Sensitivity analysis of numerically determined linear stability boundaries of a supercritical heated channel

Abstract

The large change in density which occurs when supercritical water is heated above or near to the pseudocritical temperature in a vertical channel can result in the onset of flow instabilities (density wave oscillations). Near to the critical point, substance properties such as enthalpy, density, viscosity… all have larger relative uncertainties compared to subcritical conditions. The goal of this study is to quantify the effect of these property uncertainties and system uncertainties on numerically determined stability boundaries. These boundaries were determined through an eigenvalue analysis of the linearised set of equations. The sensitivity analysis is performed in a forward way. The results show that the impact of the density and viscosity tolerance individually as well as that of the uncertainty of the imposed pressure drop are negligible. The tolerance on the derivative of the density with regard to the enthalpy propagates only noticeably at low N SUB numbers (T in > 370°C). The friction factor and the heat flux distribution uncertainties have a comparable effect, being more pronounced near the bend in the stability curve. The most significant uncertainty was found to be that of the geometry, even a ± 25µm uncertainty on length scales results in a large uncertainty. The results also showed that the stability boundary is linked to the friction distribution rather than its average value, and that different correlations result in strong changes of the predicted boundary. This emphasizes the need for an accurate friction correlation for supercritical fluids. These findings are important to assess the design of experimental facilities which use scaling fluids.

Analysis of parallel channel instabilities in the CANDU supercritical water reactor

“…The experimental research work recently carried out by Xiong et al (2012) and several numerical studies (Chatoorgoon, 2001;Gómez et al, 2008;Jain and Rizwan-uddin, 2008;Ambrosini and Sharabi, 2008;Sharabi et al, 2008;Ambrosini, 2009;Zhao et al, 2011;T'Joen et al, 2011;Ambrosini, 2011;Ampomah-Amoako and Ambrosini, 2013;Xiong et al, 2013) confirmed the possibility of flow induced DWOs for various fluids operating at supercritical conditions. The out-of-phase mode of oscillations in two parallel channels at supercritical conditions were experimentally observed by Xiong et al (2012) and then, the study was followed by a numerical investigation (Xiong et al, 2013) using a 1-D thermalhydraulic (TH) model.…”

“…The solution algorithms developed by Jain and Rizwan-uddin (2008) and Xiong et al (2013) are similar to those used in SPORTS. DWOs for supercritical fluids have also been analyzed by several other researchers (Gómez et al, 2008;Ambrosini and Sharabi, 2008;Sharabi et al, 2008;Ambrosini, 2009;Zhao et al, 2011;T'Joen et al, 2011;Ambrosini, 2011;Ampomah-Amoako and Ambrosini, 2013) using 1-D TH models. In most of these 1-D TH models, the dependence of the thermodynamic properties on the pressure is neglected and the density changes with the enthalpy only, which leads to decoupled momentum and energy conservation equations and the flow is treated as incompressible.…”

“…In most of these 1-D TH models, the dependence of the thermodynamic properties on the pressure is neglected and the density changes with the enthalpy only, which leads to decoupled momentum and energy conservation equations and the flow is treated as incompressible. Except for the works done by Xiong et al (2012), Xiong et al (2013), the rest of the works mentioned above (Chatoorgoon, 2001;Gómez et al, 2008;Jain and Rizwan-uddin, 2008;Ambrosini and Sharabi, 2008;Sharabi et al, 2008;Ambrosini, 2009;Zhao et al, 2011;T'Joen et al, 2011;Ambrosini, 2011;Ampomah-Amoako and Ambrosini, 2013) were mainly confined to analyze the inphase mode of DWOs under supercritical conditions for flows in single channels. Dutta et al (2015) carried out a numerical investigation on DWOs in the CANDU SCWR using a 1-D nonlinear TH model, Thermal-Hydraulic solveR Undertaking Supercritical waTer (THRUST), which is also based on a single channel model.…”

Analysis of flow induced density wave oscillations in the CANDU supercritical water reactor

“…The high power-to-mass flow rate ratio in SCWRs, which results in the improvement in the thermal efficiency, will cause significant reduction in the density of the water across the core similar to boiling water reactors (BWRs) and thus, strains the reactor control mechanism and increases the potential for the reactor to be susceptible to self-sustained density wave oscillations (DWOs). Several studies [2][3][4][5][6][7][8][9][10][11][12][13] confirmed the possibilities of existence of DWO for various fluids, H 2 O and CO 2 , undergoing forced or natural flow circulation under supercritical conditions. On the other hand, the DWOs, which are caused by nonlinear interactions among the various thermal and flow variables, may considerably be influenced by the nuclear coupled density and temperature reactivity feedback effects leading to power oscillations in addition to the flow oscillations.…”

“…The results confirmed the existence of flow oscillations at some operating conditions and the predicted instability thresholds obtained by different approaches agreed well. T'Joen et al [11], using the channels described by Ambrosini and Sharabi [7], predicted stability boundaries by the eigenvalue analysis of the linearized set of perturbed equations. Ampomah-Amoako and Ambrosini [13] predicted DWOs for fuel-bundle slices using another CFD program, STAR-CCM+, for supercritical water.…”