Design and Off-design Performance Analysis of a Zigzag Channeled Precooler for Indirect Cooling System of Supercritical CO2 Recompression Cycle Incorporated with a Flow-Bypass System

Abstract

The employment of a Printed Circuit Heat Exchanger (PCHE) as a Precooler in an indirect cooling system of a supercritical CO2 (sCO2) power block is the prevailing trend in research since cooling the working fluid with water offers superior cooling performance compared to an air-cooled system. The enhanced cooling performanceofthe Printed Circuit Heat Exchanger offers the desired sCO2 compressor inlet temperature close to the pseudo-critical point, maximizing the thermodynamic efficiency of the cycle. The improbable fluctuating properties of sCO2 near the critical region make it arduous to design a component that operates near the critical region. However, the high heat transfer coefficient in the near-critical region increases the power cycle’s performance and reduces the cycle components’ size, making it cost-effective. In the indirect cooling system of the sCO2 recompression cycle, the working fluid (sCO2) is cooled by cooling water in a Printed Circuit Heat Exchanger known as the Precooler. Thus, the heat gained by the cooling water is cooled by the air-cooled heat exchanger unit inside a Natural draft dry cooling system. In this study, an iterative nodal approach is implemented to develop a Python code for designing a Zigzag channeled Printed Circuit Heat Exchanger as the Precooler for the indirect cooling system of the sCO2 recompression cycle for the Concentrated Solar Power application. The off-design performance study is conducted under different sCO2 inlet temperatures (338 K–378 K), inlet pressure (7 MPa–10 MPa), and a wide range of cooling water inlet temperatures (283 K–318 K), suggesting the heat transfer rate can be enhanced by lowering the water inlet temperature and sCO2 working pressure. Nevertheless, the variation in sCO2 input temperature has little influence on the precooler heat transfer rate. The result also demonstrates that the pressure drop on the sCO2 side decreases upon increasing these parameters. The off-design performance improvement during low ambient temperature is achieved by introducing a flow bypass in the power block, which optimizes the precooler sCO2 mass flow to maintain the desired compressor inlet temperature.