Effects of Defibration Conditions on Mechanical and Physical Properties of Wood Fiber/High-Density Polyethylene Composites

Defibration conditions influence wood fiber characteristics and thereby properties of fiber-based materials. In this study, the effects of several defibration conditions on mechanical and physical properties of fiber-based wood-plastic composites (WPCs) are illustrated. Various WPCs were tested containing different thermo-mechanical pulps (TMPs) or groundwood pulp (GWP), whereby material composition (50 wt% wood fibers, 47 wt% polymer, 3 wt% coupling agent) and the production process (internal mixer, injection molder) were kept consistent. The data from the experiment revealed that differing defibration conditions led to statistically significant differences in the tested flexural, tensile, and impact properties as well as in the water absorption of WPC. Overall, the GWP and the TMP which was produced under the mildest defibration conditions performed best in fiber-based WPCs. Therefore, grinders and refiners may be equally suitable to produce pulp for WPC usage. As a side-effect within this study, the reinforcing effect of fiber application on flexural and tensile properties was on an extraordinarily high level.     

Online Characterization of Syngas Particulates Using Aerosol Mass Spectrometry in Entrained-Flow Biomass Gasification

Entrained flow gasification is a promising technique where biomass is converted to a synthesis gas (syngas) under fuel-rich conditions. In contrast to combustion, where the fuel is converted to heat, CO₂, and H₂O, the syngas from gasification is rich in energetic gases such as CO and H₂. These compounds (CO and H₂) represent the building blocks for further catalytic synthesis to chemicals or biofuels. Impurities in the syngas, such as particulates, need to be reduced to different levels depending on the syngas application. The objective of this work was to evaluate the amount of particulates; the particle size distribution and the particle composition from entrained flow gasification of pine stem wood at different operating conditions of the gasifier. For this purpose, online time resolved measurements were performed with a soot particle aerosol mass spectrometer (SP-AMS) and a scanning mobility particle sizer (SMPS). The main advantage of SP-AMS compared to other techniques is that the particle composition (soot, PAH, organics, and ash forming elements) can be obtained with high time resolution and thus studied as a direct effect of the gasifier-operating conditions. The results suggest that syngas particulates were essentially composed of soot at these tested process temperatures in the reactor (1200–1400°C). Furthermore, the AMS analysis showed a clear correlation between the amounts of polycyclic aromatic hydrocarbons (PAH) and soot in the raw syngas. Minimization of soot and PAH yields from entrained flow gasification of wood proved to be possible by further increasing the O₂ addition.

Copyright 2014 American Association for Aerosol Research     

Experimental and numerical investigation of the dynamics of loop seals in a large‐scale DFB system under hot conditions

The dynamics of the loop seals in a large‐scale dual fluidized bed (DFB) system is investigated as a function of variations in the flux of the bed material through the seal and changes in the bed material density. These investigations are performed numerically with a computational fluid dynamics (CFD) model and experimentally for the loop seals of the Chalmers 2–4 MW_th DFB gasifier. Both experiments and simulations show that more of the aeration gas leaves the loop seal in the direction of the solids when a low‐density bed material (silica) is used rather than a high‐density one (bauxite). The simulations also reveal homogeneous fluidization in a vertical connection to the loop seal, whereas an inclined connection yields heterogeneous fluidization. The minor discrepancies between the experiments and simulations with silica are attributed to particle agglomeration, and it is proposed that CFD models applied to loop seals should account for this phenomenon. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3580–3593, 2015     

Computation of Effective Steady‐State Creep of Porous Ni–YSZ Composites with Reconstructed Microstructures

This paper investigates the effective steady‐state creep response of porous Ni–YSZ composites used in solid oxide fuel cell applications by numerical homogenization based on three‐dimensional microstructural reconstructions and steady‐state creep properties of the constituent phases. The Ni phase is found to carry insignificant stress in the composite and has a negligible role in the effective creep behavior. Thus, when determining effective creep, porous Ni–YSZ composites can be regarded as porous YSZ in which the Ni phase is counted as additional porosity. The stress exponents of porous YSZ are the same as that of dense YSZ, but the effective creep rate increases by a factor of 8–10 due to porosity. The relationship of creep rate and volume fraction of YSZ computed by numerical homogenization is underestimated by most existing analytical models. The Ramakrishnan–Arunchalam creep model provides the closest approximation among all analytical models.     

Safety effects of traffic signing for left turn flashing yellow arrow signals

In 2010, the left turn flashing yellow arrow (FYA) signal displays were installed at signalized intersections on state routes in the Peoria, Illinois, area. Supplemental traffic signs with text “Left Turn Yield on Flashing Yellow Arrow” were mounted on the mast arm adjacent to the left turn signal at over half of the FYA installations. The purpose of this paper is to present the results of the effectiveness evaluation of the FYA supplemental sign on safety. Analyses are presented on the effects of the FYA supplemental sign for all drivers and a subset of drivers age 65 and older. A crash-based comparison of 164 FYA approaches including 90 approaches with the sign and 74 approaches without the sign showed greater crash reductions when the supplemental FYA sign was present. The results also showed that crashes involving drivers age 65 and older did not experience the same magnitudes of crash reductions as compared to all drivers. The findings of this research indicate that supplemental FYA signs may help in improving safety for left-turning vehicles during the permissive interval. Thus, it is recommended that supplemental signs be used when initially implementing the FYA, and that effort to educate the driving public on new traffic control be made to further improve safety at signalized intersections.     

A 60 GHz receiver front-end with PLL based phase controlled LO generation for phased-arrays

This paper presents a front-end architecture for fully integrated 60 GHz phased array receivers. It employs LO-path beamforming using a phase controlled phase-locked loop (PC-PLL). To demonstrate the architecture a circuit is implemented featuring a two stage low noise amplifier, two cascaded active mixers, and a PC-PLL. The receiver downconverts the 60 GHz signal in two steps, using LO signals from the 20 GHz QVCO of the PLL. A differential 2nd-order harmonic is coupled from the sources of the current commutating pairs of the QVCO, feeding the LO-port of the first mixer and downconverting the 60 GHz RF signal to a 20 GHz intermediate frequency. Quadrature 20 GHz LO signals are then used in the second mixer to down-convert the IF signal to baseband. The PLL is locked to a relatively high reference frequency, 1.25 GHz, which reduces the size of the PLL loop filter and enables a compact layout. The measurements show an input return loss better than ?10 dB between 57.5 and 60.8 GHz, a 15 dB voltage gain, and a 9 dB noise figure. Two-tone measurements show ?12.5 dBm IIP3, 29 dBm IIP2, and ?24 dBm ICP1. The PC-PLL phase noise is ?105 dBc/Hz at 1 MHz offset from a 20 GHz carrier, and the phase of the received 60 GHz signal is digitally controllable with a resolution of 3.2°, covering the full 360° range with a phase error smaller than 1°. The chip consumes 80 mA from a 1.2 V supply, and measures 1,400 μm × 660 μm (900 μm × 500 μm excluding pads) including LNAs, mixers, and PC-PLL in a 90 nm RF CMOS process.     

Gradient-based selection of cross sections: a novel approach for optimal frame structure design

Optimization of frame structures composed of beams, columns and joints is considered. The problem is to find the optimal combination of standard cross sections from a provided catalog. The approach taken utilizes the Discrete Material Optimization (DMO) method to parameterize the problem and optimize using a gradient based method. It has roots in continuum topology optimization and thus strong parallels are drawn hereto in terms of methodology. The MATLAB implementation can take mass, compliance and stress criteria into account. In addition continuous joint stiffness design variables will indicate whether the joint should be rigid or pinned. Issues related to the non-convexity of the design spaces and the numerous local minima are discussed. The numerical results with benchmark models of varying complexity successfully validate the method as a design tool.     

Managing short-term efficiency and long-term development through industrialized construction

There is a strong need for a productive and innovative infrastructure sector because of its monetary value and importance for the development of a sustainable society. An increased level of industrialization is often proposed as a way to improve efficiency and productivity in construction projects. In prior literature on industrialized construction, there are however neither many studies addressing more long-term aspects of innovation and sustainability nor studies within the infrastructure context. Organizational theory suggests that firms need to be ambidextrous and focus on both long-term exploration of new knowledge and technologies and short-term exploitation of current knowledge and technologies, in order to achieve sustainable development. Therefore, an investigation of how both short-term exploitative performance objectives and long-term explorative development can be addressed when implementing industrialized construction in infrastructure projects was conducted. A case study consisting of four infrastructure projects shows that the main drivers for increased industrialization are of an exploitative nature, focusing on cost savings and increased productivity through more efficient processes. The main barriers to increased industrialization are however related to both explorative and exploitative activities. Hence, by managing the identified barriers and explicitly addressing both exploitation and exploration, industrialized construction can improve both short-term efficiency and long-term innovation and sustainability.     

Alternative "global warming" metrics in life cycle assessment: a case study with existing transportation data

The Life Cycle Assessment (LCA) impact category "global warming" compares emissions of long-lived greenhouse gases (LLGHGs) using Global Warming Potential (GWP) with a 100-year time-horizon as specified in the Kyoto Protocol. Two weaknesses of this approach are (1) the exclusion of short-lived climate forcers (SLCFs) and biophysical factors despite their established importance, and (2) the use of a particular emission metric (GWP) with a choice of specific time-horizons (20, 100, and 500 years). The GWP and the three time-horizons were based on an illustrative example with value judgments and vague interpretations. Here we illustrate, using LCA data of the transportation sector, the importance of SLCFs relative to LLGHGs, different emission metrics, and different treatments of time. We find that both the inclusion of SLCFs and the choice of emission metric can alter results and thereby change mitigation priorities. The explicit inclusion of time, both for emissions and impacts, can remove value-laden assumptions and provide additional information for impact assessments. We believe that our results show that a debate is needed in the LCA community on the impact category "global warming" covering which emissions to include, the emission metric(s) to use, and the treatment of time.