Nonlinear time‐series analysis of optical signals to identify multiphase flow behavior in microchannels

Abstract

This study provides an insight into the instability and irregularity of multiphase flows in microchannels. Using a homemade optical measuring system, time series related to two‐phase flow dynamics under different operating conditions, fluids, and channel lengths were collected and analyzed via a nonlinear characteristic parameter, Kolmogorov entropy (KE). Our results reveal that higher KE corresponds to unstable flow behavior, while lower KE refers to steady flow behavior; higher KE values appear at comparatively low or high gas flow rates, and most Taylor flow regime appeared at proper operating conditions with small KE. An equation derived based on the definition of KE is proposed to better understand KE characteristics, which include bubble break‐up impact and gas/liquid flow rate ratio. Predictions from the proposed analytical equation agree with experimental results, suggesting that the equation effectively identifies unstable flows and can be used to ensure stable and predictable multiphase flows in microchannels. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2378–2385, 2017