# How to calculate the time delay created by a tube.

Hi,
I am trying to model a pressure tube of length 'L', where a fan is attached at one end and the other end is open.
I know that Pressure in the tube will vary w.r.to space and time when there is some change in excitation at the input. I got the pressure drop equation ,
[Pressure drop] dP = 4 f dx V^2 /(gD)
f - friction created by the walls of the tube. dx - distance. V - velocity of air flow. D- diameter of the tube. g- gravity
Using the above equation, I can calculate pressure drop at any distance (dp/dx) directly. But how can I get the time delay created by the tube. Please some one guide or teach me how to derive P(x,t).
Thanks srinivas
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srinivas wrote:

As far as I know the time dependency will be on the order of the speed of sound within the tube, times it's length. So unless you're working with a really long tube, or a really short time span, you'll be OK.
--

Tim Wescott
Wescott Design Services
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Tim Wescott wrote:

Arg! No, that can't be right for significant pressure rises. There's a differential equation in there involving the fill time of the tube, the amount of material you're cramming in and the pressure, but I'd have to actually work to derive it (not to mention learning more fluid dynamics than I know now).
--

Tim Wescott
Wescott Design Services