Heat transfer to immersed surfaces in gas-fluidized beds of large particles and powder characterization

A particle classification scheme is proposed for fluidized beds by considering simultaneously the hydrodynamic and thermal properties. The powder characterization is obtained by considering Archimedes number together with Reynolds number at minimum fluidization. The powders are classified in three groups and the validity of the scheme is demonstrated by considering heat transfer data from fluidized beds of sands (d_p = 0.794 and 1.225 mm) and fire clay (3.0 mm) at ambient temperature and pressure in conjunction with heat transfer correlations and models developed for ‘large-particles’.     

Fire performance of external wall claddings under a performance-based building code

New Zealand Building Code Performance requirements relating to fire performance of external walls are considered and methods of evaluating the potential for vertical fire spread are discussed. Classifying external wall claddings on the basis of performance in the ‘combustibility’ test has proved overly restrictive where some external cladding materials are concerned. Performance criteria based on heat relase or ‘degree of combustibility’ are proposed and they seem to provide a better classification scheme for external wall cladding materials. Heat release test data for ten different external wall cladding materials are presented.     

Preparation of extruded melt‐mixed polypropylene/montmorillonite nanocomposites with inline monitoring

This article advances the use of an inline optical detector to monitor the disaggregation of the montmorillonite (MMT) clay tactoids during the preparation of polypropylene (PP)/MMT nanocomposites via polymer melt compounding. During the exfoliation of the tactoids their size are reduced below the minimum particle size to produce light extinction and so, the signal of the inline detector reduces as the nanosize composite is formed. The measurement is done at the transient state with the MMT clay added as a pulse with constant weight into the PP extrusion melt flow and followed by the optical detector. The data comes out as the common residence time distribution curves having its maximum intensity related to the tactoids average particle size, keeping all other variables constants. The light extinction was measured for composites with different clays (Cloisite® 15A, 30B, Na⁺, and Sintered 20A) using the same PP grafted with maleic anhydride compatibilizer. The dissaglomeration/exfoliation efficiency increases as: ‘‘Sintered 20A’’ < ‘‘Na+ clay’’ < ‘‘organo‐modified clay’’ < ‘‘organo‐modified clay + compatibilizer’’. The best result is obtained using Cloisite® 15A and Cloisite® 20A following the expected reduction of the particle size obtained during a nanocomposite melt processing. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Coiled flow inverter as a heat exchanger

In the present work attempts are made to investigate the hydrodynamics and heat-transfer characteristics of a coiled flow inverter (CFI) as heat exchanger at the pilot plant scale. The experiments are carried out in counter-current mode operation with hot fluid in the tube side and cold fluid in the shell side. Experimental study is made over a range of Reynolds numbers from 1000 to 16,000 using water in the tube side of the heat exchanger. The shell side fluids used are either cooling water or ambient air. The coiled flow inverter is made up of coils and 90^° bends and inserted in a closed shell. The shell side is fitted with three types of baffles to provide high turbulence and avoid channeling in the shell side. The bulk mean temperatures at various downstream positions are reported for different flow rate on tube side, as well as the heat transfer efficiency of the heat exchanger is also reported. Pressure drop and overall heat-transfer coefficient is calculated at various tube and shell side process conditions. The outer and inner heat-transfer coefficients are determined using Wilson plot technique. The results show that at low Reynolds numbers, heat-transfer is 25% higher as compared to coiled tubes. At high Reynolds numbers, the configuration has less influence on heat transfer. New empirical correlations are developed for hydrodynamic and heat-transfer predictions in the coiled flow inverter.     

The use of CVD-diamond for heavy-ion detection

The suitability of CVD-diamond detectors is investigated for applications in heavy-ion accelerator facilities with high intensity beams. Various diamond films of ‘optical’ and ‘electronic grade’ used and unpolished (as grown) are tested with different ions from α-particles (²⁴¹Am-source) up to the heaviest ions like ²⁰⁸Pb and ²³⁸U. The diamond signals are processed in a single-particle mode with current sensitive low-noise broadband electronics. An intrinsic time resolution of σ_i(ΔT)=29 ps is achieved using detectors of ‘optical grade’ with a thickness of 100 μm. The time resolution improves for thicker samples and for higher electric field applied to the detector. Determined by the strip capacitance and the electronics used, a single-particle counting rate capability >10⁸ ions/s is obtained. The charge collected from different particles increases linearly with the energy loss of the particle and non-linearly with the detector thickness. The pulse-height resolution depends strongly on the material texture and on the irradiation state of the sample and weakly on the ionisation density produced by the particle. ‘Priming’ is observed up to a fluence of 10¹⁰ ions/cm². The homogeneity over the detector area increases significantly. The charge-collection efficiency improves by a factor of 2 and the pulse-height resolution significantly by a factor of 5. The bandwidth of available electronics limits the results obtained at present. Nevertheless, the selection of data presented demonstrates an excellent suitability of CVD diamond for a variety of heavy-ion applications.     

Partikelgrößenanalyse von dispersen farbstoffsystemen,II. Photonen-korrelations-spektroskopie an latexsuspensionen und ‚modellblindfärbungen’︁ von polyethylenterephthalat-fasern

As a first step to analyse the particle size distribution of dyebaths, photoncorrelation-spectroscopy is used to determine the particle sizes of latex suspensions. To simulate the procedure of dyeing polyester fibres with disperse dyes, latex suspensions are used as model for dyes. The ‘dyeing’ is carried out at various temperatures and the resulting particle size distribution of the ‘dyebath’ is measured using photon-correlation-spectroscopy.     

Investigations on twenty Australian sewage sludges — their evaluation by means of chemical analysis

To evaluate twenty sludges from different places in Australia for disposal on arable land, these sludges were extracted with (a) HNO₃ to determine the ‘total’ contents of some heavy metals and other elements; (b) a solution containing DTPA to determine contents of ‘available’ heavy metals; and (c) with a CaCl₂-solution to determine contents of water-soluble heavy metals and some other elements. Measurements of the pH of the sludges, their electrolytic conductivity, NaHCO₃-extractable P, water-extractable Cl, and contents of ash and organic carbon were also made. The HNO₃-extractable Cd, Cu, Mn, Ni, Pb, and Zn in the sludges were compared with those in sludges from three other countries. High correlations between HNO₃-extractable and DTPA-extractable metals were found in the Australian sludges; therefore, the HNO₃ is equally good as the DTPA as an extractant of heavy metals in sewage sludges. The correlations between HNO₃- and CaCl₂-extractable Cd, Cu, Mn, and Zn were not significant. ‘Young’ and ‘aged’ sludges from the same treatment plants consistently differed in their Na and Cl contents, which were lower in the ‘aged’ sludges. A wheat experiment treated with high application rates of a saline and metalliferous sludge showed that the balance of nutrients and the amount of soluble salts in a sewage sludge are of greater direct importance to the growth of plants than the heavy metal content of that sludge.     

Triboelectric charging of powders: A review

Particles are often electrostatically charged by frictional contact during powder-handling operations. This phenomenon is called ‘triboelectric charging’ or ‘contact electrification’. The charged particles cause problems such as particle deposition and adhesion. In addition, if particles are excessively charged, an electrostatic discharge may occur, which can pose a risk of fire and explosion hazards; thus, to mitigate the adverse effects, it is important to elucidate the underlying triboelectric charging mechanisms. The electrostatics is, on the other hand, very useful in a number of applications that have been developed using the principles. In this review, the basic concepts and theories of charge transfer between solid surfaces are summarized, and chemical factors depending on materials and environmental effects are described. To theoretically analyze the process of particle charging, relevant models are discussed. Using the models, particle charging by repeated impacts on a wall is formulated. To experimentally evaluate particle charging, measurement and characterization methods are outlined. Furthermore, important applications and computer simulations are described.     

Adduct Formation with Metal Chelates Involved in Liquid-Liquid Extraction

Abstract

The factors that influence the formation of metal chelate adducts which are of importance in liquid-liquid extraction are evaluated and correlations between the structures and properties of these adducts discussed. A scheme for the classification of metal chelate adducts is suggested on the basis of available experimental data.     

A model for the circulating fluidized bed

A model for the hydrodynamics of circulating fluidized beds is proposed. The model combines existing entrainment and bed expansion correlations with a system pressure balance. Starting from a knowledge of the powder size distribution, particle density, gas velocity, equipment geometry and solids inventory, the variation of voidage within the riser is predicted, together with distribution of solids between the riser and supply hopper (or ‘slow’ bed). Qualitative trends with gas velocity and solid circulation flux show good agreement with experiment, but better quantitative agreement must await the development of an improved correlation for entrainment.     

Particle-to-fluid heat and mass transfer in dense systems of fine particles

A new model is proposed for predicting the anomalously low heat and mass transfer coefficients that have been derived from experiments in packed and fluidized beds of fine particles or fine wire packs at low Reynolds number. No arguments of flow channeling, particle agglomeration or axial conduction are required. The mathematical model consists of treating stagnant molecular diffusion from a multiple particle system. Instead of applying the boundary condition for the ‘sink’ infinitely far away from the particle surface it is expressed at the position where the concentration gradient vanishes symmetrically between particles. One free parameter arises in the model, and it is chosen by requiring the solution to match the classical boundary layer theory when the particles are infintely far apart. The predictions of the model agree well with available experimental data.     

Low-temperature oxidation of a bituminous coal. Infrared spectroscopic study of samples from a coal pile

A Fourier-Transform i.r. spectroscopic study has been made of coal samples from a test pile of a bituminous coal which was subject to spontaneous heating. Samples taken from the pile at various depths (various temperatures) and at intervals of 3 months were fractionated into four fractions with different particle sizes so as to distinguish ‘macropore’ oxidation effects from ‘micropore’ oxidation effects. The spectra show that initially a carboxylic acid-type compound is formed. This compound seems to decompose in a later stage of the oxidation. Analysis of the results suggests that macropore oxidation (a diffusion-limited process across the macroscopic interface of the particle) predominates. If so, removal of a small proportion of fines with a relatively large, specific macroscopic surface area would result in a reduction of the spontaneous heating of the pile.     

搅拌槽中高粘度液体的传热研究

本文应用内外螺带-锚、双螺带-锚及螺带-螺旋轴-锚三种组合桨,研究了牛顿流体及假塑性流体,在层流域及过渡流域的传热关联式。分别获得了三种组合桨的传热膜系数关联式。为了得到三种组合桨的传热膜系数的通用关联式,本文采用了传热膜系数与单位质量功之间的关联。     

气-液-固三相逆流化床热量传递研究

在内径0.152 m,高2.5 m的气-液-固三相逆流化床中系统研究了热量传递特性特性。获得了气体和液体速度及聚乙烯和聚丙烯颗粒密度对内置加热器与床层间热量传递系数的影响规律。研究结果表明密度相对高的聚乙烯颗粒的逆流化床的热量传递系数比密度相对低的聚丙烯颗粒的逆流化床的热量传递系数大;随着气体速度的增加,热量传递系数增加。然而,随着液体速度增加,热量传递系数具有最大值。在热量传递系数达到最大值时对应的液体速度随着颗粒密度或气体速度的增加而降低。     

On the correlation of minimum porosity with particle size distribution

It has long been recognised that the major factors which influence the density of cohesionless material are the type of distribution of particle size, and particle shape. However, the difficulty of measuring particle shape and of expressing a particle size distribution comprehensively has proved a stumbling block to the determination of a successful correlation with porosity. None of the correlations so far has yielded an empirical relationship which can be employed with confidence to a wide range of types of particle size distribution.This paper examines some of the difficulties which are encountered with such correlations when attempting to describe the particle size distribution by Gaussian measures, and develops a new method of expression, by a single ‘offset‘ value, of a particle size distribution. A good empirical relationship is found between minimum porosity and this value, having taken due account of particle shape. It is suggested that the method will give engineers greater appreciation of the grading curve of cohesionless materials.     

Physical Forms of Dyes

Presented to the Scottish Region at a one–day conference entitled ‘A Profile of the 80s’, held at the Eurocrest Hotel, Glasgow, on 23 May 1980. The development of new physical forms of dyes has become increasingly important over the last decade. The need for ease of handling and dispensing, together with health and safety requirements and advances in application methods, has led to significant improvements in the physical form of many dyes that are available on the market. This has resulted in the introduction of granular forms of dyes in place of powders and stable liquids to replace pastes. Improved wet–milling techniques for insoluble dyes have enabled stable liquid versions of vat and disperse dyes of controlled ultimate particle size to be made available. The additives necessary for the different physical forms are discussed and the ideal properties required for the next decade are outlined. The physical forms of dyes now available can help to establish new standards of accuracy in dispensing and industrial hygiene wherever they are used.     

Publication Sponsored by the Society's Scarce Resources Committee – III Potential Energy Savings in Dyeing and Finishing

In its Industrial Energy Thrift Scheme, the Department of Industry is publishing a series of reports on energy use and conservation in the different sectors of the manufacturing industry. Report No. 20*, ‘Energy Use in the Textile Finishing Sector’, published in August 1980, is based on work carried out under the scheme by Shirley Institute. Although the Report is readily available from the Department at Ashdown House, 123 Victoria Street, London, SW1E 6RB, and it is necessary to read the full account to get the maximum benefit, the Society's Scarce Resources Committee felt that an extended summary should be prepared and published in the Journal.     

Mixing of randomly moving particles in liquid—solid fluidized beds

The deterministic diffusion equation of the Fickian type has been widely employed in modeling solids mixing in fluidized beds. In this work, a stochastic or statistical model has been proposed for the solids mixing in a liquid—solid fluidized bed of relatively large particles. Specifically, the particle diffusivity under the steady fluidized state has been derived by combining the well-known ‘Ornstein-Uhlenbeck’ equation of stochastic processes and the so-called partition function of particle velocities. The values of particle diffusivity calculated from the model have been shown to agree well with the available experimental data. Furthermore, it has been shown that the solids-mixing process in the bed can be related to the time-dependent nature of particle motion.     

From Riemann's metric to the graph metric,or applying Occam's razor to entanglements

In 1854 Riemann prophesied: ‘Either the reality underlying space must form a discrete manifold, or the reason for measurability must be sought externally, through forces acting thereon to constrain it.’ Matter is in a graph-like state if its particle coordinates have been or are being randomized in all dimensions but one, by Brownian motions induced by random forces which maintain equipartition of kinetic energy. The graph-like particle generates a graph metric, which is one-dimensional and discrete. Physical theories of amorphous polymers generally evolve intuitively by embedding the particles in a three-dimensional continuum regarded as physically real, or in a configuration space regarded as an auxiliary. After integration over random coordinates, it appears that the end results no longer depend on the embedding space at all. The historical theories of amorphous polymer systems by Hermans and Kramers, Debye, Zimm and Stockmayer, Rouse, Fixman and some others may have the added advantage of demonstrating how the Riemann metric degenerates to the non-trivial graph-metric. The analysis of random networks, embedded in a three dimensional space with all the complications arising from chain entanglements, generally seems to result in small semi-empirical corrections which graph-like-state theories could readily develop without such complications. A programme for establishing a new axiomatic basis is suggested along these lines. The benefits would include not only a clearer relation between strikingly different theories and between their geometric and physical ingredients, but substantially simpler calculations and algorithms. Simplifications, especially some inspired by the achievements of Chompff and of Forsman, are briefly sketched. An analogy is drawn with the early programme culminating in the proof that, by virtue of their metric structures, the continum and discrete (matrix) formulations of quantum theory are isomorphic. It is suggested that the operator calculus of Rota, especially as recently perfected in his work with Roman, should be helpful in making explicit the isomorphism sought for the graph-like state.     

Fire-gas hazards in rail traffic

A review is given of the various national requirements and test procedures concerning testing and classification of smoke produced in the case of a fire in rolling stock. A comparison of the various test methods is made using the relevant available literature. The toxic potency philosophy of SC3 ‘Toxic Hazard in Fire’ from ISO TC92 is used to provide a concept for assessing the possible smoke hazard in the case of a fire.