PDF-based modeling on the turbulent convection heat transfer of supercritical CO₂ in the printed circuit heat exchangers for the supercritical CO₂ Brayton cycle

Experimental and numerical investigations on forced convection heat transfer of supercritical CO₂ within a semi-circular printed circuit heat exchanger have been performed in the present study. Primary operational parameters included inlet pressure of 7.5 MPa to 8.5 MPa, mass fluxes ranged from 160 kg/m²s to 760 kg/m²s and the average heat fluxes of 20 kW/m² to 90 kW/m². A physically improved semi-empirical correlation for the forced convection heat transfer of supercritical CO₂ within the PCHE was developed by implementing probability density function (PDF)-based property revised technique for more reasonably interpreting the influence of the instantaneous turbulent temperature and fluctuating properties. The comparison results showed that the simple DB correlation could not reproduce the experiments and the Jackson correlation with the properties ratio correction terms could qualitatively capture the heat transfer features under different working conditions, however, it still overestimated the average value of the heat transfer coefficients in the whole range of the working conditions. The predictions of the PDF-based new developed correlation are significantly improved so that more than 96% data in the heating mode and more than 92% data in the cooling mode with various heat fluxes are captured and collapsed to an ideal straight line within an accuracy of 25%.