【摘要】 考虑到气体的压缩性,按渗流力学给出了多孔介质中的非均匀流场,并进一步研究多孔介质内的多相气固反应和传输。与不可压缩气体对流、反应、扩散的比较表明,两种流动的孔隙压力分布差别很小,但渗流速度的差别却较大。由于小的速度差会引起Peclet数的大的差别,最终引起气体浓度的较大差别,因而有必要考虑气体的压缩性。入口处的流速与多孔介质内由于气体膨胀产生的附加速度是有实质差别的两种对流,前者使气体浓度上升,后者使其浓度下降。对流对反应气体和产物气体传输的影响不同,但这仅是表面现象的不同,对流的本质不变。对颗粒堆积的多孔介质,颗粒半径和孔隙率越小,以Mach数作为判别气体压缩性是否可以忽略的指标就越不合理。因此对多孔介质中的气体流动,应该用压降作指标判别是否可以忽略气体的压缩性。更多还原

【Abstract】 Considering the compressibility of gas, the non-homoeneous velocity field of gas in a packed channel can be obtained from the fluid dynamics in porous media. Then multi-phase gas-solid reaction and mass transport are studied. The comparison with the convection, reaction and diffusion of incompressible fluid motion in a packed channel shows that, even though the difference of pressure fields induced by the different compressibility of gases is small, the difference of velocity fields is larger. Because minor difference of convection velocity can yield big difference of Peclet number, it induces great difference of the concentration of gas components. For the concentration of gas components, the convection velocity at the inlet of reactor, and the additional convection velocity taking place within reactor due to the gas expanding have different effect, the former raises the concentration of gas components and the latter reduces it. The convective flow has different impact on the mass transfer of reactive gas and gas product. But this is only the difference of apparent phenomena, behind the apparent phenomena the intrinsic nature of convective flow is the same. The less is the radius of pellet, the less is the rationality that Mach number is taken as the criterion to identify the compressibility of gas. So, it should be relative pressure drop rather than Mach number that is taken as the criterion to identify if the compressibility of gas can be ignored.更多还原