Thermogravimetric study of the decomposition of pelletized cellulose at 315°C–800°C

The thermal decomposition rate of pelletized cellulose cylinders in a laboratory furnace was studied to simulate the pyrolytic and combustive behavior of pelletized refuse-derived fuel (RDF). The decomposition rate was determined by measuring the mass-loss rate of three mass groups of cylinders at several fixed furnace temperatures over the range of 315°C–800°C and in both air and nitrogen atmospheres. The decomposition for all conditions tended to follow first-order reaction kinetics throughout the majority of the reaction and the rate of mass loss for cylinders in atmospheres of flowing air and nitrogen was found to be similar. The apparent Arrhenius activation energy ranged throughout the major course of the decomposition from 2.1 to 8.0 kcal/mol. A simple model is developed to describe the rate of weight loss. This study with cellulose cylinders as a model system aids the use of pelletized refuse-derived fuel (RDF) by providing information on the rate of fuel reaction in varying pyrolytic and combustive conditions.     

150°C蒸汽管道直埋技术

1 蒸汽管道直埋保温材料具备性能 蒸汽、蒸汽管道与热水及热水管道性能的差异如下:     

An Experimental Study of Small-Diameter Wickless Heat Pipes Operating in the Temperature Range 200°C to 450°C

An experimental investigation is reported for medium-temperature, wickless, small-diameter heat pipes charged with environmentally sound and commercially available working fluids. The wickless heat pipes (thermosyphons) studied have many applications in heat recovery systems since their operational temperature range is between 200°C and 450°C. The heat pipes investigated had an internal diameter of 6 mm and a length of 209 mm. The lengths of evaporator and condenser sections were 50 mm and 100 mm, respectively. The working fluids tested were diphenyl based: Therminol VP1 and Dowtherm A. High-grade stainless steel was chosen as the shell material for the heat pipes to provide chemical compatibility between heat pipe casing material and working fluids at elevated temperatures. Thermal resistances of less than 0.4 K/W have been achieved at working temperatures of up to 420°C with an effective thermal conductivity of 20 kW/m-K, which corresponds to an axial heat flux of 2.5 MW/m². Even for such small-diameter heat pipes, the experimental data for the evaporator showed good agreement with Rohsenow's pool boiling correlation.     

Effective thermal conductivity of Mexican geothermal cementing systems in the temperature range from 28°C to 200°C

The effective thermal conductivity of six Mexican cementing systems used in geothermal well completion were experimentally determined in the temperature range from 28°C to 200°C. Measurements were carried using the classical line-source method. The experimental system was calibrated by measuring the thermal conductivity of standard fused quartz samples. An experimental procedure for preparation of the cement specimen samples was also developed. Results show that thermal conductivity depends on the particular cement system and tends to increase with temperature for most cement systems. Experimental uncertainties of thermal conductivity were less than 4%. From this experimental work, new empirical equations for correlating thermal conductivity with temperature for geothermal cementing samples were obtained.     

Simple Formulas for Thermophysical Properties of Liquid Water for Heat Transfer Calculations (from 0°C to 150°C)

Abstract

In this communication, simple formulas (based on the latest experimental tabulated data) for 11 physical properties of liquid ordinary water substance at saturation state—saturation pressure, density, volumetric thermal expansion coefficient, specific volume of saturated vapor, specific enthalpy, specific heal, latent heal of vaporization, thermal conductivity, dynamic viscosity, Prandtl number, and surface tension as a function of temperature (from 0 to 150°C)—which are used in heat transfer calculations for heat exchangers in heating systems and also for many other technological applications, are presented. Also, the uncertainties of these formulas are given. In most practical cases the pressure of liquid water is within the range from 1 to 10 absolute bar, which makes it possible to neglect the effect of pressure. All properties of saturated liquid water calculated with the recommended formulas are tabulated with a temperature increment of 5°.     

GH4698合金在500 °C下裂纹扩展特性研究

涡轮盘用GH4698合金材料断裂性能数据不足，难以支撑该材料用于燃气轮机涡轮盘损伤容限工程 设计。通过裂纹扩展试验研究,建立该材料在500 ℃下裂纹扩展模型，并进行数值模拟,验证模型的有效性, 为该材料用于燃气轮机涡轮盘损伤容限设计打下基础。     

15°~35°N、105°~130°E海域台风极值风速分析

采用非对称台风风场模型,对1961~2007年进入(15°~35°N,105°~130°E)的每个热带气旋(TC)风场进行计算,得到0.5°×0.5°网格上的TC风速。使用近岸自动气象站实测资料对计算结果进行对比分析,结果表明计算风速与实测风速较吻合,计算风速基本合理。采用Poisson-Gumbel联合概率分布模型,计算每个网格TC影响下不同重现期10 m高度的极值风速;使用海上、小岛共10座测风塔14个台风影响过程的大风观测数据计算得到10~90 m切变系数为0.0791,使用该关系式将各网格点TC影响下不同重现期10 m高度的极值风速推算到90 m高度,可作为中国近海风资源开发和其他海洋工程开发及安全运行的科学依据。     

The properties of high toughness low-temperature −70°C steel 09MnNiDR

The weldability and comprehensive mechanical properties of steel 09MnNiDR have been researched and its practical applications in petroleum and chemical equipments are discussed. It was found that the excellent weldability and low-temperature toughness is useful in the manufacture of low-temperature pressure vessels.     

Hot deformation behaviour of niobium in temperature range 700–1500°C

Abstract

Niobium was hot deformed in vacuum in uniaxial compression to a true strain of 0·6 in the temperature range of 700–1500°C and the strain rate range of 10^?3–10 s^?1. Strain rate sensitivity was calculated from the compression tests data and mapped out in contour plots with the aim to optimise the hot workability of niobium. The domain of hot workability was identified in the temperature range of 1200–1500°C and strain rate range of 10^?2–1 s^?1. In this domain the strain rate sensitivity was ～0·15, the stress exponent 7·5 and the activation energy 246 kJ mol^?1. Microstructure of the deformed samples showed features of dynamic recrystallisation within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. Compared to a previous study on Nb–1Zr–0·1C alloy, Nb showed a lower flow stress and an optimum hot working domain at lower temperatures.     

Magnetohydrodynamic free convection flow of water at 4°C through a porous medium

MHD forced and free convection flow of water at 4°C through a porous medium in the presence of a uniform transverse magnetic field is considered. A family of solutions of the coupled non-linear equations is presented using shooting numerical techniques for two point boundary value problems. Velocity and temperature profiles are shown for different values of the parameters Ha²/Re, Gr/Re² and K.     

Natural convection boundary layer flow of water at 4°C past slender cones

This paper is concerned with an analysis of the transverse curvature effects on axisymmetric free convection boundary layer flow of water at 4°C past a slender, vertical cone. Numerical solutions are provided for the governing equations for momentum and energy. Missing values of the velocity and thermal functions which are proportional to the surface friction factor and the dimensionless heat transfer rate, have been tabulated for a Prandtl number of 11.4. The results indicate that the heat transfer rate increases with increasing transverse curvature.     

Energy-Saving Optimization Study on 700°C Double Reheat Advanced Ultra-Supercritical Coal-Fired Power Generation System

700°C double reheat advanced ultra-supercritical power generation technology is one of the most important development directions for the efficient and clean utilization of coal. To solve the great exergy loss problem caused by the high superheat degrees of regenerative steam extractions in 700°C double reheat advanced ultra-supercritical power generation system, two optimization systems are proposed in this paper. System 1 is integrated with the back pressure extraction steam turbine, and system...     

Experimental study on a small Brayton air refrigerator under −120 °C

A small Brayton air refrigerator with high-speed gas bearing turbo-expander and compact plate-fin heat exchanger was designed and fabricated. Performances of the two key components (turbo-expander and heat exchanger) and the refrigerator as a whole were investigated. The bearings used in the refrigerator were compliant foil journal bearings with elastic support, and stability inspection was conducted on them. The results indicate that the refrigerator had a high cooling capability, and that the gas bearings used here achieved good performance in a wide speed region up to 250,000 rpm. While the expander operated at its design speed (220,000 rpm), the refrigerator had a cooling capacity of 1500 W at ?80 °C, and the lowest no-load refrigeration temperature of ?124.5 °C was obtained. Moreover, the influence of nozzle number and velocity ratio on the turbo-expander and the effect of flow rate and cold inlet temperature on the heat exchanger are discussed in detail.     

Thermal degradation of alloy CCA617 in pure steam at 750 and 850°C

Oxidation and oxidation-induced microstructure evolution of CCA617 alloy was studied in pure steam at 750 and 850°C. Results showed that the alloy was oxidised approximately following a parabolic law. Temperature increase greatly promoted the external and internal oxidation. A single (Cr, Mn)₂O₃ layer with distribution of minor TiO₂ and MnCr₂O₄ formed at 750°C whereas a duplex oxide scale formed at 850°C consisting of a thin MnTiO₃ outer layer and a thicker (Cr, Mn)₂O₃ inner layer. TiO₂ and Al₂O₃ were formed internally especially along grain boundaries. Intragranular Mo-rich M₂₃C₆ type carbides were also observed. The carbides dissolved into the matrix as oxidation progressed. Based on detailed compositional and microstructural characterisation of the oxidised alloy, the mechanisms of external and internal oxidation as well as dissolution of the intragranular carbides are presented.     

Investigation of PEMFC operation above 100 °C employing perfluorosulfonic acid silicon oxide composite membranes

Various perfluorosulfonic acid membranes (PFSAs) were studied as pure and silicon oxide composite membranes for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFCs) from 80 to 140 °C. The composite membranes were prepared either by impregnation of pre-formed PFSAs via sol–gel processing of a polymeric silicon oxide, recasting a film using solubilized PFSAs and a silicon oxide polymer/gel. All composite membranes had a silicon oxide content of less than or equal to 10% by weight. Decreasing the equivalent weight and thickness of the PFSAs, in addition to the incorporation of silicon oxide helped improve water management in a PEMFC at elevated temperatures. Fourier transform-infrared spectroscopy–attenuated total reflectance (FT-IR–ATR), and scanning electron microscopy (SEM) experiments indicated an evenly distributed siloxane polymer in all of the composite membranes. At a potential of 0.4 V the Aciplex 1004/silicon oxide composite membrane in a humidified H₂/O₂ PEMFC at 130 °C and a pressure of 3 atm delivered six times higher current density than unmodified Nafion 115 under the same conditions, and 1.73 times the current density when unmodified Nafion 115 was operated with humidified gases at 80 °C and 1 atm of pressure. Furthermore, the PEMFC performances with the PFSA/silicon oxide composite membranes were physically more robust than the control membranes (unmodified PFSAs), which degraded after high operation temperature and thermal cycling.     

Hydrogen impact on the shrinkage behaviors of wustite packed beds above 900 °C

The steel industry is facing increasing pressure and challenges from the environment in recent years. The urgent utilization of clean energy not only reduces greenhouse gas emissions, but also promotes future innovations in blast furnace iron making technology. Hydrogen (H₂) energy is considered to be one of the most promising alternatives to carbon-based fossil energy for the reduction of iron oxides. Therefore, the gaseous reduction of iron oxides by H₂ has been intensively studied for decades. However, the impact of H₂ on the shrinkage behavior of iron oxide packed beds above 900 °C has rarely been studied, and the interaction between H₂ and carbon monoxide (CO) in the shrinking process is not fully understood. Therefore, this study uses H₂, CO and H₂+CO mixture gas for the well-designed high temperature experiments of wustite (FeO) packed beds. The results show that H₂ protects the coke from further damage in the packed bed at 900–1000 °C, and the corresponding shrinkage rate (SR) decreases from 0.31%/°C for CO case to 0.16%/°C. Meanwhile, when the temperature exceeds 1350 °C, the packed bed under the CO atmosphere accelerates shrinkage due to the melting and dripping of the metallic iron after carbonization. By contrast, when CO is replaced by H₂, the carbonization process is controlled by the solid state diffusion of coke carbon rather than the reverse Boudouard reaction. As a result, the lower carbonization efficiency not only increases the transition temperature by up to 100 °C, but also reduces the weight of the melted hot metal by one third, which significantly improves the bed permeability.     

Fatigue and creep–fatigue crack growth in 316 stainless steel cracked plates at 650°C

This paper presents experimental results on fatigue and creep–fatigue experiments consisting of a wide cracked plate subjected to cyclic bending loads at 650°C. Six tests have been realised with different loading histories. The specimen is a large 316SS plate containing a wide semielliptical surface notch precracked by fatigue.Fatigue and creep crack growth laws are determined, using an adapted stress intensity factors compendium calculated by F.E. elastic analysis, and compared to tests results conducted on CT specimen. A good correlation of the experimental results for fatigue tests is obtained. For creep crack growth law, the CT specimen gives an intermediate result between plate results at the deepest point and at the surface point.A16 guideline assessment procedures are used; results are found to be in good agreement with experimental crack growth.     

Achieving high mechanical-strength CH4-based SOFCs by low-temperature sintering (1100 °C)

Despite much progress achieved in the past decades in the process of advancing the low-temperature sintering technologies for Solid oxide fuel cells (SOFCs), such as via the structure design of the electrode materials, the practical application of low-temperature sintered SOFCs (with disqualified mechanical strength) remains challenging. In this work, first, we demonstrate that the appropriate amount of CuO as sintering aids can successfully reduce the co-firing temperature of conventional micron size NiO-YSZ (yttrium-stabilized zirconia (Y₂O₃)_0.08–(ZrO₂)_0.92) anode from about 1400 °C to only 1100 °C. Second, the quantitative structure-activity relationship among the mechanical strength (low-temperature sintering ability) of anode cermets with the inclusion of CuO contents and the densification of YSZ electrolyte was synthetically evaluated, and the optimal Cu–NiO-YSZ anode composition demonstrates almost the equal mechanical strength when compared with the traditional NiO-YSZ anode (sintering at 1400 °C). At last, by comprehensive assessment, 8%Cu–52NiO-40YSZ (8%CuO–NiO-YSZ) shows excellent low-temperature sintering ability, high mechanical strength, optimal power output, and anti-carbon deposition when using as hydrocarbon-based anode for SOFCs.     

Experimental results of chemical-looping combustion with NiO/NiAl2O4 particle circulation at 1200 °C

Chemical-looping combustion is the indirect combustion by use of solid medium. This combustion with circulation of solid particles was investigated experimentally. There were two reactors: a reduction column and an oxidation column. The slurry of solid powder of NiO mixed with Al₂O₃ prepared by a dissolution method was fed into a spray dryer, and a spherical particle of diameter about 97 μm was obtained. The rates of both reduction and oxidation for the produced fine particles were measured in advance by a thermogravimetric analyzer.Then reactions with circulation of reacting solid particles were performed at elevated temperatures. In this paper, the results at 1200 °C by use of hydrogen as fuel are presented. The features of the reactions are discussed based on the analyses of the composition of the exhaust gas. Examination of the surface of the solid particles by a scanning microscope revealed that the condition of the solid particle in both reduction and oxidation columns was much milder than that in the TGA experiment, and significant change of the particle was not observed.