An approximate analytical prediction about thermal performance and optimum design of pin fins subject to condensation of saturated steam flowing under forced convection

An approximate analytical method has been suggested for solving the governing equation for horizontal pin fins subject to condensation while saturated steam flowing over its under laminar forced convection. Adomian decomposition method is used for determination of the temperature distribution, performance and optimum dimensions of pin fins with temperature dependent thermal conductivity under the condensation of steam on the fin surface. From the results, a significant effect on the temperature distribution in the fin and its performances are noticed with the variation in fin-geometric parameters and thermo-physical properties of saturated vapor. Next, a generalized scheme for optimization has been demonstrated in such a way that either heat-transfer duty or fin volume can be taken as a constraint. Finally, the curves for the optimum design have been generated for the variation of different thermo-physical and geometric parameters, which may be helpful to a designer for selecting an appropriate design condition.     

An analytical prediction for performance and optimum design analysis of porous fins

Enhancement of heat transfer rate through porous fins is one of the common choices nowadays. As the energy equation is highly nonlinear, researchers never concentrated on analyzing porous fins analytically. In the present study, an effort has been devoted to develop an analytical model for determination of the performance and optimum dimensions of porous fins with consideration of different models of predictions. Every result has been presented in a comparative way so that the merit of the models adopting in the present work can easily be understood. The optimum design analysis of porous fins has also been carried out. The influences of all the dependent parameters on the performances and optimization conditions have been studied for the selection of a design criterion of porous fins in such applications where the requirement of heat dissipation is essentially high.     

Approximate methods for predicting J-integral of a circumferentially surface-cracked pipe subject to bending

This study proposes two new methods to estimate the energy release rate of a circumferentially cracked pipe with an internal, constant-depth, finite-length surface flaw subjected to pure bending loads. The methods are based on the deformation theory of plasticity, constitutive law characterized by Ramberg-Osgood model, and an equivalence criterion incorporating reduced thickness analogy for simulating system compliance due to the presence of a crack. Closed-form solutions were developed in terms of elementary functions for an approximate evaluation of J-integral. They are general and can be applied in the complete range between elastic and fully plastic conditions. Several numerical examples are presented to illustrate the proposed methods. The comparisons with the results of elastic-plastic finite element analysis showed satisfactory prediction of J-integral by one of the proposed methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

Measurement of turbulent pressure and velocity fluctuations in a vapor flow by the condensation method

The inertial characteristics of the thermal processes underlying a new method of measuring turbulent pressure and velocity fluctuations are analyzed.     

An analytical method for the performance evaluation of echelon kanban control systems

We develop a general purpose analytical approximation method for the performance evaluation of a multi-stage, serial, echelon kanban control system. The basic principle of the method is to decompose the original system into a set of nested subsystems, each subsystem being associated with a particular echelon of stages. Each subsystem is analyzed in isolation using a product-form approximation technique. An iterative procedure is used to determine the unknown parameters of each subsystem. Numerical results show that the method is fairly accurate. Correspondence to: George Liberopoulos     

Approximate numerical method for prediction of temperature distribution in flow through narrow gaps containing porous media

The paper examines an approximate solution to the problem of temperature distribution in the flow through a narrow gap filled with porous medium. This problem is relevant for composite material manufacturing processes, such as the resin transfer molding and its derivatives. In such processes, cold resin is sometimes injected into a closed heated cavity containing a network of stationary fibers. The cavity can be long and wide, but it is usually only a few millimeters thick. The approximate solution is based on an estimated through-the thickness temperature profile that allows one to reduce the complexity from fully three-dimensional to two-dimensional and significantly improve the computational efficiency. The implementation of this solution within an existing simulation code for non-isothermal filling of closed mold is briefly described. Finally, several examples are presented to illustrate the accuracy of the proposed method to predict the midplane temperature of the resin as it impregnates the preform to fill the mold cavity.The support for this work has been provided by the Office of Naval Research (ONR) under Grant #N00014-97-C-0415 for the Advanced Materials Intelligent Processing Center at the University of Delaware.     

Approximate analytical models for phonon specific heat and ballistic thermal conductance of nanowires

We introduce simple approximate analytical models for phonon specific heat and ballistic thermal conductance of nanowires. The analytical model is in excellent agreement with the detailed numerical calculations based on the solution of the elastic wave equation and is also in good agreement with the ballistic thermal conductance data by Schwab et al. (Nature 2000, 404, 974). Finally, we propose a demarcating criterion in terms of temperature, dimension, and material properties to capture the dimensional crossover from a three-dimensional (3D) bulk system to a one-dimensional (1D) system.     

Effect of precursor supply on structural and morphological characteristics of fe nanomaterials synthesized via chemical vapor condensation method

Various physical, chemical and mechanical methods, such as inert gas condensation, chemical vapor condensation, sol-gel, pulsed wire evaporation, evaporation technique, and mechanical alloying, have been used to synthesize nanoparticles. Among them, chemical vapor condensation (CVC) has the benefit of its applicability to almost all materials because a wide range of precursors are available for large-scale production with a non-agglomerated state. In this work, Fe nanoparticles and nanowires were synthesized by chemical vapor condensation method using iron pentacarbonyl (Fe(CO)5) as the precursor. The effect of processing parameters on the microstructure, size and morphology of Fe nanoparticles and nanowires were studied. In particular, we investigated close correlation of size and morphology of Fe nanoparticles and nanowires with atomic quantity of inflow precursor into the electric furnace as the quantitative analysis. The atomic quantity was calculated by Boyle's ideal gas law. The Fe nanoparticles and nanowires with various diameter and morphology have successfully been synthesized by the chemical vapor condensation method.     

A predictive model for life assessment of automotive exhaust mufflers subject to internal corrosion failure due to exhaust gas condensation

A study has been presented on pitting corrosion on internal walls of automotive exhaust muffler due to exhaust gas condensation. The problem mainly exists in the rear section of the exhaust system close to the tail end pipe such as the muffler, especially when the temperature of the muffler does not go up during short distance run or winter. The water vapour condenses on the muffler's inner wall in the form of water droplets. The dissolution of corrosive gases coming from the internal combustion of engine as well as condensation of low-pH acidic vapours in the water droplet can cause severe pitting corrosion on standard exhaust steel. In this work, an experiment is reported for internal corrosion, by using mufflers as test bed subjected to different environmental conditions. Based on observations, a mechanistic model has been developed which involves three main techniques: (i) the dropwise condensation technique predicts the condensation rate and is based on heat and mass transfer theory, (ii) the species breakdown in the droplet is established through the main thermodynamic and chemical equilibrium, and (iii) the pitting corrosion involving pit depth is predicted using electrochemical kinetic reactions, species transport and chemical reactions occurring inside the droplet. Lastly, the accuracy of the model has been validated by comparison between experimental and predicted results showing good agreement.     

An efficient analytical method for performance evaluation of transfer lines with unreliable machines and finite transfer-delay buffers

Buffers are widely adopted in transfer lines to reduce the fluctuations caused by the imbalances of systems or machine failures. This paper presents an efficient analytical method to evaluate the performance of transfer lines with unreliable machines and finite transfer-delay buffers. Firstly, the buffers with transfer delays are transformed equivalently into a series of perfect machines and buffers without transfer delays. Correspondingly, the initial transfer line is replaced by an equivalent transfer line with more machines and zero-transfer-delay buffers. Since in the equivalent transfer line the orders of magnitude of machines’ reliability parameters (mean times between failures and mean times to repair) are not at the same level, an advanced decomposition method is introduced to analyse the equivalent transfer line, using the general-exponential distributions instead of the exponential distributions to approximate the repair time distributions of the fictitious machines. Finally, extensive simulation and numerical cases are carried out to verify the performance of the developed method.     

转子系统不平衡响应的灵敏度和估算方法

本文采用有限元法首次推导出系统的稳态不平衡响应关于各类参数的灵敏度公式,提出了用灵敏度公式估算不平衡响应的近似方法。在转子模型算例中,用所推公式研究了系统参数对不平衡响应的影响,并对不平衡响应进行了估算,将其与重新计算值相比较。当参数变化40%时,不平衡响应的估算误差低于3%,且估算与重算的机时比约为1∶5。     

Electrochemical performance of conducting polymer and its nanocomposites prepared by chemical vapor phase polymerization method

In this work, conducting polymers poly(3,4-ethylenedioxythiophene) (PEDOT), PEDOT/carbon nanotubes (CNTs), and PEDOT/reduced graphene oxide (RGO) were prepared via an in situ chemical vapor phase polymerization (VPP) process. Experiment results showed that PEDOT and PEDOT nanocomposites were uniformly constructed in oxidant and oxidant nanocomposite films through a modifying template effect. The VPP PEDOT and its nanocomposites were built on aluminium film as supercapaitor electrode materials and electrochemical capacitive properties were investigated by using cycle voltammetry and charge/discharge techniques. The VPP PEDOT exhibited a specific capacitance of 92 F/g at a current density of 0.2 A/g. The VPP PEDOT composites consisting of CNTs and RGO displayed specific capacitances of 137 and 156 F/g, respectively, at the same current density. For VPP nanocomposites, more than 80 % of initial capacitance was retained after 1,000 charge/discharge cycles, suggesting a good cycling stability for electrochemical electrode materials. The good capacitive performance of the conducting polymer nanocomposites are contributed to the synergic effect of the two components.     

Approximate analytical method for determining the vibration-diagnostic parameter indicating the presence of a crack in a distributed-parameter elastic system at super- and subharmonic resonances

An approximate method for calculating the vibration-diagnostic parameter indicating the presence of a crack in an elastic distributed-parameter system at super- and subharmonic resonances is considered. The method involves the finding of the non-linearity characteristic of an elastic system based on the analysis of its forced vibrations in the undamaged state and the use of results of the approximate analytical determination of parameters of nonlinearity for vibrations of an elastic body with a closing crack, which is simulated by a single-degree-of-freedom system with an asymmetric bilinear characteristic of the restoring force at the above-mentioned resonances.     

Hybrid Subset Simulation method for reliability estimation of dynamical systems subject to stochastic excitation

A hybrid Subset Simulation approach is proposed for reliability estimation for general dynamical systems subject to stochastic excitation. This new stochastic simulation approach combines the advantages of the two previously proposed Subset Simulation methods, Subset Simulation with Markov Chain Monte Carlo (MCMC) algorithm and Subset Simulation with splitting. The new method employs the MCMC algorithm before reaching an intermediate failure level and splitting after reaching the level to exploit the causality of dynamical systems. The statistical properties of the failure probability estimators are derived. Two examples are presented to demonstrate the effectiveness of the new approach and to compare with the previous two Subset Simulation methods. The results show that the new method is robust to the choice of proposal distribution for the MCMC algorithm and to the intermediate failure events selected for Subset Simulation.     

Prospects of the rolling method for measuring linear displacements and dimensions

This article examines aspects of the interaction of a measurement disk with a specimen through a flexible elastic element. A method is proposed for determining the main parameters of measuring devices with allowance for the displacement of the neutral axis of the elastic element as it is bent by the disk. Examples are presented to illustrate the use of the rolling method in measuring instruments with flexible elements. Translated from Izmeritel'naya Tekhnika, No. 5, pp 23–24, May, 1996.     

Application of the Taguchi analytical method for optimization of effective parameters of the chemical vapor deposition process controlling the production of nanotubes/nanobeads

Seven variable parameters of the chemical vapor deposition system have been optimized with the help of the Taguchi analytical method for getting a desired product, e.g., carbon nanotubes or carbon nanobeads. It is observed that almost all selected parameters influence the growth of carbon nanotubes. However, among them, the nature of precursor (racemic, R or Technical grade camphor) and the carrier gas (hydrogen, argon and mixture of argon/hydrogen) seem to be more important parameters affecting the growth of carbon nanotubes. Whereas, for the growth of nanobeads, out of seven parameters, only two, i.e., catalyst (powder of iron, cobalt, and nickel) and temperature (1023 K, 1123 K, and 1273 K), are the most influential parameters. Systematic defects or islands on the substrate surface enhance nucleation of novel carbon materials. Quantitative contributions of process parameters as well as optimum factor levels are obtained by performing analysis of variance (ANOVA) and analysis of mean (ANOM), respectively.     

An analytical method for determination of the performance of a fin assembly under dehumidifying conditions: A comparative study

The present paper establishes an analytical method for determining the performance of a fully wet fin assembly under dehumidifying conditions. A cubic relationship between the humidity ratio of the saturated air and its temperature is taken for calculating driving force for the mass transfer. With this relationship, the governing equation of a fin assembly becomes nonlinear. The Adomian decomposition method is suggested for the solution. The performance parameters, namely, surface efficiency and augmentation factor, are furnished as a function of different design variables. To establish the merit of the work, present results are compared with those values obtained from the previous model and a reasonable difference in results has been noticed. In this point, it can be highlighted that the error associated with the previous model increases with the relative humidity. Finally, the present model is equally useful to predict the performance of a wet fin assembly with the consideration of any other nonlinear effect.     

基于耦合法的二维三轴编织复合材料热学性能预测及验证

为了改善传统方法建模划分网格繁杂和计算效率低的缺点,利用耦合建模法创建二维三轴编织复合材料的单胞模型,用耦合的思维将增强相单元网格与整体区域单元网格进行耦合处理,协调两者之间的位移场自由度和温度场自由度,通过匹配材料的热学性能,施加温度周期性边界条件,获得单胞模型的等效传热系数和等效热膨胀系数,基于该方法预测并分析编织角和纤维体积含量对各个方向的热传导系数和热膨胀系数的影响程度和规律。