An analytical method for quickly evaluating the performances of refractory alloys in sCO2 Brayton cycle applications

Abstract: A rapid and effective analytical method has been developed to assess the performance of structural materials in sCO2 power cycle applications. This method combines a conjugate heat transfer model, considering constant heat flux boundary conditions, with a corresponding mechanical model. By applying this method, the allowable working fluid temperatures and minimum required wall thicknesses of three refractory alloys, namely Inconel 617, Haynes 230, and SS 253MA, have been compared under various boundary conditions. It has been observed that the allowable working fluid temperature does not change monotonically with the tube's external surface temperature but exhibits a peak value. Generally, Nickel-based alloys (Inconel 617 and Haynes 230) outperform SS 253MA. However, for applications with low working fluid temperature and low heat flux, the performance difference becomes less significant. Inconel 617 tends to offer slightly higher allowable working fluid temperature than Haynes 230 in most operating conditions, but the minimum required wall thickness is considerably larger for Inconel 617 compared to Haynes 230. Furthermore, setting the allowable working fluid temperature slightly lower than its peak value can lead to a substantial reduction in the minimum required wall thickness. This is due to the rapid decline of maximum allowable stresses at high temperatures. Such optimization can be valuable for potential techno-economic considerations in heat exchanger designs.