Modeling local interfacial area concentration for adiabatic and boiling bubbly flows

Bubbly flows appear in various heat and mass transfer systems, and interfacial area concentration (IAC) is a critical geometrical parameter for the flows. The fidelity of accurately computed IACs is essential for reliable three-dimensional computational fluid dynamics analyses of bubbly flows because the IACs directly affect the interfacial force and interfacial heat and mass transfer rates. This study targeted development of a simple and robust model for predicting the local IAC under steady-state bubbly flows with and without phase change. The dependent two-phase flow parameters of the IAC were derived by considering bubble coalescence and breakup rates. The IAC transport equation simplified under steady-state conditions was used for this purpose. A simplified turbulence model was introduced to formulate the energy dissipation rate per unit mass necessary for computing the bubble coalescence and breakup rates. The prediction accuracy of the local IAC model for bubbly flow conditions with area-average void fraction values less than 10 % was estimated to be 20 % based on 803 local data collected for adiabatic air-water bubbly flows in round tubes with diameters ranging from 9.0 to 200 mm. The model was also applied to predict the local IAC data of subcooled boiling flows in heated channels with hydraulic diameters ranging from 18.5 to 22.2 mm. The test conditions covered pressures from 0.1 to 1.46 MPa. The model prediction accuracy for bubbly flow conditions with area-average void fraction values less than 10 % was estimated to be 40 % based on 155 subcooled boiling flow data.

Automated summary

This study aimed to develop a simple and robust model for predicting the local interfacial area concentration (IAC) under steady-state bubbly flows with and without phase change. The model derived the dependent two-phase flow parameters of the IAC by considering bubble coalescence and breakup rates, and used a simplified turbulence model for computing the energy dissipation rate per unit mass. The prediction accuracy of the model was estimated to be 20% for adiabatic air-water bubbly flows and 40% for subcooled boiling flows with area-average void fraction values less than 10%.