Numerical investigation for comprehensive understanding of endothermic decomposition characteristics of supercritical n-Dodecane in a regenerative cooling channel

A numerical investigation was conducted to characterize the endothermic decomposition of supercritical n-dodecane in a single regenerative cooling mini-channel using a quasi-global, multi-step proportional product distribution (PPD) reaction model. A two-dimensional axisymmetric computational domain was employed to represent a cylindrical channel with an inner diameter of 2.0 mm and a total length of 1,100 mm. Simulations were performed under supercritical conditions at an operating pressure of 3 MPa and an inlet fuel temperature of 665 K. An extensive parametric study was conducted over a range of wall heat fluxes and mass flow rates to elucidate their effects on the endothermic pyrolysis characteristics of n-dodecane. The results demonstrate that fuel residence time plays a critical role in determining endothermic performance. At a fixed mass flow rate, a lower heat flux results in a longer residence time, whereas at a fixed heat flux, decreasing the mass flow rate similarly increases the residence time. A longer residence time generally enhances the total heat sink, fuel conversion rate, and heat sink ratio R h at a given fuel temperature, while promoting alkane formation and thereby reducing the alkene-to-alkane ratio. Further analysis over a broad range of operating conditions using the heat flux-to-mass flux ratio ( q/G ) reveals the existence of an optimal q/G at which R h , a measure of the relative contribution of chemical to physical heat absorption, reaches its maximum for the channel geometry considered. These findings highlight the coupled effects of thermal loading, mass flow rate, residence time, and product distribution on fuel endothermicity and provide further insight into the pyrolysis behavior of supercritical n-dodecane in regenerative cooling channels.