HELIUM AIR EXCHANGE FLOW-THROUGH ANNULAR AND ROUND TUBES

Air ingress by buoyancy-driven exchange flow occurs during a standpipe rupture accident in a high-temperature engineering test reactor (HTTR ). The exchange flow of helium and air through annular and round tubes is investigated. The method of mass increment is applied to measure t he exchange flow rate. A test cylinder with a small tube on the top is used for the experiment. The following results were obtained: The exc hange velocity is largest for the short vertical round tube as compare d with the orifice and long tube. In the annular tube, the exchange-ve locity or the volumetric exchange flow rate decreases with the equival ent diameter of the annular passage under 6 mm. The annular tube is ef fective to reduce the air ingress flow rate from the broken standpipe of the HTTR. In the inclined round tube, the inclination angle for the maximum densimetric Froude number decreases with the increase of the length-to-diameter ratio of the tube for the helium-air system. On the other hand, this angle remains almost constant for the water-brine sy stem. Flow visualization results indicate that the exchange flows thro ugh the inclined round tubes take place smoothly and stably in the sep arated passage of the tube. The flow pattern in the vertical annular t ube seems to be similar to that in the inclined round tube.