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| 1 | Competing effects of surface catalysis and ablation in hypersonic reentry aerothermodynamic environment显示文摘Under hypersonic flow conditions, the complicated gas-graphene interactions including surface catalysis and surface ablation would occur concurrently and intervene together with the thermodynamic response induced by spacecraft reentry. In this work, the competing effects of surface heterogeneous catalytic recombination and ablation characteristics at elevated temperatures are investigated using the Reactive Molecular Dynamics(RMD) simulation method. A GasSurface Interaction(GSI) model is established to simulate the collisions of hyper-enthalpy atomic oxygen on graphene films in the temperature range of 500–2500 K. A critical temperature Tcaround900 K is identified to distinguish the graphene responses into two parts: at T < T_(c), the heterogeneous surface catalysis dominates, while the surface ablation plays a leading role at T > T_(c). Contradicting to the traditional Arrhenius expression that the recombination coefficient increases with the increase of surface temperature, the value is found to be relatively uniform at T < T_(c) but declines sharply as the surface temperature increases further due to the competing ablation effect. The occurrence of surface ablation decreases the amounts of active sites on the graphene surface for oxygen adsorption, leading to reduced recombination coefficient from both Langmuir-Hinshelwood(L-H) and Eley-Rideal(E-R) mechanisms. It suggests that the traditional Computational Fluid Dynamics(CFD) simulation method, which relies on the Arrhenius-type catalysis model, would result in large discrepancies in predicting aerodynamic heat for carbon-based materials during reentry into strong aerodynamic thermal environment. | Zhiliang CUI Jin ZHAO Guice YAO Jun ZHANG Zhihui LI Zhigong TANG Dongsheng WEN | 2022 | Chinese Journal of Aeronautics2022，35，10： | 2 |
| 2 | Pore-scale simulation of water/oil displacement in a water-wet channel显示文摘Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery.Volume of fluid method was used to capture the interface between oil and water and a pore-throat connecting structure was established to investigate the effects of viscosity,interfacial tension(IFT)and capillary number(Ca).The results show that during a water displacement process,an initial continuous oil phase can be snapped off in the water-wet pore due to the capillary effect.By altering the viscosity of the displacing fluid and the IFT between the wetting and non-wetting phases,the snapped-off phenomenon can be eliminated or reduced during the displacement.A stable displacement can be obtained under high Ca number conditions.Different displacement effects can be obtained at the same Ca number due to its significant influence on the flow state,i.e.,snapped-off flow,transient flow and stable flow,and ultralow IFT alone would not ensure a very high recovery rate due to the fingering flow occurrence.A flow chart relating flow states and the corresponding oil recovery factor is established. | Jin Zhao Guice Yao Dongsheng Wen | 2019 | Frontiers of Chemical Science and Engineering2019，13，4： | 0 |
| 3 | Working state map of hydrocarbon fuels for regenerative cooling显示文摘Regenerative cooling by endothermic hydrocarbon fuel(EHF)is one of the most promising techniques for thermal management of supersonic or hypersonic aircraft.How to maintain the fuel working in proper states is an important issue to maximize the cooling potential of EHT.This work proposes a novel working state map,including risking zone(RZ),thermal cracking zone(TCZ),supercritical zone(SupZ)and subcritical zone(SubZ),to differentiate possible working states of an EHF during regenerative cooling.Using n-decane flowing in a circular tube as an example,the boundaries of four zones are determined by numerical simulation covering different heat fluxes(0.2-4.0 MW·m^(-2))and mass flow rates(0.5-10.5 g·s^(-1))under two operating pressures(3.45 and 5.00 MPa).Empirical correlations for three boundary lines are obtained and the maximum cooling capacity is identified,as well as the identification of the pressure effect.The revelation of such new perspective of regenerative cooling is of great implication to the design and optimization of cooling system for future thermal management. | Chen Zhang Hui Gao Jiajun Zhao Guice Yao Dongsheng Wen | 2023 | Propulsion and Power Research2023，12，2： | 0 |
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