Thermodynamic optimization for work-assisted heating and drying operations

We construct thermodynamic criteria for optimization of sequential work-assisted heating and drying operations which run jointly with ‘endoreversible’ thermal machines. The total power input is minimized with constraints which take into account the dynamics of heat and mass transport and rate of work consumption. Finite-rate, endoreversible models include the irreducible losses of classical exergy potential caused by the thermal resistances. Extremum performance functions for optimal work, which incorporate residual entropy production, are formulated in terms of end states, duration and (in discrete processes) number of stages. Formal analogies between entropy production expressions for work-assisted and conventional drying operations help formulate optimization models of the former. An optimization procedure for a two-stage drying operation with an endoreversible heat pump at each stage is outlined.     

Mechanics of three-dimensional braided structures for composite materials – part I: fabric structure and fibre volume fraction

This paper is the first part of a series on the mechanics of three-dimensional braided structures for composite materials which include fabric structure and fibre volume fraction models, prediction of mechanical properties, finite element analysis and simulation of deformations. In the present paper, the normalized pitch length is introduced as a key parameter of three-dimensional braided structures. It is demonstrated that the braiding angles and fibre volume fractions can be represented as functions of this key parameter. The structures of three-dimensional braids were simulated and the braided fabrics and preforms were designed and produced. Fibre volume fraction models were established. The predictions from the fibre volume fraction models are supported by experimental results.     

A Local Extrapolation Method for Hyperbolic Conservation Laws. I. The ENO Underlying Schemes

In this paper, we introduce a local extrapolation method (LEM) for the essentially non-oscillatory (ENO) schemes solving nonlinear hyperbolic conservation laws. The method extrapolates the numerical flux of the underlying scheme so that it keeps conservativity. We use a minmod type limiter to avoid spurious oscillations. We propose a new balancing technique that preserves the symmetry of a symmetric wave that works well for a wide range of CFL numbers. We also introduce two artificial compression procedures to the LEM which yield sharp resolutions of contact discontinuities. Numerical examples are presented to illustrate the performance of the method.     

日本历史环境保护的理论与实践——法律、政策与公众参与

历史环境是指与一定范围的土地密切相关的历史文化遗产构成一体的实体环境状态，它与居民的精神生活息息相关，1966年日本制定了《古都保存法》来保护古都的“历史风上”，1975年修订了《文化财保护法》，创立了“传统建造物群保存地区”制度，对一般城镇内的历史街区以及以村落聚落景观为代表的历史环境进行切实保护与合理再利用。70年代又对全国综合开发规划中的国土政策进行了重大调整，在这人转变过程中，历史保护运动中的公众参与和地方自治体条例起了积极的推动作用。     

引信对制导系统提供的目标信息综合利用研究

在提取雷达制导型空空导弹的制导信息的基础上，开展了利用制导信息的引战配合，引信抗干扰，引信超低空工作技术研究，并给出了一些仿真结果。     

Efficiency gained with the use of scanning in precision photoelectric systems for measurement of displacement

Questions related to efforts aimed at decreasing the position error of the moving parts of measuring transducers when measuring displacements are considered. It is remarked that scanning by the indicator element of the measurement coupling is most effective in photoelectric transducers, since it makes it possible to optimize the measuring circuit of the system and mode of operation of the system’s transducers. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 13–14, March, 2008.     

Problem size scaling in the presence of parallel overhead

In this paper we study the performance of applications on multiprocessor systems. In particular we investigate the effect of synchronization and parallelization overhead where the fact that part of the application may be inherently sequential is taken into account. By relating our assumptions to an earlier work by Flatt and Kennedy we establish that the overhead function can be characterized using the concept of convex functions. In order to observe a satisfactory payoff for increased processing power it is essential to increase the problem size accordingly. We discuss linear and nonlinear scaling schemes and compare the corresponding asymptotic performance behaviour. Throughout this investigation we profit from the well developed mathematical apparatus of convex functions.     

Averaging Pore Statistics of Two-Dimensional Images for Predicting Permeability

Effective medium theory (EMT) was employed to estimate permeability of fine-grained estuarine sediments. X-radiographs were taken of sediment cores collected in the field and from laboratory aquaria, designed to mimic the benthic environment of an estuary. Image analysis of two-dimensional X rays provided values of pore parameters required by the EMT model, which include pore body and throat radii, pore throat length, porosity, and the interconnectivity of pores. Values of these parameters were used to quantitatively calculate permeability based upon Darcy’s law. The EMT model with an arithmetic mean for averaging pore parameters predicted permeability 1 order of magnitude higher than measured values. The harmonic mean for averaging pore parameters in the EMT model provided estimates of permeability similar to measured values.     

Second law analysis of two‐stage compression transcritical CO2 heat pump cycle

Because of the global warming impact of hydro fluorocarbons, the uses of natural refrigerants in automotive and HVAC industries have received worldwide attention. CO₂ is the most promising refrigerant in these industries, especially the transcritical CO₂ refrigeration cycle. The objective of this work is to identify the main factors that affect two‐stage compression transcritical CO₂ system efficiency. A second law of thermodynamic analysis on the entire two‐stage CO₂ cycle is conducted so that the exergy destruction of each system component can be deduced and ranked, allowing future efforts to focus on improving the components that have the highest potential for advancement. The inter‐stage pressure is used as a variable parameter in the analysis study. The second law efficiency, coefficient of cooling performance and total exergy destruction of the system variations with the inter‐stage pressure are presented graphically. It was concluded that there is an optimum inter‐stage pressure that maximizes both first law and second law efficiencies. Copyright © 2008 John Wiley & Sons, Ltd.     

An examination of exergy destruction in organic Rankine cycles

The exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy‐based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems. Copyright © 2008 John Wiley & Sons, Ltd.