Investigation of Taylor bubble wake structure in liquid nitrogen by PIV technique

The Taylor bubble wake structures of liquid nitrogen in circular tubes with five different inner diameters under various inclination angles were investigated using particle image velocimetry (PIV) technique. Optical distortions produced by tube curvature and the refractive index difference between the tube and fluid were corrected by a new correction algorithm, which requires fewer equations than the existing one. The uniform grid validation shows the maximum error of the developed algorithm is only 3%. Experimental results have shown that the criterion for determining the wake structure of Taylor bubble in normal atmospheric temperature fluid in vertical tube from reference is still applicable for liquid nitrogen at higher Eötvös numbers 173 and 226; but the criterion is no longer applicable when the Eötvös numbers are at lower values of 8, 22 and 57. For the inclined tube, the vortex size in Taylor bubble wake was found to increase with the decreasing of inclination angle.

► We study the wake structures of Taylor bubbles flowing liquid nitrogen using PIV technique.
► We correct the optical distortions by a new correction algorithm.
► The existing criterion for determining the wake structure in normal atmospheric temperature fluid is not applicable for LN2.
► Both the transitional and laminar flow patterns are observed with the Nf numbers much larger than the critical value 1500.