NUMERICAL INVESTIGATION OF THERMOHYDRAULIC CHARACTERISTICS OF SUPERCRITICAL CARBON DIOXIDE RECUPERATOR WITH HYBRID, ZIGZAG, AND SINUSOIDAL CHANNELS

The design of flow paths in mini/microchannel heat exchangers is a critical aspect for optimizing the performance of supercritical carbon dioxide (sCO<sub>2</sub>) Brayton cycle systems. This study introduces two innovative hybrid zigzag channel designs, developed by modifying conventional zigzag channels, aimed at enhancing heat transfer efficiency. The designs, termed hybrid_SAHI (with smaller angles on the hot side and larger on the cold side) and hybrid_SACI (with smaller angles on the cold side and larger on the hot side), are evaluated based on both local performance metrics (e.g., pressure drop and heat transfer coefficients) and global parameters (e.g., friction factor, Colburn j factor, and volume goodness factor). The findings highlight that both hybrid designs outperform traditional configurations (sinusoidal and zigzag) in terms of heat transfer, although they come with higher pressure penalties. Specifically, the hybrid_SAHI and hybrid_SACI designs exhibit significant enhancements of 42% and 26% in thermal performance on the hot side, and 35% and 14% on the cold side, respectively, when compared to conventional zigzag channels. However, these improvements are associated with approximately fourfold and threefold increases in pressure drop factors for the hot and cold sides, respectively. Additionally, while the inserted straight channel shows marginally better heat transfer capabilities than sinusoidal and zigzag designs, the sinusoidal channel offers the best overall performance due to its significantly lower pressure drop, thus presenting a balanced solution. These insights are crucial for determining the optimal channel configurations for sCO<sub>2</sub> recuperators, ensuring higher thermal performance while managing the trade-off with pressure drop. The proposed hybrid designs demonstrate potential for advancing the efficiency and viability of sCO<sub>2</sub> Brayton technology by facilitating more effective heat transfer management in compact heat exchangers.