The two-fluid model with interfacial area transport equation in gas-dispersed condensing flows

Condensation;Validation;Interfacial area concentration;Void fraction;Annulus;Two-phase;Steam-water flow

Kumar, Vineet

关键词: Condensation;    Validation;    Interfacial area concentration;    Void fraction;    Annulus;    Two-phase;    Steam-water flow;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/106164/KUMAR-DISSERTATION-2019.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The interfacial area transport equation (IATE) has been proposed to satisfy the closure of the interfacial area concentration in the two-fluid model. The IATE provides a dynamic prediction of flow structure consistent with the two-fluid model and has been studied extensively for adiabatic two-phase flows. However, the IATE still requires attention in flows with phase change, specifically the benchmarking of the IATE in condensing gas-dispersed bubbly flows. Extending the analysis to condensing cap/slug flows, in the present two-group IATE model formulation, the inter-group mass transfer term, which is critical for proper accounting of the bubble groups, only considers the expansion of group-1 bubbles (spherical and distorted bubbles) to group-2 bubbles (cap, slug and churn-turbulent bubbles). In condensing flows, the inter-group mass transfer term is dominated by group-2 bubbles condensing to group-1 bubbles. Therefore, the modeling of the condensation interfacial area and volume sink term is revisited, and by coupling the IATE and continuity equations the sensitivity of modeling parameters is directly investigated. A new annulus facility is built in which experimental adiabatic steam-water flow data is collected which includes gas-dispersed condensing flow data for validating the proposed one-group and two-group condensation model. The facility includes five instrumentation ports located in the unheated section to provide high-resolution two-phase measurements in addition to local pressure and local liquid temperature measurements. The dataset consists of a total of eighty-five conditions spanning across system pressures, mass fluxes, inlet liquid subcooling, and inlet void fractions. The new dataset is developed for validation of one-dimensional system codes and multi-dimensional fluid dynamics codes and fills an important gap in the adiabatic steam-water flow database literature. Three datasets have been used for validation consisting of condensing two-phase flow data in the unheated section of a vertical annulus with conditions spanning a range of pressures, inlet subcoolings and mass fluxes. For bubbly flows, the coupled void transport - IATE simulation results in good agreement in the predictions of the void fraction and the interfacial area concentration under nearly all sixty conditions with the proposed modifications to the condensation model. Considering the two-group two-fluid IATE model formulation, the inter-group mass transfer term is modified to be applicable for all flow conditions. The group-2 Nusselt number correlation is also modified to account for the appropriate heat transfer length scale for group-2 bubbles. A second inter-group transfer coefficient is introduced for the proposed model, and a closure relation is provided. Validation of the proposed two-group two-fluid model against the new dataset shows good agreement with experimental data with the significant improvement over the one-group IATE model for conditions with substantial group-2 void fraction throughout the simulation domain.