Approximating printed circuit heat exchangers dynamics in a sCO2 RCBC as a low-order system via an optimal time constant

The low-order approximation emerges as a promising method for capturing the dynamic behavior of Printed Circuit Heat Exchangers (PCHEs) in sCO 2 Recompression Closed Brayton Cycles (RCBCs). However, two primary challenges hinder widespread adoption: concerns regarding feasibility and the determination of key parameters, such as the time constant. To address these challenges, this study first affirms the feasibility of approximating PCHE ' s dynamic behaviors with a low-order system. In specific, the validity of first-order approximation on the dynamics of high-temperature recuperator (HTR) with mild non-linear property variations is initially assumed. However, a discrepancy is noticed under various operating conditions by employing the same time constant after being compared with the reference model (SCOPE). Then, a novel concept of the optimal time constant, T op , is introduced to underscore the influence of operating conditions on parameter accuracy. Through extensive parameter sweeping, the impact of operating conditions on approximation error is evaluated from two perspectives. First, utilizing T op effectively reduces approximation errors to acceptable levels. The mean squared error remains below 2 degrees C 2 for mass flow rate fluctuations below 32.5 kg/s, and below 4 degrees C 2 for temperature variations below 40 degrees C . Second, the optimal time constant is significantly influenced by mass flow rate, notably affected by geometry configuration, and minimally influenced by hot inlet temperature. Additionally, this study provides insights for design optimization and control strategy selection, as the findings highlight the trade-off between response speed and thermal performance, and the relatively rapid response of sCO 2-PCHEs to temperature control, compared with mass flow rate control.