Measurement of time varying thickness of liquid film flowing with high speed gas flow by a constant electric current method (CECM)

This paper presents both experiment and simulation of alumina molten flow in a solid rocket motor (SRM), when the propellant combusts, the aluminum is oxidized into alumina (Al2O3) which, under the right flow conditions, tends to agglomerate into molten droplets, impinge on the chamber walls, and then flow along the nozzle wall. Such agglomerates can cause erosive damage. The goal of the present study is to characterize the agglomerate flow within the nozzle section by studying the breakup process of a liquid film that flows along the wall of a straight channel while a high-speed gas moves over it. We have used an unsteady-flow Reynolds-Averaged Navier-Stokes code (URANS) to investigate the interaction of the liquid film flow with the gas flow, and analyzed the breakup process for different flow conditions. The rate of the wave breakup was characterized by introducing a breakup-length-scale for various flow conditions based on the Volume Fraction (VF) of the liquid, which is an indicator of a two-phase flow liquid breakup level. A smaller breakup-length-scale means that smaller drops have been created during the breakup process. The study covers the breakup and fluid behaviors based on different gas-liquid momentum flux ratios, different surface tension and viscosity settings, different Ohnesorge numbers (Oh), and different Weber numbers. Both water and molten aluminum flows were considered in the simulation studies. The analysis demonstrates an effective method of correlating the liquid breakup with the main flow conditions in the nozzle channel path.

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Periodic Interface Destabilization in High-Speed Gas-Liquid Flows at the Capillary Scale

ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B ◽

10.1115/icnmm2006-96183 ◽

2006 ◽

Author(s):

Alexandru Herescu ◽

Jeffrey S. Allen

Keyword(s):

Liquid Film ◽

High Speed ◽

Gas Flow ◽

Two Phase Flow ◽

Travelling Waves ◽

Phase Flow ◽

Capillary Tubes ◽

Two Phase ◽

Sequence Of Events ◽

Number Systems

Recent research efforts have illustrated the importance of capillarity on the behavior of two-phase flow (gas-liquid) in low Bond number systems; that is, systems where capillary forces are important relative to gravitational forces. Such systems include capillary tubes and microchannels as well as the gas flow channels of a PEM fuel cell. High speed microscopy experiments visualizing air-water flow through a 500 micrometer square glass capillary, 10 cm long were conducted. The flow rates are significant with velocities of 6.2 m/s for the air and 0.2 m/s for the water. A unique annular flow with periodic destabilization of the gas-liquid interface has been observed. Standing waves develop on the liquid film and grow into annular lobes typical of that observed in low speed two-phase flow in capillary tubes. Atypical is the interface destabilization phenomena. The leading face of the lobe will decelerate and suddenly become normal to the wall of the square capillary while the trailing face of the lobe will remain gently sloped back into the annular liquid film. The transition between the leading and trailing faces acquires a sharp edge having a exceptionally large curvature. The entire structure then rapidly collapses and produces travelling waves which propagate upstream and downstream along the annular liquid film. The entire sequence of events takes approximately a half millisecond. This destabilization phenomenon is regular and periodic. Visualization of the destabilization from the high speed microscopy setup and preliminary analysis are presented.

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