Flow and heat transfer of supercritical CO₂ in the honeycomb ultra-compact plate heat exchanger

The honeycomb Ultra-compact Plate Heat Exchanger (UCPHE) with hexagonal channels is proposed to be the recuperator in the supercritical CO₂ (SCO₂) Brayton cycle. The flow and heat transfer characteristics of the SCO₂ in the UCPHE are investigated numerically by means of SST k-ω turbulence model. The study shows that the buoyancy effect has weak effect on heat transfer due to the insignificant variation in the thermo-physical properties of the SCO₂ under the high temperature condition. The turbulent kinetic energy and the intensity of secondary flow reach the maximal value near the pseudo-critical point due to the significant buoyancy effect, resulting in the heat transfer enhancement. The performance evaluation of the UCPHE via Nu/f^1/3 is implemented and its optimum geometry is proposed. The study concludes that the UCPHE has a better comprehensive performance than the Printed Circuit Heat Exchanger (PCHE) within the range of the Reynolds number from 3000 to 35,000.