# help! flow in square duct

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 December 19, 2003, 11:46 help! flow in square duct #1 chris Guest   Posts: n/a Sponsored Links I am an academic in the UK and I have constructed a kinetic instrument that uses a small flow channel 0.25 mm square. This channel is imaged during steady state flow conditions using a CCD. I know the volume comming through the channel per unit time (around 1 mL per second and so I can calculate the linear velocity of the solution in the flow channel. When I use this linear velocity to generate my time base, I get an error of 1.3 in my kinetic rates compared with other measurements. This assumes the flowing channel cross section is 0.25 x 0.25 mm, i.e. 0.0625 mm ^3. However if I assume a flowing channel of diameter 0.25 mm I get the correct answer!! Is there any way of simulating flow in this channel and showing that the corner quadrants are static, i.e. that the true flow is down a 0.25 mm diameter cylinder in the middle? Any help would be appreciated as I am a biologist!!

 December 22, 2003, 11:13 Re: help! flow in square duct #3 chris Guest   Posts: n/a Dear Jim Thanks for your response. Yes, by linear velocity I mean bulk velocity. I call it linear because I know the field of view calibration in my image from the CCD camera (i.e., 1 pixel = 0.01 mm for example). Then knowing my bulk velocity I can caculate the time domain, i.e. the solution has zero age at the begining of the channel and age 1 millisecond or so at the end. This time domain allows me to calculate the rate of the chemical reaction which is out by the factor of 1.3. The channel is closed , i.e 4 walled and I believe I have conditions for turbulent flow (approx 1 mL/second down a channel 0.25 x 0.25 mm). It sounds as if it is likely that the flow is static in the corner quadrants although it is not a trivial calculation?? I will buy you that pint (somehow, even if i have to FEDEX it) if it can be done. (The viscosity of the solution will be that of water since it is all done in dilute aqueous phase). thanks for your help chris

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