Dynamic model of supercritical CO2 based natural circulation loops with fixed charge

• Published in: Applied thermal engineering 2020-03, Vol.169, p.114906, Article 114906
• Main Authors: Pegallapati, A. Saikiran, Banoth, Prashanth, Maddali, Ramgopal
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Dynamic model; Dynamic models; Finite volume method; Fluid dynamics; Mass flow rate; Mathematical models; Method of lines; Modelica; Natural circulation loop; Partial differential equations; Steady state; Studies; Working fluids
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2020.114906

•Dynamic model of fixed charge sCO2 natural circulation loop (NCL) is developed.•Modelica is used for model development and Method of lines is used to solve PDEs.•The test model showed good agreement with experimental data.•For a fixed charge NCL, mass flow rate increases monotonically with heater power.•Wall thermal capacitance must be considered for accurate dynamic modeling of NCLs. A dynamic model of natural circulation loops (NCLs) using supercritical carbon dioxide as working fluid is presented. An NCL with constant mass of working fluid is considered. The mathematical model is developed by considering 1-D balance equations for mass, momentum and energy, duly considering the variation in the properties of the CO2. Method of lines is used to convert the partial differential equations into ordinary differential equations in time and a finite volume method is used for spatial discretization. Modelica language is used to develop a generic dynamic model of the NCL which allows for an easy change in the loop configuration and also implementation of control systems. The results from the model developed showed good agreement with the experimental studies reported in literature on an air cooled supercritical CO2 based NCL. Results show that wall thermal capacitance is an important factor to be considered in the dynamical analysis of the NCL as it suppresses oscillations during loop transients and increases the time required to reach steady state. When operated under fixed mass of working fluid, the mass flow rate of the NCL at steady state increases monotonically with heat input without exhibiting any maximum.