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In the research of porous media and the interior of microelectronic devices, fluids frequently shuttle among pores and wall cracks, therefore it is of great significance to explore the influence of media wall on fluid flow and heat transfer. In this paper, CFD-DSMC coupled iterative algorithm is first used in the research of the flow and heat transfer of gas near the wall in the porous media, which simplified into the flow and heat transfer in micron-scale tube with smooth and rough wall conditions. It is found that compared with the pure CFD method, the velocity field obtained by the coupled method is quite different in the region close to the wall, and this will affect the flow field in the mainstream region, that is, with the higher roughness of the wall, the velocity in the central region will be smaller. There is no significant difference in the temperature distribution in the microtube before and after coupling, but the temperature in the mainstream decreases with the increase of the roughness of the wall. In addition, the temperature jump was found from some of the coupling results close to the wall. The results will contribute to a deeper understanding of the influence of rough surfaces on gas flow and heat transfer near the wall, and provide guidance for the regulation of flow and heat transfer in porous media. [ABSTRACT FROM AUTHOR]

A two-dimensional numerical simulation study is conducted to investigate the combustion process of n-heptane spray in a porous medium burner (PMB) based on the previous experimental work performed by this research group. In order to adapt the model for the conditions of different wall temperatures and different splash Mach numbers, the wall-impingement model in this study is based on the model by O'Rourke and Amsden and the interaction mechanism between the spray droplets and the wall is optimized through user-defined functions (UDFs). The effects of air inlet velocity, injected fuel quantity and preheating temperature on spray combustion are analyzed. The results show that the downstream velocity of the combustion flame increases when the inlet air velocity increases or the fuel injection rate decreases or the preheating temperature decreases. Under the same equivalence ratios, the flame propagation velocity increases as the increase of the dimensionless gas-oil joint effect parameter. The flame area also increases with the increase of inlet air velocity, but the rate of increase in the flame area gradually decreases as the reaction proceeds. An initial preheating temperature of 1060 K is conducive to the stable combustion of n-heptane spray for flame lengths less than 0.060 m. [ABSTRACT FROM AUTHOR]

A numerical investigation of the rapid turbulent filtration combustion within a packed pebble bed is conducted at a fixed superficial velocity of 0.5 m/s, equivalence ratio of 1.0 (methane/air) under two background pressures of 1.0 and 0.5 MPa. Turbulence is modeled with the detached eddy simulation (DES) method. The interaction between turbulence and chemical reaction is considered through the fast reaction method, i.e., burning velocity model (BVM). To validate the DES method, the relative turbulence intensities in a 3D staggered cylinders are verified previously which are in excellent agreement with the experimental data (no reaction). With the confidence in the DES method, the turbulent combustion characteristics in a 3D packed pebble bed are studied in detail, including pressure fluctuation, spatial inhomogeneities of velocity and temperature fields, and evolution of the flame surface. Numerical results show that a strong pressure fluctuation arises after ignition due to thermal expansion contributing significantly to the velocity and temperature fluctuations for the case of 1.0 MPa, whereas it is relatively moderate for the case of 0.5 MPa. Though the evolution of the flame surface both can be divided into two stages for the two cases, i.e., initial-rapid spreading stage, and stable propagating stage, there is a slight difference between them. Specifically, it closely resembles to an atomic blast for the former, while it is similar to a volcanic eruption for the later. Undergoing this stage, about 20 ms, the wrinkle and fragmented flames or flamelets creep over the pebbles through the thin layers close to the walls. Statistical stability is identified in the process of flame propagating upstream. Turbulent flame speeds obtained in this study agree well with the experimental data, especially for the case of 1.0 MPa. [ABSTRACT FROM AUTHOR]