To elucidate details of the fascinating nonlinear phenomena of gas-liquid two-phase flow, precise spatiotemporal knowledge of flow pattern transition is essential. This paper presents an experimental result of flow patterns in air-water adiabatic vertical flows with tubes of high, medium, and low wettability surfaces. In the test, water-parent and water-repe1lent coating tubes were used as high- and low- wettability surfaces. As water tended to migrate near wall in water-parent coating wall or high wettability surface, bubbly-slug flows transition in high wettabilitv surface wall tube caused at lower gas flow rate than that in medium wettability surface wall tube. In the water-repellent coating or low wettability tube, non-contact condition of water with to wall surface caused an inverted Chum flow in which one or two liquid rivulets existed in continuous gas phase.

Inv.Churn Flow

Droplet Flow

In the water-shedding coating pipe, the inverted-churn flow regime (see Fig. 2) was observed in the region where the churn flow regime was to be observed in a no-coating pipe, whereas the droplet flow regime was observed in the region where the annular flow regime was to be observed in a no-coating pipe.  The criteria for the slug flow-to-inverted-churn flow transition and the inverted-churn flow-to-droplet flow transition were modeled by force balance approaches.  The modeled transition criteria could predict the observed flow transition boundaries reasonably well.

二相流流動特性に及ぼす壁面濡れ性の影響
CONTENTS
TEST LOOP
TEST TUBE
RESULTS

The estimated contact angles on the surfaces of high, medium and low wettability pipes were 7 o, 45 o and 146 o deg., respectively, see Fig. 3.