Numerical Study of Flow and Heat Transfer of n-Decane with Pyrolysis and Pyrolytic Coking under Supercritical Pressures

Abstract

Pyrolysis and pyrolytic coking of hydrocarbon fuel have significant influences on the regenerative cooling process. In this article, a three-dimensional (3D) model is developed for numerically investigating the flow and heat transfer of pyrolytically reacted n-decane with pyrolytic coking in the engine cooling tube under supercritical pressure. The one-step global pyrolytic reaction mechanism and the kinetic coking model are incorporated into the numerical model to simulate the pyrolysis and pyrolytic coking process of n-decane. The numerical method is validated based on the good agreement between the current predictions and the experimental data. Numerical studies of the characteristics of pyrolysis and surface coking rate at the start time under various outer wall heat fluxes from 1.2 to 1.8 MW/m 2 have been conducted under 5 MPa. Results reveal that heat flux has huge effects on the pyrolytic reaction and the distribution of pyrolytic coking rate. In order to better understand the complicated unsteady physicochemical process, further investigations on coupling relationships between the turbulent flow, heat transfer, pyrolysis and pyrolytic coking in 20 min under a high heat flux of 1.8 MW/m 2 have been performed. It is found that surface coking brings about plenty of negative impacts on the cooling process of n-decane. The mechanisms of these physicochemical phenomena are also analyzed in detail, which would be very helpful in the development of regenerative cooling technology.

Supercritical-Pressure Heat Transfer, Pyrolytic Reactions, and Surface Coking of n-Decane in Helical Tubes

“…The reaction source terms for other chemical species can be proportionally calculated according to the PPD mechanism in Table . The PPD pyrolytic chemical reaction model of n -decane has been validated in previous studies ,,, and is found to be applicable for fuel pyrolysis up to 76%, with its relative error within 20% …”

“…The early numerical work focuses mainly on heat transfer deterioration that is caused by drastic property variations in the critical region. − Supercritical-pressure heat transfer of aviation kerosene and n -decane with consideration of fuel pyrolytic reactions was recently studied. ,− It was revealed that the extra heat sink from fuel pyrolysis plays a dictating role in the high-temperature region (pyrolytic reactions become strong once the fuel temperature rises above 900 K). The effects of the channel aspect ratio and ribbed tube surface on fuel temperature variations and pyrolytic reactions were examined. , Surface coking phenomena were further investigated. , …”

Effects of geometric parameters of rectangular cooling channel on pyrolysis carbon deposition in fuel‐cooled plates

“…Therefore, only the carbon deposition rate at a certain time can be obtained, not the amount of the carbon deposition accumulated over a period of time. Although the unsteady-state algorithm [17] can be used to simulate the carbon deposition accumulated in each time step, it requires considerable calculation amount, and is especially time-consuming for a 3D numerical simulation.…”

“…This model was further used to study pyrolysis carbon deposition combined with numerical simulation. Xu et al [15,16] studied the carbon deposition process in circular tubes and finned tubes through twodimensional numerical simulations, Tao et al [17] simulated the formation process of carbon deposition using the two-dimensional dynamic mesh technique, and Sun et al [18] studied the amount of carbon deposition on the circumferential line on the helical tube section. However, as a carbon deposition model with properties of surface reaction, the radial average component concentration was used during the model build.…”

Differential Global Reaction Model with Variable Stoichiometric Coefficients for Thermal Cracking of n-Decane at Supercritical Pressures

“…Further research then investigated the coupled influence of the cracking products on the heat transfer. Tao et al , simulated n -decane thermal cracking using a CFD model with the global reaction model established by Ward et al , Bao et al also applied the model by Ward et al to simulate n -decane thermal cracking in a three-dimensional (3D) rectangular duct. Zhou et al developed a one-step model containing 11 species, which was efficient for n -decane conversions up to 12%, to calculate the chemical heat sink.…”