Mechanisms of corrosion in surface layers at solid-solution interfaces

Smart, Roger St. C.

doi:10.1007/bf02373561

Cited by 3 publications

(3 citation statements)

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“…This type of expression was developed over 100 years ago. , The dissolution process has become critical for modeling the release of drugs in the pharmaceutical industry . However, the dissolution process is also important for modeling the removal of foulants in the chemical and food processing industries , and for understanding corrosion …”

Section: Theorymentioning

confidence: 99%

“…8 However, the dissolution process is also important for modeling the removal of foulants in the chemical and food processing industries 9,10 and for understanding corrosion. 11 For the dissolution of a solid into a falling liquid film, earlier studies have focused on processes in which the dissolved substance does not penetrate deeply into the falling film. 12−15 This is only true for situations with short contact times, but this assumption makes it possible to simplify the boundary condition for the liquor−gas interface and thereby enables an analytical solution for laminar flow.…”

Section: ■ Introductionmentioning

confidence: 99%

“…29 The first is for nonevaporative conditions with a constant wall temperature. The correlation consists of three parts: expressions for the laminar, turbulent, and transition regions: (11) However, most of the work on falling film heat transfer presented in the literature is based on measurements during evaporation. The second correlation is for evaporative heat transfer, which has been proven accurate for conditions with constant wall temperature:…”

Section: ■ Introductionmentioning

confidence: 99%

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Solid Dissolution into a Vertical Falling Film under Industrial-like Conditions

Karlsson

Gourdon

Vamling

2014

Ind. Eng. Chem. Res.

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During the evaporation of black liquor, a residual stream in pulp mills, scales form on heat transfer surfaces due to the crystallization of sodium carbonate and sodium sulfate salts. As a result, falling film evaporators need regular cleaning to remove these water-soluble scales, and therefore, knowledge about the dissolution process is important. In this work, dissolution of the aforementioned salts was tested experimentally in a pilot evaporator close to the industrial scale. Dissolution was diffusioncontrolled and could be described by film theory, where the concentration difference between the saturated wall and an assumed perfectly mixed bulk was the driving force of the process. The measured mass transfer coefficient could be predicted to within 30% accuracy using the Chilton−Colburn heat and mass transfer analogy together with a standard heat transfer correlation. ■ INTRODUCTIONHeat and mass transfer between a solid wall and falling liquid film is of interest in many industrial applications. For instance, falling film evaporation is often used to efficiently concentrate different liquids. Other applications of falling film technology are crystallizers and condensers. In this study, the dissolution of scales consisting of double salts of sodium carbonate and sodium sulfate are investigated. These scales are formed by crystallization fouling during the black liquor evaporation process, the most steam-consuming part of a pulp mill. Regular cleaning is needed to maintain operation. Because these salts are easily dissolved in water, the normal procedure for cleaning is to recirculate condensate or weak black liquor. Previous research has mainly focused on how to prevent fouling by optimizing operating conditions rather than on how to efficiently remove scales. 1−3 Cleaning the evaporators' surfaces is also an important part of the operation, but the cleaning process is based on trial and error due to a lack of fundamental knowledge. 4 The aim of this work was to gain an understanding of the process of scale dissolution into a falling film of water and to determine how this dissolution can be modeled under industrial-like conditions. Emphasis was placed on making a simple and robust model that can be implemented in industry. The parameters of interest were the solvent temperature, flow rate, and inlet salt concentration. First, dissolution experiments were conducted on a relatively large scale, and then, a dissolution model was developed and used to fit a mass transport coefficient to the experiments. Another aim of this work was to compare the mass transport coefficient using the Chilton−Colburn analogy with heat transfer.■ THEORY Solid Dissolution. The dissolution process, i.e., the mass transfer from a solid surface to a liquid, can be controlled by both reaction and diffusion. 5 In the case of a salt, the reaction involves breaking bonds in the crystal lattice to generate free ions. When dissolution is diffusion-controlled, the limiting step is the diffusion of the substance from the solid−liquid interface ...

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Section: Theorymentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Solid Dissolution into a Vertical Falling Film under Industrial-like Conditions

Karlsson

Gourdon

Vamling

2014

Ind. Eng. Chem. Res.

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Development of novel materials through interface engineering

Gerson

Druitt²,

Ikuma

et al. 2001

Ionics

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Abstract. The impact of interfaces in the processing and properties of polycrystalline material is briefly discussed. The local properties of the interfacial layer are considered in terms of composition, structure and related properties that differ substantially from those of the bulk phase. It has been postulated that novel materials with desired properties for specific industrial applications may be processed through interface engineering rather than through bulk chemistry. This paper considers the impact of interfaces on the properties of materials for technological applications, such as electrochemical devices for reduction of greenhouse gases, through energy conversion and environmental monitoring. The procedures that may be applied for the modification of interfacial chemistry are considered.

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