Authors : Edward Shitsi, Seth Kofi Debrah, Vincent Yao Agbodemegbe, Emmanuel Ampomah-Amoako and Henry Cecil Odoi
Abstract: Research into flow instability has attracted attention of many scientists and engineers in recent years because of its importance in water-cooled and water moderated nuclear reactors and steam generators at both subcritical and supercritical pressures. Supercritical Water-cooled Reactor SCWR, a GEN IV reactor is prone to flow instability just like Boiling Water Reactor BWR because of drastic variations in fluid properties at the vicinity of the pseudo-critical temperature. Flow instability at supercritical pressures needs to be addressed as it is undesirable and can threaten design safety limits and eventually cause mechanical damage of heat transfer equipment. This study seeks to examine two flow instability analysis methods used to describe flow instability results. The flow instability analysis methods including dimensional and dimensionless stability diagrams (dimensional and Ambrosini’s dimensionless parameters) were adopted to obtain stability boundaries for the various systems considered in this work. Axially decreased and homogeneous axial power shapes/distributions were adopted in heating the heated channels/sections of the parallel channel system considered. This study examines also the influences of parameters including mass flow rate, pressure and gravity on flow instability at supercritical pressures in parallel channels. Data used for the study were obtained from literature. The results show that both the dimensional and dimensionless stability diagrams could be used for flow instability analysis as the two different types of stability diagrams almost produced the same findings in this research. The following additional findings were obtained during the investigation using both the dimensional and dimensionless stability diagrams. At low mass flow rates, stability of the system with HAPS (Homogeneous Axial Power Shape) or ADPS (Axially Decreased Power Shape) decreases and increases respectively below and above a certain threshold power with inlet temperature. At high mass flow rates, there is a threshold power below which stability decreases and above which stability increases with inlet temperature for HAPS but there is only lower threshold for ADPS and the stability deceases with inlet temperature. The system with HAPS is more stable than that with ADPS. The type of axial power shape adopted in supplying heat to the fluid flowing through heat transfer system has significant effect on the stability of the system. Comparing the numerical results with experimental results, the 3D numerical tool, STARCCM+ CFD code could predict flow instability in the parallel channels irrespective of the type of axial power shape adopted. The numerical tool could predict experimental results quite better for a system with HAPS than that with ADPS. The numerical tool adopted largely under-predicted experimental amplitude and quite well predicted experimental period of the inlet mass flow oscillations. Supercritical systems operated under 25 MPa are more stable than those operated under 23 MPa.
Edward Shitsi, Seth Kofi Debrah, Vincent Yao Agbodemegbe, Emmanuel Ampomah-Amoako and Henry Cecil Odoi, 2020. Flow Stability Investigation in Parallel Channels with Supercritical Water by Comparing Axially Decreased and Homogeneous Axial Power Shapes: A Review. Journal of Engineering and Applied Sciences, 15: 2998-3009.