Hold-up formation in bubble channel reactors: A bubble-scale investigation

Experiments were carried out to measure the air volume fraction and the hold-up in a bubble channel reactor fed by porous pipes. A new processing method was proposed for the signal acquired by means of a resistivity probe for the air volume fraction. This method avoids the loss of the bubble residence time on the probe tip, which affects the most used signal processing procedures. The probe measurements were compared with other studies regarding bubble curtains. The measured air hold-up was in agreement with correlations available in the literature and formulated for bubble columns fed by a porous sparger. A bubble-scale model was proposed to explain the functional form of the dependence of the hold-up on the air superficial velocity. Moreover, a link between the hold-up and the Koide equation for bubble dimensions was established. The experiments were reproduced by means of CFD simulations. The air volume fraction measurement method and the hold-up model found a confirmation in the numerical results. Moreover, the latter showed how the bubble plumes interact inside the reactor and the consequences on the air hold-up.