Numerical Investigation of Pressure Drop and Local Heat Transfer of Supercritical CO2 in Printed Circuit Heat Exchangers

by Eric N. Van Abel, Mark H. Anderson, & Michael L. Corradini
University of Wisconsin - Madison

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Advanced Generation IV nuclear power plant designs include those that are proposing to use a Supercritical CO2 (S-CO2) Brayton Cycle for power generation due to its high cycle efficiencies and compact turbomachinery. Possible reactor designs that have proposed use of an S-CO2 secondary side include the Very High Temperature Gas Reactor (HTGR), the Sodium-Cooled Fast Reactor (SFR), the Prismatic Reactor (PMR), the Lead Cooled Fast Reactor (LFR), and others. The highly compact power generation equipment has the potential to reduce capital costs, while the higher efficiencies would reduce the operating cost to revenue ratio.

The current study involves numerical simulations of the fluid flow characteristics within printed circuit heat exchangers (PCHEs) with zigzag channel configurations. The channels are semi-circular with a hydraulic diameter of Dh = 1.16 mm. Three-dimensional computational fluid dynamics (CFD) calculations with the FLUENT code were used to investigate the accuracy of the numerical simulations versus the existing experimental data set.

Full-length 3D CFD models were created and meshed using hexahedral meshing techniques. The k-ω Shear Stress Transport (SST) turbulence model was found to provide much better pressure drop prediction than the k-ε model. The boundary layer was fully resolved in the models, with the first row wall cells having y+ values around 1.0. The analyzed experimental inlet conditions ranged from T inlet = 34°C to 95°C, G = 325 to 760 kg/m2s, and P = 7.5 to 8.1 MPa. Measurements and analyses were concentrated near the pseudo-critical temperatures.

The heat fluxes and pressure drops were compared to the experimentally calculated values, and it was found that the CFD predictions for heat flux averaged about 5 to 25% below measured values. The pressure drops were found to be in relatively good agreement, with about a 10% over-prediction for high mass flux cases and a 10% under-prediction for low mass flux cases. A parametric study of the pressure drop versus the corner radius was also performed, and it was found that pressure drop had a strong dependence on the corner radius for r < 0.4 mm.