Hi al;l, it's Mr. ALKIADT again (A Little Knowledge Is A Dangerous Thing)...in this case, my knowledge of Bernoulli effect. I know that when a fluid passes through a restriction, the flow rate speeds up to maintain the flow rate of the wider cross sectional area behind it...so if you've got one litre per minute going through a 1 square metre cx area pipe, if you halve that to 0.5 square metres, flow is maintained at 1 litre per minute, which means that through the restriction the fluid is moving much faster. I also know that this results in a lower pressure in the restriction, which is a bit counter-intuitive for most. A few things I don't know... Cross-sectional area...is this always measured perpendicular to the direction of flow? If the restriction ends suddenly (imagine a square ended tube within a tube, so the end of the restriction is perpendicular to the direction of the flow), how quickly does the fluid resume it's original slower velocity and higher pressure? Is it instantaneous? If there are multiple channels of different cross sectional areas, does the fluid travel faster in narrower restriction than in wider ones? Reason for asking...I'm wondering if it's possible to create/control air movement using side by side restrictions of varying dimensions - or indeed a restriction that is coaxial with the main channel...I'll try and explain... If I had a a flow of three litres per minute in a pipe with a rectangular hole measuring 30cm x 10 cm. If I divided the pipe such that a channel along one edge of it measured 10cm x 10cm...I was wondering if the pressure drop would induce a "turn" on the total flow when it rejoined...but that would need the higher speed and lower pressure to be maintained for some non-zero period "x" I guess, and I don't know if that's the case. Similarly, I wondered if running a narrow diameter pipe down a main pipe would cause faster flow at the centre, which when the flows rejoin, would cause material in the "outer flow" to gravitate towards the area of lower pressure at it's core - which could be used to prevent "spread" of the whole stream... Is any of this even close to scientific, or is it just bunkum? Thanks!