Non‐Uniform Distribution of Two‐Phase Flows through Parallel Identical Paths

When a single‐phase fluid splits, passes through identical paths in parallel, and then recombines, the flow distributes itself uniformly among the multiple paths. However, when multi‐phase suspensions travel through identical parallel paths, the flow distribution can be significantly non‐uniform. Although the uniform distribution is a solution of the governing equations, this solution may be an unstable steady‐state solution between two or more stable solutions, or one of an array of possible steady‐state solutions. This multiplicity has arisen in practice for multiple vertical channels within fluidized beds, for cyclones in parallel, and for distributed feed suspension flows. Simple theories are employed to explain the principles involved for two cyclones and for a pair of risers in parallel.     

Age differences in visual search for compound patterns: Long- versus short-range grouping.

Visual search for compound patterns was examined in observers aged 6, 8, 10, and 22 years. The main question was whether age-related improvement in search rate (response time slope over number of items) was different for patterns defined by short- versus long-range spatial relations. Perceptual access to each type of relation was varied by using elements of same contrast (easy to access) or mixed contrast (hard to access). The results showed large improvements with age in search rate for long-range targets; search rate for short-range targets was fairly constant across age. This pattern held regardless of whether perceptual access to a target was easy or hard, supporting the hypothesis that different processes are involved in perceptual grouping at these two levels. The results also point to important links between ontogenic and microgenic change in perception (H. Werner, 1948, 1957). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Women and gender in research on work and family stress.

Research on work-related stress has tended to focus on males and to neglect gender as a variable; often, findings from studies of men are incorrectly generalized to women. The failure to "build women in" to conceptual models has impaired our understanding of both work and family role stressors. This article focuses on assumptions, gaps, and biases in the literature; the home, for example, has been viewed as a stress-free sanctuary, whereas workplace stress has been overemphasized and seen as particularly dangerous for women. To better understand the costs and benefits of employment and of multiple roles for women, and the stressfulness of family roles, more attention to the qualitative aspects of roles is needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

600年,在颤悠中屹立——闽西客家土楼之精华:南靖下坂村"东倒西歪"楼

田螺坑下行4km就到了下坂村，村里十二座土楼井然有序地排列在南溪河两岸，我要看的“东倒西歪“楼就在这个村里，学名叫裕昌楼。从外面看，它和正常土楼没什么区别，可是当你踏入它的大门，你就会猛然发现全楼的回廊支撑木立柱左歪右倒，最大的倾角达到了150，似乎稍有大风它就会轰然倒塌。     

Heat transfer from immersed vertical tube in a fluidized bed of group A particles near the transition to the turbulent fluidization flow regime

Experiments were performed in a 0.29 m ID fluidization column to investigate heat transfer from a vertical tube immersed in a bed of 70 μm FCC particles in the range of superficial velocities close to the transition to the turbulent fluidization regime. The results show that the transition is a gradual process and that the changing hydrodynamics affect the heat transfer. The highest heat transfer coefficients were found in the range of superficial gas velocities where the transition to turbulent regime occurred. Radial profiles of heat transfer coefficient were almost flat in the turbulent fluidization regime and changed very little with increasing superficial gas velocity.     

Characterization of gas fluidized beds of group C,A and B particles based on pressure fluctuations

Pressure fluctuation data were obtained with a quick response transducer at a sampling frequency of 100 Hz for periods of 100 s (i.e. 10,000 points) in order to characterize the gas-solid flow behaviour of fluidized beds of six powders. For beds of Geldart group B and group A particles, the occurrence and movement of bubbles caused vigourous pressure fluctuations of relatively large scale and weak dominant frequency. For beds of group C particles, on the other hand, pressure fluctuations were significantly smaller in scale and exhibited large dominant frequencies, with no clear formation of bubbles. The standard deviation of pressure fluctuations was markedly higher for the group A particles than for the group C powders. Group C particles could be characterized by gas voids and channels which exhibit periodic behavior, while beds of group A and B particles behaved in a less periodic manner and were dominated by more random and intensive bubble motion. Chaotic time series analysis was carried out for the six different species of particles. The Hurst exponent demonstrated differences between the three different powder groups. The two-phase character of gas-solids flow was more distinguishable for the group B and A powders than for the group C powders.     

A MODEL TO EXPLAIN COMPOSITION EFFECTS IN SMELT-WATER EXPLOSIONS

A salt bridge model, which takes into account mass transfer of components between the two fluids, was developed and proved successful in interpreting the effects of composition on explosiveness in the smelt-water system. The model is based on the fact that the main smelt constituent, sodium carbonate, is not soluble in water at temperatures approaching the critical point, while certain other constituents are soluble. The soluble substances allow a substantial increase in the critical temperature of the solution, which in turn shifts the range of contact interface temperatures at which spontaneous explosions can occur (between the spontaneous nucleation temperature and the critical temperature of the coolant) to higher values. The model was able to provide an explanation of why sodium chloride, sodium hydroxide, and sodium sulfide act as smelt sensitizers and a semiquantitative definition of the concentration ranges in smelt and in the quench solution where spontaneous explosions are likely     

Comparison of decoupling methods for analyzing pressure fluctuations in gas‐fluidized beds

Two methods of decoupling pressure fluctuations in fluidized beds by using the incoherent part (IOP) of absolute pressure (AP) and differential pressure (DP) fluctuations are evaluated in this study. Analysis is conducted first to demonstrate their similarities, differences, and drawbacks. Then, amplitudes, power spectral densities, mean frequencies, coherence functions, and filtering indices of the IOP of AP and DP fluctuations are calculated and compared based on experimental data from a two‐dimensional fluidized column of FCC particles. Derived bubble sizes are also compared with the sizes of bubbles viewed in the two‐dimensional bed. The results demonstrate the similarity of these two methods in filtering out global compression wave components from absolute pressure fluctuations, especially those generated from oscillations of fluidized particles and gas flow rate fluctuations. However, both methods are imperfect. Neither can filter out all the compression wave components and retain all the useful bubble‐related wave components. Their amplitudes can be used to characterize global bubble property and quality of gas–solids contacting in bed, but they do not give accurate measurement of bubble sizes. © 2009 American Institute of Chemical Engineers AIChE J, 2010