Resumo

We studied the onset of flow reversal in upflow condensation of refrigerants in an inclinable 5-mm ID tube. As part of the condensate begins to flow downwards, solitary waves grow on the liquid substrate and are carried upwards by the vapor. As a result of the periodic changes in liquid velocity, the vaporliquid interface becomes highly disturbed. Image processing techniques were applied to high-speed video sequences to identify the onset of flow reversal and to quantify the frequency and velocities of disturbance waves and Sekoguchi-type huge waves characteristic of the transition to churn flow.

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