An experiment was conducted to investigate the two-phase flow instability in the vertical parallel rifled tubes and inclined parallel rifled tubes using six-head rifled tubes with a diameter of 31.8 mm in the mass flow rate range of 200-450 kg/(m
2
·s)in a high pressure test loop. The experimental results show that the boundary heat flux of the pressure-drop type oscillation or the density-wave type oscillation increased with the increase of the inlet pressure and the mass flow rate
and the boundary heat flux for the vertical parallel rifled tubes was greater than that for inclined parallel rifled tubes
indicating that the flow in vertical parallel rifled tubes would be more stable. The effects of inlet subcooling degree on the boundary heat flux and the oscillation period exhibited two different trends in the test. In addition
non-dimensional correlations of thresholds of heat flux both in the vertic
al parallel rifled tube and the inclined parallel rifled tube were obtained by the regression calculation of the test data.
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