Tribological behavior of graphene reinforced chemically bonded ceramic coatings

To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.     

Direct-Contact Heat Transfer during n-Pentane Vaporization in a Two-Dimensional Water Column

Direct-contact vaporization heat transfer is investigated by analyzing the heat transfer coefficient with the area of liquid-liquid direct-contact interface. The interface areas of liquid-liquid heat transfer are determined by stroboscopic images. At higher temperature, the heat transfer area per unit volume decreases. The water temperature has no significant influence on the heat transfer coefficient. The effects on droplet size distributions of operating variables including inlet water temperature, n-pentane flow rate, and test position with packing and without packing are compared.     

Improving fire retardancy of medium density fiberboard by nano-wollastonite

The improving effects of addition of nano-wollastonite on some fire properties of medium-density fiberboard (MDF) were studied in this work. Nano-wollastonite was added at four levels (2%, 4%, 6%, and 8%). The size range of at least 70% of nano-wollastonite particles were 30 to 110 nm. The results showed statistically significant improving effect of nano-wollastonite on time to onset of ignition. The improving effect was primarily attributed to an increase in thermal conductivity of board containing nano-wollastonite. This increase in turn resulted in better curing of resin, and a higher integrity of fibers thereof. Moreover, nano-particles provided a surface with reduced combustibility and therefore, penetration of fire to the inner layers of boards was delayed, thus improving fire properties. High and significant correlations were found between thermal conductivity coefficients of boards with different fire properties. It was concluded that for applications where fire properties are of prime importance, nano-wollastonite content of 8% can be recommended. Moreover, further studies are needed to compare and standardize the results obtained from the apparatus used here with those obtained from internationally recognized apparatuses like cone calorimeter.     

Kernel-based fourth-order diffusion for image noise removal

The fourth-order partial differential equations have good performance on noise smoothing and edge preservation without creating blocky effects on smooth regions. However, for low signal-to-noise ratio images, the discrimination between edges and noise is a challenging problem. A novel kernel-based fourth-order diffusion is proposed in this paper. It introduces a kernelized gradient operator in the fourth-order diffusion process, which leads to more effective noise removal capability. Experiment results show that this method outperforms several previous anisotropic diffusion methods for noise removal and edge preservation.     

Elasto-Thermodiffusive Response in a Spherically Isotropic Hollow Sphere

The present work deals with the investigation of elasto-thermo diffusion interactions inside a spherically isotropic hollow sphere in the context of linear theory of generalized thermoelastic diffusion based on Green and Lindsay theory. The inner and outer boundaries of the body are free from stresses and are subjected to a time-dependent thermal shock and also the chemical shock. Laplace transform techniques are used to write the basic equations in the form of a vector matrix differential equations, which is then solved by the eigenvalue approach. The inversion of the transformed solution is carried out by applying the method of Bellman. The stress, temperature, mass concentration and chemical potential are computed and presented graphically. A comparative study of diffusive medium and thermoelastic medium is carried out, and it was seen that the effect of diffusion is significant on the stresses. A comparison of spherically isotropic body with isotropic body has also been presented, and a significant difference is observed.     

Effect of thermal noise on random lasers in diffusion regime

In this paper, we study the effects of thermal noise on the time evolution of a weak light pulse (probe) in the presence of a strong light pulse (pump) within a gain medium which includes random scatterer particles. Suitable thermal noise term is added to a set of four coupled equations including three diffusion equations for energy densities and a rate equation for the upper level population in a four-level gain medium. These equations have been solved simultaneously by Crank–Nicholson numerical method. The main result is that the back-scattered output probe light is increased as the thermal noise strength is increased and simultaneously, with the same rate, the amplified spontaneous emission is decreased. Therefore, the amplified response of the random laser in diffusion regime for the input probe pulse is enhanced due to effect of the thermal noise.     

Different chemical effect of hydrogen addition on soot formation in laminar coflow methane and ethylene diffusion flames

Previous studies showed that adding hydrogen (H₂) can have an opposite chemical effect on soot formation: its chemical effect enhances and suppresses soot formation in methane (CH₄) and ethylene (C₂H₄) diffusion flames, respectively. Such opposite chemical effect of H₂ (CE-H₂) remains unresolved. The different CE-H₂ is studied numerically in the two laminar coflow diffusion flames. A detailed chemical mechanism with the addition of a chemically inert virtual species FH₂ is used to model the gas-phase combustion chemistry in this study. Particularly, a reaction pathway analysis was performed based on the numerical results to gain insights into how H₂ addition to fuel affects the pathways leading to the formation of benzene (A₁) in CH₄ and C₂H₄ flames. The numerical results show that the CE-H₂ in CH₄ diffusion flame to prompt soot formation is ascribed that the higher mole fraction of H atom promotes the formation of A₁ and Acetylene (C₂H₂) and leads to higher nucleation rate and eventually higher soot surface growth rate. In contrast, adding H₂ to C₂H₄ diffusion flames decreases soot nucleation and surface growth rate. The lower soot nucleation rate is due to the lower mole fractions of pyrene (A₄), while the lower soot surface growth rate is due to the lower mole fractions of H atom and C₂H₂, higher mole fraction of H₂ and lower soot nucleation rate. Furthermore, the CE-H₂ in C₂H₄ diffusion flames promotes the formation of A₁, but suppresses the formation of A₄.     

Exploring the relationship between the physical properties of activated carbon catalysts and their efficiency in catalyzing hydrogen iodide decomposition to produce hydrogen

Using simple and efficient methods to synthesize biological activated carbon catalysts (ACCs) with the decomposition of hydrogen iodide (HI) in the sulfur-iodine cycle as a typical reaction is urgently needed for the commercialization of hydrogen energy production and development. In this study, a series of ACCs with different specific surface areas (SSAs) and pore structures are prepared by comparing and controlling the changes in carbonization and activation methods of activated carbon (AC) preparation process. Hierarchical porous AC with larger SSA has higher HI decomposition efficiency. The representative samples H240H1h and H240C4h are hierarchical porous ACCs with 48.96% and 46.88% micropores, respectively, and have the highest catalytic activity in the entire series. The nitrogen adsorption and desorption curve is combined with pore size distribution data and analyzed using the capillary aggregation (Kelvin) and monolayer adsorption (Langmuir) theories. And ACC pore grading coefficient—which can improve data visualization—is introduced.