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Optical fibre interferometric system for Doppler effect measurement

100%

Jaroszewicz L. R. , Krajewski Z.

2002

tom Vol. 10, No. 3

185-191

A novel idea of optical fibre laser Doppler velocimetry especially useful for non-contact testing of rotation elements is presented. The main idea of the system is based on an application of interferometric measurement of Doppler effect by a specially constructed optical fibre interferometer. The standard single-mode coupler, connected with laser diode operated at 0.68 µm, has been used as the main optical element. A suitable selection of a target distance from the specially constructed optical head makes the system work as a single-reflection Fabry-Perot fibre interferometer. Such device provided polarisation stability as well as good environmental shielding. The special numerical processing of interferometric output signals by a technique based on FFT gives a possibility of rotation element testing. The theoretical investigation was compared with experimental data obtained for the commercially available magnetic hard disc and the dynamically tuned electromechanical gyro.

Laser-Doppler velocimetry - a powerful tool to investigate the flow behavior of polymer melts

63%

Merten A. , Schwetz M. , Münstedt H.

2003

tom Vol. 8, no spec.

283-288

The flow behavior of a low density polyethylene (LDPE) and a high density polyethylene (HDPE) melt in the entrance region, the interior of slit, and within a slit die was investigated by means of laser-Doppler velocimetry (LDV). Large vortices were found upstream of the die with for the LDPE. The HDPE did not exhibit any vortices. The velocities within the vortices are about 100 times smaller than those in the center of the flow. Far-reaching consequences for processing arise as the residence time of the melt in the vortices is long. The velocity distribution along the channel axis reveals large elongational deformations near the contraction. The elongational velocities are much higher than those attainable by elongational rheometers. For the HDPE it could be shown that the material slips at the wall.