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I want to measure the avg. inner cross-section area of a flexible tube of outer diameter 5mm. Since the cross-section isn't a circle exactly, use of vernier caliper to measure inner diameter fails. The idea that I wish to try is, to take a tube of known length, fill it with water, then pour the water on to something like a volume flask and from the volume obtained compute the cross-section area.

My questions are, 1 - how valid does this method sound? 2 - Is there a better way to do this? 3 - How much error would the water stuck in the tube due to surface tension introduce?

Would appreciate any help. Thanks.

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Probably offtopic. Can't you measure the thickness of the tube, though? Keep in mind you have to measure it in a curved state. – Kvothe Apr 4 '14 at 10:01
I can measure the thickness, but a 5mm flexible tube isn't exactly 5mm in diameter always, parameters like temperature, liquid pressure comes it. Doing that wont be accurate enough. – Prashanth Apr 4 '14 at 10:31
up vote 1 down vote accepted

Your method seems fine to me. Essentially you're measuring volume by filling it with a fluid, and this is a method commonly used for determining the densities of powders or other materials where it's hard to measure the volume. The method is known as pycnometry if you feel the urge to Google it.

To improve the accuracy I would:

  1. weigh the tube
  2. fill it with water and block the ends
  3. weigh it again

That avoids errors introduced by trying to decant the water from the tube into a weighed container.

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That's brilliant! Thanks a lot - let me test it out and let you know. – Prashanth Apr 4 '14 at 12:38

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