Abstract: Helium-xenon (He-Xe) gas mixtures, with their advantageous thermophysical properties, low fast-neutron absorption cross-section, and favorable compressibility, are promising coolants for gas-cooled fast reactors (GFR). Open-lattice channels, a typical configuration in compact cores, govern the thermal-hydraulic performance and safety margins of the reactor through the complex flow and heat transfer behavior of the He-Xe mixture. This study presents a numerical investigation of the flow and heat transfer characteristics of a He-Xe mixture (molar mass of 40 g/mol) in triangular-array open-lattice channels. The primary objective is to develop accurate predictive correlations for key thermal-hydraulic parameters, specifically the friction factor, Nusselt number, and transverse mixing coefficient, within a parametric space defined by pitch-to-diameter ratios ( P/D) ranging from 1.15 to 1.33 and Reynolds numbers ( Re) from 1×10 ⁴ to 1×10 ⁵. A comprehensive numerical methodology was established. First, a dedicated property model for the He-Xe mixture was developed and validated against reference data to ensure accurate representation of its thermodynamic and transport properties. Subsequently, a computational fluid dynamics (CFD) model was constructed and validated against benchmark data to confirm its predictive capability for the targeted flow regimes. Systematic numerical simulations were then performed across the specified ranges of P/D and Re, generating a database for the analysis of flow and heat transfer phenomena. The results reveal that, within the entire investigated range, the He-Xe flow remains in a fully developed turbulent state. A distinct velocity boundary layer forms in the near-wall region, where steep velocity gradients dominate the wall shear stress. Based on these observations and the simulation data, a new friction factor correlation was developed. This correlation builds upon the classical Blasius formula framework and is specifically calibrated for He-Xe flow in open-lattice channels, effectively capturing the influence of P/D and Re. Furthermore, the temperature field analysis indicates that the fluid temperature increases from the wall toward the channel center, with the maximum temperature gradient occurring within the thermal boundary layer. Utilizing the functional form of the classic Kays correlation, a new Nusselt number correlation was derived from the numerical results. This correlation accurately predicts convective heat transfer for He-Xe mixtures in the studied geometry and flow conditions. Finally, the transverse mixing intensity, quantified by the transverse mixing coefficient, was found to increase with Re. Notably, beyond Re=8×10 ⁴, the flow enters a vigorously turbulent regime where the mixing coefficient approaches an asymptotic value. The channel geometry, particularly the P/D, exerts a significant influence on the mixing intensity. A dedicated correlation for the transverse mixing coefficient was proposed, accounting for both Re and P/D effects. In conclusion, this study provides a set of validated, geometry-specific predictive correlations for friction factor, Nusselt number, and transverse mixing coefficient for He-Xe flow in triangular open-lattice channels. These correlations offer essential tools for the thermal-hydraulic design, performance optimization, and safety assessment of helium-xenon gas-cooled fast reactors, bridging the gap between fundamental fluid dynamics and practical engineering applications.