Effect of hydrogen enrichment and electric field on lean CH4/air flame propagation at elevated pressure

Electric assisted combustion for hydrogen enriched hydrocarbons may even extend the lean burn limit and provide the further improvement on combustion stability. This study investigates the effect of hydrogen enrichment and DC electric field on lean CH₄/air flame propagation. Electric field inside the chamber was generated by mesh and needle electrodes. Effect of hydrogen enrichment on the ion mole fraction in the flame was discussed based on reaction mechanism included neutral and ion reactions. The flame propagation images, flame displacement speed were used to evaluate the combined influences of hydrogen enrichment and electric field on propagating flame. Results showed that the hydrogen addition would increase positive ions mole fraction and the peak value is mainly determined by H₃O⁺. This would be due to that CH increases with hydrogen fraction, which is the main species in the initial reaction for the ion reactions. Electric field effect about flame propagation was suppressed with hydrogen addition due to the competition between the increment in ion mole fraction and the decrement in flame time. Electric assisted combustion is more evident at leaner conditions and elevated pressure. The ratio of ionic wind velocity to flow velocity may be the determined factor to predict the electric field effect about propagating flame. The tendency based on this ratio is in accordance with the experimental results for various hydrogen fraction and equivalence ratio at elevated pressure.     

Compressive strength and microstructure of alkali-activated fly ash/slag binders at high temperature

This paper reports the results of the compressive strength and microstructure of various alkali-activated binders at elevated temperatures of 300 and 600 °C. The binders were prepared by alkali-activated low calcium fly ash/ground granulated blast-furnace slag at ratios of 100/0, 50/50, 10/90 and 0/100 wt.%. Specimens free of loading were heated to a pre-fixed temperature by keeping the furnace temperature constant until the specimens reached a steady state. Then the specimen was loaded to failure while hot. XRD, SEM and FTIR techniques were used to investigate the microstructural changes after the thermal exposure. The fly ash-based specimen shows an increase in strength at 600 °C. On the other hand, the slag-based specimen gives the worst high-temperature performance particularly at a temperature of 300 °C as compared to ordinary Portland cement binder. This contrasting behaviour of binders is due to their different binder formulation which gives rise to various phase transformations at elevated temperatures. The effects of these transformations on the compressive strength are discussed on the basis of experimental results.     

Effects of steam dilution on laminar flame speeds of H2/air/H2O mixtures at atmospheric and elevated pressures

The laminar flame speeds of H₂/air with steam dilution (up to 33 vol%) were measured over a wide range of equivalence ratio (0.9–3.0) at atmospheric and elevated pressures (up to 5 atm) by an improved Bunsen burner method. Burke, Sun, HP (High Pressure H₂/O₂ mechanism), and Davis mechanisms were employed to calculate the laminar flame speeds and analyze different effects of steam addition. Four studied mechanisms all underestimated the laminar flame speeds of H₂/air/H₂O mixtures at medium equivalence ratios while the Burke mechanism provided the best estimates. When the steam concentration was lower than 12%, increasing pressure first increased and then decreased the laminar flame speed, the inflection point appeared at 2.5 atm. When the steam concentration was greater than 12%, increasing the pressure monotonously decrease the laminar flame speed. The chemical effect was amplified by elevated pressure and it played an important role for the inhibiting effect of the pressure on laminar flame speed. The fluctuations of the chemical effect at 1 atm were mainly caused by three-body reactions, while the turn at 5 atm was mainly caused by the direct reaction effect. Elevated pressure and steam addition amplified the influences of uncertainties in the rate constants for elementary reactions, which might leaded to the disagreement between experimental and simulation results.     

Gas-Liquid Mass Transfer Characteristics in a Gas-Liquid-Solid Bubble Column under Elevated Pressure and Temperature

abstract The volumetric mass transfer coefficient kLa of gases (H2, CO, CO2) and mass transfer coefficient kL on liquid par-affin side were studied using the dynamic absorption method in slurry bubble ...     

Seismic response of liquid-filled elevated tanks

The main focus of the current study is to evaluate the performance of elevated tanks under seismic loading. In this study, the finite element (FE) technique is used to investigate the seismic response of liquid-filled tanks. The fluid domain is modeled using displacement-based fluid elements. Both time history and modal analyses are performed on an elevated tank. Using the FE technique, impulsive and convective response components are obtained separately. Furthermore, the effect of tank wall flexibility and sloshing of the water free surface are accounted for in the FE analysis. In this study complexities associated with modeling of the conical shaped tanks are discussed. This study shows that the proposed finite element technique is capable of accounting for the fluid-structure interaction in liquid containing structures. Using this method, the study of liquid sloshing effects in tanks with complex geometries such as conical tanks is made possible. The results of this study show that the current practice predicts the response of elevated tanks with reasonable accuracy.     

Shear strength of plate girder web panel at elevated temperature

This paper presents a theoretical model to predict the failure loads of plate girders with transverse stiffeners subjected to a specified constant temperature or isothermal condition. The work is based on classical plate girder theory at normal ambient conditions subjected to increasing load. The equations incorporating the temperature-dependent material properties and thermally-induced axial stress arising from surrounding structural restraint are derived. They can be used for the case when the plate girder is subjected to pure shear or to a combination of shear and axial stresses. To simplify the analysis, uniform temperature distribution is assumed within the full depth of web panel. Solution procedures are presented for the fire resistance analysis of web plate girder, either in terms of the shear strength corresponding to isothermal condition, or the limiting temperature for a prescribed set of constant shear force and axial thermal restraint. For both procedures, the predictions agree well with the finite element analyses.     

Behaviour of grouted sleeve connections at elevated temperatures

Tubular steel jointing system that incorporates prestressed grout sleeve connections has superior strength under both static and dynamic loading. This paper reports an investigation into the effect of elevated temperatures on the load carrying capacity of such connections. Eleven specimens were heated in a furnace and the load was applied through an Instron machine. Three different grout lengths were chosen. The load deflection behaviour at different temperatures was compared. It was found that the ultimate load reduces almost linearly as temperature difference (TD) between outer and inner tubes increases. It is encouraging to observe the ductile behaviour of grouted connections at elevated temperature. Thermal analysis was also conducted to predict the temperature field in the connection.     

Effects of heat treatment on the mechanical properties at elevated temperatures of plain-woven SiC/SiC composites

The effects of heat treatment on the mechanical properties of plain-woven SiC/SiC composites at 927 °C and 1200 °C in argon were evaluated through tensile tests at room temperature and at elevated temperature on the as-received and heat-treated plain-woven SiC/SiC composites, respectively. Heat treatment can improve the mechanical properties of composites at room temperature due to the release of thermal residual stress. Although heat treatment can damage the fiber, the effect of this damage on the mechanical properties of composites is generally less than the effect of thermal residual stress. Heat treatment will graphitize the pyrolytic carbon interface and reduce its shear strength. Testing temperature will affect the expansion or contraction of the components in the composites, thereby changing the stress state of the components. This study can provide guidance for the optimization of processing of ceramic matrix composites and the structural design in high-temperature environments.     

城市背景下高架交通的景观意义--以上海市为例

在解决大城市伴生的交通问题的诸多对策中，高架交通方式的有效性已经得到广泛的认同。基于城市景观的理念要求，这一全新交通方式所引发的美学特征成为该文主旨所在。     

Damage accumulation modeling under uniaxial low cycle fatigue at elevated temperatures

The paper presents a fatigue damage accumulation model, which allows us to predict fatigue life under low cycle uniaxial loadings at elevated temperatures. The structure of the model has been based on the stress–strain curves obtained during the experimental study. The model has been verified experimentally by applying experimental studies carried out on ENAW-2024T3 aluminum alloy and 2Cr–2WVTa steel. Moreover, a comparison between the results of fatigue life prediction using the proposed damage accumulation model was done with the results obtained on the basis of various generally applied models, based on the Manson–Coffin dependency. Furthermore this paper presents the results of experimental studies carried out on the aluminum alloy ENAW 2024 T3 under uniaxial low cycle fatigue loadings in the conditions of elevated temperatures. In the course of the study, material constants and the parameters of the stress–strain curve in the range of low cycle fatigue for four levels of temperatures (20, 100, 200 and 300 °C) were set.