COMPARATIVE MEASUREMENTS IN BUBBLY TWO-PHASE FLOW USING LASER-DOPPLER AND HOT-FILM VELOCIMETRY

The subject of this paper is the relative merits of laser-doppler and hot-film measurement techniques in studies of bubbly two-phase flow processes as typically encountered in biological fermentation reactors. A comparison of the two diagnostic systems is made on the basis of simultaneous measurements of local mean velocities and root-mean-square values of velocity fluctuations in a 1100-mm high bubble column of 120-mm square plan. Findings are presented which suggest that optical obscuration may prevent the successful application of laser-doppler velocimetry in bubbly two-phase flow. On the other hand. where applicable, both measurement techniques yield comparable results, a finding which is consistent with observations in single-phase flow.