A partitioning design method for regenerator in transcritical CO2 power cycle based on heat matching

The regenerators are the key components affecting the efficiency of CO2 rankine cycle. The degree of heat transfer matching between the hot and cold working fluids in the regenerator is the core factor that determines its coupled heat transfer efficiency. However, due to the significant nonlinear variation of the thermophysical properties of CO2 in the critical region, it leads to a serious mismatch in the heat capacity of CO2 on the hot and cold-sides of the regenerator, which significantly reduces its coupled heat transfer performance. To address this issue, the partitioning design method for the regenerator based on thermal matching is proposed. The method achieves better heat transfer performance matching between the hot and cold-sides by identifying thermophysical property mismatch region and optimising the heat exchange structure within. In addition, the flow performance is significantly improved compared with the commonly used full optimisation methods. In this study, a mismatch degree index is proposed to quantify the size of mismatch regions. A three-dimensional numerical model was then used to investigate the performance optimization effect of the proposed method under various operating conditions. Subsequently, a one-dimensional predictive model and a zero-dimensional predictive expression were developed to quickly and accurately calculate the mismatch region locations. Finally, experimental tests were conducted for the regenerator. Based on this, it was optimised according to the proposed method. The results demonstrate that the partitioning design method offers excellent performance optimization across various operating conditions. At the cost of sacrificing unit pressure drop, the heat transfer increment achievable through the partitioning design method is 51 % greater than that of the fully optimised structure. The one-dimensional predictive model developed exhibits a maximum error of 3.3 %, indicating good accuracy. In contrast, the zero-dimensional predictive expression has a maximum error of 20 %, providing reasonable reliability but with lower precision. The operating parameters that most influence the location of the mismatch region are cold-side pressure and heat transfer quantity. The coupled heat transfer performance of the optimised structure is improved by 6.6 % compared with the original regenerator. The research provides a new method for improving the coupled heat transfer performance between working fluids with strongly variable thermophysical property characteristics.