Investigation of Scale Formation in Heat Exchangers of Phosphoric Acid Evaporator Plants

The primary problem in concentrating phosphoric acid is due to fouling on the tube‐side of the heat exchangers of the evaporator units. Scaling on the heat transfer surfaces occurs because of high supersaturation of phosphoric acid liquor with respect to calcium sulphate. A review of the existing literature reveals that no information is available on heat transfer and on crystallization fouling of industrial phosphoric acid solutions. In this investigation, the solubility of different calcium sulphate types in phosphoric acid solution was studied and its dependency on acid concentration and temperature was investigated. A large number of fouling experiments were carried out in a side‐stream of a phosphoric acid plant at different flow velocities, surface temperatures and concentrations to determine the mechanisms, which control the deposition process. After identifying the effects of operational parameters on the deposition process, a model was developed for prediction of fouling resistances. The reaction of calcium sulphate crystallization followed a second order rate with respect to the supersaturation. The activation energy evaluated for the surface reaction of the deposit formation was found to be 57 kJ/mol. The predicted fouling resistances were compared with the experimental data. Quantitative and qualitative agreement between measured and predicted fouling rates is good.     

Biosorption of Phenol onto Posidonia oceanica (L.) Seagrass in Batch System: Equilibrium and Kinetic Modelling

In this research, the biosorption of phenol using the fibres of a Mediterranean seagrass Posidonia oceanica (L.) was studied. Batch experimental procedures were made to investigate the ability of this novel marine biomass to remove phenol from aqueous phase. The influences of pH and contact time at different initial concentrations were evaluated. The results showed that biosorption capacity was enhanced using solution pH equal to 5.2. The modelling results showed that pseudo‐second‐order and Redlich‐Peterson models were found to be the most suitable to satisfactory describe the kinetic and equilibrium adsorption data, respectively.     

Adhesive Contact of a Membrane with a Hemispherical Indenter: Theoretical Analysis and Model Liquid System

The axisymmetric Laplace equation is solved numerically to extract contact-angle data for a flat liquid/vapor interface contacting a submerged hemispherical solid. The liquid/vapor interface is treated as a membrane, with a membrane tension equal to the surface energy of the liquid. By measuring the vertical displacement of the membrane and the projected contact area the membrane makes with the hemisphere, the contact angle and correspondingly the driving force for motion of the contact line can be measured. We show that characteristic receding and advancing contact angles can be obtained by measuring the contact radii formed upon initial contact between the interface and hemisphere and final contact just prior to detachment of the interface, respectively. Use of the technique is illustrated with a model experiment involving the contact of an air/water interface with a poly(methyl methacrylate) surface.     

Effects of temperature, ammonium and glucose concentrations on yeast growth in a model wine system

In enology, alcoholic fermentation is a complex process involving several mechanisms. Slow and incomplete alcoholic fermentation is a chronic problem for the wine industry and factors leading to sluggish and stuck fermentations have been extensively studied and reviewed. The most studied cause of sluggish and stuck fermentation is the nitrogen content limitation. Nevertheless, other factors, such as temperature of fermentation and sugar concentration can affect the growth of yeasts. In this study we modelled the yeast growth‐cycle in wine model system as a function of temperature, sugar and ammonium concentrations; the individual effects and the interaction of these factors were analysed by means of a quadratic response surface methodology. Cell concentrations and weight loss were monitored in the whole wine fermentation process. The results of central composite design show that lower is the availability of nitrogen, higher is the cell growth rate; moreover, initial nitrogen concentration also influences survival time of Saccharomyces cerevisiae.     

管内材料高温放气性能的测试及应用研究

管内材料放气性能的优劣直接影响着整管的性能和寿命.本文简介了测试管内材料高温放气性能的原理、装置和方法.文中列举的几项应用实例表明,本项测试结果对产品质量控制、工艺技术改进和材料进厂检验及国产化攻关都具有指导意义.     

A numerical model for induction heating processes coupling electromagnetism and thermomechanics

This paper presents a mathematical and numerical model developed for coupling the various physical phenomena (electromagnetic, thermal and mechanical) taking place in axisymmetrical induction heating processes. All three electromagnetic, thermal and mechanical models are time dependent and take full account of the electromagnetic and thermal non‐linear effect especially with magnetic materials. The electromagnetic problem is discretized and solved in the workpiece, air and inductors. The heat transfer equation and the mechanical equilibrium equations are solved in the workpiece only, both using a finite element method. The mechanical model can take into account thermoelastic–plastic behaviour for the part. The model has been successfully applied to several cases of induction heating. Comparisons between numerical and experimental results show an excellent agreement. Copyright © 2003 John Wiley & Sons, Ltd.     

Modelling of the extraction equilibrium of zinc from chloride solutions with tri-n-octylphosphine oxide

The extraction of zinc from chloride solutions with tri-n-octylphosphine oxide (TOPO) dissolved in benzene has been thermodynamically studied based on the law of mass action. A model employing the simplified Pitzer equations for stoichiometric activity coefficient estimations is found to be effective for the explanation and prediction of the distribution data, and the thermodynamic extraction constant is determined as log K_et = 5.16 ± 0.11 at 20°C.     

Reactor modelling for electrochemical processes

This paper presents a relatively straightforward approach to the modelling of electrochemical reactors operated in batch or continuous modes. The models are based on ideal flow assumptions of either well-mixed or plug flow and incorporate reaction rate models based on electrochemical kinetics and mass transport at one electrode. General characteristics of the reactor models are described, particularly with regard to the need for good mass transport in metal recovery applications. An example is given on the use of the model in the recovery of a heavy metal (Cd²⁺) from an acidified solution containing Cd(II) and Fe(III) ions. The reaction rate model is based on experimental data.     

Immobilized α-amylase from Bacillus licheniformis: a potential enzymic time—temperature integrator for thermal processing

Biphasic and nth-order models were tested as to their usefulness to fit experimental inactivation data of Bacillus licheniformis α-amylase, immobilized on glass beads, and were discussed with respect to their suitability to characterize the considered enzymic system as a time—temperature integrator (TTI) to evaluate heat processes. Both isothermal and non-isothermal inactivation experiments were carried out. Model (kinetic) parameters (rate constant k, activation energy E_A and reaction order n) were estimated using a non-linear regression procedure. The results obtained, especially the activation energy of about 293 kJ mole^–1, indicated a potential use of this system as a TTI for heating processes in the temperature range of 96–108°C.     

The rate of corrosion of concrete reinforcement and possibilities of its mathematical modelling

The paper describes a method for the mathematical modelling of steel reinforcement corrosion rate. This method is based exclusively on experimental results and expression of the influence of significant corrosion factors in the form of functional relations. The method takes into account the reality of the effects of corrosion factors, their contigency and complexity, and various circumstances occurring in practice. It represents one way towards the development of methods for the prediction of service life of reinforced concrete and structures.