Numerical modelling of bubbly flows with and without heat and mass transfer

In this paper, modelling gas–liquid bubbly flows is achieved by the introduction of a population balance equation com-bined with the three-dimensional two-fluid model. For gas–liquid bubbly flows without heat and mass transfer, an average bubble number density transport equation has been incorporated in the commercial code CFX5.7 to better describe the temporal and spatial evolution of the geometrical structure of the gas bubbles. The coalescence and breakage effects of the gas bubbles are modelled according to the coalescence by the random collisions driven by turbulence and wake entrain-ment while for bubble breakage by the impact of turbulent eddies. Local radial distributions of the void fraction, interfa-cial area concentration, bubble Sauter mean diameter, and gas and liquid velocities, are compared against experimental data in a vertical pipe flow. Satisfactory agreements for the local distributions are achieved between the predictions and measurements. For gas–liquid bubbly flows with heat and mass transfer, boiling flows at subcooled conditions are consid-ered. Based on the formulation of the MUSIG (multiple-size-group) boiling model and a model considering the forces act-ing on departing bubbles at the heated surface implemented in the computer code CFX4.4, comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter, interfacial area con-centration, and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling tempera-tures. Good agreement is achieved with the local radial void fraction, bubble Sauter mean diameter, interfacial are