An experimental investigation of flow instability between two heated parallel channels with supercritical water

•Flow instability experiment between two heated channels with supercritical water is carried out.•Two kinds of out of phase flow instability are found and instability boundaries under different working conditions are obtained.•Dynamics characteristics of flow instability are analyzed. Super critical water reactor (SCWR) is the generation IV nuclear reactor in the world. Under normal operation, water enters SCWR from cold leg with a temperature of 280°C and then leaves the core with a temperature of 500°C. Due to the sharp change of temperature, there is a huge density change in the core, which could result in potential flow instability and the safety of reactor would be threatened consequently. So it is necessary to carry out relevant investigation in this field. An experimental investigation which concerns with out of phase flow instability between two heated parallel channels with supercritical water has been carried out in this paper. Due to two INCONEL 625 pipes with a thickness of 6.5mm are adopted, more experimental results are attained. To find out the influence of axial power shape on the onset of flow instability, each heated channel is divided into two sections and the heating power of each section can be controlled separately. Finally the instability boundaries are obtained under different inlet temperatures, axial power shapes, total inlet mass flow rates and system pressures. The dynamics characteristics of out of phase oscillation are also analyzed.