A comparative study of UVP and LDA techniques for pulp suspensions in pipe flow



For the first time, noninvasive measurements in pulp suspensions at consistencies ranging from 0.74%(w/w) up to 7.8%(w/w) have been performed simultaneously using ultrasound velocity profiling (UVP) and laser doppler anemometry (LDA) in an experimental pipe flow loop. Results show that both techniques can be used to determine the plug flow velocity with good agreement in much more concentrated pulp suspensions than what has been reported so far in the literature. Instantaneous velocity profiles have been obtained noninvasively in pipe flow using the UVP technique, and it is shown that combined with simultaneous pressure drop measurements, the UVP technique can be used to determine the yield stress in-line. Results further show that LDA works, with limited penetration depth of up to several millimeters, even in strongly opaque systems, such as in 7.8%(w/w) pulp. Deviating results were however obtained in the near wall region and more work is needed. © 2005 American Institute of Chemical Engineers AIChE J, 2006