Preliminary study for the development of PCHE off-design performance model for S-CO₂ power conversion cycle of nuclear power plant applications

Fluid flow channels are etched chemically on metal plates. The channels are semicircular with 1-2mm diameter. Etched plates are stacked and diffusion bonded together to fabricate as a block. These processes are shown in Fig. 1. In addition, for the same thermal duty and pressure drop, a PCHE is up to 85% smaller than an equivalent shell and tube heat exchanger. A relative size comparison is shown in Fig. 2. However, the conventional heat exchanger analysis methods (LMTD, ε-NTU) cannot be applied to a precooler of S-CO₂ system due to substantial change of properties near the critical point. A PCHE computation time problem becomes more pronounced if it is expanded to the level of power system analysis from component level analysis. Since the iteration scheme of KAIST_HXD is sensitive to initial value, more computational time is needed if the change in heat exchanger inlet conditions is large during the cycle iteration process. When finding the optimum operating condition of the power system under the off-design condition, a myriad of PCHE analysis are carried out depending on the combination of cycle variables. Therefore, the goal of this study is to develop a PCHE off-design performance model, which can accelerate the computation time by using non-dimensional parameters while preserving similar accuracy. The reference PCHE is the water-cooled precooler in an S-CO₂ Brayton cycle, which is operating very close to the critical point of CO₂. This new model will be compared with the results of the analysis with the existing discretized method. PCHE off-design modeling was performed for the reference of water-cooled precooler in an S-CO₂ Brayton cycle. The results show that the correlation that is presented in this study matches well with the PCHE design code under off-design condition. The off-design performance can be easily obtained by using this model.