On the occurrence of superimposed density wave oscillations on pressure drop oscillations and the influence of a compressible volume

Although two-phase flow instabilities are attributed to be one of the impediments for achieving high heat flux in boiling systems, most of their fundamental characteristics remain uncharted. In particular, pressure drop oscillations and density wave oscillations are two types of dynamic two-phase flow instabilities that can cause large variations in pressure and temperature. Under particular working conditions, both oscillations have been observed to interact, resulting in long-period pressure drop oscillations with superimposed short-period density wave oscillations. However, in this situation, the amplitude of the density wave oscillations is typically larger than the corresponding to a pure density wave oscillation. Here, we show that a compressible volume in the system, essential for the occurrence of pressure drop oscillations, plays a major role in amplifying the amplitude of the superimposed density wave oscillations.