AbstractThe effects of ratio of draft tube to reactor diameter (Dd/D), liquid nozzle diameter (dN), aeration tube diameter (dG) and immersion height of the two‐fluid nozzle into the draft tube (HN) on overall and annulus gas holdups for the air‐water system were evaluated experimentally in a reversed flow jet loop reactor over wide ranges of gas and liquid flow rates. Both the gas holdups increased with increasing gas and liquid flow rates and with decreasingdNandHN. The influence ofdGon gas holdups is found to vary with gas flow rates. Correlations are proposed to predict gas hold