Study of creep,stress relaxation,and inverse relaxation in mulberry (Bombyx mori) and tasar (Antheraea mylitta) silk

The phenomena of creep, stress relaxation, and inverse relaxation/stress recovery were observed for mulberry and tasar silk. Instantaneous extension and secondary creep are both higher for tasar than for mulberry. The magnitude of inverse relaxation increases with the increase in peak tension and reduction in retraction for both varieties of silk. The extent of inverse relaxation was found to reduce because of cycling stressing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3077–3084, 2006     

On the effect of gap size between baffle outer diameter and tube inner diameter on the mixing characteristics in an oscillatory‐baffled column

We report our experimental investigation on the effect of gaps between baffle outer diameter and inner tube diameter on the mixing characteristics, in terms of mixing time and axial dispersion coefficient, in a batch oscillatory‐baffled column. Local concentration profiles are measured using conductivity probes at two locations along the height of the column. The mixing time was determined based on the equilibrium concentration concept, and the axial dispersion coefficient was obtained by solving the axial dispersion governing equation. Comparison of mixing time between the ‘push‐fit’ and ‘loose‐fit’ baffle arrangements was carried out and the results showed that the existence of a gap of various sizes between the baffle outer and the tube diameters lengthened the time at which the state of uniform mixing is achieved in such a device. © 1999 Society of Chemical Industry     

An investigation on the rheological and sulfur-retention characteristics of desulfurizing coal water slurry with calcium-based additives

Desulphurizing coal water slurry is a kind of new clean coal water slurry(CWS), which has good performance on SO₂ emission during combustion and gasification process. But, the addition of sulfur-retention agents have some effects on the stability and fluid characters of the coal water slurry. In this paper, the viscosity, stability and rheology of Xinwen coal water slurry have been studied by adding different kinds of calcium-based sulfur-retention agents and different dosage. The results show that the sulfur-retention agents have little effect on rheological nature of CWS, which still presents pseudoplastic fluid. The addition of sulfur-retention agents will increase the viscosity of CWS, but the stability will decrease a little. The results also show that inorganic calcium has less negative effect on the performance of CWS than the organic calcium. The viscosity of the CWS with organic calcium agent keeps 1000–1200 mPa s when Ca/S molar ratio is 2. Sulfur release of the CWS with CaCO₃ reduces to 52% at Ca/S = 2 compared to original of 98%.     

Deposition of colored inorganic coating layers on lamellar sericite surface and the pigmentary performances

The inorganic composite pigments, Fe₂O₃/sericite, Bi₂O₃/sericite, and CoAl₂O₄/sericite, were prepared by the homogeneous hydrolysis of metal salts, such as FeCl₃, Bi(NO₃)₃, and Co(NO₃)₂/Al(NO₃)₃. The deposition of the inorganic coating layers on sericite surfaces was explored by X-ray diffraction, scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. The inorganic coating layers were uniformly and tightly anchored at sericite surfaces via chemical bonding at the interface between the coating layer and the sericite substrate. The pigmentary performances of the inorganic composite pigments were analyzed by CIE, indicating that red, yellow, and blue colored pigments were achieved by coating Fe₂O₃, Bi₂O₃, and CoAl₂O₄ on sericite surfaces, respectively. The pigmentary performances of the inorganic composite pigments were significantly affected by the morphology and thickness of inorganic coating layers.     

AFM investigation of solid product layers of MgSO4 generated on MgO surfaces for the reaction of MgO with SO2 and O2

The nucleation, growth and arrangement of MgSO₄ product layers during the reaction of single-crystal MgO with SO₂ and O₂ were investigated via atomic force microscopy (AFM). The morphology of the single-crystal MgO surface after reacting with SO₂ and O₂ consisted of three-dimensional cone-shaped MgSO₄ product islands. Most of the islands appeared at locations with terraces, steps and kinks. With increasing reaction time, small product islands grew to large islands, finally coalescing into continuous islands. The nucleation, growth and arrangement of the solid products on the reactant surface are controlled by thermodynamics and kinetics. The morphology of the MgSO₄ product islands is governed by the competition between the intrinsic chemical reaction rate and the product molecular diffusion rate, which are both significantly affected by the reaction temperature. As the reaction temperature increases, the mean size of the MgSO₄ islands increases while the island density decreases. The nucleation, growth and arrangement of the solid product layers and the product layer morphology on the solid reactant surface directly affect the mechanism of the gas–solid reaction.     

A photoelectrochemical and spectroscopic investigation of oxide layers on AISI 301 in sulfate solutions at different pH

Photocurrents flowing at AISI 301 stainless steel electrodes, polarized anodically in sulfate solutions of various pH, were related to the nature of the surface oxides formed in these environments. The oxides were identified by surface Raman and IR spectroscopies. Correlations among pH, surface coverage with different types of oxides and photocurrent were recognized by mapping Raman spectroscopy, optical microscopy and image analysis. A high photoresponse is mainly related to high surface coverage with magnetite, formed at high pH. Exposure to low-pH solutions gives rise to preferential formation of hematite. Magnetite formed at high pH is irreversibly transformed into hematite if the oxide layer is subsequently exposed to a low-pH solution.     

Fabrication of microstructure controlled cathode catalyst layers and their effect on water management in polymer electrolyte fuel cells

Although cathode catalyst layers (CCLs) are at the center of water management in polymer electrolyte fuel cells (PEFCs), the understanding of water movement in CCLs and their roll on fuel cell performance is still limited. In this present study, several CCLs with controlled microstructure, including main pore size, pore volume and porosity ranging from 30 to 70 nm, 0.443 to 0.962 cm³/g_Pt/C, and 45.4 to 64.4%, respectively, were prepared by changing the hot-pressing pressure in a decal process, and their water management ability and cell performance were evaluated. The electrochemical analyses reveal that, as the pore size and pore volume of CCLs increase, the diffusion resistance mainly arising from water accumulation in the pores is evidently reduced by capillary water equilibrium, which leads to better cell performance. Water balancing between accumulation and discharging in the pores also depends on the CCL pore structure, and the CCLs with greater pore sizes and larger pore volumes reveal more stable cell performance by better water management in steady state operation, even under extremely humid conditions. Based on these MEA technologies such as fabrication of CCLs, further study will be performed to understand microscopic phenomena in nano pores of CCLs by combining the experimental approach with CCL numerical modeling.     

An investigation on the reaction mechanism for the partial oxidation of methane to synthesis gas over platinum

The partial oxidation of methane to synthesis gas has been investigated by admitting pulses of pure methane, pure oxygen and mixtures of methane and oxygen to platinum sponge at temperatures ranging from 973 to 1073 K. On reduced platinum the decomposition of methane results in the formation of surface carbon and hydrogen. No deposition of carbon occurs during the interaction of methane with a partly oxidised catalyst. Oxygen is present in three different forms under the conditions studied: platinum oxide, dissolved oxygen and chemisorbed oxygen species. Carbon monoxide and hydrogen are produced directly from methane via oxygen present as platinum oxide. Activation of methane involving dissolved oxygen provides a parallel route to carbon dioxide and water. Both platinum oxide and chemisorbed oxygen species are involved in the oxidation of carbon monoxide and hydrogen. In the presence of both methane and dioxygen at a stoichiometric feed ratio the dominant pathways are the direct formation of CO and H₂ followed by their consecutive oxidation. A Mars-van Krevelen redox cycle is postulated for the partial oxidation of methane: the oxidation of methane is accompanied by the reduction of platinum oxide, which is reoxidised by incorporation of dioxygen into the catalyst.     

An investigation of the effects of spray angle and injection strategy on dimethyl ether (DME) combustion and exhaust emission characteristics in a common-rail diesel engine

An experimental investigation was performed on the effects of spray angle and injection strategies (single and multiple) on the combustion characteristics, concentrations of exhaust emissions, and the particle size distribution in a direct-injection (DI) compression ignition engine fueled with dimethyl ether (DME) fuel. In this study, two types of narrow spray angle injectors (θ_spray = 70° and 60°) were examined and its results were compared with the results of conventional spray angle (θ_spray = 156°). In addition, to investigate the optimal operating conditions, early single-injection and multiple-injection strategies were employed to reduce cylinder wall-wetting of the injected fuels and to promote the ignition of premixed charge. The engine test was performed at 1400 rpm, and the injection timings were varied from TDC to BTDC 40° of the crank angle.The experimental results showed that the combustion pressure from single combustion for narrow-angle injectors (θ_spray = 70° and 60°) is increased, as compared to the results of the wide-angle injector (θ_spray = 156°) with advanced injection timing of BTDC 35°. In addition, two peaks of the rate of heat release (ROHR) are generated by the combustion of air-fuel premixed mixtures. DME combustion for all test injectors indicated low levels of soot emissions at all injection timings. The NO_x emissions for narrow-angle injectors simultaneously increased in proportion to the advance in injection timing up to BTDC 25°, whereas BTDC 20° for the wide-angle injector. For multiple injections, the combustion pressure and ROHR of the first injection with narrow-angle injectors are combusted more actively, and the ignition delay of the second injected fuel is shorter than with the wide-angle injector. However, the second combustion pressure and ROHR were lower than during the first injection, and combustion durations are prolonged, as compared to the wide-angle injector. With advanced timing of the first injection, narrow-angle injectors with multiple injections could achieve low NO_x levels and soot levels similar to single-injection cases.     

An investigation on the initiation and propagation of damaged zones in adhesively bonded lap joints

In this study, the initiation and propagation of damaged zones in the adhesive layer and adherends of adhesively bonded single and double lap joints were investigated considering the geometrical non-linearity and the non-linear material behaviour of the adhesive and adherends. The modified von Mises criteria for adherends and Raghava and Cadell's failure criteria (J. Mater. Sci. 8, 225 (1973) [1]) including the effects of the hydrostatic stress states for the epoxy adhesive were used to determine the damaged adhesive and adherend zones which exceeded the specified ultimate strains. The stiffness of all finite elements corresponding to these zones was reduced so that they could not contribute to the overall stiffness of the adhesive joint. This approach simplifies to observe the initiation and propagation of the damaged zones in both the adhesive layer and adherends. A tensile load caused first the damaged adhesive zones to appear at the right free end of the adhesive-lower adherend interface and at the left free end of the adhesive-upper adherend interface, and then to propagate through the adhesive regions near the adhesive-adherend interfaces (interfacial failure). In the bending test, the damaged zone initiated at the left free end of the adhesive-upper adherend interface in tension, and similarly propagated through the adhesive regions close to the adhesive-adherend interface (interfacial failure). In the double-lap joint subjected to a tensile load, the damaged adhesive zones initiated first at the right free end of the adhesive-middle adherend interface and then propagated through the adhesive region near the adhesive-adherend interface. After the damaged zone reached a specific length it also grew through the adhesive thickness, and the adhesive joint failed. The SEM micrographs of fracture surfaces around the free edges of the overlap region indicated that the failure was interfacial. An additional damaged zone growth was observed in the side adhesive regions due to lateral straining, called the Poisson effect.     

An investigation on gas hydrate formation and slurry viscosity in the presence of wax crystals

Clarifying the interaction effect between hydrate and wax is of great significance to guarantee operation safety in deep water petroleum fields. Experiments in a high‐pressure hydrate slurry rheological measurement system were carried out to investigate hydrate formation and slurry viscosity in the presence of wax crystals. Results indicate that the presence of wax crystals can prolong hydrate nucleation induction time, and its influence on hydrate growth depends on multiple factors. Higher stirring rate can obviously promote hydrate growth rate, while its influence on hydrate nucleation induction time is complicated. Higher initial pressure will promote hydrate formation. Gas hydrate slurry shows a shear‐thinning behavior, and slurry viscosity increases with the increase of wax content and initial pressure. A semiempirical viscosity model showing a well‐fitting is established for hydrate slurry with wax crystals by considering the aggregation and breakage of hydrate particles, wax crystals, and water droplets. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3502–3518, 2018     

Experimental investigation on the combustion and exhaust emission characteristics of biogas-biodiesel dual-fuel combustion in a CI engine

An experimental investigation was performed to study the influence of dual-fuel combustion characteristics on the exhaust emissions and combustion performance in a diesel engine fueled with biogas-biodiesel dual-fuel. In this work, the combustion pressure and the rate of heat release were evaluated under various conditions in order to analyze the combustion and emission characteristics for single-fuel (diesel and biodiesel) and dual-fuel (biogas-diesel and biogas-biodiesel) combustion modes in a diesel engine. In addition, to compare the engine performances and exhaust emission characteristics with combustion mode, fuel consumption, exhaust gas temperature, efficiency, and exhaust emissions were also investigated under various test conditions. For the dual-fuel system, the intake system of the test engine was modified to convert into biogas and biodiesel of a dual-fueled combustion engine. Biogas was injected during the intake process by two electronically controlled gas injectors, which were installed in the intake pipe.The results of this study showed that the combustion characteristics of single-fuel combustion for biodiesel and diesel indicated the similar patterns at various engine loads. In dual-fuel mode, the peak pressure and heat release for biogas-biodiesel were slightly lower compared to biogas-diesel at low load. At 60% load, biogas-biodiesel combustion exhibited the slightly higher peak pressure, rate of heat release (ROHR) and indicated mean effective pressure (IMEP) than those of diesel. Also, the ignition delay for biogas-biodiesel indicated shortened trends compared to ULSD dual-fueling due to the higher cetane number (CN) of biodiesel. Significantly lower NO_x emissions were emitted under dual-fuel operation for both cases of pilot fuels compared to single-fuel mode at all engine load conditions. Also, biogas-biodiesel provided superior performance in reductions of soot emissions due to the absence of aromatics, the low sulfur, and oxygen contents for biodiesel.     

Variations in interfacial properties during cell conditioning and influence of heat-treatment of ionomer on the characteristics of direct methanol fuel cells

Variations in interfacial properties in the anode catalyst layer during cell conditioning were characterized, and influence of the heat-treatment of ionomer on the characteristics of direct methanol fuel cells was investigated in this work. The anode catalyst layer was made by mixing a solvent-substituted Nafion solution with unsupported Pt/Ru black and curing the mixture in an oven with an inert environment. Materials characterization (SEM and optical microscopy) and electrochemical characterization (cell polarization, anode polarization, electrochemical impedance spectroscopy, and CO-stripping cyclic voltammetry) were performed. During cell conditioning, the enhanced kinetics of MeOH electrochemical oxidation and severe limiting current phenomenon are due to the combination of variations in interfacial properties and swelling of ionomer in the anode catalyst layer over time. Ru oxides at the catalyst surface are reduced continuously during cell conditioning. The nearly constant integrated areas under the CO-stripping CV peaks and broadened peak shapes indicate a stable number of Pt/Ru bimetallic alloy surface sites, yet the surface composition distribution is broadened. Heat-treatment influences ionomer crystallinity, altering its swelling behavior and hence affecting the characteristics of the direct methanol fuel cell (DMFC) anode.     

An investigation of the change in the properties and orientation effects of phenoplasts of phenolaniline–formaldehyde resol resin and kaolin filler depending on the degree of elastification of the resin with nitrile rubber

An investigation is made of the dependences of the values of 13 types of standard physical, mechanical, and electric insulation indicators for phenoplasts of phenolanilineformaldehyde resol resin on the degree of kaolin filling (within the limits of 24 to 47 vol-%) and different degrees of elastification (expressed in SKN-40 nitrile rubber content ranging from 0 to 40 vol-% as to the polymer). After expressing these dependences as a function of the recalculated average thickness of the adsorption coating of elastified resin on the filler particles, it is established that the characteristic periodical recurrence of concave and convex sectors in the curves for the individual indicators with the nonelastified phenoplasts, which is due to the orientation effects, is preserved also with the elastified phenoplasts. A method is elaborated of determining the average weighted value of the average thickness of the adsorption coating in the points of the orientation extremums of these curves. It is found that the places of the individual extremums change relatively little with the increase in the degree of elastification. A considerable change in the relative values of the orientation effects is observed after the point of phase inversion of the elastified resin (18 to 20 vol-% of SKN-40 as to the polymer) in connection with the sharp increase in the mobility of the resin globules. The author believes that the proposed mechanism of change of the properties with the filling will be observed, under definite conditions, also when filling with powdered fillers other polymers or blends of polymers, in so far as the latter are made up of supramolecular structural formations with a definite statistical distribution of their average sizes.     

An investigation of silver electrodeposition from ionic liquids: Influence of atmospheric water uptake on the silver electrodeposition mechanism and film morphology

The electrodeposition of silver from two ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF₄]) and N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ([C₄mPyr][TFSI]), and an aqueous KNO₃ solution on a glassy carbon electrode was undertaken. It was found by cyclic voltammetry that the electrodeposition of silver proceeds through nucleation–growth kinetics. Analysis of chronoamperometric data indicated that the nucleation–growth mechanism is instantaneous at all potentials in the case of [BMIm][BF₄] and [C₄mPyr][TFSI], and instantaneous at low overpotentials tending to progressive at high overpotentials for KNO₃. Significantly, under ambient conditions, the silver electrodeposition mechanism changes to progressive nucleation and growth in [C₄mPyr][TFSI], which is attributed to the uptake of atmospheric water in the IL. It was found that these differences in the growth mechanism impact significantly on the morphology of the resultant electrodeposit which is characterised ex situ by scanning electron microscopy and X-ray diffraction.     

分离型热管蒸发段流动特性和传热特性的试验研究

对分离型热管管内蒸发段流动特性和传热特性进行了试验研究 :在保证热管工作效率及安全性的前提下 ,分离型热管蒸发段工质流动形式除单相液流和泡状流 (低热流密度时为弹状流 )外 ,在蒸发段上部约有 42 %～ 50 %的不稳定飞溅降膜区 ;合理充液率随热流密度的增加而减少 ;随着热流密度的增加 ,核态沸腾区及飞溅降膜区的换热系数均增加 ,蒸发段总换热系数也增加。     

Utilization of multiple graphene layers in fuel cells. 1. An improved technique for the exfoliation of graphene-based nanosheets from graphite

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp² domains of graphene nanosheets obtained after the reduction of graphite oxide.     

Theoretical and experimental investigation on the characteristics of fly‐ash scrubbing in a fixed valve tray column

The goal of this study is to evaluate the performance of a fixed valve tray column designed to remove fly‐ash particles. A series of experiments were carried out at room temperature to demonstrate the collection efficiency of a fixed valve tray column at different gas and liquid superficial velocities. The fly‐ash particles removal characteristics of the fixed valve tray column were evaluated by measuring variations of concentration and size distribution of particles in the outlet. The mechanism of particle removal in this turbulent dispersion system was theoretically analyzed on the basis of diffusion, interception, sedimentation and impaction, and a model was proposed to predict the collection efficiency. The results show that the simulation results agree well with the experimental data. In contrast to most of the conventional models, the present model is capable of evaluating the effects of bubble hydrodynamics, system property, and operation conditions on the collection efficiency. The model is expected to guide effectively the design and operation of valve tray washing columns, which is widely applied nowadays. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2168–2178, 2013     

Theoretical study on the use of collars and outer wrapping to improve liquor flow in fabric beam dyeing

It is often difficult to obtain shade levelness in beam dyeing due to non-uniform liquor flow, owing to the fabric remaining stationary while dye liquor is pumped through it. The flow profile of liquor through the fabric affects how uniformly dye is applied to the fabric. In this study, computational fluid dynamics was applied to model liquor flow in the beam dyeing of highly permeable fabrics. It was found that there are areas of fabric that receive appreciably less liquor flow than others. When the outer layer of the fabric beam is wrapped with a less permeable material, liquor flow uniformity improves. The use of collars to block perforations in the beam covered by the edges of the fabric also improved liquor flow uniformity. Some data from this paper was presented at the Industrial Simulation Conference, Valencia, Spain (2003).     

A comparison of the change from inhibiting to enhancing anions in the electrochemical oxidations of ethylene glycol and formaldehyde

Techniques dealing with inhibiting anions have previously been employed to measure their properties. The present approach is to change the behavior of inhibiting anions. Anions, which have long been considered to inhibit reactions, are shown to enhance some electrochemical reaction rates. Fluoroborate, nitrate, and (hydrogen) sulfate are separately shown to increase the current response of the electrochemical oxidation of formaldehyde. The reaction rate of the oxidation of ethylene glycol is increased but for a restrictive set of conditions. Experimental data, as well as theoretical considerations lead to the conclusion that adsorption of the added anions is the slow step of the process that increases the reaction rate. The differences in the response of ethylene glycol and formaldehyde follow well-documented changes of surface CO. These observations are consistent with general properties of the step in the part of the mechanism on the electrode surface that enhances the reaction rate.