Effect of Channel Length on the Gas–Liquid Two-Phase Flow Phenomena in a Microchannel

An optical measurement system was used to investigate the effect of microchannel length and inlet geometery on adiabatic gas–liquid two-phase flow. Experiments were conducted with 146-mm- and 1571-mm-long, circular microchannels of 100 μm diameter. Void fraction and gas and liquid plug/slug lengths and their velocities were measured for two inlet configurations for gas–liquid mixing: (a) reducer and (b) T-junction. The superficial gas velocity was varied from 0.03 to 14 m/s, and superficial liquid velocity from 0.04 to 0.7 m/s. The test section length was found to have a significant effect on the two-phase flow characteristics measured at the same axial location (37 mm from the inlet) in both microchannels. The mean void fraction data for the short (146 mm) microchannel with the reducer inlet agreed well with the equation previously proposed by Kawahara et al. (2002). On the other hand, the mean void fraction data for the long (1571 mm) microchannel obeyed the homogeneous flow model and Armand's equation for both the reducer and T-junction inlet configurations. Many long and rapidly moving gas plugs/slugs and long, slowly moving liquid plugs/slugs were observed in the short microchannel compared to the long microchannel, leading to the differences in the time-averaged void fraction data. The mean velocity of liquid plugs/slugs generally agreed well with Hughmark's equation and the homogeneous flow model predictions, regardless of the inlet configurations and microchannel lengths. Thus, both the microchannel length and inlet geometry were found to significantly affect the two-phase flow characteristics in a microchannel.     

Study on the slurrying and rheological properties of coal–oilfield wastewater–slurry

In this study, oilfield wastewater (OWW) was used to prepare coal–oilfield wastewater–slurry (COWS), and the apparent viscosity, solid concentration, and rheological curve were studied. Compared with original coal–water–slurry (CWS), the maximum solid concentration of COWS increased, and the viscosity decreased; therefore, the slurrying ability of the coal slurry was improved with the use of OWW. However, although the oil in OWW promoted the slurrying ability of the coal slurry, its effectiveness was insufficient, and a chemical additive was still needed to obtain a coal slurry with enhanced slurrying ability. Both COWS and CWS exhibited shear-thinning behavior, and the rheological index value of COWS was lower, which indicated that pseudoplasticity of COWS was more obvious, and OWW improved the rheological properties of coal slurry.     

Development of high-chromium steel for the sodium-cooled fast reactor in Japan and creep–fatigue assessment of the steel

This paper presents the provisional material specification and characteristics of the high-chromium (Cr) steel for the sodium-cooled fast reactor (SFR) in Japan and creep–fatigue assessment of the steel. Based on the mechanical test and metallurgical examination results, it was clarified that tungsten (W) should be diminished to achieve better ductility and toughness. Then the provisional specifications of the high-Cr steel for SFR components were proposed. Material characteristics, e.g. cyclic stress–strain relationship and creep strain curve, were also presented based on the material test results. Using these characteristics, a creep–fatigue strength assessment of the steel was performed. Conservative predictions were obtained and it was clarified that such conservatism resulted from over estimation of creep damage caused by too large initial stress at the beginning of stress relaxation. For precise assessment, it is essential to develop an appropriate model accounting for the effect of creep softening due to strain hold.     

On the C^r-Closing Lemma and the Koebe–Morse Coding of Geodesics on Surfaces

We consider the -closing lemma for vector fields with finitely many singularities on an orientable closed surface M of genus g2. Given a nontrivially recurrent trajectory, there is the corresponding geodesic having the same asymptotic directions (both negative and positive). Using the Koebe–Morse coding for the corresponding geodesic, we introduce the notion of p-expansions in the form of two sequences of nonnegative integers. The main result is the following. Suppose a vector field , r, has a nontrivially recurrent trajectory l through a point m; then there exists arbitrarily close to X (in the -topology) having a periodic trajectory through m provided that the Koebe–Morse coding of the corresponding geodesic g(l) has p-expansions of unrestricted type.     

Selected Papers from the Eleventh Brazilian Congress of Thermal Sciences and Engineering—ENCIT 2006

The Brazilian Congress of Thermal Sciences and Engineering—ENCIT is organized under the auspices of the Brazilian Society of Mechanical Sciences and Engineering—ABCM. It has been held every other year since 1986, and its last editions had more than 400 presentations of peer-reviewed papers. The ENCIT series of congresses has successfully served as the major forum for the interaction of professionals from academia, industry, and government within the heat transfer, thermodynamics, and fluid mechanics communities in Brazil.     

Interactive relationships between crude oil prices,gold prices,and the NT–US dollar exchange rate—A Taiwan study

This investigation examines the correlations of oil prices, gold prices and the NT dollar versus U.S. dollar exchange rate during 2007/09/03–2011/12/28. Johansen co-integration test, VAR model, Granger causality test, impulse response analysis, and variance decomposition method were used to clarify the interactive relationships among the three variables. These tests and models show that the oil price, gold price and exchange rate remain considerably independent from one another, which implies policymakers should consider the separation of energy and financial policies.