Vijay Chatoorgoon

Supercritical Flow Stability in Two Parallel Channels

An analytical study of supercritical flow stability in two parallel channels is reported here. This would be of immense value to new reactor designs that propose to use supercritical light water on the primary side. The finding is that two-phase flow instability and supercritical flow instability are not identical, as there are notable phenomenological differences as well as mathematical differences.Copyright

Static Instability in Supercritical Parallel-Channel Systems

An analytical study of static instability in parallel channels at supercritical pressure is conducted. Until now, primarily the density-wave type has been investigated and reported. This paper derives an analytical expression for the static instability in parallel channels, which lends useful insight. This topic that would be of immense value to the new reactor designs that aim to use supercritical light water on the primary side. The finding is that static instability would unlikely be a problem in a supercritical pressure reactor because of the low inlet core temperature that it would be encountered.Copyright

Sensitivity Studies of Shear Stress Transport Turbulence Model Parameters on the Prediction of Seven-Rod Bundle Benchmark Experiments

This paper reports the findings of a sensitivity study of parameters in the shear stress transport (SST) turbulence model in a commercial computational fluid dynamics (CFD) code to predict an experiment from the Generation IV International Forum Supercritical-Water-Cooled Reactor (GIF SCWR) 2013–2014 seven-rod subchannel benchmark exercise. This study was motivated by the result of the benchmark exercise that all the CFD codes gave similar results to a subchannel code, which does not possess any sophisticated turbulence modeling. Initial findings were that the CFD codes generally underpredicted the wall temperatures on the B2 case in the region where the flow was supercritical. Therefore, it was decided to examine the effect of various turbulence model parameters to determine if a CFD code using the SST turbulence model could do a better job overall in predicting the wall temperatures of the benchmark experiments. A sensitivity study of seven parameters was done, and changes to two parameters were found to make an improvement.

A Study of Acoustic Wave Resonance in Water-Filled Tubes with Different Wall Thicknesses and Materials

Acoustic resonance of a fluid-filled tube with closed and open outlet ends for zero and turbulent mean flows is investigated both experimentally and numerically for different wall materials and thicknesses. The main goal is to create a data bank of acoustic wave resonance in fluid-filled tubes at a frequency range of 20 to 500 Hz to validate and verify numerical prediction models used by the nuclear industry and to determine if there is a better method with existing technology. The experimental results show that there is a strong effect of turbulent flow, wall material and wall thickness on resonant amplitudes at frequencies above ~250 Hz. A numerical investigation is performed solving the linear wave equation with constant and frequency dependent damping terms and a computational fluid dynamic (CFD) code. Comparing the 1D and CFD results shows that CFD solution yields better predictions of both resonant frequency and amplitude than the 1D solution without the need for simplified added damping methods, which are required by the 1D methodology. This finding is valid especially for frequencies higher than ~300 Hz.

Experimental Flow Instability Study of a Natural Circulation Loop with Supercritical CO 2

Flow instabilities of a natural circulation loop were experimentally studied with supercritical CO2 as the working fluid. The experimental loop is a rectangular loop with single horizontal heated channel locating on the bottom of a rectangular loop. Parameters such as system pressure, inlet temperature, and outlet throttling effects’ on both steady state and flow instabilities were studied. Results show that the increase in system pressure would shift the peak mass flow rate to the right side of flow-power map and stabilize the system. The increase in outlet throttling caused the opposite effect. The instability boundary did not change much within the given test range of inlet temperature. Instabilities were found when the outlet temperature of the heating section went far beyond the pseudo-critical temperature. All the instability points were located on the negative slope of flow-power curve. One of the interesting findings was that the instability will disappear when the accumulator is isolated from the main loop. Numerical studies were also conducted with both the SPORTS and CATHENA codes to model the experimental results. Results show that the CATHENA code is capable of predicting flow instabilities in natural circulation loop at supercritical pressures. A new method of converting the CO2 results to H2O results is proposed by making use of the dimensionless Fr-N tpc map, and the method is verified numerically.

Numerical Instability Study of Supercritical Water Flowing Upward in Two Heated Parallel Channels

A three-dimensional (3D) numerical simulation has been carried out using a RANS model in CFD ANSYS CFX v15.0 to investigate the out of phase oscillation instability between two heated parallel channels with supercritical water flowing upward. Spatial and temporal grid sizes effects on flow instability are studied first. High sensitivity of the CFD code on time step size is investigated, while spatial grid size refinement influence is not noteworthy. Oscillatory instability boundaries of three experimental cases are predicated by CFD code with the standard k-e turbulence model. Chatoorgoon’s 1D nonlinear SPORTS code is also used to determine the instability boundary for comparison purposes. These new numerical results are compared with experimental data and previous numerical results. In general, there is a good agreement between numerical instability results of this paper and the experiments. Certain instability thresholds difference is observed among different numerical simulations, and possible reasons are pointed out. A previous finding that CFD results clearly yield better predictions of the instability boundary than a 1D solution is disputed in this paper.

The Influence of Geometry, Wall Thickness, and Material on the Acoustic Resonance Predictions in Closed-Ended Water-Filled Piping

Acoustic pressure resonances in liquid-transporting pipe systems affect performance and safety. Accurate predictions of acoustic pressure resonances are a necessary requirement for any practical piping system undergoing some acoustic excitations. Thus, understanding the nature of acoustic wave propagation in water filled piping systems needs to be established based on fundamental experiments and analysis. To investigate acoustic resonance, no flow experiments with different configurations, wall thicknesses and materials were compared with theoretical and numerical calculations.This paper presents an experimental study showing that how linear wave theory, based on a transmission matrix method, and ABAQUS as commercial software do predict the acoustic resonance frequency peaks from 20 to 500 Hz, and discusses the resonant frequency shifts. Study of tube wall thickness, material (stainless steel and Aluminum), some equal and unequal branch configurations and combination of all investigated parameters for “Closed-end” tubes are discussed.© 2013 ASME

Study of Wall Thickness and Material Effect on Acoustic Wave Propagation in Water-Filled Piping

The operation of many industries, such as power plants or many piping systems, demands knowledge of generated pressure pulsations. The effect of acoustic wave amplification in piping systems can be detrimental to the integrity and life of whole plant. Therefore, understanding of the nature of acoustic wave propagation in water filled piping systems needs to be established based on fundamental experiments and analysis. Chatoorgoon et al. [1] and Rzentkowski et al. [2], compared their no flow experiments with theoretical calculation, and realized that the resonant frequency shifts increased linearly, with resonant frequency increasing.This paper presents an experimental study showing that linear wave theory, based on a transmission matrix method does predict well the acoustic resonance frequency from 50 to 500 Hz. and the resonant frequency shifts were negligible. Study of tube wall thickness, material (stainless steel and Aluminum) and some equal branch configurations for “Closed-end” tubes are discussed.Copyright

Experiments on Damping of Acoustic Waves in Water-Filled Pipes

A simple, fundamental experimental study was conducted to better understand acoustic wave propagation is fluid-filled pipes. Three experiments were undertaken: the first with zero flow and a closed outlet end, the second with turbulent flow and an open outlet end and the third with zero flow and an open outlet end. The intent was to obtain data for model comparison and to determine the effect of turbulent flow on the system response. New insights are obtained and reported.Copyright