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Über dieses Buch

Contemporary Chemical Process Engineers face complex design and research problems. Temperature-dependent physical properties and non-Newtonian flow behavior of substances in a process cannot be predicted by numerical mathematics. Scaling-up equipment for processing can often only be done with partial similarity methods. Standard textbooks often neglect topics like dimensional analysis, theory of similarity and scale-up. This book fills this gap! It is aimed both at university students and the process engineer. It presents dimensional analysis very comprehensively with illustrative examples of mechanical, thermal and chemical processes.

Inhaltsverzeichnis

Frontmatter

Introduction

Abstract
The chemical engineer is generally concerned with the industrial implementation of processes in which chemical or microbiological conversion of material takes place in conjunction with the transfer of mass, heat, and momentum. These processes are scale-dependent, i.e. they behave differently on a small scale (in laboratories or pilot plants) and a large scale (in production). They include heterogeneous chemical reactions and most unit operations (e.g., mixing, screening, sifting, filtration, centrifugation, grinding, drying, and combustion processes). Understandably, chemical engineers have always wanted to find ways of simulating these processes in models to gain insights that will assist them in designing new industrial plants. Occasionally, they are faced with the same problem for another reason: an industrial facility already exists but will not function properly, if at all, and suitable measurements have to be carried out to discover the cause of the difficulties and provide a solution.
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1. Dimensional analysis

Abstract
The end result of dimensional analysis is a complete set of dimensionless numbers that describe a physical process and that outline the conditions under which this process behaves “similarly” in the model and its full-sized counterpart; dimensional analysis is the basis of scale-up methods. Lord Rayleigh was aware of this when he referred to the studies in which he employed dimensional analysis as the study of similitude. Let us take this reference as our starting point in a historical survey of dimensional analysis which begins with the first attempts at scaling up a model, attempts made at a time when the very concept of dimensions was still unknown.
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2. Description of a Physical Process with a Full Set of Dimensionless Numbers

Abstract
All the essential (“relevant”) physical quantities (variables, parameters) which describe a physical or technological interrelation must be known before this process can be described with a full set of dimensionless numbers. This demands a thorough and critical appraisal of the process being examined.
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3. Similarity and scale-up

Abstract
In the Introduction it was pointed out that using dimensional analysis to handle a physical problem, and thus to present it in the framework of a complete set of dimensionless numbers, is a sure way of producing a simple and reliable scale-up from the small-scale model to the full-scale technical plant. The theory of models states that:
Two processes may be considered completely similar if they take place in similar geometrical space and if all the dimensionless numbers necessary to describe them have the same numerical value (Πi = idem).
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4. Treatment of variable physical properties by dimensional analysis

Abstract
When using dimensional analysis to tackle engineering problems, it is generally assumed that the physical properties of the material system remain unaltered in the course of the process. Relationships such as the heat transfer characteristics of a technical device (e.g., vessel, pipe): Nu = f (Re, Pr), see example B1, are valid for any material system with Newtonian viscosity and for any constant process temperature, i.e. for constant physical properties.
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Backmatter

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