Characterization of non-equilibrium condensation of supercritical carbon dioxide in a de Laval nozzle

Abstract

On a ten - year timescale, Carbon Capture and Storage could significantly reduce carbon dioxide (CO 2 ) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO 2 to supercritical conditions, which can re quire up to 15 % of the plant’s gross power output. To reduce the power requirements supercritical carbon dioxide compressors must operate at reduced temperatures and near saturation where phase change effects are important. Non - equilibrium condensation can occur in the high - speed flow at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on the metastable fluid properties. In this paper we assess the metastable behavior and nucleation characteristics of high - pressure subcooled carbon dioxide during the expansion in a Laval nozzle. The assessment is cond ucted with numerical calculations, supported and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41 and 82 bar and near the critical point. The state of the metastable fluid is fully charact erized through pressure and density measurements, with the latter obtained in a first of its kind laser interferometry set up. In a systematic analysis the inlet conditions of the nozzle are moved close to the critical point to allow for large gradients in fluid properties and reduced margin to condensation. The results of calculations using a direct extrapolation of the Span and Wagner equation of state model are compared with the experimental measurements. The analysis suggests that the direct extrapolati on using the Span and Wagner model yields results within 2% of the experimental