Abstract
The radical change in physical properties near the critical point may limit the heat exchange rate of printed circuit heat exchangers (PCHE) due to the presence of a pinch point inside the regenerative heat exchanger. Experimental and numerical investigations on forced convection heat transfer of carbon dioxide at supercritical pressures within a semi-circular PCHE have been performed in the present study. Primary operational parameters included inlet pressure ranged from 7.5MPa to 8.5MPa, mass fluxes ranged from 108 kg/m^2s to 760 kg/m^2s and the average heat fluxes was from 20kW/m^2 to 90kW/m^2. Good agreement was found between the experiments and numerical simulations by SST k-w model with the near-wall region being completely and accurately resolved. A physically improved semi-empirical correlation for the forced convection heat transfer of supercritical CO_2 within the PCHE was developed by implementing probability density function (PDF)-based property revised technique for more reasonably interpreting the influence of instantaneous turbulent temperature and fluctuating properties. 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%.
