| For the objective of reducing the emissions of pollutants and improving the utilization of fuel in combustion process, which are two hot research topics in the field of combustion, a variety of new combustion technologies have been put forward. In the past twenty years, the porous media combustion technology which has attracted wide attention is one of the important technologies to solve these two problems. It provides a new way for the development and design of new advanced combustion system. The combustion in porous media, also known as filtration combustion, is a widespread phenomenon in nature and engineering, but the understanding of filtration combustion is far from deep and comprehensive at present, compared with free combustion. Despite the study of filtration combustion has made great progress and gratifying achievements, so far, both at home and aboard, there are still many problems and gaps in this field, especially the basic scientific issues, which needs to be further studied and proven. Based on the computational fluid dynamics (CFD) method and the direct simulation Monte Carlo (DSMC) method, the characteristics of gas flow and combustion at micro scale are studied in this paper, which is helpful to enhance the understanding of the phenomena of flow and combustion in the local area of porous media, and also benefits the design and development of micro electro mechanical system (MEMS) involved in pharmaceutical, chemical, biology, aerospace and other fields.Firstly, a CFD/DSMC coupled iterative algorithm is applied to simulate the gas flow and heat transfer in a micro channel with a width of 50 microns, assumed to be infinitely long. The algorithm combines two kinds ie, smooth and rough wall boundary conditions. The result shows that compared with the CFD method, the velocity field obtained by coupling algorithm, exhibits a phenomenon of velocity slip which give rise to a large difference near the wall thus affects the flow field of main stream. With the increase of the roughness of the wall, the velocity of main stream is getting smaller. There is no significant difference in the temperature distribution before coupling and after. However, the temperature of the main stream decreases with the increase of the roughness of wall. Near the wall, the result of coupling shows a phenomenon of temperature jump.Secondly, a combustion reaction mechanism which includes 6 species and 7 steps reversible elementary reactions is applied in the case of chemical reaction, and the CFD/DSMC coupling iterative algorithm of the combustion of hydrogen and oxygen is applied to the microtube of 25?m in length, to study the fluid flow, heat transfer characteristics and species transport. The tube consists of two parts, the first half part is in a convergent form with a length of 10?m, the second part is a straight pipe.The computation shows that under the condition of 50 m/s, the result of simulation has a close relationship with the wall slip velocity after using DS2V to update the data on the Fluent boundary. The influence of the wall slip velocity is greater than that of the wall temperature jump in the example. In the area of large slip velocity, the product components are of small amount, while in the area of small slip velocity, the product components are much greater. In addition, the velocities in the centeral of the coupled flow field are increased in comparison with the non-coupled flow. The velocity of theY direction is disturbed by the wall boundary conditions, and the velocity is non-zero generally after entering the straight pipe. |
PDF Full Text Request