Posted:
Sun Aug 08, 2004 3:04 pmby rob hilton
Bruce: Flow straightening?
I don't understand, if you are drawing a vacuum, why do you need a flow strightener? On the otherside of the coin, if you are blowing air, there might be some advanage to using a flow strightener, but in case of a cylinder head, if you have a dummy cylinder under the head, again why do you need a flow strightener?
In my quest for flow bench infomation, I was told that if you build a long tube bench, no Plenum Box under the Bore Adapter, you shouldn't have to worry about air stabilization.
Long tube bench is defined, as, the tube lenght is 50 times the dia. of the test bore, in my case 4ins.=200 ins. of tube or 16.6 ft. of tube
Posted:
Sun Aug 08, 2004 6:46 pmby bruce
Flow straightening (laminar flow) will allow you to use less tubing length 16.6' of straight tube would make the bench quite large? If you have any turns in your bench, every time it makes a turn the flow will not be straight coming out of the turn. So in your design you need one section of straight tubing of 16.6'? With flow straighteners you create laminar flow and can use shorter runs of tube.
Is your bench design a pitot design or orifice? I would think on an orifice design that laminar flow would be less of a concern. On a pitot if you are not using annubars (averaging pitot tubes) then laminar flow is a must as you will not get a true reading of the flow within your test tube area.
The averaging pitots take a sample in various heights within the testing tube and average them out. Currently I am using soda straws hot glued together in a peice of pvc pipe for my flow straighteners. My flow straighteners are install at the end of 90* turn at the base of my plenum. This pipe goes from 4" to a 4"x3" 90* reducer. After this I can install a flow element of different dias (I have one in 3", 2" and 1.5") based on the range of flow I am testing. I would say that the surface area of the work you are testing should be a tad larger or the same as the surface area of the flow element on a pitot bench, this will allow you to see a finer change in cfm's.
As for price I do not have a firm price yet, not sure what the shipping cost is from the manufacturer.
Posted:
Sun Nov 21, 2004 6:34 pmby hollywood63
Hi everyone being new to the site and in the process of gathering info to build a bench I have a question. With using flow straightners how short can you going with the piping?
Thanks Art
Posted:
Mon Nov 22, 2004 7:50 pmby bruce
My annubar is located approx 12" from the end of the 90* turn. I personally do not see a difference in flow with or without the flow straighteners installed. My test pipe dia is 1.5" dia. I think having them installed instills a level of confidence in my readings. My readings on this bench are very repeatable and thats the goal repeatable readings.
