Two-phase flow across elbows exists widely in nuclear reactors, heat exchangers, oil transport pipelines, and chemical processing plants.  In general, this process involves combined effects of the gravitational, centrifugal and the buoyant forces, which tends to produce complicated flow structures such as flow reversal, flooding, and secondary flow.  As a result, the local and global two-phase flow parameters including the flow regime transition, the pressure drop, the velocity advection, the inhomogeneous phase distribution, and particle interaction mechanisms.  These effects can lead to corrosion, burn-out and subsequent tube failure, and consequently the hydrodynamic behavior of a two-phase mixture flowing through vertical elbows is of prime importance to designers.  Previous investigations on two-phase flows across elbows mostly use experimental methodology, which demonstrating the effects of elbow on flow regime transition, two-phase pressure drop, interfacial area transport and dissipation length of elbow effects.  And the models and correlation are mostly empirical as they are usually developed based on the characteristics of gas-phase parameters.  However, gas-phase parameters are usually the consequences of liquid-phase effects.  For example, the double peaked void fraction distribution after the elbow is the results of the bubbles entrained by the secondary flow of the liquid-phase.  The bubble distribution is the competed effects of liquid-phase inertia and the gas-phase buoyance force.  The bubble coalescences can be caused by the turbulent induced bubble collision.  The turbulence of the liquid-phase can also cause the bubbles on the scales of the turbulence vortex break.  Therefore, it is important to study the effects of elbow on the liquid-phase in two-phase flow.  The experimental methodology such as the Partial Image Velocimetry (PIV) measurement in two-phase flow encounters difficulties of interface reflection, interface refraction, and gas-phase removal.  This study investigates the effects of elbow on two-phase across elbows with CFD numerical simulation.  The simulation results will be benchmarked with the global and local two-phase flow parameters, including the liquid and gas superficial velocities, the two-phase pressure drop, the cross-sectional void fraction distribution, and other parameters.  The simulation results will be analyzed to study the elbow effects on the liquid-phase velocity field and the liquid-phase turbulence field.  The liquid-phase turbulence will be analyzed to investigate its effects on the bubble coalescence and breakup downstream of the elbow.  The results will be used to improve the elbow minor pressure loss model, the drift flux model, the elbow dissipation length model, and the interfacial area transport model downstream of the elbow. 


Numerical Simulation of the Air-Water Two-Phase Flow Across a 90-Degree Vertical-Upward Elbow

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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