Bubble characteristics in pressurized bubble column associated with micro-bubble dispersion

Bubble characteristics of air-kerosene system and air-water system in a pressurized bubble column were analyzed. Experiments were carried out at system pressure up to 3.5 MPa on a cylindrical stainless column with an inner diameter of 0.097 m and a height of 1.8 m. Kerosene and tap water were used as liquids while air was used as gas. Bubble characteristics were observed by varying gas velocity up to 98 × 10⁻³ m/s at 0.1 MPa and up to 31.1 × 10⁻³ m/s at 3.5 MPa. Bubble chord length and bubble rising velocity were measured with a single tip probe installed at the top of the distributor at 0.5 m. In addition, pressure difference between the top and bottom of the column was measured with a differential pressure transducer to confirm gas holdup. In the air-kerosene system, gas holdup tended to increase with increasing system pressure. From the analysis of drift flux, transition from homogeneous to heterogeneous flow regime was observed only under atmospheric pressure. In the air-kerosene system, drift flux tended to be kept constant as gas holdup increased under pressurized conditions. The system pressure was varied from 0.1 MPa to 3.5 MPa to confirm micro-bubble generation under pressurized conditions. Dynamic gas disengagement (DGD) analysis and image analysis at the same time showed that gas holdup fraction of micro-bubbles was almost constant (ε_m/ε_g = 0.4) at atmospheric pressure. However, it was increased from 0.48 at gas velocity of 12.3 × 10⁻³ m/s to 0.57 with gas velocity of 32.1 × 10⁻³ m/s at 3.5 MPa.