THE BUBBLY WALL SHEAR STRESS IN A VERTICAL UPWARD LAMINAR TUBE FLOW

The results of experimental investigation of upward laminar flow with bubbles are presented. An electrodiffusional technique is used to detect perturbation of the wall shear stress caused by bubbles in the tube flow. A bubble generator based on the flow focusing technique has been developed for production of a submillimeter monodispersed bubbles mixture. It is proven that submillimeter bubbles significantly increase the flow mass transfer: the smaller the bubble diameter, the greater is the wall shear stress. Some peculiarities of the interaction are the detection of inherent liquid turbulence and pseudoturbulence induced by bubbles. It is shown that the additivity of pseudoturbulence and inherent liquid pulsations is fulfilled only for Re-b > 100, when for some smaller Re-b values this is not valid. The shear stress perturbations by single bubbles have complex structure. It is possible to define three components of perturbation caused by a single small bubble. The perturbation by a Taylor bubble contains only two components due to the main flow symmetry around the bubble. An unexpectedly long shear stress pulsation zone is registered behind single small almost spherical bubbles and Taylor bubbles.