Startup transient simulation for natural circulation boiling water reactors in PUMA facility

In view of the importance of instabilities that may occur at low-pressure and -flow conditions during the startup of natural circulation boiling water reactors, startup simulation experiments were performed in the Purdue University Multi-Dimensional Integral Test Assembly (PUMA) facility. The simulations used pressure scaling and followed the startup procedure of a typical natural circulation boiling water reactor. Two simulation experiments were performed for the reactor dome pressures ranging from 55 kPa to 1 MPa, where the instabilities may occur. The experimental results show the signature of condensation-induced oscillations during the single-phase-to-two-phase natural circulation transition. The results also suggest that a rational startup procedure is needed to overcome the startup instabilities in natural circulation boiling water reactor designs.     

Crystal growth of sapphire filaments by a laser-heated floating zone technique

A laser-heated floating zone technique is employed to grow a filamentary c-axis sapphire. Crystal growth is directly recorded during the process by photography, and crystals grown under various conditions are examined by means of a transmission optical microscope to obtain the relationships between microvoid formation and growth conditions. Observations of filaments indicated that the microvoid results from shrinkage due to dendritic growth. Microvoids are eliminated by choosing a growth rate less than 4.7 cm h^–1 or by focusing the laser beam. By using this method, a void-free filament of 1.4 mm diameter is obtained.     

An analysis of transport phenomena for multi-solid particle systems at higher Reynolds numbers by a 5th order polynomial Karman-Pohlhausen method

Using the concentric spheres free surface model and a 5th order polynomial Karman-Pohlhausen method of the laminar boundary layer theory, the dimensionless tangential stress distributions, the dimensionless pressure distributions around a solid sphere in a swarm and the viscous, form and total drag coefficients for multi-solid sphere systems were numerically computed at higher Reynolds numbers, based on the first assumption that the pressure distribution equals that of potential flow between concentric spheres up to the separation point, and behind the separation point in the wake region the pressure does not recover and keeps constant, and on the second assumption that the pressure distribution varies according to the measurement of Flachsbart.The theoretical drag coefficient of single solid spheres in an infinite medium based on the second assumption agreed with the experimental data in the range of the Reynolds numbers from $\text{3 × 10}{}^2\text{to 10}{}^5$.The friction factor for multi-solid particle systems based on the first assumption is almost the same as that on the 4th order polynomial and agreed with the experimental data of packed and distended beds.The void functions obtained from the drag coefficients for multi-solid particle systems based on both first and second assumptions were almost the same as the one on the 4th order polynomial.Using the velocity profiles based on concentric spheres free surface model and a 5th order polynomial Karman-Pohlhausen method of the laminar boundary layer obtained previously, the diffusion equation was solved numerically at higher Reynolds numbers on the first assumption of the pressure distribution around a solid sphere in a swarm equals that of potential flow between concentric spheres from the frontal stagnation point to the separation one, and the pressure does not recover, but keeps constant behind the separation point in the wake region. The mass transfer rate for multi-solid particle systems so computed was almost the same as that on the 4th order polynominal and agreed with the experimental data of single Solid spheres, and packed and particulate fluidized beds at higher Reynolds numbers.     

Endogenous determination of historical amenities and the residential location choice

Brueckner et al. (Econ Rev 43:91–107, 1999) remark that city’s historical amenities, which are considered exogenous today, may have been formed endogenously over time. This paper develops a simple two-period model based on this idea. It assumes there are two locations in a city and two income types. Lot sizes are decided myopically in the first period and cannot be adjusted later. Without historical amenities, locations of the rich and the poor are never reversed (the poor always locate closer to the center) for increasing population, income and utility levels of each type. If the rich leave some “historical amenity” behind for the residents in the second period, locations are reversed when the population of the first period is moderate, income disparity between the two types is low and the rich is sensitive to amenity. An earlier version of this paper was presented at International Symposium on Spatial Economics and Transportation, Sendai, Japan, June 13, 2005. The paper has benefited greatly from the comments of Dr. Jan Brueckner, who participated in the symposium, and Dr. Charles de Bartolomé, my academic adviser in the University of Colorado at Boulder.     

Water-retention properties of porous ceramics prepared from mixtures of allophane and vermiculite for materials to counteract heat island effects

Porous ceramics for anti-heat island effect were prepared from mixtures of allophane and vermiculite (VA samples). Allophane and vermiculite which had been ground for 0.5–2 h was mixed in various mass ratios, formed into pellets by uniaxial pressing at 40 MPa, and heated at 600–800 °C to form porous ceramics. The large thermal expansion of the vermiculite upon explosive dehydration of interlayer water causes cracking of the pellets with higher vermiculite contents. However, this can be controlled by grinding the vermiculite prior to heating. Grinding the vermiculite for ≥2 h suppresses its expansion, enabling pellet samples with high vermiculite contents to be prepared without cracking. The bulk densities of samples prepared at 800 °C from vermiculite ground for 2 h decrease from 1.72 to 0.94 with increasing allophane content. The pore size distribution in these samples shows a distinct peak at about 1 μm irrespective of the mixing ratio. The number of smaller pores (<50 nm) increases with increasing allophane content while the number of larger pores (20–40 μm) increases with increasing vermiculite content. The compressive strengths of the samples range from 1 to 3 MPa except for samples containing a high proportion of vermiculite ground for 1 h. The water absorption (W_a) of the samples increases from 37 to 63% with increasing allophane content. This absorption rate is fast enough to absorb >90% of the W_a within 1 min for samples of 10 mm Ø × 5 mm³ size. By contrast, the release of the absorbed water is very slow, with 50% of the W_a retained for ≥30 h in the VA samples at a relative humidity of 55% at 20 °C; this is slower than in pure allophane and much slower than in a reference sample of foamed glass (about 4 h). All these properties make the VA samples useful as water-retaining materials to combat “heat island” effects.     

Product quality and regional accessibility to knowledge among Japanese manufacturing industries

This paper develops an analytical framework for a multiregional market in monopolistic competition. Regional firms compete on the basis of research and development activities which are designed to increase the quality of their products. Product quality is related to the size of each firm's knowledge-handling workforce and its accessibility to stocks of knowledge. A case study into five major R&D-intensive manufacturing industries reveals that accessibility to local sources of knowledge is a crucial factor in the location decisions of Japanese firms. Face-to-face communication is shown to be just as effective for knowledge workers in the Kansai Region as for those in Tokyo.The first author acknowledges financial support from the Japan Society for the Promotion of Science towards the work described in this paper. He is also indebted to Kyoto and Tottori universities for their generosity and cooperation during his visiting periods in Japan.     

可用于结构健康监测的BOTDR光纤变形检出特性试验研究

应用BOTDR检测技术对用于结构物健康监测的光纤变形检出特性进行了试验研究,包括光纤锥重拉伸试验和光纤压缩与拉张试验。通过试验,分析了光纤应变区长度对检测结果的影响,确定了光纤应变检测段长度的选择区间,验证了BOTDR检测光纤压应变和张应变的有效性。     

Lift force in bubbly flow systems

From the significance of three-dimensional simulation of dispersed flow systems in many engineering fields, extensive study was conducted for lift force in a single particle system as well as a multiparticle system. In this study, the lift force in a single particle system was modeled by considering the effect of bubble deformation on the lift force. The model was finalized based on existing data obtained in the range of particle Reynolds number from 3.68 to 78.8, viscous number from 0.0435 to 0.203 and Eötvös number from 1.40 to 5.83. The viscous number is defined by where μ_f, ρ_f, σ, g and Δρ are, respectively, fluid viscosity, fluid density, surface tension, gravitational acceleration and density difference between phases. The applicability of the model to higher particle Reynolds number system such as an air-water system was qualitatively examined. The lift force model developed in a single particle system was extended to a multiparticle system. The applicability of the extended lift force model was qualitatively examined. The similarity between drag and lift forces were also discussed.