From coal to biomass gasification: Comparison of thermodynamic efficiency

The effect of fuel composition on the thermodynamic efficiency of gasifiers and gasification systems is studied. A chemical equilibrium model is used to describe the gasifier. It is shown that the equilibrium model presents the highest gasification efficiency that can be possibly attained for a given fuel. Gasification of fuels with varying composition of organic matter, in terms of O/C and H/C ratio as illustrated in a Van Krevelen diagram, is compared. It was found that exergy losses in gasifying wood (O/C ratio around 0.6) are larger than those for coal (O/C ratio around 0.2). At a gasification temperature of 927 °C, a fuel with O/C ratio below 0.4 is recommended, which corresponds to a lower heating value above 23 MJ/kg. For gasification at 1227 °C, a fuel with O/C ratio below 0.3 and lower heating value above 26 MJ/kg is preferred. It could thus be attractive to modify the properties of highly oxygenated biofuels prior to gasification, e.g. by separation of wood into its components and gasification of the lignin component, thermal pre-treatment, and/or mixing with coal in order to enhance the heating value of the gasifier fuel.     

Solid solubility of hydrogen in Pb83Li17 alloy: A preliminary investigation

Lead–lithium alloy Pb₈₃Li₁₇ (0.6 wt.% lithium) is a potential candidate to be used as a neutron multiplier, tritium (fuel) breeder and heat transfer agent (coolant) in the International Thermonuclear Experimental Test Reactor (ITER). The tritium produced in the alloy could be soluble in the alloy or appear as a new phase. During reactor shut down condition, Pb₈₃Li₁₇ will be solidified and stored in a storage tank. Investigation on the solubility of tritium in solid Pb₈₃Li₁₇ is essential to quantify the trapped tritium in solid Pb₈₃Li₁₇ alloy to estimate the extent of radioactive contamination (with respect to tritium) and valuable tritium loss. Tritium being the isotope of hydrogen behaves more or less similar to hydrogen. In the present study solid-solubility of hydrogen in Pb₈₃Li₁₇ alloy has been investigated as a function of temperature and pressure. It was found that the hydrogen solubility increases with temperature (373–473 K) and follows the Sieverts law. Hydrogen solution enthalpy has been calculated using Seiverts constant and found to be −4.81 kJ/mole of hydrogen.     

落地铣镗床虚拟装配序列规划与优化

采用基于层次向、属性向和关系向的多视图方法对TK6813大型落地铣镗床进行装配建模。采用新型SAP树结构建立了TK6813大型落地铣镗床装配序列模型,以SAP树中A,AP节点以下的数据子节点为研究对象,通过分层搜索,运用模糊综合评价法来确定各数据子节点的相对装配优先关系,进而判断所有子数据节点的装配顺序。根据宽度优先的分层搜索原则,完成A向AP和S向SP的转变,从而实现TK6813大型落地铣镗床装配序列的优化。     

Event oriented analysis of series structural systems

The event oriented analysis of technical objects is in general accomplished by representing them as complete or incomplete systems and subsystems of events. It is argued in the article how the compound engineering systems of events can be partitioned by inclusion-exclusion expansion into individual and common cause modes. The event analysis is based on the random variable model and employs the results of operational modes and effect analysis, of the reliability analysis and of the uncertainty analysis. The system redundancy and robustness are considered as uncertainties, due to the fact that really a number of events are possible, expressed by the entropy concept in probability theory, conditioned by operational and failure modes, respectively. Relative and average uncertainty measures are introduced to facilitate uncertainty interpretations in engineering problems. It is investigated how the sensitivity analysis of reliability measures can be applied to the assessments of system uncertainties. Numerical examples presented in the article illustrate the application of event oriented system analysis to series structural systems with common cause failures. Additionally, system performance presentation and optimization with constraints, as well as potential improvements in system analysis, design and maintenance are investigated.     

Entropy production due to free convection in partially heated isosceles triangular enclosures

A numerical analysis of the entropy production has been performed due to natural convection heat transfer and fluid flow in isosceles triangular enclosures with partially heated from below and symmetrically cooled from sloping walls. Governing equations are solved by finite difference method. Governing parameters on flow and temperature fields are Rayleigh number (10³  Ra  8.8 × 10⁵), dimensionless length of heater (0.25  (ℓ′ = ℓ/L)  1.0), dimensionless location of heater (0.25  (c′ = c/L)  0.75) and inclination angle of slopping walls (30°  β  60°). Heat transfer results are presented in terms of local and mean Nusselt numbers (Nu) while entropy production results are shown with entropy production number (N_s) and Bejan number (Be). Isotherms, streamlines, contours of entropy production due to heat transfer and fluid friction irreversibility are plotted. It is observed that entropy production number increases but Bejan number decreases with increasing of Rayleigh number. However, both entropy production due to heat transfer and fluid friction irreversibility are affected by higher inclination angle of triangle and length of heater.     

一种基于WSN时变性与节点剩余能量均衡的机会路由算法

 为了解决数据报文在无线传感网络中动态路由以及网络内各节点剩余能量均衡问题,该文提出了一种机会路由算法。首先,利用热力学第2定律描述数据报文在无线传感器网络中动态路由的传输过程,其中,为了表征网络内各节点状态的时变性以及剩余能量,提出了机会熵模型;其次,以机会熵模型作为选择下一跳节点的理论依据,并结合蚁群优化(ACO)算法,设计并实现了考虑网络中各节点时变性与剩余能量均衡的机会路由算法(ACO for Time Dependent Opportunistic-routing Protocol, ATDOP),使得数据报文在转发过程时,能够有效地选择下一跳节点,从而使网络内各节点的通信资源和能量资源达到负载均衡。最后,通过实验证明,相对于已有的机会路由协议,ATDOP具有报文成功传输率高、网络有效吞吐量大以及网络工作寿命长等优点。     

基于信息熵模型的企业纳税信用评级应用分析

利用我国计算机、通信和其他电子设备制造业上市公司财务数据,选取了17个用于纳税信用评级的定量指标。构建信息熵评估模型,得出各样本企业的纳税信用综合值并排序。实证结果表明信息熵法能够提高纳税信用评估的可信度和精确度。     

Average Case Analyses of List Update Algorithms, with Applications to Data Compression

We study the performance of the Timestamp (0) (TS(0)) algorithm for self-organizing sequential search on discrete memoryless sources. We demonstrate that TS(0) is better than Move-to-front on such sources, and determine performance ratios for TS(0) against the optimal off-line and static adversaries in this situation. Previous work on such sources compared on-line algorithms only with static adversaries. One practical motivation for our work is the use of the Move-to-front heuristic in various compression algorithms. Our theoretical results suggest that in many cases using TS(0) in place of Move-to-front in schemes that use the latter should improve compression. Tests using implementations on a standard corpus of test documents demonstrate that TS(0) leads to improved compression. Received December 3, 1995; revised April 5, 1997.     

Prediction of the size distribution of secondary ejected droplets by crown splashing of droplets impinging on a solid wall

Crown splashing is frequently observed during the impact of a droplet on a rough or wet wall. The size distribution of secondary ejected droplets has been experimentally observed to satisfy the log–normal distribution which contains two free parameters: the most probable diameter d_s and the width of the distribution γ. The most probable diameter will be determined through a simplified physical analysis. The width of distribution will be determined by using the principle of maximum rate of entropy production. The theory, containing no free parameters, predicts known experimental results with an acceptable engineering accuracy, provided the Froude number is high enough.