Printed circuit heat exchangers (PCHEs) are key components in supercritical carbon dioxide (S-CO2) Brayton cycles because of their compact structure and high heat transfer capability. However, existing studies have mainly focused on steady-state structural optimization or isolated component analysis, while the influence of geometric parameters on thermal-hydraulic responses under system-level transient disturbances remains insufficiently understood. In this study, a Modelica-based dynamic simulation framework is developed for the system-level analysis of recuperators in an S-CO2 Brayton cycle. A one-dimensional dynamic PCHE model is established and validated against benchmark data, with a maximum relative error of 0.87%. A continuously varying heat sink temperature ranging from 22 ° C to 26 ° C is introduced as a representative offdesign disturbance. The effects of channel diameter and channel length on heat transfer coefficient and pressure drop are investigated under both design reference and transient operating conditions. The results show that smaller channels and longer flow paths enhance heat transfer performance but introduce larger pressure-drop penalties under the design reference condition. Under transient heat sink temperature disturbances, smalldiameter and long-channel configurations exhibit stronger thermal-hydraulic response variations than under steadystate conditions. These results indicate that parameter trends obtained under steady-state conditions may not directly represent transient thermal-hydraulic behavior under off-design operation. The proposed framework provides an efficient approach for preliminary parametric assessment and system-level transient analysis of recuperators in S-CO2 Brayton cycles.

To be come

Complex thermodynamic cycle systems play a critical role in advanced energy applications, where modeling and simulation constitute a fundamental component of Model-Based Systems Engineering (MBSE). Conventional sequential modular approaches rely heavily on predefined calculation sequences and empirical parameter settings, leading to limited adaptability for complex cycle topologies with strong coupling, flow splitting, and multiple recuperation processes. This study proposes an equation-oriented (EO) modeling framework for thermodynamic cycle systems, in which the entire cycle is formulated as a coupled nonlinear algebraic equation system and solved simultaneously. Standardized algebraic component models are established for compressors, turbines, and recuperators. An ε–NTU-based heat exchanger formulation is adopted to avoid the predefined minimum temperature difference commonly required in conventional approaches. In addition, a bi-level solution strategy combining outerlayer parameter scanning and inner-layer Newton iterations is introduced to handle additional design degrees of freedom. The proposed framework is validated using supercritical CO₂ simple recuperated and recompression Brayton cycles. Simulation results show that the predicted cycle efficiencies agree well with published reference data, with deviations below 1% under all investigated operating conditions. The framework demonstrates stable convergence behavior and strong adaptability to complex thermodynamic topologies. The proposed approach exhibits acausal, modular, and topology-decoupled characteristics consistent with the declarative modeling philosophy of Modelica. It provides a unified and extensible solution framework for MBSEoriented modeling and simulation of complex thermodynamic energy systems.