we are going to conduct PIV-Measurements in a tube diameter 2.7 [mm]. We must design our own calibration plate.
FOV: 2.7 [mm]*2.7[mm]
Magnification : 4.5
Maximum velocity: 15 [m/s]
1) How to determine appropriate point diameter and distance of points for a given PIV measurement with given magnification and maximum flow rate ?
2) - What material should the plate be made of? Is a chrome-plated glass plate with holes in the chrome layer suitable?
3) Number of points in horizontal and vertical directions ?
4)acceptable tolerances for point diameter and point distance?
1. make sure that your tube is also submerged into the fluid bath and the bath walls are straight and perpendicular to the imaging axis. calibration won't be able to compensate for the 2.7 mm tube curvature.
2. not sure there is any point to insert a calibration into the 2.7 mm tube - are you going to use laser sheet through the pipe? if you're going to use a light through or volumetric lighting, the rules of game change, see 3D-PTV like calibration targets - with depth.
3. 15 m/s flow speed through a pipe of 2.7 mm is extremely challenging - the particles will pass the field of view within 0.00018 sec, so to use PIV there you need to image 2.7 mm over e.g. 512 pixels with about 6 micron resolution per pixel and a typical 32 pixel window will be just 180 microns and that means the time is very short. The resolution also means that you need very small holes to make a sufficient number of those for the plate.
4. if the light is PIV-like thin laser sheet and you manage to insert the small plate inside (obviously not 2.7 mm as it's your inner diameter, so e.g. 2 mm, with some spacing on each side to manage to insert the plate, you can make 10 x 10 points and it'll be sufficient I think. The whole point is that your calibration plate would have to be parallel and aligned with the laser sheet and then the only correction is due to small mismatches of the index of refraction, curvature, camera angle, etc.
5. yes, glass plate or just laser-cut metal plate would be fine.
Alex
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