New, reliable, and innovative methods (the new hybrid index (NHI) and the information index (II)) for flow regime (FR) identification in bubble columns (BCs) operated with air–deionized water or nitrogen–tap water systems (at ambient conditions), as well as nitrogen–ethanol systems (at pressures of 0.1 and 0.3 MPa) systems have been successfully developed. New parameters extract useful hidden information from time series measurements by division of various signals (gas holdup, differential pressure (DP) and gauge pressure fluctuations) into different equal parts. Salient advantage of the new parameters is that their definitions are not based on any assumption.

Based on the local minima in the NHI profile extracted from gas holdup time series, two transition gas velocities U_trans at 0.032 and 0.046 m/s have been identified in an air–deionized water BC (0.1 m in ID). The NHI profile based on DP fluctuations in a nitrogen–tap water BC (0.102 m in ID) distinguishes similar U_trans values at 0.029 m/s and 0.047 m/s. In a nitrogen–ethanol system at ambient pressure, the NHI identifies only the first U_trans value at U_g=0.028 m/s. At elevated pressure (0.3 MPa), it has been found that this first U_trans value shifts to a higher U_g value (0.045 m/s). In the annularly aerated BC (operated with an air-deionized water system), the main transition velocities have been identified at U_g=0.026 m/s and 0.073–0.079 m/s (depending on the clear liquid height), respectively, based on the newly defined II profile.

In summary, this work presents novel and reliable methods for FR identification in several BCs and reports new, useful experimental results about the FR boundaries based on them.

Polystyrene microcapsules were prepared by using the solvent evaporation method from S/O/W emulsion which contains fine particles of CaCl₂ in the organic phase. The microcapsules were fractionated by their size and permeability of the wall using settling difference in methanol. Further, phase change materials that have two different wet-ability characters were successfully impregnated. The hydrophobic compound was easily impregnated to microcapsules which have hydrophobic wall material. Meanwhile, the hydrophilic compound, which is salt hydrate, was not impregnated to the same microcapsules via direct impregnation but the salt hydrate was successfully impregnated by the volatile exchange impregnation method. Simple thermal properties of the prepared phase change material microcapsules were examined by TGA and DSC methods.