]

Like Professor Fish's work with humpback[*] flippers. The nobs on the leading edge perform much better than the typical smooth leading edges on modern aircraft wings. Expect to see knobby wings on future aircraft :-)

[*]

[J. Clarke]

Don't. It's called a "turbulator" and it works fine in low reynolds number flows. Put them on high speed aircraft and they create all manner of chaos. Been tried, repeatedly, in various forms. A whale is not an airplane.

[G. Lewin]

Whoa! Slow down, everyone. Let's back up.

[G. Lewin]

I guess it depends on the definition of nationality. I have no idea what citizenship rules were like then, or if it's relevant. His dad, Johann, was Swiss and was working in the Netherlands at the time of Daniel's birth. Were I to move to, say, Sweden and have a child, I would still consider my child an American. Would it be Swedish? Technically, I suppose.

Let's just say that he was a member of the Axis of Fine Chocolate Producing Countries (not sure what the third would be)...

G

[Bill Leonhardt]

This didn't seem quite right to me so I took a look at the numbers. IIRC, recommended duct velocities are 3000 to 4000 fpm.

Reynolds number = Re = (density)(velocity)(diameter)/(viscosity)

At 70 deg F: density = 0.075 lbm/cu ft viscosity = 0.044 lbm/ hr ft

A lower limit could be 3000 ft/min in a 4 inch duct.

Re = (0.075 lbm/ cu ft) (3000 ft/min) (60 min/hr) 4 in) / (0.044 lbm/hr ft) (12 in/ ft)

Re = 102,273

Since transition from laminar to turbulent flow (in internal duct flow) is in the range 2,000 to 10,000, this is clearly turbulent. Higher values for the flow rate and/or duct diameter will yield higher Re numbers.

I would expect you would want to stay away from laminar flow, and certainly stay away from transition for good performance.

Bill Leonhardt

[G. Lewin]

Damn. I'm sure I calculated a much lower Re once, but I can't find my notes to see where I made the mistake (I assume it was me, but I'll check yours). Probably got screwed up on the whole lbm/lbf thing...

G

Bill Le> SNIP

[G. Lewin]

In metric:

V = 3000 ft./min. X 1 m/3 ft. X 1 min. / 60 sec. = 16.7 m/s D = (1/3) ft X 1 m / 3 ft. = 0.11 m nu = 1.46 E-5 m^2/s

Re = VD/nu = 16.7 X 0.11 / (1.46 E-5) = 125,000

A little higher than yours, but I rounded. So, you're correct.

G

Bill Le> SNIP