Model Comparisons of Flow and Chemical Kinetic Mechanisms for Methane–Air Combustion for Engineering Applications

The reasonably accurate numerical simulation of methane–air combustion is important for engineering purposes. In the present work, the validations of sub-models were carried out on a laboratory-scale turbulent jet flame, Sandia Flame D, in comparison with experimental data. The eddy dissipation concept (EDC), which assumes that the molecular mixing and subsequent combustion occur in the fine structures, was used for the turbulence–chemistry interaction. The standard k-ε model (SKE) with the standard or the changed model constant C1ε, the realizable k-ε model (RKE), the shear-stress transport k-ω model (SST), and the Reynolds stress model (RSM) were compared with the detailed chemical kinetic mechanism of GRI-Mech 3.0. Different reaction treatments for the methane–air combustion were also validated with the available experimental data from the literature. In general, there were good agreements between predictions and measurements, which gave a good indication of the adequacy and accuracy of the method and its further applications for industry-scale turbulent combustion simulations. The differences between predictions and measured data might have come from the simplifications of the boundary settings, the turbulence model, the turbulence–reaction interaction, and the radiation heat transfer model. For engineering predictions of methane–air combustion, the mixture fraction probability density function (PDF) model for the partially premixed combustion with RSM is recommended due to its relatively low simulation expenses, acceptable accuracy predictions, and quantitatively good agreement with the experiments.

A Molecular Foaming and Activation Strategy to Porous N-Doped Carbon Foams for Supercapacitors and CO2 Capture

Hierarchically porous carbon materials are promising for energy storage, separation and catalysis. It is desirable but fairly challenging to simultaneously create ultrahigh surface areas, large pore volumes and high N contents in these materials. Herein, we demonstrate a facile acid–base enabled in situ molecular foaming and activation strategy for the synthesis of hierarchically macro-/meso-/microporous N-doped carbon foams (HPNCFs). The key design for the synthesis is the selection of histidine (His) and potassium bicarbonate (PBC) to allow the formation of 3D foam structures by in situ foaming, the PBC/His acid–base reaction to enable a molecular mixing and subsequent a uniform chemical activation, and the stable imidazole moiety in His to sustain high N contents after carbonization. The formation mechanism of the HPNCFs is studied in detail. The prepared HPNCFs possess 3D macroporous frameworks with thin well-graphitized carbon walls, ultrahigh surface areas (up to 3200 m2 g−1), large pore volumes (up to 2.0 cm3 g−1), high micropore volumes (up to 0.67 cm3 g−1), narrowly distributed micropores and mesopores and high N contents (up to 14.6 wt%) with pyrrolic N as the predominant N site. The HPNCFs are promising for supercapacitors with high specific capacitances (185–240 F g−1), good rate capability and excellent stability. They are also excellent for CO2 capture with a high adsorption capacity (~ 4.13 mmol g−1), a large isosteric heat of adsorption (26.5 kJ mol−1) and an excellent CO2/N2 selectivity (~ 24).

Effective interfacial tension in flow-focusing of colloidal dispersions: 3-D numerical simulations and experiments

An interface between two miscible fluids is transient, existing as a non-equilibrium state before complete molecular mixing is reached. However, during the existence of such an interface, which typically occurs at relatively short time scales, composition gradients at the boundary between the two liquids cause stresses effectively mimicking an interfacial tension. Here, we combine numerical modelling and experiments to study the influence of an effective interfacial tension between a colloidal fibre dispersion and its own solvent on the flow in a microfluidic system. In a flow-focusing channel, the dispersion is injected as core flow that is hydrodynamically focused by its solvent as sheath flows. This leads to the formation of a long fluid thread, which is characterized in three dimensions using optical coherence tomography and simulated using a volume of fluid method. The simulated flow and thread geometries very closely reproduce the experimental results in terms of thread topology and velocity flow fields. By varying the interfacial tension numerically, we show that it controls the thread development, which can be described by an effective capillary number. Furthermore, we demonstrate that the applied methodology provide the means to measure the ultra-low but dynamically highly significant effective interfacial tension.

Mix Width, Bubble and Spike Amplitudes in Three-Dimensional Numerical Simulations of Turbulent Mixing Driven by Spherical Implosions

Three-dimensional numerical simulations of turbulent mixing at a perturbed interface of a dense shell compressed by a spherically imploding shock wave are presented. This case is a simplified version of inertial confinement fusion implosion (ICF) where a small capsule containing nuclear material is compressed to extremely high pressure and temperature to achieve fusion burn. The current simulations were performed using a high-order spherical method and a semi-Lagrangian moving mesh algorithm implemented in our in-house code Flamenco. Results of narrowband and broadband initial perturbations are presented at different grid resolutions along with mix layer limits, molecular mixing, turbulent kinetic energy and bubble/spike heights. The initial multimode perturbations applied at the interface consist of a superposition of cosine waves and are determined according to a specified power spectrum and standard deviation. These are employed in a spherical segment, enabling the efficient computation of a wide range of low to relatively high mode-number perturbations. The overall grid convergence of the solution is analysed and the different findings from the integral quantities and bubble/spike amplitudes are indicated.

Molecular blends of methylated-poly(ethylenimine) and amorphous porous organic cages for SO2 adsorption

Porous organic cage (POCs) are explored as a support for hazardous gas sorbents. The molecular mixing between the POC and methylated poly(ethylene imine) was observed and resulted in the improvement of mass transfer and thermal stability of the composite material.