Meßmethoden konvektiver Stoffübertragung

Methods of measuring convective mass transfer . The principal methods of measuring convective transfer of momentum, heat, and mass are surveyed on the basis of the three-fold analogy existing between the transfer of momentum, heat, and mass. The most simple and most sensitive method is the mass transfer technique based on the principle of absorption with chemical reaction and coupled colour reaction. It is shown by selected examples that this measuring technique is already developed to the point where it serves adequately for the solution of most complex problems met with in practice. It is distinguished by its high accuracy of measurement, simple application, high local resolution, and its utilizability both for developable as well as for undevelopable surfaces. By way of the local mass transfer observable as colour-intensity distribution it also affords a simple and illustrative means of making flow processes on solid surfaces visible. The quantitative evaluation is accomplished by reflectance photometry; quantitative image processing methods are available for complex distributions. In addition, it is shown that the mass transfer technique is also suitable for practical utilization as a method for measuring turbulence. The measuring principle is based on the extremely high dependence of the length of transitional separation bubbles in the nose section of flat plates of finite thickness in longitudinal flow on the turbulence intensity.     

Neuere wäßrige PUR-Systeme

A brief survey is given of results of reactions between isocyanate prepolymers and water. Then a variety of improvements concerning the preparation of aqueous dispersions of ionic and nonionic polyurethanes are discussed, namely: Advances in the solvent dispersion and melt dispersion processes, electrolyte and freeze/thawstable dispersions, direct dispersions of solid polyurethanes, and the “ketimine” and ?ketanzine”? processes. The solvent dispersion process is discussed in detail. New products have recently been developed for high quality coatings of textile, leather and flexible PVC as well as special adhesives. New applications for aqueous PUR dispersions are thought to be glass fiber sizing and cathodic dip coating (car bodies). New applications have also been found for emulsfield polyisocyanates and prepolymers as well as for aqueous PUR solutions. Other aqueous systems include micro capsule suspensions, support casts, as well as hydrophilic foams. Interest rigid foams can be made from W/O emulsions which contain inorganic substart dispersed or dissolved in the aqueous phase.     

LIGHT BACKSCATTERING AS A TECHNIQUE TO MEASURE SOLIDS PARTICLE SIZE AND CONCENTRATION IN SUSPENSION

Measurement of high concentrations of solids in a suspension and measurement of large particle sizes (>1 mm) in suspensions often present large problems. In this paper a new measuring technique is described, based on light backscattering. This technique may be used for monitoring a process in which rapid and large changes in particle size occur, or for controlling processes with large concentrations of small particles.

Theoretical backgrounds of the method are also presented. The measuring apparatus is described and some results are given to illustrate its possibilities.     

Über die Analyse von Propylenoxyd-/Äthylenoxyd-Blockmischpolymerisaten mittels Infrarot-Spektroskopie

Analysis of Propylene Oxide / Ethylene Oxide Mixed Block Polymers by Infrared Spectroscopy For the determination of the ratio propylene oxide / ethylene oxide in the corresponding mixed block polymer, the following analytical methods are described: 1. ?Infrared fundamental method”?, 2. ?Infrared overtone method”?, 3. Chemical method according to. A. Kotzschmar. The methods are compared with one another. The ?infrared fundamental method”? was found uptil now to be most suitable. The above mentioned infrared methods are currently discussed on an international level. Furthermore, methods for the determination of molecular weight of these products are dealt with.     

Prozeßentwicklung: Von der Exergieanalyse bis zur EDV-gestützten Optimierung

Process development: From exergy analysis to computer-aided optimisation. In processes in which chemical compositions or states are altered, limiting case analyses based on the first and second laws of thermodynamics are often of use during preliminary process analyses. Since the introduction of computers for process calculations exergy analyses can be carried out in a simple way and weak points in initial designs in the sense of the second law conveniently located. It is also possible to use exergy analyses to make product predictions if transferable practical exergy losses are available from past experience. In low temperature and energy technology the use of suitably defined efficiencies have been of use for many years in eliminating less attractive processing routes and thus reducing the number of possible designs to be investigated. For many decades so-called ?Sum Q/T Diagrams”? have been used in low temperature processing to visualize and improve temperature profiles in heat exchanger networks. Recently technology has been further developed into ?Pinch Technology”?. At the end of process development comes the final detailed optimization. The expensive and time consuming sequential way of working used in the past is being gradually replaced today with equation-oriented simulation and optimization tools such as the OPTISIM program. Expert systems, in principal, offer the chance of supporting the chemical engineer during the initial design of complete and complex processes. However, the experience with such systems to date has shown that a practical solution lies a long way into the future.     

Experience of using synchrotron radiation for studying detonation processes

Results of studying detonation processes in condensed high explosives, which are obtained by methods based on using synchrotron radiation, are summarized. Beam parameters are given, and elements of the station and measurement system are described. Data on the density distribution in the detonation front for several high explosives are presented, and values of parameters in the Neumann spike and at the Jouguet point are determined. A method used to reconstruct a complete set of gasdynamic characteristics (density fields, particle velocity vector, and pressure) from the experimentally measured dynamics of the x-ray shadow of the examined flow is described. Results of using this method for studying detonation of a charge of plastic-bonded TATB are presented. A method of measuring small-angle x-ray scattering in the course of detonation conversion is described. Based on results obtained by this method for a number of high explosives with an excess content of carbon, kinetics of condensation of free carbon and dynamics of the mean size of nanoparticles being formed thereby are analyzed.     

Chemorheology of thermosets—an overview

A review of current chemorheological techniques and measurement systems is presented for unfilled and filled thermoset resins. The specific measurement techniques for the kinetics, chemorheology, and modeling of these systems are presented, with particular emphasis on the chemorheological techniques and measuring systems. These techniques and measurement systems provide a greater understanding of traditionally complex thermoset processes, provide effective quality control measures for these processes, and will reduce design and operating costs in associated industries.     

Mischer mit mikrostrukturierten Folien für chemische Produktionsaufgaben

Mixers with Microstructured Foils for Chemical Production Purposes Since about 10 years the Institut für Mikrotechnik Mainz GmbH (IMM) is engaged with the application of microstructures for chemical micro process engineering. Their advantages – more efficient heat exchange and mass transport – lead to, among other things, an increase in yield and selectivity even while saving resources. The development of microstructured mixers thereby played a key role for carrying out advanced syntheses of fine chemicals as well as for the generation of dispersions, creams, foams, and emulsions. So far, microstructured mixers were mainly limited for laboratory‐scale or at best pilot plant‐scale – typical maximum flow rates were from 2 – 100 L/h for watery fluid systems. With the introduction of the StarLaminators StarLam300 and StarLam3000 this barrier could be lifted far beyond 300 L/h up to the m³/h domain. Both apparatus yield at high flow rates a mixing efficiency which reaches the high performance of today's low‐capacity (L/h) micro mixers. Therefore, continuity from the ”?real”? micro mixers over the herein described high‐throughput tools to conventionally manufactured static mixers with even higher flow rates is given.     

聚合物精密挤出过程中挤出流量的在线测量及控制方法

介绍了以PLC为控制核心的聚合物精密挤出成型过程的参数测量控制系统,针对描述挤出过程稳定性指标的参数.挤出流量的测量进行了详细描述,根据控制精度和挤出制品的不同,可以分别采用齿轮泵转速测量法、失重计量加料法、制品外径测量法3种不同在线测量及相应的控制方法,同时从测量原理、测量精度及应用范围等方面进行比较分析.     

Tomographic Measurement Techniques – Visualization of Multiphase Flows

Tomographic measurement techniques have become increasingly popular for the application in the field of chemical and process engineering. With this techniques, the fields of density, concentration, temperature, velocity or local void fraction can be measured without interfering with the multiphase flow. These fields are often either instationary or even have transient character. Therefore, the used tomographic measurement techniques have to have a high spatial and temporal resolution. In this paper known tomographic measurement systems are described and compared to each other. The sensor systems and reconstruction methods are explained. As an example, the applications of electrical and x-ray tomography are described for the imaging the flow inside random and structured packings. With the electrical tomographic measurement technique a temporal resolution of up to 100 frames per second is achieved, whereas with the x-ray tomography spatial resolutions of 0.4mm are possible.     

Sortieren von Mineralsalzen nach spezifischen Eigenschaften

Separation of mineral salts on the basis of specific material properties. This survey explains how different specific properties which are ?inherent”? to the material, such as density, magnetizability, and conductivity, can be utilized to separate mixtures of solids into individual components. As for salt minerals, the differences in their physical characteristics are very small and mostly not significant enough to allow a technical separation. Therefore the selective leaching based on the difference in hydration of the crystal components (ions) has been the predominant process. However, the selective dissolution of a specific type of salt and its subsequent recrystallization requires a high energy input and leads occasionally to environmental problems. It is for this reason that the mechanical procedures of ?flotation”? and ?electrostatic separation”? (ESTA-process) have meanwhile become interesting alternatives. In these processes specific surface properties, i. e. ?external”? properties, are used for the separation. Non-utilizable residual liquids, which often occur in the dissolution process and result in waste water problems, can thus be avoided. The principle of these two separation procedures as well as their application to the refinement of crude salts containing potassium and magnesium are described.     

Wechselbeziehungen zwischen Physikalischer und Technischer Chemie

Interactions between physical and industrial chemistry. The most important interactions for the two areas of chemistry are found in the following three fields: (1)states of materials (states of aggregation) and thermodynamics; (2) kinetics of molecular processes as a basis for macroscopic models; (3) methods of testing and measurement and development of equipment. The ?classical state”? of each of these areas is first sketched out and then the principal developments which are still in course of flux; directions of future development are then deduced. Such directions are exposed to be: extension of the scope of application of supercritical states as solvents and reaction media, as part of a general expansion of industrial application of elevated pressures; increase in knowledge of nonlinear dynamics of chemical systems with regard to transient behaviour and control mechanisms; increase in basic research on molecular structure and dynamics at the interfaces of dispersed systems – especially micelles and catalyst surface – using ?in situ”? methods, and more extensive utilization of the results in industrial chemistry.     

Reinraumtechnik

Clean room technology is essentially concerned with the control of particulate contamination. Sources of contamination are: air, work benches, personnel, machines, services. The control of airborne particles has already reached a high level. The cleanliness of process equipment can be further improved by the integration of laminar flow units. Cleanliness requirements and particle analysis meanwhile even cover liquidborne submicron particles. Classification systems for the cleanliness of liquids are in preparation. The contamination of powders results from different particle sources over the whole production process. The quality factor ?particle control”? is in tended to prevent trouble and improve the economic efficiency and reliability of an increasing number of processes.     

Mensch-Prozeß-Kommunikation

Man-process communication . Computers are extensively used to control technical processes, but man is still irreplacable as observer and decision maker. The paper gives an overview of the channels existing between man and process. These channels have to deliver as much information as necessary, but as little as possible to allow the right decisions. Good models, concerning the production process and its individual phases, the structure of the control system, and the behaviour of man are required to extract the relevant information out of a large amount of data. Methods of signal processing and pattern recognition help to reduce the dimensionality of the active state vector allowing the control system to provide ?information”? instead of a collection of ?signals”?. The paper also describes the state and future development of important technological aspects, e. g. interactive display systems and real time data base systems.     

Critical considerations on the use of a bi‐directional probe in heat release measurements

In various medium to large scale fire test equipment, such as the ISO room corner (RC) test and more recently the single burning item (SBI) test, the mass flow measurement of the combustion gases plays a key role in the determination of the heat release rate and smoke production rate. To date a bi‐directional low‐velocity pressure probe has been used to calculate this flow based on a differential pressure measurement on the axis of the exhaust duct. The objectives of this paper were to evaluate this bi‐directional probe—and the modified SBI version—when used for measuring flows in exhaust ducts. Recommendations are given on the future use of pressure probes measuring exhaust gas mass flows. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrodynamik in Blasensäulen – Messung von relativem Gasgehalt und Blasengröße

In bubble column reactors mass transfer kinetics are determined by local hydrodynamic processes (bubble formation, velocity, coalescence, break‐up, etc.). For a better understanding of the influence of pressure and particle load on these processes, a measurement system for detection of local bubble size distributions in opaque bubbly flows is needed. Therefore, in this work an optical needle probe was applied in a bubbly flow. In a first step, the needle probe was validated by means of single‐bubble measurements. The measurement technique shows high potential for application in more complex and opaque systems.     

Expertensysteme – ein Hilfsmittel der Prozeß-Synthese

Expert systems for process syntheses . Commercial programs used in computer-aided development of chemical processes need a process flowsheet as starting point. Preparation of flowsheets is based largely on human experience, an uncertain kind of knowledge expressed by heuristic rules. These rules are recognized as true and advantageous in most cases without having the validity of a law. Logic programming languages derived from research on artificial intelligence are proven tools for handling heuristics with so-called “expert systems”. The flowsheets proposed by the expert system reduce all theoretically possible results to a few structures. The example of structuring distillation sequences illustrates what can be expected using an “expert system” in the area of “problem solving” by comparing its proposed sequences with optimized problems.     

Optimization of stabilizer formulations for polyolefin processing

An approach to formulation is presented that is based on a statistical experimental design package for use on a personal computer. The total level of phosphite + hindered phenol, and the ratio of phosphite to hindered phenol are used as experimental variables. The approach was tested on extrusions of polypropylene using melt flow retention and yellowness index as observed variables. A quadratic model gave a satisfactory fit to the data for both variables. Contour plots are presented of the performance of the systems for two commercially available hindered phenols and two polypropylene samples. The largest difference between the resins is in the degree of color generation on extrusion. For both hindered phenols, a resin made using “3rd generation” or “high activity” catalyst gave lowest color development on extrusion. There were also small differences in the response of the melt flow of the resins to phosphite level.     

Die Anwendung von Prozeßrechnern in der Waschmittelproduktion

The Use of Process Control Computers in the Production of Laundry Detergents Modern laundry detergent production plants require highly sophisticated measuring and controlling systems in order to maintain high and even quality of the products. In addition, the detergent industry is under a very high cost pressure due to market circumstances. It appeared to be efficient to improve the measuring and controlling technology by using process control computers and to come to production methods with lower cost rates. Also, even and safe operation methods are desirable for every production process as well as rapid recognizing and elimination of troubles and early warnings in case of breakdowns. Prerequisites with regard to computer control are a high level of the process equipment and a continuous recording of measuring data, which is very important. The method of operation of the computer control is discussed in general the resulting efficiency is presented. The efficacy can be quantitated with regard to the desired decrease of raw material costs, conservation of energy and saving manpower. The efficiency can not be quantitated with regard to deepening of knowledge of the process, accelerating of the performance of trials, collecting experience for other processes and as prerequisite for a composite system of electronic data processing in the production department.     

Titanium dioxide,extenders, fillers,not-in-kind replacements—what does it mean for plastics?

Recent publication and presentations extol the virtues of filler pigments as titanium dioxide extenders. Theory predicts and experiment shows that in plastic systems, where pigment concentrations are relatively low, compared to paints and inks, fillers do not significantly improve the optical efficiency of titanium dioxide. Close examination of published data shows that there are many unanswered questions such as: How do variations in compounding conditions affect efficiency? Has sufficient attention been paid to measurement of light reflectance and transmission? Have the effects of light scattering and absorption been taken into account to explain optical measurements? What we have found is that there is no easy “fix” to improve the efficiency of titanium dioxide by the use of filler pigments. Serious questions also remain unanswered regarding the effect of ad hoc replacement of TiO₂ with filler in systems requiring light stability such as rigid polyvinyl building products.