wyes and wherefores; caution contains obsessive adult concerns fixable with duct tape
I am thinking about transitions. I have read that a taper of 7 degrees total angle is desirable to use where space allows, following the "principle of pressure energy and velocity energy conversions seen in the Bernoulli/ Euler energy equation". This sounds like a Catholic Catechism that I will have to take on faith. But to me it means that I want to get the chips and dust to the modest 12" impeller/5hp blower (New York Blower Compact model direct drive size 126) first and worry about getting it to the outdoors second. I have already committed to 8" mains to match the 8" round inlet of the blower and I can place the blower unit just on the other side of the wall from the shop in a basement crawlspace where it can blow like the the winds in the heath scene of King Lear and not trouble anyone. I am coming off the mains with 6" wyes down to the machines, of which only one will operate at a time in this small one dude basement/garage hobby workshop. You would think I was designing a high dollar pharmaceutical recovery system with all I have been reading and thinking about this stuff. But it really is fascinating and not my field of study.
My question is about the size of the exit duct which is currently in the to be decided category. System effects and the need to get the chips out the door being the relevant factors that come to mind. So if I mount the blower to the joists at the level of the main ducts, the mystery to be solved, and the point of this post, is the shape and size of the transition and size of duct to the outside wall. I have about 3' of space down to the dirt floor from the blower outlet to work with. Then there is 16' to the outside wall which is in line with my main inlet putting the blower outlet perpendicular to its intended goal line. But it is all downhill from there and no filter or separator in the way, which is in my favor. The side yard is all ivy and shade trees with my nearest neighbor 100 yards from the line so he will not be calling any fouls. Unless I get chickens out there and then he could cry fowl.
I had this brilliant idea to duct to the front of the home which would be in the direction of the blower outlet and save me about 10' of length to the wall out to the side yard. But my wife thought it indecorous and less than responsible to litter her front flower bed and grass yard with dust and chips. She was even less impressed with my idea to use a dog igloo that was big enough for our now deceased Great Dane as a dust bin that would contain the big stuff and let the air flow swirl and go out the front of the igloo. "But Honey, It would be mostly hidden behind a Rhododendron." The thing is tough heavy plastic that has been collecting dust for over 15 years. But, true to form, she did not appreciate the practical and comic genius of using the dog igloo for something as practical as real dust collection. Geesh, where does a guy get any emotional support these days?
But back to the point and more importantly, how do I fashion the transition for my blower outlet which is 9"x7-5/8"?
If a transition should be 7 degrees from this rectangle to the round end what is the length of this thing? I know the social science rubric of 7 degrees of separation but this is geometry. Then once this thing is shape changed to round it will be pointing in the wrong direction since my wife is not keen on it going out the front yard. The blower cover can be rotated so it can blow around the clock in 22 degree increments. It could go out the left top or rotated to the other side bottom right. For that matter it could point straight down. Depending on the length of the transition it would make sense to go straight down and then with an elbow or fittings to get it straight out to the wall exit. But I have no idea if it makes a difference to a transition if the dust is being flung out and the direction is along the short side of the rectangle to the round or the long side of the rectangle to the round. If this mattered then going down and out instead of to the side and out would make a difference.
But first things first. I need to make or get a transition made and I would appreciate some direction and advise on the dimensions and shape of this critter. Then there is the size of the duct and in my mind it would be as big as it could be so as not to rob the front end of static pressure but not so large as to promote chip build up in the duct and clogging.
To me this is an interesting puzzle to be solved with facts and science. It is not an upset that keeps me from more productive avocations like watching basketball which is going on non stop in my home at present. Go Vols!
WWBD? (What would Bernoulli do?)
