Development of one-group interfacial area transport equation in bubbly flow systems

To finalize one-dimensional one-group interfacial area transport equation in bubbly flow systems, this study has conducted the developments of (I) refined sink and source terms of the interfacial area concentration based on mechanisms of bubble–bubble and bubble–turbulent eddy random collisions, (II) the correlations of two adjustable variables in sink and source terms, and (III) the correlation of the initial interfacial area concentration. The finalized one-dimensional one-group interfacial area transport equation has been validated by 55 data sets taken in extensive adiabatic air–water bubbly flow conditions in four different vertical pipes (pipe diameter: 25.4–50.8 mm). The flow conditions of the data sets cover most of the bubbly flow regime, including finely dispersed bubbly flow and partly bubbly-to-slug transition flow (superficial gas velocity: 0.0144–4.88 m/s, superficial liquid velocity: 0.262–5.00 m/s, void fraction: 0.0124–0.443, interfacial area concentration: 22.1–1085 m−1). Excellent agreement is obtained between predicted and measured interfacial area concentrations with an average relative deviation of ±11.5%. Detailed discussions have been made on (i) the sensitivity analysis to the adjustable variables in the sink and source terms, (ii) the predominant term, (iii) the sensitivity analysis to the initial bubble size, and (iv) the comparison with TRAC-P code.