Fundamental and Higher-Mode Density-Wave Oscillations in Two-Phase Flow

Abstract

This paper treats the oscillatory two-phase flow instabilities commonly referred to as density-wave oscillations. A dynamic analysis of the single-phase region of a boiling channel, accounting for wall heat capacity and the effect of pressure variations on the movements of the boiling boundary, is summarized. Experiments conducted with a Freon-113 channel at atmospheric pressure revealed the existence of “higher-mode” oscillations. These appeared at high subcoolings and low power levels and were characterized by unexpectedly short periods that were fractions of the transit time. The presence of the higher modes and other observations are explained in terms of the dynamic behavior of the boiling boundary.

Surface Structure Enhanced Microchannel Flow Boiling

“…However, minimizing flow instabilities during boiling while enhancing the critical heat flux (CHF) to maximize heat dissipation has been difficult to achieve [4][5][6]. These flow instabilities which can be triggered by several mechanisms including explosive bubble expansion [7], upstream compressibility [8,9] and density wave oscillation [10] can lead to large pressure drop fluctuations across the channels and temperature spikes associated with liquid dry-out. This dry-out severely limits the heat removal ability of these microchannel heat sinks and leads to device failure once reaching CHF [11].…”

On Density Wave Instability Phenomena – Modelling and Experimental Investigation

“…by Yadigaroglu & Bergles (1972) and recently confirmed by the noteworthy review of Kakaç & Bon (2008), ascribes the origin of the instability to waves of heavier and lighter fluids, and respective delays through the channel. The difference in density between the fluid entering the heated channel (subcooled liquid) and the fluid exiting (low density two-phase mixture) triggers delays in the transient distribution of pressure drops along the tube, which may induce self-sustained oscillations.…”

“…Density wave instability mechanism in a single boiling channel, and respective feedbacks between main physical quantities. (Reproduced from (Yadigaroglu, 1981)) Going more into details, the physical mechanism leading to the appearance of DWOs is now briefly described (Yadigaroglu & Bergles, 1972). A single heated channel, as depicted in Fig.…”

The effect of inlet subcooling on two-phase flow instabilities in a horizontal pipe system with augmented surfaces

“…The generation of density-wave oscillations has been described by Yadigarogy lu and Bergles (1972) as follows: &The density-wave-type oscillations are due to the multiple regenerative feedbacks between the #ow rate, the vapour generation rate, and the pressure drop (#ow-void feedback instabilities). Inlet #ow #uctuations create enthalpy perturbations in the single-phase region.…”