Thermohydraulic Characteristics of Printed Circuit Recuperators in a Supercritical CO2 Brayton Cycle with Nonuniform Minichannels

Abstract

Supercritical carbon dioxide (SCO2) technologies have been under the spotlight of developed countries because they believe that such applied sciences can be ingenious solutions to resolve energy and environmental problems. The SCO2 power cycle is one of the most promising technologies in this field due to its high efficiency and low expenditure. However, optimal designs of heat exchange devices are a vital issue in the SCO2 power cycle because they account for almost 80% of the capital costs. In this study, the comparison of diverse combinations of convergent and divergent minichannels inside the low temperature recuperator (LTR) and high temperature recuperator (HTR) is suggested to recognize the strengths and weaknesses of nonuniform minichannels at high operating pressures and temperatures. Three-dimensional conjugate simulations are carried out, and existing data in the literature are used to validate the obtained results. The comparison reveals a slight deviation (less than 10%) in temperature and pressure profiles. After the evaluation of the studied cases in terms of thermal and hydraulic characteristics, different criteria are employed to explore optimal combinations of the hot side and cold side minichannels. Totally, the minichannel convergence enhances thermal performance of recuperators (up to 26%), and their divergence improves the hydraulic behavior. Nonetheless, diverging the minichannels imposes greater positive effects than converging them. The overall analysis specifies that the most efficient LTR and HTR would be attained by diverging the hot side minichannel, while the cold side minichannel is kept unchanged. This combination of minichannels allows reaching the highest SCO2 temperature at the outlet of LTR and HTR (456 K and 656 K) with the minimum pressure drops (around 0.02% of inlet pressures) and achieving the best performance indexes (approximately 2). Finally, the comparative study discloses that at low Reynolds numbers (less than 14000 for the hot side and 10000 for the cold side), the nonuniform patterns of minichannels perform better than the complicated structures, such as zigzag, wavy, and other optimized geometries. The average performance enhancements for the hot and cold sides are 36.3% and 37.4%, respectively.