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991.
In/SBA-15催化剂的一步法制备及其在水介质中Barbier反应中的应用 总被引:1,自引:0,他引:1
采用金属In的石蜡溶液浸渍载体, 一步法制备具有介孔结构的In/SBA-15催化剂. 在水介质中苯甲醛与烯丙基溴的Barbier反应中, 发现负载量为w(In)=13%的In/SBA-15的催化活性显著高于金属In颗粒催化剂, 而选择性相似, 目标产物1-苯基-3-丁烯基-1-醇的得率可达89.2%. In/SBA-15的高活性主要归因于In活性位在SBA-15上的高分散, 以及规整的介孔结构有利于反应物分子的扩散. 同时, 金属In与SBA-15间较强的相互作用也可稳定In活性位, 显示出良好的应用潜力. 相似文献
992.
993.
994.
利用拟线性双曲型方程组极值原理,改进了HSIAO Ling和D.Serre得到的关于多孔介质中可压缩流体力学方程组解的存在性结果,给出了其Cauchy问题的一个关于经典解整体存在和破裂的完整结果.这些结果说明强耗散有助于“小”解的光滑性. 相似文献
995.
996.
Using the principle of diffusion-limited aggregation(DLA),a new model is introduced to simulate the displacement of one fluid by another in porous media.The results agree with experiments.apparently they do not leave out film-flow phenomena.Simultaneously,we also present a new numerical method to treat our results by the lattice Boltzmann method(LBM),All these will be helpful for analysing similar subjects. 相似文献
997.
Most models for multiphase flows in a porous medium are based on a straightforward extension of Darcy’s law, in which each fluid phase is driven by its own pressure gradient. The pressure difference between the phases is thought to be an effect of surface tension and is called capillary pressure. Independent of Darcy’s law, for liquid imbibition processes in a porous material, diffusion models are sometime used. In this paper, an ensemble phase averaging technique for continuous multiphase flows is applied to derive averaged equations and to examine the validity of the commonly used models. Closure for the averaged equations is quite complicated for general multiphase flows in a porous material. For flows with a small ratio of the characteristic length of the phase interfaces to the macroscopic length, the closure relations can be simplified significantly by an approximation with a second order error in this length ratio. This approximation reveals the information of the length scale separation obscured during an averaging process and leads to an equation system similar to Darcy’s law, but with additional terms. Based on interactions on phase interfaces, relations among closure quantities are studied. 相似文献
998.
M. F. El-Sayed 《Archive of Applied Mechanics (Ingenieur Archiv)》2009,79(1):19-39
In this paper, we consider the instability of the interface between two superposed streaming conducting and dielectric fluids
of finite depths through porous medium in a vertical electric field varying periodically with time. A damped Mathieu equation
with complex coefficients is obtained. The method of multiple scales is used to obtain an approximate solution of this equation,
and then to analyze the stability criteria of the system. We distinguish between the non-resonance case, and the resonance
case, respectively. It is found, in the first case, that both the porosity of porous medium, and the kinematic viscosities
have stabilizing effects, and the medium permeability has a destabilizing effect on the system. While in the second case,
it is found that each of the frequency of the electric field, and the fluid velocities, as well as the medium permeability,
has a stabilizing effect, and decreases the value of the resonance point, while each of the porosity of the porous medium,
and the kinematic viscosities has a destabilizing effect, and increases the value of the resonance point. In the absence of
both streaming velocities and porous medium, we obtain the canonical form of the Mathieu equation. It is found that the fluid
depth and the surface tension have a destabilizing effect on the system. This instability sets in for any value of the fluid
depth, and by increasing the depth, the instability holds for higher values of the electric potential; while the surface tension
has no effect on the instability region for small wavenumber values. Finally, the case of a steady electric field in the presence
of a porous medium is also investigated, and the stability conditions show that each of the fluid depths and the porosity
of the porous medium ɛ has a destabilizing effect, while the fluid velocities have stabilizing effect. The stability conditions
for two limiting cases of interest, the case of purely fluids), and the case of absence of streaming, are also obtained and
discussed in detail. 相似文献
999.
The mechanical behaviour of Polyvinylidene Fluoride (PVDF) is analysed. To this end, tensile tests are performed on both smooth and notched specimens, for several values of the notch radius in order to set specific values of the stress triaxiality ratio in the net section. Tests were performed at various temperatures and at various strain rates. Experimental data together with fracture surface examinations by SEM allow the dependence of deformation and void growth processes on strain rate and temperature to be investigated. This experimental work was carried out in order to test the mechanics of porous media model. For each investigated temperature, constitutive relations take both porosity and strain rate sensitivity into account. The model is proposed for deformation leading to crazing. The material coefficients are optimised by imposing a continuous dependence on temperature. 相似文献
1000.
The problem of the onset of convective roll instabilities in a horizontal porous layer with isothermal boundaries at unequal
temperatures, well known as the Horton–Rogers–Lapwood problem, is revisited including the effect of pressure work and viscous
dissipation in the local energy balance. A linear stability analysis of rolls disturbances is performed. The analysis shows
that, while the contribution of viscous dissipation is ineffective, the contribution of the pressure work may be important.
The condition of marginal stability is investigated by adopting two solution procedures: method of weighted residuals and
explicit Runge–Kutta method. The pressure work term in the energy balance yields an increase of the value of the Darcy–Rayleigh
number at marginal stability. In other words, the effect of pressure work is a stabilizing one. Furthermore, while the critical
value of the Darcy– Rayleigh number may be considerably affected by the pressure work contribution, the critical value of
the wave number is affected only in rather extreme cases, i.e. for very high values of the Gebhart number. A nonlinear stability
analysis is also performed pointing out that the joint effects of viscous dissipation and pressure work result in a reduction
of the excess Nusselt number due to convection, when the Darcy–Rayleigh number is replaced by the superadiabatic Darcy–Rayleigh
number. 相似文献