CLUSTERS IN CIRCULATING FLUIDIZED BEDS: KINETIC THEORY APPROACH

The hydrodynamic behavior of particles in circulating fluidized beds has been studied by means of a Boltzmann-like kinetic model. Two main regimes of flow: a homogeneous and a heterogeneous regime have been delimited. In the homogeneous regime, for concentrations below a critical value, the flow consists of upward moving solids. Above the critical concentration, clusters appear. Particles velocity distribution at different values of the solid concentration and the ratio of particles being in clusters to those being in homogeneous flow are calculated for different solid mass fluxes, particle size distributions and superficial gas velocities. Slip factors and the effect of gas radial velocity profile have been predicted. Qualitative agreement with experimental data is obtained.     

水系局部改变对河网水情及水质影响的分析

给出了平原水网地区水系局部改变后用于预测水情变化的水力边界条件的确定方法,以及因水系改变造成的水情、水质变化的计算方法,并将该方法应用于苏州市区水系水质变化分析。得出结论:水系变化必然产生局部水流形态的改变,最终影响污染物的对流扩散输运;局部水域水系改变愈大,模拟边界涵盖的范围应愈大。     

加热方式对挤压冰淇淋品质的影响

在配方和其他工艺条件相同的基础上,通过平行实验,证实了加热方式是影响挤压冰淇淋品质的一个重要因素。     

中国大陆地区沉积盆地的热状况、热历史和生烃史

1. Introduction The thermal regime or thermal background is an important tool for revealing the geodynamic processes of the continental lithosphere and establishing the onset of the generation of hydrocarbons from source rocks in sedimentary basins (Chapm…     

冰蓄冷空调技术的现状及其应用

降低空调能耗,合理利用电能,将冰蓄冷技术用于空调工程是新的趋势。蓄冷空调系统分为水蓄冷系统和冰蓄冷系统,后者又可分为静态蓄冰系统和动态蓄冰系统。它们各有其不同的特卢。冰蓄冷系统目前已开始在我国得到应用,可望把空调节能工作推向一个新高度。     

Tensile cracks in polycrystalline ice under transient creep: Part II — Numerical simulations

This paper discusses predictions of a numerical model presented in the companion paper (Nanthikesan and Shyam Sunder, 1995) to analyze tensile cracks in polycrystalline ice undergoing transient creep. The numerical model is based on the internal state variable constitutive theory of transient creep in ice developed by Shyam Sunder and Wu (1989a,b, 1990). The finite element model uses the boundary layer approach of Rice (1968), in conjunction with a mid-point crack-tip element and reduced integration, to simulate the asymptotic stress and deformation fields in the vicinity of the crack tip, including incompressible creep deformations.

The problem of a stationary, traction-free, tensile (mode I) crack is analyzed to predict the size, shape and time evolution of the creep-dominated fracture process zone surrounding the crack-tip. The numerical simulations quantify the effects of transient creep, material strain hardening, fabric anisotropy, loading rate, temperature, and finite fracture test-specimen boundary on the development of the creep zone. A range of stress-intensity rates from 1 to 100 kPa s⁻¹ and temperatures from −5° to −25°C is considered in the simulations.

The results from a comprehensive numerical simulation study show that: (i) transient creep increases the creep zone size by more than an order of magnitude over that for a power-law creeping material, i.e., about 40 times for the isotropic, equiaxed granular ice tested by Jacka (1984); (ii) material strain hardening significantly affects the creep zone size, i.e., the creep zone for the transversely-isotropic columnar-grained ice tested by Sinha (1978), with the crack loaded in the plane of isotropy, is about 4 times smaller than that for the granular isotropic ice; (iii) fabric anisotropy increases the size of the creep zone by a factor of at least two for cracks in the transversely-isotropic, columnar-grained ice loaded in the plane of isotropy; (iv) the Riedel and Rice (1980) equation, which was derived for an isotropic power-law creeping material subjected to a suddenly applied constant stress-intensity, overestimates the creep zone size by a factor of 4.2 for a constant stress-intensity rate loading; and (v) as the crack size increases, linear elastic fracture mechanics becomes increasingly applicable at lower loading rates and higher temperatures.     

层拉平方法在沉积前古地貌恢复中的应用——以济阳坳陷东营三角洲发育区为例

层拉平方法是近年来在层序地层学理论和物探新技术基础上发展起来的一种古地貌恢复方法。在陆相湖盆中进行古地貌恢复时,本文分析认为该方法具有一定的适用范围,首次提出只有在具有斜交前积结构的地区,该方法才能有最好的应用效果。本文利用该方法在东营凹陷东营三角洲发育区成功进行了古地貌恢复,较好的解决了该区沉积相研究中存在的一些矛盾问题,为准确分析该区沉积相奠定了基础。     

Comparison of buoyancy and surface tension in a square cavity

Laminar natural convection induced by free surface temperature gradient has been investigated numerically. Buoyancy effect and surface tension effect were made to oppose against each other. For fluid of unit Prandtl number and cavity of unit aspect ratio, the flow field was examined to determine the relative importance of surface tension force and buoyancy force. The flow patterns of each regime are: free surface-concentrated streamlines for surface tension flows, opposite direction circulation for buoyancy driven flows, and surface tension cell above with buoyancy driven cell below for mixed flows. The borderlines of each flow regime were obtained by interpolation and the flow regime map was obtained.     

The influence of oil viscosity and refrigerant quality on evaporator performance

The presence of oil in an evaporator degrades performance by reducing evaporator heat pick-up and by increasing the evaporator pressure drops. It can be demonstrated that there is an optimum refrigerant mass flow rate for a given refrigerant-oil combination and oil concentration. Also, oil viscosity has an effect on the evaporator performance at low oil concentrations. Finally, it is suggested that low viscosity oil be used at low oil concentrations and high viscosity oil at high oil concentrations.