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Validation of High Speed Reactive Flow Solver in OpenFOAM® with Detailed Chemistry
An OpenFOAM® based hybrid-central solver called reactingPimpleCentralFoam is validated to compute hydrogen-based detonations. This solver is a pressure-based semi-implicit compressible flow solver based on central-upwind schemes of Kurganov and Tadmor. This solver possesses the features of standard OpenFOAM® solvers namely, rhoCentralFoam, reactingFoam and pimpleFoam. The solver utilizes Kurganov & Tadmor schemes for flux splitting to solve the high-speed compressible regimes with/without hydrodynamic discontinuity. In this work, we present the validation results that were obtained from one-dimensional (1D) and two-dimensional (2D) simulations with detailed chemistry. We consider three different mixtures that fall into the categories of weakly unstable mixture (2H2 + O2 + 3.76Ar and 2H2 + O2 + 10Ar), and moderately unstable mixture (2H2 + O2 + 3.76N2), based on their approximate effective activation energy. We performed the numerical simulations in both laboratory frame of reference (LFR) and shock-attached frame of reference (SFR) for the 1D cases. The 1D simulation results obtained using this solver agree well with the steady-state calculations of Zel’dovich von Neumann Döring (ZND) simulations with an average error below 1% in all cases. For the 2D simulations, circular hot-spots were used to perturb the initially-planar detonations to develop into spatio-temporally unstable detonation front. The convergence is declared when the front does not deviate much from the CJ speed (Chapman-Jouguet) and the regularity of cellular pattern on the numerical smoke foils reaches a steady state. We have verified from our preliminary studies that the SFR-based simulations are computationally cheaper in comparison to the LFR simulations and that the required grid resolution is always lesser in the former than the latter to reach the same level of accuracy (in terms of speed of the detonation front and cell sizes from the numerical smoke foil). We have also verified that at least 24 points per induction zone length (for weakly unstable mixture) and 40 points per induction zone length (for moderately unstable mixture) are required to sufficiently resolve the detonation structures that are independent of grids, boundary and initial conditions. Further reduction in computational cost of approximately 50% is achieved by using non-uniform grids, which converge effectively to the same solutions in comparison to the results from twice the number of grids with uniform resolution.
Experimental characterization of the cell cycle for regular Chapman-Jouguet detonations
The detonation front’s unstable structure leads to an unsteady and threedimensional (3D) phenomenon that renders the study of the cell cycle challenging. Traditionally, fundamental studies are carried out in narrow channels where the detonation behaviour is very peculiar (quasi two-dimensional with velocity deficit). In this study, we propose a fully experimental approach to study the cell cycle in the case of non-marginal detonations. The cell cycle is characterized through three techniques: systematic and statistical analysis of soot foil, planar laser-induced fluorescence on nitric oxide, and Rayleigh scattering. These techniques provide measurements for cell size, induction length, and local shock speed, respectively. The work is carried out in the 2H2-O2-3.76Ar mixture at 20 kPa and 293 K. These conditions ensure that the cell pattern is extremely regular, thus, a shot-to-shot reconstruction of the cell cycle is possible. The cell widths follow a normal distribution, from which a quantitative parameter (2σ/λ) is proposed to assess the cell regularity, experimentally. The evolution of the speed and of the local induction length are reconstructed along the cell cycle. The results agree with the available data for narrow channels and constitute the first of their kind for 3D detonation (i.e., non-marginal detonation). Two methods are proposed and compared to determine the Zel’dovich–von Neumann–Döring (ZND) induction length Δi from the presented experimental measurements. The technique can be applied to mixtures where the mean cell width is a meaningful parameter from highly regular to irregular mixtures.
Nanodomain Control in Carbon Molecular Sieve Membranes via Nanomaterial Footprinting
Carbon molecular sieve (CMS) membranes, fabricated via pyrolysis, are attracting attention owing to their stability under harsh environments, including high temperatures, organic media, and extreme pH. Herein, the fabrication of composite CMS (CCMS) membranes by incorporating sphere-shaped C60(OH) and ellipsoid-shaped C70(OH) fullerenol nanomaterials into intrinsically microporous 4,4′-(hexafluoroisopropylidene) diphthalic anhydride 3,3′-dimethyl-naphthidine polyimide is reported. The encapsulation of the nanomaterials by the polymer matrix, their chemical footprint, and the variation in the local chemistry of the pyrolyzed membranes are successfully revealed via nanodomain analysis using nano-Fourier-transform infrared spectroscopy. The incorporation of fullerenol nanomaterials into CMS membranes can induce the formation of fractional free volume upon pyrolysis, which can translate into molecular sieving enhancement. The effects of the concentration and geometrical shape of the fullerenol nanomaterials are successfully correlated with the membrane separation performance. The CCMS membranes demonstrate excellent stability and pharmaceutical and dye separation performance in organic media. Herein, nanodomain control is pioneered in CCMS membranes via nanomaterial footprinting to induce porosity during pyrolysis and subsequent control molecular sieving performance.
Developable Quad Meshes and Contact Element Nets
The property of a surface being developable can be expressed in different equivalent ways, by vanishing Gauss curvature, or by the existence of isometric mappings to planar domains. Computational contributions to this topic range from special parametrizations to discrete-isometric mappings. However, so far a local criterion expressing developability of general quad meshes has been lacking. In this paper, we propose a new and efficient discrete developability criterion that is applied to quad meshes equipped with vertex weights, and which is motivated by a well-known characterization in differential geometry, namely a rank-deficient second fundamental form. We assign contact elements to the faces of meshes and ruling vectors to the edges, which in combination yield a developability condition per face. Using standard optimization procedures, we are able to perform interactive design and developable lofting. The meshes we employ are combinatorial regular quad meshes with isolated singularities but are otherwise not required to follow any special curves on a developable surface. They are thus easily embedded into a design workflow involving standard operations like remeshing, trimming, and merging operations. An important feature is that we can directly derive a watertight, rational bi-quadratic spline surface from our meshes. Remarkably, it occurs as the limit of weighted Doo-Sabin subdivision, which acts in an interpolatory manner on contact elements.
Atomic Layer Deposition Reaction Parameters Influence on ZnO’s Electrical Properties on Cotton Fabric for Textile Electronics
Textile electronics is a newly emerging field that is gaining the interest of researchers due to its wide range of applications and prospects. Despite the variety of materials and methods used to fabricate textile electronic devices, there is a lack of the necessary focus and direction required for the rapid advancement of this field. A suggested solution is concentrating the efforts on versatile methods and materials that can create multiple devices. Atomic Layer Deposition (ALD) is a suitable method for textile substrates since it can deposit solid-state materials conformally and at low temperatures. It can deposit semi-conductive Zinc Oxide (ZnO), which is used to fabricate various devices, including transistors, capacitors, and sensors. However, there is limited information about the characteristics of ZnO deposited via ALD on textile substrates. By exploring the influence of the following parameters, this research aims to optimize the deposition process for fabric-based electronics and sensors while investigating the impact of various ALD reaction parameters on the electrical properties of ZnO deposited on cotton fabric. The ALD reaction utilized two precursors, Diethylzincite and water, to facilitate the deposition of ZnO on the cotton substrate. The reaction involved a ligand exchange process with gaseous ethane as a byproduct, which was purged after each cycle. The experiment involved conducting the ALD process under different testing conditions, including varying reaction temperatures, dose time for the precursors, purge time, and the duration of holding the precursors in the chamber before purging. Consequently, the results indicated that the optimized recipe showed a low resistivity of 1.25 Ω.cm and an atomic concentration ratio of oxygen per zinc atoms of 22.8. The reaction was conducted at a temperature of 180 oC and had 100 ms DEZ dose time, 25 ms water dose time, and 1 s purge time. The findings contribute to the broader understanding of thin-film deposition processes and their impact on electronic performance, opening avenues for the development of innovative and efficient electronic systems integrated into textile materials.