Steady-state and nonlinear stability analysis for the feasibility of different fluids in a supercritical natural circulation loop

2021 ◽  
pp. 095440892110439
Author(s):  
Neetesh S Raghuvanshi ◽  
Goutam Dutta ◽  
Manoj K Panda
Keyword(s):  
Stability Analysis ◽  
Nonlinear Stability ◽  
Natural Circulation ◽  
Stability Boundary ◽  
Operating Conditions ◽  
Circulation Loop ◽  
Marginal Stability ◽  
Nonlinear Stability Analysis ◽  
Natural Circulation Loop ◽  
Stable Operating

A numerical model for a supercritical natural circulation loop is developed to examine the flow instabilities by nonlinear stability analysis. The supercritical natural circulation loop is a loop geometry, which is driven by natural circulation with supercritical fluids as a coolant. A mathematical formulation is developed to study the steady-state and transient solution procedure for supercritical natural circulation loop. This mathematical model is then used to perform various parametric studies with different supercritical fluids (water, [Formula: see text], R134a, ammonia, R22, propane, and isobutane). The behavior of all the fluids is analyzed on identical geometrical and operating conditions. A comprehensive numerical study of the nonlinear stability analysis is presented with particular emphasis on the feasibility of various fluids in a natural circulation loop environment. The 50% increment in loop diameter and height increased the stable operating zones and shifted the marginal stability boundary upward respectively by approximately three times and 25–40% of the previous value. However, further increase in diameter and height reduces the increment of stable operating zones; hence the marginal stability boundary shifts upward marginally than the previous value. Furthermore, the marginal stability boundaries are generated to identify the stable and unstable zones for the available geometrical and operating conditions.

Steady State and Dynamic Analyses of Supercritical CO2 Natural Circulation Loop

2006 ◽  
Author(s):  
Prashant Jain ◽  
Rizwan Uddin
Keyword(s):  
Steady State ◽  
Natural Circulation ◽  
Stability Boundary ◽  
Operating Conditions ◽  
Circulation Loop ◽  
Steady State Flow ◽  
Natural Circulation Loop ◽  
Dynamic Analyses ◽  
The Stability ◽  
Flow Power

Numerical studies have been carried out to investigate supercritical flow instabilities in a CO2 natural circulation loop. For the steady state and dynamic analyses of the loop under supercritical conditions, a single-channel, one-dimensional model is developed. In this model, equations for the conservation of mass, momentum and energy are discretized using an implicit finite difference scheme. A computer code called FIASCO (Flow Instability Analysis under SuperCritical Operating conditions) is developed in FORTRAN90 to simulate the dynamics of natural circulation loops with supercritical fluid. Results obtained for the stability boundary substantially deviate from the results reported by previous investigators, and thus contradict some of the reported findings. The disagreement in results is most likely due to the undesirable dissipative and dispersive effects produced from the large time steps used in previous studies, thereby leading to a larger stable region than those found using smaller time step. Results presented here suggest that the stability boundary of a natural circulation loop with supercritical fluid, is not confined to the near-peak region of the (steady state) flow-power curve. Additional and more extensive experimental data are needed to resolve the differences between results obtained here and those reported earlier. However, results obtained for the range of parameter values used in this investigation always predict the stability threshold to be in the positive slope region of the (steady state) flow-power curve. Parametric studies for different operating conditions reveal the similarity of stability characteristics under supercritical conditions with those in two-phase flows.

Linear and Nonlinear Stability Analysis of a Supercritical Natural Circulation Loop

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Manish Sharma ◽  
P. K. Vijayan ◽  
D. S. Pilkhwal ◽  
D. Saha ◽  
R. K. Sinha
Keyword(s):  
Stability Analysis ◽  
Supercritical Water ◽  
Natural Circulation ◽  
Computer Code ◽  
Circulation Loop ◽  
Nonlinear Stability Analysis ◽  
Stability Behavior ◽  
Natural Circulation Loop ◽  
Linear And Nonlinear ◽  
The Stability

Supercritical water (SCW) has excellent heat transfer characteristics as a coolant for nuclear reactors. Besides it results in high thermal efficiency of the plant. However, the flow can experience instabilities in supercritical water cooled reactors, as the density change is very large for the supercritical fluids. A computer code SUCLIN has been developed employing supercritical water properties to carry out the steady-state and linear stability analysis of a SCW natural circulation loop (SCWNCL). The conservation equations of mass, momentum, and energy have been linearized by imposing small perturbation in flow rate, enthalpy, pressure, and specific volume. The equations have been solved analytically to generate the characteristic equation. The roots of the equation determine the stability of the system. The code has been benchmarked against published results. Then the code has been extensively used for studying the effect of diameter, heater inlet temperature, and pressure on steady-state and stability behavior of a SCWNCL. A separate computer code, NOLSTA, has been developed, which investigates stability characteristics of supercritical natural circulation loop using nonlinear analysis. The conservation equations of mass, momentum, and energy in transient form were solved numerically using finite volume method. The stable, unstable, and neutrally stable points were identified by examining the amplitude of flow and temperature oscillations with time for a given set of operating conditions. The stability behavior of loop, predicted using nonlinear analysis has been compared with that obtained from linear analysis. The results show that the stability maps obtained by the two methods agree qualitatively. The present paper describes the linear and nonlinear stability analysis models and the results obtained in detail.

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