PREDICTIONS OF DEVELOPING FLOW WITH BUOYANCY-ASSISTED FLOW SEPARATION IN A VERTICAL RECTANGULAR DUCT: PARABOLIC MODEL VERSUS ELLIPTIC MODEL

ABSTRACT

This article reports the unsteady-state heat transfer analysis of unpaved and paved granite soil media in a closed system in order to predict the temperature profiles along a buried pipeline and the frozen penetration depth (FPD). These studies focused on the development of a computational scheme by applying the effective heat capacity model to numerical procedures. The proposed model took into consideration the phase-change effect of in-situ pore water in the frozen fringe. To realize these objectives, several physical values for granite soil of South Korea at various subzero temperatures were determined in laboratory tests. The comparison of results obtained from an unpaved freezing soil medium by the proposed model and the actual performances was valuable in establishing a level of confidence in the application of the theory introduced.     

Bubble-assisted film evaporation correlation for saline water at sub-atmospheric pressures in horizontal-tube evaporator

In falling film evaporators, the overall heat transfer coefficient is controlled by film thickness, velocity, liquid properties and the temperature differential across the film layer. This article presents the heat transfer behavior for evaporative film boiling on horizontal tubes, but working at low pressures of 0.93–3.60 kPa (corresponding solution saturation temperatures of 279–300 K) as well as seawater salinity of 15,000 to 90,000 mg/l or ppm. Owing to a dearth of literature on film-boiling at these conditions, the article is motivated by the importance of evaporative film boiling in the desalination processes such as the multi-effect distillation (MED) or multi-stage flashing (MSF): It is observed that in addition to the above-mentioned parameters, evaporative heat transfer of seawater is affected by the emergence of micro-bubbles within the thin film layer, particularly when the liquid saturation temperatures drop below 298 K (3.1 kPa). Such micro bubbles are generated near to the tube wall surfaces and they enhanced the heat transfer by two or more folds when compared with the predictions of conventional evaporative film boiling. The appearance of micro-bubbles is attributed to the rapid increase in the specific volume of vapor, i.e., dv/dT, at low saturation temperature conditions. A new correlation is thus proposed in this article and it shows good agreement to the measured data with an experimental uncertainty of 8% and regression RMSE of 3.5%.     

伺服阀前置级流场气穴现象的仿真及试验研究

针对液压阀中的气穴现象会引起液压阀的噪音、性能恶化,甚至导致液压阀失效等问题,对伺服阀前置级喷嘴和挡板之间流场中的气穴现象进行了研究.利用Pro/E软件对流场进行了三维建模,用前处理软件Gambit对三维模型进行了网格划分及边界条件设置,利用标准k-ε模型和混合气穴模型建立流场的数学模型,运用FLUENT软件对不同喷嘴入口流速下流场的分布特性及气穴特征进行了仿真分析;同时利用高速摄像机对喷嘴挡板之间的流场分布进行了观测和记录.研究结果表明,在低雷诺数流动条件下,气穴开始在喷嘴外壁和挡板前端的边缘形成;随着雷诺数的增大,在挡板弯曲的附体气穴逐渐长大并随着射流流速的增加出现云状的气穴.将不同流动条件下流场结构和气穴分布的数值计算结果与试验观测结果进行比较,两者基本吻合,说明伺服阀前置级流场气穴仿真模型和数值计算方法是可靠的.     

Plastic-Buckling of Rectangular Plates under Combined Uniaxial and Shear Stresses

This paper is concerned with the plastic-buckling of rectangular plates under uniaxial compressive and shear stresses. In the prediction of the plastic-buckling stresses, we have adopted the incremental theory of plasticity for capturing the inelastic behavior, the Mindlin plate theory for the effect of transverse shear deformation, the Ramberg-Osgood stress–strain relation for the plate material, and the Ritz method for the bifurcation buckling analysis. The interaction curves of the plastic uniaxial buckling stress and the plastic shear buckling stress for thin and thick rectangular plates are presented for various aspect ratios. The effect of transverse shear deformation is examined by comparing the interaction curves obtained based on the Mindlin plate theory and the classical thin plate theory.     

Partial Logistic Artificial Neural Network for Competing Risks Regularized With Automatic Relevance Determination

Time-to-event analysis is important in a wide range of applications from clinical prognosis to risk modeling for credit scoring and insurance. In risk modeling, it is sometimes required to make a simultaneous assessment of the hazard arising from two or more mutually exclusive factors. This paper applies to an existing neural network model for competing risks (PLANNCR), a Bayesian regularization with the standard approximation of the evidence to implement automatic relevance determination (PLANNCR-ARD). The theoretical framework for the model is described and its application is illustrated with reference to local and distal recurrence of breast cancer, using the data set of Veronesi (1995).     

Novel corrosion experiments using the wire beam electrode. (I) Studying electrochemical noise signatures from localised corrosion processes

This series of papers presents four novel experiments that were designed to study localised corrosion phenomena using an electrochemically integrated multi-electrode array namely the wire beam electrode (WBE). This present paper reports a WBE based experimental method that has been employed, for the first time, to study electrochemical noise patterns (called noise signatures) from localised corrosion processes. The objective of this work is to demonstrate the applicability of the WBE for investigating the origin of spontaneous electrode potential/current fluctuations and their effects on electrochemical processes. The key strategy of this work is to apply the WBE in a novel experimental set-up to simultaneously measure electrode potential noise and WBE current distribution maps--an approach that allows the direct comparison and correlation of electrochemical noise and corrosion events. Preliminary experiments have been carried out using a classic pitting corrosion system: stainless steel in a solution containing FeCl₃. A large number of anodic sites were found to exist on WBE surface at the very beginning of its exposure to the corrosion environment. Correlation between characteristic patterns in electrode potential noise and corrosion behaviour has been observed. More specifically, the characteristic sharp peaks in potential noise data (called noise signature I) were found to correlate with the sudden disappearance of single unstable anode in WBE current distribution maps. The characteristic noise pattern of quick potential changes followed by partial or no recovery (called noise signature II) was found to correspond with the massive disappearance of minor anodes in WBE current distribution maps. This result suggests that, in the corrosion system under study, electrode noise activities were associated with the disappearance of minor anodic sites, which lead to the eventual disappearance of most anodic sites. Localised corrosion was the result of the accelerated anodic dissolution of a small number of remaining anodic sites. The characteristics features in electrochemical noise and in WBE maps were reproducible.     

Studying the Influence of Temperature on the Operation of a Resonator of a Frequency Micromechanical Accelerometer

Russian Microelectronics - A micromechanical accelerometer (MMA) is used to measure the acceleration based on the change in frequency of the resonator when the acceleration is caused by the...