Numerical Simulation of Flow through a piping system - Recirculation and Mixing

This research presents the methodology and the results of numerical studies on turbulent flows in a piping system that resembles the geometry of the Fission Product Venting System (FPVS) in High-Temperature Gas-Cooled Fast Reactors (HTGR). The fission product includes graphite particulates carried by coolant as flows through the core and fission gases like Krypton, Xenon, Cesium, and Iodine produced from thermonuclear reaction. Knowing the location of mixing and the magnitude of various gaseous components is necessary to manage and mitigate the adverse effects of fission products on power generation. In this work, scaling analysis was used to identify the geometry, surrogate gases, and surrogate particles. The turbulent flow fields in the piping system were simulated using the openFOAM v7 and Large Eddy Simulation (LES). The grid independence was established using the Grid Convergence Index (GCI) concept. In addition, numerical simulations were validated against the experimental data and the Direct Numerical Simulation (DNS) data reported in the literature. The quantities of interest, such as reattachment length and critical point of flows through axisymmetric expansion and the Absolute Mixing Index (AMI) through a piping system with 90 deg bend, were calculated. The reattachment length represents the length of the recirculation region, and the critical points (Cr1 and Cr2) represent the cross-over points from laminar to transition region, and the transition region to turbulent flow. A series of parametric runs were made by varying flow Reynolds number (Re), turbulence intensity (TI) at the inlet, and surrogate gas concentration at the injection point. Using the parametric runs design, correlation expressions for reattachment length and the critical point were developed. The gradient of log10AMI represents the mixing rate, and the highest value is observed downstream of the pipe’s expansion. The AMI is the standard deviation of the concentration of the surrogate gas Argon in the piping system. The Proper Orthogonal Decomposition (POD) technique was used to study the coherent turbulent structure downstream of a sudden expansion. Finally, simulation of the surrogate solid particles was carried out using the Lagrangian approach. The deposition velocity particles in a square horizontal channel were estimated using a discrete random walk model

Graphene-enhanced raman spectroscopy reveals the controlled photoreduction of nitroaromatic compound on oxidized graphene surface

Although graphene-enhanced Raman spectroscopy has been investigated for several years, there have been no studies that have applied it to real-time observations of chemical catalytic reactions. Here, we report that UV/ozone-treated oxidized graphene was used to both control and monitor the photoreduction of an adsorbed nitroaromatic dye compound. Graphene-enhanced Raman spectroscopy studies show that more oxidized graphene surface leads to faster photoreduction. This is due to the lowering of the Fermi level in the oxidized graphene, which is in agreement with the highest occupied molecular orbital level of the adsorbed dye molecule, leading to a rapid electron transfer from graphene to the dye. Our findings will be useful in understanding and exploiting the photocatalytic properties of oxidized graphene on adsorbed molecular species.

Observation and analysis of low temperature leak characteristics of the O-ring for hydrogen electric vehicles

Please click Additional Files below to see the full abstrac

Optical Probing of Electronic Interaction between Graphene and Hexagonal Boron Nitride

Even weak van der Waals (vdW) adhesion between two-dimensional solids may perturb their various materials properties owing to their low dimensionality. Although the electronic structure of graphene has been predicted to be modified by the vdW interaction with other materials, its optical characterization has not been successful. In this report, we demonstrate that Raman spectroscopy can be utilized to detect a few % decrease in the Fermi velocity (vF) of graphene caused by the vdW interaction with underlying hexagonal boron nitride (hBN). Our study also establishes Raman spectroscopic analysis which enables separation of the effects by the vdW interaction from those by mechanical strain or extra charge carriers. The analysis reveals that spectral features of graphene on hBN are mainly affected by change in vF and mechanical strain, but not by charge doping unlike graphene supported on SiO2 substrates. Graphene on hBN was also found to be less susceptible to thermally induced hole doping.Comment: 19 pages, 4 figure

N-(2,5-Dimeth­oxy­phen­yl)-N′-(4-hy­droxy­pheneth­yl)urea

In the title compound, C17H20N2O4, the 2,5-dimeth­oxy­phenyl unit is almost planar, with an r.m.s. deviation of 0.015 Å. The dihedral angle between the 2,5-dimeth­oxy­phenyl ring and the urea plane is 20.95 (8)°. The H atoms of the urea NH groups are positioned syn to each other. The mol­ecular structure is stabilized by a short intra­molecular N—H⋯O hydrogen bond. In the crystal, inter­molecular N—H⋯O and O—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional network

1-[3-(Hy­droxy­meth­yl)phen­yl]-3-phenyl­urea

In the title compound, C14H14N2O2, the dihedral angle between the benzene rings is 23.6 (1)°. The H atoms of the urea NH groups are positioned syn to each other. In the crystal, inter­molecular N—H⋯O and O—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional network

Thermal Effects of Microwave Reduced-Graphene-Oxide Coated Polyester Fabric on a Simulated Human Skin in Cool and Neutral Air Temperatures

Batteryless wearable technology has wide applications. In particular, human body surface temperature controlling fabrics can help regulate skin temperature in heat or cold. This study investigated surface temperature distribution of the fabrics coated with reduced graphene oxide (rGO) on simulated human body skin conditions at 18 degrees C (cool) and 27 degrees C (neutral) ambient air temperatures. Polyester fabrics were spin-coated with a graphene-oxide (GO) solution of 0.2 wt%. Preparation of rGO was processed by using a microwave oven (MW-rGO). Non-treated fabric (CON) was compared to GO and MW-rGO. The surface temperature of a hot plate was maintained at 35 degrees C or 40 degrees C. The test fabrics were put on the heated hot plate or non-heated-outer portions of the hot plate. Surface temperatures of MW-rGO on the heated hot plate at an air temperature of 18 degrees C (cool) were higher than those of non-treated fabric (CON) under the same conditions (p < 0.01). No effects from the graphene treatment were found on non-heated portions of the graphene oxide fabric (GO) or the reduced graphene oxide fabric (MW-rGO). On the non-heated portions, surface temperatures were higher at the location closer to the hot plate compared to the location farther from the hot plate (p < 0.05). These results partially represent thermal effects of MW-rGO under a specific environment and heat source. Our findings enable an application of reduced graphene oxide to body temperature regulating clothing.