Interfacial area concentration correlation for bubbly flows in small-diameter pipes under normal and reduced gravity conditions

Abstract

The accurate modeling of interfacial area concentration (IAC) is essential to improve the predictive performance of two-fluid-model-based simulations for state-of-the-art two-phase thermal systems under normal and reduced gravity conditions, such as two-phase heat sinks and space fission power systems. Although numerous empirical and semi-theoretical IAC correlations have been proposed to predict the IAC variations for different two-phase systems, the IAC correlation for small-diameter (hydraulic diameter from 1mm to 10mm) flow channels under normal gravity conditions is still underdeveloped and no IAC correlation has been developed for reduced gravity conditions. The present study collected 456 experimental IAC data measured in bubbly flows in small-diameter pipes under normal and reduced gravity conditions from the open literature and evaluated the predictive performance of 8 representative IAC correlations. The evaluation results illustrated that none of the existing IAC correlations could maintain acceptable predictive ability under both normal and reduced gravity conditions. Therefore, a new IAC correlation applicable to normal and reduced gravity conditions for bubble flows in small-diameter pipes was proposed semi-theoretically by (1) considering the IAC variation caused by the bubble breakup due to turbulent impact and the bubble coalescence mainly from wake entrainment and (2) employing the concept of effective body acceleration to extend the applicability of newly-developed IAC correlation to reduced gravity conditions. The performance of newly-developed IAC correlation has been evaluated against the collected bubbly IAC data taken in small-diameter pipes and the obtained mean relative errors are 0.134, 0.158 and 0.145 for 260 normal gravity data, 196 reduced gravity data and all collected data, respectively.