For the design of an ultra supercritical 1 000 MW unit boiler with spirally water wall tubes

an experiment was conducted on the instability of the steam-water two-phase flow inside a smooth tube with an inclined angle of 20 from the horizon.The boundary conditions about the occurrence of the pressure drop oscillations and the density wave oscillations were discussed.The effects of the compressible volume

pressure and mass flux were primarily analyzed.The results show that the above parameters show regular influences on the boundary heat flux for the mentioned two oscillations

which are accordant with existed experimental conclusions

but some of them displays variable influence

which depends on the experimental operation conditions

on the boundary dryness.The boundary heat flux of the pressure drop oscillations in the test smooth tube at low sub-cooling can be higher than that in the rifled tube at high sub-cooling.Under variable system parameter conditions

the variation range of boundary heat flux as well as boundary dryness was derived and the empirical correlations on oscillation initial point for the pressure drop oscillations and the density wave oscillations were obtained.