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

Abstract

An analytical method has been developed to quickly evaluate structure materials' performances in sCO2 power cycle applications. This analytical method combines a conjugate heat transfer model for a tube with constant heat flux boundary conditions with its corresponding mechanical model to obtain the allowable working fluid temperatures and minimum required wall thickness. Three refractory alloys, Inconel 617, Haynes 230, and SS 253 MA, have been selected for implementing this analytical method by comparing their allowable working fluid temperatures and minimum required wall thicknesses under various boundary conditions. The allowable working fluid temperature has been observed not to change with the external surface temperature of the tube monotonically but with a peak. In general, Nickel based alloys (Inconel 617 and Haynes 230) have better performances than the SS 253 MA, but the difference becomes insignificant for low working fluid temperature and low heat flux applications. Besides, Inconel 617 can offer slightly higher allowable working fluid temperature than Haynes 230 in most work conditions, but the minimum required wall thickness is also significantly larger than that of Haynes 230. In addition, the minimum required wall thickness can be significantly reduced when the allowable working fluid temperature is set slightly lower than its peak value due to the rapid decrease of the maximum allowable stresses at high temperatures, which will be useful in potential techno-economic optimization for heat exchanger designs.