Flow pattern and flow characteristics for counter-current two-phase flow in a vertical round tube with wire-coil inserts

Flow pattern, void fraction and slug rise velocity on counter-current two-p hase flow in a vertical round tube with wire-coil inserts are experimentall y studied. Flow pattern and slug rise velocity are measured visually with a video camera. The void fraction is measured by the quick-closing valve met hod. Four kinds of coils with different cod pitches and coil diameters are used as inserts. The presence of wire-coil inserts induces disturbance into gas and liquid flows so that the shape and motion of gas slug or bubbles i n a wire-coil inserted tube are quite different from those observed in a sm ooth tube without insert. The bubbly flow occurs in the low gas superficial velocity region in the wire-coil inserted tube, while the slug or churn/an nular flow only appears in the smooth tube without insert over the all test range. The measured slug rise velocity in the wire-coil inserted tube is h igher than that in the smooth tube. With modified mean flow velocity calcul ated with core area, the slug rise velocity in wire-coil tube inserted is i n good agreement with Nicklin's correlation. The void fraction in a wire-co il inserted tube is lower than that in a smooth tube in the range of high g as superficial velocities. By introducing a simple assumption on considerin g the effective flowing area, the measured void fractions in a wire-coil in serted tube are in relatively good agreement with the predicted result base d on the drift flux model proposed by others with the correlation for slug rise velocity given by others when the coil pitch is dense. (C) 2001 Elsevi er Science Ltd. All rights reserved.