Denny,
1.) Not sure where the test guys got the canned smoke. It came in an aerosol can. It was actually fine talcum powder with a CO2 propellant. I think McMaster would be a good start. We used a walmart fog machine (holloween thing) while in the shop because it lasted much longer than the cans did.
2.) A lip is a single ring around the round opening in the shroud. A box shroud is simply a plate with 4 bent sides going towards the radiator and a hole in it for the fan. A venturi is the rounded edge (found on most Class 4-Class 8 trucks) as well as high dollar mobile equipment. (the low end stuff gets brake-press formed box shrouds).
3.) with a 3.5" hub (should be counted to the point where the blades start their profile) you would be a minimum of 1.75" away. For bigger fans, I had hubs from 6" on small diesels to 2' on large diesels. Air likes to move in as straight a path as possible. It generally wont turn more than 90 degrees without turning vanes to help it, so assume a perfect 90 degree cone covering the hub with the point at the radiator. The height of the cone would be 1/2 the diameter of the hub. You can run it closer, however it leaves a dead air spot in the middle where the hub is.
4.)yes.
5.)it is a rule of thumb, and it usually is where the box portion of the shroud is. The lip simply reduces tip losses. The rule is more for a box shroud (back of box you mentioned) - puller, 1/3", for a pusher 2/3 in. I did a test once with the launch of the 644e / 944e Lull's where we had 6 different fan spacer combinations and 4 shroud lip lengths. This rule requirement diminishes as the tip clearance is minimized and as the lip length gets longer. However for fans under 24", 1" is a simple lip length to keep. I wouldnt go less than 1/2" on an 18" diameter fan.
20 gauge aluminum works well, can be bent on the edge of the workbench with a rubber mallet and can be riveted easily.
Dave for what its worth. spinning a fan faster robs much more power than spinning a properly designed fan slower. It also makes more noise. Going back to the comment that fan speed is a function of fan blade design. Having discussed fan profiles with the folks at Multi-Wing and GT fans for years, to determine a fan speed, I need to know the radiator pressure drop and fan stall points.
