Instantaneous mass transfer measurement and its relation to large-scale structures in pipe flow

Highlights: • A low-pass filter was applied to ensure that the frequency associated with large-scales (length scale > 2.4R, f • The time-series contour of stream-wise velocity fluctuation and mass transfer fluctuation verified that the footprint of large-scale turbulent structures in the log region affects the near-wall region, enhancing the mass transfer rate. • The comparison of the two-point correlations of stream-wise velocity fluctuation and mass transfer fluctuation indicates a certain relationship between the mass transfer rate at the wall and large-scale velocity structures in the log region - Abstract: The flow field and mass transfer rate in a straight pipe are measured simultaneously using particle image velocimetry (PIV) and an electrochemical method, respectively. Turbulence structures of length scales larger than 2.4R in the log region are studied in relation with the mass transfer fluctuations in the near-wall region. The time-series contours of the fluctuations in mass transfer and stream-wise velocity are compared, and their correlation coefficient is discussed. Using the time-series contour, it can be confirmed that the footprint of the large-scale turbulent structures in the log region affects the near-wall region, which enhances the mass transfer rate. By comparing the two-point correlations of the stream-wise velocity fluctuation and mass transfer fluctuation, the mass transfer rate at the wall is observed to be related with the large-scale velocity structures in the log region.