(An) experimental study of the effects of the mixing vane on air-water mixed flow

Abstract

The effects of a mixing vane on air-water mixed flow have been experimentally studied in this work, to investigate the basic mechanisms that the mixing vane affects critical heat flux (CHF). Experiment was performed for various flow rates focusing on bubbly flow and annular flow patterns. To measure various fluid flow rate, four rotameters were used for each fluid(Air : 0.02 - 30 kg/㎡s, Water : 10 - 1000 kg/㎡s). The test section was made of acrylic tube(1.7m long, 11 mm I.D.) to facilitate visual observation, and ring-type conductance probes were used to measure the liquid film thickness in annular flow. In the tube test section, the split vane type mixing vane was installed in the round tube test section. The tests were conducted under atmospheric pressure. Experimental results show that, (a) the liquid film thickness in annular flow is decreased near the mixing vane for mass fluxes in the range of 100- 1000 kg/㎡s, (b) in bubbly flow region, the mixing vane breaks the bubbles into smaller ones and forwards bubbles to the center region of the tube by the centrifugal force, (c) bubbly-to slug flow transition and churn-to- annular flow transition occur at higher liquid velocity and the lower gas velocity respectively near the mixing vane compared to the tests without mixing vane.