Visualized investigation of the onset of flow boiling dynamic instabilities in a horizontal arranged tube under a high-temperature thermal storage boundary condition

Abstract

A visualized experimental test rig of flow boiling in high temperature thermal storage module was presented. The effects of high-temperature sensible heat thermal storage boundary condition on the oscillation characteristics at the onset of dynamic instability were investigated in this work. The flow boiling tests were carried out in a 1.6-meter-long horizontal tube with an inner diameter of 16.0 mm, which was embedded in a sensible thermal storage module using solid graphite. A series of thermal storage temperatures (200–340 °C), inlet subcooling degrees (5–45 °C) and mass flow rates (0–593.5 kg/m2s) were applied. Based on the dimensionless stability map, an early onset of dynamic instability was observed in comparison with the traditional constant heat flux condition. Meanwhile, both the pressure drop oscillations (PDO) and density wave oscillations (DWO) were observed. Based on the development of flow pattern and heat transfer distribution characteristics, the regulation mechanisms of the high-temperature thermal storage boundary on the development of dynamic instability were analyzed. The results show that the characteristics of dynamic instability are highly related to the development of flow pattern. The thermal storage boundary has affected the development of flow pattern by determining the wall superheat. The comprehensive effects of superheat, subcooling degree and mass flux on the development of flow pattern were also interpreted.