AbstractBubble characteristics and gas hold‐up were studied in a two phase (air‐aqueous CMC solution) bubble column provided with helical coils and straight tubes as internals. The effects of superficial gas velocity, rheological properties, and volume fraction covered by the internals, on gas hold‐up were studied. Hold‐up values determined directly and by simultaneous pressure drop measurements matched well. Enhancement of gas hold‐up values up to 55 per cent was achieved in systems using internals. The gas hold‐up results were also compared with the values obtained from correlations reported in the