Industrial Moisture and Humidity Measurement E-Book

Roland Wernecke

• Herausgeber: Wiley-VCH
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 679

Veröffentlichungsjahr: 2013

Beschreibung

Moisture analysis covers a variety of methods for measuring high levels of moisture, as well as trace amounts, in solids, liquids, or gases. There are many applications where trace moisture measurements are indispensable for manufacturing and for process quality assurance. Trace moisture in solids must be controlled for plastics, pharmaceuticals and heat treatment processes. Measurement applications in gases and liquids include, for example, drying processes, hydrocarbon processing, pure gases in the semiconductor industry, natural gas pipeline transport, the conditioning of food and other products.

Written by experts with over 20 years of experience in the field, this one-stop guide covers all aspects of these measurements, including both the theory and a wealth of practical know-how. As such, it includes guidelines on installation, on the realization of standards for absolute and relative humidity, verification and traceability measurements, equipment calibration methods and the latest research developments.

Backed by numerous case studies, this practical book serves the needs of those working in the industry tasked with performing or developing new techniques and processes for moisture and humidity measurement. As a result, the scientist or engineer has all the information required for accurate, reliable, economically viable and efficient moisture measurement.

Leseprobe

Contents

Cover

Related Titles

Title Page

Copyright

Preface

Chapter 1: Water – Substance of Life

1.1 Water as a Natural Resource

1.2 Physical and Chemical Properties of Water

1.3 Significance of Water for Energy Conversion

1.4 General Terminology

Further Reading

Chapter 2: Thermodynamic Terms and Definitions

2.1 Terms in Humidity Measurement

2.2 Terms in Moisture Measurement in Solid and Liquid Materials

2.3 Terms and Definitions in Measurement and Controlling Technology

References

Further Reading

Chapter 3: Water in Solid, Liquid, and Gaseous Materials

3.1 Specialties of Solid and Liquid Materials

3.2 Contact and Noncontact Measurement Methods

3.3 Bonding Types of Water in Solid and Liquid Materials

3.4 Analogy Models

References

Further Reading

Chapter 4: Moisture and Humidity Measurement Methods in Solid, Liquid, and Gaseous Substances

4.1 Introduction

4.2 Measurement of Electrical and Magnetic Properties

4.3 Measurement of Water Vapor Pressure in Gases

4.4 Water Content Measurements Using Chemical Methods

4.5 Measurement of the Optical Properties of Water and Water Vapor

4.6 Measurement of Acoustic Properties of Water Vapor

4.7 Measurement of Suction Pressure in Solid Materials

4.8 Measurement of Nuclear Properties of Water

4.9 Nuclear Magnetic Resonance Spectroscopy

4.10 Thermogravimetry

4.11 Measurement of the Thermal Properties of Solids

4.12 Nanostructured Measurement Devices

References

Further Reading

Chapter 5: Selection of a Measurement Method

5.1 Assessment of the Measurement Task

5.2 Evaluation of Different Measurement Methods

5.3 Selection of Hardware

Further Reading

Chapter 6: Reliability and Traceability of Measurements

6.1 Metrological Terminology

6.2 Moisture and Humidity Metrology

6.3 Typical Terms in Industrial Applications

References

Chapter 7: Moisture Measurement in Meteorology, Agriculture, and the Environment

7.1 Agriculture and Horticulture

7.2 Waste Management

7.3 Measurement of Weather Conditions

References

Further Reading

Chapter 8: Applications in the Food and Beverage Industry

8.1 Water Activity Measurement

8.2 Food Processing

8.3 Monitoring and Control of Production Stages in the Food Industry

8.4 Storage and Transport of Food

References

Further Reading

Chapter 9: Moisture and Humidity Measurement in Industrial Plants

9.1 Humidity Measurement Under Extreme Conditions

9.2 Moisture Measurement During Running Production Processes

9.3 Moisture Measurement in the Automotive and Aircraft Construction Industries

9.4 Moisture and Humidity Measurement in Electrical Engineering, Electronics, and Optics

Reference

Further Reading

Chapter 10: Applications in the Chemical, Pharmaceutical, and Plastics Industries

10.1 Moisture Measurement in Plastic Granules and Powders

10.2 Drying of Solid Materials

10.3 Storage of Moisture-Sensitive Products

10.4 Inline Measurement in Nonaqueous Fluids

References

Further Reading

Chapter 11: Applications in the Manufacture and Processing of Paper and Textiles

11.1 Random Test Measurements and Inspection of Goods

11.2 Continuous Measurement of Paper and Fabric Webs

11.3 Storage and Transport of Paper and Textiles

References

Further Reading

Chapter 12: Moisture Measurement in the Building Industry

12.1 Moisture Measurement in Aggregates

12.2 Measurement on Buildings and Brickwork

12.3 Climate Control in Rooms and Buildings

Further Reading

Chapter 13: Laboratory-Based Moisture Measurement

13.1 Laboratory Measurement Stations for Humidity and Moisture Measurement

13.2 Generation of Gases with a Defined Humidity

13.3 Humidity Measurement in Medical Applications

References

Further Reading

Chapter 14: Moisture and Humidity Measurement in Space

14.1 Model Representations of the Formation and Distribution of Water

14.2 Measurement Methods in Aerospace

14.3 Requirements for Measurement Equipment in the Aerospace Industry

References

Further Reading

Appendix A: Relevant Units of Thermodynamics

A.1 Basic Units of the International System of Units (SI System)

A.2 Conversion of Units

A.3 Conversion of Units (Material Properties)

A.4 Conversion of Units (Thermodynamic)

Appendix B: Tables and Diagrams of Thermodynamics

B.1 Mollier Diagram

B.2 Details of Mollier Diagram

B.3 Calculation of Pressure Dew Point

B.4 Water Vapor Over Water

B.5 Water Vapor Over Ice

B.6 Psychrometer Charts

B.7 Psychrometer Charts

Appendix C: Constants and Parameters

C.1 Relevant Constants

C.2 Parameters of Dry Air

C.3 Parameters of Water, Water Vapor, Ice

C.4 Parameter of Carbon Dioxide

C.5 Other Parameters

Appendix D: Material Parameters

D.1 Specific Electric Resistance of Different Materials

D.2 Relative Permittivity of Different Insulators

D.3 Spectral Lines of Different Chemical Elements

D.4 Density of Various Solid Materials

D.5 Heat of Evaporation of Different Gases

D.6 Cooling Temperature of Common Coolants

Appendix E: Water Adsorption in Products

E.1 Sorption Isotherm of Wood Fiber

E.2 Sorption Isotherm of Grinded Natural Stone

E.3 Sorption Isotherm of Soot

E.4 Sorption Isotherm of Flour

E.5 Sorption Isotherm of Freeze-Dried Coffee Powder

E.6 Sorption Isotherm of Milled Coffee Beans

E.7 Sorption Isotherm of Paper

E.8 Storing Conditions of Fruit and Vegetables

E.9 Storing Conditions of Fruit and Vegetables Under Controlled Atmosphere

Index

Related Titles

Tsotsas, E., Mujumdar, A. S. (eds.)

Modern Drying Technology

5-Volume Set

2014

ISBN: 978-3-527-31554-3 (Also available in digital formats)

Weinberg, S.

Cost-Contained Regulatory Compliance

For the Pharmaceutical, Biologics, and Medical Device Industries

2011

ISBN: 978-0-470-55235-3

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at 〈http://dnb.d-nb.de〉.

© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978-3-527-33177-2

ePDF ISBN: 978-3-527-65244-0

ePub ISBN: 978-3-527-65243-3

Mobi ISBN: 978-3-527-65242-6

oBook ISBN: 978-3-527-65241-9

Preface

Industrial humidity and moisture measurement is a complex topic that requires extensive knowledge of the underlying physical principles, the specifics of a wide range of available measurement technologies, the methods of industrial process control, and practical experience in facility control systems. Humidity and moisture of different concentrations play a significant role in almost any step of processing, for example, as a quality monitoring parameter that must be kept within a defined range, or simply as a disturbance variable that needs to be compensated or accounted for.

The humidity and moisture of a material and its surrounding environment influence the technology and effectiveness of a process, and have a major impact on the properties of the final product. This makes moisture and humidity an important parameter for in-process measurements, as well as for laboratory-based measurements.

The demands on the versatility, precision, and accuracy of the sensor equipment are ever-increasing. The importance of standardization, certification, and traceability of the measured data and of the applied measurement procedure, for example, in quality management, has grown in recent years. This requires a careful and intelligent selection of the most suitable measurement technique and equipment from the variety of available methods and devices.

Measurement techniques for gas humidity measurement are most frequently based on fundamental thermodynamic effects. In practice, however, it is often a challenging and complex task to reproducibly generate reference gases and very low water vapor concentrations (i.e., the field of trace humidity). New devices for humidity measurement, for example, cavity ring-down spectroscopy or nanotechnology, have been developed in recent years and have become increasingly common in practical applications.

In contrast to gas humidity, no complete theory for the description of moisture in solids and liquids exists. Depending on the material to be measured, suitable models of physics, chemistry, and material science need to be applied. Another challenge in practice is that few reference materials are available for calibration.

From the point of physics and material science, it makes sense to divide the detection of water in matter into gas humidity measurement and material moisture measurement. However, most gas humidity measurement methods can also be used for moisture measurement in solid and liquid materials. Therefore, such division makes little sense from the application point of view.

The number of moisture measurement methods has barely increased over the last 50 years but technological advancements in electronics and optics, the development of new materials, and the spread of capable microcontrollers have opened up new areas of application, a high degree of integration, and miniaturization. At the same time, manufacturing costs have reduced and reliability and precision have improved. A successful strategy, in many cases, is to consider and evaluate a traditional, well-established measurement technique against the requirements of modern manufacturing processes and equipment technology.

This book is a completely revised, updated, and extended edition of the book Industrielle Feuchtemesstechnik (published in 2001 in German). It deals with the different aspects of industrial moisture and humidity measurement. This book is written for practitioners, students, and all those interested in looking for solutions to moisture and humidity measurement tasks in industrial applications. It is intended for process engineers from many different industrial sectors. The book provides up-to-date user knowledge for engineers, measurement experts, and laboratory technicians in the areas of facility control, quality management, and process monitoring and control. It is intended to offer an introduction to the topic of industrial moisture measurement and should help the reader to make informed choices with regard to technical solutions and investments.

Numerous case studies, typical examples of applications, processes, and fabrication steps are used to outline general solution strategies. The methodological approach used to analyze and implement typical moisture measurement tasks is explained in each application chapter.

The first chapters in this book are dedicated to the fundamentals of the interactions of water and matter. This is followed by a presentation of the theoretical and technical aspects of individual moisture and humidity measurement methods, grouped according to the underlying physical principle. Thereafter, general strategies in selecting the optimal measurement method as well as the basics of measurement uncertainties, traceability (i.e., relating a measurement value to the International System of Units), and calibration are presented. From Chapter 7 onward, industrial measurement applications from many different sectors and the practical realization of typical measurement tasks are discussed. The focus is always on the specific requirements and boundary conditions imposed by the industrial or laboratory practice. Thermodynamic constants, parameters, material curves, and characteristics can be found in the appendices. They provide further information and illustration of specific topics and serve as a starting point for the dimensioning, optimization, and development of specific custom moisture and humidity measurement applications.

We would like to express our gratitude to the people who contributed to the creation of this book. We are indebted to Dr. habil. Lothar Martini for the countless discussions, his many helpful remarks, and for the thorough revision of the book. The extensive support in laboratory measurements that was provided by Dr. habil. Thomas Hübert is also greatly appreciated. The chapter on aerospace industry would not have been possible without the valuable and longstanding cooperation of Prof. Dr. Dietrich Möhlmann. Our special thanks go to Liz Kelly from Dublin, Ireland, for the patient and thorough, proofreading of the book. Her work made the release of the English edition of this book possible. The support of Katja Wernecke in the research, creation, and revision of tables and figures is greatly appreciated.

We would also like to express our gratitude to our family members Gabi, Anja, and Henry for their constant support and the great amount of patience they showed during the creation of this book.

Potsdam, GermanyRoland WerneckeJanuary 2014Jan Wernecke

1

Water – Substance of Life

1.1 Water as a Natural Resource

Water plays a key role in the formation and evolution of our planet and the life it supports. Water is present, in different aggregate states, throughout all parts of the Earth. In solid and liquid forms, water covers approximately 71% of the Earth's surface, while the large amount of gaseous, liquid, and solid water in the atmosphere governs both the global climate and the local weather. Global climatic balance and heat transfer are determined mainly by the large oceanic circulations of warm and cold water. Water has a high degree of transparency for visible light, one of the key factors that enabled the formation and evolution of life in the primeval oceans. The atmospheric layer of water vapor reflects heat emitted from the surface of the Earth and thus prevents the freezing of the planet. Liquid water forms the landscapes on continents, and its presence or absence determines the degree of biological activity and suitability for agriculture.

Every form of life on Earth requires water vapor in the respiratory air. Water is an essential component of each organism, and needs to be present in sufficient amounts at all times. Humans, for example, may survive without the intake of proteins, carbohydrates, and fiber for several weeks. Without water, however, survival is possible for only a few days. Humans require a daily amount of 2–3 l of water in order to maintain biological functions. Water has thus always been a central element in human consciousness and culture. In the ancient philosophies, for example, water is one of the four basic elements, and it is a symbol of purity and life in every religion.

Apart from its immediate nutritional function, humans make use of the different properties of water in many ways, for example,

for the generation of energy,for the transportation of people and goods,as a building material,in industrial manufacturing processes,for relaxing and recreation,for the removal of waste,as a cleaning agent, andfor the interim or final storage of many different materials.

1.2 Physical and Chemical Properties of Water

1.2.1 The Water Molecule

Water is a molecule consisting of two hydrogen atoms and one oxygen atom (Figure 1.1).

Figure 1.1 Binding angles in a water molecule.

The difference in electronegativity between oxygen and hydrogen, and the arrangement of atomic orbitals, results in an angle of 104.5° and thus the formation of an electric dipole. The negative charge of the molecular dipole is located at the free pair of valence electrons of oxygen, while the hydrogen ions form the positively charged pole. Different symmetric and asymmetric oscillation modes (Figure 1.2) can be excited and result in a variation of the dipole moment. The dipole character of water molecules is the reason for the formation of the strong intermolecular hydrogen bonds that cause clustering (Figure 1.3).

Figure 1.2 Vibration states of a water molecule.

Figure 1.3 Clustering of water molecules.

This results in a density that is significantly lower than that of chemically similar substances. The diameter of H2O molecules of 0.28 nm also differs from that of other components of air, such as

H2: 0.23–0.29 nm,N2: 0.32–0.36 nm,O2: 0.29–0.35 nm, andCO2: 0.33 nm,

which makes the physical and chemical properties of water so unique. More than 40 anomalies of water, in terms of chemical, thermodynamic, electrical, or optical properties, to name but a few, have been observed in various experiments. Details can be found in the specialist literature.

1.2.2 Physical Properties

In the terrestrial atmosphere, water can be present in the solid, liquid, and gaseous states. All three phases are colorless and possess a high optical transparency in the visible and ultraviolet range. Infrared and microwave radiation, in contrast, is absorbed by water molecules due to the positions of the molecular energy orbitals. Water molecules are electrically neutral, but possess a dipole moment due to the inhomogeneous charge distribution.

The formation of clusters during freezing is the reason for the anomalous density change of water, compared to other molecules with similar structure. Due to clustering, water expands in volume during the phase transition from liquid to solid, which is associated with a reduction in density (Figure 1.4). This process continues as temperatures further decrease, as long as crystallization occurs. The crystal structure of water molecules in ice is a monocrystalline hexagonal lattice. Water has the highest density (e.g., smallest volume) at a temperature of around T ≈ 4 °C. A further increase in temperature results in a decrease in density, similar to any other liquid. This anomaly of density has direct implications on the landscape, and on natural processes: Lakes freeze from top to bottom, which allows fish to survive during winter. Water that penetrates into rock crevices and freezes during the night can cause significant frost wedging due to the volume expansion.

Figure 1.4 Density of water as a function of pressure.

A further anomaly of water is the temperature at which melting and freezing occurs. According to the chemical properties of compounds of hydrogen and other elements from group VI of the periodic table, the phase transition temperatures should be as shown in Figure 1.5.

Figure 1.5 Melting and boiling temperatures of hydrogen compounds in the oxygen group of the periodic table and the expected values for H2O.

The reason for this significant deviation is the strong hydrogen bonds between the molecules, which need to be overcome by using an increased amount of energy. As a consequence, the melting and evaporation temperatures of water at standard pressure are shifted to Tmelt = 0 °C and Tevapo = 100 °C, respectively. The strong hydrogen bonds also cause a strong surface tension at interfaces, which results in a high viscosity and a good wetting behavior on polarized surfaces.

Water possesses a high heat capacity, which dampens the low temperature change upon heating or cooling. Thus, the transition between the aggregate states is associated with a significant release or absorption of thermal energy.

1.2.3 Chemical Properties

Water is formed during the combustion or, more precisely, the oxidation of hydrogen according to

(1.1)

The oxidation is an exothermic process, where hydrogen is oxidized and oxygen is reduced. Water can be used as a solvent for a wide range of chemicals, because

it is soluble in many substances and forms free ions by dissociation,it can be easily absorbed due to the low molar mass of the molecule,the dipole of the molecules allows for the formation of stable bonds, andthe hydrogen bonds cause an interlinking with other polar molecules.

Salts, bases, and acids can be dissolved and diluted in water and are used for many chemical reaction processes. Dissolved oxygen is an important factor for life and biological activity. In the atmosphere, the ratio of oxygen to nitrogen is roughly 1 : 4. This ratio is 1 : 1.8 in water, that is, a much higher oxygen content, which is essential for the respiration processes of underwater life forms.

Metals are only corroded by liquid water and in environments with a relative humidity of U > 70%rh. Dissociation of water molecules yields unbound hydroxide ions, OH−, which are highly reactive. In the atmosphere, OH− ions react with many substances and pollutants and thus act as a cleaning agent. An example of this process is the natural decomposition of ozone by a reaction with water according to

(1.2)

Man-made atmospheric substances, for example, industrial sulfur compounds, are also, to a certain extent, decomposed and bound by water. This generates condensation nuclei, which causes cloud formation. The particles are then washed out of the atmosphere by precipitation, and into the ground. Investigations into the distribution of these substances yield information on the amount and the location of atmospheric pollution.

Water is an amphoteric substance, which means that it can act as both an acid (hydronium, H3O+) and a base (OH−); the equation of the dynamic dissociation equilibrium is

(1.3)

A consequence of the amphoteric character of water is that is acts as a buffer for acids and bases; that is, pH-value fluctuations due to the application of small amounts of acid or bases are balanced out. This property of water is again a basic requirement for the formation of more complex life, as we know it, because it enables the continuous reactions of enzymes throughout many different metabolic processes.

1.3 Significance of Water for Energy Conversion

Many of the physical, chemical, mechanical, and thermodynamic properties of water can be used for the conversion, transport, and storage of energy. Some techniques have been in use by humans for thousands of years, while others have only very recently been developed.

Water molecules are inert compounds with a low redox potential that can be used for the conversion and storage of energy, for example, thermal energy. However, water can also be dissociated into hydrogen gas by electrolysis, which is a highly combustible fuel in itself. Hydrogen is used in engines, jet propulsion, and can be used for the conversion of electrical energy in fuel cells. The by-product of the reaction is simply water, which does not pollute the environment. The dynamic equilibrium of dissociation can be expressed as

(1.4)

The combustion of hydrogen, also called bright-gas reaction, is highly significant for the generation of clean energy. Water is dissociated into hydrogen and oxygen by solar cells. The gases can be transported through pipes over long distances. The reverse reaction of hydrogen to water in combustion engines, power plants, or fuel cells is associated with a release of energy, that is,

(1.5a)

(1.5b)

(1.5c)

Life forms use water and the energy of this process for metabolic activities, for example, for photosynthesis and chemosynthesis. In power plants, steam, with a high temperature and at a high pressure, is guided through the blades of a turbine. The resultant rotation is converted into electrical energy in a generator. The cooled and depressurized water vapor is further cooled, liquefied, and fed back into the heating circuit. The physical principle of this energy conversion process is governed by the thermodynamic state transitions and phase transitions of water. This is a very general principle in energy conversion, and is also the fundamental operating principle of nuclear plants and of wind turbines, for example.

Hydropower plants make use of accumulated water that possesses a high potential energy. Turbines that generate electrical energy are driven by the conversion of the potential energy into kinetic energy by flowing water through sloped pipes and channels. In this way, large amounts of electrical energy can be generated at lakes and rivers, but the environmental impact of massive installations such as dams should always be considered first. Hydropower plants also play an ever-increasing role in the storage of energy. The fluctuating energy of renewable energy sources (e.g., wind, sun) needs to be stored during phases of excess generation, until it is needed. This energy can then be used to pump the water to a higher level, thus increasing the potential energy of the water. At times when the consumption of energy is higher than that generated, the water can be directed through turbines to generate additional electrical energy.

Tidal and wave power plants convert the kinetic energy of water due to the tides into electrical energy.

These are only a few examples of how electrical energy can be generated either directly from or by the involvement of water. Many more principles and methods can be found in the specialist literature on this topic.

1.4 General Terminology

For clarity and in order to avoid ambiguity, the terminology used in this book to identify the different states of water is described briefly in the following.

The naming of physical and chemical states (such as triple point, redox potential, etc.) is unambiguous and generally accepted by consensus. The aggregate states of water and thus associated terms (e.g., dew point, water vapor pressure) are described and defined by the laws of thermodynamics. It should be noted that, occasionally, identical terms are used in the context of technical applications (e.g., in energy conversion or for drying) with a different definition.

The term humidity describes the states and interactions of gaseous water in other gases. A general definition does not exist.

The term moisture describes the states and interactions of liquid or gaseous water in either solids or liquids, regardless of the specific type of physical or chemical bonding. As in the case of humidity, no general definition exists.

Other humidity- or moisture-related terms that can be found occasionally (e.g., trace humidity, high temperature humidity) are used for particular states of water and measurement ranges for specific manufacturing processes.

The term water steam is frequently used for energy conversion processes. This term is used to describe water as an aerosol, possibly at elevated temperatures. Such a mixture of small water droplets and a gas has a high significance as an energy source (e.g., hot steam, supersaturated steam). In gas humidity measurement, however, the term water vapor is used, which implies the description of water as a real gas, for example, as a van der Waals gas.

Further Reading

DeMan, J.M. (1999) Principles of Food Chemistry, Springer.

Falbe, J., Römpp, H., and Regitz, M. (1990) Römpp Chemie Lexikon, vol. 3, Thieme.

Gerthsen, C. and Meschede, D. (2010) Gerthsen Physik, Springer.

Langmuir, D. and Drever, J.I. (1997) Environmental Geochemistry, Prentice Hall, New Jersey.

Pauling, L. (1988) General Chemistry, Courier Dover Publications.

Pauschmann, H. (1990) Gaschromatographie, in Untersuchungsmethoden in der Chemie (eds H. Naumer and W. Heller), Thieme.