https://orcid.org/0000-0001-9914-778X
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Abstract
The Two-Fluid Model (TFM) has long been the backbone of engineering-scale two-phase flow simulation in system-analysis codes and computational fluid dynamics codes. The classical TFM is limited in how it can capture the differences in the transport of small and large bubbles. The two-group TFM provides the ability to specify the unique transport characteristics of small and large bubbles separately. Expanding to two sets of conservation equations for the two bubble groups presents the additional challenge of bubble group accounting as bubbles can cross the group boundary. The three mass transfer terms in the two-group TFM are evaluated for flashing, condensing, and boiling flows using a partitioning method. The axial trends in the source terms are examined for these flow conditions with the available intergroup models. Two-group interphase models are implemented and evaluated against experimental data for flashing, condensing, and boiling flows with accurate two-group results. The capabilities of the two-group TFM are evaluated for these flow types, demonstrating the ability to predict two-group vapor properties without the need for flow regime transitions.
Nomenclature
| Ac | = | = channel area (m2) |
| ai | = | = interfacial area concentration (m–1) |
| cp | = | = specific heat [J/(kg‧K)] |
| D | = | = diameter (m) |
| hfg | = | = heat of vaporization (J/kg) |
| k | = | = thermal conductivity [W/(m‧K)] |
| ṁ | = | = mass transfer rate [kg/(m3‧s)] |
| n | = | = number density (m–3) |
| Nu | = | = Nusselt number |
| pc | = | = fraction of bubbles in inertia-controlled region |
| Pr | = | = Prandtl number |
| q″w | = | = wall heat flux (W/m2) |
| Re | = | = Reynolds number |
| v | = | = velocity (m/s) |
Greek
| α | = | = void fraction |
| β | = | = nondimensional bubble diameter |
| Γ | = | = vapor mass generation rate [kg/(m3‧s)] |
| η | = | = volume generation rate per unit volume (s–1) |
| κ | = | = shape factor |
| ξh | = | = heated perimeter (m) |
| ρ | = | = density (kg/m3) |
| σ | = | = surface tension (N/m) |
| χ | = | = intergroup mass transfer coefficient |
| ψ | = | = shape factor |
Subscripts
| c | = | = critical, condensation |
| e | = | = evaporation |
| f | = | = liquid |
| g | = | = vapor |
| max | = | = maximum |
| n | = | = group number |
| NW | = | = near wall |
| ph | = | = phase change |
| RC | = | = random collision |
| sat | = | = saturation |
| sm | = | = Sauter mean |
| SO | = | = shearing off |
| sub | = | = subcooling |
| t | = | = total |
| TI | = | = turbulent impact |
| V1 | = | = volume from group 1 |
| V2 | = | = volume from group 2 |
| w | = | = wall |
| WE | = | = wake entrainment |
Disclosure Statement
No potential conflict of interest was reported by the authors.