This paper presents practically unknown outside Russia experimental data about density wave instability (DWI) regions and its thresholds, as well as their primary analysis. This database has been produced by IPPE installation [1–3] with two vertical boiling channels with risers. Regime conditions: 6÷16 MPa pressures; −0.3÷0.75 MW/m2 heat fluxes; low mass velocities 120 ÷ 600 kg/m2s, with different flow additional throttling at the inlet and exit of the channels. Input coolant temperatures served as a DWI threshold parameter and varied in these experiments between 20 °C and Ts − (5÷50) °C. The bottom and top instability thresholds were determined, accordingly, by growth or attenuation of mass flow regular out-of-phase oscillations in both channels. The basic experimental tendencies and peculiarities of DWI instability thresholds behavior typical to all researched pressures are: 1) presence of two instability regions (with stability zone between them) — high subcooled boiling DWI-1 and low subcooled boiling DWI-2, shaping as a descending ‘wedge’ of DWI region widening with growing Zu number; 2) stability zone diminishes with increasing Zu numbers and reduces right up to merging of DWI-1 and DWI-2 regions; 3) increasing additional inlet throttling diminish area of DWI-1 and 2 regions and move it to more higher Zu number; 4) the instability thresholds lines curvature grows with Zu number; 5) the threshold lines behavior directly points at the existence of asymptotic subcooling values restricting the beginning and end of density wave’s oscillation regions and intervals with possible linear approximation.

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