Measurements of Some Characteristics of Thermal Radiation in a 400-kW Grate-Fired Furnace Combusting Biomass

A comprehensive experimental investigation relevant to thermal radiation has been performed in a grate-fired test furnace. Thermal radiation is the dominating mode of heat transfer in the grate-fired furnace and yet only a few studies have focused on thermal radiation. No previous works, to the authors' knowledge, have been carried out concerning measurements on radiative heat transfer in grate-fired furnaces. In this work measurements of temperature have been carried out for all boundaries and the flue gases at a large number of locations. The gas species volume fraction, particle mass–size distributions, and wall irradiation have also been measured at a number of spatial locations. These data are useful in a computational framework to describe the radiative heat transfer reaching the boundaries. Comparing modeled wall irradiation to the measured one makes it possible to obtain a deeper insight into the thermal radiative transport inside the grate-fired furnace.     

车用永磁同步电机三维温度场分析

为了研究车用永磁同步电机的温度场,以一台额定功率为25kW的车用永磁同步电机为研究对象,基于传热学基本理论,建立其三维求解域模型,通过仿真分析,得出了电机额定工况下的温度场及温升变化,并对连续变功率工况下的电机内关键部分的温升进行仿真分析,以研究车辆实际行驶时电机温度场的变化情况。通过搭建的实验平台,对电机工作在额定工况和连续变工况条件下的温升进行了测试。经对比分析,实验数据与仿真数据误差较小,验证了仿真的正确性。     

Chloride retention and release in a boreal forest soil: effects of soil water residence time and nitrogen and chloride loads

The common assumption that chloride (Cl-) is conservative in soils and can be used as a groundwater tracer is currently being questioned, and an increasing number of studies indicate that Cl- can be retained in soils. We performed lysimeter experiments with soil from a coniferous forest in southeast Sweden to determine whether pore water residence time and nitrogen and Cl- loads affected Cl- retention. Over the first 42 days there was a net retention of Cl- with retention rates averaging 3.1 mg CI- m(-2) d(-1) (68% of the added Cl- retained over 42 days). Thereafter, a net release of Cl- at similar rates was observed for the remaining experimental period (85 d). Longer soil water residence time and higher Cl- load gave higher initial retention and subsequent release rates than shorter residence time and lower Cl- load did. Nitrogen load did not affect Cl transformation rates. This study indicates that simultaneous retention and release of Cl- can occur in soils, and that rates may be considerable relative to the load. The retention of Cl- observed was probably due to chlorination of soil organic matter or ion exchange. The cause of the shift between net retention and net release is unclear, but we hypothesize that the presence of O2 or the presence of microbially available organic matter regulates Cl- retention and release rates.     

Effects of agglomerate model parameters on transport characterization and performance of PEM fuel cells

A three-dimensional, non-isothermal and two-phase flow model for proton exchange membrane (PEM) fuel cells is developed. In the cathode catalyst layer, a spherical agglomerate model with consideration of catalyst layer structure and liquid water effect is applied to determine the electrochemical kinetics. The size and structure of the agglomerates are determined by the following parameters, i.e., the agglomerate radius (r_agg), the volume fraction of ionomer within the agglomerate (L_i,agg), and the thickness of the ionomer film over the agglomerate (δ_i). It is noted that a random combination of the three above parameters is widely used in agglomerate models by researchers. In this paper, the effects of r_agg and L_i,agg on the cell performance and local transport characteristics are numerically investigated by using the developed model with consideration of the relationships between agglomerate parameters. It is concluded that the cell performance is significantly improved by decreasing r_agg and increasing L_i,agg at medium and high current densities when the volume fractions of the solid phase (L_Pt/C) and ionomer phase (L_i) are maintained constant. In addition, the distributions of oxygen concentration, liquid water saturation, volumetric current density and effectiveness factor are also strongly influenced by the variation of the two parameters.     

流化床-化学气相沉积技术的应用及研究进展

流化床-化学气相沉积(FB-CVD)技术是一种多学科交叉的材料制备技术,兼有流化床传热传质性能良好以及化学气相沉积均匀、产物单一等优点,在工业生产中有着广泛的应用,但因其属于交叉学科,散见于各种研究,没有进行专门的进展评述。本文拟对FB-CVD的工业应用进行专题综述,分析其发展和研究趋势。首先探讨了FB-CVD的基本原理,分别综述了其在颗粒包覆、一维纳米材料、多晶硅制备、颗粒表面改性及粉体制备等方面的应用,介绍了FB-CVD的过程模拟及反应器结构优化方面的研究进展。通过以上讨论,梳理了FB-CVD研究的科学内涵。可以看出,该过程具有明显的多尺度特征,即材料制备的微观层次、颗粒流化均匀性的介观层次以及反应器结构设计的宏观尺度。总结得出:FB-CVD技术的未来发展取决于3个尺度的耦合分析,其研究重点也应关注尺度间的相互影响效应,如材料制备的均相成核、非均相成核和颗粒流化及运动规律的相互耦合等。     

Oxygen Activity Calculations of Molten Steel: Comparison With Measured Results

This study sets out to find some model/s that could calculate the closest oxygen activity of molten steel to the measured oxygen activity in an ASEA‐SKF ladle furnace. Ten steel heats grade SAE 52100 were chosen, the oxygen activities of the molten steel after vacuum degassing process were measured, then by means of two different equations and one computer programs the theoretical oxygen activities were calculated and compared to the measured results. In order to calculate the activities of Al₂O₃ in the top slag four different models and two different constants were applied. Both Wagner and Turkdogan's equations were found to be useful. It was seen that increasing the wt% Al from 0 up to 0.05 in molten steel, increasing CaO/Al₂O₃ ratio in top slag, and reducing equilibrium temperature of slag‐steel could contribute to reduction of oxygen activity of molten steel. The scanning electron microscope observations revealed that the main types of observed non‐metallic inclusions in these samples were spinels and calcium aluminates and by increasing the CaO content of the inclusions their equivalent circle diameters grew.     

Computational Fluid Dynamics in Research and Design of Heat Exchangers

This paper gives a brief summary of computational methods in heat transfer equipment, such as CFD (computational fluid dynamics), methods for thermal problems (computational heat transfer), and turbulence modeling for single-phase applications in the design, research and development of heat exchangers. Details of the finite volume method and their extension to arbitrary geometries are presented. An overall presentation of turbulence modeling is provided. Some of the most common commercially available computer codes are listed. Ways to apply CFD to heat exchangers are discussed. The paper presents results from some examples of application of CFD methods for real heat exchangers in order to demonstrate how such methods can be used in the research, development, and design of heat transfer equipment. Limitations and shortcomings as well as needs for further research are also highlighted.     

Fibre-rich additives--the effect on staling and their function in free-standing and pan-baked bread

BACKGROUND: The use of dietary fibre in bread products is increasing because of consumer demand for healthier products. However, an increase in dietary fibre level changes the rheological properties of the dough and also the quality properties of the final bread product. In this study, effects on dough and bread staling were followed after replacing 3% of wheat flour by fibre‐rich additives (fine durum, oat bran, rye bran and wheat bran). Free‐standing and pan‐baked loaves were baked to compare the influence of baking method and loaf shape. RESULTS: All additives increased dough stability, with oat bran giving the greatest stability and longest development time. Parameters measured during storage were distribution, migration and loss of water, cutability, crumbliness, firmness and springiness. Furthermore, amylopectin retrogradation and amylase‐lipid complex formation were assessed. Oat bran provided similar or better results than the control for all staling parameters, while other additives gave no general improvements. Cutability reached a plateau when crumb firmness was ≥ 4 N. CONCLUSION: Small amounts of fibre‐rich additives had a significant influence on staling. However, the baking method (free‐standing or pan‐baked bread) had a greater impact on staling than the additives, thus displaying the importance of the baking method. Cutability was found to be related to firmness. Copyright © 2011 Society of Chemical Industry     

Identification and decarboxylase activities of bacteria isolated from decomposed mahimahi (Coryphaena hippurus) after incubation at 0 and 32°C

Identification and amine-forming ability of bacterial isolates from decomposed mahimahi (Coryphaena hippurus) were studied in order to identify spoilage microflora and determine the potential for a chemical index of spoilage based on the metabolites produced. Mesophilic bacteria isolated from a fish incubated at 32°C for 24 h were essentially all Gram-negative rods; 89% of these were Vibrio alginolyticus. Strong histamine-forming (> 100 mg/100 ml) mesophiles consisted of eight cultures of Morganella morganii and one of Proteus mirabilis. Weak histamine-forming (< 10 mg/100 ml) mesophiles were all V. alginolyticus, and these comprised 15% of the isolates assigned to that species. Decarboxylation of ornithine and lysine occurred in 38 and 92%, respectively, of the mesophilic isolates. Psychrotrophic isolates obtained from a fish incubated 14 days at 0°C were predominantly Gram-negative genera. Of these, 9% were histamine-forming cultures of Alteromonas putrefaciens, a weak histamine former that produced < 1 mg/100 ml at 5 and 20°C. Decarboxylation of ornithine and lysine occurred in 13 and 15%, respectively, of the psychrotrophic isolates.     

On the validity of unintentional doping densities extracted using Mott–Schottky analysis for thin film organic devices

The organic electronic devices are often understood invoking the concept of ‘unintentional doping’. However, the applicability and usefulness of this controversial concept is not very clear and is under much recent debate. In this work, we revaluate the validity of this concept through careful experiments and detailed numerical simulations. Specifically, we use the Capacitance Voltage (CV) measurement of pentacene devices as a testbed to unravel the role of injecting electrodes and unintentional doping (if any). Indeed, our results indicate that the CV of pentacene capacitors can be solely understood in terms of properties of the contact electrodes. The unintentional doping, if present, has an inconsequential role in device performance. Our conclusions indicate that, often, an incorrect interpretation of CV results would lead to unphysical values of unintentional doping and have obvious implications towards the fundamental understanding of organic semiconductor device physics, modeling, and characterization; thus resolving many ambiguities in literature by providing a consistent interpretation through a coherent conceptual framework.