抄録
The discharging flow rate from safety or relief valves is restricted with the minimum flow area between disk and seat. The flow rate is usually smaller than the calculation with the minimum flow area due to the vena contraction. The clarification of vena contraction is very important but actually difficult to visualize as the rapid radial expansion occurs just after the minimum flow area. It has a possibility that the rapid flow-directional change of disk-seat contraction enhances the non-equilibrium behavior. The simple disk-seat flow contraction was fabricated to measure the discharging flow rate at different valve lifts, seat and nozzle configurations. Furthermore the two kinds of nozzles used in actual safety valves were installed instead of the simple straight nozzle to verify the effect on vena contraction. The discharging flow rate of water was affected with the lift, seat and nozzle configuration due to the different formation of vena contraction. The adequate shape of nozzle was effective to increase the vena contraction ratio to the minimum flow area. The air flow rate could be well predicted with the expansion delay model by using the vena contraction ratio as same as the water flow and the adequate expansion delay factor.
