DEPOSITION IN FRACTURES

Fractures are relatively planar discontinuities in rocks induced by the huge internal stresses which are created by the slow but constant motions of the underground masses. Deposition of a single solute in a single fracture is addressed in the limit where the geometrical changes are very slow compared to the average fluid velocity. The deposition fluxes are calculated by means of a finite-difference scheme which is much more efficient than random walks. Examples of deterministic fractures, random but uncorreiated fractures, Gaussian and self-affine fractures are studied for four different values of the Peclet and the Peclet-Damkohler numbers. Some general trends are discussed.     

颗粒污泥的生物相和最佳状态的初步研究

本文对厌氧污泥颗粒化各个阶段的消化液中的优势菌和颗粒污泥的内部菌体进行了初步的研究,并通过筛选出不同粒径的颗粒污泥和选用不同的环境温度,对颗粒污泥的此活性变化情况也进行了探讨。结果发现污泥颗粒化过程中菌体的变化趋势是以球菌占优势,逐步过渡到杆菌占优势,并且从比活性和沉降性能考虑,有必要对颗粒污泥最佳直径的控制和确定问题进行研究。     

搅拌槽内温度场分布的实验研究

在对称装有四组垂直加热列管、直径为500mm的搅拌槽中使用CBY桨进行搅拌,以甘油为工作物料,让液晶粒子均匀分散在某中,然后采用LC测温技术测量搅拌槽内温度场的分布。分别研究了搅拌槽中轴向、径向的温度分布随时间的变化以及同一轴截面的温度分布随搅拌转速不同而变化的情况。     

AN EXPERIMENTAL STUDY OF RAYLEIGH-BENARD CONVECTION IN LIQUID TIN

The onset and interaction of the thermocapillary and buoyancy driven flows in molten tin heated from below are studied experimentally under UHV conditions in a Rayleigh-Benard geometry by using the Schmidt-Milverton technique. The experimentally determined critical parameters agree within experimental error with those predicted by the linear stability theory of Nield (1964). The observed temperature drop across a layer of molten tin 0.582 cm thick with an aspect ratio of 11.8 was 1.56 ± 0.35°C at the onset of convection.     

渐缩渐扩管内径向颗粒浓度不均匀性的实验研究

流动结构的不均匀性是气固两相流反应器的主要弊端之一。采用变截面反应器，使沿流向速度不断变化，从而达到流场均匀的目的，实验结果表明，变截面反应器内流场均匀性得到很大改善，颗粒浓度趋于均匀。     

AN EXPERIMENTAL STUDY OF LIQUID-PARTICLE FLOW IN CIRCULATING FLUIDIZED BED

A liquid-solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant and between the conventional liquid fluidized bed and the dilute phase liquid transport regimes. LSCFB has potential applications in the fields of food processing, biochemical processing, and petrochemical and metallurgical processing. It is well known that the flow characteristics in a liquid-solid circulating fluidized bed are different from those of a conventional liquid-solid fluidized bed. The limited studies available in literature do not provide complete understanding of the flow structure in this typical regime.

In the present work, experiments were carried out in a 0.0762 m ID and 3 m height laboratory-scale liquid-solid circulating fluidized bed apparatus by using various solid particles and tap water as fluidizing medium. In the experimental setup, two distributors (specially designed) were used to monitor solid circulation rate in the riser. The effects of operating parameters, i.e., primary liquid flow rate in the riser (Up), solid circulation rate (G_s), and particle diameter (dp), were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate average solid holdup in the riser, and it was compared with present experimental and available data in the literature. They agree well with a maximum root-mean-square deviation of 7.83%.     

MASS TRANSFER FROM SOLID PARTICLES TO FLUID IN GRANULAR BED

Mass transfer from assemblage of irregularly shaped particles to fluid was analysed using a combination of “cell” and “channel” concepts. The theoretical analysis predicts that blending active grains with inert spheres will result in an enhancement of the mass transfer due to a decrease of the overlapping of the neighbour particles and to a change of the bed geometry. The comparison between the derived relationship and available literature and our own experimental data shows a reasonably good agreement.     

转笼式悬浮填料生物反应器启动性能试验

为了研究转茏式悬浮填料生物反应器的启动性能,简化其启动工艺,进行了常温和变温时的反应器的自然挂膜启动实验。实验结果表明,转笼式悬浮填料生物反应器构造的特定微环境有利于自然挂膜,启动比传统生物转盘快10d以上：经过启动参数优化,在水流量为2m^3／h,曝气量为3．6m^3／h、转笼转速为1．5r／min时,启动效果较好。     

AN EXPERIMENTAL STUDY OF PARTICLE FLOW VELOCITIES IN SOLID-LIQUID FOOD MIXTURES

The design of equipment to sterilise solid-liquid food mixtures continuously requires that the flow properties of such mixtures be understood. Little information is available on food flows, which can consist of high solids fractions of particles of a range of densities in non-Newtonian and viscous liquids. A metal detection system which can log two types of particle in the same experiment has been constructed and used in a loop flow rig to study flows of single particles and carrot-water mixtures. Results can be correlated using the particle Froude number; some preliminary analysis is presented to suggest that data can be correlated against 1/Fr_p. The effect of solids fraction on particle flow velocity has been investigated; greatest variations in the particle velocity appear for stratified flows for solids fractions between 10-20%.     

AN EXPERIMENTAL STUDY OF MELTING VERTICAL ICE CYLINDERS IN COLD WATER

Short vertical ice cylinders were melted in quiescent ambient cold fresh water to visualize the melting and the resulting convective motions. Melting rates and heat transfer parameters were also determined. The cylinder penetrated the water surface, to model the melting of floating surface ice. Melting experiments over the ambient medium temperature range, t ∞, from 2 to 7°C covered the whole gamut of differing and complicated effects found to be associated with the occurance of a density extremum. At t ∞ = 2°C, simple general upflow is found, at t ∞ = 7°C simple downflow. Between these two limits, three different and much more complicated regimes arose. Buoyancy force reversal arises first, with increasing t ∞, at about 4°C. Then local flow reversal follows, in the range to about 5.3°C. Finally a convective inversion, that is, an average flow reversal, occurs. A tremendous variation of flow pattern occurs over a range of only a few degrees. Melting rates become very low in the region of inversion. This was also found in previous measurements with the simpler flows which occur adjacent to thin and completely submerged vertical ice slabs. However, many flow and transport effects were quite different, with a flat bottom surface and with the ice-water-air interface. Three flows of different configurations interact. It appears that the realistic modelling of the melting of multidimensional pieces of surface ice will require a composite of the different characteristics of these multiple regions.     

AN EXPERIMENTAL STUDY OF MELTING VERTICAL ICE CYLINDERS IN COLD WATER

Short vertical ice cylinders were melted in quiescent ambient cold fresh water to visualize the melting and the resulting convective motions. Melting rates and heat transfer parameters were also determined. The cylinder penetrated the water surface, to model the melting of floating surface ice. Melting experiments over the ambient medium temperature range, t ∞, from 2 to 7°C covered the whole gamut of differing and complicated effects found to be associated with the occurance of a density extremum. At t ∞ = 2°C, simple general upflow is found, at t ∞ = 7°C simple downflow. Between these two limits, three different and much more complicated regimes arose. Buoyancy force reversal arises first, with increasing t ∞, at about 4°C. Then local flow reversal follows, in the range to about 5.3°C. Finally a convective inversion, that is, an average flow reversal, occurs. A tremendous variation of flow pattern occurs over a range of only a few degrees. Melting rates become very low in the region of inversion. This was also found in previous measurements with the simpler flows which occur adjacent to thin and completely submerged vertical ice slabs. However, many flow and transport effects were quite different, with a flat bottom surface and with the ice-water-air interface. Three flows of different configurations interact. It appears that the realistic modelling of the melting of multidimensional pieces of surface ice will require a composite of the different characteristics of these multiple regions.     

AN EXPERIMENTAL STUDY OF CHEMICAL WAVE PROPAGATION

A study was made of chemical waves which were propagated through the coupling of diffusion and reaction in an isothermal multicomponent system. The waves traveled down small-bore tubing the end of which was attached to a stirred tank reactor in which an oscillating reaction was occurring. The stirred tank thus functioned as a wave source whose frequency could be controlled. Frequency and speed were measured in the tube. At a fixed position the wavelength (the quotient of speed by frequency) decreased with increasing frequency while the speed increased slightly. Neither frequency, speed, nor wavelength changed greatly as a wave propagated down the tube.     

AN EXPERIMENTAL STUDY OF POLYMER DIFFUSION IN CONCENTRATED SOLUTION: IMPLICATIONS FOR DIFFUSION IN POLYMERIZATION

The Trommsdorf or gel effect in free radical polymerization is due to the fact that the termination reaction becomes strongly diffusion controlled above a critical concentration associated with the onset of molecular entanglements. Therefore, an understanding of polymer self-diffusion in entangled systems becomes essential to understanding the Trommsdorf effect. Our group has previously proposed a molecular model for the gel effect which uses a specific theory for polymer diffusion (reptution). The present work represents an experimental attack on the same problem Experimental studies of polymer self-diffusion in entangled systems are scarce. Quasielastic light scattering from ternary systems composed of solvent(l)-polymer(2)-polymer(3), in which species (3) is isorefractive to the solvent (i.e. 0n/0c ₃ = 0), offers an attractive way to study the tracer diffusion coefficient of species (2) in a binary mixture of composition c ₃. In regimes of low momentum transfer (qR _G < 1,) where q is the scattered wave vector and R _G is the polymer radius of gyration, we have shown that the correlation function of the scattered electric field should decay with a single exponential decay time, given by (D₂₂ q ²)^?1 where D ₂₂(c ₂, c ₃) is the main ternary diffusion coefficient of component (2). Extrapolation to zero concentration of 2) at fixed concentration of (3) yields the tracer diffusion coefficient of (2) in the binary mixture of (1) and (3). The systems toluene(l)-polystyrene(2)-polymethylmethacrylate(3) (0n/0c ₃ ≈ 0.007 at 25°C) and toluene(l)-polystyrene(2)-polyvinylmethylether (3) (0n/0c ₃ ≈ 0.012 at 60°C) very nearly satisfy the above criteria. In both systems, we have found that the tracer diffusion coefficient of the polystyrene decreases with increasing concentration of the isorefractive polymer. Further studies have focused upon the dependence of the tracer diffusion coefficient upon polystyrene molecular weight, and upon the effect of incomplete index matching.     

MULTIPHASE HYDRODYNAMICS AND SOLID-LIQUID MASS TRANSPORT IN AN EXTERNAL-LOOP AIRLIFT REACTOR—A COMPARATIVE STUDY

The solid-solid mass transfer performance of an external-loop airlift reactor was measured by dissolution of benzoic acid coated on nylon-6 particles, and the hydrodynamics of the gas-liquid-solid multiphase system in the airlift reactor were investigated. The solid-liquid system was designed to simulate the micro-carrier culture of animal cells, and some typical suspensions of immobilized enzyme particles.

The solid-liquid mass transfer coefficient remained constant below a superficial air velocity of 0.04 ms^-1 for the particles examined, but increased rapidly with further increase in gas velocity. Solids loading (0.3-3.5% w/w) did not affect the mass transfer coefficient in turbulent flow.

The mass transfer coefficient was correlated with energy dissipation rate in the airlift reactor. The mass transfer coefficient in stirred vessels, bubble columns, fluidized beds, and airlift reactors was compared.

Over an energy dissipation Reynolds number of 4-400, the solid-liquid mass transfer coefficient in the airlift device was comparable to that obtainable in fluidized beds. The performance of the airlift was distinctly superior to that of bubble columns and stirred tanks.     

AN EXPERIMENTAL STUDY OF GAS HOLDUP IN TWO-PHASE BUBBLE COLUMNS WITH FOAMING LIQUIDS

Gas-liquid upward flow experiments have been performed in two bubble columns of different diameters (0.10 and 0.29 m,) using air as gas phase and several liquids: water, aqueous solutions of ethanol and glycerine, kerosene, and a solution of a surfactant in kerosene. The main goal of the study is the analysis of foaming systems, including the comparison of their behavior with respect to non-foaming systems. The gas holdup was determined experimentally as a function of the gas and liquid superficial velocities in bubbling, churn-turbulent and foaming regimes. It was found that, for foaming systems, semi-batch operation enhances foam formation, yielding higher holdups than those obtained in continuous operation at very low liquid velocities. Opposite to what is observed in non-foaming systems, the liquid superficial velocity affects the gas holdup appreciably in foaming systems. An increase in column diameter results in a decrease in gas holdup for all the systems studied. In aqueous foaming systems, this trend is more drastic since foam is inhibited as the column diameter increases.     

AN EXPERIMENTAL STUDY OF DISPERSED LIQUID/LIQUID TWO-PHASE UPFLOW IN A PIPE

This paper presents experimental data for dispersed liquid/liquid upflows. Water was the continuous phase and mineral oil was the dispersed droplet phase. For this flow regime reduced gravity bubbly flow phenomena was simulated because the mineral oil and water had almost the same density. The mean velocity and turbulence fields, the size distributions of the oil droplets, the volume fraction, and interfacial area density distribution were measured using fiber optic Laser Doppler Anemometer (LDA) and phase Doppler Anemometer (PDA) systems. Significantly, the results presented in this paper are similar to those for bubbly air/water flows in microgravity conditions (Kamp el at., 1995).     

EXPERIMENTAL STUDIES OF NUCLEATION PHENOMENA WITHIN THERMAL BOUNDARY LAYERS—INFLUENCE ON CHEMICAL VAPOR DEPOSITION RATE PROCESSES

In carrying out partial vapor condensations using actively cooled surfaces it is known that 'mist' formation can occur within thermal boundary layers (Rosner and Epstein, 1968), dramatically modifying total deposition fluxes. Using a combination of flash-evaporation (Rosner and Liang, 1986) and laser probing techniques, we report new experimental results on binary alkali salt (K₂SO₄ + Na₂SO₄) deposition from combustion gases showing that the deposition rate of potassium sulfate first increases with the addition of sodium sulfate until the concentration of Na₂SO₄ reaches a (target surface temperature dependent) 'threshold' value. Further increases in the concentration of Na₂SO₄ dramatically decrease the total deposition rate of K₂SO₄, implying that potassium sulfate-containing microdroplets are formed within the thermal boundary layer, which, despite their thermophoretic drift toward the target, are not collected as effectively as the 'parent' K₂SO₄-vapor species. Laser light scattering measurements clearly reveal that suspended particles exist near the deposition surface under these conditions. Our experimental results on mass transfer rate and light scattering are consistent with those predicted using laminar boundary layer theory (Castillo and Rosner, 1989b) coupling both binary salt vapor deposition with particle vapor scavenging and deposition. Comparisons of our observed mist onset conditions (implying critical supersaturations near unity) with those expected using homogeneous nucleation theory suggest that the binary alkali sulfate mist nucleation mechanism is, instead, heterogeneous, even in our relatively 'clean' combustion products. Because of the; well-known vapor pressure reduction phenomenon associated here with the formation of non-ideal solutions, binary systems are shown to provide convenient 'vehicles' to investigate BL mist formation onset conditions and CVD-rate consequences without requiring the more extreme surface coolings characteristic of unary condensible vapor systems. An understanding of this dramatic phenomenon, obtained via such laboratory experiments and calculations, will allow its inclusion in future deposition rate calculations of engineering importance.     

AN EXPERIMENTAL STUDY OF AN INCLINED BUOYANT PLANE TURBULENT AIR JET

An experimental study of the effects of buoyancy forces resulting from temperature differences on the mean flow and turbulence characteristics of a plane turbulent jet discharged at an angle to the horizontal has been undertaken. The jets were generated by discharging air through a rounded nozzle which was 10 mm wide by 580 mm long. The discharged air could be heated and tests were undertaken with discharge temperatures of 20° and 40°C above the ambient air temperature at a single nozzle discharge velocity which gave a discharge Reynolds number of approximately 1700. Tests were undertaken with angles of jet discharge to the horizontal of 0°, 30°, 60° and 90°. Velocity and temperature measurements were undertaken using hot wire anemometers. Measurements of the mean velocity and temperature, the turbulence normal and shear stresses, the temperature fluctuation intensity and the two components of the turbulence heat flux were obtained. Profiles of these quantities were measured at six equally spaced positions to a distance of approximately 60 nozzle widths from the discharge plane. Measurements at much more closely spaced intervals were also taken along the jet “centre-line”, this being defined as the locus of the point of maximum velocity in the jet.