Measurements of Heat Transfer and Pressure Drop Characteristics of Supercritical Carbon Dioxide Flowing in Zig-Zag Printed Circuit Heat Exchanger Channels

by Matthew D. Carlson, Alan Kruizenga, Mark H. Anderson, & Michael L. Corradini
University of Wisconsin, Madison

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Closed-loop Brayton cycles using supercritical carbon dioxide (SCO2) have been gaining interest recently for use in high-temperature power generation applications including High Temperature Gas Reactors (HTGR) and Sodium- Cooled Fast Reactors (SFR). Compared to Rankine cycles SCO2 Brayton cycles offer similar or improved efficiency and the potential for decreased capital costs due to a reduction in equipment size and complexity. Compact printed-circuit heat exchangers (PCHE) are being considered as part of several SCO2 designs to further reduce equipment size with increased energy density. Several plan to use a regenerator operating near the pseudo-critical point of carbon dioxide to benefit from large variations in thermo-physical properties, but further work is needed to validate correlations for heat transfer and pressure-drop characteristics of SCO2 flows in candidate PCHE channel designs for a variety of operating conditions. This paper presents work on experimental measurements of the heat transfer and pressure drop behavior of miniature channels using carbon dioxide at supercritical pressure. A zig-zag plate geometry based on the cold-fluid side of a Heatric printed circuit heat exchanger was tested in a horizontal orientation in the cooling mode for bulk temperatures from 20 to 65 degrees Celsius at pressures of 7.5 and 8.1 MPa and a mass flux of 326 kg/m2-sec. Heat transfer coefficients and bulk temperatures are calculated from measured local wall temperatures and local heat fluxes. The experimental results are compared to previous data for semi-circular PCHE channels, and to several correlations used for cooling-mode flows in millimeter-scale channels.