Experimental correlations of CO2 jet diffusion angles under subcritical, transcritical, and supercritical conditions

This study deals with the diffusion angle of CO 2 jets under subcritical, transcritical, and supercritical conditions. Phase-shift interferometry is used to obtain quantitative density fields, and the half-width at half-maximum criterion is adopted to determine the jet diffusion angle. The measured results are compared with several classical correlations, and a new empirical correlation is developed by fitting multiple influencing parameters, including flow and thermophysical properties. To account for the continuous evolution of jet-interface morphology, the data are further classified according to transcritical paths and fractal characteristics, and regime-dependent correlations are established. It is found that the measured diffusion angles generally fall between the predictions of Chehroudi and Reitz and Bracco, while some data approach the trend of Dimotakis’s mixing-layer theory. The results also show that the dependence of diffusion angle on density ratio is nonlinear, indicating that density ratio alone is insufficient for accurate prediction. The proposed correlation predicts the diffusion angle within about ± 20 %, while the regime-classified correlation reduces the uncertainty to about ± 10 %. Analysis of the fitted exponents further shows that Reynolds number and Prandtl number exert relatively stable suppressing and promoting effects, respectively, whereas the density and viscosity ratios exhibit strong regime dependence, reflecting the coupled roles of inertia, transport, and real-fluid thermophysical effects in governing near-critical jet diffusion.