I haven't looked much into the blower, but I did note a concern about it being to push air with some decent pressure, as possibly a more important/relevant spec than the cfm: 4"wc is not obvious, for any fan.
An axial fan would fail miserably, without a doubt, at any diameter and in any configuration. A blower ought to do well, but I suspect that it would have to be of a fair diameter, in order to achieve a pressure of 4"wc. I'm guesstimating 8" diameter, possibly more, hence the large box (also a noise suppressor). I'm all for DC control, but these are limited, so I believe that the blast plate is still needed. Agreed on the duct; an elbow is going to be the equivalent of ~24 feet of the same duct!
As for the calculation, I used the
Basic program, with these:
Duct Diameter: 32 (could be wrong, but impact is negligeable)
Throat diameter: [insert nozzle size]
Upstream static pressure: 14.7
Upstream static temperature: 70
name of gas: air
The program then returns gas viscosity, upstream gas density, beta, gamma, and the critical pressure ratio.
then I put in the dP (0.1, 1, 3 or 4, "wc) and it returns:
downstream static pressure, pressure ratio, exit velocity, Mach#, downstream static density, Reynolds, Mass flow rate, CD, the flow rate (converted in various units), and the "pressure recovery".
I see that 0.1" wc as a minimal pressure drop for the nozzle, in the sense that a dP that is any lower, will not produce results that are meaningful. I'm going by the fantester instructions, which state that 1.0"wc is the minimum dP, before one should switch to a smaller nozzles. I'm interpreting the instructions as:
min dP: 1.0"wc and max dP: 3.0"wc (across any nozzle). This seems to fall inline with a "desired measuring range".
Today I've got a lot of catching up to do, having been offline since Thursday, but I'll look into pressure drops of larger blowers, and see how to get to 4"wc+. Sidenote; might be able to use a combination of two (or more) 5" blowers, with DC control.
[edit: removed off topic ramblings]