Experimental test on 1.8 MW class printed circuit heat exchanger for precooler of supercritical CO2 Brayton cycle

초록

Supercritical CO2 (sCO2) Brayton cycles are gaining attention as next-generation power conversion systems for various heat sources owing to their high thermal efficiency and compact system design. Because the turbomachinery can be made more compact owing to the thermophysical properties of sCO2, compact heat exchangers must also be used to achieve overall system compactness. A representative compact heat exchanger is the printed circuit heat exchanger (PCHE), which is suitable for high-pressure sCO₂ applications. Therefore, the PCHE is considered an appropriate precooler for the sCO2 Brayton cycle. However, experimental research on the large-scale, MW-class PCHEs with zigzag channels operated as a precoolers remains scarce. In this study, a 1.8 MW-class PCHE was designed and manufactured as a full-scale precooler for a 500 kW-class sCO2 power conversion system for waste heat recovery. The overall dimensions of the precooler were 1900 mm × 1000 mm × 1066 mm (2.025 m3). The total volume of the heat-transfer core was 0.27 m³ , corresponding to a volumetric heat duty of approximately 6.667 MW/m³ . Zigzag channels were incorporated on both sides to achieve high heat-transfer performance, and a single-banking configuration was adopted. The effectiveness and pressure drop of the PCHE were investigated to verify whether they met the design requirements. In the experiments, the sCO2 average Reynolds number varied from 5632 to 15,212. The inlet and outlet temperatures of sCO2 varied from 32.31 to 50.85 °C and from 31.35 °C to 35.68 °C, respectively. On the water side, the average Reynolds number varied from 78 to 798. Inlet and outlet temperatures of water varied from 13.93 to 24.35 °C and from 32.08 to 45.59 °C, respectively. The effects of the average Reynolds number and temperature on the heat transfer and pressure drop in the PCHE were tested, and its effectiveness was assessed. New empirical correlations for the friction factor of the zigzag PCHE both sCO2 turbulent regime and water laminar regime were proposed based on the experimental data for the precooler design in the sCO2 Brayton cycle. The proposed friction factor correlations showed maximum deviations of ±5.71% for sCO2 and maximum deviations of ±8.9% for water.

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