Density-Wave Flow Oscillations in a Water Boiling Horizontal Tube with Inserts

Density-wave type oscillations are one of the main types of two-phase flow dynamic oscillations frequently encountered in industrial thermal-hydraulic systems. These oscillations are caused by the dynamic interaction between flow rates, density distribution, and pressure drop distribution within the system, and are high-frequency oscillations. To avoid or control density-wave oscillations is of vital importance for two-phase systems, since they can induce thermal oscillations, accelerating the thermal fatique of the tube and finally resulting in burn-out damage. In this study, an experimental investigation on two-phase flow density-wave type instabilities in a horizontal pipe with inserts was conducted. Four different heat transfer surface configurations containing one bare tube and three different enhancement inserts were used. The point on the characteristic curve, where pure density-wave oscillations started, changed with the tube configurations. This point was near the middle of the characteristic curve for the smooth tube, whereas it went towards the maximum point of the characteristic curve in the tubes with inserts. The amplitudes and periods of the density-wave type oscillations were lower than those of the pressure-drop type oscillations. By comparing the bare tube and the tubes with inserts on the basis of density-wave type oscillations, it was observed that the amplitudes and periods for the tube configurations with inserts were higher than those of the bare tube. There was no important difference among the tubes with inserts on the basis of density-wave type oscillations.