Triangular and Rectangular Channels

The experiments of co-current upward air-water two-phase flow patterns in vertical triangular micro-channels were carried out by Zhao and Bi (2001a). Three equilateral triangular channels 270 mm in length, having side lengths of 5.0, 2.5, and 1.5 mm, corresponding to hydraulic diameters of 2.886,1.443, and 0.866 mm, were tested. 

Dispersed bubbly flow (DB) is usually characterized by the presence of discrete gas bubbles in the continuous liquid phase. As indicated in Fig. 5.2, for the channel of db = 2.886 mm, dispersed bubbles appeared at a low gas superficial velocity but a very high liquid superficial velocity. It is known that for large circular mbes dispersed bubbles usually take a sphere-like shape. For the triangular channel of dh = 2.886 mm, however, it is observed from Fig. 5.2 that the discrete bubbles in the liquid phase were of irregular shapes. The deformation of the gas bubbles was caused by rather high liquid velocities in the channel. 

As shown in Fig. 5.2, churn flow (C) appeared at moderate gas superficial velocities and the entire range of liquid superficial velocities. How was extremely chaotic and the gas-liquid interface was rather irregular. The gas phase and liquid phase had no distinct shapes. 

Annular flow (A) existed at high gas superficial velocities and at the entire range of liquid superficial velocities. In annular flow, liquid film formed at the side wall with part of the liquid remaining in the three corners of the channel, while the continuous gas core flowed concurrently with the liquid phase. 

The images of the representative flow patterns, together with the measured simultaneous pressure fluctuations, for the equilateral triangular channel having a side 

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